Mordenite acidity: dependence on the silicon/aluminum ratio and the framework aluminum topology. 2. Acidity investigations

The Journal of Physical Chemistry 04/2002; 96(21). DOI: 10.1021/j100200a051
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    ABSTRACT: H-ZSM-5 zeolite was modified with phosphorus. The obtained P/ZSM-5 catalyst was subjected to further treatments with chromium and nickel. The distribution and strength of different acid sites of zeolites were investigated by means of temperature-programmed desorption of ammonia. The active and strong acid sites were confirmed by measuring the rate constants for cracking ofn-hexane, as a probe molecule. Reduction of pore opening size of the modified ZSM-5 was monitored by a standard test reaction of probe molecules ofm-xylene and ethylbenzene. Selective alkylation of toluene with methanol top-xylene was studied over ZSM-5 and modified zeolite catalysts. The P/ZSM-5 zeolite was the most selective catalyst top-xylene but the toluene conversion decreased drastically. The addition of chromium to P/ZSM-5 zeolite increased the toluene conversion and the yield ofp-xylene was very close to P/ZSM-5 catalyst. The addition of nickel did not exhibit a significant improvement of the catalyst performance. The deactivation of catalysts, due to coke deposition during run, was also considered. P/ZSM-5 zeolite showed the lowest stability with time on stream. The addition of chromium and nickel to P/ZSM-5 zeolite increased the stability of the catalyst.
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