THE EFFECT OF ZEOLITE STRUCTURES ON THE CREATION OF INO-SITES FOR NOXREDUCTION WITH METHANE( ACTIVE)

Catalytic activities of indium oxide (In2O3) physically mixed with var ious I-I-form zeolites for NO, reduction with methane were investigate d, and the effects of zeolite type, acidity, and structure on the cata lytic activity are discussed. K-mordenite. H-ZSM-5, and H-beta gave hi gher activities with In2O3 for reduction of NO2 than in the absence of In2O3. This indicates that InO+, formed by the solid slate ion exchan ge between In2O3 and protonic acid sites of zeolites, is active for th is reaction. The level of solid state ion exchange was well correlated to the strength of zeolitic acidity; the sequence of the catalytic ac tivity was on the order of H-mordenite > H-ZSM-5 > I-I-beta much great er than H-Y > SiO2-Al2O3. The size of H-ZSM-5 particles made a differe nce in the catalytic activity for NO2-CH4 reaction; the activity decre ased with increasing particle size. There exists a particle structure effect on the creation of InO+ on the zeolite structure: mesopores are needed for the dispersion of In2O3 into ZSM-5 zeolite structures, whi le the In2O3 is not always used for the creation of InO+ sites. In/H-Z SM-5 having larger amounts of In on the external surface of ZSM-5 show ed lower catalytic activities for NOTCH, reaction in the case that the same ZSM-5 grains are used. The decrease of the In/Si ratio on the ou ter surface of zeolite corresponds to the decrease in the amount of NH , desorbed during TPD measurements, that is, the increase in the numbe r of InO+ sites. There might be a diffusion limitation on In/H-ZSM-5 d uring NO2-CH4 reactions in the reaction conditions studied. (C) 1998 E lsevier Science B.V. All rights reserved.