Cyclohexanone Selectivity Research Articles

Liquid-phase Hydrogenation of Phenol to Cyclohexanone over Supported Palladium Catalysts

The ZSM-5, g-Al2O3, SiO2 and MgO supported Pd-catalysts were prepared for the phenol hydrogenation to cyclohexanone in liquid-phase. The natures of these catalysts were characterized by XRD, N2 adsorption-desorption analysis, H2-TPR, CO2-TPD and NH3-TPD. The catalytic performance of the supported Pd-catalyst for phenol hydrogenation to cyclohexanone is closely related to nature of the support and the size of Pd nanoparticles. The Pd/MgO catalyst which possesses higher basicity shows higher cyclohexanone selectivity, but lower phenol conversion owing to the lower specific surface area. The Pd/SiO2 catalyst prepared by precipitation gives higher cyclohexanone selectivity and phenol conversion, due to the moderate amount of Lewis acidic sites, and the smaller size and higher dispersion of Pd nanoparticles on the surface. Under the reaction temperature of 135 oC and H2 pressure of 1 MPa, after reacting for 3.5 h, the phenol conversion of 71.62% and the cyclohexanone selectivity of 90.77% can be obtained over 0.5 wt% Pd/SiO2 catalyst. Copyright © 2016 BCREC GROUP. All rights reservedReceived: 7th March 2016; Revised: 13rd May 2016; Accepted: 7th June 2016How to Cite: Fan, L., Zhang, L., Shen, Y., Liu, D., Wahab, N., Hasan, M.M. (2016). Liquid-phase Hydrogenation of Phenol to Cyclohexanone over Supported Palladium Catalysts. Bulletin of Chemical Reaction Engineering & Catalysis, 11 (3): 354-362 (doi: 10.9767/bcrec.11.3.575.354-362)Permalink/DOI: http://doi.org/10.9767/bcrec.11.3.575.354-362

Decomposition of cyclohexyl hydroperoxide over bimetallic mesoporous materials containing cobalt and chromium

AbstractBimetallic mesoporous Co‐Cr‐TUD‐1 and its counterparts Co‐TUD‐1 and Cr‐TUD‐1 were synthesized by a direct hydrothermal treatment (DHT) method with triethanolamine as a template. The products were characterized by many techniques. Results show that Co and Cr are incorporated into the framework of TUD‐1. The catalytic behaviours of the samples were tested in decomposition of cyclohexyl hydroperoxide (CHHP). Co‐Cr‐TUD‐1 (Si/(Co + Cr) = 25) shows the highest catalytic efficiency with a CHHP conversion of 96.9 % and total selectivity of cyclohexanone and cyclohexanol of 95.9 %, which outperforms Co‐TUD‐1 and Cr‐TUD‐1 and indicates a synergistic effect between Co and Cr in Co‐Cr‐TUD‐1. The catalysts are mainly heterogeneous as shown in various experiments, while the catalytic performances of recovered catalysts declined modestly, indicating non‐negligible amounts of Co and Cr are leached after some cycles.

Synthesis and Oxidation Catalysis of [Tris(oxazolinyl)borato]cobalt(II) Scorpionates

The reaction of CoCl2·THF and thallium tris(4,4‐dimethyl‐2‐oxazolinyl)phenylborate (TlToM) in tetrahydrofuran (THF) provides ToMCoCl (1) in 95 % yield; however, appropriate solvents and starting materials are required to favor 1 over two other readily formed side‐products, (ToM)2Co (2) and {HToM}CoCl2 (3). ESR, NMR, FTIR, and UV/Vis spectroscopies were used to distinguish these cobalt(II) products and probe their electronic and structural properties. Even after the structures indicated by these methods were confirmed by X‐ray crystallography, the spectroscopic identification of trace contaminants in the material was challenging. The recognition of possible contaminants in the synthesis of ToMCoCl in combination with the paramagnetic nature of these complexes provided impetus for the utilization of X‐ray powder diffraction to measure the purity of the ToMCoCl bulk sample. The X‐ray powder diffraction results provide support for the bulk‐phase purity of ToMCoCl in preparations that avoid 2 and 3. Thus, 1 is a precursor for new [tris(oxazolinyl)borato]cobalt chemistry, as exemplified by its reactions with KOtBu and NaOAc to give ToMCoOtBu (4) and ToMCoOAc (5), respectively. Compound 5 is a catalyst for the oxidation of cyclohexane with meta‐chloroperoxybenzoic acid (mCPBA), and the rate constants and selectivity for cyclohexanol versus cyclohexanone and ε‐caprolactone were assessed.

