SERVPR-233-2658 

UC Category: 61f 

DE85012172 

Synthesis and Catalysis for 

Alcohol Fuels 

3. C. Smart 

August 1985 

Prepared under Task No. 5150.20 

Solar Energy Research Institute 

A Division of Midwest Research Institute 

161 7 Cole Boulevard 

Golden, Colorado 80401 

Prepared for the 

U.S. Department of Energy 

Contract No. DE-AC02-83CH10093 
PREFACE 

This progress report describes the chemical synthesis of new materials and their evaluation as homogeneous and heterogeneous catalysts for the conversion of biomass-derived syngas (H2/CO) to 

alcohol fuels and fuel additives. This research was conducted by 

Alex Miedaner, Calvin Curtis, and James Smart of the Photoconversion Branch, Solar Fuels Division, SERT, and David Wickham and 

Scott Cowley of Colorado School of Mines. 

1 nJ. u Smart, Leader 

Synthesis and Catalysis Task 

Approved for 

SOLAR ENERGY RESEARCH INSTITUTE 

Solar Fuels Research fiivisian 
Objective 

Active and selective catalysts are needed for the conversion of biomassderived syngas (H2/CO) to alcohol fuels and fuel additives. The synthesis, 

characterization, and evaluation of selected dinuclear organometallic complexes of zirconium for reactions with H2/C0 have been completed in an effort 

to develop new homogeneous syngas catalysts. 

Discussion 

Screening studies and prelim.inary results have been obtained with heterogeneous modified alumina-supported palladium catalysts for the production of 

higher alcohols from syngas. Following the recent discovery that selected 

early transition metal organometallic complexes with hydride ligands will 

stoichiometrically reduce carbon monoxide to coordinated ethylene glycolate, a 

two-carbon alcohol, we have demonstrated that dinuclear analogues of these 

complexes are even more reactive. We have studied the synthetic organometallic chemistry of dinuclear zirconium complexes with bridging fulvalene 

ligands. Reactions with H2 and CO yielded reactive zirconium hydride and carbony1 derivatives that were isolated and characterized. Combined H2/C0 

reactions and in situ Fourier transform nuclear magnetic resonance (FT-NMR) 

studies demonstrate that low pressure and temperature reduction of coordinated 

CO can be accomplished. This important step in the development of a catalytic 

CO hydrogenation cycle has led us to develop new technical approaches to this 

catalysis problem, based on the synthetic and reaction studies presented in 

this report. Future work is outlined on both homogeneous and heterogeneous 

catalysis. 
TABLE OF mNTENTS 

Page 

1.0 Introduction ........................................................ 1 

2.0 Synthesis. Characterization. and Reaction of Organometallic 

Complexes ........................................................... 9 

2. 1 Organic Synthesis of Ligands .................................. 9 

2.2 Synthesis of Dinuclear Zirconium Complexes .................... 9 

3.0 Conclusions and Recommendations ..................................... 15 

4. 0 References ......................................................... 23 

Appendix ................................................................. 25 

SECTION 1.0 

INTRODUCTION 

The development of catalysts for syngas (H*/co) conversion that are both 

active at low temperatures and pressures and selective for higher alcohols is 

being actively investigated in academic, industrial, and government laboratories in virtually all developed countries [l ,2] . Such catalysts will be 

particularly important in the production of oxygenated hydrocarbon fuels and 

fuel additives from relatively small-scale biomass-based gas if iers that yield 

syngas. Even if most of the syngas produced from such biomass conversion 

plants is converted to methanol (CH30H), there will be a need for higher 

alcohols and derived ethers for use as fuel additives to improve the octane 

value of methanol or serve as cosolvent s in methanol/gasoline blends. 

This report presents an overview of our FY 1984 research and development 

studies on new homogeneous and heterogeneous catalysts for syngas conversion 

to oxygenated hydrocarbons. A more detailed introduction to the important 

industrial role of homogeneous catalysis in the production of fuels and chemicals was presented in our report for FY 1983 (SERI/PR-233-2231, February, 

1984). 

Figure 1-1 represents an overview of existing and proposed technologies that 

convert biomass to syngas (H2/CO), or syngas and ethylene (H~/co/c~H~), followed by catalytic liquefaction to alcohols. Current coal-based processes 

involve partial oxidation of coal to syngas followed by catalytic "shift" conversion, by the water-gas shift reaction, to a suitable H2:C0 ratio. Catalytic liquefaction of the syngas by ~ischer-~rb'~schatalysis then yields a 

mixture of alcohols and alkanes. This overall process is not particularly 

efficient and yields a wide variety of ~ischer-~ro~sch products. However, 

this technology is appealing in situations where hydrocarbon fuels from coal 

are required. In contrast to heterogeneous iron-based ~ischer-~ri~sch 

cetalysts, the well-developed heterogeneous Cu-ZnO catalysts for the conversion of syngas to methanol are remarkably selective. Suitable heterogeneous 

catalysts for the selective production of higher alcohols from syngas do not 

exist. These alcohols are currently being produced from H2/C0 and olefins 

such as ethylene by homogeneous "oxo" catalysis. In this process the formation of aldehydes by the hydroformylation reaction is followed by hydrogenation to yield alcohols that are one carbon higher than the starting 

olefin. Both reactions are catalyzed by soluble cobalt or rhodlum complexes . 

in homogeneous solution. Suitable heterogeneous catalysts do not exist for 

the production of "oxo" alcohols. 

