Catalytic decomposition of HFC-134a over metal oxide and phosphate catalysts to VDF: Reaction pathways of CH4 addition

Abstract

HFC-134a refrigerants are commonly used in air-conditioners and refrigerators. HFC-134a has a GWP 1,430 times higher than that of CO₂ and contributes significantly to climate change. Therefore, research has been conducted to eliminate HFC-134a via catalytic decomposition. The catalytic decomposition of HFC-134a with the addition of CH₄ over metal oxide (CaO, MgO, and Al₂O₃) and phosphate catalysts (Ca₂P₂O₇, Mg₂P₂O₇, and AlPO₄) is described herein. The prepared catalysts were characterized by NH₃-TPD, TGA, and BET analysis. Metal phosphate catalysts exhibited higher HF resistance than metal oxide catalysts. XRD, XRF, and SEM-EDS confirmed the superior resistance of metal phosphates to corrosive hydrogen fluoride (HF). VDF (C₂H₂F₂) is a valuable feed product that can be polymerized into polyvinylidene fluoride (PVDF). In addition, the VDF yield increased with CH₄ addition during the HFC-134a decomposition reaction. The CaP-calcium phosphate-catalysts exhibited an efficiency of more than 80 % and the highest VDF yield of 28.8 % after 10 h at 900 °C, 1 bar, and HFC-134a:CH₄:N₂ = 1:2:17 and RT = 1.0. The introduced CH₄ feed acts as a CH₃ donor during the decomposition of HFC-134a. Consequently, a comprehensive mechanism of VDF synthesis was proposed by comparing the presence of CH₄ feed.