Effect of temperature and time in the hydrothermal treatment of HY zeolite

Zeolite HY was steamed at 1 bar water pressure in steps of 100 K from 473 K to 1073 K in dependence of the time (0.5-20 h). Three routes of hydrothermal reactions can be outlined: At low temperature (473 K), a partly framework dissolution occurs accompanied by the formation of X-ray amorphous material. At intermediate temperatures (773-873 K), framework dealumination takes place with the occurrence of different non-framework species. Thereby, with increasing steaming time, saturation of the Si/Al ratio occurs oil low levels (Si/Al ratios of about 4 and 5, respectively). At 973 K, a crossover from a low level saturation in Si/Al (6) towards higher values (11) is observed, which is accompanied by a partial amorphization of the zeolite with formation of aluminium oxide and silica gel and a significant decrease in crystal size as well. At high temperatures (1073 K), a fast thermal decomposition occurs. The IR spectra directly reveal an aluminosilicate phase as decomposition product of the framework. At 573 K, the zeolite framework remains unchanged. (c) 2005 Elsevier Inc. All rights reserved.