Enhui Xing

Synthesis, characterization and application of MCM-22 zeolites via a conventional HMI route and temperature-controlled phase transfer hydrothermal synthesis

With less environmental and economical impact, temperature-controlled phase transfer hydrothermal synthesis of MWW zeolites was realized with hexamethyleneimine as a structure-directing agent and aniline as a structure-promoting agent. MCM-22 zeolite, synthesized via temperature-controlled phase transfer hydrothermal synthesis, is nearly identical concerning chemical composition and structure, and possesses nearly identical properties with respect to porosity, Si/Al ratio, thermal behavior and catalytic activity at 200 °C, compared with that made from conventional synthesis with hexamethyleneimine as the only template.

Temperature-controlled phase transfer hydrothermal synthesis of MWW zeolites

Temperature-controlled phase transfer hydrothermal synthesis of MWW zeolites was realized with hexamethyleneimine as a structure-directing agent and aniline as a structure-promoting agent. During crystallization, hexamethyleneimine and aniline were completely soluble. After crystallization with decreased temperature, aniline extracted hexamethyleneimine from the mother liquid to the organic phase for reuse.

Size-controlled synthesis of MCM-49 zeolites and their application in liquid-phase alkylation of benzene with ethylene

Size-controlled synthesis of MCM-49 zeolites was achieved via topology reconstruction from NaY zeolites with different sizes. SEM images showed that the sizes of the reconstructed H-MCM-49 zeolites were controlled by those of the parent NaY zeolites. Smaller NaY zeolites improved the diffusion of reactants on the parent NaY zeolites during the topology reconstruction, the final H-type zeolites, the relative crystallinity, the BET surface areas, and the number of Bronsted and total acid sites. Moreover, a substantial improvement in both ethylene conversion and ethylbenzene selectivity was observed for the H-type catalyst originating from the smaller NaY zeolite (300 nm) in liquid-phase alkylation of benzene with ethylene. This alkylation performance may provide a new strategy for enhancing both catalytic activity and product selectivity, and our method could be applicable to many diffusion-limited or external surface reactions.

Temperature-controlled phase-transfer hydrothermal synthesis of MWW zeolites and their alkylation performances

MWW zeolites have been synthesized with hexamethyleneimine/aniline as the structure-directing/promoting agent. As structure-promoting agent, aniline contributes to the crystallization of MWW zeolites without being trapped within zeolites. Meanwhile the temperature-controlled phase-transfer hydrothermal synthesis of MWW zeolites could be achieved because the solubility of aniline increases with a rise of temperature. For delaminated MCM-56 with intermediate nature, the conversion to MCM-49 could be avoided even when subjected to a much longer crystallization time. Partially delaminated MWW monolayers of MCM-56 possesses larger external surface area, pore volumes, better accessibility of active centers, which resulted in higher ethylene conversion than MCM-22 and MCM-49 in the liquid-phase alkylation of benzene with ethylene above 210 °C.