Table 1-1 lists some general comparisons between homogeneous and heterogeneous 

catalysts and indicates the different operating conditions of the various processes that utilize H~/CO. 

Homogeneous catalysts or catalyst precursors are soluble compounds, often 

transition metal complexes, that combine reactant molecules in a series of 

stoichiometric transformations to yield stable products and regenerated catalysts. The intermediate species in such a catalytic cycle have varying 

degrees of kinetic stability, and a detailed understanding of such transformations forms the molecular basis for the design and synthesis of new and 

Table 1-1. Coaparison of Homogeneous and Heterogeneous Catalysts 

Homogeneous Catalysts 

In single-phase systems, reactants, products, and catalysts-- 

typically a transit ion metal complex-are dissolved in an organic 

solvent. Compared with heterogeneous catalysts, they 

0 Are more active at lower temperatures and pressures 

a Are more active per metal center 

Are more selective in products formed 

a Allow for better heat transfer 

Use discrete, well-defined catalytic species that arc more 

easily studied and modified 

a Operate at 50°-1500~ and 50-500 psi to produce kI2/CO 

Heterogeneous Catalysts 

In two-phase systems, gaseous or liquid reactants and products and 

a solid catalyst material--typically a metal or metal oxide--are 

often dispersed on ceramic supports. Compared with homogeneous 

catalysts, they 

a Are thermally more stable, because they 

- Allow higher reaction rates at higher temperatures 

- Have longer catalyst lifetime 

- Regenerate the catalyst in situ 

a Produce reactants and products that are more readily separated from catalyst 

Operate at 200~-300~~ and 500-1500 psi to produce H2/C0 

improved homogeneous catalysts. Compared with heterogeneous catalysts, homogeneous catalysts are usually more active and allow transformations to take 

place at lower temperatures and pressures. For this reason, and because of 

their well-defined molecular composition and structure, homogeneous catalysts 

tend to be much more selective in the products they form. 

Heterogeneous catalysts are solid materials, typically transition metals on 

ceramic supports, that react with gaseous reactants to yield gaseous products. 

They operate at higher temperatures and pressures and usually yield a wider 

range of products than homogeneous catalysts do. In some areas of catalysis, 

such as the hydrogenation of olefins, both homogeneous and heterogeneous catalysts exist, and both are used industrially in different applications. In 

some areas, such as methanol synthesis from syngas, well-developed and very 

selective heterogeneous catalysts exist, such as Cu-Zn0/Al2O3, for which there 
are no analogous homogeneous catalysts- In the area of "oxo" catalysis, or 

hydroformylation of olefins with hydrogen and carbon monoxide to yield 

aldehydes and higher alcohols, homogeneous cobalt and rhodium catalysts are 

used industrially. Analogous heterogeneous hydroformylation catalysts do not 

exist. 

Efforts to explore the interrelationship of heterogeneous and homogeneous 

catalysts are increasing in various laboratories. One of the goals of our 

research program is to contribute to such efforts. Our expertise in inorganic 

and organometallic synthesis is being utilized in the synthesis and evaluation 

of both homogeneous and heterogeneous catalysts. This broad effort includes 

collaborative research with groups doing structural studies and theoretical 

calculations of electronic structure, spectroscopic studies, reaction and 

mechanistic studies, and surface analysis and characterization of heterogeneous catalysts. A specific research goal is the development of catalysts 

for the hydrogenation and homologation of carbon monoxide to convert "syngas" 

(R2/CO) to higher (C2-C6) alcohols. The Synthesis and Catalysis Task of the 

SERI Alcohol Fuels Program combines in-house research and collaborative subcontractual research with nearby academic institutions to develop distinctly 

new, as well as improved, catalysts for alcohol fuels production and utilization. A major focus of this effort has been the development of active and 

selective homogeneous catalysts for low-temperature, low-pressure conversion 

of biomass-derived syngas to oxygenated hydrocarbons containing two to six 

carbon atoms. This general effort seeks to efficiently utilize the inherently It clean" syngas with a suitable H2/C0 ratio that is available from biomass 

downdraft oxygen gasifiers. 