Pd/TiN nanocomposite catalysts for selective hydrogenation of phenol and its derivatives

Abstract Pd/TiN nanocomposite catalysts were fabricated for one-step selective hydrogenation of phenol to cyclohexanone successfully. High conversion of phenol (99%) and selectivity of cyclohexanone (98%) were obtained at 30 °C and 0.2 MPa H2 for 12 h in the mixed solvents of H2O and CH2Cl2. The Pd nanoparticles were stable in the reaction, and no aggregation was detected after four successive runs. The catalytic activity and selectivity depended on slightly the Pd particle sizes. The generality of the catalysts for this reaction was demonstrated by the selective hydrogenation of phenol derivatives, which showed that the catalyst was selective for the formation of cyclohexanone.

Synthesis of novel N4O4 type bis(diazoimine)–metal complexes supported on mesoporous silica: Microwave assisted catalytic oxidation of cyclohexane, cyclooctane, cyclohexene and styrene

Cu(II), Co(II), Mn(II) and Ni(II) complexes of silica-supported N4O4 type bis(diazoimine) ligands were synthesized and characterized by using FT-MIR/FAR, TG/DTA, elemental analysis, ICP-OES, SEM and EDX techniques. Catalytic activities of the complexes were investigated on the selective oxidation of cyclohexane, cyclohexene, cyclooctane and styrene under microwave power. In cyclohexane oxidation, L1-Cu(II) catalyst showed the best catalytic activity with the conversion of 73.31% and 46.05% cyclohexanol and 34.87% cyclohexanone selectivity. L1-Cu(II) and L2-Cu(II) catalyst were selective for 2-cyclohexen-1-ol (40.54% and 65.01%) in the cyclohexene oxidation with high conversions (66.77% and 54.59%). Cycloctanone selective L1-Cu(II), L2-Cu(II), L2-Cu(II) and L1-Ni(II) (75–80%) complexes showed very selective catalytic properties in the catalytic oxidation of cyclooctane. L1-Ni(II), L2-Ni(II) and L3-Ni(II) catalysts have had 81.28%, 73.70% and 81.39% selectivities respectively in styrene oxidation. Generally, it can be said that Cu(II) complexes are highly active and selective catalysts on the oxidation of cyclohexane, cyclohexene and cyclooctane. Nevertheless, Ni(II) complexes of L1 and L2 showed important selective catalytic performances towards the epoxidation of styrene.

The synthesis of Co-doped SAPO-5 molecular sieve and its performance in the oxidation of cyclohexane with molecular oxygen

