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

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 Ba1−xLaxF2+x solid solution is inhibited as Ba and La are separated by carbon layers derived from the decomposition of PVDF. The Ba1−xLaxF2+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.