The more specific goal of research on C2-C6 oxygenated hydrocarbons, in particular higher alcohols, stems from a need for octane enhancers and blending 

fuels for neat methanol and mixed alcohol/gasoline transportation fuels. The 

availability of such blending fuels from biomass-derived syngas would have a 

significant impact on the acceptability of alcohol-based alternate fuels. In 

addition, there is a long-term need for more active low-temperature and lowpressure methanol synthesis catalysts for fuels production from dispersed, 

small-scale biomass gasifiers. The development of either homogeneous or 

heterogeneous catalysts systems that yield various mixtures of methanol and 

higher alcohols would be particularly useful for the production of blended 

transportation fuels, which will require new, mixed-function catalysts if a 

single catalyst train is used. 

 figure 1-2 outlines a general mechanism for the conversion of %/CO to 

methanol and higher alcohols at a mononuclear metal center. This catalytic 

cycle does not specify a metal, its oxidation state, ancillary ligands, or 

overall geometry of the complex. The reaction cycle depicts two kinds of 

metal forql hydride intermediates [M(CHO)(H)], with subsequent transfer of 

hydride to yield either a metal formaldehyde [M(CH20)] or a metal hydroxy 

carbene [M(C(OH)H)] complex. The metal formaldehyde complex with the addition 

of H2 is shown to yield a methoxy metal hydride complex [M(OCH3) (H)] with an 

M-0 bond that then eliminates methanol (CH30H). The metal hydroxycarbene is 

depicted adding H2 to yield an intermediate hydroxymethyl metal hydride complex [M(CH20H) (H) I with an M-C bond. This intermediate can either eliminate 

methanol or undergo CO coordination and migratory insertion, or carbonylation, 

to yield a two-carbon hydroxyacyl metal hydrfde complex [M(COCH20H)(H)l. 

Elimination or hydrogenslysis of this intermediate yields hydroxy acetaldehyde 

[HCOCH~OH], which can be hydrogenated in a separate cycle with the same 

catalyst to yield ethylene glycol (CH20HCH20H). Dehydration followed by 

hydrogenation under the same reaction conditions, or in a separate cycle, will 

yield ethanol (CII3CH20H). Higher alcohols can be formed by successive 

carbonylation and hydrogenation steps of the M-C bonded intermediate, with 

perhaps some dramatic control of the size of the product alcohol from the 

formation of a relatively stable metallocycle, 

This precursor would yield the final product [ CH3 (CH2)n-10Hl by H2 additionThis report describes the synthesis and characterization of new soluble 

organometallic complexes of zirconium and a preliminary evaluation of their 

potential for homogeneous syngas catalysis. Figure 1-3 depicts the molecular 

structures of the various kinds of compounds under investigation. They 

include "planar" metallocenes [(C5H5)2M] and "bent" derivatives [(C5H5)2ML] 

with various additional ligands (L) that include carbon monoxide (M-CO) and 

hydrogen (bl-H). Such complexes, with transition metal metallocenes from the 

left of the period table, can be prepared directly from H2/C0 under mild 

conditions (1-10 atm, room temperature). The stoichiometric reduction of 

H2/C0 to a coordinated ethylene glycolate C2 product has been demonstrated 

with the very reactive complex permethyl zirconocene dihydride [(C5Me5)2ZrH2] 

as shown in Figure 1-4 [3]. The stability of the Zr-0 products formed from 

the very reactive Zr-H intermediate does not allow this stoichiometric process 

to yield a catalytic cycle. 

Figure 1-4 also depicts the structure of dinuclear analogues of the mononuclear metallocenes. The class of bimetallocenes [ (C5~5)2(C10H8)M2] is presently much smaller and less explored. than the bis(fulva1ene)dimetal complexes 

[(C10~8)2~2]. Work to prepare such bimetallic complexes is described in this 

report. Future work in bod homogeneous and heterogeneous catalysis is 

proposed. 


SYNTaESZS, CHARACTEBIZATION, AND aEPlCTIOH OF ORCAHoMETBU,IC COWPLEgES 

1,2,3,4,5-Pentamethylcyclopentadiene and the derived ligand anion sodium pentamethylcyclopentadienide (NaC5Me5) were prepared by a previously published 

procedure [4] . We used these reagents to prepare the new starting complex, 

(C5Me5) ZrC13 . The bridging fulvalene or bicyclopentadienyl ligand system for the synthesis 

of dinuclear bimetallocene complexes was prepared by the reductive coupling of 

sodium cyclopentadienide (NaC5H5) [S] as indicated on Figure 2-1 . Deprotonation of the resulting dihydrofulvalene yields the fulvalene dianion as the 

lithium salt Li2CI0H8 . A particularly important reagent for the preparation 

of early transition metal complexes, such as titani- and zirconium, that we 

have synthesized is the f ulvalene bistrimethyl t in derivative C1 (SnMe3) 2. 

