SOLID-STATE NMR-STUDIES OF THE SHAPE-SELECTIVE CATALYTIC CONVERSION OF METHANOL INTO GASOLINE ON ZEOLITE ZSM-5

13C Magic angle spinning (MAS)-NMR of thermally treated samples of zeolite H-ZSM-5 with adsorbed methanol identifies the organic species present in the adsorbed phase, monitors their fate, and distinguishes between mobile and attached species. Only MeOH is present at room temperature; in samples treated at 150 °C dimethyl ether (DME) is also found. At 250 °C and above a new signal, due to CO intermediate, appears. A number of aliphatic and aromatic compounds form at 300 °C and above, and the role of CO in this process is discussed. Neither 1,2,3- or 1,3,5-trimethylbenzene is found in the products, but both are present in the adsorbed phase, which is the first direct experimental demonstration of product selectivity. Tetramethylbenzenes have not been found in the products of the reaction at 300 °C, but all three are present in the adsorbed phase in considerable concentrations. Their distribution (tetramethylbenzenes are not formed in the thermodynamic equilibrium distribution) reveals the presence of a new kind of shape selectivity. At 370 °C the shape-selective action is still present but is different because of the increased effective channel diameters. MAS-NMR has a considerable potential for monitoring and prediction of the course of catalytic reactions directly at the active centers in molecular sieves and will assist the design of shape-selective solids. © 1990, American Chemical Society. All rights reserved.