Effect of Metal-Support Interactions on Ir/TiO2 Catalyst Properties

To investigate the effects of metal-support interactions and the influence of titanium dioxide (titania) structure on the catalytic properties of iridium supported on titania, three catalysts with a low metal loading (0.5% by weight) were synthesized. Three titania supports were selected, two commercial nanoparticles with rutile and anatase structure (selected so that the surface areas and particle sizes were as close as possible), and rutile titania nanorods synthesized using a hydrothermal method. An iridium precursor, IrCl₄, was deposited onto the rutile nanorods, rutile nanoparticle, and anatase nanoparticle supports using a urea precipitation method. To reduce variability in the amount of iridium deposited during synthesis of the catalysts, an IrCl₄ solution was first mixed and later distributed amongst each support type.

The overall Brunauer-Emmett-Teller (BET) surface areas were measured on each catalyst as well as their supports, to confirm that the synthesis method did not alter the supports. Temperature Programmed Reduction (TPR) experiments were performed by monitoring the hydrogen uptake as a function of temperature up to 500 °C. The TPR data reveal a complex reduction pattern with multiple peaks corresponding to IrO_x and TiO₂ reduction.

The catalysts were tested for performance in the hydrogenation of propene to propane and in both methane partial oxidation and methane combustion reactions as a function of pretreatment conditions, primarily reduction temperature. The catalysts are effective in the oxidation of methane, and preliminary data reveal that iridium supported on the rutile titania structure is more active than iridium on anatase titania. Reduction at 500 °C before reaction did not significantly alter the activity compared with a reduced catalyst.