Selective Hydrogenation Of Phenol Research Articles

Oxygen Vacancy-Enriched Alumina Stabilized Pd Nanocatalysts for Selective Hydrogenation of Phenols.

The prevalence of electronic defects has not been successfully demonstrated in nonreducible oxides. This work presents a straightforward approach to the preparation of a yellow alumina rich in F-centers (oxygen vacancies containing free electrons), which is well characterized by systematic spectral methods. The surface electron density of the as-prepared F-center enriched alumina sample was estimated to be approximately 0.35 mmol·g-1. Free electrons on the surface can reduce palladium precursors in situ, leading to the deposition of fine Pd nanoparticles on alumina. The produced Pd nanocatalysts are highly effective in the selective hydrogenation of phenol to cyclohexanone, achieving a high catalytic performance under mild conditions (30 °C and 0.1 MPa of H2). Systematic mechanism investigations reveal that hydroxyl radicals generated at the catalyst interfaces facilitate the activation of phenol. The activated phenol is then sequentially hydrogenated to give the intermediate 2-cyclohexenone and then the desired cyclohexanone. The catalyst system demonstrates efficacy in selectively hydrogenating substituted phenols into a wide array of functional ketones.

Regulating the electronic state of Pd nanoclusters and Lewis acid density by the carbon doping for synergistically enhancing phenol hydrogenation in green solvent

Pd-based catalysts have been widely applied in selective hydrogenation of phenol. However, avoiding excessive hydrogenation of C=O functional groups is still challenging. Here, we synthesized Pd nanoclusters supported by N-doped C-Al2O3 (Pd/CN-Al2O3) catalyst for phenol hydrogenation. Remarkably, the cyclohexanone yield shows a volcano trend with the doping of carbon content, where Pd/CN-Al2O3 with carbon content of 6.76 % (Pd/CN-Al2O3-2) exhibits the highest cyclohexanone yield. Under the optimized conditions, the phenol conversion and cyclohexanone selectivity over Pd/CN-Al2O3-2 are 99.5 % and 96.7 %, respectively. The corresponding TOF value is 1731.7 h−1, which is 5.8 times higher than that of Pd/Al2O3 (299.7 h−1). Mechanism studies reveal the excellent catalytic performance of Pd/CN-Al2O3-2 is mainly attributed to the synergistic effect of electron-deficient Pd clusters and Lewis acid sites. Pd nanoclusters with moderate electron-deficient state and moderate Lewis acid density are beneficial to the adsorption of phenol and the desorption of cyclohexanone, thereby exhibiting the best phenol conversion and cyclohexanone selectivity. This work provides a carbon modification strategy to regulate the structure of Pd-based catalysts, which is a helpful guide for the hydrogenation reactions.

Nickel Nanoparticles on Hydroxyl and Defect-rich Hollow Carbon Spheres as Catalysts for Efficient Selective Hydrogenation of Phenol

Nickel Nanoparticles on Hydroxyl and Defect-rich Hollow Carbon Spheres as Catalysts for Efficient Selective Hydrogenation of Phenol

Easily recyclable pd-decorated hierarchically porous nanofibers for the selective hydrogenation of phenol

The electrospun nanofibers are good candidates for the catalyst carriers, however the fabrication of electrospun nanofibers with well-developed porous structures is still a big challenge. Herein, the SiO2 nanofibers obtained by electrospinning and pyrolysis are functionalized with polydopamine (PDA) and UiO-66-NH2, and after Pd loading the hierarchically porous Pd/UiO-SiO2 nanofiber catalysts were developed. The surface properties and microstructures of the Pd/UiO-SiO2 nanofiber catalysts were regulated by adjusting the concentrations of dopamine (DA) and zirconium tetrachloride (ZrCl4), and the catalytic performance was tested in the selective hydrogenation of phenol to cyclohexanone. The as-prepared Pd/UiO-SiO2-3–21.44 has abundant hierarchical pores and amino groups, high Pd content with good dispersion, and rich Pd(0), thus exhibiting a superior specific activity of 47.3 h−1 higher than most Pd-based catalysts. Most importantly, the Pd/UiO-SiO2-3–21.44 nanofiber catalyst can be directly taken out from the reaction solution and used for the next run, and has good catalytic stability.

