Sub-nano MgF2 embedded in carbon nanofibers and electrospun MgF2 nanofibers by one-step electrospinning as highly efficient catalysts for 1,1,1-trifluoroethane dehydrofluorination

Abstract

Hydrofluorocarbons (HFCs) which are usually potent greenhouse gases are regulated by the Montreal Protocol and its amendments, especially the recent Kigali Amendment. Dehydrofluorination of HFCs is an efficient route for the conversion of these greenhouse gases to value added and environmentally benign chemicals. Although AlF₃ with strong Lewis acidity catalyzes dehydrofluorination, it also favors carbon deposition. MgF₂ with weak acidity inhibits coking significantly. Unfortunately, MgF₂ sinters dramatically at temperatures below 300 °C leading to the low activity for dehydrofluorination. In the present work, we report that sub-nano MgF₂ embedded in carbon fibers and electrospun MgF₂ fibers prevent sintering of MgF₂ during dehydrofluorination reaction. Via simple and one-step electrospinning and calcination in a N₂ (for embedded MgF₂) or air (for MgF₂ fibers) atmosphere, embedded MgF₂ with particle sizes between 3–6 nm and pure MgF₂ fibers with diameters of around 100 nm were fabricated. No sintering was observed following reaction at 450 °C. The fine MgF₂ particles and MgF₂ fibers facilitate the formation of under coordinated Mg species in MgF₂ which are the weak acid sites. By embedding MgF₂ or fabrication of MgF₂ fibers, weak acid sites are increased significantly, while strong acid sites remain almost unchanged. Hence, they show significantly higher reaction rates than MgF₂ prepared by precipitation of Mg(CH₃COO)₂·4H₂O with NH₄F for the dehydrofluorination of 1,1,1-trifluoroethane (HFC-143a) to VDF (CH₂CF₂) at 450 °C.