Catalytic CO2 Cycloaddition and Methanation by ZSM-5 Synthesized from Coal Gangue

Coal gangue, the primary solid waste generated during coal mining, is mainly composed of silicon and aluminum oxide. Achieving its high-value utilization is crucial for resource recycling and sustainable development. In this study, we developed a method to synthesize ZSM-5 zeolite (ZSM-5-CG) using coal gangue as the sole silica–alumina source. The synthesis process, crystal growth mechanism, and catalytic performance of the resulting zeolites were systematically investigated. Compared with ZSM-5 prepared from commercial raw materials (ZSM-5-C), the coal gangue-derived synthesis required a significantly lower amount of template due to the favorable interaction between gangue-derived species and the template. Although crystallization in both systems follows the “solid–liquid phase transformation” mechanism, coal gangue, as a natural mineral source, exhibits significant differences in Si and Al coordination environment compared to commercial inorganic raw materials. These differences alter the dissolution and migration behaviors of Si and Al species in the mother liquor, leading to a synchronous release of these components during crystallization. As a result, nucleation and crystal growth processes happen more slowly, yielding a lower overall growth rate than that observed in systems derived from commercial raw materials. The obtained ZSM-5-CG was further applied in CO2 cycloaddition and methanation reactions, exhibiting catalytic activity comparable to that of ZSM-5-C, owing to its abundance of acid sites and large surface area. A cost analysis revealed that the total production cost of ZSM-5-CG was 29.7% lower than that of ZSM-5-C. This work provides a novel and economically viable route for the high-value utilization of coal gangue and highlights the potential of ZSM-5-CG in CO2 catalytic conversion.