Stabilizing Catalytic Pt-OH-Fe(III) Interfaces by Mesoporous TiO2 with Rich Surface Hydroxyl Groups

In supported heterogeneous catalysis, supports are used not only to enhance the metal diversion and catalytic stability of metal catalysts, but also to create metal-support interfaces for improving their catalytic performance in specific reactions. For interfaces controlled catalytic system, the construction of abundant and stable interfaces is very important. For this purpose, the physical and chemical properties of the support especially their surface species play the central role. In this work, mesoporous TiO2 (m-TiO2) with ultrahigh surface area (490 m(2)/g) was prepared by the hydrolysis of titanium glycolate complex. Highly dispersed metallic Pt nanoparticles (ca. 2.7 nm) with 1.9 wt% Pt loading were then supported onto the mesoporous TiO2 by a UV deposition method at room temperature. While, for commercial P25 as the support, following the same protocol, ca. 6.7 nm Pt nanoparticles with only 0.2 wt% Pt loading were obtained. The Pt-OH-Fe(III) interfaces were then successfully constructed by a facile deposition-precipitation procedure on both Pt/m-TiO2 and Pt/P25. The as-prepared catalysts exhibited high activity for low temperature CO oxidation, 100% conversion was achieved at 313 K for the m-TiO2 supported Fe(OH)(x)-Pt catalyst, Fe(OH)(x)-Pt/m-TiO2, under 50% humidity condition with weight hourly space velocity (WEISV), ca. 400 L/g(pt)/h (1 vol% CO). In comparison, under the same conditions the P25 supported Fe(OH)(x)-Pt catalyst, Fe(OH)(x)-Pt/P25, reached 100% conversion at 323 K in the first light-off test but gradually deactivated in further test cycles. The performance of Pt-OH-Fe(III) interfaces on m-TiO2 were highly relied on the humidity of the feed gas. Despite the low activity under dry feed gas condition, Pt-OH-Fe(III) interfaces exhibited robust catalytic performance during the long-time and humid/dry feed gas switch test, and the catalytic activity immediately recovered upon introduction of humid feed gas. It was revealed that, m-TiO2 possessed rich surface hydroxyl groups (10.6 mmol/g, 12.5 nm(-2)) which were very sensitive to the humidity of feed gas. Through protons transfer on the surface, the rich and sensitive hydroxyl groups on m-TiO2 maintained the Pt-OH-Fe(III) interfaces from irreversible dehydration By contrast, for the hydroxyl groups on P25, a much lower density and smaller change were detected under both the dry and humid conditions, which resulted in irreversible deconstruction of the Pt-OH-Fe(III) interfaces during the exothermic CO oxidation.