Cs-Beta with an Al-rich composition as a highly active base catalyst for Knoevenagel condensation

Ion-exchange of an Al-rich zeolite beta, synthesized by organic structure-directing agent-free method (Beta-OF), was studied for application as a base catalyst. While the as-synthesized Beta-OF in Na-form itself had base sites and showed moderate catalytic activity for Knoevenagel condensation, the ion-exchange with Cs⁺ improved the catalytic activity. For Knoevenagel condensation of benzaldehyde with ethyl acetoacetate, the catalytic activity of Beta-OF ion-exchanged with Cs⁺ largely surpassed that of the conventional zeolite beta with less Al content. CO₂-TPD and IR observation with chloroform as a probe molecule revealed that the Cs-exchanged Beta-OF had strong base sites comparable to Cs-exchanged Y zeolite. Base strength of Beta-OF was stronger than that expected by Sanderson's theory. A local high density of Al atoms in the framework of Beta-OF resulted in the unexpected base property and high catalytic activity.