An efficient, largescale organic synthesis of this intermediate has been 

developed. This reagent has the potential for selective transmetallation 

reactions to transfer one or perhaps two fulvalene ligands to yield homodinuclear metal complexes. The reaction of C10H8(SnMe3)2 with one equivalent of 

n-BuLi yields the mixed lithio-tin reagent LiCl0H8SnMe3, in which the distinct 

differences in metal reactivity of each five-membered ring can be used to prepare heterob imetallic complexes containing two different transition metal 

moieties 

Characterization of these organic ligands typically includes multinuclear 

Fourier transform nuclear magnetic resonance spectroscopy (FT-NMR) such as 

'H, 13c, lZ9sn, as well as infrared spectroscopy (IR) at SERI. Elemental 

analyses are performed commercially outside of SERI. 

2.2 SYNTBESIS OF DINUCLEAR ZIRCONIUM COMPLWS 

The synthetic routes used to prepare the new zirconium fulvalene complexes are 

shown in Figure 2-2. A new preparation of the lithium salt of fulvalene 

dianion was recently developed that yields a material free of solvent and 

alkali metal halides. Treatment of this material with (C5Me5)ZrC13 in toluene 

produces good yields of the yellow, air stable tetrachloride complex (a). In 

principle, there are a aumber of ways to convert this chloride precursor into 

the desired hydride complex (c). We chose to try hydrogenolysis of a suitable 

tetraalkyl derivative under mild conditions in hydrocarbon solvents because we 

have had success with this method in similar systems. For this purpose, the 

tetramethyl complex (b) was synthesized by addition of methyl lithium to 

complex (a). However, hydrogenolysis of this material, even at hydrogen 

pressures up to 20 atm, was slow and seems to yield intermediate complexes 

with both methyl and hydride ligands rather than the tetrahydride complex. 

Less stable . alkyls , such as the n-butyl, are generally more easily hydrogenolyzed, so the complex a was treated with butyllithim under a hydrogen 

atmosphere, and tetrahydride was produced. 
Figure 2-1. Synthesis of Dinuclear Biretallocene Coaaplexes 

The interesting hydride bridge$ structure for (c) depicted in Figure 2-2 is 

assigned on the basis of its +H NMR spectrum. This complex is highly reactive, sensitive to oxygen and water, and thermally sensitive. It decomposes, 

even in the solid state, at room temperature, probably by loss of hydrogenDecomposition appears to be followed by the oxidative addition of a ring 

methyl C-H bond to the resulting zirconium(I1) center, as shown in 

Figure 2-3. This sequence is probably repeated to give the symmetrical, 

multiply bridged complex shown. 

This type of reactivity suggests that complex (c) will not effectively promote 

the reduction of carbon monoxide. CO reduction would be expected to occur 

only when CO is a good enough lfgand to break the hydride bridges in complex 


(c) and form a strong complex at temperatures 

decomposition by hydrogen loss. It was found that 

complex (c) at low temperature and that upon warming 

predominates . 

low enough to retard 

CO does not react with 

thermal loss of hydrogen 

Another useful complex for studying syngas reactions in this system is the 

tetracarbonyl zirconium(I1) complex (d in Figure 2-2). This complex was prepared by reducing complex a with activated magnesium powder under carbon 

monoxide pressure. The NHR and infrared spectra of complex (d) are consistent 

with the structure drawn. 

The other possibility for observing CO reduction in this dinuclear zirconium 

system involves treating the carbonyl complex. (d) with hydrogen, as shown in 

Figure 2-4. We found that this procedure yields more promising results. When 

complex .(d) in solution is exposed to low pressures of hydrogen, no reaction 

takes place until the solution is warmed to 70°c0 At that temperature a 

reaction occurs that yields products consistent with stoichiometric reduction 

of carbon monoxide. Several products are obtained under these conditions, but 

they have not been separated and characterized. Recent efforts have been 

directed toward finding conditions of hydrogen pressure and temperature that 

-11 give a cleaner product, and this work is still in progress* 

Figure 2-4. Reduction of Carbon lbnoxidc with the Mnuclear 

Zfrconium Complex (d) 
Related studies that should be continued involve the hydrolysis of zirconium 

complexes containing H2/C0 reduction products and gas chromatographic (GC) 

analysis of the oxygenated hydrocarbon products. Related synthetic studies 

with partially oxidized complexes, e.g., z~~(o)(H)~ and ~r~(0)(C0)~, may allow 

CO hydrogenation to occur, followed by hydrogenolysis of the now less 

"oxophilic" Zr-OCH2-Zr bonds to yield a catalytic cycle. 

