Role of hydrotalcite precursors as supports for Pd catalysts in hydrodechlorination of CCl2F2

Abstract

The selective synthesis of CH2F2 by the hydrodechlorination of CCl2F2 is studied over calcined Mg–Al and Mg–Cr hydrotalcites (CMA-HT and CMC-HT) supported Pd catalysts. Their activities are compared with the corresponding oxides, viz., MgO, γ-Al2O3 and Cr2O3 supported Pd catalysts. Pd catalyst on the support from Mg–Al HT precursor is found to be superior and advantageous in terms of higher selectivity towards CH2F2 formation and stability of the catalyst. The catalysts followed the order: Pd/CMA-HT > Pd/MgO > Pd/γ-Al2O3 > Pd/Cr2O3 > Pd/CMC-HT in terms of the selectivity towards CH2F2 formation. Pd/CMC-HT showed deeper hydrogenation activity towards the formation of CH4. Pd/CMA-HT and Pd/MgO showed a higher increase in the acidity of the catalyst after the reaction, which facilitates to maintain the Pd site in electron deficient environment and thereby yielding higher selectivity towards CH2F2. The lack of sufficient acidity on Pd/CMC further explains the poor selectivity to CH2F2 observed over this catalyst. XPS results also confirm the enrichment of surface fluoride over Pd/CMA-HT and Pd/MgO used catalysts.