Phenol Conversion Research Articles

A selective alkaline etching strategy to prepare hierarchical Beta molecular sieves for the hydrodeoxygenation of phenol

A selective alkaline etching strategy is reported to prepare hierarchical Beta molecular sieves with cetyltrimethyl ammonium bromide (CTAB). The homogeneityof mesopores is tuned by surface modification of Beta molecular sieves. CTAB selectively interacts with crystal defects and protects primary etched small mesopores from continuous destruction to form large mesopores. Under the synergistic effect of NaOH solution and CTAB, the acidity retention of Beta molecular sieves is higher due to the removal of Si(OSi)4 rather than Si(OSi)3 (OAl) species. When employed as the support of Pt/Beta catalysts, hydroxyl adsorption of phenol on Beta molecular sieves and Pt particles are observed. Dispersion of Pt on the surface of Beta molecular sieves is improved due to the uniform distribution of mesopores. A higher dispersion of Pt attributes to a higher deoxygenation conversion of phenol. The unique contribution of the current research is to propose the role of CTAB in alkaline etching process, realizes the controllable porosity regulation, and alleviates the acidity loss of Beta molecular sieves. These results are important to broaden the application fields of aluminum–silicon molecular sieves especially for large molecules engaged reactions and preparation of supported catalysts with a high metal dispersion.

The synergetic effect of lanthanide (La and Ce) and N co-doping of ZnO NPs for high-rate photocatalytic phenol degradation.

Simultaneously, lanthanide and N-modified ZnO NPs were synthesized and applied for the photocatalytic phenol degradation under LED irradiation. Among La and Ce, Ce-doped ZnO exhibited more efficiently photocatalytic activity. XRD analysis confirmed that most of Ce3+ was oxidized to Ce2O3/CeO2 over the photocatalyst surface as a secondary phase. This is due to the larger ionic radius of Ce3+ relative to that of Zn2+. Ce and N co-doping of ZnO led to narrowing the band gap and suppressing charge recombination rate. The effect of key variables, dopant type, dopant concentration, catalyst loading, initial dye concentration, light source power, solution pH, and H2O2 content on the photocatalytic degradation of phenol was systematically investigated. The utmost conversion of phenol, 100%, was observed by ZnO-Ce5-N0.33 sample under optimum conditions. Kinetics investigation revealed that under the optimum conditions, photodegradation of phenol follows a pseudo-first-order kinetics model with rate constant of 0.0631min-1. Given the fact that the ZnO-Ce5-N0.33 is a heterostructure composed of Zn1-xCexO1-yNy and Ce2O3 and CeO2, a double Z-scheme pattern is suggested as a plausible charge transfer mechanism.

Study on the pyrolysis characteristics of sawdust catalyzed by spent FCC catalyst and blast furnace ash

Two industrial wastes, spent FCC catalyst (sFCCc) and blast furnace ash (BFA), were used as catalysts in the fast pyrolysis of sawdust, and the catalytic pyrolysis reaction characteristics of sawdust in the temperature range of 400–700 °C were explored. The results showed that both catalysts promoted the conversion from liquid products to gaseous products, and the highest gas yield was 52.60% at 700 °C catalyzed by BFA. The sFCCc had stronger deoxygenation activity at 500–600 °C, resulting in higher CO and CO2 production in gaseous products. While BFA had higher polycondensation and dehydrogenation activity at 600–700 °C, and promoted the formation of polycyclic aromatic compounds and H2. Pyrolysis oil was mainly composed of phenols. The sFCCc promoted the conversion of methoxy phenol to benzenediol. FT-IR analysis of pyrolysis oil showed that sFCCc promoted the removal of C–O and C=O, resulting in decreased acid and ester compounds and increased CO2 yield.

