Selective hydrogenation of benzoic acid to cyclohexane carboxylic acid over microwave-activated Ni/carbon catalysts

A Ru/RuO2 heterostructure boosting electrochemistry-assisted selective benzoic acid hydrogenation

Electrocatalytic hydrogenation of benzoic acid (BA) to cyclohexanecarboxylic acid (CCA) at ambient temperature and pressure has been recognized as a promising alternative to thermal hydrogenation since water is required as the hydrogen source. So far, only a few Pt-based electrocatalysts have been developed in acidic electrolyte. To overcome the limitations of reactant solubility and catalyst corrosion, herein, carbon fiber-supported Ru electrocatalysts with abundant Ru/RuO2 heterojunctions were fabricated via cyclic electrodeposition between -0.8 and 1.1 V vs. Ag/AgCl. In an alkaline environment, a Ru/RuO2 catalyst achieves an excellent ECH reactivity in terms of high BA conversion (100%) and selectivity towards CCA (100%) within 180 min at a current density of 200/3 mA cm-2, showing exceptional reusability and long-term stability. 1-Cyclohexenecarboxylic acid (CEA) was identified as the reaction intermediate, whose the selectivity is governed by the applied potential. Kinetic studies demonstrate that ECH of BA over Ru/RuO2 follows a Langmuir-Hinshelwood (L-H) mechanism. In situ Raman spectroscopy and theoretical calculations reveal that the Ru/RuO2 interface enhances the adsorption strength of CEA, thereby facilitating the production of fully hydrogenated CCA. This work provides a deep understanding of the ECH pathway of BA in alkaline media, and gives a new methodology to fabricate heterostructure electrocatalysts.

Air-Stable Ni Catalysts Prepared by Liquid-Phase Reduction Using Hydrosilanes for Reactions with Hydrogen

The liquid-phase reduction method for the preparation of metal nanoparticles (NPs) by the reduction of metal salts or metal complexes in a solvent with a reducing agent is widely used to prepare Ni NPs that exhibit high catalytic activity in various organic transformations. Intensive research has been conducted on control of the morphology and size of Ni NPs by the addition of polymers and long-chain compounds as protective agents; however, these agents typically cause a decrease in catalytic activity. Here, we report on the preparation of Ni NPs using hydrosilane (Ni-Si) as a reducing agent and a size-controlling agent. The substituents on silicon can control not only the size but also the crystal phase of the Ni NPs. The prepared Ni NPs exhibited high catalytic performance for the hydrogenation of unsaturated compounds, aromatics, and heteroaromatics to give the corresponding hydrogenated products in high yields. The unique feature of Ni catalysts prepared by the hydrosilane-assisted method is that the catalysts can be handled under air as opposed to conventional Ni catalysts such as Raney Ni. Characterization studies indicated that the surface hydroxide was reduced under the catalytic reaction conditions with H2 at around 100 °C and with the assistance of organosilicon compounds deposited on the catalyst surface. The hydrosilane-assisted method presented here could be applied to the preparation of supported Ni catalysts (Ni-Si/support). The interaction between the Ni NPs and a metal oxide support enabled the direct amination of alcohols with ammonia to afford the primary amine selectively.

Microcalorimetric adsorption and infrared spectroscopic studies of supported Pd, Ru and Pd–Ru catalysts for the hydrogenation of aromatic rings with carboxyl groups

Pd–Ru/SiO₂ showed special surface chemical properties that were totally different from those of Pd/SiO₂ and Ru/SiO₂ and exhibited high activity and selectivity for the hydrogenation of benzoic acid to cyclohexanecarboxylic acid.

Chemoselective hydrogenation of heteroarenes and arenes by Pd-Ru-PVP under mild conditions

Monometallic (Pd, Ru or Rh) and bimetallic (Pd_0.5–Ru_0.5) alloy NPs catalysts were examined for the hydrogenation of quinoline. Pd–Ru alloy catalyst showed superior catalytic activity to the traditional Rh catalyst. The characterization of Pd_0.5–Ru_0.5 catalysts, HAADF-EDX mapping and XPS analysis suggested that the alloy state of PdRu catalysts remained unchanged in the recovered catalyst. Furthermore, the catalyst was highly selective for the hydrogenation of different arenes.

Recyclable Pd_0.5Ru_0.5–PVP catalyst showed higher activity than monometallic Pd or Ru catalyst for the hydrogenation of quinoline. Furthermore, Pd_0.5Ru_0.5–PVP was able to hydrogenate different arenes.

Plant-mediated synthesis of dual-functional Eggshell/Ag nanocomposites towards catalysis and antibacterial applications

Advances in nanotechnology provide plenty of exciting solutions to environmental issues affecting air, soil as well as water. To solve the water pollution problem caused by organics and microorganisms, development of a simple, environment-friendly, and cheap method for the synthesis of nanomaterials is of paramount importance. Herein, we prepared a novel nanocomposite (named Eggshell/Ag) using waste eggshell as a support and Cacumen platycladi extract as reducing and stabilizing agents in aqueous solutions at room temperature. Biogenic-stabilized Ag nanoparticles (Ag NPs) with an average diameter of 60 nm were well-dispersed on the surface of eggshells, exhibiting dual-functional properties of organics catalytic degradation and bacterial growth inhibition. Through five repeated assays, it was established that the reduction efficiency of the nanocomposite for 4-nitrophenol (4-NP) was high. The reduction could be completed rapidly at room temperature. Moreover, significant inhibition zones were observed for Staphylococcus aureus (S. aureus) agar plates and Escherichia coli (E. coli). Meanwhile, the minimum inhibition concentrations (MIC) were determined to be 0.08 and 0.04 mg mL^-1, respectively, while the minimum bactericidal concentration (MBC) was measured as 0.64 mg mL^-1. The biogenic Eggshell/Ag nanocomposites are promising candidates for a series of applications in the fields of biomedicine, environment as well as energy.

Selective Hydrogenation of 3-Nitrostyrene over a Co-promoted Pt Catalyst Supported on P-containing Activated Charcoal

A series of Co-modified Pt catalysts supported on P-containing activated charcoal were studied for the selective hydrogenation of 3-nitrostyrene (NS) to 3-aminostyrene (AS). The addition of Co decreased the rate of hydrogenation but enhanced the selectivity to AS, being 92% at nearly 100% conversion over an optimized catalyst. The high AS selectivity should result from the configuration of NS adsorption on the catalyst, which occurs preferentially with its -NO2 group on the Pt–POx interface layer over the surface of supported Pt particles. The formation of such a Pt–POx area is promoted by the Co additive.