SnO2 modified intermetallic PdSn for selective hydrogenation of phenol to cyclohexanone with hydrogen donor

Lignin oil consists of a large amount of phenolic compounds, and how to economically and efficiently utilize its phenolic compounds remains challenging while chitin is the second largest natural organic compounds in quantity, and finding its more application is highly desired. In this work, we demonstrate to use chitin as supports to prepare SnO2 modified intermetallic PdSn bifunctional catalysts for hydrogenation of phenolic compounds to cyclohexanone derivatives. Under mild reaction conditions and HCOONa as hydrogen donor, the synthesized Pd1Sn2Ox/chitin exhibits 99.3 % of phenol conversion and 99.8 % of cyclohexanone selectivity, and illustrates a wide adaptability for selective hydrogenations of various methylphenols and dihydroxybenzenes. Theoretic calculations and experimental results suggest that the significant enhancement can be attributed to the synergistic effect between SnO2 and the formation of PdSn intermetallic phase, where the Lewis acid SnO2 promotes the activation of the benzene rings of phenolic compounds and intermetallic PdSn accelerates HCOONa in water medium to release H2 for hydrogenation.

Palladium nanoparticles supported over acetylene black for selective hydrogenation of phenol to cyclohexanone

Exploring loaded noble metal catalysts for hydrogenation of phenol to cyclohexanone under a mild reaction condition of atmospheric and low temperature is desirable but challenging. In the present work, Pd supported over acetylene black catalyst (Pd/ACET) was prepared by a simple impregnation method using industrial waste acetylene black as a carbon carrier. The catalyst is able to hydrogenate phenol to cyclohexanone with a high conversion of 97.3 % and a high selectivity of 99.9 %. Different metal loadings were found to have a large effect on the bonding state and functional structure of the acetylene black surface. A higher Pd0/Pd2+ ratio in the catalyst could produce a better catalytic performance on the phenol hydrogenation. The kinetic process of phenol hydrogenation was investigated to kinetically reveal the nature of high selectivity.

Synergistic Effects of Hierarchically Porous Structures and Amino Groups in Pd@MOFs for the Selective Hydrogenation of Phenol

Synergistic Effects of Hierarchically Porous Structures and Amino Groups in Pd@MOFs for the Selective Hydrogenation of Phenol

Highly Selective Hydrogenation of Phenol to Cyclohexanone Using WO3 Supported Tiny Pd Clusters Catalysts

Highly Selective Hydrogenation of Phenol to Cyclohexanone Using WO3 Supported Tiny Pd Clusters Catalysts

The influence of carbon supports and their surface modification on aqueous phase highly selective hydrogenation of phenol to cyclohexanol over different Ni/carbon catalysts

Cyclohexanol is an important feedstock in the chemical industry. Highly selective hydrogenation of phenols to cyclohexanol over non-noble metal catalysts remains a challenge. Herein, four distinctive carbon materials, carbon black (CB), activated carbon (AC), activated carbon fiber (ACF) and carbon nanotube (CNT) were selected as catalyst supports to load Ni nanoparticles for effective phenol hydrogenation. The results show that the phenol conversion and cyclohexanol selectivity in aqueous phase hydrogenation reaction at 180 °C for 2 h over 10 wt% Ni/AC catalyst could reach 99.7% and 94.8%, respectively. These values are better than those obtained over 10 wt% Ni/ACF, Ni/CNT and Ni/Al2O3. After surface modification of carbon supports, the catalytic activity and reuse effect of modified catalysts are significantly enhanced and the optimal temperature decreases to 150 °C. This is because that modified carbon supports have abundant surface functional groups so as to provide a high dispersion and stable anchor of ultrafine active Ni nanoparticles (∼12 nm). Phenol hydrogenation catalyzed by different Ni/carbon catalysts conforms to a first-order reaction, and their apparent activation energies are in a range of 49∼68 kJ mol−1 (49 corresponds to the modified catalyst Ni/MAC), which are markedly lower than that of Ni/Al2O3 (∼96 kJ mol−1). The potential mechanism of highly selective hydrogenation of phenol to cyclohexanol in this work is mainly controlled by the reaction kinetics, which is closely related to the different desorption abilities of cyclohexanone and cyclohexanol from the catalysts.

Pd Nanoparticles Supported on N-Incorporated Hybrid Organosilica as an Active and Selective Low-Temperature Phenol Hydrogenation Catalyst

A heterogeneous Pd-NPMO hybrid-silica catalyst is synthesized and its application for aqueous phase selective hydrogenation of phenol to cyclohexanone at near ambient temperature (40 °C) and under atmospheric hydrogen pressure is demonstrated. The homogeneously distributed Pd nanoparticles on N-bridged hybrid mesoporous organosilica showed remarkable activity and selectivity for cyclohexanone compared to the unmodified Pd-SBA-15 catalyst. Control experiments strongly claim the role of nitrogen domains in the organic framework of hybrid silica support in stabilizing small Pd nanoparticles and possibly modifying the Pd sites responsible for catalysis to activate the substrate molecules in water. The hybrid silica catalyst was stable and reused several times without any significant drop-in activity, proving the heterogeneity of the bifunctional Pd catalyst. Based on the density functional theory study and experimental interventions, a possible reaction mechanism for the low-temperature phenol hydrogenation explaining the role of organic domains in the hybrid-silica framework is proposed.

