Patent Publication Number: US-2023150823-A1

Title: CO2 hydrogenation catalysts for the commercial production of syngas

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
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     STATEMENT OF FEDERALLY SPONSORED RESEARCH 
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     REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM 
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     BACKGROUND OF THE INVENTION 
     The impact of ever-increasing CO 2  levels on the anthropogenic induced climate change have been widely documented (Shukla et al, IPCC, 2019). During 1970 to year-end 2019, global radiative forcing increased by an average of 3.03 Watts/square meter (W/m 2 ), due to increases in the greenhouse gases, CO 2 , CH 4 , N 2 O and H 2 O, with a concurrent, average global temperature increase of 1.18° C. (2.13° F.). Climate models predict that average global temperatures could reach +2.00° C. (+3.60° F.) sometime between 2026 and 2028, and 2.36° C. (+4.28° F.) by year end 2031 compared to the average global temperature in 1970. Since CO 2  accounts for two thirds of these increases, rapid reductions in CO 2  emissions and atmospheric CO 2  are needed by no later than 2030 (Schuetzle, 2020). 
     CO 2  can be captured efficiently from emissions generated by industrial processes. Since CO 2  is a useful carbon source, the first priority should be to utilize this carbon source for the production of low-carbon fuels and chemicals, instead of sequestering the CO 2  in geological formations (Hepburn et al, 2019). CO 2  can also be captured from air (called Direct Air Capture—DAC) which allows for CO 2  collection from any location globally without being tied to an industrial source (Artz et al, 2018). 
     Since there are very few locations where suitable geological formations are available to sequester captured CO 2 , it is much more suitable to produce fuels and chemical products from the CO 2 . Furthermore, CO 2  is a valuable feedstock that can be used to produce low-carbon fuels and chemicals. 
     Syngas can potentially be commercially produced from the catalytic conversion of low-carbon H 2  and captured CO 2  mixtures. This catalytic process is referred to as CO 2  Hydrogenation, or the Reverse Water-Gas Shift (RWGS) reaction (Equation 1) (Daza et al, 2016; Vogt et al, 2019; Chen et al, 2020). 
       CO 2 +H 2 =CO+H 2 O  Eq. 1
 
     The reaction is endothermic and requires heat to proceed. Elevated temperatures and efficient catalysts are required for significant CO 2  conversion to CO with minimal or no coking (carbon formation) or degradation in catalyst performance with time. 
     Since no commercially viable catalysts have been developed to date for the efficient production of syngas from H 2  and CO 2  mixtures, an improved catalyst and process has been developed and is described herein for the efficient commercial production of low-carbon syngas from mixtures of low-carbon H 2  and captured CO 2 . 
     This low-carbon syngas is an excellent feedstock for producing a wide range of other chemical products, including liquid and gaseous hydrocarbon fuels, alcohols, acetic acid, dimethyl ether, and many other chemical products (Olah et al, 2009; Centi et al, 2009; Jiang et al, 2010; Schuetzle et al, 2010-2020; Fischer et al, 2016; Gumber et al, 2018; Tan et al, 2018; Li et al, 2019; NAS, 2019). 
     Many patent applications, patents and publications have described the development of RWGS catalysts for the conversion of H 2  and CO 2  mixtures to syngas (Bahmanpour et al, 2021). There is a second emerging approach that encompasses electrolysis processes for the conversion of mixtures of CO 2  and H 2 O to syngas (Wang et al, 2016). However, this electrolysis approach is in the early research and development stages, and it is not considered as a viable commercial scale method at this time. 
     Most of the RWGS catalysts described in the current art operate at conditions that are not relevant to industrial relevant process conditions, or have significant limitations such as high costs, not amenable to large-scale manufacturing, or they have limited operational lifetime. We therefore have developed catalysts per the invention that are commercially viable and meet the following specifications outlined in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Quality and Performance Specifications for the Effective 
               
               
                 Catalytic Conversion of H 2 /CO 2  Mixtures to Syngas 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 1. 
                 The catalyst is comprised of one or more low-cost metals selected from the alkali metals 
               
               
                   
                 (Group 1), the alkaline earth metals (Group 2), the transition metal group, and the rare-earth 
               
               
                   
                 metals which are impregnated and calcines on substrates that do not chemically react with the 
               
               
                   
                 metals. The catalyst contains no precious metals. 
               
               
                 2. 
                 One or more of the metals are formulated as metal salts (e.g., nitrates, acetates, carbonates, 
               
               
                   
                 etc.) or metal hydroxides which are impregnated on the chemically inert substrates at a 
               
               
                   
                 concentration from 0.0 to about 35 wt. %. 
               
               
                 3. 
                 The inert substrates are one or more metal alumina spinels produced from the stoichiometric 
               
               
                   
                 mixture of alumina with one of the following metals (Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, 
               
               
                   
                 Cu, Zn, La and Ce) by calcining up to 2,100° F. 
               
               
                 4. 
                 The catalyst contains low-cost constituents with no precious metals comprising Rh, Pt, Au, 
               
               
                   
                 Ag, Pd, or Ir. 
               
               
                 5. 
                 The catalyst is robust, meaning a hardness of between 3 Mohs and 10 Mohs, more preferably 
               
               
                   
                 between 4 Mohs and 7 Mohs (or equivalent on the Rockwell scale). 
               
               
                 6. 
                 The catalyst is chemically and physically stable up to 2,100° F. By chemical and physical 
               
               
                   
                 stable, it is meant that the surface area of the catalyst as measured by using the Brunauer- 
               
               
                   
                 Emmet-Teller (BET) method, before and after thermal treatment is essentially the same and 
               
               
                   
                 is considered stable when there is between 0 and 20% change in the measurement, and 
               
               
                   
                 preferably between 0 and 10% change, and even more preferably between 0 and 5% change. 
               
               
                 7. 
                 The catalyst can be loaded readily into catalytic reactors (e.g., tubular, or packed bed 
               
               
                   
                 reactors). The pressure drop from the top to the bottom of the catalytic reactor is preferably 
               
               
                   
                 between 0 and 50 psi, and even more preferably between 0 and 25 psi and even more 
               
               
                   
                 preferably between 0 and 10 psi. 
               
               
                 8. 
                 Catalyst activation should be able to be carried out in-situ in the reactor. The activation gas 
               
               
                   
                 for the catalyst activation process should be readily available. Preferably the catalyst 
               
               
                   
                 activation can be accomplished by using a gas comprising hydrogen. More preferably the 
               
               
                   
                 catalyst activation can be accomplished using a gas comprising hydrogen and carbon dioxide. 
               
               
                 9. 
                 The CO 2  to CO conversion efficiency is between 70% and 100%, but preferably between 
               
               
                   
                 75% and 100% at space velocities of between 2,000 hr −1  and 1,000,000 hr −1 . 
               
               
                 10. 
                 The CO 2  to CO conversion occurs at temperatures between 1,300° F. and 1,800° F., and 
               
               
                   
                 pressures above 50 psi. 
               
               
                 11. 
                 The catalyst does not coke (e.g., form carbon deposits), meaning that during the conversion 
               
               
                   
                 of carbon dioxide to carbon monoxide, the percent carbon as measured on the catalyst is 
               
               
                   
                 between 0 and 1% by weight, and more preferably between 0 and 0.1% by weight. 
               
               
                 12. 
                 The catalyst during testing under planned commercial operating conditions meets the 
               
               
                   
                 performance criteria such that CO 2  conversion declines by between 0 and 1% per 1000 hours 
               
               
                   
                 of operation, and more preferably between 0 and 0.5% per 1000 hours of operation. 
               
