Effect of Cu content on the bimetallic Pt–Cu catalysts for propane dehydrogenation

Abstract

Silica supported, 2 nm Pt and Pt–Cu catalysts with different Cu:Pt atomic ratios and similar size were evaluated for propane dehydrogenation at 550 °C. Monometallic Pt showed low propylene selectivity of 61% at 20% conversion and a TOR of 0.06 s−1. For the Pt–Cu catalysts, the dehydrogenation selectivity and TOR continuously increased with increasing Cu level in the nanoparticle, to eventually 96% selective at 20% conversion with a TOR of 0.98 s−1 for a catalyst with a Cu:Pt atomic ratio of 7.3. Synchrotron in situ X-ray diffraction and X-ray absorption spectroscopy analysis showed that Pt–Cu catalysts with increasing Cu loading formed solid solution type bimetallic structures. For example, a Pt–Cu catalyst with Cu:Pt atomic ratio of 7.3 formed solid solution containing 87% Cu. In this catalyst, the Pt active sites were geometrically isolated by the inactive metallic Cu, which was suggested to be responsible for high selectivity to propane dehydrogenation. The Cu neighbors surrounding the Pt also likely modified the energy level of Pt 5d orbitals and contribute to a TOR about 16 times higher than that of monometallic Pt.