Selective hydrogenation of phenol to cyclohexanone over small amount of Ru-promoted Pd/ZrHP catalysts

Selective hydrogenation of phenol to cyclohexanone is a vital step in the manufacture of fiber (nylon), which is currently carried out over expensive Pd catalyst with low productivity. In this work, a series of Ru-promoted Pd catalysts were synthesized in a facile microwave-assisted method and tested in the hydrogenation of phenol to cyclohexanone. It was found that small amount of Ru in Ru-Pd alloy can increase the conversion of phenol obviously without loss of cyclohexanone selectivity. The selectivity of cyclohexanone over Ru0.15Pd4.85/ZrHP remained higher than 99%, while the conversion of phenol increased from 20.5% (over Pd5/ZrHP) to 97.9% at 100 °C and 1 MPa. And the highest turnover frequency (TOF) of surface metal in Ru0.15Pd4.85/ZrHP at 100 °C and 2 MPa reached 1605 h−1. Characterization results revealed that the addition of Ru can improve the dispersion of Ru-Pd alloy and enhance its electron density. In addition, the activated hydrogen on Ru-Pd alloy and acid sites in ZrHP played a synergistic effect for the selective formation of cyclohexanone from phenol.

Space-Confined Carbon-Doped Pd Nanoparticles as a Highly Efficient Catalyst for Selective Phenol Hydrogenation

Pd-based catalysts have been widely applied in hydrogenation reactions for production of both bulk and fine chemicals; however, selective and efficient hydrogenation of substrates with multiple functional groups is challenging. Here, we synthesize the C-doped Pd NPs confined in the hollow-structured carbons with a closed shell (C-Pd@HCS), a single hole in the shell (C-Pd@HCH), and a bowl-like shell (C-Pd@HCB). Based on the three comparative samples, void-confinement effects in phenol hydrogenation are investigated. It is found that the reaction rate of phenol hydrogenation is always decelerated gradually in the order of C-Pd@HCS > C-Pd@HCH > C-Pd@HCB, regardless of what reaction conditions are applied. The highest rate over C-Pd@HCS should be related to the void-confinement effect induced by its closed space. Moreover, the selectivity toward cyclohexanone over C-Pd@HCS/HCH/HCB is always higher than 95% due to the C-doped Pd NPs (hindering the Pd β-hydride formation and disfavoring the cyclohexanone adsorption as revealed by experimental and theoretical results).

SiO2-supported Pd nanoparticles for highly efficient, selective and stable phenol hydrogenation to cyclohexanone

Cyclohexanone is significant chemical reagent for organic synthesis, so it is key to design and prepare a highly active and environmentally friendly catalyst for the conversion of phenol to cyclohexanone. The results in this work show that the Pd-based supported nanocatalysts (Pd/SiO2) with various Pd contents (Pd/SiO2–1 with 0.16 wt% Pd, Pd/SiO2–2 with 0.26 wt% Pd, Pd/SiO2–3 with 0.52 wt% Pd, Pd/SiO2–4 with 2.60 wt% Pd) have high conversion and selectivity in phenol selective hydrogenation to cyclohexanone under relatively moderate reaction parameters, Pd/SiO2–2 with the highest conversion of 80.6%, selectivity of 92.1% and turnover frequency (TOF) of 1106.1 h−1. This excellent activity is attributed to the highly dispersed Pd nanoparticles (NPs) on silica with high surface area. The Pd/SiO2 catalysts are with high Pd dispersion and strong interaction of Pd-SiO2, which have been proved by XRD, XPS, BET, TEM, HRTEM, STEM, STEM-EDS elemental analysis techniques. The as-prepared materials have good catalytic behaviors in the selective hydrogenation of phenol and good stability, facilitating phenol hydrogenation to cyclohexanone and preventing the excessive hydrogenation of cyclohexanone to cyclohexanol.

