Oxidation of Bio‐Aldehyde and Bio‐Alcohol to Carboxylic Acid by Water over Modified CuZnAl Catalysts

Abstract

AbstractA series of NiCuZnAl catalysts with various Cu/Ni molar ratios and XCuZnAl (X=Ni, Co, Mn, Mg, La) catalysts were prepared and used in the aldehyde‐water shift (AWS) reaction with propanal as model compound. Although copper is the main site for AWS reaction, some additives also showed some effects on enhancing the catalytic activity to varying degrees. Mn promoted catalyst showed the highest propanal conversion of 22 % at 260 °C, much better than Co, La etc. Among the Ni promoted catalysts, NCZA‐33 with Ni/(Ni+Cu) molar ratio of 33 % showed the best activity. The trend of activity happened to match the catalyst reducibility expressed by reduction peak temperature in TPR analysis, thus an MVK mechanism was suggested. Introduction of Ni decreases the proportion of Cu0/Cu+ in surface Cu species, thus suppressed the hydrogenation activity and decreased the selectivity of corresponding alcohols. The carboxylic acid selectivity increased from 86.3 % of pristine CuZnAl to more than 90 % on modified catalysts, even 99.6 % on NCZA‐83 catalyst. Both pristine and modified CuZnAl catalysts showed good stability under AWS reaction conditions and carbon deposition is not responsible for the deactivation. AWS reaction was also extended to other aliphatic aldehydes and alcohols, but it's invalid for furfural and Cinnamaldehyde under the employed reaction conditions. The results indicate AWS reaction is very sensitive to the nature of reactants.