Carboxylic Acid Hydrodeoxygenation over Supported Noble Metal Catalysts

Carboxylic acid hydrodeoxygenation (HDO) over supported noble metal catalysts was carried out in order identify the main challenges associated with supported monometallic catalysts and identifying solutions that may increase the practicality of these high activity metals. Using propionic acid as a probe molecule, it was found that supported platinum (Pt) and ruthenium (Ru) catalysts have two main issues: selectivity and stability. Both metals are quite unselective towards HDO products, multiple chemistries occur over the catalysts that lead to a myriad of undesired products. Decarbonylation (DCN) is the most selective pathway over Pt catalysts, while both DCN and methanation chemistries are heavily dominant over Ru catalysts. The high selectivity to DCN products for both catalysts snowballs into the second issue which is the lack of stability, carbon monoxide is a product of DCN which has an inibitive characteristic on the active metal sites; it essentially poisons the catalyst. The addition of an oxophilic promoter metal, Tin (Sn), drastically improves the catalytic properties. PtSn bimetallic catalysts showed to be only selective to HDO products, and it also demonstrated a resistance to carbon monoxide poisoning. Investigations into PtSn catalysts using chemical adsorption, shows than Sn reduces the irreversible uptake capabilities of carbon monoxide onto Pt sites, which is indicative of the binding characteristics being altered. We developed a microkinetic model that sucessfully represents propionic acid HDO activity over Pt, while also being able to accurately provide useful kinetic parameters. Through applying microkinetic modelling, the energies associated with the species’ interactions on the catalyst surface of both mono- and bi- metallic systems can be compared in order to pin point the source of what alters the catalyst behaviour