(60d) Optical Modification on Acidity and Pore Structure of Y Zeolite-Based Catalysts for High Alkylation Stability

Zeolites catalyzed isobutane-butene alkylation has attracted much research in oil refining and catalysis fields in recent years. Development of high stability zeolite-based catalysts is the key to the industrialization of this technology. Based upon our results, catalytic life is closely related to the competition between hydride transfer and oligomerization. Optical modification on the catalysts’ acidity is the key to obtain high alkylation stability, however the major challenge lies in the fact that the acidity would be greatly influenced upon modification. Herein, a new idea on the modification of the whole catalyst is proposed to tailor the acidity and pore structure of catalyst through the zeolites-alumina interaction.

The whole catalyst modification upon zeolites-alumina interaction was applied, the effect of Al₂O₃ binders’ particle size and SiO₂ doping on acidity and alkylation performance of Zeolite‑Y based catalysts were studied. The catalysts were characterized by N₂ adsorption/desorption, X-ray powder diffraction (XRD), pyridine adsorbed FT-IR and MAS NMR. The interaction between Y and Al₂O₃ was enhanced with the decreasing Al₂O₃ particle size. The unit cell parameters increase with the decreasing Al₂O₃ particle size. At the same time, the acidity of catalysts increases with decreasing Al₂O₃ particle size. The Al₂O₃ phase’s transition temperature was increased with SiO₂ doping, which enhance the interaction between Al₂O₃ binders and zeolite. The shrinkage of the unit cell was inhibited. The acid amount of the catalysts was far more improved comparing with undoped samples, and the optimal doping amount was 12%. The interaction mechanism between Zeolite Y and Al₂O₃ binder was proposed: (i) the interaction occurred only at phase α-Al₂O₃·H₂O during calcination, Al(OH)₃ from Al₂O₃ could immigrate into zeolite, react with Si-OH and form new Brönsted acid sites. (ii) Particle dispersion was enhanced by decreasing the particle size of α-Al₂O₃·H₂O, which could strengthen the interaction between zeolite and Al₂O₃ binder. (iii) The phase transformation temperature from α-Al₂O₃·H₂O to γ-Al₂O₃ was improved by the doping of oxide, which could increase the interaction time, and enhance Al(OH)₃ immigration and the interaction between zeolites and Al₂O₃ binder. The alkylation lifetime of the modified catalyst upon zeolites-alumina interaction was 38 h longer than that of the original sample, and the C₈ selectivity was 4 percentage point higher. This study will also provide a scientific basis for the regulation of acidity of other solid acid catalysts.