Coupling acidic sites and oxygen vacancies in sulphation-modified ceria-titania catalyst for the simultaneous degradation of toluene and nitrogen oxides: insights into competitive adsorption of NH3 and toluene.

Understanding the intricate relationship between the oxidation of volatile organic compounds (VOCs) and the reduction of nitrogen oxides (NOx) during the coupled reaction process is crucial for developing highly efficient bifunctional catalysts that can simultaneously degrade both VOCs and NOx. This study investigated the concurrent degradation of toluene and NOx on the sulphation-modified ceria-titania (Ce-Ti-S) catalyst, with particular emphasis on the interactions among toluene, NH3 and NOx. The Ce-Ti-S catalyst achieved over 90% conversion efficiency for both toluene and NOx within 350 °C-450 °C while exhibiting excellent N2 and CO2 selectivity. The competitive adsorption was existed between toluene and NH3 during the co-degradation. Toluene oxidation adhered to the Mars-van Krevelen mechanism, whereas NH3-assisted selective catalytic reduction followed the Eley-Rideal mechanism, with amide species acting as the critical active intermediates. Compared to the unmodified ceria-titania (Ce-Ti) catalyst, the surface sulphation modification towards the Ce-Ti catalyst raised the concentrations of Lewis and Brønsted acids by 39.18 μmol/g and 12.40 μmol/g, respectively. Likewise, the oxygen vacancy concentration increased by 12%. The newly created Lewis acidic sites enabled NH3 activation, and the increased oxygen vacancy concentration expedited the migration of lattice oxygen. Theoretical calculations confirmed that the bandgap of Ce-Ti-S decreased from 1.72 eV to 1.19 eV, stabilising the electronic structure of the active sites and effectively alleviating the competitive adsorption between toluene and NH3.