(19e) Selective Reduction of Carboxylic Acids to Aldehydes over Promoted MoO3 Catalyst | AIChE

(19e) Selective Reduction of Carboxylic Acids to Aldehydes over Promoted MoO3 Catalyst


Gomez Gomez, L. A. - Presenter, university of Oklahoma
Crossley, S., University of Oklahoma
Komarneni, M. R., university of Oklahoma
Gutierrez, J. A., University of Oklahoma
Selective activation of carboxylic acids to form alcohols and aldehydes with highly oxophilic catalysts could enable the formation of a variety of highly valuable renewable products. Selective reduction with highly oxophilic supports carries the advantage of activating the acid functional group without perturbing other functionalities. The use of traditional metal catalysts for this purpose generally favors C-O cleavage followed by rapid decarbonylation to yield alkenes. These alkenes are readily converted to less desirable alkanes in the presence of H2 or often lead to coke and catalyst deactivation in the absence of co-fed H2. This limits applicability to produce high value chemicals such as butadiene via these routes.

In this contribution, we report a new chemistry that has been explored with aldehydes and ketones, reverse mars van Krevelen chemistry over MoOx, for the selective conversion of carboxylic acids. Our study focusses on the selective conversion of pentanoic acid (PA) to aldehyde over MoO3 at different temperatures via hydrodeoxygenation (HDO) reaction. Here, we hypothesize that the selective C-O cleavage reactions are occurring over the defects on the sub stoichiometric oxide via reverse Mar-Vars Krevelen chemistry. Reducibility of MoO3 is well known to be challenging at low temperatures, therefore in order to facilitate the reduction process, very low loadings of platinum (Pt) were incorporated on the catalyst (0.05%Pt/MoO3). The net effect is the increase on the rate of conversion of PA at lower temperature over MoO3 by hydrogen spillover to promote partial reduction of the MoOx while minimizing side reactions that may occur on the metal directly. X-Ray photoelectron spectroscopy (XPS) was used to investigate effect of H2 during the partial reduction on both MoO3 and 0.05% Pt/MoO3 catalysts. Kinetics analysis reveals that low loading of Pt on MoO3 decrease the apparent activation barrier for acid conversion by over 33 kJ/mol.