Activity enhancement of core–shell Pd@mCeO2 catalysts for phenol hydrogenation to cyclohexanone by tuning metal-support interactions

A core–shell catalyst composed of mCeO2 shell and Pd metal core was prepared by one-pot wet chemical method and used for the hydrogenation of phenol to cyclohexanone. The phenol conversion and cyclohexanone selectivity were 96.3 % and 95.3 % at reaction conditions of 50 min, 80 °C and 1 MPa H2. The effects of Ce species and Br species in the preparation of catalysts was studied, and the synthesis mechanism of core–shell Pd@mCeO2 catalysts was preliminarily revealed. By discussing the phenol adsorption mechanism and the redox properties of the catalyst, the activation of H2 by Pd sites and phenol by cerium oxide (CeO2) sites of the surface were studied. H2-TPR and XPS characterization were used to explain the effect of Ce species and Br species for the catalytic performance. These results indicated that the electronic structure of Pd was regulated by the interaction between Pd and Ce, and different O sites were generated around the Pd sites. In situ IR spectra indicated that phenol was adsorbed and dissociated on cerium to form phenoxy species and water, this synergistic catalytic pattern of carrier activated substrate and hydrogenation site promoted the hydrogenation of phenol and improved the catalytic efficiency.

Hydrodeoxygenation of lignin-derived phenolics to cycloalkanes over Ni–Co alloy coupled with oxophilic NbOx

Hydrodeoxygenation (HDO) of lignin-derived bio-oil is a promising route to produce advanced biofuels. However, the removal of oxygen-containing functional groups with high bond strength in bio-oil challenges the development of efficient, stable, and inexpensive catalysts. In this study, a series of bifunctional catalysts were synthesized by coupling Ni–Co alloy with an oxophilic NbOx support, which was used for the HDO of lignin-derived phenolics to produce cycloalkanes. The Ni–Co alloy formed on the bimetallic catalysts during calcination and reduction was verified by TEM, XPS, and H2-TPR measurements, which showed excellent hydrogenolysis activity. The composition of the Ni–Co alloy was the most uniform with a Ni/Co molar ratio of 1, and the catalyst achieved the highest catalytic activity. The oxygen vacancies provided by the NbOx support also enhanced the adsorption of phenolics and promoted the removal of oxygen-containing functional groups by forming a specific configuration. The synergistic catalysis of Ni–Co alloy and oxygen vacancies achieved complete conversion of guaiacol with a high cycloalkane selectivity of 98.9 % under optimal conditions (300 °C, 3 MPa H2, and 2 h). More importantly, only marginal deactivation occurred on the 5Ni–5Co/NbOx catalyst after 5 cycles and it was also successfully applied to the efficient conversion of other complex lignin-derived phenolics. Therefore, an efficient and economical strategy of coupling the Ni–Co alloy with an oxophilic NbOx support to catalyze the HDO of lignin-derived phenolics to produce cycloalkanes was prospective.

Optimized Ni/Al2O3–SiO2 Catalyst for Steam Reforming of Phenol with Enhanced Hydrogen Production and Stability

Abstract Well-designed Ni/Al2O3–SiO2 catalysts synthesized with nickel as the active metal and alumina–silica as the catalyst mixture support were investigated for steam reforming of phenol with enhanced hydrogen production and stability. The prepared catalysts were characterized using x-ray diffraction, field emission scanning electron microscopy, Brunauer–Emmett–Teller (BET), Fourier transform infrared, hydrogen temperature-programmed reduction, pyridine diffuse reflectance infrared Fourier transform spectroscopy (Py-IR), and thermal gravimetric-differential scanning calorimetry (TG-DSC) techniques in detail. The BET results show that their specific surface areas ranged from 29.832 to 220.330 m2·g–1. The Py-IR results indicate the existence of large Lewis acid regions in the pure C-Ni (“C-Nix-Siy” means the Ni/Al2O3-to-SiO2 catalyst prepared with Ni(CH3COO)2 · 4H2O with SiO2 support mass ratios of y/(x + y).) and C-Ni4-Si1. The effects of the Ni/Al2O3-to-SiO2 mass ratio, reaction temperature, and active metal salt anion species on catalytic activity were studied. The results show that the C-Ni4-Si1 catalyst using nickel acetate tetrahydrate as the active metal salt with an SiO2 mass ratio of 20 wt% achieves a maximum phenol conversion of 97.3 % and hydrogen production of 92.7 % at 550°C. The stability of C-Ni4-Si1 was further investigated, and it was shown to react continuously and stably for more than 800 min at 550°C with excellent catalytic reaction stability. A final weight loss of only 9.31 % shown in the TG-DSC result of the spent C-Ni4-Si1 catalyst confirmed the excellent thermal stability and low coking rate of C-Ni4-Si1.

