Phenol Selectivity Research Articles

Photo-switchable imprinted adsorbent towards a selective phenol recovery from wastewater

• Synthesis of wettability UV switchable adsorbent for a selective phenol adsorption. • Synergy of photosensitive TiO 2 with hydrophobic crosslinker to reverse wettability. • Extremely high phenol adsorption capacity of 8.24 mg-phenol/m 2 -adsorbent. • Easy recovery of 98% phenol from the saturated adsorbent. • Robust regeneration performance of the adsorbent upon cyclic testing. Here we report the design and synthesis of a novel surface imprinted adsorbent, with an UV-switchable wettability towards an efficient and highly selective phenol recovery from wastewater. The high selectivity of phenol is achieved through surface molecularly imprinted cavities featuring a smart phenol identification function, whilst the UV-switchable wettability is accomplished by the co-loading of nano-sized, photosensitive TiO 2 and hydrophobic 3-(trimethoxysilyl) propyl methacrylate imprinted layer. Through numerous adsorption experiments and extensive characterizations including FESEM, TEM, FT-IR, BET, XRD, XPS, and synchrotron NEXAFS, it is confirmed that upon a prior 0.5 h - long UV irradiation, the imprinted surface of the as-synthesized adsorbent can be switched from hydrophobic to hydrophilic, which in turn results in an equilibrated adsorption capacity of 8.24 mg-phenol/m 2 -adsorbent that are superior over all the reported values. More intriguingly, with the progress of the adsorption in the dark, the surface of the adsorbent can be gradually reversed to hydrophobic. This in turn enhances the repulsion of particles from the aqueous phase, leading to a quick self-agglomeration and precipitation of the spent adsorbent for an easy recovery. Moreover, 98% of the adsorbed phenol can be recovered via a subsequent washing by methanol, and the regenerated adsorbent is also confirmed to exhibit a nearly stable adsorption capacity upon five cycles.

Production of renewable phenols from corn cob using catalytic pyrolysis over self-derived activated carbons prepared with torrefaction pretreatment and chemical activation

The present work unveiled that the combination of chemical activation and torrefaction pretreatment was a promising approach for improving catalytic performance of activated carbon (AC) during conversion of corn cob into phenols. The characterization results demonstrated that P-containing functional groups (bands between 1000 and 1200 cm−1) were imbedded into AC samples successfully. The increase in acid concentration and carbonization temperature could improve the porosity of as-prepared ACs. GC/MS results revealed that the selectivity of phenols was boosted (from 19.0% to 79.3%) during pyrolysis of corn cob over torrefaction pretreated AC catalyst. The high carbonization temperature (from 369 °C to 581 °C) and H3PO4 concentration (from 26.7% to 83.3%) favored the selectivity of phenols attained. The optimal condition for phenols selectivity (79.3%) was achieved at a carbonization temperature of 550 °C with H3PO4 concentration of 75%. The current study may provide an efficient pathway of converting agriculture waste corn cob into AC catalyst and phenols-enriched bio-oil, simultaneously, which will advance the utilization of renewable agriculture biomass.

Comparative study on the two-step and one-step pyrolysis of lignin: effects of pyrolysis temperature and residence time on the product distribution

