Hydrodechlorination is an attractive process for the treatment of toxic chlorinated waste, such as 1,2-dichloroethane, to produce valuable hydrocarbon products. Previous studies have shown Group VIII metals, such as Pt and Pd to be active for this reaction. The addition of Group IB metals, such as Cu or Ag has been shown to improve selectivity to produce ethylene over ethane. Although numerous studies in the literature have examined hydrodechlorination reactions over AgPd catalysts, traditional catalyst synthesis methods produce bimetallic catalysts with a wide range of structures, making it challenging to elucidate structure activity relationships. In this work, AgPd catalysts have been synthesized by controlled surface reactions to form well defined active site structures. We present our results on the hydrodechlorination of 1,2-dichloroethane to form ethane, ethylene, and chloroethane over Pd and AgPd catalysts synthesized using controlled surface reactions on carbon, SiO2, and TiO2 supports. UV visible spectroscopy is used to quantify the extent of interaction between the Pd precursor (cyclopentadienyl Pd allyl) and the support. It is determined that the formation of bimetallic AgPd structures is most effective for AgPd/TiO2, followed by AgPd/C and then AgPd/SiO2 catalysts. FTIR spectra of adsorbed CO on the AgPd catalysts provide additional evidence for variations in the active site structure depending on the degree of interaction between Ag and Pd. Differences in CO adsorption on the TiO2- and SiO2- supported catalysts indicate that Pd is well dispersed on the Ag nanoparticles for the TiO2-supported catalyst, while a higher fraction of contiguous Pd sites is present on the SiO2-supported catalyst. The ethylene selectivity decreases from 97% on AgPd/TiO2 to 82% on the AgPd/C catalyst. The AgPd/SiO2 catalyst, however, is 91% selective to ethane. These results indicate that the well-dispersed Pd achieved at low Pd loadings on TiO2 supported catalysts and carbon supported catalysts are selective to ethylene, while the contiguous Pd species formed on SiO2 are selective to ethane. The range of surface structures formed on these supports at various Pd loadings has allowed us to develop structure-selectivity relationships for the hydrodechlorination of 1,2-dichloroethane, observing high ethylene selectivity when Pd is well isolated because of intimate contact with Ag.

Hydrodechlorination of 1,2-dichloroethane over AgPd catalysts prepared by controlled surface reactions

2019 Spring National Meeting

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