A review and comparison of the reaction kinetics of the catalytic oxidation of PCDD/Fs and model compounds

Abstract

Due to convenience and toxicity, the development of active catalysts for the catalytic oxidation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) typically relies on research conducted on model compounds in place of PCDD/Fs. The comparability between experiments conducted on PCDD/Fs and model compounds is however unresolved, questioning the design of catalysts for PCDD/F removal by conducting experiments with model compounds. For this reason, the current literature on catalytic destruction of PCDD/Fs and model compounds is reviewed and analyzed. A review of reaction kinetics indicates that similar effects are induced for the catalytic oxidation of PCDD/Fs and model compounds by changes in the gas phase composition, with few deviations. Based on the review of reaction kinetics, a first-order rate expression with respect to PCDD/F or model compound was selected and used to extract activation energies (Ea) and rate constants at 200 °C (k200) for 5 data sets of PCDD/F and 265 data sets for model compounds. It was found that V2O5/TiO2-based catalysts are the most studied catalyst formulation and generally achieve higher k200 than the other non-precious metal catalyst formulations. Comparing the kinetic parameters for the different model compounds and PCDD/Fs reveals that catalytic oxidation of PCDD/Fs has significantly lower Ea and significantly higher k200 compared to commonly used model compounds. It is evident that more laboratory research on catalytic oxidation of PCDD/Fs is required in order to establish the relevance of using model compounds for optimizing catalysts for PCDD/F oxidation, whereas it is established that kinetics for catalytic oxidation of PCDD/Fs only can be developed using actual PCDD/Fs at realistic operating conditions.