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

  • Padmasri A
  • Venugopal A
  • Siva Kumar V
 et al. 
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Abstract

The selective synthesis of CH2F2by the hydrodechlorination of CCl2F2is 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-Al2O3and Cr2O3supported 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 CH2F2formation 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 CH2F2formation. 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 CH2F2observed over this catalyst. XPS results also confirm the enrichment of surface fluoride over Pd/CMA-HT and Pd/MgO used catalysts. The selective synthesis of CH2F2by the hydrodechlorination of CCl2F2is studied over calcined Mg-Al and Mg-Cr hydrotalcites (CMA-HT & CMC-HT) supported Pd catalysts and their activities are compared with the corresponding oxides viz., MgO, γ-Al2O3and Cr2O3supported 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 CH2F2formation and stability of the catalyst. Enhanced acidity of the used catalyst of Pd/CMA-HT compared to the fresh one manifested the higher selectivity towards CH2F2. The higher stability of Pd/CMA-HT can be attributed to the absence of any change in the surface Pd composition in the XPS analysis and the synergistic interaction of Pd with the support, calcined Mg-Al HT. © 2004 Elsevier B.V. All rights reserved.

Author-supplied keywords

  • CCl2F2
  • CH2F2
  • CMA-HT
  • CMC-HT
  • Hydrodechlorination
  • Hydrotalcite
  • MgO

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Authors

  • A. H. Padmasri

  • A. Venugopal

  • V. Siva Kumar

  • V. Shashikala

  • B. M. Nagaraja

  • P. Seetharamulu

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