(448f) Multicomponent Catalysis: Directing Reaction Pathways for Hydrodeoxygenation of Furfuryl Alcohol at Pd/TiO2 Interfaces

Biomass has potential to generate liquid fuels after processing to reduce oxygen content. Catalytic hydrodeoxygenation(HDO) uses a hydrogen rich environment to deoxygenate, generating products with suitable chemical and thermal stabilities without any loss of carbon. Biomass-derived furfural is a fuel precursor and model compound for exploring HDO. Furfural HDO preferably leads to methyl furan (a potential fuel additive). Recently, core-shell catalysts where individual noble metal nanoparticles (e.g. Au, Ag, Pt, and Pd) are isolated in the core/yolk–shell nanostructure of metal oxides (e.g. TiO₂, CeO₂, and ZrO₂) claim to bring unique collective and synergetic function in comparison with single-component materials [1]. Palladium nanoparticles encapsulated by porous TiO₂ showed high selectivity and activity towards HDO and minimal non-selective decarbonylation (DC), with the optimal catalyst having the smallest TiO₂ pore sizes [2]. Despite this encouraging performance, the mechanistic role of TiO₂ or the porous encapsulation that dictates the improved selectivity is unknown. TiO₂ can both accept a proton from H₂ to generate active sites and donate a proton to assist in cleaving the C−O bond of hydroxylated reactants[3]. Therefore, interfacial sites between metals and metal oxides have been proposed to play a vital role in assisting this complex reaction pathway with amplified selectivity to HDO and also hindering the side reactions like decarbonylation or aromatic ring hydrogenation.

We use density functional theory (DFT) to study the elementary surface reactions of furfuryl alcohol at a series of models for the Pd-TiO₂ interface. Interfacial models include Ti₂O₄ clusters and rutile TiO₂ nanowires over Pd(111) and a surrogate Helium pore model. The Helium pore model provides an inert interfacial site to probe the effect of binding orientations of adsorbates on its reaction pathways[4]. Elementary reaction energetics using the pore model suggest the hindering of decarbonylation in constrained pores, emphasizing that DC requires a large ensemble of sites and, hence, most favourably occurs in flat lying conformations [5]. HDO kinetics remain unaffected even with the change in binding orientations. DFT kinetics studies over Ti₂O₄ clusters imply a reduction in activation barrier for conversion of furfuryl alcohol to methyl furan through direct deoxygenation, pointing out the coupled effect of components across the interface.

This fundamental understanding of the elementary processes occurring at the interfaces will have significant implications in developing novel catalysts that combine unique functionalities across materials for improved selectivity and activity.

References:

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