               
                   
               
            
           
         
       
     
     FIELD OF THE INVENTION 
     The field of the invention is the application of improved catalysts for the conversion of renewable H 2  and captured CO 2  to syngas, which is then used concurrently to produce low-carbon fuels and chemicals. The improved catalysts use low-cost metals, they can be produced economically in commercial quantities, and they are chemically and physically stable up to 2,100° F. CO 2  conversion efficiencies are between 80% and 100% with CO selectivity of greater than 99%. The catalysts don&#39;t sinter or form coke when converting H 2 :CO 2  mixtures to syngas at 1,300-1,800° F., 75-450 psi and space velocities of 2,000-100,000 hr −1 . The catalysts are robust, exhibiting a reduction in CO 2  conversion of between 0 and 1.0% per 1000 hours. 
     DESCRIPTION OF RELATED ART 
     Iwanani et al (1995) developed a catalyst comprised of transition metals with rare metals (such as Ni, Fe, Ru, Rh, Pt, W, Pd, Mo) on a ZnO/Al 2 O 3  substrate for the conversion of CO 2  and H 2  mixtures to CO, targeting specifically catalytic performance with feeds containing H 2 S. They achieved relatively low conversions of CO 2  of up to 37% at 1,100° F. at 3,000 hr −1  for a 12.4% Ni/21.2% Zn catalyst without significant loss of catalyst activity after 150 hours but testing for longer periods was not carried out. This catalyst doesn&#39;t meet any of the specifications in Table 1. 
     Dupont et al (2003) developed a catalyst consisting of 0.78% ZnO/0.21% Cr 2 O 3 /0.01% NiO for the conversion of an H 2 /CO 2  (3.5/1.0 v/v) mixture to CO. The CO 2  conversion efficiency was 36% with a 92% CO and 8% CH 4  selectivity at 950° F., a pressure of 580 psi, and a space velocity of 5.0 hr −1 . No data was presented on the efficiency of the catalyst with time. This catalyst does not meet all of the criteria outlined in Table 1. 
     Kim et al (2014) determined the CO 2  hydrogenation efficiency for a BaZr 0.8 Y 0.16 Zn 0.04 O 3  perovskite catalyst with a 1/1 H 2 /CO 2  blend at 1,110° F. and 15 psi. They achieved a low 38% conversion of CO 2  with a CO selectivity of 97%. The long-term catalyst durability was not determined since the catalyst was only run for 5 hours. 
     Chen et al (2015) reported the synthesis of a nano intermetallic catalyst (InNi 3 Co 0.5 ) that proved to be active and selective for the RWGS reaction. The catalyst was fabricated by carburizing the In—Ni intermetallic base which produced dual active sites on the catalyst surface. They achieved a moderate 52-53% CO 2  conversion for 150 hours at 1125° F. at high gas hourly velocities of 30,000 hr −1 . As based upon its structure, this catalyst may meet criteria #3 and #7. It would be difficult and costly to manufacture this catalyst in multiple ton quantities (criteria #1 and #2) and it is not known if can be used commercially in traditional catalytic reactors (criteria #5 and #6). This catalyst does not meet CO 2  to CO conversion efficiency requirements (criteria #8) and CO production selectivity. Since this catalyst was only tested for 150 hours, its stability and lifetime are not known. 
     Daza and Kuhn (2016) developed a La/Sr (3.0/1.0 w/w) catalyst impregnated on an FeO 3  substrate. They observed a 16% conversion of H 2 /CO 2  (1.0/1.0 v/v) to CO with a 95% selectivity at 1,300° F. and 15 psi. The CO 2  conversion efficiency and CO selectivity were relatively constant over the period of a 150-hr. test. This catalyst meets criteria #1, #7 and #9 presented in Table 1. Since this catalyst was only run for 150 hrs. its long-term lifetime is not known. 
     Daza et al (2016) determined the CO 2  hydrogenation efficiency for a La 0.75 Sr 0.25 FeO 3  perovskite catalyst with a 1/1 H 2 /CO 2  (v/v) blend at 1,020° F. and 15 psi. They achieved a very low 15% conversion of CO 2  with a CO selectivity of 95%. The long-term catalyst durability was not determined since the catalyst was only run for less than 24 hours. In summary, no data has been published to date that indicates perovskites could be acceptable catalysts for CO 2  hydrogenation. 
     Alumina has been widely studied as a catalyst support for both CO 2  hydrogenation and dry reforming of methane (DRM). The benefits of alumina lay primarily in its high surface area, low cost and stability at high temperatures. It is also relatively cheap compared to other support materials. Yang et al (2018) synthesized a 10% Ni/20% CeO 2  catalyst on γ-Al 2 O 3 . They tested this catalyst with a 4/1 H 2 /CO 2  (v/v) blend at 1,300° F., 15 psi and a space velocity of 400 k. They observed a CO 2  conversion of 67%, a CO selectivity of 90% and a CH 4  selectivity of 10%. The catalyst efficiency dropped by 37% after 50 hrs. due to carbon formation and Ni sintering. Therefore, this is not a viable commercial catalyst. 
     While a Ni catalyst on Al 2 O 3  substrate is a potential RWGS catalyst, the spinel nickel aluminate NiAl 2 O 4  is easily formed, which can result in at least some loss of activity (Ryu et al, 2021). However, the resistance to coke formation of Ni/Al 2 O 3  is highly dependent on the catalyst structure and composition. At high temperatures, the formation of the spinel phase NiAl 2 O 4  results in increased resistance to coke formation. This is a result of the strengthening of the Ni—O bond in NiAl 2 O 4  with respect to NiO crystal, thus increasing the difficulty of Ni 2 + reduction to elemental nickel (Hu et al, 2004). 
     Magnesia is a promising support for due to its enhanced chemisorption of CO 2  and high basicity. The benefits of magnesia and alumina can also be combined in mixed MgO-Al 2 O 3  supports. The effect of the increased basicity and specific surface area has been reported by Jun et al using a catalyst for dry reforming of methane (Jun et al, 2015). The influence of the Mg/Al on the catalytic activity and catalyst lifetime remains unclear. Also, none of the catalysts reported fully meets the requirements stated in Table 1. 
     Depending on the reaction conditions and preparation methods of the catalysts, mixed MgO-Al 2 O 3  systems doped with nickel both form spinels from the respective components. Based on a systematic study with varying nickel content in Ni x Mg 1-x Al 2 O 4 , Park et al reported that RWGS conversion was preferred at high magnesium atomic ratios (2021). The results which were supported by DFT calculations, indicating that CO selectivity increased with increasing magnesium content. Zhang et al (2021) described a 0.43% Ni on MgAl 2 O 4  catalyst for CO 2  hydrogenation of a 1/1 H 2 /CO 2  blend at 1,472° F. They observed a modest 46% CO 2  conversion efficiency with no discernable loss in conversion efficiently after 75 hours. However, this efficiency doesn&#39;t meet the CO 2  conversion efficiency of between 70% and 100% above 1,300° F. and above 50 psi as outlined in Table 1. They didn&#39;t report CO production selectivity and the long-term deactivation rate of the catalyst is unknown. 
     The preparation of mixed Ni—Mg—Al—O phases has also been reported for the dry reforming of methane (DRM), where hydrotalcite-like mixed layered hydroxides were thermally decomposed, showing high activity and enhanced stability (Bhattacharyya et al.). Bhattacharyya et al. also compared the catalytic activity to commercial NiO supported catalyst. Hydrotalcite is a naturally occurring layered mineral, discovered in Sweden in 1842, with the chemical formula: Mg 6 Al 2 (OH) 16 CO 3 .4H 2 O, a name stemming from the high-water content of the material as well as its resemblance to talc. It can also easily be synthesized by co-precipitation methods (Cavani et al, 1991). Many minerals with different molecular compositions but with similar empirical elemental structures have been reported. The term hydrotalcite (hydrotalcite-like compounds—HTs, layered double hydroxides—LDHs) is used to describe a large group of naturally occurring minerals and synthetic materials that possess the typical layered structure of hydrotalcite. The general formula of hydrotalcites can be summarized as: [M 2+   1-x M 3+   x (OH) 2 ][(A n−   x/n ).mH 2 O] where M 2+ , M 3+  are di- and tri-valent cations; A are interlayer anions; and x is the mole fraction of trivalent cations. The part [M 2+   1-x M 3+   x (OH)] 2  describes the composition of brucite-like layers and [(A n−   x/n ).mH 2 O] describes the composition of interlayer spaces. 
     For the DRM catalyst synthesis, nickel was introduced using various methods including incipient wetness impregnation, ion-exchange, as well as co-precipitation. Nickel based hydrotalcite based catalysts have been considered for DRM and are well investigated. 
     Ni-Hydrotalcite catalysts with low nickel content are highly active towards CO 2  conversion, pointing at a simultaneous occurrence of reverse water gas shift (RWGS) (Lin et al, 2021). Numerous heterogeneous catalysts have been developed based on the cation-exchange ability of the Brucite layer, the anion-exchange ability of the interlayer, the surface tunable basicity, as well as the adsorption capacity (Debek et al, 2017; U.S. Pat. No. 8,388,987B2, 2013). Hydrotalcites have also been found for the production and processing of polymers, as neutralizing additives, or as part of building materials (Figueras et al, 2010; Sikander et al, 2017). However, to our knowledge there are no reports on the application of hydrotalcites in commercial RWGS catalysts, either with or without the additional metal active sites such as for example Ni. 
     Hydrotalcite based materials were also reported as possible solid sorbents for pressure swing CO 2  adsorption, a technology known as sorption-enhanced water-gas shift (SEWGS). Hydrotalcites showed high thermal and mechanical stability with sufficiently high cyclic working capacity and fast adsorption kinetics. The regeneration step (desorption of CO 2  by feeding steam to the adsorbent) is slower and limits the cyclic working capacity of the adsorbent. It was found that a higher operating temperature is beneficial because of enhanced desorption kinetics. Steam induces the desorption of a second adsorption site available for CO 2  which cannot be desorbed with N 2  (Boon et al, 2014). Calcination of hydrotalcites leads to dehydration, dihydroxylation and decarbonation, and eventual formation of the spinel. While the formation of the spinel phase from alumina and magnesia precursors is performed at temperatures above 1500° C., spinel phase forms at significantly lower temperatures during the calcination of hydrotalcites. When applying hydrotalcite precursors for the synthesis of commercial RWGS catalysts, the spinel phase can form as low as 700° C. (Jatav et al, 2016). 
     Bahmanpour et al (2019) studied an in situ formed Cu—Al spinel as an active substrate for the hydrogenation of CO 2  with H 2  into syngas. They used co-precipitation followed by hydrogen treatment to form the Cu—Al spinel with excess Cu in different weight ratios. A 4% Cu catalyst on the Cu—Al spinel was found to be the most efficient for CO 2  conversion. A low CO 2  conversion rate of 47% at 1,110° F. was achieved at relatively high space velocities with no detectable deactivation after a 40-hr. test. In comparison, a 4% Cu on gamma-alumina converted 33% of the CO 2  at 1,110° F. This catalyst meets criteria #1 and it possibly meets criteria #2, #3, #5, #6 and #7. However, copper containing catalysts tend to deactivate over time by sintering at high temperatures, which is problematic especially for the Cu excess formulation. In addition, this catalyst formulation needs to be tested for 1,000 hrs. or longer to assess long-term lifetime (criteria #10). 
     Table 2 summarizes the above catalytic systems and other potential catalysts for the catalytic CO 2  hydrogenation to CO. Most of these catalysts were tested for less than 48 hrs. which is not a sufficient length of time to assess catalyst durability. Since the lifetime of a commercial catalyst needs to be 2 years or longer, the reduction in CO 2  conversion must be between 0% and 1.0% conversion decline per 1000 hours. 
     Since these catalysts will be run in commercial reactors, they need to operate efficiency at pressures above 50 psi, and preferably above 150 psi. All the catalysts listed in Table 2 have been evaluated at 15 psi, except for Dupont et al, 2003; Kharaji et al, 2012; and Chen et al, 2019 who tested their catalyst at 300, 150 and 145 psi, respectively. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Prior Art Summary for Catalytic CO 2  Hydrogenation to CO 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 H 2 /CO 2   
                 T 
                 P 
                 SV 
                 (−)CO 2   
                 (+)CO 
                 (+)CH 4   
                 Time 
                 (−)CO 2 /dt 
               
