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It is shown that Raman spectra and thermal analysis data (TGA and DSC) both discriminate among the hydroxycarbonate precursors that lead to successful Cu Zn - containing catalysts and those that lead to inactive catalysts. For binary Cu/Zn catalysts, the optimum precursor is single-phase three-dimensional aurichalcite, (Cu,Zn)5(OH)6(CO3)2, which is readily distinguished by these techniques from undesirable precursor materials such as copper hydroxynitrate [Cu2(OH)3NO3], rosasite [(Cu,Zn)2(OH)2CO3] and hydrozincite [Zn5(OH)6(CO3)2]. Ternary Cu Zn/Al catalysts are successfully made via a layer-structured hydrotalcite-like precursor, i.e., (Cu,Zn)6Al2(OH)16CO3·4H2O. Thermal decomposition and infrared analyses indicate that the interlayer carbonate anion is retained by the ternary catalyst even to calcination temperatures of 350–450 °C, which has implications for the subsequent aqueous surface doping treatments used to further promote these catalysts

The reactions of ethanol with CO/H2 or CH3OH to form 1-propanol proceed most efficiently over Cs/Cu/ZnO catalysts with selective oxygen retention from CO/H2 or CH3OH and removal of oxygen associated with the OH group of ethanol, in contrast to that predicted by the classic aldol condensation mechanism. Isotopic labeling experiments reveal a novel path12CH3 13CH2OH+12CO/H2→13CH3 12CH2 12CH2OH.

The synthesis of higher (C+2) alcohols and esters has been studied over cesium-doped Cu ZnO catalysts. Under higher alcohol synthesis conditions, e.g., 583 K, 7.6 MPa, and gas hourly space velocity = 3260 liters (STP)/kg cat/hr with a H 2 CO = 0.45 synthesis gas, the presence of cesium promoted the formation of higher oxygenates, especially 2-methyl-1-propanol. The yields of products passed through distinct maxima at cesium nominal concentrations of 0.3–0.5%. These nominal concentrations generated optimum surface cesium concentrations of 15–25%. Under the reaction conditions employed, the principal role of cesium was to increase the ethanol synthesis rate and to provide an even greater enhancement in the rate of ethanol conversion to 1-propanol and subsequently to higher alcohols. To obtain insight into the mechanism of the carbon chain growth, e.g., C1 → C2, C2 → C3, and linear versus branched carbon chain growth, a 13C-NMR study of the C2C4 products formed over Cu ZnO and 0.4 mol% Cs/Cu/ZnO catalysts was performed. Separate injections into the CO H 2 synthesis gas of methanol and ethanol with natural-abundance 13C and enriched by 13C in specific positions showed that (i) lower alcohols were incorporated into the synthesis to form higher alcohols; (ii) carbon chain growth occurred in a stepwise manner dominated by the addition of oxygenated C1 intermediates at the β carbons of the oxygenated Cn (n ≥ 2) intermediates but also proceeding via linear addition Cn + C1 (n ≥ 1); and (iii) the presence of cesium had a dramatic effect on the reaction mechanism and promoted greatly the synthesis rates. The mechanistic effects of the alkali dopant were most pronounced in the C2 → C3 step. Over the Cu ZnO catalyst, injection of ethanol produced 1-propanol via linear chain growth, i.e., CH 3 13 CH 2 OH + CO H 2 → CH 3 13 CH 2 CH 2 OH . The presence of Cs effected a mechanistic switch and promoted β-carbon addition, CH 3 13 CH 2 OH + CO H 2 → 13 CH 3 CH 2 CH 2 OH . The position of the 13C label in the CH3 group of propanol provides evidence for retention of oxygen associated with the C1 intermediate, formed from CO H 2 , and loss of oxygen associated with the 13CH2OH group of ethanol. Mechanistically, such a retention is favored by a β-ketoalkoxide intermediate that is bonded to the cesium centers via its anionic oxygen. This unique mechanism is termed herein as aldol coupling with oxygen retention reversal and is specific to the presence of the cesium salt dopant. Higher alcohol synthetic steps C2 + C2 and Cn + Cm (n ≥ 3, m = 1, 2, 3) were also analyzed. Both oxygen retention reversal and normal oxygen retention were observed in coupling reactions leading to the higher-molecular-weight products (m + n > 3), and this observation is attributed to steric effects favoring the cis conformation of the β-alkoxide followed by rejection of either of its two oxygens.