To explore a new way of utilizing lignin and deepen the understanding of mechanism of two-step pyrolysis (TSP) of biomass, the effects of the first step pyrolysis temperature (T1) and residence time (RT1) on TSP of lignin were studied by using pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). TSP of lignin was also compared with one-step pyrolysis (OSP) of lignin. The results indicated that higher pyrolysis temperature promoted the break of ether linkage among the structural elements of lignin and the removal of side chains. With T1 increasing, the contents of monophenols (MPs), catechols (CPs), monocyclic aromatic hydrocarbons (MAHs), and polycyclic aromatic hydrocarbons (PAHs) increased in the first step, while the contents of methoxyphenols with double bond in the side-chain (MPBSs) and methoxyphenols with no double bond in the side-chain (MPSs) increased firstly and then decreased. In the second step, with T1 increasing the contents of MPs and CPs increased firstly and then decreased, the contents of MAHs and PAHs increased significantly, and the contents of MPBSs and MPSs decreased. Higher T1 increased the yields of the most identified compounds of the first step, but decreased the yields of MPs, CPs, MPBSs, and MPSs in the second step. RT1 had great effects on the pyrolysis behaviors and product distribution of TSP of lignin, and the content of MAHs and PAHs in the second step increased significantly with RT1 increasing. Compared with OSP, the yields of MAHs and PAHs could increase in the second step. TSP of lignin could improve the selectivity of value-added chemicals remarkably, such as guaiacol, vanillin, acetovanillone in the first step, and the selectivity of benzene, toluene, m-xylene, phenol, o-cresol, and p-cresol in the second step.

Ex-situ catalytic upgrading of corncob pyrolysis vapors into furans and phenols over Pt-Re/AC: Effect of Pt/Re ratio and process parameter

In order to improve the quality of bio-oils, catalytic fast pyrolysis of corncob over Pt/Re supported activated carbon (AC) catalysts was conducted to produce bio-furans and bio-phenols. The effect of Pt/Re ratio on the catalytic pyrolysis performance was evaluated. Pt and Re are uniformly dispersed on AC, but it results in the decrease of specific surface area. In addition, the amount of weak acidic sites increased and higher total weak acidity of Pt-Re/AC was contributed to the production of target products at low catalytic upgrading temperature. AC and Pt/AC inhibited the formation of phenols, and Re/AC and Pt-Re/AC promoted the formation of phenols. The relative peak area of furans over 1Pt-3Re/AC and Re/AC is 44.36 % and 41.98 %, respectively. Pt-Re/AC catalysts have a high selectivity for methylfurans (MFs) and phenol (P), remaining at 19 % ∼ 33 % and 17 % ∼ 21 %, respectively. Finally, 1Pt-3Re/AC showed good reuse performance.

O-Methylation of Phenol for High Selective Synthesis of Anisole over Calcium Oxide Catalyst

In this article, a CaO-based catalyst was prepared by impregnating potassium salt on CaO to develop a highly efficient heterogeneous catalyst for highly selective synthesis of anisole (AN) from phenol and dimethyl carbonate by a O-methylation. KF/CaO catalysts are highly active and selective towards formation of anisole via methylation of phenol with the highest yield of 97.48% AN was obtained at 200°C. Various reaction parameters including KF loading, the amount of catalyst and the calcination temperature on the catalytic activity were investigated. Scanning electron microscopy (SEM), X-ray diffraction (XRD), BET, CO2‑TPD and thermogravimetric (TG) were used to characterize the prepared catalyst. It was found that the high catalytic activity of CaO after modification with KF is associated with the structural aspects and the amount of basicity of the catalyst. Temperature programmed desorption of CO2 and XRD studies revealed the K2O species, a strong basic site formed by the substitution of the Ca2+ in CaO lattice by K+, might have great contribution for the high conversion of phenol and good selectivity of anisole.

Production of phenolic compounds in catalytic pyrolysis of bagasse lignin in the presence of Ca0.5Pr0.5FeO3