               
                 Reference 
                 Catalyst Formulation 
                 ratio 
                 (° F.) 
                 (psi) 
                 (khr −1 ) 
                 (%) 
                 (%) 
                 (%) 
                 (hrs.) 
                 (%/100 hr) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Chen (2003) 
                 9%Cu/1.9%K on 
                 1.0 
                 1,100 
                 15 
                 0.4 
                 13 
                 13 
                 0 
                 &lt;48 
                 nd 
               
               
                   
                 SiO 2   
               
               
                 Dupont (2003) 
                 0.78%ZnO/0.21% 
                 3.5 
                 950 
                 300 
                 5.0 
                 36 
                 33 
                 3 
                 &lt;48 
                 nd 
               
               
                   
                 Cr 2 O 3 /0.01%NiO 
               
               
                 Wang (2008) 
                 2%Ni on CeO 2   
                 1.0 
                 1,400 
                 15 
                 tbd 
                 40 
                 40 
                 0 
                 &lt;48 
                 nd 
               
               
                 Kharaji (2012) 
                 γ-Al 2 O 3   
                 1.0 
                 1,100 
                 150 
                 30.0 
                 16 
                 nd 
                 nd 
                 15 
                 34.0 
               
               
                 Kharaji (2012) 
                 Fe—V 2 O 5  on γ-Al 2 O 3   
                 1.0 
                 1,100 
                 150 
                 30.0 
                 25 
                 nd 
                 nd 
                 15 
                 80.0 
               
               
                 Kim (2012) 
                 1%Pt on TiO 2   
                 1.4 
                 1,600 
                 15 
                 0.4 
                 48 
                 48 
                 0 
                 &lt;48 
                 nd 
               
               
                 Kim (2012) 
                 1%Pt on γ-Al 2 O 3   
                 1.4 
                 1,100 
                 15 
                 0.04 
                 42 
                 42 
                 0 
                 &lt;48 
                 nd 
               
               
                 Lu (2014) 
                 3%NiO on CeO 2   
                 1.0 
                 1,400 
                 15 
                 tbd 
                 45 
                 45 
                 0 
                 &lt;48 
                 nd 
               
               
                 Kharaji (2014) 
                 7%Ni-5%Mo on 
                 1.0 
                 1,300 
                 15 
                 30.0 
                 35 
                 nd 
                 nd 
                 60 
                  5.0 
               
               
                   
                 γ-Al 2 O 3   
               
               
                 Kharaji (2014) 
                 9%Mo on γ-Al 2 O 3   
                 1.0 
                 1,300 
                 15 
                 30.0 
                 15 
                 nd 
                 nd 
                 60 
                 22.0 
               
               
                 Kim (2014) 
                 3%NiO/CeO 2   
                 1.0 
                 1,100 
                 15 
                 2.7 
                 38 
                 32 
                 6 
                 &lt;48 
                 nd 
               
               
                 Kim (2014) 
                 BaZr 0.8 Y 0.16 Zn 0.04 O 3   
                 1.0 
                 1,100 
                 15 
                 2.7 
                 38 
                 37 
                 1 
                 3 
                 nd 
               
               
                   
                 perovskite 
               
               
                 Lortie (2014) 
                 10%CuNi 4  Solid 
                 1.0 
                 1,300 
                 15 
                 282 
                 38 
                 38 
                 0 
                 &lt;48 
                 nd 
               
               
                   
                 Solution on 
               
               
                   
                 Sm/CeO 2   
               
               
                 Lortie (2014) 
                 1%Pt on Sm/CeO 2   
                 1.0 
                 1,300 
                 15 
                 282 
                 40 
                 40 
                 0 
                 &lt;48 
                  1.0 
               
               
                 Landau (2015) 
                 90%Fe on Fe—Al 2 O 3   
                 1.0 
                 950 
                 na 
                 0.02 
                 36 
                 13 
                 9 
                 &lt;48 
                 nd 
               
               
                   
                 Spinel 
               
               
                 Sun (2015) 
                 10%Ni/Ce/ZrO 
                 tbd 
                 1,400 
                 15 
                 tbd 
                 49 
                 49 
                 0 
                 80 
                 &lt;1.0 
               
               
                 Daza (2016) 
                 1.0%La/0.75%Sr/ 
                 1.0 
                 1,000 
                 15 
                 130 
                 16 
                 15 
                 1 
                 155 
                 &lt;1.0 
               
