Studies of pore structure, temperature-programmed reduction performance, and micro-structure of CuO/CeO2 catalysts

The reducibility and characteristics of CuO, CeO2 and CuO/CeO2 catalysts were examined by means of a CO microreactor gas chromatography, specific surface area, pore volume, H2-temperature-programmed reduction (TPR), and X-ray diffraction Rietveld analysis. Experimental results showed that the specific surface area and pore volume of the CuO/CeO2 catalysts decreased with an increase in CuO loading, whereas the average pore diameter was the same. TPR data exhibited two peaks, a low-temperature one due to the reduction of highly dispersed copper oxide and a high-temperature one due to the reduction of bulk CuO. Micro-structural analysis showed that the lattice constant of pure CeO2 is 0.54103 nm. In contrast, when CuO/CeO2 was formed, the cell parameter values of CeO2 for various loading were all smaller than that of pure CeO2, indicating that some CuO entered the CeO2 lattice. At a CuO loading of 5.0 wt.%, the crystalline size of CuO became minimal and the micro-strain maximal, indicating crystalline CuO and a high surface energy with a resulting best activity for CO oxidation. CuO/CeO2 catalysts are stable to 750°C, but at 900°C the crystallite size increased rapidly and the CuO and CeO2 phase-separated.