Catalytic Partial Oxidation of Cyclohexane by Bimetallic Ag/Pd Nanoparticles on Magnesium Oxide

Abstract

Abstract:The liquid phase oxidation of cyclohexane to cyclohexanol and cyclohexanone was investigated by synthesizing and testing an array of heterogeneous catalysts comprising: monometallic Ag/MgO, monometallic Pd/MgO and a set of bimetallic AgPd/MgO catalysts. Interestingly, Ag/MgO was capable of a conversion comparable to current industrial routes of ca. 5%, and with a high selectivity (up to 60%) to cyclohexanol, thus making Ag/MgO an attractive system for the synthesis of intermediates for the manufacture of nylon fibres. Furthermore, following the doping of Ag nanoparticles with Pd, the conversion increased up to 10% whilst simultaneously preserving a high selectivity to the alcohol. Scanning transmission electron microscopy and energy dispersive spectroscopy of the catalysts showed a systematic particle size composition variation with the smaller Ag-Pd nanoparticles being statistically richer in Pd. Analysis of the reaction mixture by Electron Paramagnetic Resonance (EPR) spectroscopy coupled with the spin trapping technique showed the presence of large amounts of alkoxy radicals, thus providing insights for a possible reaction mechanism.

Ionic Liquid-Modified Co/ZSM-5 Catalyzed the Aerobic Oxidation of Cyclohexane: Toward Improving the Activity and Selectivity

“…Therefore, developing new highly efficient and robust heterogeneous catalysts for industrial-scale selective aerobic oxidation of cyclohexane is of great importance. In the last several years, various heterogeneous catalysts have been widely exploited for cyclohexane catalytic aerobic oxidation. − For example, supported metalloporphyrins, − transition metals with Schiff base ligands, , cobalt compounds, − copper complexes, − and metal nanoparticles − have been developed to promote the cyclohexane conversion and the selectivity of KA oil under relatively mild and environmentally friendly reaction conditions. However, most of these catalyst systems either required high temperature/pressure or suffered from poor selectivity to KA oil.…”

Synthesis and Catalytic Properties of Porous Metal Silica Materials Templated and Functionalized by Extended Coordination Cages

“…In the pursuit of avoiding numerous byproducts caused by the highly nonselective intermediates, the current industrially adopted catalysts are homogeneous cobalt salts which can only convert less than 4% cyclohexane into K-A oil with a selectivity of 70–85% under harsh conditions, while the process is risky and environmentally hazardous . A tremendous amount of research endeavors have been pursued to target efficient heterogeneous catalysts for the oxidation of cyclohexane, including metal oxides, metal nanoparticles, zeolites, alumina phosphates, carbon nanotubes, and mesoporous materials that consist of reliably introduced speciation, such as Pd, Au, Fe, Mn, Cu, and Co. − However, no significant breakthrough has been made, because activation of C–H bonds within the saturated hydrocarbon is very difficult, given the fact that the single bonds with a very high C–H bond dissociation energy (∼99.3 kcal/mol) are quite stable. , …”

Synthetic Organic Transformations of Transition‐Metal Nanoparticles as Propitious Catalysts: A Review

“…Later in 2017, Hutchings et al . went on to develop the liquid phase oxidation of cyclohexane to cyclohexanol and cyclohexanone by synthesizing and testing an array of heterogeneous catalysts comprising monometallic Ag NPs/MgO, monometallic Pd NPs/MgO, and a set of bimetallic AgPd NPs/MgO catalysts . Quite remarkably, the Ag NPs on MgO catalyzed the conversion to cyclohexanol in 5 mol% catalyst and high selectivity (60%), in line with industrial protocols.…”