Effect of alkali and alkaline earth metal ions on the catalytic epoxidation of styrene with molecular oxygen using cobalt(II)-exchanged zeolite X

Liquid-phase catalytic epoxidation of styrene to styrene epoxide was carried out at 373 K using molecular oxygen at atmospheric pressure, in the presence of Co(II)-exchanged zeolite X. Styrene conversion of > 99% with styrene oxide selectivity up to 68% was achieved using NaCoX. Alkali and alkaline earth metal cations were introduced into the zeolite catalyst to increase styrene conversion and styrene oxide selectivity. Replacing the sodium ions with alkali metal cations increased styrene oxide selectivity from 68% for NaCoX19 to 77% for CsCoX20. Styrene oxide selectivity further increased on replacing the sodium ions with alkaline earth metal cations, and styrene oxide selectivity up to 85% and styrene conversion > 99% was obtained with CaCoX, SrCoX, and BaCoX. This is the first report of such a high styrene epoxide selectivity with a heterogeneous catalyst observed for styrene epoxidation using molecular oxygen. The presence of a small amount of water in the reaction system increases styrene conversion without affecting styrene oxide selectivity. The cobalt-exchanged zeolite X catalysts showed similar catalytic activity even after three catalytic reaction cycles. (c) 2006 Elsevier Inc. All rights reserved.