Acidity and sorbate shape selectivity of H-ZSM-22, H-ZSM-48, and H-ZSM-50 zeolites

Abstract

ZSM-22, ZSM-48, and ZSM-50 zeolites have unidimensional channels, formed by 10-membered rings, having pore dimensions 0.45 {times} 0.55 nm, 0.53 {times} 0.56 nm, and 0.41 {times} 0.58 nm, respectively. These zeolites belong to the class of medium-pore zeolites. The pores of ZSM-48 are near circular, whereas those of the other two zeolites are elliptical. The channels of ZSM-22 and -48 zeolites are linear and have uniform cross sections. However, the zeolite ZSM-50 has side pockets (0.58 {times} 0.68 nm in cross section and 0.81 nm deep) to the channels (4). Since these zeolites differ from each other in their channel structure, it is interesting to know the shape selectivity of these zeolites in sorption for sorbates/reactants of different critical sizes and configurations and also their acid-strength distribution. The present investigation was undertaken for obtaining information on the above. Sorbates used were: m-xylene, o-xylene, 1,2,4-TMB, isopropylbenzene, 2,2-DMB, 2,3-DMB, and isooctane.