Selectivity Dependence of 1,1-Difluoro-1-Chloroethane Dehydrohalogenation on the Metal–Support Interaction over SrF2 Catalyst

Abstract

SrF2 promotes the dehydrochlorination (DeHCl) of 1,1-difluoro-1-chloroethane, which is the key process for the manufacture of VDF (vinylidene fluoride), one of the most typical fluorinated monomers. However, the selectivity is low as dehydrofluorination (DeHF) to VCF (vinylidene chlorofluoride) competes with the formation of VDF. In this study, SrF2@C (SrF2 embedded in carbon) and SrF2@NC (N-doped carbon) catalysts were fabricated following calcination in N2 with SrC2O4, PVDF (poly vinylidene fluoride) and urea as the precursors. The catalysts were characterized by XRD, SEM, TEM, and XPS. The results show that both the calcination temperature and N-doping play an important role in the conversion of HCFC-142b and the selectivity to VDF and VCF. Calcination at elevated temperatures enhances the Sr-C interaction. For SrF2@C, improved interaction facilitates withdrawing electrons from Sr by the carbon support. By contrast, the strong interaction of Sr with N-doped carbon supply electrons from N species to Sr. The electron deficiency of Sr is favorable for the adsorption of F with higher electronegativity and consequently, DeHF reaction forming VCF. The supply of electrons to Sr by the support improves the formation of VDF (DeHCl). The present work provides a potential strategy for the improvement of selectivity to the target product.