Herein, sodium dodecylbenzene sulfonate (SDBS) was used as a template to control the synthesis of Ca0.5Pr0.5FeO3. Its microstructure, composition, and morphology were detected via X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The properties of catalyzing bagasse lignin (BL) pyrolysis were determined by thermogravimetric analysis (TG) test and evaluation of a fixed bed alumina microreactor. The results show that the sample Ca0.5Pr0.5FeO3 regulated by SDBS has a cubic crystal phase, and the addition of SDBS does not cause phase transition. Moreover, when the SDBS concentration is 0.10 mol/L, the particle size is 200–500 nm and the specific surface area is 11.26 m2/g. The yields of gas, liquid, and solid products in the BL catalytic pyrolysis are 39.58 wt%, 26.76 wt% and 32.36 wt%, respectively. The contents of CO2 and CO decrease from 54.07% and 4.98% to 45.29% and 3.23%, respectively. The liquid products are mainly guaiacol, syringol, and phenol, and the total selectivity of phenols is 83.67%, accompanied by a small amount of non-aromatic oxygen-containing compounds (five-membered ring (furan) or ester). Compared with the BL pyrolysis and Ca0.5Pr0.5FeO3 catalytic pyrolysis products, the selectivity of guaiacol compounds increases by 43.26%, while those of syringol compounds and phenylketones decrease by 30.08% and 3.39%, respectively. The selectivity of 2,6-dimethoxyphenol is 28.37%. After five catalytic pyrolysis-regeneration cycles, the characteristic peaks of the catalyst do not change significantly and the particles are uniform, suggesting that the catalyst has good crystal phase stability and regeneration stability.

Kraft Lignin Ethanolysis over Zeolites with Different Acidity and Pore Structures for Aromatics Production

To utilize its rich aromatics, lignin, a high-volume waste and environmental hazard, was depolymerized in supercritical ethanol over various zeolites types with different acidity and pore structures. Targeting at high yield/selectivity of aromatics such as phenols, microporous Beta, Y, and ZSM-5 zeolites were first examined in lignin ethanolysis, followed by zeolites with similar micropore size but different acidity. Further comparisons were made between zeolites with fin-like and worm-like mesoporous structures and their microporous counterparts. Despite depolymerization complexity and diversified ethanolysis products, strong acidity was found effective to cleave both C–O–C and C–C linkages of lignin while mild acidity works mainly in ether bond breakdown. However, when diffusion of gigantic molecules is severe, pore size, particularly mesopores, becomes more decisive on phenol selectivity. These findings provide important guidelines on future selection and design of zeolites with appropriate acidity and pore structure to promote lignin ethanolysis or other hydrocarbon cracking processes.

Chlorine-Modified Ru/TiO2 Catalyst for Selective Guaiacol Hydrodeoxygenation

The selective hydrodeoxygenation of lignin-derived guaiacol to value-added products, especially phenol, under relatively mild reaction conditions remains an important challenge. A Cl-modified Ru/TiO₂ catalyst exhibited higher phenol selectivity compared with an unmodified one in the conversion of guaiacol in 1,4-dioxane at 240 °C and 1 MPa H₂. Unlike Ru/TiO₂, the modified catalyst exhibited a modest activity of demethoxylation producing phenol but an inferior ability of hydrogenation of its aromatic ring, resulting in much slower consumption of phenol. The Cl species were likely localized at the metal–support interface and on the surface of metal particles, and these modified both Ru and Ti species electronically. It is presumed that electron-enriched Ru inhibits the ring hydrogenation reaction, and the defects on the TiO₂ surface promote the deoxygenation reaction.

Synergy of carbon defect and transition metal on tungsten carbides for boosting the selective cleavage of aryl ether C[sbnd]O bond

Transition-metal carbides are attractive heterogeneous catalysts for the transformation of lignin-derived compounds. However, the effects of the surface carbon defect (C-defect) remain unclear due to coke deposition and exposed C terminations. Herein, we transform inert tungsten carbides (WC) into active catalysts via surficial C-etching using transition metals in the presence of H2. An optimized 1% Pt–WC catalyst with synergy of Pt and C-defects can perform a 78.6% conversion in the selective hydrogenolysis of guaiacol to phenol with 89.0% selectivity at 300 °C, while the intact WC only gives a 7.1% guaiacol conversion with 51.0% phenol selectivity under the same conditions. As a result, the 1% Pt–WC catalyst exhibits 19-fold higher reaction rate and 12.6-fold higher turnover frequency than those of WC. Moreover, no substantial loss of catalytic performance has been observed with 1% Pt–WC for 50 h on stream. A rational reaction pathway is accordingly proposed through in-depth characterizations.

