(442b) Hydrodeoxygenation Pathways and Selectivity Descriptors for the Conversion of Propanoic Acid to Alkanes Over Pd(111) Catalysts

One of the principle goals of modern catalysis research is to understand reaction mechanisms on solid surfaces to a degree that practical activity and selectivity descriptors can be identified that permit the rational design of new stable catalysts with unprecedented activity and selectivity.  High selectivity towards a single reaction product is driven both by economics and the goals of green catalysis, where atom- and energy-efficient processes are required to conserve the world’s limited resources. 

In this paper we present a computational case study for the determination of activity and selectivity descriptors for the hydrodeoxygenation (HDO) of organic acids to alkanes on transition metal surfaces.  In particular, we investigated activity and selectivity issues in the decarboxylation, decarbonylation, and reductive deoxygenation of propanoic acid to propane and ethane on Pd(111) model surfaces.

Decarboxylation:   R-COOH -> R-H + CO2                 

Decarbonylation:   R-COOH + H2 -> R-H +CO + H2O

Reductive deoxygenation:  R-COOH + 3 H2 -> R-CH3 + 2 H2O

Overall, we identified that a practical activity descriptor for the conversion of propanoic acid (all pathways) is the heat of reaction of the C-OH cleavage step and a selectivity descriptor for the reductive deoxygenation versus decarbonylation/decarboxylation is the heat of reaction of the α-carbon dehydrogenation.