EDTA-assisted hydrothermal synthesis of cubic SrF2 particles and their catalytic performance for the pyrolysis of 1-chloro-1,1-difluoroethane to vinylidene fluoride

Abstract

Uniform, free-standing and cubic SrF₂ microparticles were successfully fabricated by a facile hydrothermal method with ethylenediaminetetraacetic acid (EDTA) as the chelating agent. The influences of preparation conditions, such as the pH value, amount of EDTA and hydrothermal time, on the formation of SrF₂ crystals were investigated. The formation mechanism of cubic SrF₂ particles was proposed based on the experimental results. Following calcination in air at 500 °C, SrF₂ particles were evaluated as the catalyst for the pyrolysis of 1-chloro-1,1-difluoroethane (HCFC-142b, CH₃CClF₂) to vinylidene fluoride (VDF, CH₂CF₂) at 350 °C and a space velocity of 600 h⁻¹. The results indicate that SrF₂ cubes exhibit high catalytic activity with a HCFC-142b conversion of about 70% and a selectivity to VDF of 80–87%. No significant deactivation was observed within the time on stream of 30 h. With the reaction temperature increased to 450 °C, the conversion of HCFC-142b is close to 94%, while the selectivity to VDF remains almost unchanged. Although the SrF₂ catalyst prepared by the conventional precipitation method also shows high conversion, its selectivity to VDF is only around 50–70%. We suggest that the surface acidity and specific surface area play major roles in the catalytic performance. Compared with the temperatures for industrial manufacture of VDF of 650–700 °C, the SrF₂ catalysts provide a promising pathway to produce VDF at much lower temperatures.