Effect of Metal Content on Ethanol Decomposition over Ni-Co Catalysts Supported on La-Ce Oxides

The search for catalysts with features that can improve coke resistance and decrease byproduct formation is a current goal in H2 production from renewable sources. In this work, the effect of the presence of Ni nanoparticles over Co/La-Ce oxides on the ethanol decomposition reaction was studied. Catalysts were synthetized using as precursor a La0.8Ce0.2NixCo1-xO3 perovskite-type material to ensure a low segregation of phases and a high dispersion of metals. After reduction at 873 K, the perovskite structure was destroyed, and metal Co-Ni particles were supported over a lanthanum-cerium oxide. The materials were characterized by different techniques before and after reaction. Solids exhibited metal particle sizes between 5 and 15 nm demonstrating the advantages of the preparation method to obtain Ni-Co alloys. Although the results of adsorption of ethanol followed by diffuse reflectance infrared fourier transformed spectroscopy (DRIFTS) showed acetate species strongly adsorbed on the catalyst’s surface, the material (Ni0.7Co0.3/La0.8Ce0.2) with the lowest particle size was the most stable system leading to the lowest amount of carbon deposits during ethanol decomposition. This catalyst showed the better performance, with a higher ethanol conversion (98.4%) and hydrogen selectivity (75%). All catalysts exhibited carbonaceous deposits, which were an ordered and disordered carbon phase mixture.

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title: Production of hydrogen from ethanol: review of reaction mechanism and catalyst deactivation.
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title: Enhanced bimetallic Rh-Ni supported catalysts on alumina doped with mixed lanthanum-cerium oxides for ethanol steam reforming
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title: Effect of Ni incorporation in cobalt oxide lattice on carbon formation during ethanol decomposition reaction
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title: Stable reduced Ni catalysts for xylose hydrogenation in aqueous medium
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title: In situ XAS and FTIR studies of a multi-component Ni/Fe/Cu catalyst for hydrogen production from ethanol
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title: Ethanol decomposition and steam reforming of ethanol over CeZrO2 and Pt/CeZrO2 catalyst: Reaction mechanism and deactivation
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title: Decomposition of ethanol over Ni-Al catalysts: effect of copper addition
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title: Production of hydrogen-rich gas and multi-walled carbon nanotubes from ethanol decomposition over molybdenum modified Ni/MgO catalysts
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title: Reactivity of high surface area CeO2 synthesized by surfactant-assisted method to ethanol decomposition with and without steam
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title: Structural transformations of highly porous nickel catalysts during ethanol conversion towards hydrogen
abstract: In this work, we report a liquid-phase reduction method to prepare porous non-supported amorphous nickel catalysts with high surface areas (65–250 m 2 /g). A highly crystalline face center cubic Ni (fcc-Ni) catalyst with 110 m 2 /g surface area was also prepared by frontal crystallization of the amorphous nickel catalyst. The catalytic activity and stability of these catalysts for ethanol decomposition was investigated at different time on stream (TOS) to understand structural transformations occurring at the early stages of catalyst activation-deactivation. Activity vs. TOS results obtained at 473 K show that on the amorphous catalysts the conversion increases from about 50% to 60–75% reaching a steady value at ∼30 h TOS, which remains constant during the observed 96 h of TOS. The fcc-Ni catalyst initially exhibits a higher conversion (∼85%), however, it quickly deactivates to a conversion in the similar range as the amorphous catalysts. It is also shown that BET surface areas of amorphous catalysts decreases during hydrogen pretreatment at 473 K due to crystallization, grain growth, and sintering. The structure of amorphous catalysts continuously refines to form a combination of fcc-Ni and hexagonal close-packed nickel (hpc-Ni) phases, as well as nickel carbide (Ni 3 C) and carbon layers that stabilize catalytic activity. The structure of the fcc-Ni catalyst remains unchanged during the 96 h TOS experiment indicating that carbon deposition might cause its initial deactivation. At 523 K, the amorphous catalyst shows 100% conversion, which remains constant during 96 h of TOS, while the fcc-Ni crystalline catalyst initially exhibits 95% conversion and then slowly deactivates to ∼80% at 96 h TOS. Thus at 523K the stabilized amorphous catalyst does not deactivate under the same TOS compared to the crystalline fcc-Ni catalyst, showing that the active sites on these catalysts are different. The findings of this work suggest that the liquid-phase reduction method can be used to prepare active and stable catalysts for reactions involving decomposition of alcohols and hydrocarbons to produce hydrogen.

