Phosphotungstic Acid Supported on Magnetic Mesoporous Tantalum Pentoxide Microspheres: Efficient Heterogeneous Catalysts for Acetalization of Benzaldehyde with Ethylene Glycol

In this study, magnetically-recoverable core–shell catalysts with different amount of H 3 PW 12 O 40 loading [Fe 3 O 4 @C@mTa 2 O 5 -NH 2 -PW 12 (w%)] were prepared by the application of phosphotungstic acid supported on amino group functionalized magnetic core–shell mesoporous tantalum pentoxide microspheres. The prepared samples were characterized by FT-IR, N 2 -adsorption–desorption isotherms, TEM, SEM, Pyridine-IR analysis, XRD and magnetism. Fe 3 O 4 @C@mTa 2 O 5 -NH 2 -PW 12 samples present both Brönsted and Lewis acidity, large BET surface area and high magnetization. The catalytic activity was evaluated by the acetalization of different aldehydes with diols, and the results show that Fe 3 O 4 @C@mTa 2 O 5 -NH 2 -PW 12 (14.47%) catalyst exhibits the highest catalytic activity for acetalization of aldehydes with glycols with 94.5% conversion of benzaldehyde and 99% selectivity to benzaldehyde glycol acetal at 80 °C. The catalytic activity of the catalyst for acetalization is related to its total acidity and Brönsted–Lewis acid synergy. The catalyst Fe 3 O 4 @C@mTa 2 O 5 -NH 2 -PW 12 can be easily recovered and reused for at least 5 times without obvious decrease of catalytic activity. Graphic Abstract