Studies on deactivation behavior of SO42−/ZrO2-SiO2 catalyst derived from C2F4 and C3F6 oligomers deposition

Abstract

• Catalyst deactivation derived from oligomers deposition was discovered. • Oligomers deposition could be described with modified Voorhies equation. • Effects of reaction conditions and total acid sites on oligomers deposition were revealed. • Relationship between oligomers accumulation and catalytic decay factor was unraveled. Preparation of tetrafluoroethylene (C 2 F 4 , TFE) and hexafluoropropylene (C 3 F 6 , HFP) from decomposition of trifluoromethane (CHF 3 , R23), which is produced from methane via chlorination and followed fluorination, attracts researchers’ interest. However, the deposition of TFE and HFP oligomers will lead to catalyst deactivation. Herein, the TFE and HFP oligomers deposition and resulting deactivation behavior on SO 4 2− /ZrO 2 -SiO 2 catalyst series, with different Lewis and Brønsted acid site densities, were investigated using (modified) Voorhies equation. For that purpose, the Lewis and Brønsted acid site densities in these utilized catalysts were measured by employing pyridine IR spectroscopy in combination with pyridine titration method. And the amount of oligomers deposited on catalyst was determined by thermogravimetry (TG) analysis. The effects of reaction temperature, molar fraction of feedstock and amount of total acid sites on the oligomers accumulation were revealed, as well as the relationship between catalytic decay factor and amount of oligomers deposited on catalyst. The results showed that both Brønsted and Lewis acid sites were responsible for TFE and HFP oligomers formation and deposition. The oligomers deposition over time-on-stream obeyed the Voorhies equation modified with the variables of reaction temperature, molar fraction of feedstock and total acid sites in the case of feeding TFE, HFP or TFE-HFP mixture. With the obtained exponential relationship between amount of oligomers deposited on catalyst and catalytic decay factor, the catalyst deactivation process can be regularly described by the reaction temperature, molar fraction of feedstock and total acid sites in catalyst when feeding TFE, HFP and TFE-HFP mixture, which would be helpful for further catalyst modification and reaction condition optimization in the field of R23 transformation.