Thermorubin Biosynthesis Initiated by a Salicylate Synthase Suggests an Unusual Conversion of Phenols to Pyrones.

Thermorubin is a tetracyclic naphthoisocoumarin natural product that demands investigation due to its novel mechanism of bacterial protein synthesis inhibition and its unusual structural features. In this work, we describe the identification of the biosynthetic cluster responsible for thermorubin from the sequenced Laceyella sacchari producer species and its confirmation via heterologous production in Escherichia coli. Based on an in-depth annotation of the cluster, we propose a biosynthetic pathway that accounts for the formation of the unique, nonterminal pyrone. Additionally, the expression and use of salicylate synthase TheO enabled testing of the stability properties of this extremophile-derived enzyme. TheO displayed rapid kinetics and a remarkably robust secondary structure, converting chorismate to salicylate with a KM of 109 ± 12 μM, kcat of 9.17 ± 0.36 min-1, and catalytic efficiency (kcat/KM) of 84 ± 9 nM-1 min-1, and retained significant activity up to 50 °C. These studies serve as the basis for continued biosynthetic investigations and bioinspired synthetic approaches.

Regularities in the Simultaneous Conversion of Phenol and Tetralin During Catalytic Cracking

A phenol–tetralin model mixture was used to investigate the effect of the oxygen-containing compound on the cracking of aromatic hydrocarbon. The analysis of temperature dependences of the cracking rate constant for tetralin and tetralin in a mixture with phenol indicates that the cracking of tetralin is hindered in the case of its simultaneous conversion with the oxygen-containing compound due to higher adsorptivity of phenol on the catalyst surface. It was found that the presence of phenol in the model mixture changes the composition of liquid products, especially at a low cracking temperature. In addition, the effect of water on conversion of the phenol–tetralin mixture was studied. The presence of water in the model feedstock was shown to decrease the hindering of the aromatic hydrocarbon cracking by the oxygencontaining compound. The results of catalytic transformations revealed that the addition of water increased total conversion of the mixture and conversion of tetralin irrespective of temperature. Essential qualitative differences in the distribution of cracking products of the model mixtures containing or not containing water were not found.

Highly efficient conversion of phenol to cyclohexanone on Pd-based catalysts by cobalt doping

Efficient catalysts are still the key to practical industrial applications. In this work, Pd-based catalyst was modified by doping metal Co to obtain Pd-Co@mSiO2 bimetallic core–shell catalyst. The modified bimetallic core–shell catalyst was used in the hydrogenation of phenol, and the catalytic results showed that the Co modification effectively improved the catalytic performance of the Pd-based catalyst, especially, it reduced the activation energy of the reaction and greatly improve the conversion of phenol. Combined with characterization, it was found that Co doping reduced the particle size of Pd metal particles and affected the adsorption capacity of substrate phenol on the surface of Pd metal. The conversion of phenol was close to 99.9 % within 1 h at 80 °C, while the selectivity of cyclohexanone reached 95.4 %. In addition, the core–shell structure provided a stable environment for the catalyst, which still maintained high activity after being recycled for 5 times.

Mechanism of catalytic conversion of kerosene co-refining heavy oil to BTEXN by Py-GC/MS based on “point-line-surface-body” step by step research strategy

Kerosene co-refining heavy oil (KCR-H), KCR-H six group components (KCR-HS), six typical model compounds representing the KCR-HS and its mixed model compound were selected as raw materials. The effects of the physicochemical properties of single and bi-metallic modified HZSM-5 (Me/Z-5) on the selectivity and yield of benzene (B), toluene (T), ethylbenzene (E), xylene (X), naphthalene (N) in cracking products were investigated by pyrolysis–gas chromatograph/mass spectrometer (Py-GC/MS). The results show that Ni-Mo/Z-5 exhibits superior selectivity for light aromatic in the catalytic conversion of tetradecane, benzofuran, and KCR-H, compared with Z-5. Additionally, oxygenated and aliphatic compounds are more easily converted to light aromatics than PAHs and nitrogen-containing compounds. Using Ni-Mo/Z-5 catalytic conversion benzofuran, the selectivity of BTEXN in the cracking product is 65.01 %, which is 23.44 times higher than pyrene (2.66 %). Due to the preferential cracking of benzofuran, small molecular fragments prepared by tetradecane and methyl naphthalene promote the catalytic conversion of methyl phenol, quinoline, and pyrene. Compared with the theoretical BTEXN yield (1338.39 mg/kg), the experimental BTEXN yield obtained from mixed model compounds (MCs) increasing by 37.95 %, which is 1846.40 mg/kg. In addition, the BTEXN selectivity of saturates (Satur) over Ni-Mo/Z-5 is 62.97 %, increases by 12.97 % compared with tetradecane, which represents the components of this group, indicating that the synergistic effect between oxygenated compounds and aliphatic compounds is conducive to produce light aromatics. Furthermore, based on the structural characteristics and catalytic properties of metalmodified Z-5 and the conformational relationships between points, lines, surfaces, and bodies, possible catalytic conversion mechanisms and pathways for KCR-H and KCR-HS were proposed.

