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

The reaction behaviors of CH₄/O₂ (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°C. In the interaction of CH₄/O₂ with unreduced NiO/ SiO₂, the products are exclusively CO₂ and H₂O at or below 700°C. At 800°C, besides CO₂ and H₂O, CO and H₂ are formed. The reactivity at 800°C can be ascribed to the net generation of metallic nickel site at this temperature. In the reaction of CH₄/O₂ over reduced Ni/SiO₂, the main products are CO and H₂ 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.