The positive role of cadmium in TS-1 catalyst for butadiene epoxidation

• Cd modified TS-1 were used as catalysts for butadiene epoxidation.
• The addition of Cd significantly promoted vinyloxirane yield and H2O2 utilization.
• Quantum chemical calculations were used to explore detailed Cd roles in TS-1.
• Five-membered cyclic intermediate formation was facilitated for Cd modification.
• Active O eletrophilicity in H2O2 was promoted for Cd modification.

A series of Cd modified titanium silicalite 1 catalysts with different Cd content (xCd-TS-1, x = 1–15) were successfully prepared by ultrasound impregnation. Epoxidation of butadiene over these catalysts were investigated using hydrogen peroxide as oxidant, which indicated that Cd greatly improve the catalytic performance of TS-1 and the selectivity of epoxide. Various characterization methods including quantum chemical calculation were employed to explore the specific roles of Cd in promoting TS-1 catalytic activity. Theoretical calculation consistently suggested TiO bond were weakened owing to the introduction of Cd, which resulted in the structure of Cd-TS-1 becoming more relaxant. As a consequence, it is favorable to methanol solvent and H2O2 interacting with the Ti active site to form five-member transition state during reaction. It was observed that catalysts modified with 1–5 wt% Cd presented both high catalytic activity and good reusability. The highest yield of 0.63 mol/L of vinyloxirane (VO) was obtained, while turnover number (TON, determined as the molar VO obtained per molar Ti atom) could reach to 1466.

Epoxidation of butadiene to vinyloxirane were carried out over Cd modified TS-1 catalysts. The additive of Cd provided more chances for CH3OH and H2O2 to approach the Ti active sites and hence facilitated the formation of five-membered cyclic intermediate. Moreover, O of H2O2 close to Ti in five-membered intermediate was activated with promoted eletrophilicity by Cd modification.Figure optionsDownload high-quality image (200 K)Download as PowerPoint slide