title: Co–Ni bimetal catalyst supported on perovskite-type oxide for steam reforming of ethanol to produce hydrogen
abstract: Perovskite-type oxide (PTO) of LaFeO3 supported Ni–Co bimetallic catalysts were prepared by citric acid complexation-impregnation method and were used for the steam reforming of ethanol (SRE) to produce hydrogen. The anti-sintering and anti-coking properties of the catalysts for the reaction have been investigated and compared with the monometal catalysts. The catalysts were characterized by using temperature programmed reduction, X-ray diffraction, transmission electron microscopy and thermal analysis techniques. The results indicate that the catalyst was both highly selective to hydrogen and very stable for SRE reaction. Characterization results indicated that Ni–Co was in the state of solid solution alloy. Comparing with corresponding monometal catalysts, the bimetal catalyst exhibited better anti-sintering ability and similar anti-carbon deposition ability. The valuable information indicated in this work is that based on the special characters of PTO, bimetal nano-particles can be supported on metal oxides, which should be a new and promising method for preparing supported bimetal catalysts.

title: Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984)
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title: Transfer hydrogenation from glycerol over a Ni-Co/CeO2 catalyst: A highly efficient and sustainable route to produce lactic acid
abstract: Bimetallic Ni-Co catalysts supported on nanosized CeO2 were prepared and investigated as heterogeneous catalysts for the transfer hydrogenation between glycerol and various H2 acceptors (levulinic acid, benzene, nitrobenzene, 1-decene, cyclohexene) to selectively produce lactic acid (salt) and the target hydrogenated compound. The bimetallic NiCo/CeO2 catalyst showed much higher activity than the monometallic Ni or Co counterparts (with equal total metal mass), thus indicating strong synergetic effects. The interaction between the metallic sites and the CeO2 support was thoroughly characterised by means of transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX) mapping, X-ray photoelectron spectroscopy (XPS), hydrogen-temperature programmed reduction (H2-TPR) and X-ray diffraction (XRD). Combining characterisation and catalytic results proved that the Ni species are intrinsically more active than Co species, but that incorporating Co into the catalyst formulation prevented the formation of large Ni particles and led to highly dispersed metal nanoparticles on CeO2, thus leading to the observed enhanced activity for the bimetallic system. The highest yield of lactic acid (salt) achieved in this work was 93% at 97% glycerol conversion (160 °C, 6.5 h at 20 bar N2, NaOH: glycerol = 1.5). The NiCo/CeO2 catalyst also exhibited high activity and selectivity towards the target hydrogenated products in the transfer hydrogenation reactions between glycerol and various H2 acceptors. Batch recycle experiments showed good reusability, with retention of 80% of the original activity after 5 runs.

title: X-ray photoelectron spectroscopic chemical state quantification of mixed nickel metal, oxide and hydroxide systems
abstract: Quantitative chemical state X-ray photoelectron spectroscopic analysis of mixed nickel metal, oxide, hydroxide and oxyhydroxide systems is challenging due to the complexity of the Ni 2p peak shapes resulting from multiplet splitting, shake-up and plasmon loss structures. Quantification of mixed nickel chemical states and the qualitative determination of low concentrations of Ni(III) species are demonstrated via an approach based on standard spectra from quality reference samples (Ni, NiO, Ni(OH)2, NiOOH), subtraction of these spectra, and data analysis that integrates information from the Ni 2p spectrum and the O 1s spectra. Quantification of a commercial nickel powder and a thin nickel oxide film grown at 1-Torr O2 and 300 °C for 20 min is demonstrated. The effect of uncertain relative sensitivity factors (e.g. Ni 2.67 ± 0.54) is discussed, as is the depth of measurement for thin film analysis based on calculated inelastic mean free paths.

title: New interpretations of XPS spectra of nickel metal and oxides
abstract: A current interpretation of XPS spectra of Ni metal assumes that the main 6 eV satellite is due to a two hole c3d 9 4s 2 (c is a core hole) final state effect. We report REELS observation in AES at low voltages of losses (plasmons and inter-band transitions) corresponding to the satellite structures in Ni metal 2p spectra. The satellite near 6 eV is attributed to a predominant surface plasmon loss. A current interpretation of Ni 2p spectra of oxides and other compounds is based on charge transfer assignments of the main peak at 854.6 eV and the broad satellite centred at around 861 eV to the cd 9 L and the unscreened cd 8 final-state configurations, respectively (L is a ligand hole). Multiplet splittings have been shown to be necessary for assignment of Fe 2p and Cr 2p spectral profiles and chemical states. The assignments of Ni 2p states are re-examined with intra-atomic multiplet envelopes applied to Ni(OH) 2 , NiOOH and NiO spectra. It is shown that the free ion multiplet envelopes for Ni 2+ and Ni 3+ simulate the main line and satellite structures for Ni(OH) 2 and NiOOH. Fitting the NiO Ni 2p spectral profile is not as straightforward as the hydroxide and oxyhydroxide. It may involve contributions from inter-atomic, non-local electronic coupling and screening effects with multiplet structures significantly different from the free ions as found for MnO. A scheme for fitting these spectra using multiplet envelopes is proposed.

