Formation of hydronium ions on Brønsted sites in zeolitic catalysts: a quantum-chemical ab initio study

✍ Scribed by Joachim Sauer; Hans Horn; Marco Häser; Reinhart Ahlrichs

• Publisher: Elsevier Science
• Year: 1990
• Tongue: English
• Weight: 571 KB
• Volume: 173
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(90)85297-p

✦ Synopsis

A new structure for the surface complex of water on bridged hydroxyl sites is proposed which is stabilized by two hydrogen bonds. The energy for the formation of a surface hydronium ion is estimated to be 0.5f 20 kJ/mol. Tbis conclusion is based on quantum-chemical ab initio SCF calculations (DZP basis set, geometries optimized) on the complex of water with the H,SiOH-Al(OH),OSiH, model of a bridged hydroxyl site and on the complex of the hydronium ion with the [H,SiOAl(OH),OSiH,]model of a negatively charged framework site. Electron-correlation contributions are estimated by the MP2 method on smaller models (SiHs groups replaced by H). For the latter models, second energy derivatives are also obtained. A direct SCF code was employed on workstations.