Synthesis of Titanium Oxyfluoride with Oxygen Vacancy As Novel Catalysts for Pyrolysis of Fluorinated Greenhouse Gasses to Hydrofluoroolefins

Background: Hydrofluorocarbons (HFCs) are potent greenhouse gasses with high global warming potential and the emission of which is strictly regulated by Kigali amendment. Methods: In this paper, titanium oxyfluoride (TiOF2) was firstly synthesized by simple solution combustion synthesis in the absence of highly corrosive HF, among which calcination played an important role on the phase of the products. When the precursor was calcinated at 450 degrees C, pure TiOF2 could be obtained. Significant findings: The pyrolysis of HFCs results showed that the 1,1-difluoroethane (HFC-152a) conversion over TiOF2 is about 53%, superior than TiO2 (40%) due to the enhanced Lewis acidity. Even compared with traditional metal fluoride catalysts (AlF3 and MgF2), TiOF2 held higher stability within 35 h, contributing to the suitable Lewis acidic sites. The formation mechanism of the Lewis acidity was systematically investigated: on one hand, F species made the binding energy of Ti spesies shift to high regions to enhance the Lewis acid strength of Ti species; on the other hand, more oxygen vacancies were generated by the introduction of F, which could act as the Lewis acid sites as well. Hence, this study provides a promising and potential candidate for the catalytic pyrolysis of HFCs. (c) 2021 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.