Two anatase titania model catalysts, with preferential exposure of (101) and (001) facets, were synthesized and studied for 2-propanol dehydration. A series of microscopic and spectroscopic techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ammonia temperature program desorption (NH3-TPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and chemical titration were employed to correlate the structure properties of the model catalysts to their catalytic performances. Based on selective site poisoning titration using 2,6-di-tert-butyl pyridine, surface Lewis acid sites were found to be active for 2-propanol dehydration. Surface species present during steady-state reaction were probed using temperature-dependent DRIFTS and used to construct model surface structures to describe the elementary steps of 2-propanol dehydration using density functional theory (DFT). DFT simulations demonstrated that on both anatase surfaces, 2-propanol dehydrates via concerted E2 elimination pathways, but with different initial states and thus also different intrinsic activation barriers. Molecular 2-propanol dehydration dominates on TiO2 (101) while on TiO2 (001), 2-propanol simultaneously converts to more stable 2-propoxide before dehydration, which then requires higher activation energies for E2 elimination. These DFT simulated results are consistent with reaction kinetics measurements; the latter also demonstrated that the (101) model catalyst is more active. However, the minority facets on the (001) model catalyst likely play important roles in the dehydration chemistry, causing uncertainties in the interpretation of the kinetics data.

2-Propanol dehydration on single-facet-dominant TiO2 (101) and (001) nanopowder catalysts

2019 Fall National Meeting

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