               
                   
                 0.25%FeO 3  perovskite 
               
               
                 Zhang (2016) 
                 Cu on Mo 2 C 
                 3.0 
                 1,100 
                 15 
                 300 
                 38 
                 36 
                 2 
                 40 
                 100.0  
               
               
                 Goncalves (2017) 
                 2.4%Ni on SiO 2   
                 4.0 
                 1,500 
                 15 
                 na 
                 73 
                 73 
                 0 
                 40 
                 nd 
               
               
                   
                 sputter deposited 
               
               
                 Goncalves (2017) 
                 2.4%Ni on SiO 2   
                 4.0 
                 1,500 
                 15 
                 na 
                 57 
                 57 
                 0 
                 40 
                 nd 
               
               
                 Pastor (2017) 
                 Cs/Fe/Cu on γ-Al 2 O 3   
                 4.0 
                 1,400 
                 15 
                 25 
                 70 
                 70 
                 0 
                 50 
                 nd 
               
               
                 Choi (2017) 
                 4%Pd, Cu, Ni or Ag 
                 3.0 
                 1,475 
                 15 
                 12 
                 68 
                 68 
                 0 
                 10 
                 nd 
               
               
                   
                 on γ-Al 2 O 3   
               
               
                 Zhuang (2017) 
                 0.5%Ru/40%Cu/ZnO(1:1) 
                 4.0 
                 930 
                 40 
                 40 
                 40 
                 38 
                 2 
                 25 
                 100.0  
               
               
                   
                 on γ-Al 2 O 3   
               
               
                 Zhuang (2017) 
                 40%Cu/ZnO(1:1) on 
                 4.0 
                 930 
                 40 
                 40 
                 22 
                 38 
                 2 
                 70 
                 28.6 
               
               
                   
                 γ-Al2O3 
               
               
                 Wang (2017) 
                 3%Co on CeO 2   
                 1.0 
                 1,100 
                 15 
                 200 
                 30 
                 98 
                 2 
                 50 
                 &gt;25   
               
               
                 Alamer (2018) 
                 10%Cu on Al 2 O 3   
                 1.0 
                 850 
                 15 
                 76 
                 3 
                  2 
                 1 
                 6 
                 nd 
               
               
                 Alamer (2018) 
                 10%Cu on MgO 
                 1.0 
                 850 
                 15 
                 76 
                 10 
                  3 
                 7 
                 6 
                 nd 
               
               
                 Alamer (2018) 
                 5%Cu on MgO 
                 1.0 
                 850 
                 15 
                 76 
                 20 
                 15 
                 5 
                 6 
                 nd 
               
               
                 Alamer (2018) 
                 10%Cu on MgO 
                 1.0 
                 1,475 
                 15 
                 76 
                 48 
                 48 
                 0 
                 6 
                 nd 
               
               
                 Pastor- 
                 5%Cs/15%Fe on 
                 4.0 
                 1,475 
                 15 
                 12 
                 75 
                 75 
                 0 
                 40 
                  1.5 
               
               
                 Perez (2018) 
                 γ-Al 2 O 3   
               
               
                 Yang (2018) 
                 10%Ni/20%CeO 2   
                 4.0 
                 1,400 
                 15 
                 30 
                 67 
                 61 
                 6 
                 50 
                 74.0 
               
               
                   
                 on γ-Al 2 O 3   
               
               
                 Bahmanpour (2019) 
                 4%Cu on Cu—Al 2 O 3   
                 1.0 
                 1,100 
                 15 
                 300 
                 47 
                 47 
                 0 
                 40 
                  7.0 
               
               
                   
                 Spinel 
               
               
                 Bahmanpour (2019) 
                 6%Cu on γ-Al 2 O 3   
                 1.0 
                 1,100 
                 15 
                 30 
                 47 
                 47 
                 0 
                 40 
                 23.0 
               
               
                 Bahmanpour (2019) 
                 4%Cu/ZnO on 
                 1.0 
                 1,100 
                 15 
                 30 
                 33 
                 33 
                 0 
                 40 
                 32.0 
               
               
                   
                 γ-Al 2 O 3   
               
               
                 Chen (2019) 
                 InNi 3 C 0.5   
                 3.0 
                 1,100 
                 145 
                 22 
                 53 
                 50 
                 3 
                 150 
                  1.3 
               
               
                 He (2019) 
                 MnO 2   
                 1.0 
                 1,560 
                 15 
                 40 
                 50 
                 50 
                 0 
                 &lt;48 
                 nd 
               
               
                 Ranjbar (2019) 
                 15%Ni/on MgAl 2 O 4   
                 1.0 
                 1,300 
                 15 
                 24 
                 40 
                 38 
                 2 
                 15 
                  1.3 
               
               
                   
                 spinel 
               
               
                 Zhang (2021) 
                 MgAl 2 O 4  spinel 
                 1.0 
                 1,472 
                 15 
                 225 
                 38 
                 nd 
                 nd 
                 75 
                 &lt;0.5 
               
               
                 Zhang (2021) 
                 0.43%Ni on 
                 1.0 
                 1,472 
                 15 
                 225 
                 46 
                 nd 
                 nd 
                 &lt;48 
                 nd 
               
               
                   
                 MgAl 2 O 4  spinel 
               
               
                   
               
            
           
         
       
     
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is generally directed to the production of low-carbon syngas from captured CO 2  and renewable H 2 . The H 2  is generated from water using an electrolyzer powered by renewable electricity, or from any other method of low-carbon H 2  production. The improved catalysts use low-cost metals, they can be produced economically in commercial quantities, and they are chemically and physically stable up to 2,100° F. CO 2  conversion efficiencies are between 80% and 100% with CO selectivity of greater than 99%. The catalysts don&#39;t sinter or form coke when converting H 2 :CO 2  mixtures to syngas in the operating ranges of 1,300-1,800° F., pressures of 75-450 psi, and space velocities of 2,000-100,000 hr −1 . The catalysts are stable, exhibiting between 0 and 1.0% reduction in conversion or selectivity per 1,000 hrs. The syngas can be used for the synthesis of low-carbon fuels and chemicals, or for the production of purified H 2 . The H 2  can be used at the production site for the synthesis of low-carbon chemical products or compressed for transportation use. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG.  1    describes the typical relationship of temperature with CO 2  conversion to CO using the improved catalysts of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In this section we describe our improved catalyst formulations which has been demonstrated to meet the performance and quality requirements presented in Table 1. 
     Four types of improved CO 2  hydrogenation or Reverse Water Gas Shift (RWGS) catalysts are described in these embodiments. 
     Type A. Metal-Spinel Catalysts—Pure alumina is an amphoteric substance, as it can react with both acids and bases. Depending on the morphology and crystal structure present the basicity of alumina can be complex. Acidic alumina catalyzes reactions that are typically acid catalyzed (Pines et al, 1960). However, several spinels produced from the high-temperature calcination of alumina with the Group 1 metals (Li, Cs, Rb) and Group 2 metals (Mg, Ca, Sr, Ba and Be) form metal aluminates that have defined and usually basic surface properties, also due to the increased surface concentrations of the hydroxy (—OH) groups. 
     Formates are formed when H 2 /CO 2  mixtures react with these hydroxy groups according to Equation 2. 
       H 2 +CO 2 ═HCOO-Metal Aluminate+H 2 O  (Eq. 2)
 
     These formates decompose rapidly at high temperatures in the presence of H 2  to form CO (Equation 3) with a high selectivity. Therefore, some of these spinels are excellent CO 2  hydrogenation catalysts. 
       2HCOO-Metal Aluminate+H 2 =2CO+2H 2 O  (Eq. 3)
 
