Thermal stability of TPA template and size-dependent selectivity of uncalcined TS-1 supported Au catalyst for propene epoxidation with H2 and O2

Abstract

A tetrapropyl-ammonium (TPA) template, as the most critical component inside microporous channels of an uncalcined Au/TS-1 catalyst (Au/TS-1-B), hinders the entrance of Au nanoparticles into the micropores and thus prevents the micropore blocking induced deactivation for direct propene epoxidation with H₂ and O₂. In this work, the essential stability of the TPA template at distinct reaction temperatures is first investigated. It is found that the TPA template inside micropores decomposes to H₂O, NH₃ and propene after 350 °C. Based on a suitable reaction temperature range (<350 °C), the PO formation rate shows a volcano-shaped relationship with reaction temperature and reaches a maximum value of 220 g_PO h⁻¹ kg_Cat⁻¹ at 260 °C, which is a noteworthy result compared with other reported catalysts. Moreover, due to presence of the TPA template inside micropores of TS-1, size-dependent selectivity shown on Au/TS-1-B should be intrinsic because the Au/TS-1-B catalyst exhibits uniform-sized Au nanoparticles and high stability. Hence, a series of Au/TS-1-B catalysts with different Au sizes are then tested for propene epoxidation, and the plausible reaction routes are also discussed.