Methane combustion on sol-gel Rh/ZrO2-SiO2 catalysts

Rh/ZrO2-SiO2 catalysts prepared by impregnation of mixed ZrO2-SiO2 oxides o btained by using the sol-gel method were characterised and used in the comb ustion of CH4. It was found that the specific area and porosity depend stro ngly on the pH of gelation. Two different Zr precursors were used: Zr(acac) (4) and Zr alkoxide. When the former precursor is used, no significant chan ges in the surface area are detected, however, important changes in pore si ze distribution are observed. In those samples prepared from Zr alkoxide, b oth the surface area and the porosity change significantly. No important ch anges in rhodium dispersion were observed by TEM, in agreement with XPS res ults. On the contrary hydrogen chemisorption results indicate that the hydr ogen uptake of the sulfated samples drops drastically compared with those i n which sulfate ions are absent. This behaviour has been attributed to a po isoning of rhodium particles by sulfide species produced by reduction of su lfate ions, as was revealed by TPR. The catalytic activity in the methane c ombustion is affected by the presence of chloride ions, which induce an inh ibitory effect on the combustion. Additionally, the presence of micropores also decreases the activity due to difusional Limitations. (C) 1999 Society of Chemical Industry.