Gas phase hydrodechlorination of CCl 4 over Pd–Cu and Pd–Fe bimetallic catalysts supported on an AlF 3 matrix

Abstract

Two bimetallic catalytic systems composed of Pd–Cu and Pd–Fe supported over AlF₃ were prepared by the sol–gel method and characterised by BET, X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (P-XRD). Analysis of the XPS and P-XRD data showed that the surface of these bimetallic catalysts may be described as Pd⁰–Cu^I and Pd⁰–Fe^III hydroxides. The gas phase hydrodechlorination reaction (HDC) of CCl₄ over these bimetallic catalysts showed that the presence of CuOH and Fe(OH)₃ altered their catalytic activity, selectivity and product distribution compared to their monometallic Pd/AlF₃ analogue. The bimetallic catalysts showed a very high selectivity for the formation of C₁-products (CHCl₃, CH₂Cl₂ and CH₃Cl) in contrast with the tendency shown by the monometallic Pd/AlF₃ analogue of forming coupled C₂–C₅ products. Interestingly, the pore-controlled version of the Pd–Fe^*/AlF₃ catalyst showed a greater efficiency favouring the formation of CHCl₃ and CH₂Cl₂ compared with its Pd–Fe/AlF₃ analogue which predominantly favoured the formation of CH₃Cl. The effect of temperature, in the range of 458–513 K, and time on stream on the catalytic performance of the bimetallic catalysts in terms of percentage conversion, reaction rate and product distribution are discussed.