A comparative study of the dichloromethane catalytic combustion over ruthenium-based catalysts: Unveiling the roles of acid types in dissociative adsorption and by-products formation.

Abstract

Herein, a comparative investigation of the Ru-based catalysts with different kinds of supports (TiO2, Al2O3, HZSM-5 SiO2/Al2O3\xa0=\xa027 and 130, respectively) for catalytic combustion of dichloromethane (DCM) has been performed. The characterization results showed that the C-Cl bond of DCM was cleaved on both the Brønsted and Lewis acid sites of the catalysts. However, the Lewis acid sites were more active than the Brønsted acid sites. The relatively strong Lewis acidity of Ru/TiO2 improved the dissociative adsorption of DCM, accounting for its superior activity. The yield of toxic by-products was strongly associated with the acid types of the catalysts. The Cl species deposited on TiO2 and Al2O3 supports interacted strongly with the Lewis acid sites, thereby promoting the electrophilic chlorination reactions and yielding more polychlorinated by-products, especially highly toxic dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). However, the Cl deposits on Ru/HZSM-5 (SiO2/Al2O3\xa0=\xa027) with abundant Brønsted acid sites, mainly existed as hydrogen-bonded Cl species, with good mobility and less propensity for chlorinating carbonaceous matter. Moreover, Ru/HZSM-5 (SiO2/Al2O3\xa0=\xa0130) yielded the highest polychlorinated by-products and PCDD/Fs because of its poor redox ability and high surface area. Overall, this study provides valuable insights into the CVOCs catalytic combustion catalysts development.