Electrocatalytic hydrogenation of phenol by active sites on Pt-decorated shrimp shell biochar catalysts: Performance and internal mechanism

The development of highly-active electrocatalysts and identification of active sites contribution are necessary for electrocatalytic hydrogenation (ECH) of bio-oil. Herein, the Pt-decorated shrimp shell biochar (SSB) catalysts with high nitrogen content was prepared successfully. The biochar-based catalysts were first used for the ECH of bio-oil model compounds. Results showed that the Pt/SSB catalysts exhibited excellent electrocatalytic activity and stability, realizing 100 % conversion of phenol and 98 % total selectivity of cyclohexanone and cyclohexanol within 5 h. By correlation analysis and density functional theory (DFT) calculations, the Pt, Pt-Nx, and CO sites in Pt/SSB catalysts were found to play an important role in the stepwise hydrogenation of phenol. Furthermore, the Pt-Nx sites were identified as the main contributor to the high selectivity of cyclohexanol generation. This study lays the foundation for the controllable preparation of electrocatalysts with high activity and stability, which is significant for large-scale upgrading of bio-oil in the future.

Superhydrophobic Ru Catalyst for Highly Efficient Hydrogenation of Phenol under Mild Aqueous Conditions

Selective hydrogenations of lignin-derived phenolic compounds represent essential processes in the chemical industry, especially for production of a multitude of fine chemicals. However, selective hydrogenation of phenolic compounds in water phase suffers from low conversion. Here we report a catalyst of well-dispersed Ru clusters fixed in N-doped mesoporous hollow carbon spheres (Ru@N-CS) for enhanced cyclohexanol productivity in phenol hydrogenation at mild aqueous condition. This superhydrophobicity carbon spheres appear to selectively allow diffusion of phenol and hydrogen molecules to the electron-rich coordination unsaturated Ru active sites, while confining the reactants there to enhance its reaction probability. The Ru@N-CS catalyst can selectively hydrogenate phenol at 80 °C and 0.5 MPa of H2 in 30 min in aqueous medium with phenol conversions of 100% and ~100% cyclohexanol selectivity, corresponding to cyclohexanol productivity up to 471 per g of Ru per minute. The TOF value is up to 9980 h−1, which 14 times more than Ru nanoparticles supported on N-doped carbon hollow spheres (Ru/N-CS). This work provides an important catalytic system for upgrading of bio-oil into value-added chemicals under mild aqueous-phase.

One-step microwave synthesis of micron-sized ZSM-5/MCM-41 hierarchical porous materials for phenol hydroxyl alkylation

• ZSM-5/MCM-41 hierarchical porous materials are synthesized through a one-step approach. • Microwave irradiation accelerates the formation of the composite zeolites. • ZSM-5/MCM-41 hierarchical porous materials catalytic performance better than pristine ZSM-5. The application of micron-sized zeolites ZSM-5 in industrial complex reaction system, despite of its high crystallization and stability and low price, is limited due to their single microporous structures. This study explores the one-step microwave synthesis of ZSM-5/MCM-41 hierarchical porous materials under low alkaline conditions and with the assistance of microwave, and examines their catalytic performance by the synthesis of anisole with phenol and methanol as probe reaction. The results show that the prepared ZSM-5/MCM-41 layered porous materials exhibit typical characteristics of micro-mesoporous composites. They have higher surface area and pore capacity, and good connectivity between micropores and mesopores, compared with the original ZSM-5. The above-mentioned advantages enable prepared ZSM-5/MCM-41 materials to produce higher phenol conversion, selectivity and catalyst stability of anisole. Through systematic investigations, this study develops a low-cost synthesis method for micron-sized ZSM-5/MCM-41 hierarchical porous materials, which facilitates their industrial application in complex reaction systems.

