TY - JOUR

T1 - Investigations of the mechanism of dealumination of zeolite Y by steam

T2 - Tuned mesopore formation versus the Si/Al ratio

AU - Lutz, W.

AU - Rüscher, C. H.

AU - Gesing, Th M.

AU - Stöcker, M.

AU - Vasenkov, S.

AU - Freude, D.

AU - Gläser, R.

AU - Berger, C.

PY - 2004

Y1 - 2004

N2 - The hydrothermal treatment of zeolite NH4Y was investigated as a function of steaming time in the range between 0.5 h and 20 h at 773 K, 873 K and 973 K, respectively. The evolution of the lattice parameter (ao) and the frequency of the double ring vibration mode in the infrared absorption spectra (WDR) show saturation effects for the Si/Al ratios of about 4 and 5 at 773 K and 873 K, respectively. The average crystal size remains in this case temperature and time independent between about 90 and 110 nm. Short time steaming, i.e. up to 5 h at 973 K, also indicates a saturation of the Si/Al ratio at about 7, which is accompanied by a strong decrease in the average crystal size. The Si/Al ratios calculated using the results of Si MAS NMR show similar dependencies on the steaming temperature and time as the data obtained by the IR spectroscopy. However, the absolute values of the Si/Al ratios obtained by the former method are significantly larger than those obtained by the latter. This difference is attributed to the sensitivity of the MAS NMR data to the presence of non-framework species, which leads to the overestimation of the Si/Al ratios. The steaming-time dependences of the micropore volume and micropore surface area are closely related to the steaming-time dependences of the Si/Al ratios. At 773 K and 873 K there is an increasing formation of mesopores with increasing steaming time. However, the increase in the steaming temperature up to 973 K does not lead to a faster development of the mesopore surface area, which implies that a suitable fine tuning of mesopores in steam is only possible at the lower temperatures.

AB - The hydrothermal treatment of zeolite NH4Y was investigated as a function of steaming time in the range between 0.5 h and 20 h at 773 K, 873 K and 973 K, respectively. The evolution of the lattice parameter (ao) and the frequency of the double ring vibration mode in the infrared absorption spectra (WDR) show saturation effects for the Si/Al ratios of about 4 and 5 at 773 K and 873 K, respectively. The average crystal size remains in this case temperature and time independent between about 90 and 110 nm. Short time steaming, i.e. up to 5 h at 973 K, also indicates a saturation of the Si/Al ratio at about 7, which is accompanied by a strong decrease in the average crystal size. The Si/Al ratios calculated using the results of Si MAS NMR show similar dependencies on the steaming temperature and time as the data obtained by the IR spectroscopy. However, the absolute values of the Si/Al ratios obtained by the former method are significantly larger than those obtained by the latter. This difference is attributed to the sensitivity of the MAS NMR data to the presence of non-framework species, which leads to the overestimation of the Si/Al ratios. The steaming-time dependences of the micropore volume and micropore surface area are closely related to the steaming-time dependences of the Si/Al ratios. At 773 K and 873 K there is an increasing formation of mesopores with increasing steaming time. However, the increase in the steaming temperature up to 973 K does not lead to a faster development of the mesopore surface area, which implies that a suitable fine tuning of mesopores in steam is only possible at the lower temperatures.

UR - http://www.scopus.com/inward/record.url?scp=11844297311&partnerID=8YFLogxK

U2 - 10.1016/s0167-2991(04)80658-x

DO - 10.1016/s0167-2991(04)80658-x

M3 - Article

AN - SCOPUS:11844297311

VL - 154 B

SP - 1411

EP - 1417

JO - Studies in Surface Science and Catalysis

JF - Studies in Surface Science and Catalysis

SN - 0167-2991

ER -