Effect of Zn addition on the direct synthesis of hydrogen peroxide over supported palladium catalysts

Abstract

Alumina-supported Pd-Zn bimetallic catalysts were prepared and evaluated for direct synthesis of hydrogen peroxide. The effect of Zn on the catalytic performance was studied via characterizations by transmission electron microscopy (TEM), temperature-programmed reduction (TPR), X-ray photoelectron energy spectroscopy (XPS), temperature-programmed desorption of H2/O2 (H2-/O2-TPD), CO chemisorption and diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption (CO-DRIFTS). H2O2 productivity of up to 25431molkgPd−1h−1 was observed with the optimal bimetallic catalyst 1Pd5Zn, much higher than that over the monometallic catalyst 1Pd (8533molkgPd−1h−1). This increase may be attributed to the geometric change caused by the Zn additive and the electronic interactions between Pd and Zn. The addition of Zn increases the isolated Pd sites (the primary active sites for H2O2 formation), which can promote H2O2 selectivity. PdZn catalysts show a higher Pd dispersion and incremental Pd0 content than monometallic Pd owing to electronic interactions between Pd and Zn, which result in increased H2O2 productivity. However, a high Pd dispersion and incremental Pd0 content can increase the H2O2 hydrogenation rate, negatively affecting the H2O2 selectivity.