CO in situ directed highly efficient CrOx@silicalite-1 for propane oxidation dehydrogenation by CO2

Abstract

The propane oxidation dehydrogenation assisted by CO2 (CO2-ODHP) is currently a hot research topic, not only to meet growing demand of propylene but also to favor the CO2 neutralization. In present work, a series of CrOx@S1-n-1.0 with different Cr contents (n= 2.2, 3.6 and 4.5 wt%) is synthesized based on a small gas molecule directing synthesis strategy, wherein the gaseous CO of 1.0 MPa was in situ introduced in the synthesis system to regulate the interaction and dispersion of CrOx over silicalite-1 (S1) support. The characterization results of XRD, XPS, H2-TPR, and Raman indicate that the CO can affect the oxidation state and dispersion of Cr species. As observed, the Cr species were highly dispersed over CrOx@S1–3.6 %-1.0 (in the form of Cr6+ valance state), which however would aggregate to generate Cr2O3 nanoparticles over the CrOx@S1–3.6 %-0a prepared by impregnation method in absence of CO. The activity measurement indicates that the CrOx@S1–3.6 %-1.0 possesses the highest activity by displaying an average propane conversion of 50.4 % and CO2 conversion of 23.6 % at 600 °C, which surpasses most of the literature reports. The CO2-ODHP reaction mechanism was further investigated by in situ DRIFTS, which indicates that dissociated H of propane can react with CO2 to form formate (-COOH), in turn further reacts with H to produce byproducts CO and H2O, and the formate species can also react with the CrO3 active site to form bicarbonate species (HCO-3). Generally, present work has proposed a small gas molecule directing strategy to adjust the dispersions and chemical states of the loaded guest meals over catalytic support. The study of present work would contribute to other highly efficient catalyst design.