Abstract
The state of the active constituents of the freshly prepared PdCl2-CuCl2/γ-Al2O3 catalyst for the low-temperature oxidation of the carbon monoxide by molecular oxygen was studied by X-ray absorption spectroscopy (XAS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and diffuse reflectance IR Fourier transform spectroscopy (DRIFTS). It was shown that copper in the form of a crystalline phase of Cu2Cl(OH)3 with the structure of the mineral paratacamite and palladium chloride in an amorphous state occurred on the surface of γ-Al2O3. According to XAS data, the local environment of palladium consisted of four chlorine atoms, which formed a flat square with an increased distance between palladium and one of the chlorine atoms. The evolution of the local environments of copper and palladium upon a transition from the initial salts to the impregnating solutions and chlorides on the surface of γ-Al2O3 was considered. The role of γ-Al2O3 in the formation of the Cu2Cl(OH)3 phase was discussed. It was found by the DRIFTS method that linear (2114 cm−1) and bridging (1990 and 1928 cm−1) forms of coordinated carbon monoxide were formed upon the adsorption of CO on the catalyst surface. The formation of CO2 upon the interaction of coordinated CO with atmospheric oxygen was detected. Active sites including copper and palladium were absent from the surface of the freshly prepared catalyst.
Published Version
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