Bimetallic Gold-Silver Nanoparticles Supported on Zeolitic Imidazolate Framework-8 as Highly Active Heterogenous Catalysts for Selective Oxidation of Benzyl Alcohol into Benzaldehyde

Abstract

The metal-organic zeolite imidazolate framework-8 (ZIF-8) supported gold-silver bimetallic catalysts with a core-shell structure (Au@Ag/ZIF-8 and Ag@Au/ZIF-8) and cluster structure (AuAg/ZIF-8) were successfully prepared by the deposition-redispersion method. Energy dispersive X-ray spectroscopy (EDS) elemental mapping images displayed that in the Au@Ag/ZIF-8 catalyst, Ag atoms were deposited on an exposed Au surface, and core-shell structured Au@Ag particles with highly dispersed Ag as the shell were formed. Additionally, the XPS investigation at gold 4f levels and silver 3d levels indicated that the Au and Ag particles of Au@Ag/ZIF-8, Ag@Au/ZIF-8, and AuAg/ZIF-8 were in a zero valence state. Among the resultant catalysts obtained in this study, Ag@Au/ZIF-8 catalysts showed the highest catalytic activity for the selective oxidation of benzyl alcohol, followed by AuAg/ZIF-8 and Au@Ag/ZIF-8. The turnover frequency (TOF) values were in the order of Ag@Au/ZIF-8 (28.2 h−1) > AuAg/ZIF-8 (25.0 h−1) > Au@Ag/ZIF-8 (20.0 h−1) at 130 °C within 1 h under 8 bar O2 when using THF as solvent. The catalysts of Au@Ag/ZIF-8 and Ag@Au/ZIF-8 with core–shell structures have higher benzaldehyde selectivities (53.0% and 53.3%) than the AuAg/ZIF-8 catalyst (35.2%) in the selective oxidation of benzyl alcohol into benzaldehyde. The effect of the solvent, reaction temperature, reaction time, and reaction pressure on benzyl alcohol conversion and benzaldehyde selectivity in benzyl alcohol selective oxidation over Au@Ag/ZIF-8, Ag@Au/ZIF-8, and AuAg/ZIF-8 were also investigated. All of the catalysts showed excellent performance at 130 °C under 8 bar O2 within 1 h when using THF as the solvent in the selective oxidation of benzyl alcohol to benzaldehyde. Moreover, the catalysts can be easily recycled and used repetitively at least four times.

Bimetallic Au–Pd alloy nanoparticles supported on MIL-101(Cr) as highly efficient catalysts for selective hydrogenation of 1,3-butadiene

“…73 The results exhibited that the MIL-101(Cr) structure was kept well aer loading of Au-Pd alloy, Au, and Pd nanoparticles. 45…”

“…well-dened open cavities. [45][46][47][48][49][50][51] Among various MOF-types, MIL-101(Cr) has been shown to possess extremely large windows and surface areas (S Langmuir ¼ 5900 m 2 g À1 ), remarkable thermal stability (up to 300 C), and excellent chemical stability toward many solvents. [52][53][54] These properties have enabled MIL-101(Cr) to be successfully applied in various elds, including its particularly attractive use as a supports for heterogeneous catalyst.…”

“…The pore volume and mean pore diameter of MIL-101(Cr) are 0.49 m 3 g À1 and 2.8 nm, respectively, whereas Au(2)Pd(1)/MIL-101(Cr) possesses a pore volume of 0.40 m 3 g À1 and a mean pore diameter of 2.7 nm. The BET surface area of bimetallic Au(2) Pd(1)/MIL-101(Cr) catalysts reduces compared with that of MIL-101(Cr), because of the immobilization of Au-Pd alloy nanoparticles inside the pores of MIL-101(Cr) 45,52.…”

Heterogeneous Bimetallic Cu–Ni Nanoparticle-Supported Catalysts in the Selective Oxidation of Benzyl Alcohol to Benzaldehyde

“…The BET surface area decreased significantly for the recycled Cu-Ni-supported catalysts when compared with that of the as-prepared. The decrease in the BET surface area could be due to the collapse of the structure or/and the substrate/solvents blocking the pores of the support [10]. The leaching of the CuNi/MIL-101, CuNi/TiO2, and CuNi/C catalysts was tested to further investigate the stability of the catalysts.…”

“…The details of the characterizations with XRD, XPS, nitrogen adsorption/desorption, and ICP atomic emission spectroscopy analysis are the same as those in our previous work [10]. TEM images were recorded with a Jeol JEM-1210 transmission electron microscope (Jeol, Tokyo, Japan) with a high-angle annular dark-field detector.…”