Electron-Withdrawing Effect of Silicotungstic Acid Modulating Reaction Pathway for Multipollutant Control

The synergistic catalysis of nitrogen oxide (NOx) reduction and volatile organic compounds (VOCs) oxidation is a promising approach for multipollutant control. However, competitive adsorption at active sites often reduces synergistic efficiency and leads to the formation of harmful byproducts. Herein, we demonstrate that incorporating silicotungstic acid (HSiW) on CeO2 modulates reactant adsorption via an electron-withdrawing effect, thereby altering the reaction pathway and mitigating competitive effects. Specifically, the selective catalytic reduction (SCR) mechanism shifts from the bimolecular Langmuir–Hinshelwood (L-H) mechanism to the monomolecular Eley–Rideal (E-R) mechanism. This mechanistic shift significantly mitigates reactant competition for active sites, endowing the HSiW-CeO2 with superior synergistic performance: achieving over 80% NOx conversion between 200 and 400 °C, and 87% toluene conversion at 250 °C. Furthermore, electron modulation suppresses gaseous oxygen activation, reducing undesirable NH3 overoxidation and enhancing N2 selectivity. Concurrently, enhanced lattice oxygen activity promotes complete toluene oxidation via the Mars-van Krevelen (MvK) mechanism, thereby improving the CO2 selectivity. This electron modulation strategy provides an efficient solution to active site competition in synergistic catalysis, distinct from the traditional spatial site isolation approach.