Combustion Synthesis of Amorphous Al and Cr Composite as the Catalyst for Dehydrofluorination of 1,1-Difluoroethane

Abstract

Interaction or lattice doping between Cr and Al contributes to the acidity and catalytic activity of Cr/Al catalysts, which is difficult to be achieved by the conventional preparation methods while maintaining nanostructures. We suggest that solution combustion synthesis (SCS) is one of the effective ways for this issue. Nanoscale Cr/Al composite catalysts of sheet structure with a thickness around 40−100 nm were fabricated via simple solution combustion method with Cr(NO 3 ) 3 •9H 2 O and Al(NO 3 ) 3 •9H 2 O as the precursors and glycine as the fuel. Following SCS and fluorination pretreatment, Cr species interact with Al species intimately forming an amorphous structure. The interaction provides relatively high amounts of defects and is favorable for the formation of active species, resulting in the enhanced Lewis acidity and catalytic activity. At 400 °C, a reaction rate of 33.9 mmol/h/g was achieved for the dehydrofluorination of HFC-152a over composite catalyst, which is 30−40% higher than that of Cr and Al catalysts.

Difluoromethane (HFC-32) and Pentafluoroethane (HFC-125) Sorption on Linde Type A (LTA) Zeolites for the Separation of Azeotropic Hydrofluorocarbon Refrigerant Mixtures

“…Ethane-based HFCs react over Lewis acid catalysts and some Lewis base catalysts. − Gray and Corbin showed that HFC-134 was dehydrofluorinated by zeolite 13X and proposed that the deprotonation of HFC-134 was the rate-limiting step in the reaction mechanism, followed by an attack on the framework aluminum atoms by fluoride ions . Although this process occurred at higher temperature (548.15 K), the possibility of reaction between ethane-based HFCs and basic zeolites was realized.…”

Experimental and DFT Mechanistic Study of Dehydrohalogenation of 1-Chloro-1,1-difluoroethane over Metal Fluorides

“…For the catalysts with moderate Lewis acidity, such as MgF 2 , SrF 2 , BaF 2 CrF 3 , and LaF 3 , although lower than that of AlF 3 , high conversion levels of HCFC-142b are obtained. It is well accepted that fluorinated Cr 2 O 3 possesses high affinity to fluorocarbons and excellent dehydrofluorination activity to hydrofluorocarbons. ,, Consequently, as indicated by the XRD pattern, although CrF 3 is partially oxidized to Cr 2 O 3 , high conversion of HCFC-142b is still approached.…”

“…It is well accepted that fluorinated Cr 2 O 3 possesses high affinity to fluorocarbons and excellent dehydrofluorination activity to hydrofluorocarbons. 12,13,17 Consequently, as indicated by the XRD pattern, although CrF 3 is partially oxidized to Cr 2 O 3 , high conversion of HCFC-142b is still approached.…”

“…Dehydrohalogenation of fluorinated and chlorinated carbons is one of the most efficient routes for the preparation of fluorine/chlorine-containing olefins, such as vinylidene fluoride (VDF), vinyl fluoride (VF), trifluoroethylene (TrFE), and 1,1,1,3,3-pentafluoropropane (HFO-1234ze). ,− Taking VDF as the example, generally, it is produced via the dehydrochlorination (DeHCl) of 1-chloro-1,1-difluoroethane (CH 3 CClF 2 , HCFC-142b). Industrially, the reaction is carried out at temperatures above 650 °C in the absence of a catalyst.…”

Carbon-Interacted AlF3 Clusters as Robust Catalyst for Dehydrofluorination Reaction with Enhanced Undercoordination and Stability

“…The area of the absorption peak in AlF 3 –SAPO-5 is significantly larger than that in AlF 3 -py, indicating that AlF 3 –SAPO-5 contains more Lewis acid sites. As the Lewis acid sites are the catalytic active center of HFCs dehydrofluorination, AlF 3 –SAPO-5 with more demanded Lewis acid sites shows excellent catalytic properties…”