     A spinel of the invention is any class of minerals or synthetically produced minerals with the general chemical form of AB 2 X 4 . For the invention, X is oxygen, B can be chosen from the group comprising aluminum, iron, chromium, cobalt, and vanadium. A is chosen from a group comprising Mg, Zn, Fe, Mn, Cu, Ni, Li, Cs, Rb, Mg, Ca, Sr, Ba, Be, and Ti. In one embodiment of the invention, the catalyst is a metal aluminate such that B is Aluminum, and X is Oxygen. 
     Type B. Metal Impregnated Metal-Spinel Catalysts—When selected Group 1 (alkali metals such as Li, Cs, Rb) and/or Group 2 (alkaline earth metals such as Mg, Ca, Sr, Ba, and Be) are impregnated on selected spinels in the appropriate levels, the surface abundance of hydroxy groups increases, resulting in their improved efficiency for CO 2  hydrogenation. The addition of these elements is believed to enhance the chemisorption of CO 2  due to their impact on basicity, total pore volume and surface are. Dopants may be Ni, Cu, Ce, Zr, Ti, La, or the early Lanthanides. When two or more impregnated metals on the metal aluminate spinel are calcined up to a temperature of 2,100° F., a solid solution is formed. This solid solution represents excellent catalyst for CO 2  hydrogenation. Ni and Mg form a solid solution, Ni 2 Mg, at 2,050° F. on Mg-Aluminate since Ni and Mg both crystallize in a face-centered cubic structure, and they have similar electronegativities and valences. Ni also forms a solid solution with Cu, NiCu 3 , at 2,050° F. since Ni and Cu both crystallize in a face-centered cubic structure, and they have similar atomic radii, electronegativities and valences. Solid solutions are formed when two of the metals impregnated on the metal aluminate spinel have similar crystal structures, atomic radii, electronegativities and valences. Dopants may be present as extra framework and unincorporated into the spinel or may be supported on the Metal-Spinel Catalyst, or especially at higher concentrations be both supported by spinel or be present in close proximity inside a physical mixture. 
     The RWGS catalyst is operated in the 1,300-1,800° F. range in order to achieve CO 2  conversion efficiencies above 70%, which is a temperature range where many materials sinter at increased rates as they approach their melting point. The solid solution used in the catalyst should be a solid at these temperatures. Therefore, viable solid solutions are those that are formed in the 1,850-2,100° F. range. Ni 2 Mg and NiCu 3  are stable solids at these catalyst operating temperatures, and they have excellent performance as CO 2  hydrogenation catalysts. The solid solution, Cu 2 Mg, is formed from 2 moles of Cu and 1 mole of Mg at 1,300° F. and it doesn&#39;t qualify as a candidate since the solution is a liquid at the catalyst operating temperatures. 
     Type C. Engineered Layered Solids—Hydrotalcite based materials are used as catalysts for RWGS. These materials include natural hydrotalcite as well as synthetic highly engineered anionic clays or layered double hydroxides (LDH). Natural hydrotalcites may be used as additives, or as precursors for further synthesis. Synthetic Hydrotalcites are commercially available or may be prepared by coprecipitation methods. 
     Hydrotalcite is a layered double hydroxide (LDH)—Mg 6 Al 2 CO 3 (OH) 16 .4H 2 O. Multiple structures containing loosely bound carbonate ions exist, which are known for their ion exchange capabilities as well as their ability to adsorb CO 2 . Upon calcination the material decomposes to high surface area spinel, that can easily be rehydroxylated or recarboxylated. Full thermal decomposition will lead to a spinel that is known for its hardness and durability. 
     LDH&#39;s are structurally derived from the brucite (Mg(OH) 2 ) structure by the isomorphous substitution of M 2+  ions by M 3+  ions. The LDH layers are positively charged and charge neutrality is realized by the presence of interlamellar anions. When M 3+  is Al 3+  the mineral hydrotalcite is obtained. The uniquely high surface area of LHD as well as their surface basicity significantly improve the performance of RWGS. The surface area, chemical composition as well as basicity of the layered solid is engineered to optimize the performance of the commercial RWGS catalyst. 
     Type D. Perovskite Catalysts.—Similar to the materials of Type A, perovskite materials can be used as improved RWGS catalysts. Perovskite materials have the general chemical form of ABX 3 . For the invention, X is Oxygen. A and B are cations. Perovskite materials can be chosen from simple perovskites such where A is chosen from the group comprising Sr, Ca, Ba, Mg, Fe, La, Ca, Pb, or Bi and B is chosen from the group comprising Al, Ti, Rb, Si, Fe, Yb or Mn. In addition, solid solution perovskite materials can also be used such as lanthanum strontium manganite, lanthanum aluminate-strontium aluminum tantalate (LSAT), lead scandium tantalate, or lead zirconate tantalate. These catalysts comprise perovskites or mixtures of various perovskites. 
     In the following embodiments that described the preferred catalyst compositions and catalyst performance, certain specific details provide a thorough understanding of various embodiments. Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, are to be construed in an open, inclusive sense, that is, as “including, but not limited to.” 
     Catalyst Composition Embodiments 
     1. A reverse water gas shift (RWGS) catalyst for the conversion of H 2  and CO 2  mixtures into syngas comprising the process steps of: a) introducing a H 2  and CO 2  mixture, or b) a mixture of H 2  and CO 2  and light hydrocarbons, into a catalytic reactor in a catalytic conversion system to produce syngas or carbon monoxide. The product of the catalytic reactor is further reacted to produce at least one of the following products chosen from the list consisting of liquid fuels, methanol, propane, naphtha, and chemicals 
     2. A reverse water gas shift (RWGS) catalyst of embodiment 1 (Type A) which comprises: a) a metal-aluminate spinel having a surface area between 10 m 2 /g and 1000 m 2 /g, wherein the metal spinel is selected from a group consisting of:
         a. Group 2 metals calcined with alumina to form Mg-aluminate, Ca-aluminate, Sr-aluminate, Ba-aluminate and Be-aluminate.   b. Group 1 metals calcined with alumina to form Li-aluminate, Rb-aluminate, and Cs-aluminate.   c. Transition metals calcined with alumina to form Fe-aluminate, Co-aluminate, Ni-aluminate, Cu-aluminate, and Zn-aluminate.   d. Rare-earth metals calcined with alumina to form La-aluminate, and Ce-aluminate.   e. The above specified metal spinels may be present individually, or as mixed oxides of some or all of the above.       

