(582br) Knoevenagel Condensation over Ion-Exchanged Low-Silica Beta Zeolites: Their Catalytic Properties and Kinetic Analysis

Aluminosilicate zeolites are well known heterogeneous acid catalysts possessing, in many cases, Brønsted acid sites, which is originated by protons compensating the framework negative charges. On the other hand, the Lewis basicity also expresses on framework oxygen when the counter cations are alkaline metal or organic cations.¹⁾ The presence of counter cation, however, sometimes limits the access of reactant to the catalytic sites through the crowded micropore. Thus, a large 12-membered ring pore zeolite, FAU-type, have been widely used as a model basic zeolite. Besides other zeolitic properties (e.g., Si/Al ratio), framework structure has been known as an important parameter in the catalytic reaction. There are, however, not enough dissection between the basicity and zeolite framework, because it is sometimes difficult to prepare high Al content large pore zeolties.

Here, in this study, we prepared the alkaline metal or alkylammonium ion-exchanged form of another large pore zeolite, *BEA-type, and applied to Knoevenagel condensation reactions. The synthesis of zeolite beta with a higher Al content (Si/Al ratio of around 6) has been recently achieved by using seed-assisted structure-directing agent free approach.^2),3) The catalytic activity is compared among the type of counter cations and with conventional FAU-type zeolites. The kinetic analysis clarified the reaction mechanism of Knoevenagel condensation over this heterogeneous basic catalyst.

References

1) R. J. Davis, J. Catal. 2003, 216, 396.

2) B. Xie, J. Song, L. Ren, Y. Ji, J. Li, F.-S. Xiao, Chem. Mater. 2008, 20, 4533.

3) Y. Kamimura, W. Chaikittisilp, K. Itabashi, A. Shimojima, T. Okubo, Chem. Asian J. 2010, 5, 2182.