We hope that the low thermal stability of both hydride and carbonyl derivatives presented in this report would be found in the proposed methyl, 

hydride, and carbonyl oxide derivatives. Such a feature is desirable for the 

complexes to act as reactive precursors to begin a catalytic cycle. 
SECTION 3.0 

CONCLUSIONS AND RECOHMENZIATIOHS 

We proposed to synthesize a set of dinuclear zirconium complexes with features 

that would make them able to promote reduction of carbon monoxide. Good synthetic routes to several complexes were developed, and two possible routes to 

CO reduction were examined, The first involved reaction of a dinuclear zirconium hydride complex with carbon monoxide. This route does not yield CO 

reduction because an unforeseen thermal decomposition reaction uses up the 

hydride before it can react with CO. The second route involved treatment of a 

zirconium carbonyl complex with hydrogen. We have evidence that CO reduction 

has occurred in this system, but the reduction products have not been fully 

characterized, 

We recommend that future work will proceed in three areas. First, we will 

continue to examine the zirconium carbonyl plus hydrogen system to find out 

what the products of reduction are. Second, we will try two ways to change 

the zirconium hydride system so that the thermal decomposition reaction just 

described does not occur. One way is to remove the more reactive methylsubstituted C5Me5 rings in Figure 3-1, and replace them with "norhal" C5H5 

rings. The C-H bonds on these cyclopentadienyl rings should be less 

accessible to oxidative addition reactions than those of the methyl groups in 

the present complex. 

The second means of circumventing the H2 reductive elimination is to replace 

zirconium with hafnium (Figure 2-3). Hafnium is just below zirconium in the 

periodic table and is expected to exhibit analogous chemistry, However, 

metals from the third transition series generally form more kinetically stable 

complexes than do second-row analogues. 

Finally, we are preparing new dinuclear complexes. of metal further to the 

right in the periodic table. There are limited prospects for achieving catalytic rather than just stoichiornetric reduction of CO with zirconium compounds. This is due to the relatively strong zirconium-oxygen bond strength. 

Idetals further to the right will form weaker bonds to oxygen and also have 

lower oxidation states, which are more accessible. For this reason we are 

preparing dinuclear hydride complexes of vanadium and tantalum so that a 

balance between metal-hydride reducing power and metal-oxygen bond strength 

can be achieved and a catalytic CO reduction system can be designed. 

The proposed research will involve the synthesis of new dinuclear metal 

hydride complexes using metals from group VB of the periodic table, The complexes will be of two structural types as shown in Figure 3-1, All contain a 

bridging fulvalene ligand to hold the two metals together. The two typesb 

differ in that the type I complexes contain a cyclopentadienyl ligand on each 

metal in addition to the fulvalene and hydride ligands, while the type I1 

complexes have only two unidentate electron donor ligands in addition to 

fulvalene and hydrides, The latter have fewer electrons associated with the 

metal and are more coordinatively unsaturated than the first type, Type II 

complexes give us the opportunity to correlate the degree of unsaturation with 

the ability of a complex to reduce CO. 

15 
and w 

L = PR, (trialkylphosphine) 

Type II 

Figure 3-1. Proposed Metal Bydride Complexes 

Note that the vanadium complexes in Figure 3-1 are represented in the +3 oxidation state while the niobium and tantalum complexes are shown in the +5 oxidation state. This is a reflection of the tendency for metals in the first 

transition series (like vanadium) to form stable compounds with lower oxidation states and coordination numbers. The metals below them in the second and 

third rows of the periodic chart tend to form more stable compounds with 

higher oxidation states and higher coordination numbers. 

We have developed relatively straightforward procedures, for which precedents 

exist, to synthesize the proposed complexes. The strategy will be the same in 

all cases. Dinuclear complexes will be synthesized by nucleophilic substi16 
tution reactions of the lithium salt of fulvalene dianion (Li2CI0H8) with 

known mononuclear metal halide complexes. Then the hydride ligands will be 

generated by hydrogenolysis reactions on suitable dinuclear metal alkyl complexes. The synthesis of vanadium complexes will be discussed first followed 

by the synthesis of the niobium and tantalum complexes. 

The synthesis routes to the proposed vanadium complexes are shown in 

Figure 3-2. These reaction schemes are very similar. The starting materials, 

(C5H5)VC12 (PMe3) and VC13 (PMe3) [6] , are known compounds that can be readily 

prepared on a large scale. Both are expected to react with fulvalene dianion 

to give the dinuclear vanadium chloride complexes shown. The halide complexes 

will react with alkyl lithium reagents to yield the corresponding vanadium 

alkyls, which should be stable when R - CH3 and less stable when R is a longer 

chain or branched alkyl group. We do not intend to isolate them, however. 

Instead, the reaction ell be done in a hydrogen atmosphere to yield hydride 

complexes directly. Under these conditions, the vanadium alkyl intermediates 

undergo hydrogenolysis as they are formed to yield the vanadium hydride and 

the alkane. 

The syntheses of the proposed niobium and tantalum complexes are shown in 

Figure 3-3. These routes are similar to those proposed for the vanadium complexes except that with these metals the alkyl groups, which are the precursors to the hydride ligands, must be introduced into the starting complexes 

before the cyclopentadienyl rings are added. The starting materials for these 

reactions, Me3MCI2 [7] and Np2MC13 [8] (where M = Nb,Ta; Me = methyl, 

Np = neopentyl), are known compounds that can be prepared on a large scale. 

