Electronic Properties and Reactivity of Furfural on a Model Pt(111) Catalytic Surface

The reactivity of furfural with metal surfaces, including Pt(111), has been the subject of various investigations owing to its importance in heterogeneously catalyzed biomass upgrading processes. The present work examines the electronic interaction of furfural with Pt(111) and builds correlations with its reactivity. By means of photoelectron spectroscopy, vibrating capacitance Kelvin probe, and thermal desorption, the electronic properties of condensed, chemisorbed, and decomposed furfural on Pt(111) were studied. It was shown that at low temperatures (175 K), furfural chemisorbs nondissociatively on Pt(111), with the molecular bonding at low coverages involving hybridization of the aromatic ring pi orbitals with the Pt d band. This fact can potentially lead to loss of aromaticity and ring-opening processes. The primary adsorption mechanism involves charge transfer from the furanic ring to the metal surface and a positive outward dipole moment. At higher temperatures, the decomposition that accompanies molecular desorption from clean Pt(111) leads to the decarbonylation to furan, CO, H-2, and graphite-like species. The presence of pre-adsorbed H-2 on Pt(111) favors the hydrogenation of furfural to furfuryl alcohol and 2-methylfuran due to electronic disturbance around the hydrogen adsorption site. The latter result supports the notion that the adsorbed hydrogen allows furfural to retain to some extent its aromaticity. The present study is consistent with the current understanding that hydrogenation selectivity is the highest when the ring does not coordinate with the surface.