EFFECT OF WATER-VAPOR PRESSURE ON DEALUMI NATION RATE OF HZSM-5 ZEOLITE

Dealumination rate oi HZSM-5 zeolite under various water vapor pressur es was investigated by means oi Al-27 MAS NMR. The dealumination rate was markedly dependent on the water vapor pressure. Under water vapor pressure ranging from 0.1 to 1 kg/cm(2), it was found that the dealumi nation rate was apparently third-order dependent on the content of fra mework aluminum and approximately 1.5-order dependent on water vapor p ressure. Based on these results, a plausible mechanism of dealuminatio n of HZSM-5 zeolite by steaming was proposed.