title: Interpretation of the x-ray photoemission spectra of cobalt oxides and cobalt oxide surfaces
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title: Unraveling the Chemical State of Cobalt in Co-Based Catalysts during Ethanol Steam Reforming: an in Situ Study by Near Ambient Pressure XPS and XANES
abstract: The steam reforming of ethanol (ESR) has been studied by near ambient pressure XPS (NAP-XPS), extended X-ray absorption fine structure (EXAFS), and X-ray absorption near edge structure (XANES) under in situ conditions in the ALBA synchrotron facility at 200–580 °C and S/C = 3 over different cobalt-based catalysts that showed different catalytic performances: Co3[Si2O5]2(OH)2 (Co-talc), [Co2Mg4Al2(OH)16]CO3·4H2O (Co-hydrotalcite shortened to Co-HT) calcined at 550 °C, and Co3O4 (Co-spinel). Both Co-spinel and Co-talc yield to a greater or lesser degree metallic cobalt under ESR conditions. While Co-spinel shows a complete reduction to metallic cobalt under the conditions used for the XANES measurements, the more bulk-sensitive Co-talc sample exhibits only a partial reduction. On the other hand, under the ESR conditions used with the NAP-XPS, a more surface sensitive technique, the results indicate a higher reduction degree for the Co-talc sample in comparison to the Co-spinel sample. In contrast, the catal...

title: XPS studies of damage induced by X-ray irradiation on CeO2 surfaces
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title: Steam reforming, partial oxidation, and oxidative steam reforming of ethanol over Pt/CeZrO2 catalyst
abstract: The catalytic performance of a Pt/CeZrO 2 catalyst was tested for ethanol decomposition, steam reforming, partial oxidation, and oxidative steam reforming. At low temperature, the catalyst underwent significant deactivation during ethanol decomposition and steam reforming reactions. Co-feeding oxygen decreased the deactivation rate of the catalyst but adversely affected the selectivity to hydrogen. Increasing the reaction temperature greatly improved the stability of the catalyst. A reaction mechanism was proposed based on results obtained from in situ diffuse reflectance infrared spectroscopy analyses carried out under reaction conditions. Ethanol adsorbs as ethoxy species, which may follow one of two distinct pathways: (i) decomposition and production of CO, CH 4 , and H 2 or (ii) dehydrogenation to acetaldehyde and acetyl species. The dehydrogenated species may undergo oxidation to acetate species. The addition of water to the feed promoted the formation of acetate species. Water also facilitated the decomposition of acetaldehyde and acetate reactions, resulting in the formation of methane, CO, and carbonate.

title: Hydrogen production for fuel cell applications by ethanol partial oxidation on Pt/CeO2 catalysts: the effect of the reaction conditions and reaction mechanism
abstract: This work studied the effect of reaction conditions and catalyst reducibility on the performance of the Pt/CeO2 catalyst in the partial oxidation of ethanol. Oxygen storage capacity (OSC) measurements allowed evaluation of the oxygen transfer capacity of the catalysts. Metal dispersion was determined through cyclohexane dehydrogenation, a structure-insensitive reaction. Infrared spectroscopy of adsorbed ethanol, temperature-programmed desorption, and temperature-programmed surface reaction of ethanol was performed to establish the reaction mechanism. The low dispersion and low oxygen transfer capacity led to a decrease in both the activity and stability of Pt/CeO2 catalysts on partial oxidation of ethanol. The higher amount of oxygen near the metal particles promotes the mechanism of carbon removal from the metallic surface, which takes place at the metal–support interfacial perimeter. Moreover, the increase in particle size decreases the metal–support interfacial area, reducing the effectiveness of the mechanism of carbon removal from the metallic surface. Furthermore, the results obtained on partial oxidation of ethanol showed that an increase in the residence time or reaction temperature increased the ethanol conversion and H2 yield. Regarding selectivity for hydrocarbons and oxygenated products, the production of methane increased and the selectivity for acetaldehyde decreased as the residence time or reaction temperature was increased. At low conversions, the ethanol dehydrogenation dominates, forming acetaldehyde, whereas at high conversions the decomposition of ethanol is favored, producing CH4, H2, and CO. A reaction mechanism is proposed to explain the catalytic tests.

