Study on sulfur resistance of MnO2/Beta zeolite in toluene catalytic combustion: The effect of increased acidity on catalytic performance

Abstract

Sulfur dioxide (SO₂) frequently coexist with volatile organic compounds (VOCs) in exhaust gas. The competitive adsorption of SO₂ and VOCs can adversely affect the efficiency of catalytic combustion, leading to catalyst poisoning and irreversible loss of activity. To investigate the impact of sulfur poisoning on the catalysts, we prepared the MnO₂/Beta zeolite, and a corresponding series of sulfur-poisoned catalysts through in-situ thermal decomposition of (NH₄)₂SO₄. The decrease in toluene catalytic activity of poisoned MnO₂/Beta zeolite primarily results from the conversion of the active species MnO₂ to MnSO₄. However, the crystal structure and the porous structure of MnO₂/Beta zeolite were stable, and original structure was still maintained when 1.6% (mass) sulfur species were introduced. Furthermore, the extra-framework Al of Beta zeolite could capture sulfur species to generate Al₂(SO₄)₃, thereby reducing sulfur species from reacting with Mn⁴⁺ active sites. The combination of sulfur and Beta zeolite was found to directly produce new strong-acid sites, thus effectively compensating for the effect of reduced Mn⁴⁺ active species on the catalytic activity.