Defect-assisted mesopore formation during Y zeolite dealumination: The types of defect matter

The present work reports an easy and low-cost way of industrial relevance for post-synthetic upgrading of zeolite Y, achieved by the rational application of chemical induced framework defects to engineering zeolite mesoporosity. Si-defects and Al-defects, formed as a result of the selective removal of framework Si and Al atoms by alkaline treatment and oxalic acid leaching, respectively, are introduced into the framework of an as-synthesized zeolite Y. Such defect-containing zeolites were ion-exchanged, steamed and acid washed, and the final products were subjected to a comprehensive physico-chemical characterization. The results show that Al-defects, due to its inclination to condensation during the heating stage before steaming, hamper the migration and coalescence of steaming induced framework defects, hence suppressing the propagation of mesoporosity during steaming. In contrast, the presence of Si-defects favors the formation of mesoporosity in zeolite Y framework during dealumination. Further, we demonstrate that the introduction of Si-defects can be incorporated into the zeolite synthesis process without compromising the ability to enhance zeolite mesoporosity. The derived catalysts show higher gasoline selectivity than the base catalysts in the catalytic cracking of a wax oil from Daqing.