Effects of Dealumination and Desilication of Beta Zeolite on Catalytic Performance in n-Hexane Cracking

Catalytic cracking of n-hexane to selectively produce propylene on Beta zeolite was carried out. The H-Beta (HB) (Si/Al = 77) zeolite showed higher catalytic stability and propylene selectivity than the Al-rich HB (Si/Al = 12), due to its smaller number of acid sites, especially Lewis acid sites (LAS). However, catalytic stability and propylene selectivity in high n-hexane conversions were still not satisfactory. After dealumination with HNO3 treatment, catalytic stability was improved and propylene selectivity during high n-hexane conversions was increased. On the other hand, catalytic stability was not improved after desilication with NaOH treatment, although mesopores were formed. This may be related to the partially destroyed structure. However, propylene selectivity in high n-hexane conversions was increased after alkali treatment. We successfully found that the catalytic stability was improved and the propylene selectivity in high n-hexane conversions was further increased after the NaOH treatment followed by HNO3 treatment. This is due to the decrease in the number of acid sites and the increase in mesopores which are beneficial to the diffusion of coke precursor.