Study on Adsorption Performance of Lignite Activated Carbon for Coal Gasification Wastewater

In order to ensure the excellent adsorption performance, this paper choosed lignite activated carbon to study the adsorption performance of typical pollutants phenol, indole and quinoline in coal gasification wastewater, and analyzed its adsorption performance under single matrix and co-substrate conditions. The experimental results showed that among the three kinds of organic substances, lignite activated coke has the strongest adsorption capacity for phenol, while the adsorption capacity for quinoline was relatively low. Under mixed matrix conditions, activated coke has strong adsorption selectivity for phenol and indole.

New Insights for the Future Design of Composites Composed of Hydrochar and Zeolite for Developing Advanced Biofuels from Cranberry Pomace

This study provides fundamental insight and offers a promising catalytic hydrothermal method to harness cranberry pomace as a potential bioenergy and/or hydrochar source. The physical and chemical properties of Canadian cranberry pomace, supplied by Fruit d’Or Inc., were examined and the optimum operational conditions, in terms of biocrude yield, were obtained by the I-optimal matrix of Design Expert 11. Afterward, cranberry pomace hydrochar (CPH) and zeolite were separately introduced to the hydrothermal liquefaction (HTL) process to investigate the benefits and disadvantages associated with their catalytic activity. CPH was found to be a better host than zeolite to accommodate cellulosic sugars and showed great catalytic performance in producing hydrocarbons. However, high amounts of corrosive amino and aliphatic acids hinder the practical application of CPH as a catalyst. Alternatively, zeolite, as a commercial high surface area catalyst, had a higher activity for deoxygenation of compounds containing carbonyl, carboxyl, and hydroxyl groups than CPH and resulted in higher selectivity of phenols. Due to the low hydrothermal structural stability, coke formation, and narrow pore size distribution, further activations and modifications are needed to improve the catalytic behavior of zeolite. Our results suggest that a composite composed of CPH and zeolite can resolve the abovementioned limitations and help with the development and commercialization of advanced biofuels from cranberry pomace.

Phenol-derived products from fast pyrolysis of organosolv lignin

Lignin is the largest aromatic bio-polymer feedstock with a huge potential of being refined for aromatic chemical platform and building block. Organosolv process for lignin extraction has a low impact on the environment due to its low chemical requirement, the absence of sulfur, and as it is more practical for chemical recovery. Therefore, refinement of extracted lignin to valuable molecular compounds such as purified lignin and its derivative is the key success for biorefinery industry. In this study, sugarcane bagasse from a local sugar manufacturer in Thailand, noted as BG-lignin, was selected as feedstock for lignin extraction using ethanol and water. The chemical composition of this lignin was slightly different than that of commercially available organosolv lignin, noted as Comm-OS-lignin, in that BG-lignin has more combustible constituents (volatile organic compounds and fixed carbon) of 96.14% and low ash content of 0.09%. The chemical structure of BG-lignin contains a higher number of aliphatic hydrocarbon and aliphatic hydroxy side chains than Comm-OS-lignin, as confirmed by the FT-IR and 1H-NMR analyses. The study on fast pyrolysis of lignin, using Py-GCMS technique, found 2, 3-dihydrobenzofuran as a major constituent at any tested pyrolysis temperature. H-unit, G-unit, and S-unit are distributed in resemble fraction with a H∕G∕S ratio of 1∕1∕0.7 and 0.8∕1∕1 for Comm-OS-lignin and BG-lignin, respectively, at pyrolysis temperature of 400–600 °C, except for H-unit which was enhanced at 700 °C to 28.82% of Comm-OS-lignin and 29.66% of BG-lignin. At a temperature of 400–600 °C, phenolic selectivity of pyrolyzed products, mainly methoxy phenol (Ph-OCH3) and alkylated phenol (R-Ph-OCH3), was done. A higher pyrolysis temperature of 700 °C led to the elimination of aromatic side group and is more favorable in alkyl phenol (R-Ph) and phenol selectivity. However, reduction of the phenolic compound was observed with a higher temperature due to thermal fragmentation of the C–C linkage in the aromatic structure. Products selectivity related to lignin feedstock and pyrolysis temperature could be applied as a conceptual guideline for conducting further study of chemical upgrading process to obtain high-value biochemical products.

