S. Faramawy et al., Selective alkylation of toluene with methanol over p-modified H-ZSM-5: Effect of treatment with chromium and nickel, REACT KIN C, 66(2), 1999, pp. 257-263
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.