Group IB metals show little catalytic activity on metal oxide supports, including rutile TiO2(TiO2-R), ZrO2, CeO2, Al2O3, and SiO2for the hydrogenation of guaiacol, a representative lignin model compound. However, these metals on anatase TiO2(TiO2-A) are all active hydrodeoxygenation (HDO) catalysts, selectively producing phenolics at 300°C. The performance of the catalysts for the reaction was not significantly sensitive to the particle size of the supported metals. For example, gold particles ranging from 1 to 40 nm had only a small effect on the catalyst performance at Au loading of 0.4 to 0.7 wt%. Hydrogen spillover from the metal sites to the TiO2-A support substantially lowered the reduction temperature of reducible surface TiO2. At a Ag loading of 0.05 wt% on the TiO2-A, H2consumption based on the quantitative temperature programmed reduction experiment corresponded to a H/Ag ratio of 675, occurring at much lower temperature than the reduction of pure TiO2-A. At least three spillover H species were identified by2H NMR spectroscopy. In contrast, Ag supported on rutile TiO2(TiO2-R) did not show H2consumption for the reduction of TiO2-R, and no 2H NMR signal was observed from similar treatment. The hydrogen spillover was found to be responsible for the creation of active HDO sites on TiO2-A, and for the HDO of guaiacol. As an active hydrogenation metal catalyst, Ni on TiO2-R, ZrO2, CeO2, Al2O3, and SiO2 supports was capable of producing saturated oxygenates and saturated hydrocarbons by hydrogenatively saturating the aromatic ring of guaiacol. Strikingly, Ni supported on TiO2-A produced only phenolics, even at sufficiently high Ni loadings that resulted in the formation of large Ni particles. The surface overlayer of TiOx on large Ni particles, the migration of Ni atoms to the TiO2-A surface, and the hydrogen spillover on the Ni/TiO2-A are the unique characteristics of TiO2-A supported Ni catalysts for the selective HDO of guaiacol to phenolics.

Hydrogen spillover, cross metal/support migration and deoxygenation sites on metal/anatase TiO2 catalysts

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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