Controlling Reaction-Induced Loss of Active Sites in ZnOx/Silicalite-1 for Durable Nonoxidative Propane Dehydrogenation

ZnO-based catalysts are promising for nonoxidative propane dehydrogenation (PDH) to propene owing to their low cost and environmental friendliness but experience serious loss of the active component because of the reduction of ZnO to metallic Zn that evaporates. Here, we demonstrate that MgO-modified ZnOx/silicalite-1 materials prepared through one-pot hydrothermal method are active, selective, and durable in the PDH reaction. The undesired loss of Zn could also be successfully suppressed without negative effect on the PDH performance owing to a strong interaction between Mg2+ and ZnOx, as concluded from the results of X-ray photoelectron and Fourier-transform infrared spectroscopic measurements as well as temperature-programmed reduction with CO. X-ray absorption spectroscopy revealed that atomically dispersed Zn2+ sites are responsible for PDH. Using an industrially relevant feed with 40 vol % propane, propene selectivity between 88 and 95% at propane conversion between 15 and 32% was achieved over six PDH/oxidative regeneration cycles lasting for about 20 h on stream at 550 °C without loss in the initial activity, while some deactivation occurred after longer (up to about 60 h) time on stream. The deactivation (caused by Zn loss) constant of Mg-modified ZnOx/silicalite-1 considering the 2nd and 20th cycles is more than 3 times lower than that of its Mg-free counterpart.