NO abatement with CH₄ in the presence of O₂ on H-ZSM5 with Si/Al=15–200: the dependence of activity on the proton concentration

Abstract

The abatement of NO with methane in the presence of oxygen was studied on commercial H-ZSM5 samples with Si/Al = 15–200 in a conventional flow apparatus. H-ZSM5 samples were used in the acid form or after exchanging protons with sodium ions to various extents. Their catalytic activity was compared with that of commercial H-mordenite and H-Y. On all H-ZSM5 catalysts, reaction rates R _NO and $R_{{\text{CH}}_{\text{4}} }$ (molecules s⁻¹ g⁻¹) increased proportionally to the proton concentration, showing that either all protons or a constant fraction of them were equally active. On sodium-exchanged H-ZSM5 samples with Si/Al = 15–17, both R _NO and $R_{{\text{CH}}_{\text{4}} }$ nearly exponentially increased with the proton concentration. Conversely, on sodium-exchanged H-ZSM5 with Si/Al = 50, both R _NO and $R_{{\text{CH}}_{\text{4}} }$ linearly increased with the proton concentration. At lower Si/Al ratios, replacing the H-ZSM5 protons with sodium ions partly inactivated the remaining protons.