Silicoaluminophosphate (SAPO) molecular sieves doped with cobalt (Co-SAPO-5) were synthesized hydrothermally with different concentrations of Co. Each sample was characterized by X-ray diffraction, N2 adsorption-desorption, scanning electron microscopy, ultraviolet-visible spectroscopy, temperature-programmed desorption of NH3 (NH3-TPD), and infrared spectrascopy of adsorbed pyridine (Py-IR). The results showed that Co was highly dispersed in the Co-SAPO-5 samples. In addition, a part of the Co content had been incorporated into the SAPO-5 framework, while the remainder existed on the surface as extra-framework Co. The surface areas of the Co-SAOP-5 samples were similar to the SAPO-5 sample. However, the pore volumes of the Co-SAOP-5 samples were lower than that of the SAOP-5 sample. As the concentration of Co increased, the pore volume gradually decreased because extra-framework cobalt oxide was present on the catalyst surface. NH3-TPD and Py-IR results revealed that the amount of Brønsted acid and the total amount of acid for the Co-SAPO-5 samples were higher than that for the SAPO-5 sample. These values were also higher for samples with higher Co content. The catalytic activity of the Co-SAPO-5 samples was evaluated for the oxidation of cyclohexane with molecular oxygen. When Co was added to the SAPO-5 catalyst, the catalytic activity of the Co-SAPO-5 catalysts improved. In addition, the conversion of cyclohexane increased as the Co content in the Co-SAPO-5 catalysts increased. However, with a high conversion of cyclohexane (>6.30%), the total selectivity of cyclohexanone (K) and cyclohexanol (A) decreased sharply. The K/A ratio ranged from 1.15 to 2.47. The effects of reaction conditions (i.e., reaction temperature, reaction time, initial oxygen pressure, and the catalyst amount) on the performance of the Co-SAPO-5 catalysts have also been measured. Furthermore, the stability of the Co-SAPO-5 catalyst was explored and found to be good for the selective oxidation of cyclohexane by molecular oxygen.

Solvent-free selective oxidation of cyclohexane with molecular oxygen over manganese oxides: Effect of the calcination temperature

The effects of calcination temperature on the physicochemical properties of manganese oxide catalysts prepared by a precipitation method were assessed by X-ray diffraction, N2 adsorption-desorption, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, O2 temperature-programmed desorption, and thermogravimetry-differential analysis. The catalytic performance of each of these materials during the selective oxidation of cyclohexane with oxygen in a solvent-free system was subsequently examined. It was found that the MnOx-500 catalyst, calcined at 500 °C, consisted of a Mn2O3 phase in addition to Mn5O8 and Mn3O4 phases and possessed a low surface area. Unlike MnOx-500, the MnOx-400 catalyst prepared at 400 °C was composed solely of Mn3O4 and Mn5O8 and had a higher surface area. The pronounced catalytic activity of this latter material for the oxidation of cyclohexene was determined to result from numerous factors, including a higher concentration of surface adsorbed oxygen, greater quantities of the surface Mn4+ ions that promote oxygen mobility and the extent of O2 adsorption and reducibility on the catalyst. The effects of various reaction conditions on the activity of the MnOx-400 during the oxidation of cyclohexane were also evaluated, such as the reaction temperature, reaction time, and initial oxygen pressure. Following a 4 h reaction at an initial O2 pressure of 0.5 MPa and 140 °C, an 8.0% cyclohexane conversion and 5.0% yield of cyclohexanol and cyclohexanone were achieved over the MnOx-400 catalyst. In contrast, employing MnOx-500 resulted in a 6.1% conversion of cyclohexane and 75% selectivity for cyclohexanol and cyclohexanone. After being recycled through 10 replicate uses, the catalytic activity of the MnOx-400 catalyst was unchanged, demonstrating its good stability.

Visible light-triggered vanadium-substituted molybdophosphoric acids to catalyze liquid phase oxygenation of cyclohexane to KA oil by nitrous oxide

