Synergistic catalysis of carbon-partitioned LaF3–BaF2 composites for the coupling of CH4 with CHF3 to VDF

Abstract

Catalytic coupling of CH₄ with potent greenhouse gas CHF₃ to vinylidene fluoride (VDF) was investigated over composite catalysts. Carbon-partitioned LaF₃–BaF₂ catalysts were prepared by PVDF (polyvinylidene fluoride)-mediated calcination. During catalyst preparation, PVDF functions as the fluorine source and carbon source. Compared with the catalysts prepared by the conventional HF co-precipitation method, the transformation of LaF₃ and BaF₂ to Ba_1−xLa_xF_2+x solid solution is inhibited as Ba and La are separated by carbon layers derived from the decomposition of PVDF. The Ba_1−xLa_xF_2+x phase is not favorable for the coupling of CH₄ with CHF₃ to VDF. In addition, PVDF-mediated calcination facilitates the formation of LaOF which is one of the key species for coupling of CH₄ with CHF₃ to VDF. O⁻ species, which is the most active oxygen species for the activation of CH₄, increases significantly following PVDF-mediated calcination due to the formation of LaOF. Consequently, the formation rate of VDF over the catalyst derived from PVDF-mediated calcination is 3.6 times higher than the HF co-precipitation catalyst at a reaction temperature of 700 °C. The formation rate of the HF co-precipitated catalyst declines to nearly half of the initial rate in a time-on-stream of 15 h. By contrast, only slight deactivation is observed over the catalyst prepared by PVDF-mediated calcination. The present work provides a promising strategy for the preparation of composite catalysts.