Reaction of CHF₃ and CH₄ over CaBr₂ was investigated at 400-900 degrees C as a potential route for transforming the highly potent greenhouse gas, CHF₃, into the valuable product CH₂=CF₂. The homogeneous reaction of CHF₃ with CH₄ was also studied to assist in understanding the chemistries involved. Compared to the gas phase reaction, the addition of CaBr₂ as a reactant increases the conversion of CHF₃ and CH₄ significantly at low temperatures while to a lesser extent at higher temperatures. In the absence of CaBr₂, besides the target product, CH₂=CF₂, a large amount Of C₂F₄ forms. On addition of CaBr₂, the rate of formation Of C₂F₄ drops dramatically to near zero, while the rate of formation of CH₂=CF₂ increases considerably at temperatures below 880 degrees C. Experimental and theoretical studies suggest that CHF₃ strongly interacts with CaBr₂, resulting in the fluorination of CaBr₂ to CaF₂, the release of active Br species results in the selective formation of CBrF₃. The subsequent reactions involving Br, methane, and CBrF₃ play a major role inthe observed enhanced yield of CH₂=CF₂.
Environmental Science & Technology Vol. 42, Issue 15, p. 5795-5799