Unraveling the Origins of the Synergy Effect between ZrO2 and CrOx in Supported CrZrOx for Propene Formation in Nonoxidative Propane Dehydrogenation

In this work, steady-state tests of propane dehydrogenation, density functional theory calculations, operando UV–vis spectroscopy, ex situ and in situ electron paramagnetic resonance spectroscopy, IR spectroscopy, and temperature-programmed techniques were combined to provide fundamentals for tuning activity and onstream stability of low-loaded catalysts with supported CrZrOx species. Two neighboring Zrcus (cus = coordinatively unsaturated) sites were concluded to be mainly responsible for propane dehydrogenation to propene. They are formed upon reductive catalyst treatment, and their concentration depends on the strength of interaction among CrOx, ZrO2, and support and on the size of ZrO2 crystallites in CrZrOx. SiO2 weakly interacting with CrOx was found to be a more preferable support than Al2O3- or TiO2-based supports. CrOx species promotes formation of Zrcus sites and improves their intrinsic activity for the desired reaction. CrOx also contributes to coke formation as concluded from operando UV–vis analysis. Cr20Zr80/SiO2 possessing about 3.9 or 2.5 times lower amounts of chromium or zirconium in comparison with an analogue of industrial K-CrOx/Al2O3 or state-of-the-art Ru/LaZrOx revealed about 2 times higher space-time yield of propene at 30% propane conversion at 550 °C. Moreover, this catalyst was durable over 50 dehydrogenation/regeneration cycles lasting 150 h.