A Pt/TiH2 catalyst having hydrogen storage and release capability was investigated for selective hydrogenation of trans-cinnamaldehyde (CAL) to cinnamyl alcohol (COL) with gaseous dihydrogen. The catalytic behavior of this catalyst was significantly different from that of a reference Pt/TiO2 catalyst with respect to the product selectivity and the hydrogenation mechanism. The Pt/TiH2 catalyst showed a COL selectivity of 97% at a CAL conversion of 98%, which was ascribed to the function of a Pt crystallite–support boundary layer that caused the preferential adsorption of CAL with its carbonyl group. Furthermore, the carbonyl group was hydrogenated by hydride species (H+, H–) supplied from the support and the hydride species consumed were compensated from gaseous dihydrogen; hydrogen atoms were formed by ordinary homolytic cleavage on Pt and then these hydrogen atoms moved onto the surface of TiH2 and diffused into the bulk of the support, during which those simultaneously changed to hydride species (H+, H–) via electron transfer with titanium species and hydride vacancies therein. The surface and bulk diffusion of the hydrogen atoms from Pt to TiH2 support should be the dominant step rather than their addition to the carbonyl group of CAL (ordinary hydrogenation). That is, ionic hydrogenation occurs with Pt/TiH2 in the presence of gaseous dihydrogen.

The selective hydrodeoxygenation of lignin-derived guaiacol to value-added products, especially phenol, under relatively mild reaction conditions remains an important challenge. A Cl-modified Ru/TiO 2 catalyst exhibited higher phenol selectivity compared with an unmodified one in the conversion of guaiacol in 1,4-dioxane at 240 °C and 1 MPa H 2 . Unlike Ru/TiO 2 , the modified catalyst exhibited a modest activity of demethoxylation producing phenol but an inferior ability of hydrogenation of its aromatic ring, resulting in much slower consumption of phenol. The Cl species were likely localized at the metal−support interface and on the surface of metal particles, and these modified both Ru and Ti species electronically. It is presumed that electron-enriched Ru inhibits the ring hydrogenation reaction, and the defects on the TiO 2 surface promote the deoxygenation reaction.