(682g) Effects of TiO2 Structure on the Methane Partial Oxidation over IrOx/TiO2 Nanomaterials

Partial oxidation of methane (POM) is an exothermic alternative pathway to produce synthesis gas (syngas), a mixture of CO and H₂, compared to the endothermic steam reforming of methane. Noble metals supported on various metal oxides, such as TiO₂, and Al₂O₃, are active and stable catalysts in the methane partial oxidation reaction, and IrO₂/TiO₂ is a particularly interesting combination with high selectivity to syngas. Despite the potential for IrO₂/TiO₂ in the POM reaction, few articles report on the differences in metal-support interactions between iridium and three main crystal phases of TiO₂, namely rutile, anatase, and brookite phase. To determine how the crystal phase of TiO₂ influences the activity and selectivity in the POM reaction, we synthesized IrO₂/TiO₂ catalysts with four different TiO₂ supports. Iridium was deposited onto the TiO₂ supports using the urea deposition-precipitation method, and calcination in air at 350 °C resulted in the IrO₂/TiO₂ catalyst. The catalytic performance of the IrO₂/TiO₂ in the methane partial oxidation reaction was then evaluated as a function of pretreatment conditions. Reduction at 200 °C is expected to reduce only the IrO₂ to metallic Ir, while reduction at 500 °C can also reduce some of the TiO₂, dependent on the crystal structure of the TiO₂. Reducing condition can alter the Ir-TiO₂ interactions, which in turn can influence the catalytic properties of IrO₂ under the reaction conditions. The IrO₂ on rutile TiO₂ nanoparticles after 500 °C reduction (Figure 1(a)), exhibits the best CH₄ conversion (88.8%) as well as 100% CO selectivity at 650 °C, while the worst performing catalyst is supported on anatase TiO₂ (Figure 1 (b)).