THE EFFECT OF DEALUMINATION ON ZEOLITE-SUPPORTED RU CATALYSTS

The physical and catalytic properties of a series Ru/dealuminated Y-zeolite catalysts prepared by ion exchange have been investigated in order to better understand the effect of the Si/Al ratio of a zeolite on the catalytic properties of a supported metal. Dealumination up to 52% was shown not to have affected the crystallinity of the zeolite. The reduced Ru catalysts exhibited increased metal dispersions, as measured by H2 chemisorption, with increased zeolite dealumination. Turnover frequency (TOF) for CO hydrogenation vs Si/Al ratio showed a volcano shape. Maximum TOF occurred at a Si/Al ratio of about 5. While the overall product distribution was unaffected by Si/Al ratio, an increase in the selectivity for iso-C4 with increasing dealumination indicated that secondary reactions of the F-T primary products were enhanced by the presence of stronger acid sites. It is well known that the concentration of acid sites in a dealuminated Y-zeolite decreases with increasing Si/Al ratio, while the strength of the acid sites increases and reaches a maximum for Si/Al = 4.5. Since overall chain growth probability was not apparently affected by dealumination of the zeolite support, it is suggested that the increase in overall activity for CO hydrogenation on the dealuminated Ru catalysts may have been primarily due to an enhancement in secondary reactions as a result of the increase in acid strength lessening readsorption of olefinic primary products on Ru CO hydrogenation sites. © 1993 Academic Press, Inc.