The higher alcohol synthesis over promoted Cu/ZnO catalysts

Abstract

Alkali oxides added to methanol catalysts increase the formation of ethanol, n‐propanol and isobutyl alcohol. This result has been known for many years, yet few quantitative studies have been reported in the literature. Data obtained on a commercial copper‐zinc oxide catalyst promoted with K2 CO3 are presented and compared with published work. The optimum promoter concentration was about 0.5% by weight. The H2 to CO feed ratio was important in determining the higher alcohol selectivity. The rate of production of isobutyl alcohol varied as p H2−0.7 p CO2.2 while for methanol, ethanol and n‐propanol both exponents were positive and less than 1.6. Decreasing the hydrogen to carbon monoxide ratio from 2 to 0.5 more than doubled the isobutyl alcohol selectivity. Chain growth schemes predicting the higher alcohol selectivity are presented and estimates of the parameters are given.

Synthesis of higher alcohols on copper catalysts supported on alkali-promoted basic oxides

“…5. These chain growth pathways are consistent with those proposed by Smith and Anderson [3], Smith et al [23] and Breman et al [6,7] for modi®ed methanol synthesis catalysts. This scheme suggests the possibility of applying chain growth analysis methods similar to those developed by Herrington [42] to examine chain growth kinetics for the Fischer±Tropsch synthesis.…”

“…Methyl acetate and other esters can be formed by Canizzaro-type condensations of two aldehydes, by reactions of surface carboxylates with formyl or formaldehyde, or by Tishchenko-type reactions of aldehyde species with surface alkoxides [3]. The latter reaction seems to be the most plausible pathway, in view of the expected presence of both aldehydes and surface alkoxides on our catalytic materials.…”

“…K and Cs were added by incipient wetness using K 2 CO 3 (0.25 M) and CH 3 COOCs (0.25 M) aqueous solutions (K 2 CO 3 , Fisher Scienti®c, A.C.S. certi®ed; CH 3 COOCs, Strem Chemicals, 99.9%). The Pd-promoted catalyst was prepared by incipient wetness impregnation of Cu 0.5 Mg 5 CeO x with an aqueous solution of Pd(NH 3 ) 2 (NO 2 ) 2 , followed by air oxidation (0.5 K/min to 723 K, 4 h) before impregnation with K.…”

“…High CO 2 concentrations (>10% mol) lead to surface oxidation and inhibit methanol synthesis on these catalysts [17]. Cs-modi®ed methanol synthesis catalysts reach maximum rates at very low CO 2 concentrations ($2% mol) [3]. The relative rates of oxidation and reduction of Cu surface atoms determine the steady-state coverage of oxygen reaction intermediates during methanol synthesis.…”

Revisiting Catalyst Structure and Mechanism in Methanol Synthesis

“…Esters especially methyl formate and methyl acetate, ketones especially acetone and butanone, ethers, hydrocarbons, acids and aldehydes can also be detected [4]. Higher alcohols are synthesized due to the alkali residues such as K + and Na + remaining in the catalysts from their manufacturing [31], which affects production of formyl species as the key precursor. These alkali cations and their OH -anions serve as the active centers to adsorb and activate CO and methanol and produce formate [32].…”