Synthesis N-Doped Ni@C-PTA-N-T Catalysts for Highly Selective Hydrogenation of Phenol to Cyclohexanol

Synthesis N-Doped Ni@C-PTA-N-T Catalysts for Highly Selective Hydrogenation of Phenol to Cyclohexanol

Pd-Decorated Hierarchically Porous Carbon Nanofibers for Enhanced Selective Hydrogenation of Phenol

Pd-Decorated Hierarchically Porous Carbon Nanofibers for Enhanced Selective Hydrogenation of Phenol

The critical role of Zr in controlling the activity of Pd/Beta on the hydrogenation of phenol to cyclohexanone

The promoting effect of zirconium addition on Pd/Beta catalysts has been investigated in the selective hydrogenation of phenol to cyclohexanone in the aqueous phase. The activity of the catalyst in the reaction was greatly improved by introducing Zr atoms into the framework of H-Beta zeolite. An important synergy between the Zr species and Pd, affecting the Pd dispersion state on the support, has been observed. The modification of the support with Zr4+ improves the Lewis/Brønsted acid ratio of the catalyst, suppressing the further transformation of cyclohexanone. The kinetics of Pd/Zr-Beta catalyst showed high selectivity to cyclohexanone. The catalytic results showed that the Pd/Zr-Beta had the best catalytic performance at the desired temperature of 80 °C for 5 h.

Metal-acid interface encapsulated in hybrid mesoporous silica for selective hydrogenation of phenol to cyclohexanone

The traditional multi-functional catalytic system is to physically mix each catalyst to meet the multi-step reaction process, so the multi-point synergy is insufficient. Here, we obtained the hybrid mesoporous silica shell by aluminum doping and coated it on Pt particles, showing a synergistic mode between different sites. This strategy realized the shortest geometric contact distance between metal and acid, formed a stable metal-acid interface and enhanced the catalytic efficiency. In the hydrogenation of phenol, Pt@Al-mSiO2 bifunctional catalyst showed 96% selectivity for cyclohexanone. Hybrid silica stabilized the metal-acid interface and showed good stability in application, which was better than general supported catalysts.

Electron-Deficient Pd clusters induced by spontaneous reduction of support defect for selective phenol hydrogenation

A facile and green synthesis route to fabricate the stable and highly-dispersed Pd catalyst was reported by utilizing the reducibility and defect structure of Co3O4. Specifically, nanoshaped Co3O4 with different Co and O vacancies was prepared. Taking these as support, Pd2+ precursors were introduced and preferentially anchored in isolated Co vacancies, confirmed by density functional calculations. Notably, Pd2+ species were reduced by support without any reducing agent. More interestingly, as-obtained Pd catalysts exhibited different product distribution in selective phenol hydrogenation, whereas Pd/hexagonal Co3O4 only generated the cyclohexanol as product, while the cyclohexanone was dominant in rod and commercial Co3O4 supported Pd catalysts. This phenomenon was ascribed to electron-deficient Pd clusters influenced by Co vacancy in hexagonal Co3O4, facilitating further hydrogenation of reaction intermediate rather than desorption. This work provides a feasible way to construct well-distributed and electron-deficient Pd clusters, offering an opportunity to control product distribution in selective hydrogenation.

Light-Irradiated Thermal Energy-Promoted Selective Phenol Hydrogenation on Cellulose-Supported Palladium Catalyst with Green Hydrogen

Light-Irradiated Thermal Energy-Promoted Selective Phenol Hydrogenation on Cellulose-Supported Palladium Catalyst with Green Hydrogen

Nb2O5 promoted Pd/AC catalyst for selective phenol hydrogenation to cyclohexanone

Phenol hydrogenation is a green route to prepare cyclohexanone, an intermediate for the production of nylon 66 and nylon 6. The development of high-performance catalysts still keeps a great challenge. Herein, the activated carbon (AC) was modified with an acidic material Nb2O5 to adjust the microstructure and surface properties of AC, and the influences of the calcination temperature and Nb2O5 content on the catalytic performance of the Pd/AC-Nb2O5 catalysts for the phenol hydrogenation to cyclohexanone were investigated. The Nb2O5 with proper content can be highly uniformly distributed on the AC surface, enhancing the acidity of the Pd/AC-Nb2O5 catalysts with comparable specific surface area and Pd dispersion, thereby improving the catalytic activity. The hybrid Pd/AC-10Nb2O5-500 catalyst exhibits the synergistic effect between the Pd nanoparticles and AC-10Nb2O5, which enhances the catalytic activity for the hydrogenation of phenol. Furthermore, the as-prepared Pd/AC-10Nb2O5-500 catalyst shows good reusability during 7 reaction cycles.