We present results on recently achieved understanding of distinctively different interactions of NiO, CuO and Ag2O with the surfaces of anatase TiO2 (TiO2-A) and rutile TiO2 (TiO2-R) that induced the dramatic differences in the formation of electronically and structurally different metal sites for deoxygenation of lignin derived substrates. Two types of reduced Ni species were formed on Ni/TiO2-A: metallic Ni particles and atomically dispersed electron-rich Niδ- atoms. Ni particles, formed only at high Ni loadings, are fully encapsulated by an overlayer of partially reduced TiOx, making the surface of Ni particles totally inactive. The electron-rich Niδ- atoms are favorably formed at all Ni loadings on TiO2-A surface and serves as the site for H2 dissociation in the hydrogenolysis of CAr-O bonds in guaiacol and other model compounds. For a catalyst with low Ag loading, the ratio of spillover H to Ag was as high as 675, and the Ag/TiO2-A catalysts are active for hydrogenolysis. Three spillover hydrogen species are collectively consumed in the selective hydrogenolysis of oxygenates. Cu2O nanoparticles dominantly formed on TiO2-R provide site for H2 dissociation, but hydrogenolysis takes place mainly on TiO2-R surface by spilt-over H from Cu2O nanoparticles.

Colonized groups of sites for H2 dissociation and hydrogenolysis of CAr-O bonds in lignin derived substrates on TiO2 supported transition metal catalysts

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