Enhancing the pervaporation performance of PEBA/PVDF membrane by incorporating MAF-6 for the separation of phenol from its aqueous solution

Phenol is highly toxic and carcinogenic even at low concentrations. This study focused on preparing high-performance mixed matrix membranes (MMMs) for the pervaporation separation of phenol from its aqueous solution. A highly-efficient zeolitic metal azolate framework, RHO-[Zn(Heim)2] (MAF-6, Heim = 2-ethylimidazole) was incorporated into the polyether block amide (PEBA-2533) supported on the polyvinylidene fluoride (PVDF) ultrafiltration membrane. The MAF-6 was chosen as the filler due to its inherent hydrophobic surfaces and aperture size (7.6 Å), which is larger than the molecular kinetic diameter of phenol (6.6 Å). Effects of the casting solution concentration, active layer thickness, MAF-6 loading, operating temperature, and phenol concentration were systematically investigated. With the increase of the MAF-6 loading ratio X from 0 to 7, the phenol flux of the membrane was gradually enhanced, but the water flux was reduced. For 1000 ppm phenol aqueous solution at 80 °C, MAF-6–7@MMM displayed the optimal separation factor of 25.9 with a phenol flux of 89.2 g∙m−2∙h−1. The pervaporation separation index (PSI) of the MAF-6–7@MMM was 1317.7 kg∙µm∙m−2∙h−1 at 80 °C, which was much higher than the PEBA/PVDF membrane (787 kg∙µm∙m−2∙h−1). Impressively, an increasing feed temperature enhanced the phenol flux more prominently than water, owing to the hydrophobicity and porosity of MAF-6. Consequently, the resultant MAF-6-X@MMMs broke the trade-off limitation between phenol permeability and selectivity. The as-prepared membrane also exhibited exceptional long-term stability, suggesting its prospect of industrial application.

High-grade bio-oil produced from coconut shell: A comparative study of microwave reactor and core-shell catalyst

The quality of bio-oil can be improved by conducting biomass pyrolysis either over a core-shell hierarchical zeolite catalyst or in a microwave reactor. However, there is a lack of comparative studies on the individual effects of each factor (e.g., catalysts, reactors) on bio-oil production. In this regard, the catalytic pyrolysis of coconut shell in a fixed-bed reactor and in a microwave reactor using the conventional ZSM-5 and core-shell hierarchical ZSM-5@SBA-15 catalysts was evaluated. With an emphasize on the production of hydrocarbons and phenols, the comparative effect of the core-shell catalyst and microwave reactor was demonstrated. The core-shell catalyst had the dual effect of regulating the bio-oil yield and composition. Compared to conventional ZSM-5 (25) with a SiO2/Al2O3 ratio of 25, the core-shell ZSM-5 (25)@SBA-15 not only increased the bio-oil yield by at least 40%, but also approximately doubled the production of hydrocarbons, irrespective of the reactor type. In contrast, the microwave reactor played a greater role in regulating the bio-oil composition. Irrespective of the catalyst used, the fixed-bed reactor tended to generate phenolic-rich bio-oil, while the microwave reactor sharply reduced the phenol selectivity by at least doubling that for aromatics.

