The Ultra-Selective Hydrogenation of Furfural on PtCu Supported Bimetallic Nanoparticles and on Pt(111) under Ultra-High Vacuum

Abstract

The selective transformation of furfural, a biomass platform molecule, was studied on Pt based heterogeneous catalysts and model single crystal surfaces. Hydrogenation reactions were carried out at pressures ranging from ultra-high vacuum to 20 bar. Temperature Programmed Desorption data in conjunction with Scanning Tunnelling Microscopy suggest that the decarbonylation of furfural on clean Pt(111) and the hydrogenation of furfural on hydrogen pre-covered Pt(111) is governed by surface crowding, molecular orientation and hydrogen bonding networks of the adsorbed molecules. Liquid phase experimentation on Pt nanoparticles, dispersed on a wide range of oxide supports, show that Pt is a very active hydrogenation catalyst even at very mild temperature and pressure conditions. The reaction was found to be highly dependent on the solvent used, while catalyst support is critical for maintaining thermally stable, monodisperse nanoparticles. The addition of Cu into Pt nanoparticles was investigated in a range of Pt:Cu metal molar ratios varying from pure Pt to pure Cu. This was achieved by using a modified polyol synthesis to generate colloidal nanoparticles, followed by thermal processing. Bimetallic particles synthesized using a sulphur free Cu precursor, were found to be beneficial for the suppression of CO adsorption, normally a poison for this reaction, which is formed from the decarbonylation of furfural. The alloying of these two metals had a profound effect on the overall catalytic activity by providing superior initial rates of reaction and catalytic turnover, as well as achieving high selectivities towards furfuryl alcohol, surpassing the behaviour of pure Pt catalyst across 3 different pressures. Finally, Single Atom Alloys (SAA), formed via the galvanic replacement of dispersed host Cu nanoparticles by Pt was investigated. Pt:Cu nanoparticles with atomic ratios ranging from 1:20 to 0.5:250 were synthesized and tested. After overcoming a brief induction period due to the reduction of surface CuO and possibly the reordering of the surface atoms, SAAs exhibit extremely high rates of hydrogenation, surpassing the catalytic turnover for monometallic and bimetallic catalysts. These cutting edge materials are at the frontier of catalyst research, proving to be ideal materials for the future of green chemistry due to both their activity and economic viability