Raman spectroscopy has been used to distinguish the individual carbonate minerals belonging to the calcite, dolomite, and aragonite structural groups. With the use of the in situ laser microprobe technique, it is demonstrated that particle-size effects do not hinder the mineral identification and that high precision in line position is achieved. Spectra can be obtained from samples in any form and provide rapid, nondestructive analyses on a microscopic scale of the hard-to-discriminate carbonate minerals.

The formation, decomposition, and reconstitution of hydrotalcite-like hydroxy carbonates (Cu{sub 0.4}Zn{sub 0.6}){sub 6}M{sub 2}(OH){sub 16}CO{sub 3}{center dot}4H{sub 2}O (M = Al, Cr, Ga) have been studied to determine the causes of the high long-lasting catalytic activity (M = Cr) and the severe deactivation (M = Al, Ga) of the Cu/ZnO/M{sub 2}O{sub 3} method synthesis catalysts doped with cesium after thermal decomposition of the hydrotalcite-like precursors. The alumina-based (M = Al) and gallia-based (M = Ga), but not the chromia-based (M = Cr), CuO/ZnO/M{sub 2}O{sub 3} mixed oxides that were produced by thermal treatment at 623 K of the hydrotalcite-like compounds reconstituted the original hydrotalcite-type compounds during the aqueous doping procedure carried out with the cesium formate promoter, CsOOCH. The re-formation of the Al- and Ga-containing catalysts to their hydrotalcite-like precursors is due to incomplete decomposition of the hydroxy carbonates prior to doping. Electron diffraction and transmission electron microscopy give evidence for the reconstitution reactions. The alkali-metal-promoted methanol synthesis catalyst of choice from hydrotalcite-type precursors is based on chromia. 27 refs., 13 figs., 4 tabs.

Cesium formate significantly promotes methanol and C2 oxygenate (methyl formate MF and ethanol EtOH) synthesis over the CuZnO catalyst. 13C NMR analysis of the product obtained from 13CH3OH and 12COH2 shows that MF is formed by direct carbonylation of methanol and EtOH is formed by coupling of oxygenated C1 intermediates originating from methanol. The C1 coupling mechanism overrides various CO insertion paths to ethanol over the present Cs/Cu/ZnO catalyst. The kinetic significance of C1 aldehydic species such as adsorbed formyl and formaldehyde is supported by experimental evidence and theoretical calculations.

Cu/ZnO and MoS 2 catalysts promoted by heavy alkali have been shown to produce alcohol mixtures consisting of isobutanol/methanol and ethanol/methanol, respectively, as the major products. The two catalyst systems exhibit contrasting behavior upon exposure to iron-carbonyl containing CO-rich synthesis gas. While the molybdenum-based catalysts remain active, the copper-based catalysts exhibit selectivity changes and deactivation proportional to the iron deposition rates. The iron centers function as Fischer-Tropsch sites for the synthesis of linear high molecular weight hydrocarbons, and the wax-like materials produced lead to fouling of the catalyst. Alternative deactivation mechanisms, including catalyst sintering and loss of the alkali promoter, have been addressed and found to be less significant than that caused by iron-generated hydrocarbons.