Low‐Temperature Catalytic Hydrogenolysis of Guaiacol to Phenol over Al‐Doped SBA‐15 Supported Ni Catalysts

AbstractSelective hydrogenolysis of aromatic carbon‐oxygen (Caryl−O) bonds is a key strategy for the generation of aromatic chemicals from lignin. However, this process is usually operated at high temperatures and pressures over hydrogenation catalysts, resulting in a low selectivity for aromatics and an extra consumption of hydrogen. Here, a series of Al‐doped SBA‐15 mesoporous materials with different Si/Al molar ratios (Al‐SBA‐15) were prepared via a post‐synthesis method using NaAlO2 as the Al source, and then Al‐SBA‐15 supported Ni catalysts (Ni/Al‐SBA‐15) were prepared by a deposition‐precipitation method using urea as the hydrolysis reagent. The prepared supports and catalysts were extensively characterized using various techniques such as XRD, N2 adsorption/desorption, TEM, 27Al NMR, NH3‐TPD, XPS, H2‐TPR, and pyridine‐FT‐IR, and the catalysts were evaluated in the hydrogenolysis of the Caryl−O bond in guaiacol and lignin derived compounds under mild conditions. The effects of the Si/Al ratio in catalyst and reaction parameters on guaiacol conversion and product distribution were investigated in detail, associated with solvent effect. The incorporation of Al into the framework of SBA‐15 can improve the Lewis acidity and the dispersion of the supported Ni particles and yet modulate the metal‐support interactions, which are propitious to the hydrogenolysis of the Caryl−O bond in guaiacol. The catalyst Ni/Al‐SBA‐15 with a Si/Al molar ratio of 10 shows the best performance with a guaiacol conversion of 87.4 % and a phenol selectivity of 76.9 % under the mild conditions conducted, because of its proper acidity, suitable metal‐support interactions, and high dispersion of the active species. The present study would stimulate research and development in multi‐functional catalysts for the generation of valuable chemicals from biomass.

Effects of mesopore introduction on the stability of zeolites for 4-iso-Propylphenol dealkylation

Low rank coal- and biomass-derived liquids generally contain a mixture of alkylphenols, which can be dealkylated over zeolites into phenol as a basic chemical. Zeolites with different pore structures were evaluated for the dealkylation of 4-iso-propylphenol as a model alkylphenol, among which HZSM-5 and HMCM-22 displayed the highest phenol selectivity above 96 %. However, HZSM-5 deactivated fastest among the catalysts due to coke deposition. Thus, mesopores were introduced by desilication into HZSM-5 catalysts to improve the catalytic stability. The mesopore incorporation enhanced the connectivity of the micropores with the crystal surface, and shortened the diffusion lengths. Coke location analysis revealed that micropore occlusion by the coke shell occurred on the parent HZSM-5, whereas the acid sites in the desilicated catalysts were more accessible for fully utilization, even though the coke mainly deposited in the micropores. Furthermore, the coke on the desilicated HZSM-5 displayed a lower graphitization degree.

Effects of operating parameters on products yield and volatiles composition during fast pyrolysis of food waste in the presence of hydrogen

Recently, the resource utilization of food waste is receiving more attention by government and scholars. In this investigation, the high-temperature fast pyrolysis in the presence of hydrogen of food waste carried out by the laboratory-scale downdraft tube reactor, to explore the impact of operating parameters including pyrolysis temperature (700–900 °C), carrier gas flow rate (100–250 mL min−1) and hydrogen content (0–15%). The products yields were calculated based on experimental results, it can be found that the yield of gas, bio-oil and bio-char under Run 6 (900 °C, 100 mL min−1 and 10% hydrogen) were 63.01%, 5.02% and 31.97%, respectively. The gas composition in volatiles at different conditions was detected by Gas Chromatograph, which can be inferred that increasing the pyrolysis temperature, shortening the carrier gas flow rate and improving the hydrogen content were beneficial to improve the gaseous product yield, quality and heating value. In the presence of hydrogen, the molar content of H2 and CH4 in gas increased significantly. Moreover, the bio-oil composition was analyzed by Gas Chromatograph/Mass Spectrometry, and the effect of operating parameters on product species and typical compounds were also explored in this investigation. The results showed that hydrogen can inhibit the formation of nitrogen-containing heterocycles and improve the selectivity of phenols in bio-oil during pyrolysis. It can be found that food waste pyrolysis in the presence of hydrogen can improve products yield and quality under the proper operating conditions.