The introduction of the fulvalene ligand into the complexes parallels the work 

of R. R. Schrock and coworkers at MIT [7,9] on the synthesis of mono- and 

bis(cyclopentadieny1) complexes of these metals. We have reacted the MegTaClp 

with fulvalene dianion and found that it yields (CIOH8) (TaMegC1)2, as 

expected. The proposed hydrogenolysis reactions are expected to proceed as 

shown to yield the desired hydride complexes. Neopentyl ligands are proposed 

in the second reaction rather than methyls because neopentyl complexes undergo 

hydrogenolysis much faster than the analogous methyl complexes, especially 

when n;-basfc ligands such as chloride, alkoxide, or pyridene are 

present [lo] . Schrock has demonstrated that I (C5Me5)TaCT2H] can be made by 

hydrogenolysis of the neopentyl ligands in (C5Me5)TaCl28p2 under 40 psi H2 at 

room temperature [ll]. Comparable methyl complexes require mch higher 

hydrogen pressures and higher temperatures [lo] . Once the dinuclear metal hydride complexes have been synthesized, reactions 

with carbon monoxide will be examined. A proposed cycle for the conversion of 

CO/H2 to ethylene glycol using one of the complexes is shown in Figure 3-4. 

Two key features of this cycle should be addressed. First, the bridging formaldehyde complex at the bottom of the cycle will be the key to selectivf tg for 

producing a two-carbon product. If this intermediate reacts rapidly with H2, 

methanol would be produced and the starting tantalum complex would be regenerated. If the intermediate reacts rapidly with CO, then the cycle will be 

followed as indicated in Figure 3-4 and ethylene glycol will be produced 

selectively. If the intermediate reacts with H2 and CO at comparable rates, a 

mixture of ethylene glycol and methanol would be produced. However, it should 

be possible to produce either product as the major component by adjusting the 

CO/H2 ratio. 



The second key step in this cycle is the reaction of hydrogen with the final 

intermediate to yield ethylene glycol and regenerate the starting tantalum 

complex. There is no precedent for this reaction, so we are guardedly optimistic that it will occur. Our choice of compounds will make it possible to 

systematically probe this reaction. Metal-oxygen bond strength decreases from 

tantalum to niobium to vanadium. If the tantalum system does a11 but the last 

step in the cycle, it may be possible to use the analogous niobium or vanadium 

complex to achieve a catalytic cycle. 

Similar cycles can be drawn for each of the proposed compounds. They differ 

slightly depending on the number of hydrides present in the starting complex, 

but the concepts are the same and the intermediates derived from CO reduction 

are expected to be the same for a31 the systems. 

The major points of this proposal are as follows. Based on mechanistic analysis of systems that reduce carbon monoxide stoichiometrically, we have 

proposed the synthesis of new complexes that contain features which we feel 

are important to make the reduction catalytic. These new complexes can be 

prepared by the straightforward synthetic routes we have developed: the standard techniques of inf rared and FT-NMR spectroscopy, elemental analysis, and, 

in selected cases, X-ray crystal structure analysis. Reactions of these cow 

plexes with carbon monoxide and hydrogen will be carried out, and systems that 

reduce carbon monoxide will be identified. In selected cases, CO-reducing 

s stems will be examined in more detail by isotopic labeling studies using 

lgCO and D2 and by product analysis to determine the important mechanistic 

features of the reaction. All of this is done to produce a system that shows 

a high selectivity for the production of two-carbon products. 

The demonstration of a complete catalytic cycle in a homogeneous system that 

reduces carbon monoxide -11 be a major scientific breakthrough. In addition, 

a detailed understanding of the mechanism of reactions of well-characterized 

complexes with CO will allow relationships between structure and reactivity to 

be developed, which will form the scientific basis for new and improved H2/C0 

reduction catalysts. 

The technological consequences of such a scfentific breakthrough are also significant. A homogeneous catalyst should operate at lower temperatures and 

lower pressures of CO/H2, compared to possible heterogeneous analogues. Also, 

a homogeneous catalyst would probably be more selective in terms of the products produced. It should therefore be less costly to implement and operate 

using a homogeneous catalyst system than it would using comparable heterogeneous technology. This might be particularly true for small-scale biomassbased pyrolysis/inditect liquefaction plants. 

In addition, the potential flexibility of producing various two-carbon products and higher alcohols would allow for various octane boosters and fuel 

additives to be generated for use in methanol fuel blends. For example, the 

catalytic studies proposed depict ethylene glycol as the resulting two-carbon 

product. Various catalysts and processes already exist to dehydrate this to 

vinyl alcohol or acetaldehyde, which can be catalytically hydrogenated further 

to ethanol. Such products may also be catalyzed by the complexes described in 

this proposal in the presence of excess hydrogen. 
Vinyl alcohol is an excellent precursor to ether and mixed alcohol ethers for 

use as blending agents for methanol/gasoline mixtures. Catalysts for such 

transformations already exist in various states of development, but the most 

important catalyst development needed is for converting H2/C0 to two-carbon 

and higher oxygenated products. 
SECTION 4.0 

1. (a) Parshall, George C., Homogeneous Catalysis - The Application and 

Chemistry of Catalysis by Soluble Transition Metal Complexes, New 

York: John Wiley and Sons, 1980. 

