期刊
CHEMCATCHEM
卷 12, 期 1, 页码 287-293出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cctc.201901728
关键词
silica-alumina; acidity; solid-state NMR; cyclohexane dehydration; glyceraldehyde conversion
资金
- Australian Research Council [DP150103842, DE190101618]
- SOAR fellowship from the University of Sydney
- Australian Research Council [DE190101618] Funding Source: Australian Research Council
Amorphous silica-aluminas (ASAs), possessing both Bronsted acid sites (BAS) and Lewis acid sites (LAS), are important bifunctional catalysts in various industrial applications. Solid-state NMR spectroscopy has been widely used for characterizing the local structure and the surface sites of ASAs with probe molecules. In this work, four-, five- and six-coordinated Al species have been observed on the flame-made ASAs by Al-27 MQ MAS NMR experiment. H-1/Al-27 TRAPDOR MAS NMR experiments confirmed that surface Al species contribute to the formation of BAS and protonate ammonia probe molecules. The adsorption of ammonia on Lewis acidic Al sites (delta(1H)=3.0 ppm) was evidenced by various H-1 MAS NMR experiments on samples dehydrated at different temperatures, allowing the distinction from ammonium ions (delta(1H)=6.7 ppm) formed at BAS. The signal of ammonia adsorbed on LAS increased with increasing Al content in the ASAs. These properties together with the absence of pore diffusional constraints render the flame-made ASAs excellent catalysts for cyclohexanol dehydration and the conversion of glyceraldehyde in ethanol to ethyl lactate, outperforming the performance of other ASAs or zeolites.
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