The development of a mild and highly efficient process for utilization of nitrous oxide (N2O) as a green oxidant has very important academic and applied values in the synthesis of oxygenated products. This paper first discloses that a series of vanadium-substituted molybdophosphoric acids (PMo12−nVn, n=1–3), assisted by HCl aqueous solution, can efficiently catalyze the visible light-driven liquid phase oxygenation of cyclohexane by N2O in acetonitrile (MeCN), providing ca. 26.2% cyclohexane conversion and 90.2% selectivity for cyclohexanol and cyclohexanone (KA oil) under optimized conditions, along with a small quantity of chlorination. Among the catalysts examined, PMo10V2 and especially PMo9V3 showed a higher activity for this photocatalytic oxygenation than PMo11V. Furthermore, the amount of water added strongly influenced this HCl-promoted photocatalysis oxygenation. The selectivity of cyclohexanone was continuously and significantly improved from 21.8 to 82.7% with increasing water amount from 0 to 0.15mL, but the conversion of cyclohexane obviously decreased when the amount of water added was higher than 0.12mL. The promoting effect of HCl on the present photocatalysis reaction is probably due to the fact that the donor–acceptor (D–A) adduct between HCl and PMo12−nVn can be excited by visible light to achieve its intra-molecular electron transfer from Cl− to PMo12−nVn anions, which leads to the generation of Cl radicals and the reduction of catalysts. The subsequent reactions initiated by the Cl radicals result in the oxygenation of cyclohexane by N2O to KA oil and the regeneration of catalysts, as supported by UV–vis spectral and cyclic voltammetric measurements.

One-step semi-continuous cyclohexanone production via hydrogenation of phenol in a submerged ceramic membrane reactor

Cyclohexanone is an important chemical raw material, and the development of green production technologies is urgently desirable. In this article, a clean and efficient process of phenol hydrogenation to cyclohexanone was developed over a Pd@CN catalyst in a submerged ceramic membrane reactor, which realized the in-situ separation and reuse of catalyst. The effects of operation conditions on the reaction and filtration processes were investigated in detail. Results showed that the introduction of membrane had almost no influence on the phenol conversion and cyclohexanone selectivity, but the operation conditions greatly affected the performance of reaction and filtration. Semi-continuous phenol hydrogenation to cyclohexanone showed that the Pd@CN catalyst could maintain a high phenol conversion at ∼94.6% and a cyclohexanone selectivity above 86.5%, and the ceramic membrane exhibited better filtration performance and excellent stability during the entire hydrogenation process. This work would provide some references for green production of cyclohexanone.

Potential of Supported Gold Bimetallic Catalysts for Green Synthesis of Adipic Acid from Cyclohexane

Adipic acid (AA) is the main raw material for making nylon 6,6 fiber, which is further used in the production of different commercially important products (e.g. coatings, polymers etc.). Herein, we demonstrated a green chemistry route for the one-step oxidation of cyclohexane (CH) to AA using supported bimetallic catalysts containing gold and palladium or silver nanoparticles. The catalysts were prepared in two steps using sol–gel and impregnation techniques and were then characterized by different techniques such as ICP, BET surface area, XRD, TEM etc. Activity tests were carried out using Parr autoclave under the following optimum conditions (400 mg of catalysts, acetonitrile as solvent (5 ml), 0.1 g of TBHP as initiator, 10 bar of O2, 150 °C). XRD patterns revealed that no reflections corresponding to either Au or Pd are present in Au–Pd/TiO2 system, while a weak reflection belonging to metallic Au phase could be seen in Au–Ag/TiO2 catalyst. In terms of catalytic activity, Pd/TiO2 exhibited somewhat inferior performance (X–CH = 16 %, S–AA = 18 %) compared to Au/TiO2 solid (X–CH = 25 %, S–AA = 26 %). Interestingly, the combination of Au and Pd (Pd–Au/TiO2) markedly improved the selectivity of AA from 26 to ca. 34 %. In case of Au–Ag/TiO2, the combination of Ag and Au (i.e. 1 % Au–1 % Ag/TiO2) enhances the conversion of CH and selectivity of cyclohexanone (X–CH = 33 %, S–One = 41 %); compared to monometallic Ag/TiO2 solid. The results showed that the nature of second metal has shown a clear influence on the conversion of CH as well as the product distribution.

