Catalytic coupling of CH4 with CHF3 for the synthesis of VDF over LaOF catalyst

• Published in: Greenhouse gases: science and technology 2018-06, Vol.8 (3), p.587-602
• Main Authors: Cheng, Yimin, Wang, Jinchao, Han, Wenfeng, Song, Yanyan, Liu, Wucan, Yang, Luteng, Wang, Shucheng, Wu, Zhixing, Tang, Haodong, Zhang, Jianjun, Stockenhuber, Michael, Kennedy, Eric M.
• Format: Article
• Language: English
• Subjects: Activation; Catalysis; Catalysts; Chemical synthesis; Climate change; Conversion; Coupling; Fluorides; Fluorination; Global warming; High temperature; La2O3; Lanthanum; Lanthanum fluorides; Lanthanum oxides; LaOF; Low temperature; Methane; Organic chemistry; Phase transitions; Pretreatment; pyrolysis; Reaction mechanisms; trifluoromethane; Vinylidene; Vinylidene fluoride
• ISSN: 2152-3878; 2152-3878
• DOI: 10.1002/ghg.1769

The oxidative coupling of methane (OCM) with CHF3 facilitates the synthesis of vinylidene fluoride (VDF). The aim is to utilize CHF3, which is otherwise considered a waste with a very high global warming potential. This study focuses on the effect of a LaOF catalyst on OCM occurring in the presence of CHF3, which engenders a promoting effect of O2 on CH4 activation. It examines the structural and phase changes of the lanthanum catalyst during the reaction and then speculates on the reaction mechanism. In combining OCM with CHF3, both the conversion of CH4 and the formation rate of VDF are almost tripled at 700°C. However, at higher temperatures, gas‐phase reactions play a dominating role in the conversion of CH4 and LaOF catalyst plays a very minor role in the reaction system at elevated temperatures. Irrespective of the reaction temperature, VDF is produced via the gas‐phase coupling of CH3 radicals with CF2. During pretreatment or during the reaction itself, La2O3 is fluorinated by CHF3 and HF, yielding the formation of surface LaOF and LaF3 species. LaF3 is a relatively inactive catalyst for CH4 conversion, whereas, in comparison LaOF appears to play a very important role in the activation of CH4 at low temperatures. The activation mechanism of CH4 at relatively low temperatures is similar with that postulated to occur during the OCM. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.