(b) Ford, Peter C, , editor, "Catalytic Activation of Carbon Monoxide," 

ACS Sumposium Series, Vol. 152, Washington, DC: American Chemical 

Society, 1981. 

2. (a) Gates, Bruce C., James R, Katzer, and G, C, A. Schuit, &emistry of 

Catalytic Processes, New York: McGraw-Hill, 1971. 

(b) Kugler, Edwin L., and F. W. Staffgen, editors, "Hydrocarbon Synthesis from Carbon Monoxide and Hydrogens, Advances in Chemistry 

Series, Vol. 168, Washington, DC: American Chemical society, 19797 

(b) Bercaw, J, Em, R. H. Marvich, L. G. Bell, and H. H. Brintzinger, J. 

Am. Chem, Soc., Vol. 94, 1972, pp. 1219-1238. 

5. Smart, J, C., and C. J, Curtis, Inorg. Chem., ~ol. 16, 1977, 

pp. 1788-1790. 

(b) Juvinall, G. L., J. Am. Chem. Soc,, Vol. 86, 1964, p. 4202. 

8. Schrock, R. R., and J. Dm Fellmann, J. Am. Chem. So$, Vol. 100, 1978, 

pp. 3359-3370. 

9, Wood, C. D., S. J. YcLain, and R. R. Schrock, - J. Am. Chem. Soc,, 

Val. 101, 1979, pp. 3210-3222. 

11. Belmonte, P. A*, R. R. Schrock, and C. S. Day, J. Am. Chem. Soc., 

Vol. 104, 1982, pp, 3082-3089. 
Screening Studies of Modified Heterogeneous Catalysts for 

the Production of Higher Alcohols 

FINAL REPORT 

Submitted to SERI 

S. W. Cowley 

and 

J. C. Smart 

November 20, 1984 
srel - - 

INTRODUCTION 

This nation' s current economic recovery program calls for a restructuring of 

the synthetic fuels program, including a reduction in expenditure on coal 

research and development. The direct combustion of coal or coal liquids 

results in substantial pollution problems. Alcohol fuels do not pose the 

severe pollution problems generated by other synthetic fuels. Methanol is 

particularly attractive because it burns so cleanly. Alcohol mixtures (C1-C5) 

are also attractive fuels because they can be used as a high-octane blending 

stock for gasoline. 

One of the advantages of alcohol fuels is that they can be produced from 

synthesis gas [1,2]. Synthesis gas is available from abundant resources and 

is produced by steam reforming coal 131 or methane or thermally decomposing 

biomass [4]. Biomass has advantages over coal in that it is a renewable 

energy source and it produces a cleaner synthesis gas that has less sulfur 

than syngas from coal. Current catalytic processes are very sensitive to the 

presence of poisons such as sulfur [5]. 

Methane is often produced along with petroleum at a well site. In some cases 

this methane can be shipped to consumers if a gas pipeline is available, 

However, in remote areas such as Alaska, the Middle East, or isolated areas in 

the western United States the methane is not utilized because pipelines to 

potential consumers do not exist and the cost of building them is not justified, It has been proposed that methane produced in these areas be catalytically converted into synthesis gas and catalytically converted into methanol. 

The methanol can be transported as a liquid using the same transportation . 

facilities as those used for petroleum [6,7], Methanol produced in such a 

fashion would be relatively inexpensive compared to petroleum. Many countries 

lacking in natural gas and oil resources are very interested in obtaining and 

using methanol as an alternate fuel to petroleum. This interest has sparked a 

flurry of research activity on the production of methanol for use as a fuel 

and a chemical feedstock. 

Methanol has excellent fuel qualities and has been tested for use in both 

transportation and electric power generation. The use of methanol as an 

automotive fuel has been discussed extensively in the literature [a-121 . Methanol exhibits some important combustion qualities that give it an 

advantage over gasolfne as a fuel. Methanol demonstrates substantially lower 

carbon monoxide and nitrogen oxide emissions. Also, the higher octane value 

of methanol allows a higher engine compression ratio to be used, which gives a 

better engine efficiency, Methanol has been tested for use as a boiler fuel, 

a turbine fuel, and a diesel fuel [13,14], Because methanol demonstrates good 

cornbrlst Ion properties and has lower emission levels than conventional fuels, 

the catalytic synthesis of methanol from synthesis gas has been studled extensively [15-201. 

The production of higher alcohols (C2'C5) is another attractive way of 

utili.zing synthesis gas [ 211, Higher alcohols are also excellent fuels, 

However, initially their principal use will be as high-octane blending 

stocks. The EPA intends to cut the use of tetraethyl lead in gasoline by 91%, 

beginning January 1, 1986, and to ban the use of lead completely by 1995. 