Vanadium‐Substituted Tungstophosphoric Acids as Efficient Catalysts for Visible‐Light‐Driven Oxygenation of Cyclohexane by Dioxygen

AbstractThis paper discloses that the oxygenation of cyclohexane by dioxygen (O2) to cyclohexanol and cyclohexanone over three vanadium‐substituted tungstophosphoric acids (PW11V1, PW10V2, PW9V3) can occur in MeCN under visible‐light irradiation, but provides very low cyclohexane conversion (0.8–2.4 %) with modest cyclohexanone selectivity (51–58.3 %). Importantly, an HCl aqueous solution was found to drastically promote this photooxygenation catalyzed by PW10V2 and especially PW9V3 acids, respectively providing approximately 20.4 and 23.4 % cyclohexane conversion and approximately 82.5 and 87.1 % cyclohexanone selectivity, with a concomitant formation of a small amount of chlorocyclohexane. However, such promoting effect was negligible in the PW11V1‐ photocatalyzed oxygenation and the other acids and the chlorine‐containing salts did not show any promotion effect on the present photocatalysis reaction. Notably, the HCl‐promoted photocatalytic oxygenation was significantly influenced by the amount of water. The cyclohexanone selectivity continuously and significantly increased with water amount, but photooxygenation efficiency drastically decreased if a slight excess amount of water was added. Based on these findings and the UV/Vis spectral and cyclic voltammetric measurements, a free‐radical mechanism initiated by the Cl atoms generated in the present photocatalysis system was proposed.

Efficient Room-Temperature Aqueous-Phase Hydrogenation of Phenol to Cyclohexanone Catalyzed by Pd Nanoparticles Supported on Mesoporous MMT-1 Silica with Unevenly Distributed Functionalities

Efficient and selective aqueous-phase hydrogenation of phenol by a novel Pd catalyst supported on dually and selectively functionalized mesoporous MMT-1 silica nanoparticles has been developed. The catalyst features small (∼1.1 nm) Pd nanoparticles surrounded by unevenly distributed nitrogen- or heteroatom-free organic groups in the helical mesopores and the presence of non-hydrogen-bonded isolated silanol groups on the mesopore surface. The catalyst exhibited superior conversion of phenol and high selectivity of cyclohexanone at room temperature under atmospheric pressure of hydrogen and remained highly active after ten catalytic runs. The catalyst was active for the aqueous-phase hydrogenation of a variety of mono- and dihydroxylated aromatic compounds. The green protocol with the designed catalyst would be practical for the hydrogenation of phenol and other derivatives.

Selective liquid phase oxidation of cyclohexane over Pt/CeO2-ZrO2-SnO2/SiO2 catalysts with molecular oxygen

Partial oxidation of cyclohexane into cyclohexanone and cyclohexanol (KA-oil) is an industrially significant reaction for producing precursors for the synthesis of ɛ-caprolactam and adipic acid, which are the building blocks of nylon. However, to date, the cyclohexane conversion ratio has usually been limited to less than 6% to prevent further oxidation of the cyclohexanol and cyclohexanone targets. In this study, we report that Pt/CeO2-ZrO2-SnO2/SiO2, in which CeO2-ZrO2-SnO2 provide reactive oxygen molecules from inside the bulk, can act as efficient catalysts. Optimization of the catalyst composition and reaction conditions provided a cyclohexane conversion ratio of 24.1% and a total selectivity for cyclohexanol and cyclohexanone of 83.4% at 130 °C in 0.5 MPa (4.9 atm) air for 7 h over a 5wt%Pt/16wt%Ce0.68Zr0.17Sn0.15O2.0/SiO2 catalyst. This catalyst has significant advantages over conventional catalysts because the reaction proceeds at a lower pressure, and there is no need for toxic radical initiators or free-radical scavengers.

