Catalytic Combustion of Methane over High Copper-Loading ZSM-5 Catalysts

Two series of Cu/ZSM-5 catalysts, loading from 5 to 20 wt% CuO, were prepared by the deposition-precipitation and impregnation methods, respectively. The catalysts prepared by the impregnation method showed better catalytic performances than those prepared by the deposition-precipitation method and the increase of copper loading favored methane conversion. 20Cu(I)/ZSM-5 had the highest activity with T90% of 746 K, and for 20Cu(D)/ZSM-5, T90% was as high as 804 K. The characterization of X-ray diffraction (XRD), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS) revealed that the dispersion of copper species could be improved by using the deposition-precipitation method instead of the impregnation method, but the fraction of surface CuO, corresponding to active sites for methane oxidation, was larger on 20Cu(I)/ZSM-5 than 20Cu(D)/ZSM-5. The results of Pyridine-Fourier transform infrared spectrum (Py-FT-IR) showed that a majority of Lewis acidity and a minority of Brønsted acidity were present on Cu/ZSM-5 catalysts. 20Cu(I)/ZSM-5 presented more Lewis acid sites. The number of Lewis acid sites changed significantly with preadsorption of oxygen. Adsorption of methane and oxygen on acid sites was observed. The properties of Cu/ZSM-5 catalysts were correlated with the activity for methane oxidation.