SURFACE CHEMISTRY OF MODEL OXYGENATES ON NICKEL AND PLATINUM SINGLE CRYSTALS FOR BIO-OIL UPGRADING AND SYNTHESIS OF RENEWABLE CHEMICALS

Abstract

The adsorption and reaction of three prominent bio-oil compounds were investigated on Ni(110), Sn/Ni(110), and Pt(100) single crystal surfaces using temperature programmed desorption (TPD), infrared reflection-absorption spectroscopy (IRAS), and density functional theory (DFT) calculations. These bio-oil compounds; acetic acid (CH3COOH), furfural (C4H3OCHO), and guaiacol (C6H4(OH)(OCH3)) were chosen because of their prevalence in bio-oils, varied functional groups, and difficulty in upgrading via catalytic hydrodeoxygenation.

Acetic acid adsorption and decomposition was studied on Ni(110), Sn/Ni(110), and Pt(100) single crystal surfaces. On each surface, the acetic acid dissociatively adsorbs, forming an acetate species that decomposes upon further heating leading to desorption of H2, CO, CO2 or water. On Ni(110) and Sn/Ni(110), autocatatlytic decomposition of the acetate occurred after high initial coverages of acetic acid, which did not occur on Pt(100). DFT calculations support the presence of a bidentate acetate species at all coverages.

At high initial coverages, furfural adsorbs in a tilted configuration on Pt(100). Furfural dissociatively adsorbs forming two bonds with the surface through the ring oxygen and aldehyde carbon in a tilted configuration. This configuration undergoes decarbonylation forming furan and CO. Further decomposition of furan led to formation of propylene, additional H2, CO and surface carbon.

Guaiacol adsorption and decomposition was studied on Pt(100). At high initial coverages, guaiacol was also found to adsorb in a tilted configuration in IRAS. DFT calculations for high coverages of guaiacol also confirm this species. The OH bond in guaiacol is the first to break, followed by unselective decomposition of the functional groups, which eventually desorb as H2, CO, CH¬4, and CH2O. Benzene, small amounts of phenol were also produced. Ring dehydrogenation reactions ultimately led to production of H2 and surface carbon.