Selective transfer hydrogenation of phenol to cyclohexanone on supported palladium catalyst using potassium formate as hydrogen source under open atmosphere

A selective, effective and sustainable catalytic transfer hydrogenation of phenol to cyclohexanone on supported palladium using potassium formate as benign hydrogen source at atmospheric pressure and mild reaction conditions has demonstrated. A reaction temperature, catalyst (Pd/C), solvent (water) quantity and type of hydrogen source are found to be most influencing factors for effective phenol conversion. Hydrogen donor potassium formate playing important dual role; as hydrogen source and as additive to enhance the cyclohexanone selectivity. The catalyst Pd/C has successfully recovered through filtration and reused up to few batches without considerable loss of phenol conversion and cyclohexanone selectivity.

Heterogeneous Catalytic Oxidation of Cyclohexane with H2O2 Catalyzed by Cs- and TBA-salts of Cu- and Mn-Polyoxotungstates on MCM-41

Cs-and tetrabutyl ammonium (TBA) salts of Cu- and Mn-polyoxotungstates were synthesized. They were loaded on MCM-41 support (by impregnation method in 20-30 wt%) to increase surface area of the catalysts. The supported catalysts were characterized by inductive coupled plasma emission (ICP), Fourier-Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD) and nitrogen adsorption-desorption. Their catalytic activities for oxidation of cyclohexane were compared using green oxidant H2O2 under mild reaction conditions. The oxidized products are cyclohexanol and cyclohexanone. The activities follow the order: TBA-CuPOM/MCM > TBA-MnPOM/MCM > Cs-CuPOM/MCM > Cs-MnPOM/MCM. The Mn containing catalysts gave higher cyclohexanone selectivity than Cu containing catalysts. The Cs salt catalysts can be reused without loss of activity due to its insolubility in the reaction medium. The 30wt%Cs-CuPOM/MCM and 30wt% Cs-MnPOM/MCM gave comparable activity (16-17 % conversion with 75-76 %selectivity using H2O2/cyclohexane mole ratio = 4 at 80 ˚C in 12 h. The oxidation reaction appears to be radical process, since it was inhibited in the presence of radical scavenger.

A simple and efficient approach for preparation of hydroxylamine sulfate from the acid-catalyzed hydrolysis reaction of cyclohexanone oxime

A simple and efficient approach for preparation of hydroxylamine sulfate from the hydrolysis reaction of cyclohexanone oxime in the presence of sulfuric acid has been developed in this work. The effects of the molar ratio of cyclohexanone oxime to sulfuric acid, the concentration of reactants, the reaction temperature, the reaction time and the extraction solvents on the hydrolysis reaction were investigated. The results indicated the conversion of cyclohexanone oxime was over 30% with excellent selectivity of cyclohexanone and hydroxylamine sulfate under the optimal reaction conditions. Furthermore, the enthalpy change, entropy change, Gibbs free energy change and thermodynamic equilibrium constant of the hydrolysis reaction were determined in present work. This reaction is an endothermic reaction and higher temperature is favorable for the synthesis of hydroxylamine sulfate. This new preparation method is simple, rapid, efficient and economical. Maybe this work can serve as a direction for preparation of other hydroxylamine salts by such hydrolysis reaction.

Towards the mechanism of the oxidation of cyclohexylamine by molecular oxygen over alumina-based catalysts

The oxidation of cyclohexylamine with molecular oxygen over a heterogeneous catalyst is an attractive one-step route to prepare a commercially important cyclohexanone oxime. The effect of the reaction conditions on the conversion of cyclohexylamine during its oxidation by molecular oxygen and on the selectivity of cyclohexanone and cyclohexanone oxime formation was investigated over heterogeneous catalysts (alumina and alumina supported silicotungstic acid). The present work is aimed at the enhancement of the cyclohexanone oxime yield, for which the optimized conditions were found as: reaction temperature of 180 °C, LHSV of cyclohexylamine 1 ml g−1 h−1, oxidant 33 % O2 in nitrogen with a total GHSV of 24 ml min−1. Cyclohexanone, formed from cyclohexylamine, reacts with cyclohexylamine to N-cyclohexylidenecyclohexylamine, their Schiff base. The most intense formation of cyclohexanone was observed in the initial period of the catalytic tests. Carbonaceous deposits, responsible for the catalyst deactivation, are formed mainly from the Schiff base; their amount increases by time on stream, and the rate of their formation correlates with the concentration of oxygen in the reaction mixture, as well as with the formation rate of cyclohexanone and the Schiff base. Injection of water to the reactant stream prolongs the catalyst lifetime and reduces the tar formation. However, it deteriorates the catalyst´s activity and selectivity. The supposed mechanism of cyclohexylamine oxidation is discussed.

