Siloxane-modified MnOx catalyst for oxidation of coal-related o-xylene in presence of water vapor

Abstract

In coal-combustion energy production, presence of water vapor in flue gas causes catalyst deactivation and leads to the release of large quantities of volatile organic compounds (VOCs). In this study, design of a low-temperature, hydrophobic catalyst for flue gas purification was achieved by modifying support material with inorganic siloxane. Introduction of 5% water vapor into simulated flue gas at 300 °C reduced oxidation efficiency for o-xylene removal by 26% with unmodified MnO_x/γ-Al₂O₃ catalyst, whereas with modified catalyst MnO_x-Si_0.9/γ-Al₂O₃ oxidation efficiency was reduced by only 5%. MnOx-Si_0.9/γ-Al₂O₃ exhibited stable catalytic efficiency for o-xylene gas oxidation containing water vapor for over 200 min. Water-resistance of the catalyst was effective for removal of multi-coal combustion pollutants (Hg⁰ and NO) and moreover, hydrophobicity of the catalyst led to a reduction in surface sulfate deposition, thereby lowering toxicity of SO₂ from simulated flue gas. DRIFTS analysis showed that the hydrophobic catalyst surface not only reduces water adsorption, but also promotes water volatilization. Based on molecular adsorption energies, catalyst support modification with siloxane inhibits water adsorption and promotes organic adsorption and thus provides a new strategy for preparing water-resistant catalysts for flue gas purification.

Keywords: Catalytic oxidation; Coal combustion; Hydrophobic modification; VOCs; Water vapor.