Study on the catalytic reaction mechanism of low temperature oxidation of CO over Pd–Cu–Clx/Al2O3 catalyst

The Pd–Cu–Clx/Al2O3 catalysts were prepared by an NH3 coordination-impregnation (CI) method in water and organic solvents, and exhibited much higher activity for CO oxidation than the catalyst prepared by conventional wet impregnation (WI) method. Their chemical and physical properties were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results show that in the process of preparing the catalysts by CI, different solvents affect obviously their catalytic performance and isopropanol is the most suitable solvent among water, ethanol, acetone and isopropanol. The CO oxidation over Pd–Cu–Clx/Al2O3 catalyst (CI) can be accelerated remarkably with an increase of H2O concentration in the reactant gas, and it is weakly dependent on the CO and O2 concentrations. Compared with the catalyst prepared by WI, the catalyst prepared by CI possesses the higher dispersion and lower-temperature reducibility of copper phase, much more active Cu2+ species, and easier re-oxidation of Cu+. The Pd+ active site on the catalyst (CI) is more active than Pd2+ on the catalyst (WI), and the rate-determining step is the re-oxidation of Pd0 to Pd+ by Cu2+ on the catalyst (CI) instead of the re-oxidation of Cu+ to Cu2+ by O2 on the catalyst (WI).