H-ZSM-5 (Si/Al = 14.6) was progressively dealuminated by steaming at 350°C (1–72 h) and then characterized by transmission infra-red and solid-state NMR spectroscopies (29Si, 27Al, and 1H). The structural hydroxyl groups on the activated zeolite surface were examined by FT-IR before and after pyridine adsorption in the range 400–4000 cm-1. The number of Brönsted acid sites decreases as the steaming time increases and Brönsted sites of varying acid strength are shown to be present on the surface. Moderately steamed (25–50 h at 350°C) ZSM-5 contains three distinct types of hydroxyl groups, namely, bridged Si-OH-Al species of strong Brönsted acidity, non-acidic terminal SiOH groups, and weakly acidic hydroxylated aluminum species, which was also shown by 1H NMR. Two distinct types of Lewis acid sites were observed. The number of Si-OH defects estimated by 29Si and 27Al NMR is at maximum in a sample steamed for 25 h and then decreases due to the healing of hydroxyl nests during further dealumination.
|Journal||Applied Surface Science|
|Publication status||Published - 1994|
|MoE publication type||A1 Journal article-refereed|
|Event||2nd International Symposium on Atomically Controlled Surfaces and Iterfaces, ACSI-2, Univ. of Joensuu. Joensuu, 16 - 18 June 1993 - |
Duration: 1 Jan 1994 → …