     3. A reverse water gas shift (RWGS) catalyst (Type B) which employs one of the metal-alumina spinels described in embodiment 2 with an impregnated metal dopant such but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce. The metal dopant may not be chemically bond to the spinel. In some embodiments only one of the above elements may be added, while in other embodiments catalyst formulations may comprise complex mixtures of several of the above elements. 
     Metal dopants may be introduced by impregnation, or in some cases also by physical mixing of solid precursors with the spinel. The amount of metal precursor may range from 0 to 35 wt. % of a metal salt (e.g. nitrates, acetates, carbonates, etc.) or metal hydroxides, or a metal oxide. The formed material is then calcined at a temperature up to 2,100° F., thereby synthesizing a catalyst that is a metal-impregnated, metal-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     4. A reverse water gas shift (RWGS) catalyst of embodiment 1 (Type C), which contains an engineered layered solid in which the engineered layered solid may embody 100% of the solid catalyst without any additional additives. A reverse water gas shift (RWGS) catalyst (Type C) which employs the use of engineered layered solids with an impregnated metal dopant such but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce. The metal precursor may be a metal salt (e.g., nitrates, acetates, carbonates, etc.), or metal hydroxides, or a metal oxide. The engineered layered solid may embody 0-10% of catalyst formulation, 20-30% of catalyst formulation, 40-50% of catalyst formulation, 50-60% of catalyst formulation, 50-60% of catalyst formulation, 60-70% of catalyst formulation, 70-80% of catalyst formulation, or 80-90% of catalyst formulation. The remaining part of the formulation may be dopants or other additives needed to form a commercial catalyst. The metal dopant may not be chemically bond to the engineered layered solid. In some embodiments only one of the above elements may be added, while in other embodiments catalyst formulations may comprise complex mixtures of several of the above elements. 
     Metal dopants may be introduced by impregnation, or in some cases also by physical mixing of solid precursors with the engineered layered solid. The formed material is then calcined at a temperature up to 2,100° F. This reverse water gas shift (RWGS) catalyst (Type C) employs the use of natural occurring layered solid with an impregnated metal dopant such but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce. The metal precursor may be a metal salt (e.g. nitrates, acetates, carbonates, etc.), or metal hydroxides, or a metal oxide. The natural occurring layered solid may embody 0-10% of catalyst formulation, 20-30% of catalyst formulation, 40-50% of catalyst formulation, 50-60% of catalyst formulation, 50-60% of catalyst formulation, 60-70% of catalyst formulation, 70-80% of catalyst formulation, or 80-90% of catalyst formulation. The remaining part of the formulation may be dopants or other additives needed to form a commercial catalyst. The metal dopant may not be chemically bond to the engineered layered solid. In some embodiments only one of the above elements may be added, while in other embodiments catalyst formulations may comprise complex mixtures of several of the above elements. Metal dopants may be introduced by impregnation, or in some cases also by physical mixing of solid precursors with the engineered layered solid. The formed material is then calcined at a temperature up to 2,100° F. 
     5. A reverse water gas shift (RWGS) catalyst of embodiment 3 wherein the catalyst is comprises the following components: a) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35 wt. % of a Mg salt; b) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; mixed with up to 35 wt. % of a CaCO 3 , MgCO 3 , SrCO 3 , CaO, MgO, or SrO; c) Mg-alumina spinel according to embodiment 2 having a surface area between 5 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce. d) Ca-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, and a different metal spinel of embodiment 2 of at least 10 m 2 /g. e) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as well as a natural or engineered layered solid comprising 5-10% of the catalyst formulation, 20-30% of the catalyst formulation, 40-50% of the catalyst formulation, 50-60% of the catalyst formulation, 60-70% of the catalyst formulation, 70-80% of the catalyst formulation. The resulting formulation is calcined to up 2,100° F., resulting in a metal-impregnated, Mg-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     6. A reverse water gas shift (RWGS) catalyst of embodiment 3 wherein the catalyst comprises the following components: a) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35 wt. % of a Ca salt; b) Ca-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; mixed with up to 35 wt. % of a CaCO 3 , MgCO 3 , SrCO 3 , CaO, MgO, or SrO; c) Ca-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce; d). Ca-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, and a different metal spinel of embodiment 2 of at least 10 m 2 /g; e) Ca-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as well as a natural or engineered layered solid comprising 5-10% of the catalyst formulation, 20-30% of the catalyst formulation, 40-50% of the catalyst formulation, 50-60% of the catalyst formulation, 60-70% of the catalyst formulation, 70-80% of the catalyst formulation. The resulting formulation is calcined to up 2,100° F., resulting in a metal-impregnated, Ca-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     7. A reverse water gas shift (RWGS) catalyst of embodiment 3 wherein the catalyst is comprises the following components: a) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35 wt. % of a Sr salt; b) Sr-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; mixed with up to 35 wt. % of a CaCO 3 , MgCO 3 , SrCO 3 , CaO, MgO, or SrO; c) Sr-alumina spinel according to embodiment 2 having a surface area between 10 m2/g and 1000 m2/g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce; d) Sr-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, and a different metal spinel of embodiment 2 of at least 10 m 2 /g; e) Sr-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as well as a natural or engineered layered solid comprising 5-10% of the catalyst formulation, 20-30% of the catalyst formulation, 40-50% of the catalyst formulation, 50-60% of the catalyst formulation, 60-70% of the catalyst formulation, 70-80% of the catalyst formulation. The resulting formulation is calcined to up 2,100° F., resulting in a metal-impregnated, Sr-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     8. A reverse water gas shift (RWGS) catalyst of embodiment 3 wherein the catalyst is comprises the following components: a) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35 wt. % of a Ba salt; b) Ba-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; mixed with up to 35 wt. % of CaCO 3 , MgCO 3 , SrCO 3 , CaO, MgO, or SrO; c) Ba-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce; d) Ba-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, and a different metal spinel of embodiment 2 of at least 10 m 2 /g; e) Ba-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as well as a natural or engineered layered solid comprising 5-10% of the catalyst formulation, 20-30% of the catalyst formulation, 40-50% of the catalyst formulation, 50-60% of the catalyst formulation, 60-70% of the catalyst formulation, 70-80% of the catalyst formulation. The resulting formulation is calcined to up 2,100° F., resulting in a metal-impregnated, Ba-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     9. A reverse water gas shift (RWGS) catalyst of embodiment 3 wherein the catalyst comprises the following components: a) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35 wt. % of a Li salt; b) Li-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; mixed with up to 35 wt. % of CaCO 3 , MgCO 3 , SrCO 3 , CaO, MgO, or SrO; c) Li-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce; d) Li-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000·m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, and a different metal spinel of embodiment 2 of at least 10 m 2 /g; e) Li-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as well as a natural or engineered layered solid comprising 5-10% of the catalyst formulation, 20-30% of the catalyst formulation, 40-50% of the catalyst formulation, 50-60% of the catalyst formulation, 60-70% of the catalyst formulation, 70-80% of the catalyst formulation. The resulting formulation is calcined to up 2,100° F., resulting in a metal-impregnated, Li-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     10. A reverse water gas shift (RWGS) catalyst of embodiment 3 wherein the catalyst is comprises the following components: a) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m2/g and 1000 m2/g; impregnated with up to 35 wt. % of a Rb salt; b) Rb-alumina spinel according to embodiment 2 having a surface area between 10 m2/g and 1000 m2/g; mixed with up to 35 wt. % of CaCO 3 , MgCO 3 , SrCO 3 , CaO, MgO, or SrO; c) Rb-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce; d) Rb-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, and a different metal spinel of embodiment 2 of at least 10 m 2 /g; e) Rb-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as well as a natural or engineered layered solid comprising 5-10% of the catalyst formulation, 20-30% of the catalyst formulation, 40-50% of the catalyst formulation, 50-60% of the catalyst formulation, 60-70% of the catalyst formulation, 70-80% of the catalyst formulation. The resulting formulation is calcined to up 2,100° F., resulting in a metal-impregnated, Rb-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     11. A reverse water gas shift (RWGS) catalyst of embodiment 3 wherein the catalyst is comprises the following components: a) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35 wt. % of a Cs salt; b) Cs-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; mixed with up to 35 wt. % of CaCO 3 , MgCO 3 , SrCO 3 , CaO, MgO, or SrO; c) Ni-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce; d) Cs-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, and a different metal spinel of embodiment 2 of at least 10 m 2 /g; e) Cs-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as well as a natural or engineered layered solid comprising 5-10% of the catalyst formulation, 20-30% of the catalyst formulation, 40-50% of the catalyst formulation, 50-60% of the catalyst formulation, 60-70% of the catalyst formulation, 70-80% of the catalyst formulation. The resulting formulation is calcined to up 2,100° F., resulting in a metal-impregnated, Cs-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     12. A reverse water gas shift (RWGS) catalyst of embodiment 3 wherein the catalyst is comprises the following components: a) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35 wt. % of a Fe salt; b) Fe-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; mixed with up to 35 wt. % of CaCO 3 , MgCO 3 , SrCO 3 , CaO, MgO, or SrO; c) Fe-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce; d) Fe-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, and a different metal spinel of embodiment 2 of at least 10 m 2 /g; e) Fe-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as well as a natural or engineered layered solid comprising 5-10% of the catalyst formulation, 20-30% of the catalyst formulation, 40-50% of the catalyst formulation, 50-60% of the catalyst formulation, 60-70% of the catalyst formulation, 70-80% of the catalyst formulation. The resulting formulation is calcined to up 2,100° F., resulting in a metal-impregnated, Fe-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     13. A reverse water gas shift (RWGS) catalyst of embodiment 3 wherein the catalyst is comprises the following components: a) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m2/g and 1000 m2/g; impregnated with up to 35 wt. % of a Co salt; b) Ni-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; mixed with up to 35 wt. % of CaCO 3 , MgCO 3 , SrCO 3 , CaO, MgO, or SrO; c) Ni-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce; d) Co-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, and a different metal spinel of embodiment 2 of at least 10 m 2 /g; e) Co-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as well as a natural or engineered layered solid comprising 5-10% of the catalyst formulation, 20-30% of the catalyst formulation, 40-50% of the catalyst formulation, 50-60% of the catalyst