Preparation and characterization of Ce1-x NixO2 as oxygen carrier for selective oxidation methane to syngas in absence of gaseous oxygen

A citric acid complex method was employed to prepare Ce/Ni mixed oxides with various Ce/Ni ratios useful for selective oxidation methane to syngas in the absence of gaseous oxygen, and the catalytic activity measurement was investigated in a fixed bed reactor at 800 °C. The prepared oxygen carriers were characterized by various characterization techniques such as TG-DSC, XRD and TPR. The results of TG-DSC indicated that the Ce1-xNixO2 precursor generated a stable phase after the heat-treatment at temperatures above 800 °C. The XRD characterization suggested that some Ce-Ni solid solution was formed when Ni2+ ions was incorporated into the lattice of CeO2, and it led to the generation of O-vacancy which could improve the oxygen mobility in the lattice of oxygen carriers. It was found that Ce0.8Ni0.2O2 gave the highest activity in the selective oxidation methane to syngas reaction, and the average methane conversion, CO and H2 selectivity reached to 82.31%, 82.41% and 87.64%, respectively. The reason could be not only attributed to the fitting amount of NiO dispersed on the CeO2 surface and bulk but also to actual lattice oxygen amount increased in oxygen carrier.