Synthesis and support composition effects on CH 4 partial oxidation over Ni-CeLa oxides

Two series of Ni (6 wt%) catalysts supported over CeO2, La2O3 and mixed CeO2-La2O3 were prepared by co-precipitation and by wet-impregnation. The effect of the two Ni loading procedures on the catalyst structural properties was investigated by XRD, TPR and XPS. The catalytic behavior of the catalysts was tested in the methane partial oxidation reaction performed at 1 atm in a temperature range of 400-800 °C using dilute feed gas mixture with CH4/O2 = 2 and gas hourly space velocity of 60,000 ml g-1 h-1. Total methane combustion was observed within the 450 °C <= T<= 650 °C temperature range. Above 650 °C partial oxidation of methane started to occur, reaching at 800 °C a CO selectivity close to 90%. The lanthanum containing catalysts prepared by wet impregnation exhibited higher CPO activity at lower temperature as compared to the co-precipitated ones. Opposite behavior was observed with the Ni-CeO2 catalysts. During the stability test at high temperature, carbon formed only over the single oxide supported catalysts, Ni-CeO2 and Ni-La2O3. According to the characterization results carbon was not responsible for catalyst deactivation but it prevented the sintering of the nickel particle. The interplay of the crystallite sizes and the formation of various nickel-lanthanum oxide species with different Ni oxidation states were responsible for the differences in the CPO performance.