The effect of H2 treatment at 423-573 K on the structure and synergistic activity of Pd-Cu alloy catalysts for low-temperature CO oxidation

The effect of H-2 treatment at 423-573 K on the structure of Cu/Pd/A1(2)O(3) catalysts for low-temperature CO oxidation was studied by means of XRD, TEM, EDS, FFT, DRIFTS, and XPS methods. The formation of 5 nm alloy particles in the Cu/Pd catalyst reduced at 423 K was detected. The reaction on Cu/Pd, Pd, and Cu catalyst reduced at 423 K starts at 275, 400, and 475 K, respectively. The activation energy for CO oxidation on Cu/Pd, Pd, and Cu catalyst is 30, 90, and 110 kJ/mol, respectively. The enhanced activity of Cu/Pd catalyst is explained by oxidation on Pd-0-M0,,interfaces (M =Pd, Cu). The key steps of this process are: oxidation of CO molecules strongly bound to Pd by lattice oxygen of MOx; fast desorption of CO2 molecules; replenishment of oxygen vacancies in MO,, by oxygen molecules from reaction media. As a result, a substantial part of blocked Pd sites become available for adsorption and dissociation of O-2 molecules. This is favorable for low-temperature oxidation via Langmuir-Hinshelwood mechanism. The increase in the reduction temperature results in a separation of alloy particles into metallic particles. As a result, Cu/Pd catalysts reduced at high temperatures are characterized with a decreased content of Pd-0-MOx interfaces; an essential amount of blocked Pd-0 sites and a decreased light-off activity. (C) 2017 Elsevier B.V. All rights reserved.