Insights into the Active Sites and Kinetics of Double-site Catalysts for Semi-hydrogenation under Hydrogen Spillover

A well-defined catalyst with platinum (Pt) and gold (Au) encapsulated in micropore and mesopore of micro-mesoporous zeolite (TMSN), respectively, was designed to investigate the original active sites and kinetics of semi-hydrogenation. Specifically, hydrogen molecules are dissociated on Pt nanoclusters (NCs) to form hydrogen atoms that migrate to the surfaces of TMSN zeolite and Au nanoparticles (NPs). Meanwhile, the Au NPs with inferior H dissociation capability in the mesopore can be served as the detector and controller of hydrogen spillover. The Pt NCs in micropore act as H dissociation sites while both the Au NPs and zeolite surface are identified as the semi-hydrogenation sites. Noteworthy, the Pt-Au/TMSN catalyst with double active sites exhibits higher selectivity and rate constant ratio for semi-hydrogenation than Pt/TMSN, as well as higher turnover frequency (TOF) than Au/MSN. This work creates an effective regulation strategy of hydrogen spillover for improving active sites and kinetics of semi-hydrogenation.

Activation of Pt Nanoclusters on TiO2 via Tuning the Metallic Sites to Promote Low-Temperature CO Oxidation

Metallic Pt sites are imperative in the CO oxidation reaction. Herein, we demonstrate the tuning of Pt sites by treating a Pt catalyst in various reductive atmospheres, influencing the catalyst activities in low-temperature CO oxidation. The H2 pretreatment of Pt clusters at 200 °C decreases the T50 from 208 °C to 183 °C in the 0.1 wt % Pt/TiO2 catalyst. The T50 shows a remarkable improvement using a CO pretreatment, which decreases the T50 further to 135 °C. A comprehensive characterization study reveals the integrated reasons behind this phenomenon: (i) the extent of PtO transition to metallic Pt sites, (ii) the ample surface active oxygen triggered by metallic Pt, (iii) the CO selectively adsorbs on metallic Pt sites which participate in low-temperature CO oxidation, and (iv) the formation of the unstable intermediate such as bicarbonate, contributes together to the enhanced activity of CO pretreated Pt/TiO2.