Acidic Properties of SSZ-33 and SSZ-35 Novel Zeolites: a Complex Infrared and MAS NMR Study
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- 作者：Barbara Gil ; Stacey I. Zones ; Son-Jong Hwang ; Martina Bejblová ; Ji
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- 刊名：Journal of Physical Chemistry C
- 出版年：2008
- 出版时间：February 28, 2008
- 年：2008
- 卷：112
- 期：8
- 页码：2997 - 3007
- 全文大小：318K
- 年卷期：v.112,no.8(February 28, 2008)
- ISSN：1932-7455
文摘
Two novel zeolites SSZ-33 and SSZ-35 were investigated with respect to their acidic properties using differentprobe molecules to characterize the accessibility and acid strength of Lewis and Br
nsted acid sites. Ammonia,pyridine, pivalonitrile, and acetonitrile-d3 were used as probe molecules, and the results were correlated with27Al and 1H magic angle spinning (MAS) NMR. Both SSZ-33 and SSZ-35 zeolites were found to possessbridging Si-OH-Al groups of virtually uniform and high acid strength. For both SSZ-33 and SSZ-35, thereis the typical presence of highly disturbed OH groups (IR band around 3500 cm-1), which amounts to almosthalf of the overall Brnsted acidity. It was found that almost all bridging Si-OH-Al groups in SSZ-33 arelocated in the 12-MR rings. Both acetonitrile-d3 and pyridine sorptions suggest the presence of two types ofLewis sites in SSZ-35, differing in acid strength and electron-acceptor properties, whereas in the SSZ-33zeolite only one type is present. The relative strength of these sites is higher than that of the Brnsted typefor SSZ-35 and is of comparable strength for SSZ-33. 1H and 27Al MAS NMR measurements during thermaltreatment allowed the assignment of NMR peaks to different surface OH species and the establishment oftheir relation to IR bands. NMR spectroscopy enabled the quantitative analysis of both free and hydrogen-bonded OH groups separately, showing that for both zeolites the amount of disturbed sites is higher than thenumber of free OH groups.
nsted acid sites. Ammonia,pyridine, pivalonitrile, and acetonitrile-d3 were used as probe molecules, and the results were correlated with27Al and 1H magic angle spinning (MAS) NMR. Both SSZ-33 and SSZ-35 zeolites were found to possessbridging Si-OH-Al groups of virtually uniform and high acid strength. For both SSZ-33 and SSZ-35, thereis the typical presence of highly disturbed OH groups (IR band around 3500 cm-1), which amounts to almosthalf of the overall Brnsted acidity. It was found that almost all bridging Si-OH-Al groups in SSZ-33 arelocated in the 12-MR rings. Both acetonitrile-d3 and pyridine sorptions suggest the presence of two types ofLewis sites in SSZ-35, differing in acid strength and electron-acceptor properties, whereas in the SSZ-33zeolite only one type is present. The relative strength of these sites is higher than that of the Brnsted typefor SSZ-35 and is of comparable strength for SSZ-33. 1H and 27Al MAS NMR measurements during thermaltreatment allowed the assignment of NMR peaks to different surface OH species and the establishment oftheir relation to IR bands. NMR spectroscopy enabled the quantitative analysis of both free and hydrogen-bonded OH groups separately, showing that for both zeolites the amount of disturbed sites is higher than thenumber of free OH groups.