Silver initiated hydrogen spillover on anatase TiO2 creates active sites for selective hydrodeoxygenation of guaiacol

Abstract

Selective hydrocleavage of aromatic CO bond while preserving the aromatic ring is a desired catalytic process in hydrodeoxygenation (HDO) of biomass derived aromatic oxygenates to high value biochemicals. Guaiacol with typical methoxy and phenolic hydroxyl groups is a representative aromatic di-oxygenates of lignin fragments. Sub-nanometer sized silver, a poor hydrogenation metal catalyst, was found to initiate H2 dissociation and H spillover onto anatase TiO2 (TiO2-A) surface. The spillover hydrogen enhanced the partial reduction of TiO2-A surface at a substantially lowered temperature as compared to the reduction of TiO2-A by molecular H2. The reduction of TiO2-A surface by spillover hydrogen was enhanced at Ag loading as low as 0.01 wt% on TiO2-A. The ratio of spillover H to Ag was as high as 675 at Ag loading of 0.01 wt% and the ratio decreased with increasing Ag loading. We found that the yield of phenolic products was linearly correlated with the amount of spillover hydrogen that created oxygen vacancy (Ov) through partial reduction of TiO2-A surface. Methanol was formed as the main side-product, indicating that the direct hydrocleavage of aromatic C-OCH3 in guaiacol is favored over that of aromatic C-OH on the created site.