Oxidative upgrading of methane into carbon monoxide, methanol, lower hydrocarbons (such as ethane and ethylene), and other oxygenates has been achieved at relatively low temperatures over zeolite-based catalysts. The high tunability afforded by the framework structures of zeolites offers a unique and precious opportunity for the design of active species, resulting in outstanding catalytic performance. Thus, we categorize the various reported active species in zeolite-based catalysts into three groups in terms of their origin, viz., active species originated from intra-framework heteroatoms, active species introduced by ion-exchange, and active species prepared by impregnation. We present an overview of the performance, structure, and catalysis of each category and comment on the general outlook.
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