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Zeolites are generally defined as three-dimensional (3D) crystalline microporous aluminosilicates in which silicon (Si4+) and aluminum (Al3+) are coordinated tetrahedrally with oxygen to form large negative lattices and consequent Brønsted acidity. Two-dimensional (2D) zeolite nanosheets with single-unit-cell or near single-unit-cell thickness (~2–3 nm) represent an emerging type of zeolite material. The extremely thin slices of crystals in 2D zeolites produce high external surface areas (up to 50% of total surface area compared to ~2% in micron-sized 3D zeolite) and expose most of their active sites on external surfaces, enabling beneficial effects for the adsorption and reaction performance for processing bulky molecules. This review summarizes the structural properties of 2D layered precursors and 2D zeolite derivatives, as well as the acidity properties of 2D zeolite derivative structures, especially in connection to their 3D conventional zeolite analogues’ structural and compositional properties. The timeline of the synthesis and recognition of 2D zeolites, as well as the structure and composition properties of each 2D zeolite, are discussed initially. The qualitative and quantitative measurements on the acid site type, strength, and accessibility of 2D zeolites are then presented. Future research and development directions to advance understanding of 2D zeolite materials are also discussed. 

Direct nonoxidative methane conversion (DNMC) transforms CH₄to higher (C₂₊) hydrocarbons and H₂in a single step, but its utility is challenged by low CH₄ equilibrium conversion, carbon deposition (coking), and its endothermic reaction energy requirement. This work reports a heat‐exchanged autothermal H₂‐permeable tubular membrane reactor composed of a thin mixed ionic‐electronic conducting SrCe_0.7Zr_0.2Eu_0.1O_3–δmembrane supported on a porous SrCe_0.8Zr_0.2O_3–δ tube in which a Fe/SiO₂ DNMC catalyst is packed, that concurrently tackles all of these challenges. The H₂‐permeation flux drives CH₄ conversion. O₂from an air simulant (O₂/He mixture) sweep outside the membrane reacts with permeated H₂ to provide heat for the endothermic DNMC reaction. The energy balance between the endothermic DNMC and exothermic H₂ combustion on opposite sides of the membrane is achieved, demonstrating the feasibility for autothermal operation using a simple air sweep gas. Moreover, the back diffusion of O₂ from the sweep side to the catalyst side oxidizes any deposited carbon into CO. Thus, for the first time demonstrating all the desired attributes, a heat‐exchanged H₂‐permeable membrane reactor capable of achieving single‐step auto‐thermal DNMC catalysis while simultaneously improving CH₄conversion and preventing coking is achieved. 

 

Direct non‐oxidative methane conversion (DNMC) has been recognized as a single‐step technology that directly converts methane into olefins and higher hydrocarbons. High reaction temperature and low catalyst durability, resulting from the endothermic reaction and coke deposition, are two main challenges. We show that a millisecond catalytic wall reactor enables stable methane conversion, C₂₊selectivity, coke yield, and long‐term durability. These effects originate from initiation of the DNMC on a reactor wall and maintenance of the reaction by gas‐phase chemistry within the reactor compartment. The results obtained under various temperatures and gas flow rates form a basis for optimizing the process towards lighter C₂or heavier aromatic products. A process simulation was done by Aspen Plus to understand the practical implications of this reactor in DNMC. High carbon and thermal efficiencies and low cost of the reactor materials are realized, indicating the technoeconomic viability of this DNMC technology.

 

Direct non‐oxidative methane conversion (DNMC) has been recognized as a single‐step technology that directly converts methane into olefins and higher hydrocarbons. High reaction temperature and low catalyst durability, resulting from the endothermic reaction and coke deposition, are two main challenges. We show that a millisecond catalytic wall reactor enables stable methane conversion, C₂₊selectivity, coke yield, and long‐term durability. These effects originate from initiation of the DNMC on a reactor wall and maintenance of the reaction by gas‐phase chemistry within the reactor compartment. The results obtained under various temperatures and gas flow rates form a basis for optimizing the process towards lighter C₂or heavier aromatic products. A process simulation was done by Aspen Plus to understand the practical implications of this reactor in DNMC. High carbon and thermal efficiencies and low cost of the reactor materials are realized, indicating the technoeconomic viability of this DNMC technology.