Cu dispersed ZrO2 catalyst mediated Kolbe- Schmitt carboxylation reaction to 4-hydroxybenzoic acid

The Kolbe-Schmitt reaction is one of the industrially promising route for the production of hydroxybenzoic acids. In the present manuscript, alkali metal hydroxide free, direct carboxylation reaction has been demonstrated over heterogeneous CuO/ZrO2 catalyst. Different basic oxide (ZrO2, TiO2 and Bi2O3) and corresponding Cu dispersed oxides (CuO/ZrO2, CuO/TiO2 and CuO/Bi2O3) were tested for direct carboxylation. The performance of catalysts were elucidated by comparing 4-HBA yield, phenol conversion, TON and TOF. Amongst the tested catalysts, ZrO2 showed highest catalytic activity with TON 0.1022 and TOF 0.0043, hence selected as an efficient catalyst support for Cu dispersion. The lowest value of E-factor (0.12) and PMI (0.39) was obtained for 5 wt% CuO/ZrO2 catalyst. A series of Cu dispersed ZrO2 catalyst were synthesized via simple co-precipitation method with variable Cu precursor loading. Of the tested catalysts 1.25 wt% CuO loaded ZrO2 catalyst showed highest yield (62.57%) and phenol conversion (64.55%) under non-stringent operating condition (60 bar, 170 °C). The in-depth physicochemical characteristion were also conducted by using various analytical tools which dipicted the characterstic properties of CuO/ZrO2 catalyst. The process intensification study was conducted to obtain optimum operating parameters for high yield and conversion. The catalyst recyclability performance study showed the consistency in 4-HBA yield and conversion for four consecutive recycle runs. The plausible reaction mechanism for production of 4-HBA over CuO/ZrO2 catalyst and catalytic cycle has also been proposed. Thus, the present process provides green and efficient route for alkali hydroxide free Kolbe- Schmitt reaction.

Mixed oxidation of chlorophene and 4-tert-butylphenol by ferrate(VI): Reaction kinetics, cross-coupling products and improved utilization efficiency of ferrate(VI)

As two representative phenolic pollutants, chlorophene (CP) and 4-tert-butylphenol (4-tBP) are used in large quantities and could have adverse effects on aquatic organisms and even human health. Due to their co-occurrence in water and wastewater, the oxidative degradation of mixed solution of the two phenols by ferrate (Fe(VI)) was systematically investigated in this work. Compared with the single solution, the kapp values of CP and 4-tBP were increased by 15.7% and 91.9%, respectively in the mixed solution, and the calculated reaction stoichiometric efficiency (RSE) was also improved by more than one time. The reaction intermediates were identified by liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) analysis, from which three possible pathways including direct oxidation, oxygen transfer, ring opening and coupling reaction were proposed for mixed transformation of CP and 4-tBP in Fe(VI) system. The single/double oxygen transfer and single-electron transfer mechanism for the corresponding formation of hydroxylation products and coupling products from CP and 4-tBP were further elucidated by density functional theory (DFT) calculations. Since the cross-coupling reaction was more prone to occur than self-coupling reaction, the addition of another phenol promoted the conversion of the original phenol, leading to the increased kapp values of the two phenols in mixture solution. Finally, the salt bridge experiment also confirmed that the electron transfer between organic pollutants and Fe(VI) was enhanced in mixture solution of phenols. Findings of this study may provide useful information for eliminating co-existing water contaminants by Fe(VI).

