Distinctively different interactions of NiO with the surfaces of anatase TiO2 (TiO2-A) and rutile TiO2 (TiO2-R) cause dramatic differences in the reducibility of the supported metal oxides and in the formation of electronically and structurally different metal sites for oxygenate hydrogenations. NiO on TiO2-R requires much higher temperature to reduce than NiO on TiO2-A by H2. Surface TiO2-A is partially reduced together with NiO at much lower temperature, driven by strong interaction between reduced Ni and reducible TiO2-A surface. Two types of reduced Ni species are formed on Ni/TiO2-A: Ni0 particles and atomically dispersed electron-rich Niδ- atoms. Ni0 particles, formed only at high Ni loadings, are fully encapsulated by an overlayer of partially reduced TiOx, making the surface of Ni particles totally inaccessible to CO and to oxygenate substrates. The electron-rich Niδ- atoms are favorably formed at all Ni loadings on TiO2-A surface. The atomically dispersed Niδ- species serves as the site for H2 dissociation. Poorly active hydrogenation metals like Au and Ag in very low loadings on TiO2-A are similarly capable of dissociating H2 and initiating H spillover on the support surface. For an Ag/TiO2-A catalyst with low Ag loading, the ratio of spillover H to Ag was as high as 675. Direct 2H solid-state NMR evidence, validated by DFT 2H NMR spectral calculations, revealed the evolution of multiple spillover hydrogen species on TiO2-A supports. Three spillover hydrogen species are distinguished, two protic species adsorbed on surface oxygen sites and one hydride species formed at oxygen vacancy site. The spillover H species are collectively consumed in the selective hydrodeoxygenation of oxygenates. In contrast, the metallic Ni0 particles formed on Ni/TiO2-R surface catalyze the typical catalytic hydrogenation in preferentially saturating the aromatic ring. Four types of catalytic functions on the TiO2-A supported metals will be presented and discussed.

Evolution of H2 dissociation and hydrogenation sites/H species on TiO2 supports in selective cleavage of CAr-O and N-O bonds

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.