title: Hydrogen formation in ethanol reforming on supported noble metal catalysts
abstract: The formation and stability of surface species generated in the interaction of ethanol and ethanol–water mixture with Al2O3 and CeO2-supported noble metal catalysts were studied by FT-IR, TPD and TPR methods. It was found that water enhanced the stability of ethoxide surface species formed in the dissociation of ethanol. Dehydrogenation of molecularly adsorbed ethanol was proposed as a key reaction step. The TPD spectra of ethanol adsorbed on supported noble metals exhibited a high temperature desorption stage which was explained by the formation and decomposition of surface acetate species. Ethylene (product of the dehydration of ethanol) was mainly formed on Al2O3-supported noble metals, while on CeO2-supported noble metals significant amount of acetaldehyde (originated from the dehydrogenation of ethanol) was also formed. In the steam reforming of ethanol the selectivity of H2 formation decreased but that of C2H4 increased in time, while the conversions were stable on alumina-supported noble metals. These observations were explained by the inhibiting effect of surface acetate species.

title: Data underpinning:Nano-socketed nickel particles with enhanced coking resistance grown in situ by redox exsolution
abstract: DN thanks the European Project METSAPP (FCH JU-GA 278257) for funding. We also thank NSF and EPSRC for Materials World Network funding ref EP/J018414/1.

title: LaMnO3-based perovskite with in-situ exsolved Ni nanoparticles: a highly active, performance stable and coking resistant catalyst for CO2 dry reforming of CH4
abstract: Wet impregnation method has been widely adopted to synthesize the oxide substrate supported catalysts for CO2 dry reforming of CH4. However, their particle size and distribution are not stable and uniform, causing rapid particle growth and carbon deposition. Here, we show that these problems can be overcome by using a LaMnO3 (LM)-based perovskite in which 20 mol% Ni is doped (La0.9Mn0.8Ni0.2O3, LMN) and then exsolved (R-LMN) by in-situ reduction in 5%H2-N2 stream at 800 °C. The perfomance of such catalyst is compared with that of the Ni-impregnated LM (NLM) reduced under the same conditions (R-NLM). The SEM and TEM analyses reveal that the exsolved Ni nanoparticles in R-LMN are uniform in size, evenly distributed and partially embedded into and hence bonded strongly with the substrate; but the Ni particles in R-NLM are variable in size and weakly bonded with the substrate. Therefore, the particle growth (coalescence) is largely suppressed for the exsolved Ni nanoparticles in R-LMN but not for the Ni nanoparticles in R-NLM. It is also comfirmed that the Ni particles in R-NLM are lifted off from the substrate by carbon fibers formed during test. Consequently, R-LMN demonstrates high and stable conversion (above 80%) and selectivity (above 90%) with a strong resistance to carbon deposition at 700 °C for 24 h. But, a large amount of carbon fiber is formed with a Ni particle at the tip in tested R-NLM, resulting in rapid performance degradation. The high performance of R-LMN for CO2 dry reforming of CH4 is attributed to the stable nanosized Ni particles and LMN substrate that provides more oxygen vacancies for CO2 activation and in turn carbon oxidation.

title: A combined in situ time-resolved UV–Vis, Raman and high-energy resolution X-ray absorption spectroscopy study on the deactivation behavior of Pt and Pt-Sn propane dehydrogenation catalysts under industrial reaction conditions
abstract: The catalytic performances of Pt/Al2O3 and Pt–Sn/Al2O3 catalysts for the dehydrogenation of propane through consecutive reaction–regeneration cycles have been studied under realistic reaction conditions. A 10-fold successive dehydrogenation–regeneration cycling study, similar to that employed in an industrial propane dehydrogenation reactor, was performed in order to examine the catalyst activity and stability as well as the propene selectivity. Combined in situ UV–Vis/Raman spectroscopy measurements were taken in order to follow the coke formation processes during propane dehydrogenation. This approach allowed correlating propane conversion and propene formation with the on-line determined Raman D over G band intensity ratio and amount of coke formed. These in situ measurements on coke formation and related catalyst deactivation were supplemented by in situ high-energy resolution fluorescence detected (HERFD) XANES measurements in order to characterize the structural and electronic properties of the supported Pt and PtSn nanoparticles during the successive dehydrogenation–regeneration cycles. This combination of powerful spectroscopic techniques revealed unique information regarding the activity behavior and deactivation mechanism of Pt- and PtSn-based propane dehydrogenation catalysts, enabling us to identify important structure-electronic-performance relationships as well as fundamental insight into the dynamics of PtSn alloy formation processes in Pt nanoparticles at elevated temperatures.

title: Operando Raman spectroscopy on CO2 methanation over alumina-supported Ni, Ni3Fe and NiRh0.1 catalysts: Role of carbon formation as possible deactivation pathway
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