Optimization of Reaction Conditions for Cyclohexane to Cyclohexanone witht-Butylhydroperoxide Over CuCl2Loaded with Activated Carbon

Catalytic oxidation of hydrocarbons can be performed efficiently in the presence of tert- butylhydroperoxide (TBHP) under a low-valent transition metal as the catalyst. CuCl2 loaded with activated carbon had synthesized and characterized by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX), and then utilized as a catalyst for the oxidation of cyclohexane with molecular oxygen as the oxidant and the TBHP as the pro-oxidant under various conditions. The possible reaction mechanism was discussed and the effects of different factors on the oxidation of cyclohexane were investigated. Reaction conditions including catalyst type, oxidant, reaction time, reaction temperature, TBHP amount, solvent type and solvent amount were systematically optimized in order to achieve the highest conversion of cyclohexane and highest selectivity of cyclohexanone. Various other alkanes exhibited higher catalytic activity under the optimal conditions.

Vapour phase hydrogenation of phenol over rhodium on SBA-15 and SBA-16.

In the present work, mesoporous SBA-15 and SBA-16 were synthesised using classical methods, and their physicochemical properties were investigated by X-ray diffraction (XRD), FTIR, TEM and N2 adsorption–desorption. Rhodium (Rh, 1 wt %) was loaded on the mesoporous SBA-15 and SBA-16 by an impregnation method. The Rh surface coverage, dispersion and crystallite size were determined by room temperature H2 chemisorption on reduced samples. The catalytic activity of Rh supported on mesoporous SBA-15 and SBA-16 was evaluated for the first time in the hydrogenation of phenol in vapour phase in a temperature range between 130 and 270 °C at atmospheric pressure. The reaction over Rh/SBA-15 at 180 °C produced cyclohexanone as the major product (about 60%) along with lower amounts of cyclohexanol (about 35%) and cyclohexane (about 15%). The influences of temperature, H2/phenol ratio, contact time and the nature of the solvent on the catalytic performance were systematically investigated. The Rh/SBA-16 system offered lower phenol conversion compared to Rh/SBA-15, but both have a very high selectivity for cyclohexanone (above 60%).

Phenol and dihydroxybenzene hydrogenation catalysts based on polyamide dendrimers and rhodium species

Heterogeneous catalysts based on rhodium nanoparticles and first- and second-generation poly(amidoamine) (PAMAM) dendrimers crosslinked with hexamethylene diisocyanate have been synthesized. It has been found that catalyst samples with a particle size of 0.88 to 1.96 nm, depending on the PAMAM dendrimer generation, are effective in the hydrogenation of phenol, hydroquinone, resorcinol, and pyrocatechol (85°C, 30 atm O2, 2 h). In phenol hydrogenation, the selectivity for cyclohexanone is 100%. Cyclohexanone has not undergone further transformation under the reaction conditions. The main products of dihydroxybenzene hydrogenation have been trans-cyclohexanediols, with their proportion decreasing in the order: resorcinol > hydroquinone > pyrocatechol. The selectivity has been found to be 100% for 1,3-cyclohexanediol, 97–99% for 1,4-cyclohexanediol, and 33–91% for 1,2-cyclohexanediol. The catalysts based on the second-generation dendrimer have shown a high activity in dihydroxybenzene hydrogenation (TOF of 6600 to 35000 h−1).