Selective alkylation of toluene with methanol over p-modified H-ZSM-5: Effect of treatment with chromium and nickel

H-ZSM-5 zeolite was modified with phosphorus. The obtained P/ZSM-5 catalyst was subjected to further treatments with chromium and nickel. The distribu tion and strength of different acid sites of zeolites were investigated by means of temperature-programmed desorption of ammonia. The active and stron g acid sites were confirmed by measuring the rate constants for cracking of n-hexane, as a probe molecule. Reduction of pore opening size of the modif ied ZSM-5 was monitored by a standard test reaction of probe molecules of m -xylene and ethylbenzene. Selective alkylation of toluene with methanol to p-xylene was studied over ZSM-5 and modified zeolite catalysts. The P/ZSM-5 zeolite was the most selective catalyst to p-xylene but the toluene conver sion decreased drastically. The addition of chromium to P/ZSM-5 zeolite inc reased the toluene conversion and the yield of p-xylene was very close to P /ZSM-5 catalyst. The addition of nickel did not exhibit a significant impro vement of the catalyst performance. The deactivation of catalysts, due to c oke deposition during nm, was also considered. P/ZSM-5 zeolite showed the l owest stability with time on stream. The addition of chromium and nickel to P/ZSM-5 zeolite increased the stability of the catalyst.