Preparation of Halloysite-Based Hollow Tubular ZSM-5 and Its Catalytic Performance for CO2 Hydrogenation to p-Xylene

The development of the ZSM-5 zeolite with natural minerals is a promising strategy. In this study, natural halloysite was used as a silicon source and aluminum source, as well as a template for the expansion of mesopores and a skeletal template to prepare halloysite-based hollow tubular ZSM-5 zeolites by extending the b-axis and exposing more zigzag pore characteristics. In combination with the steam-assisted crystallization method, the outer surface of ZSM-5 zeolite is covered with high silicon or all silicon; thereby, aluminum is mainly concentrated inside ZSM-5 zeolite. This results in an encapsulated structure that passivates the acid site on the outer surface of ZSM-5 zeolite and realizes the regulation of aluminum distribution in ZSM-5 zeolite. The effect of the alkali environment on the morphology and properties of ZSM-5 zeolite during the preparation process was emphasized. The results show that low alkalinity leads to a decrease in the solubility of silicon and aluminum sources, which limits the formation of precursor solutions and thus affects the growth of the ZSM-5 zeolite. However, high alkalinity will lead to crystal defects, which will affect the structural stability and catalytic performance of the zeolite. ZnZrOx metal oxide was used as the bridge of CO2 hydrogenation catalytic system, and ZnZrOx/halloysite-based hollow tubular ZSM-5 tandem catalyst was constructed. The para-xylene selectivity was 74.5% under reaction conditions of 320 °C, 3.0 MPa, flow rate of 2400 mL·g–1·h–1, and H2/CO2 molar ratio of 3:1. This provides a sustainable development strategy for the targeted conversion of CO2, the high-value utilization of halloysite, and green chemistry.