The synthesis of higher (C+2) alcohols and esters has been studied over cesium-doped Cu ZnO catalysts. Under higher alcohol synthesis conditions, e.g., 583 K, 7.6 MPa, and gas hourly space velocity = 3260 liters (STP)/kg cat/hr with a H 2 CO = 0.45 synthesis gas, the presence of cesium promoted the formation of higher oxygenates, especially 2-methyl-1-propanol. The yields of products passed through distinct maxima at cesium nominal concentrations of 0.3–0.5%. These nominal concentrations generated optimum surface cesium concentrations of 15–25%. Under the reaction conditions employed, the principal role of cesium was to increase the ethanol synthesis rate and to provide an even greater enhancement in the rate of ethanol conversion to 1-propanol and subsequently to higher alcohols. To obtain insight into the mechanism of the carbon chain growth, e.g., C1 → C2, C2 → C3, and linear versus branched carbon chain growth, a 13C-NMR study of the C2C4 products formed over Cu ZnO and 0.4 mol% Cs/Cu/ZnO catalysts was performed. Separate injections into the CO H 2 synthesis gas of methanol and ethanol with natural-abundance 13C and enriched by 13C in specific positions showed that (i) lower alcohols were incorporated into the synthesis to form higher alcohols; (ii) carbon chain growth occurred in a stepwise manner dominated by the addition of oxygenated C1 intermediates at the β carbons of the oxygenated Cn (n ≥ 2) intermediates but also proceeding via linear addition Cn + C1 (n ≥ 1); and (iii) the presence of cesium had a dramatic effect on the reaction mechanism and promoted greatly the synthesis rates. The mechanistic effects of the alkali dopant were most pronounced in the C2 → C3 step. Over the Cu ZnO catalyst, injection of ethanol produced 1-propanol via linear chain growth, i.e., CH 3 13 CH 2 OH + CO H 2 → CH 3 13 CH 2 CH 2 OH . The presence of Cs effected a mechanistic switch and promoted β-carbon addition, CH 3 13 CH 2 OH + CO H 2 → 13 CH 3 CH 2 CH 2 OH . The position of the 13C label in the CH3 group of propanol provides evidence for retention of oxygen associated with the C1 intermediate, formed from CO H 2 , and loss of oxygen associated with the 13CH2OH group of ethanol. Mechanistically, such a retention is favored by a β-ketoalkoxide intermediate that is bonded to the cesium centers via its anionic oxygen. This unique mechanism is termed herein as aldol coupling with oxygen retention reversal and is specific to the presence of the cesium salt dopant. Higher alcohol synthetic steps C2 + C2 and Cn + Cm (n ≥ 3, m = 1, 2, 3) were also analyzed. Both oxygen retention reversal and normal oxygen retention were observed in coupling reactions leading to the higher-molecular-weight products (m + n > 3), and this observation is attributed to steric effects favoring the cis conformation of the β-alkoxide followed by rejection of either of its two oxygens.

Raman microprobe spectroscopy is a recently developed technique1–6 that can give molecular information on a microscopic scale. It covers the complete spectrum of lattice and molecular vibrations and extends the tools of vibrational spectroscopy for chemical and structural studies to the microscopic domain. Information can be derived for both inorganic and organic samples, whether crystalline or amorphous and whether transparent or opaque. The samples can be solids or liquids, e.g. liquid inclusions in minerals.3 Thus, the Raman microprobe is unique in many of its capabilities and complements the techniques of scanning electron microscopy and electron probe microanalysis that provide sizes and shapes, which the Raman microprobe can also provide, and elemental compositions of single particles in the micrometer size range.

Cesium formate significantly promotes methanol and C2 oxygenate (methyl formate MF and ethanol EtOH) synthesis over the CuZnO catalyst. 13C NMR analysis of the product obtained from 13CH3OH and 12COH2 shows that MF is formed by direct carbonylation of methanol and EtOH is formed by coupling of oxygenated C1 intermediates originating from methanol. The C1 coupling mechanism overrides various CO insertion paths to ethanol over the present Cs/Cu/ZnO catalyst. The kinetic significance of C1 aldehydic species such as adsorbed formyl and formaldehyde is supported by experimental evidence and theoretical calculations.