Selective Hydrogenation of Phenol to Cyclohexanone over Pd–HAP Catalyst in Aqueous Media

Abstract

The production of pure cyclohexanone under mild conditions over catalysts with high reactivity, selectivity, compatibility, stability, and low cost is still a great challenge. Here we report a hydroxyapatite‐bound palladium catalyst (Pd–HAP) to demonstrate its excellent performance on phenol hydrogenation to cyclohexanone. Based on catalyst characterization, the Pd nanoclusters (≈0.9 nm) are highly dispersed and bound to phosphate in HAP. Only basic active sites on HAP surface are detected. At 25 °C and ambient H2 pressure in water, phenol can be 100 % converted into cyclohexanone with 100 % selectivity. This system shows a universal applicability to temperature, pH, solvent, low H2 purity, and pressure. The catalyst reveals high stability to be recycled without deactivation or morphology change; and Pd nano‐clusters barely aggregate even at 400 °C. During the reaction, HAP adsorbs phenol, and Pd nanoclusters activate and spillover H2. The mechanism is also investigated, proposed, and verified.

Ni-Catalyzed reductive amination of phenols with ammonia or amines into cyclohexylamines

“…For o-, m-and p-cresol, the presence of a methyl group on the aromatic ring slowed down the reaction due to sterical hindrance in the order of para < meta < ortho; but the reactions still resulted in good to high yields of the corresponding methylcyclohexylamines after only 3 h (3b-d). As previously reported by Xu et al, 52 substrates with bulkier substituents -such as 4-n-propyl and 4-tert-butyl groupsslowed down the hydrogenation of phenol derivatives even more drastically; these reactions afforded the corresponding cyclohexylamines with a very high selectivity of ≥ 99% in the presence of ammonia (3e and f). 4-n-Propylphenol is one of the main reductive fractionation products derived from lignin 53,54 and its use, therefore, is very attractive in the context of green chemistry.…”

Oxidative Esterification of Methacrolein to Methyl Methacrylate over Gold Nanoparticles on Hydroxyapatite

“…Commonly, HAP, which has the formula Ca 10 (PO 4 ) 6 (OH) 2 and a hexagonal cylinder crystal structure, is used widely as a green, substrate‐tolerant, nearly‐water‐insoluble, and easily recovered catalyst support with excellent ion‐exchange/adsorption abilities and tunable surface acid–base properties . Especially, many base‐catalyzed reactions and the Guerbet reaction for the production of n ‐butanol from ethanol can be promoted efficiently by HAP‐based catalyst systems.…”

Sustainable Routes for the Synthesis of Renewable Adipic Acid from Biomass Derivatives

“…[128] For the first step, Pd-based catalysts have been shown to be effective in selective hydrogenation of phenolic compounds and the conversion of guaiacol to 2-MCO over Pd/ HAP catalyst has been actually reported with 98 % high selectivity. [129] Analogously, the catalytic reduction of guaiacol to 2-MCO with formic acid as reducing agent over Pd/C has been also realized. [130] For the following step of the oxidation of 2-MCO to AA, the authors used H 4À can decrease the reactivity of the radical with radical inhibitor.…”