Selective hydrogenolysis of C[sbnd]O bonds in benzyloxybenzene and dealkaline lignin to valuable aromatics over Ni/TiN

Lignin is an important sustainable feedstock for producing valuable aromatics, which can be achieved by catalytic hydrogenolysis over suitable heterogeneous catalysts. Herein, Ni/TiN catalysts with different Ni loadings (5%–30%) were prepared by an incipient-wetness impregnation method. The effects of Ni loadings, reaction temperature, H2 pressure, and time on hydrogenolysis of benzyloxybenzene (BOB) were investigated. The results showed that Ni/TiN presented high active for selective hydrogenolysis of CO bond in BOB to produce aromatics. The BOB conversion reached up to 100% with high selectivity of toluene (64%) and phenol (60%) over Ni10%/TiN under the optimal reaction conditions (250 °C, 1 MPa H2, and 3 h). Ni10%/TiN showed good stability and reusability with slight decrease in BOB conversion and selectivity of toluene and phenol after five runs. The morphological characteristics of the reused Ni10%/TiN remained almost unchanged. Additionally, Ni10%/TiN showed good catalytic activity in cleaving CO bridged bonds in dealkaline lignin to produce aromatics with high selectivity. Phenols are the major aromatics with the highest relative content of 60.6% obtained at 300 °C under catalytic conditions, among which guaiacols are predominant. Possible mechanisms for hydrogenolysis of BOB and dealkaline lignin were discussed according to the product distributions.

Direct Synthesis of Phenols from Phenylboronic Acids in Aqueous Media Catalyzed by a Cu(0)‐Nanoparticles Biohybrid

AbstractSelective hydroxylation of different phenylboronic acids to phenols was successfully carried out by using Cu nanoparticles‐enzyme hybrid catalysts in water and room temperature. Different Cu‐enzyme hybrids containing Cu(II), Cu(I) and Cu(0) nanoparticles species respectively were tested on the monohydroxylation of phenylboronic acid under these mild conditions being hybrids containing Cu(0)NPs the best catalysts, with total selectivity and formation of phenol as unique product. Also, the addition of hydrogen peroxide or the increase of reaction temperature were tested but did not improved these results. The substrate scope was also demonstrated and the Cu(0)NPs hybrid showed excellent results in the monohydroxylation of different o‐, m‐, p‐substituted phenylboronic acid with final yields >95 %. This catalyst showed excellent recyclability after 5 cycles of use.

Synthesis of iron nanoparticles-based hydrochar catalyst for ex-situ catalytic microwave-assisted pyrolysis of lignocellulosic biomass to renewable phenols

Selective production of phenols via ex-situ catalytic pyrolysis of lignocellulosic biomass is a promising route in biomass conversion. Therefore, developing a low-cost and effective catalyst for this process has emerged as an important topic. Here, the iron nanoparticles-based carbonaceous catalysts were prepared via combining hydrothermal carbonization and pyrolysis approach and first used in the catalytic microwave-assisted pyrolysis of torrefied corn cob for phenols production. The effects of catalyst types, catalytic temperature, and catalyst to feedstock ratio on the production of phenolic compounds were studied. The total selectivity of phenols can reach 91.07 area% with the total yield of 18706.6 µg/ml bio-oil using the FeHC@ hydrochar catalyst (prepared by hydrothermal carbonization in the Fe(NO3)3 solution and pyrolysis) at the catalytic temperature of 450 °C and catalyst to feedstock ratio of 5:10. After using seven times, partial loss of catalytic activity of FeHC@hydrochar was found. This study also presented unique insights into the deactivation of carbonaceous catalysts, showing that sintering, oxidation of α-Fe and Fe3C phases, active site coverage, and pore blockage were the causes of the reduction of catalytic performance. Regeneration experiments showed that it is impracticable to calcine deactivated catalyst at an inert atmosphere and more advanced techniques needed to be developed to solve this problem. Overall, this study can provide a reference for realistic scale-up production of renewable phenols.