(177f) Synthesis of Well-Defined IrO2/TiO2 Catalysts for Low-Temperature Activation of Methane

Previous work has shown that IrO₂(110) surfaces are very active in the low-temperature activation of methane. Inspired by this work, we synthesized IrO₂ nanoparticles and IrO₂ supported on rutile TiO₂ nanorods and investigated their activity towards methane activation at room temperature. The synthesis conditions yielded IrO₂ nanoparticles approximately 8 nm in diameter and they were shown to expose a significant fraction of the desired (110) surface facets (Figure 1a and b). After an oxygen treatment to convert any Ir₂O₃ to IrO₂, and then outgassing to remove excess oxygen, the IrO₂ nanoparticles were exposed to methane at room temperature. After removing gas phase methane, the IrO₂ nanoparticles were heated in inert to 800 K while monitoring the products released. These experiments revealed that the IrO₂ nanoparticles do indeed activate methane at room temperature, as carbon dioxide desorbed around 520 K. The effect of a mild reduction (between 375 to 475 K) was also evaluated and revealed a slight increase in the overall amount of methane activated up to a reduction treatment of 425 K, as oxygen removal exposed additional sites. However, the CO₂ desorption peak also shifted to higher temperatures, revealing that the remaining oxygen was more difficult to remove.

To decrease the IrO₂ content, TiO₂-supported IrO₂ catalysts with different IrO₂ loading were also synthesized using an urea precipitation method. A synthesis method for rutile TiO₂ nanorods were selected to maximize the (110) surface facets exposed. Even at a 10% iridium loading (by weight) on the TiO₂ support, the signals obtained from the IrO₂/TiO₂ catalysts are significantly lower compared with the pure IrO₂ but indicate that the supported catalyst can also activate methane at room temperature.