The catalytic combustion of CH2Cl2 over SO42−–TixSn1−x modified with Ru

Abstract

Ru/SO₄²⁻–Ti_xSn_1−x catalysts were prepared via impregnation with an aqueous solution of RuCl₃ on SO₄²⁻–Ti_xSn_1−x. For the samples with a Ti/Ti + Sn ratio higher or lower than 0.6, TiO₂ or SnO₂-rutile existed, and both contained the Ti–O–Sn structure. The residual SO₄²⁻ species as chelating or bridged bidentate complexes with the Ti⁴⁺ and Sn⁴⁺ ions promoted the acidity significantly. Ru as Ru⁰ and Ru⁴⁺ was highly dispersed on the matrices as a result of the interaction between the Ru and SO₄²⁻ species. Ti–O–Sn increased the surface oxygen and SO₄²⁻ complexes, while Ru promoted the redox activity. In CH₂Cl₂ oxidation, the Ru/SO₄²⁻–Ti_xSn_1−x catalysts with the Ti–O–Sn structure presented high activity with TOFs at 225 °C of 0.18–0.63 × 10⁻³ s⁻¹, which could be ascribed to the synergism between SO₄²⁻–Ti⁴⁺ and the active surface oxygen. At 90% conversion, the selectivity for CO₂ and HCl was 90% or higher. Furthermore, the Ru/SO₄²⁻–Ti_xSn_1−x catalysts maintained stable activity for 50 h in wet or dry feed without significant changes. The in situ FT-IR spectra showed that the –O–CH₂–O– organic sulfate was the main intermediate in CH₂Cl₂ oxidation. The hydroxyl activated by surface oxygen was responsible for high activity and Cl removal.