Hydrodechlorination of trichloroethylene on noble metal promoted Cu-hydrotalcite-derived catalysts

摘要

Pt and Pd containing Cu-hydrotalcite-type precursors were applied as catalysts for the hydrodechlorination of trichloroethene (TCE) to ethene in gas phase. Characterization was done by XRD, TGA, TPR, HRTEM and FTIR spectroscopy of CO adsorption. High activity (>90% conversion) and excellent selectivity of more than 90% ethene were obtained at 300 °C and stoichiometric concentrations of hydrogen and TCE. The materials were synthesized by co-precipitation according to two different synthesis protocols. HRTEM measurements of the two differently prepared materials revealed fundamental differences at the microstructural level, i.e. detecting alloy formation on the samples prepared with a reduction step before Pd (Pt) introduction (alloy composition approximately Cu_(0.4)Pt_(0.6) and Cu_(0.25)Pd_(0.75)), whereas no alloy formation was observed on the samples prepared without the previous reduction step during synthesis. Whereas the former alloyed catalysts were stable during the reaction, the latter catalysts exhibited decreasing rate of ethene formation with time on stream due to increasing Cu areas blocked by Cl, which can be explained by a less effective regeneration and less availability of hydrogen due to the worse contact between noble metal and Cu (separate noble metal and Cu particles). We propose that the reaction proceeds via cleavage of the C-Cl bond on Cu, which is then regenerated by spillover of hydrogen from the noble metal.