Pulse study of methane partial oxidation to syngas over SiO2-supported nickel catalysts

The reaction behaviors of CH4/O-2 (2/1) with unreduced and reduced SiO2-supported nickel (10 wt% metal) catalysts were investigated in a pulse micro-reactor at temperatures ranging from 600 to 800 degrees C. In the interaction of CH4/O-2 With unreduced NiO/SiO2, the products are exclusively CO2 and H2O at or below 700 degrees C. At 800 degrees C, besides CO2 and H2O, CO and H-2 are formed. The reactivity at 800 degrees C can be ascribed to the net generation of metallic nickel site at this temperature. In the reaction of CH4/O-2 over reduced Ni/SiO2, the main products are CO and H-2 with CO2 and H2O being the minor ones. The results indicate metallic nickel is the active site for methane partial oxidation to syngas. Normal deuterium isotope effects of similar magnitude were observed on the overall, as well as on the CO and CO2 formation reactions with insignificant change in the product selectivities when CD4 was used instead of CH4, indicating that methane dissociation is a key step and that CO and CO2 are formed via some common intermediates which are subject to kinetic deuterium isotope effect. The results of deuterium isotope effects can be reasonably explained based on the methane pyrolysis mechanism.