(762h) Designing Catalysts for Enhanced Pairwise Selectivity of Parahydrogen Addition to Unsaturated Hydrocarbons
AIChE Annual Meeting
Friday, November 18, 2016 - 10:15am to 10:30am
To keep the particle size of Ir on the support small and to minimize hydrogen diffusion and loss of pairwise selectivity, the Ir loading was kept low (0.5 % by weight). However, this was not sufficient to yield significant pairwise addition of hydrogen to propene. Therefore, the Ir/TiO2 catalyst was reduced at 500 °C, instead of the typical 200 °C reduction temperature, to induce strong metal support interactions. After this treatment a â?¼20-fold increase in the pairwise selectivity was observed, and this effect could be completely reversed by oxidation followed by re-reduction at 200 Â°C. X-ray photoelectron spectroscopy (XPS) data reveal partial reduction of the TiO2 support, and Scanning Transmission Electron Microscopy (STEM) data reveal flattening of Ir particles after high-temperature reduction. Non-interacting supports, such as Al2O3 and SiO2, did not show this behavior. It was also shown that chloride ions on the catalyst surface could increase the pair-wise selectivity for the Ir/TiO2 catalyst, possibly by blocking hydrogen diffusion on the catalyst surface. Other methods of designing catalysts to optimize the pairwise hydrogen selectivity over supported metal catalysts are underway.