The mechanistic study of methane reforming with carbon dioxide on Ni/α-Al2O3

The reactions of oxidized and reduced 6 wt % NiO/alpha-Al2O3 with H-2, CH4, CO2, O-2, and their mixtures are studied in flow and pulse regimes using a setup equipped with a differential scanning calorimeter DSC-111 and a system for chromatographic analysis. It is shown that treatment with hydrogen at 700 C results in the partial reduction of NiO to Ni. Methane practically does not react with oxidized Ni/alpha-Al2O3 but it does react actively with the reduced catalyst to form H-2 and surface carbon. The latter is capable of reacting with lattice oxygen of Ni/alpha-Al2O3 (slowly) and with adsorbed oxygen (rapidly). Carbon dioxide also reacts with surface carbon to form CO (rapidly) and with metallic Ni to yield CO and NiO (slowly). Thus, the main route of methane reforming with carbon dioxide on Ni/alpha-Al2O3 is the dissociative adsorption of CH4 to form surface carbon and H-2 and the reaction of this carbon with CO2 resulting in the formation of CO by the reverse Boudouard reaction. Side routes are the interaction of the products of methane chemisorption with catalyst oxygen and the dissociative adsorption of CO2 on metallic nickel. A competitive reaction of surface carbon with adsorbed oxygen results in a decrease in the CO2 conversion in methane reforming with carbon dioxide. Therefore, the presence of gaseous oxygen in the reacting mixture decelerates methane reforming (catalyst poisoning by oxygen).