Search for: All records

H2 activation is fundamental in catalysis. Single-atom catalysts (SACs) can be highly selective hydrogenation catalysts due to their tunable geometric and electronic properties. In this work, H2 activation (adsorption, splitting, and diffusion) on the anatase TiO2-supported SAC has been modeled in detail. The stable configurations of 14 transition metals from 3d to 5d (Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Os, Ir, Pt, and Au) and Sn have been screened. We compared H and H2 adsorption and H2 heterolytic and homolytic splitting on SA/TiO2. H on the SAC in neutral, hydridic, and proton forms and the preferred H2 dissociation paths are revealed. We found that the metal adatoms strengthen the Brønsted acids via forming the SA-O bonds and promote the H adsorption on Ti sites via forming the Ti3+ sites. The electronic descriptor using the energy level of the frontier d orbital, referenced to vacuum, can predict the single H and H2 dissociative adsorption energies on the metal site. As the SA-Hδ- interaction is stronger than Ti-Hδ-, the activation barriers for heterolytic paths over SA-O sites are lower than over Ti-O sites. H2 adsorption is activated on Au, Ru, Rh, Pd, and Ir in a dihydrogen complex structure with an elongated H-H bond. Homolytic splitting over SA sites is favored thermodynamically and kinetically on Rh, Pd, Os, Ir, and Pt. In contrast, for the remaining SA/TiO2, H-H splitting at the SA-O is kinetically favored compared to the Ti-O sites, but the products are less thermodynamically favored. 

Abstract We investigate solvent effects in the hydrodeoxygenation of 4-propylguaiacol (4PG, 166 amu), a key lignin-derived monomer, over Ru/C catalyst by combinedoperandosynchrotron photoelectron photoion coincidence (PEPICO) spectroscopy and molecular dynamics simulations. With and without isooctane co-feeding, ring-hydrogenated 2-methoxy-4-propylcyclohexanol (172 amu) is the first product, due to the favorable flat adsorption configuration of 4PG on the catalyst surface. In contrast, tetrahydrofuran (THF)—a polar aprotic solvent that is representative of those used for lignin solubilization and upgrading—strongly coordinates to the catalyst surface at the oxygen atom. This induces a local steric hindrance, blocking the flat adsorption of 4PG more effectively, as it needs more Ru sites than the tilted adsorption configuration revealed by molecular dynamics simulations. Therefore, THF suppresses benzene ring hydrogenation, favoring a demethoxylation route that yields 4-propylphenol (136 amu), followed by dehydroxylation to propylbenzene (120 amu). Solvent selection may provide new avenues for controlling catalytic selectivity.