摘要:

In this review, the most relevant aspects of skeletal isomerization ofn-butene to isobutene are discussed: the nature of the active sites, the prevailing mechanism of the skeletal isomerization, and the relation of this to that ofn-butane. It is concluded that the prevailing mechanism of skeletal isomerization ofn-butene ismonomolecular(in contrast to butane isomerization) and requires Brønsted acid (OH) active sites. The selectivity and catalytic stability can be influenced by the shape selectivity of zeolites and zeotypes. These effects are explained on the basis of the knowledge on the prevailing mechanism.

ISSN:0161-4940    

DOI:10.1080/01614949708007099

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Nearly all atoms contributing to the local structure of Brønsted acid sites in zeolites exhibit isotopes accessible for multinuclear solid-state nuclear magnetic resonance (NMR) investigations. Therefore, in the last 15 years, NMR spectroscopy has found numerous applications for the determination of the types of hydroxyl proton in zeolites, of their concentration, accessibility, and mobility, and for the characterization of their acid strength and local structure. It allows the study of the role of hydroxyl groups in the formation of adsorbate complexes and in heterogeneously catalyzed reactions. Meanwhile, NMR spectroscopy belongs to the most powerful techniques for the characterization of Brønsted acid sites in zeolites and related materials. The basis of this success is the invention of new sample preparation techniques, external magnetic fields with high-flux densities, effective line-narrowing methods, and new two-dimensional experiments, making the detection of highly resolved solid-state NMR spectra and the separation of spectral parameters possible. This article gives a review of these techniques and a summary of the most important applications of multinuclear solid-state NMR spectroscopy for the characterization of Brønsted acid sites in dehydrated zeolites.

ISSN:0161-4940    

DOI:10.1080/01614949708007100

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Acidities of pentasil zeolites were measured and correlated with aluminum content using the following methods: (1) Acid-base indicator method, (2) NH3-TPD spectra, (3) GC pulse adsorption of pyridine and 4-methylquinoline, and (4) FTIR spectroscopy of adsorbed pyridine.

ISSN:0161-4940    

DOI:10.1080/01614949708007101

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0161-4940    

DOI:10.1080/01614949708007102

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0161-4940    

DOI:10.1080/01614949708007103

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor