Time-Optimized 15N qNMR Determination of Lewis and Br酶nsted Site Concentrations and Chemical Bonding of Pyridine at Br酶nsted Sites in Amorphous Aluminum Hydroxide Fluoride

详细信息    查看全文

• 作者：Felix Hemmann ; Gudrun Scholz ; Kerstin Scheurell ; Erhard Kemnitz ; Christian Jaeger
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：May 17, 2012
• 年：2012
• 卷：116
• 期：19
• 页码：10580-10585
• 全文大小：285K
• 年卷期：v.116,no.19(May 17, 2012)
• ISSN：1932-7455

文摘

Time-optimized ¹⁵N quantitative NMR (qNMR) is described for the precise determination of Lewis and Br酶nsted site concentrations per gram catalyst, enabling a measurement time reduction of more than a factor of 10. The proof-of-principle is demonstrated for amorphous aluminum hydroxide fluorides with their tunable Lewis to Br酶nsted functionalities and relevance to highly active and selective heterogeneous catalysis using pyridine as a widely accepted probe molecule for Lewis and Br酶nsted sites. Two different Lewis centers were found, and reliable site concentrations down to the micromole per gram region can be determined. Furthermore, ¹H{¹⁵N} REDOR NMR for the acid proton at the Br酶nsted site yields a distance of the ¹⁵N atom of bonded pyridine to this acid proton of (0.112 卤 0.002) nm, such that fast motion/diffusion of the Br酶nsted site-bonded pyridine at the surface can be excluded.