Partial Oxidation of Methane on Nickel Carbide Catalysts

Partial oxidation of methane is a process used industrially to convert methane to syngas, a mixture of hydrogen and carbon monoxide. Syngas is then used in chemical syntheses such as hydrogen and methanol, or upgraded through the Fischer-Tropsch process to produce longer-chained hydrocarbons, and ultimately products like gasoline. Rhodium is commonly used as a catalyst for this process; however, rhodium is prohibitively expensive. Due to this expense, a new catalyst for partial methane oxidation is desirable. Nickel has been investigated as this alternative catalyst, and is in fact used in some industrial processes. However, lower activity, deactivation by oxidation, and formation of coke are problems associated with the use of metallic nickel as the catalyst. In separate studies, metal carbides have been shown to have catalytic properties similar to that of noble metals, a class into which rhodium falls.

In this work, the effectiveness of nickel carbide as a catalyst for partial methane oxidation is investigated. Nickel carbide nanoparticles were synthesized and characterized by XRD and TEM, and found to be nickel carbide particles with diameter of approximately 30 nm. These nanoparticles were then used in a temperature programmed reduction (TPR), and reacted under atmospheres of varying Ar, CH₄, and O₂ composition under varying temperature ramps ranging from nominal temperatures of 20^oC to 800^oC. After pretreatment under Ar at 350^oC, the nickel carbide showed evolution of hydrogen starting near 460^oC. Under a mixture of Ar, CH₄, and O₂, oxygen consumption and hydrogen production started around 300^oC. The characterization of the nickel carbide after the reaction showed agglomeration of the nickel carbide particles and degradation of the nickel carbide phase and associated formation of a metallic nickel phase. Further results of the methane partial oxidation activity and stability of the nickel carbide catalyst will also be presented and discussed.