Mechanistic and kinetic studies of elemental mercury oxidation over a RuO2/rutile TiO2 catalyst

Abstract

Mechanistic and kinetic studies of the heterogeneous oxidation of elemental mercury (Hg(0)) vapor by HCl gas over a RuO₂/rutile TiO₂ catalyst were conducted. It was found that under reaction conditions, chemically adsorbed HCl was dissociated on the catalyst surface, and the formation of a Ru–H bond was observed by in situ Fourier transform infrared spectroscopy (FTIR). The active chlorine species on the surface generated from HCl was found to be responsible for the Hg(0) oxidation. The intensity of the Ru–H IR signal could be used as an indicator of the available surface chlorine. Based on the in situ FTIR and performance results, Hg(0) oxidation over the RuO₂/TiO₂ catalyst was proposed to follow an Eley–Rideal followed by Langmuir–Hinshelwood mechanism where HCl is an adsorbed species and reacts with gas-phase Hg(0) to form HgCl(ad), then HgCl(ad) reacts with another Cl(ad) to form HgCl₂(ad). A steady-state kinetic study was conducted to determine an intrinsic reaction kinetic expression for Hg(0) oxidation over the catalyst under HCl, NH₃ and SO₂ gases for the first time. The kinetic expression could reasonably predict the Hg(0) oxidation performance under the competitive adsorption of NH₃ and SO₂ gases.