Catalytic Performance for the Conversion of Potent Fluorinated Greenhouse Gases by Aluminium Fluorides with Different Morphology

Abstract

The AlF3 catalysts with controlled morphology (cubic, hexahedron and octahedron) were synthesized via hydrothermal method using different solvents. The dehydrofluorination of 1,1,1,3,3-pentafluoropropane (HFC-245fa) was used as the model reaction to evaluate the catalytic performance of the AlF3 catalysts with different morphology. Results showed that surface area, crystal structure, surface acidic properties together with the chemical composition of the AlF3 catalyst were substantially influenced by the different morphology. XRD results showed that κ-AlF3 crystalline structure was formed when using ethanol as solvent while β-AlF3 crystalline structure was formed when using water as solvent. Among the three prepared AlF3 samples, the AlF3-C catalyst with cubic shape demonstrated not only largest surface area but also most amount of medium-strength surface acid sites, resulting in enhanced reaction activity towards the dehydrofluorination reaction. The characteristic high Miller index crystal planes of (402) and (321) exposed on the cubic shaped AlF3-C catalyst is believed to be the main reason accounting for the high catalytic performance as there are equal amount of Al and F atoms exposed. Moreover, a reaction mechanism describing dedehydrofluorination of HFC-245fa on AlF3 catalyst with equal amount of Al and F atoms exposed on certain crystal planes was proposed.