formulation, 60-70% of the catalyst formulation, 70-80% of the catalyst formulation. The resulting formulation is calcined to up 2,100° F., resulting in a metal-impregnated, Co-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     14. A reverse water gas shift (RWGS) catalyst of embodiment 3 wherein the catalyst is comprises the following components: a) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m2/g and 1000 m2/g; impregnated with up to 35 wt. % of a Ni salt; b) Ni-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m2/g; mixed with up to 35 wt. % of CaCO 3 , MgCO 3 , SrCO 3 , CaO, MgO, or SrO; c) Ni-alumina spinel according to embodiment 2 having a surface area between 10 m2/g and 1000 m2/g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce; d) Ni-alumina spinel according to embodiment 2 having a surface area between 10 m2/g and 1000 m2/g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, and a different metal spinel of embodiment 2 of at least 10 m 2 /g; e) Ni-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as well as a natural or engineered layered solid comprising 5-10% of the catalyst formulation, 20-30% of the catalyst formulation, 40-50% of the catalyst formulation, 50-60% of the catalyst formulation, 60-70% of the catalyst formulation, 70-80% of the catalyst formulation. The resulting formulation is calcined to up 2,100° F., resulting in a metal-impregnated, Ni-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     15. A reverse water gas shift (RWGS) catalyst of embodiment 3 wherein the catalyst is comprises the following components: a) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35 wt. % of a Cu salt; b) Cu-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; mixed with up to 35 wt. % of CaCO 3 , MgCO 3 , SrCO 3 , CaO, MgO, or SrO; c) a Cu-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce; d) Cu-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as a different metal spinel of at least 10 m 2 /g; e) Cu-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as well as a natural or engineered layered solid comprising 5-10% of the catalyst formulation, 20-30% of the catalyst formulation, 40-50% of the catalyst formulation, 50-60% of the catalyst formulation, 60-70% of the catalyst formulation, 70-80% of the catalyst formulation. The resulting formulation is calcined to up 2,100° F., resulting in a metal-impregnated, Cu-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     16. A reverse water gas shift (RWGS) catalyst of embodiment 3 wherein the catalyst is comprises the following components: a) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35 wt. % of a Zn salt; b) Zn-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; mixed with up to 35 wt. % of CaCO 3 , MgCO 3 , SrCO 3 , CaO, MgO, or SrO; c) Zn-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce; d) Zn-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as a different metal spinel of at least 10 m 2 /g; e) Zn-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as well as a natural or engineered layered solid comprising 5-10% of the catalyst formulation, 20-30% of the catalyst formulation, 40-50% of the catalyst formulation, 50-60% of the catalyst formulation, 60-70% of the catalyst formulation, 70-80% of the catalyst formulation. The resulting formulation is calcined to up 2,100° F., resulting in a metal-impregnated, Zn-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     17. A reverse water gas shift (RWGS) catalyst of embodiment 3 wherein the catalyst is comprises the following components: a) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35 wt. % of a La salt; b) La-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; mixed with up to 35 wt. % of CaCO 3 , MgCO 3 , SrCO 3 , CaO, MgO, or SrO; c) La-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce; d) La-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as a different metal spinel of at least 10 m 2 /g; e) a La-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as well as a natural or engineered layered solid comprising 5-10% of the catalyst formulation, 20-30% of the catalyst formulation, 40-50% of the catalyst formulation, 50-60% of the catalyst formulation, 60-70% of the catalyst formulation, 70-80% of the catalyst formulation. The resulting formulation is calcined to up 2,100° F., resulting in a metal-impregnated, La-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     18. A reverse water gas shift (RWGS) catalyst of embodiment 3 wherein the catalyst is comprises the following components: a) Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35 wt. % of a Ce salt; b) Ce-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; mixed with up to 35 wt. % of CaCO 3 , MgCO 3 , SrCO 3 , CaO, MgO, or SrO; c) Ce-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce; d) Ce-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as a different metal spinel of at least 10 m 2 /g; e) a Zn-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; impregnated with up to 35% of mixtures of primary, secondary, ternary, or more mixtures of salt mixtures including but not limited to Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, as well as a natural or engineered layered solid comprising 5-10% of the catalyst formulation, 20-30% of the catalyst formulation, 40-50% of the catalyst formulation, 50-60% of the catalyst formulation, 60-70% of the catalyst formulation, 70-80% of the catalyst formulation. The resulting formulation is calcined to up 2,100° F., resulting in a metal-impregnated, Ce-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     19. Although the embodiments 5-18 cover the formulations of a CO 2  hydrogenation catalyst that focuses on the impregnation of a specific metal on a metal-alumina spinel synthesized from the same metal, the various permutations of the other metals in embodiment 3 on the other metal-spinels in embodiment 2 are covered (e.g., Ni on Mg-aluminate; Ni on Ba-aluminate, etc.). 
     20. This embodiment comprises a reverse water gas shift (RWGS) catalyst (Type C) which employs one of the metal-alumina spinels described in embodiment 2 with a) the impregnation of up to 35 wt. % of two metal salts (e.g. nitrates, acetates, carbonates, etc.) or metal hydroxides selected from a group comprising Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, which don&#39;t chemically bond to the spinel; b) calcining the metal-alumina spinel impregnated with the two or more metals at a temperature up to 2,100° F., thereby synthesizing a solid-solution of the two metals on the metal-alumina spinel. 
     21. The reverse water gas shift (RWGS) catalyst of embodiment 20 wherein the catalyst is produced by a process comprising the steps of: a) synthesizing a Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; b) impregnating the spinel with up to 35 wt. % of a mixture of Ni and Mg; c) calcining the Ni- and Mg-impregnated, Mg-alumina spinel at a temperature up to 2,100° F.; d) thereby producing a solid-solution of the two metals that has the composition Ni 2 Mg. Ni and Mg form a solid solution at 2,100° F. since Ni and Mg both crystallize in a face-centered cubic structure, have similar electronegativities and valences. 
     22. The reverse water gas shift (RWGS) catalyst of embodiment 20 wherein the catalyst is produced by a process comprising the steps of: a) synthesizing a Mg-alumina spinel according to embodiment 2 having a surface area between 10 m 2 /g and 1000 m 2 /g; b) impregnating the spinel with up to 35 wt. % of a mixture of Ni and Cu; c) calcining the Ni- and Mg-impregnated, Mg-alumina spinel at a temperature up to 2,100° F.; d) thereby producing a solid-solution of the two metals that has the composition NiCu 3 . Ni and Cu form a solid solution at 2,100° F. since Ni and Cu both crystallize in a face-centered cubic structure, have similar atomic radii, electronegativities and valences. 
     Catalyst Performance Embodiments 
     Most of the improved CO 2  hydrogenation catalysts described above in the Catalyst Composition Embodiments meet the commercial quality and performance specifications summarized in Table 1. 
     1. Low-Cost Constituents—The catalysts are formulated primarily using low-cost Group 1 elements (Alkali Metals) comprising Na, K, Li, Cs and Rb; the Group 2 elements (Alkaline Earth Metals): Mg, Ca, Sr, Ba and Be; the Transition Metals comprising Ni, Co, Fe and Cu; and the Rare-Earth elements comprising Ce, Y, La. It has been found that the addition of small quantities of precious metals (such as Au, Ag, Pt, Pd, Ir) do not improve the performance of these improved CO 2  hydrogenation catalysts. 
     2. Commercial Production—The substrates and catalysts are economically produced in multiple ton quantities using well established commercial-scale production processes. The metal alumina spinel substrates may be prepared by a) coprecipitation methods or b) by mixing appropriate molar quantities of a metal precursors and alumina particles to form a slurry, drying the slurry, and then calcining the mixture up to 2,600° F. The catalysts are prepared by the impregnation of the metal(s) on the metal-alumina spinel substrates followed by calcination up to 2,100° F. 
     3. Physically Robust—The disclosed catalysts have hardness of between 4 Mohs and 10 Mohs, or an equivalent Rockwell hardness. This high level of hardness eliminates the potential problem of catalyst breakage, cracking and ablation. 
     4. Chemically and Physically Stable—These a). metal-alumina spinels, b). metal impregnated metal metal-alumina spinels and c). solid solutions impregnated on the metal metal-alumina spinels maintain their chemical and physical properties (such as not melt) up to 2,100° F. 
     5. Compatible with Commercial Catalytic Reactors—The catalyst pellets, tablets, or hollow tablets are easy to load into catalytic reactors (tubular, or packed bed reactors). The pressure drop from the top to the bottom of the catalytic reactors is between 0 and 50 psi and usually between 0 and 25 psi. The activation of the catalyst (e.g., reduction with H 2 ) is carried out in-situ if required. 
     6. High CO 2  Conversion Efficiency—The CO 2  to CO conversion efficiency for H 2 /CO 2  blends with ratios higher than 3.0/1.0 is between 70% and 100%, preferably between 75% and 100%, and more preferably between 80% and 100% at space velocities between 2,000 hr −1  and 1,000,000 hr −1  and temperatures between 1,300° F. and 1,800° F. 
     7. High CO Production Selectivity—The disclosed catalyst formulations have CO of at least 90%. Some of the preferred catalyst formulations have CO selectivities greater than 99% with methane selectivities below 1%, and CO selectivities as low as 0.1% in some cases. 
     8. Doesn&#39;t Coke or Change Composition—These improved catalyst formulations do not coke or change chemical composition during operation. 
     9. Long-Term Performance—Several of the improved CO 2  hydrogenation catalysts have been tested for more than 1,500 hrs. on stream and it has been determined that the reduction in CO 2  conversion is between 0 and 0.50% per 1000 hours. 
     Examples 
     Example 1: Improved RWGS Catalyst Formulation A—A stream comprising CO 2  is produced by an industrial process or captured from ambient air. This CO 2  stream is fed to a CO 2  capture facility. The CO 2  capture facility uses methyl diethanolamine (MDEA) in an absorber tower to capture the CO 2 . Relatively pure CO 2  is regenerated from the MDEA by heating. Low-carbon electricity from a wind farm, a solar farm, a nuclear power plant, or other low-carbon power sources is available at the site of the carbon capture facility. High-purity water is produced from locally available water. Low-carbon H 2  is produced from the purified water via electrolysis. 
     This reaction uses the low-carbon electricity to split the water into H 2  and O 2 . The electrolyzer in this example is a PEM Electrolyzer. The electrolyzer produces two streams, H 2  and O 2 . 
     This improved catalyst formulation A of embodiment 2 (above) is manufactured by a method comprising the steps of: a) synthesizing a metal-aluminate spinel having a surface area between 10 m 2 /g and 1000 m 2 /g, wherein the metal spinel is selected from a group comprising:
         a. Group 2 metals calcined with alumina to form Mg-aluminate, Ca-aluminate, Sr-aluminate, Ba-aluminate and Be-aluminate.   b. Group 1 metals calcined with alumina to form Li-aluminate, Rb-aluminate, and Cs-aluminate.   c. Transition metals calcined with alumina to form Fe-aluminate, Co-aluminate, Ni-aluminate, Cu-aluminate, and Zn-aluminate.   d. Rare-earth metals calcined with alumina to form La-aluminate, and Ce-aluminate.       

