Interaction Mechanism for Simultaneous Elimination of Nitrogen Oxides and Toluene over the Bifunctional CeO₂–TiO₂ Mixed Oxide Catalyst

Abstract

Simultaneous catalytic elimination of nitrogen oxides (NO_<i>x</i>, <i>x</i> = 1 and 2) and volatile organic compounds (VOCs) is of great importance for environmental preservation in China. In this work, the interactions of simultaneous removal of NO_<i>x</i> and methylbenzene (PhCH₃) were investigated on a CeO₂-TiO₂ mixed oxide catalyst, which demonstrated excellent bifunctional removal efficiencies for the two pollutants. The results indicated that NO_<i>x</i> positively promotes PhCH₃ oxidation, while NH₃ negatively inhibits through competitive adsorption with PhCH₃. The underlying mechanism is that a pseudo PhCH₃-SCR reaction happened in this process is parallel to NH₃-SCR. Combined with <i>in situ</i> diffuse reflectance infrared Fourier transform spectroscopy and quasi <i>in situ</i> X-ray photoelectron spectroscopy, the interaction mechanism between NO_<i>x</i> and PhCH₃ is proposed. Specifically, NO_<i>x</i> is adsorbed on the catalyst surface to produce nitrate species, which reacts with the carboxylate generated during PhCH₃ oxidation to form organic nitrogen intermediates that create N₂ and CO₂ in the following reactions. In the reaction process, the superoxide (O₂^-) generated by O₂ activation on the catalyst surface is an important species for the propelling of oxidation reaction. This work could provide guidelines for the design of state-of-the-art catalysts for simultaneous catalytic removal of NO_<i>x</i> and VOCs.