Nickel-magnesium mixed oxide catalyst for low temperature methane oxidation

A series of nickel-magnesium mixed oxides (NiMg) of varying molar ratios, Ni9Mg, Ni2Mg, NiMg, NiMg2 and NiMg9, were synthesized using the co-precipitation technique. These materials were prepared as possible lower cost alternatives to Pd-based methane oxidation catalysts. The NiMg catalysts were characterized by means of X-ray diffraction (XRD), photoelectron spectroscopy (XPS) and H2-temperature programmed reduction (H2-TPR). Their activity for complete methane oxidation was investigated using temperature programmed oxidation. Ni9Mg was found to be the most active catalyst of the series. Characterization results showed that most of the materials formed solid solutions of the NixMg1-xO type. The activity of the Ni9Mg was attributed to its highest surface area and highest oxygen mobility. It was further tested and aged in simulated natural gas engine exhaust that contained 10 vol% water vapor. The results were compared to a reference 1 wt% Pd/Al2O3 methane oxidation catalyst tested under the same conditions. Ni9Mg exhibited approximately 94% methane conversion after 40 h of aging which was higher than that of the Pd-based reference catalyst with methane conversion below 80% after only 16 h of aging. Ni9Mg is thus proposed as a promising alternative to PGM-based catalysts for complete methane oxidation.