We consider data obatained in the conversion of propanoic acid on Pt/SiO2 under H2. Under these conditions, Pt is active for hydrogenation and hydrodeoxygenation, which enables the synthesis of potential C3 platform molecules like formation of propionaldehyde and 1-propanol. Unfortunately, Pt also facilitates total deoxygenation to form propane, as well as decarbonylation of both propanoic acid and propionaldehyde to form ethane and CO, the latter of which accumulates to poison the catalyst at longer residence times. We further observe that sequential reactions play a critical role in determining product distributions, and we resolve their contributions from those of primary reactions through the analysis of rates and selectivities during the conversion of propanoic acid, propionaldehyde, 1-propanol, CO, and CO2 in various environments. We conclude that the main challenge in the selective production of partial hydrodeoxygenation products---namely propionaldehyde and 1-propanol---is that one must facilitate dehydroxylation of propanoic acid while avoiding thermodynamically favorable decarbonylation and alcohol hydrogenolysis pathways. We reconcile macroscopic trends with a reaction mechanism that includes parallel and sequential reactions occurring during the hydrodeoxygenation of propanoic acid over Pt/SiO2.

Mechanistic interpretation of trends in the hydrodeoxygenation of propanoic acid over Pt-based catalysts

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