     The improved catalyst is used to convert the captured CO 2  and renewable H 2  stream into syngas. Example 1 provides the relationship between temperature and % CO 2  conversion to CO for the improved CO 2  hydrogenation catalyst. In this example, the H 2  to CO 2  ratio is 3.4/1.0, the pressure is 300 psig, and the space velocity is 20,000 hr −1 . The conversion of CO 2  varies from 75% to 83.5% from 1,250-1,650° F. with between 0 and 0.5% conversion reduction after 1,000 hrs. on stream. Since the catalysts at these relevant temperature ranges exhibits very little sintering, their lifetime is excellent. The CO selectivity is &gt;99.5% with between 0 and 0.5% CH 4  selectivity. The dotted line is the trendline which shows that the relationship between CO 2  conversion and temperature is nearly linear. 
     Example 1—The Typical Relationship between Temperature and % CO 2  Conversion to CO for the Improved RWGS Catalysts.  FIG.  1    shows the typical relationship between Temperature and % CO 2  Conversion to 0 for the Improved RWGS Catalysts. The X-Axis is temperature in degrees Fahrenheit. The Y-Axis is the CO 2  Conversion in mole percent to CO. As can be seen at a temperature of 1200° F. to 1750° F., the CO 2  conversion is between 70 and 85%. 
     Example 2: Improved RWGS Catalyst Formulation B—This improved catalyst formulation B is described in embodiment #3 (above) as a metal on a metal aluminate. This type B CO 2  hydrogenation catalyst employs one of the metal-alumina spinels described in embodiment 2 with a) the impregnation of up to 35 wt. % of a metal salt (e.g. nitrates, acetates, carbonates, etc.) or metal hydroxide selected from a group comprising Mg, Ca, Sr, Ba, Li, Rb, Cs, Fe, Co, Ni, Cu, Zn, La and Ce, which don&#39;t chemically bond to the spinel; b) calcining the impregnated, metal-coated metal-alumina spinel at a temperature up to 2,100° F., thereby synthesizing a catalyst that is an metal-impregnated, metal-alumina spinel that has a surface area between 5 m 2 /g and 1000 m 2 /g. 
     In this example the catalyst is MgO or Mg(OH) 2  impregnated on a Mg-Alumina Spinel. The MgO or Mg(OH) 2  is reduced in-situ with H 2 , producing Mg, MgO and Mg(OH) 2  on the surface of the spinel. 
     The improved catalyst is used to convert the captured CO 2  and renewable H 2  stream into syngas. In this example, the H 2  to CO 2  ratio is 3.4/1.0, the temperature is 1,650° F., the pressure is 300 psig, and the space velocity is 20,000 h −1 . The conversion of CO 2  is 82% at 1,650° F. with between 0 and 0.5% conversion reduction after 1,000 hrs. on stream. The CO selectivity is greater than 99%. 
     Example 3: Improved RWGS Catalyst Formulation C—This improved RWGS catalyst C is described in embodiments 20-23 for the efficient conversion of CO 2  and H 2  into syngas by a process comprising the steps of: a) synthesizing a Mg-aluminate spinel having a surface area between 10 m 2 /g and 1000 m 2 /g; b) coating the spinel with up to 20 wt. % of Mg to provide a metal-coated spinel; c) impregnating the metal-coated spinel with a solution comprising water soluble nickel salts and either nitrate or acetate salts of rare-earth metals; d) calcining the impregnated, metal-coated spinet at a temperature up to 2,100° F., thereby synthesizing a catalyst that is an impregnated spinel that is comprised with up to 35 wt. % nickel and of 0.1 wt. % to 5.0 wt. % of the rare earth metals. The catalyst may contain 0.1 to 5 parts-by-weight of cerium, ruthenium, lanthanum, platinum, or rhenium, and 2 wt. % to 20 wt. % nickel per 100 parts-by-weight of the spinel support. As described in embodiment #21, the solid solution catalyst is Ni 2 Mg. 
     Another improved catalyst type C for the efficient conversion of CO 2  and H 2  into syngas is produced by a process comprising the steps of a) synthesizing a Cu impregnated Cu-aluminate spinel having a surface area between 10 m 2 /g and 1000 m 2 /g; b) coating the spinel with up to 20 wt. % of Cu to provide a metal-coated spinel; c) impregnating the metal-coated spinel with a solution comprising water soluble Ni salts and either nitrate or acetate salts of rare-earth metals; d) calcining the impregnated, metal-coated spinel at a temperature up to 2,100° F., thereby synthesizing a catalyst that is an impregnated spinel that is comprised with up to 20 wt. % nickel and of 0.1 wt. % to 5.0 wt. % of the rare earth metals. As described in embodiment #22, the primary solid solution catalysts are NiCu 3 . 
     The relationship between temperature and CO 2  conversion efficiency (Example #1) is similar for catalyst #1 and catalyst #2. The difference is that catalyst #1 has between 0 and 0.5% CH 4  selectivity compared to up to 7.0% CH 4  selectivity (depending upon temperature and pressure) for catalyst #2. However, catalyst #2 is more efficient at higher space velocities. 
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