Abstract
Direct observation of the activation and transformation of reactant molecules is extremely attractive but very challenging in the study of most chemical processes. Here is reported the first case of dynamic activation of C1 molecules in zeolite-catalyzed chemistry. During the methanol conversion over the HZSM-5 zeolite, a sequence of progressive activation states of dimethyl ether (DME) evoked by the special catalysis from CH(3)-Zeo, a hybrid supramolecular catalytic system formed by the organic methylic species growing on the inorganic silico-aluminate zeolite framework, has been directly observed by in situ ssNMR spectroscopy at programmed temperatures. Operando simulations visually display the variability of this hybrid supramolecular system of which the C-O bond property goes through a dynamic transition from covalent to ionic with the temperature increase, and thus the gradually enhanced electrophilicity of CH(3) (δ+) and nucleophilicity of Zeo (δ-) lead to the dynamic activation of DME. This dynamic transition is generally reflected in the alkyl-Zeo system with other alkoxy groups, which linked the alkoxy species and carbocations in zeolite catalysis. Consequently, this work not only sheds light on the key issue of the first carbon-carbon (C-C) bond formation in the methanol to hydrocarbons (MTH) process but also brings a new awareness on the essence of acid catalysis in zeolite mediated chemical processes.