(449f) Tuning Activity and Selectivity in the Partial Oxidation of Methane over Iridium and Ruthenium Mixed Oxides Supported on Titanium Dioxide Nanoparticles

Selective oxidation of natural gas to higher value chemicals in a one-step reaction process would be highly desirable in a transition away from petroleum-based chemicals and fuels. However, avoiding overoxidation to the most thermodynamically stable oxidation products, i.e. carbon dioxide and water, is challenging, partially due to the high temperatures needed to break the strong C-H bond of methane, the major constituent of natural gas. Iridium dioxide is a very promising material that, under certain conditions, can activate methane at room temperature. However, at room temperature catalytic turnover is challenging, and higher temperatures are needed for the catalytic formation of oxidized products, temperatures at which overoxidation tends to prevail. One strategy to avoid overoxidation is to add a less active (more selective) oxide to an unselective and highly active oxide catalyst. We have therefore added RuO₂ to IrO₂ in an attempt to better control the oxidation properties of the resulting catalysts. Due to the cost of these active metals (Ru and Ir), low loadings (0.5% by weight) were utilized, and the ruthenium and iridium oxides were supported on commercial rutile nanoparticles. The temperature programmed reduction (TPR) data (using 5% H₂ in N₂) reveal that the temperature of reduction is indeed different and varies with the Ir:Ru ratio (Figure 1). Preliminary reaction data run under stoichiometric conditions for the partial oxidation of methane to synthesis gas (carbon monoxide and hydrogen), i.e. CH₄/O₂/Ar/He at 2.0/1.0/2.0/95 standard cm³/min and 50 mg of catalyst, indicate that both the activity (CH₄ conversion) and selectivity to CO and H₂ in this probe reaction are influenced by the Ir:Ru ratio.