Influence of Nanoscale Intimacy in Bi-Functional Catalysts for CO2-Assisted Dehydrogenation of C-5-Paraffins

Abstract

In this study, Pt1Sn1 intermetallic nanoparticles (NPs) on SiO2/CeO2@SiO2 composites were located either on SiO2 or on CeO2@SiO2, thereby varying the average distance (intimacy) between metal sites and CeOx sites from "closest" to "nanoscale". The catalytic performance of these catalysts was compared to dual-bed mixtures of Pt1Sn1@SiO2 and CeO2@SiO2 powders, which provided a "milliscale" distance between sites. Several beneficial effects on the catalytic performance of CO2-assisted oxidative dehydrogenation of C-5-paraffins were observed when Pt1Sn1 nanoparticles were located on SiO2 in nanoscale proximity to the CeO2 sites, as opposed to Pt and Sn species located on CeO2@SiO2 with the closest proximity and milliscale intimacy between Pt1Sn1 and CeO2. The former catalysts exhibited the highest C-5-paraffin conversion of 32.8%, with a C-5 total olefin selectivity of 68.7%, while the closest-proximity sample had a lower conversion of 17.4%, with a C-5 total olefin selectivity of 20.9%. The FT-IR (Fourier transform infrared spectroscopy) spectroscopic study of the CO adsorption and X-ray photoelectron spectroscopy results revealed that the closest proximity between Pt and Ce inhibited PtSn alloy formation due to their strong interaction. However, for the nanoscale-proximity sample, neighboring CeO2@SiO2 did not disturb Pt1Sn1 intermetallic formation. This strategy can be applied to other CO2 activation catalysts, instead of CeO2@SiO2. This paper aims to provide insights into the influence of metal-CeOx intimacy in bi-functional catalysts.