Synergetic Effect of Acid and Nickel Site on Bifunctional MWW Zeolite Catalyst for Ethylene Oligomerization and Aromatization
The corresponding H- and Ni-form MWW zeolite were synthesized and compared to investigate the influence of acidity strength and bifunctional sites synergetic effect on the catalytic performance of ethylene oligomerization and aromatization. The acidity of ERB-1 and MCM-22 zeolite with MWW structure was adjusted by deboronation and desilication to synthesis of MCM-56 and ITQ-1. The physicochemical properties of the catalyst were measured by XRD, EDS, EPMA, N2 sorption, SEM, FT-IR, pyridine adsorption FT-IR, NH3-TPD, XPS and H2-TPR. The effect of the acid strength and Ni/acid sites ratio on the products distribution was studied on 523 and 723 K, which are two typical optimal reaction conditions for oligomerization and aromatization, respectively. According to the characterizations results and catalytic performance of this series catalyst zeolite with similar structure and different acid sites, the fundamental mechanism of different elementary steps for ethylene oligomerization and aromatization was applied to explain the synergetic effect of acid and Ni site on bifunctional MWW zeolite The synergetic effect with different acid strength MWW zeolite structure shows that the Ni-ion on weak acidity zeolite is superior for ethylene conversion and determines the Anderson-Schultz-Flory products distribution at 523 K, and the strong acid site of MCM-22 is preponderant for ethylene conversion and dominates products distribution at 723 K. The Ni species are not only favorable to dimerization of α-olefins at 523 K, but also to dehydrogenation for aromatics generation at 723 K. The increasing acidity strength of zeolite produces an obviously positive effect on the production of aromatics.