MOF-derived NiM@C catalysts (M = Co, Mo, La) for in-situ hydrogenation/hydrodeoxygenation of lignin-derived phenols to cycloalkanes/cyclohexanol

MOF-derived Ni-based bimetallic catalysts were found to be effective for the in-situ hydrogenation/hydrodeoxygenation of lignin-derived monophenols and dimers with isopropanol as the hydrogen-donor solvent (without external hydrogen). The synergistic effects of bimetallic catalysts were studied, and their catalytic properties afforded the best conversion rate of phenols and cyclohexanol/cycloalkane yields. The detailed physicochemical characterization was conducted by means of XRD, H2-TPR, NH3-TPD, and pyridine-IR analysis. The effects of reaction temperature (200–260 ℃) and reaction time (2–5 h) on the performance of lignin-derived monophenols and dimers were investigated. During the in-situ hydrogenation/hydrodeoxygenation of lignin-derived phenols, the steric effects and the effects of various functional groups, notably methoxy groups, were investigated. In-situ conversion of lignin-derived phenols with isopropanol was achieved over different Ni/M ratios of NiM@C (M = Co, Mo, and La) catalysts, from which NiLa0.33@C produced satisfactory yields of cyclohexanol/cycloalkanes.

Hydrothermal gasification of phenol with Ru added carbon-metal oxide composite-supported Ni catalysts prepared by sol-gel method

Ru promotion effect on carbon-metal oxide composite-supported Ni catalysts were tested for hydrothermal gasification of phenol in aqueous phase as a model process of wastewater treatment. The catalysts were prepared by the combination of aluminum, titanium and zirconium alkoxide, and polyethylene glycol as an organic template, with the addition of active metals, nickel nitrate hexahydrate and ruthenium chloride. In the hydrothermal gasification at 350 °C, pressure 20 MPa and phenol concentration in water 20 g/L, the effect of the addition of Ru to Ni/C/oxide was observed and the conversion of phenol increased. When the effect of metal oxide was compared at 5 wt% of Ru and 16 wt% of Ni contents, the conversion of phenol increased in the order ZrO2 < Al2O3 < TiO2. The activity of Al2O3 -supported catalysts increased with increasing Ru content while that of TiO2 -supported catalysts did not change with the Ru content.

Partial deoxygenation of pyrolysis intermediates toward fossil fuel miscible bioliquids

AbstractCatalytic fast pyrolysis of sunflower seed shells was performed using a two‐stage fixed bed reactor to produce partially deoxygenated bio‐oils. Ketonization and aldol condensation reactions were performed in a dual bed reactor using a CeO2 catalyst followed by a bifunctional Cu/Ni/ZrO2 catalyst. An ethanol‐saturated N2 stream was supplied to increase the H/C ratio of the pyrolysis intermediates. The oxygen content decreased from 23 to 13 wt % over the CeO2 fixed‐bed due to the almost complete conversion of methoxy phenols and the formation of ketones and alkyl‐substituted phenols. The Cu/Ni/ZrO2 catalyst in the presence of ethanol vapor increased the fraction of alkanes in the condensed product and favored the formation of larger ketones and higher molecular weight species. Miscibility tests showed that the partially upgraded bio‐oil could be homogeneously blended with fossil fuel oil in a 1:4 mass ratio. The oily fraction of the non‐catalytic pyrolysis bioliquid (oxygen content up to 23 wt %) was also partially miscible with the petroleum‐derived fuel.

Palladium-catalyzed allylic etherification of phenols with vinyl ethylene carbonate.

The palladium-catalyzed decarboxylative reactions of phenols and vinyl ethylene carbonate to produce allylic aryl ethers under mild conditions have been established. Adopting an inexpensive PdCl2(dppf) catalyst promotes the efficient conversion of phenols to the corresponding allylic aryl ethers via the formation of a new C-O bond in good isolated yields with complete regioselectivities, acceptable functional group tolerance and operational simplicity. The robust procedure could be completed smoothly by conducting a scaled-up reaction with comparable efficiency to afford the target product.

Energy optimization of wet air oxidation reactors with sub-millimeter bubble intensification

The huge investment in equipment and energy consumption required for wet air oxidation (WAO) severely limits its industrial application due to harsh operating conditions with high temperatures and pressures. In this work, the energy consumption of phenol WAO was calculated considering gas compression, pumping, preheating and bubble generation. The relationship between energy consumption, bubble diameter and phenol conversion was constructed to evaluate the main influencing factors. It was found that sub-millimeter bubbles can effectively improve the WAO process by enhancing the oxygen mass transfer, resulting in a decrease in operating temperature and pressure. Considering the maximum conversion and minimum cost, the initial air bubble diameter for phenolic WAO is preferably between 0.2 ∼ 0.4 mm. The model was validated using experiments with a WAO reactor dominated by sub-millimeter air bubble, and good agreement was obtained between simulated results and plant data.