Experiment and mechanism investigation on simultaneously catalytic reduction of NOx and oxidation of toluene over MnOx/Cu-SAPO-34

Simultaneous catalytic abatement of NOx and VOCs is investigated with MnOx/Cu-SAPO-34 facilely synthesized as bifunctional catalyst. It is found that SAPO-34 framework provides selectivity for toluene and SCR reactants, enabling SCR and toluene oxidation to proceed simultaneously inside and outside SAPO-34, which avoids their mutual inhibition. Meanwhile, the higher loading of Mn, the stronger redox performance of catalyst. Correspondingly, the active temperature range for simultaneous removal of NOx and toluene shifts to lower temperature. Among them, the best simultaneous removal performance of NOx and toluene are ≥ 80 % in 300 °C–380 °C with high CO2 selectivity (∼100 %) and N2 selectivity (>80 %) over 20 %MnOx/SAPO-34. Furthermore, the simultaneous reaction mechanism is explored through a series of temperature programmed experiments. The toluene is oxidized to CO2 and H2O by lattice oxygen of MnOx, while the decomposition of intermediates is a presumable rate-control step. The NOx is reduced by NH3 or NH4+ adsorbed on isolated Cu2+ or Brønsted acid sites inside SAPO-34, which follows the E-R and L-H mechanism respectively. Moreover, there is obvious competitive effects on NH3 adsorption by toluene, which further inhibits its oxidation and enhancing the N2 selectivity at high temperature.