25 
Assuming that the ban of lead is inevitable, there will be a need for 

processes that can provide large quantities of octane boosters for gasoline. 

Several researchers have investigated the catalytic production of higher 

alcohols. Klier et al. have used Cu-ZnO catalysts doped with cesium to 

promote the production of higher alcohols [22]. However, copper-based 

catalysts are extremely sensitive to sulfur poisoning and overreduction. 

Recently a molybdenum-sulfide-based catalyst was developed by Dow Chemical 

Company [23]. This catalyst is extremely resistant to sulfur' poisoning; 

however, it has a low surface area, which increases the cost of the catalyst 

significantly. 

Our objective is to investigate the catalytic production of higher alcohols 

using the technical information we have gained from the study of methanol 

decomposition catalysts. It is important to find a catalyst system that will 

provide the necessary stability, activity, and selectivity required for the 

production of an alcohol mixture. Control of the alcohol product distribution 

is essential if higher alcohols are to be successfully used as a blending 

stock. After testing several catalysts, the most successful will be further 

investigated to establish the fundamental chemistry behind their activity and 

selectivity. This information will be used to improve future catalyst 

designs. 

CATbLYST TESTING RESULTS 

Several catalysts were screened in a microcatalytic plug-flow reactor at the 

SERI catalyst laboratory, and the results are given in Tables 1 and 2. The 

catalysts were selected because of their expected behavior for the production 

of higher alcohols. It is believed that the catalyst must have some ability 

to synthesize CHx surface groups to permit chain growth, which is necessary 

for the production of higher alcohols. Chain growth requires a catalyst that 

can dissociate some carbon monoxide on the surface and hydrogenate the others 

to the alcohol. None of the catalysts demonstrate any activity for the 

production of the higher alcohols as expected. Instead, methanol was the only 

alcohol product observed. Other products such as methane, carbon dioxide, 

water, and dimethyl ether were also produced. Although no higher alcohols 

were detected, it is possible that they were produced in quantities below the 

detection limit of our equipment. The higher alcohols are typically produced 

in very small amounts, which makes their analysis very difficult by gas chromatography. The production of methanol and methane is very encouraging and 

suggests that our criteria for CO dissociation and hydrogenation are achieved 

on this catalyst. 

FUTURE STUDIES 

We are planning to evaluate our analytical procedure for higher alcohols. We 

hope to use a quadrupole mass spectrometer to monitor the products in the 

future. This instrument is under construction, hut progress has been slow 

because of funding problems. 

We are planning to investigate other catalysts such as sulfided molybdenum, 

which looks promising because of its stability and selectivity. We plan to 

26 
Table 1. Alcohol Synthesis Catalysts 

wt X Metals 

Catalyst 

La Pd Rh Ru Fe 

a~lumina support was Norton 1/16-in. spheres. All 

other alumina supports were 14-30 mesh by Alfa 

Company. 

Table 2. Alcohol Synthesis Over Various Catalysts 

Mole % Products 

catalys tsa 

H2 CO CH4 C02 H20 CH30H DME 

Pd/La20j/u20g 69.1 19.0 2.4 1.6 3.6 2.9 o 

~d-Rh/A1203 61.9 29.9 2.9 0 5.1 0.2 0.1 

Rh/La2o3/Al2O3 65.0 32.2 0.9 0 1.9 0 0 

~d-~h/~a~0~/~1~0~ 61 07 32 05 1.3 0.3 3.4 0.4 0 

P~/L~~o~/AL~o~~ 59.4 30.1 2.2 1.7 4.1 0-7 1 9 

Rti/~a~O~/A1~0~ 57.3 20m6 9.0 0.6 11.8 0.7 0 

P~-Ru/L~~o~/A~~o~ 56 -2 43.8 0 0 0 0 0 

~d-Fe/La203/A1203 66.1 31.9 0 0.3 0.6 0.4 0.7 

%sting conditions: temperature = 300'~; pressure = 620-640 mm Hg; 

f ead flow - 49-83 cm3/min. 

b~umina support was Norton 1/16-in. spheres. All other alumina 

supports were 14-30 mesh by Alfa Company. 
impregnate the molybdenum catalysts onto the modified aluminas that were 

prepared for the methanol decomposition studies. 

We are also planning to look at ways of making ether products in addition to 

the higher alcohols. Methanol is an excellent diesel fuel, but its quality is 

markedly improved by the addition of dimethyl ether. We are certain that the 

modified aluminas will serve as excellent catalysts for the controlled production of ether. 

These studies provide valuable information about the ~ischer-~r&~sch (FT) 

process in general. It would be interesting to apply some of the principles 

discovered during methanol decomposition and alcohol synthesis to the production of FT products. 

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1982. 

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2 8 
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