Selective hydrogenolysis of 5-hydroxymethylfurfural to 2,5-dimethylfuran with high yield over bimetallic Ru-Co/AC catalysts.

Catalytic hydrogenolysis of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) has become a hot topic in the bioenergy field in recent years. It remains a challenge to mediate the activation/hydrogenation/hydrogenolysis of C-O and C[double bond, length as m-dash]O bonds of HMF at high temperatures. Herein, bimetallic Ru-Co/AC catalysts were prepared by the "two-step" reduction method and were used to catalyze the hydrogenolysis of HMF to DMF. The effects of different reduction methods, Ru/Co ratios, and Ru loading on the catalytic performances of the Ru-Co/AC catalysts were investigated, and the physicochemical properties of the catalysts were characterized by TEM, XPS, H2-TPR, etc. It was found that the catalysts reduced by the "two-step" reduction method exhibited better catalytic activities than those fabricated by a single H2 or NaBH4 reduction method. The introduction of Co metals promoted the dispersion of Ru nanoparticles (NPs) on AC and the transfer of electrons from Co to Ru, thereby improving the catalytic activity. An excellent yield of DMF up to 97.9% and 98.7% conversion of HMF were achieved in a short time (1.5 h) under the optimal conditions (200 °C, 1 MPa). Furthermore, the possible reaction pathway for the hydrogenolysis of HMF to DMF over 5%Ru-1%Co/AC catalyst is also discussed. The work shows that the Ru-Co/AC catalysts have great potentials for the conversion of HMF into liquid fuel DMF.

Toluene oxidation removal from air over CoxOy/AC catalyst.

The CoxOy/AC catalysts were prepared by wet impregnation method for toluene oxidation removal from air. The thermal stability of cobalt nitrate and Co oxide on the activated carbon (AC) support surface was analysed by thermal analysis. The physicochemical properties of the prepared catalysts were characterised by XRD, SEM, H2-TPR, and XPS. AC support with high specific surface area and developed pore structure can promote the dispersion of Co species on its surface to form highly dispersed Co oxide species. The participation of AC supports can promote the partial reduction of Co3O4 species to CoO species to coexist in the prepared CoxOy/AC catalyst. The Co2+/Co3+ ratio was significantly affected by the calcination temperature, and the appropriate Co2+/Co3+ ion pairs in the studied CoxOy/AC catalyst is helpful to the activity of O2 molecules to form reactive oxygen species. The oxygen species composition on the catalyst surface is obviously affected by the calcination temperature, which plays an important role in toluene oxidation reaction. The studied CoxOy/AC catalysts exhibited excellent toluene oxidation removal performances. The conversion of toluene exceeded 97% and 99% at 240°C and 250°C, respectively, and maintained good stability within 700 min. That is to say, the concentration of toluene in the air can be reduced from 10,000 ppm to less than 40 ppm by using the CoxOy/AC catalyst.

Catalytic Pyrolysis of Nonedible Oils for the Production of Renewable Aromatics Using Metal-Modified HZSM-5 Catalysts.

Catalytic pyrolysis of triglycerides to aromatics over zeolites is an advanced technology for a high value-added utilization of renewable biomass resources. Therefore, in this research, the catalytic performance of M/HZSM-5 catalysts (M = Zn, Ga, In, Ni, and Mo) during the pyrolysis process of glycerol trioleate and the effect of the compositional difference of several woody oils and waste oils on aromatic formation were investigated. Results revealed that Zn/HZSM-5 with appropriate acidity and metal sites reached the maximum aromatics yield (56.13%) and significantly enhanced the catalytic stability. In addition, these renewable nonedible oils were effectively converted to aromatics over the Zn/HZSM-5 catalyst, the aromatic yield of jatropha oil reached up to 50.33%, and the unsaturation and double bond number of feedstocks were crucial for the production of aromatics. The utilization of biomass resources to produce high value-added aromatics can alleviate the problems caused by the shortage of fossil resources and achieve sustainable green development.

Recent Advances in the Catalytic Conversion of Biomass to Furfural in Deep Eutectic Solvents.

Lignocellulose is recognized as an ideal raw material for biorefinery as it may be converted into biofuels and value-added products through a series of chemical routes. Furfural, a bio-based platform chemical generated from lignocellulosic biomass, has been identified as a very versatile alternative to fossil fuels. Deep eutectic solvents (DES) are new "green" solvents, which have been employed as green and cheap alternatives to traditional organic solvents and ionic liquids (ILs), with the advantages of low cost, low toxicity, and biodegradability, and also have been proven to be effective media for the synthesis of biomass-derived chemicals. This review summarizes the recent advances in the conversion of carbohydrates to furfural in DES solvent systems, which mainly focus on the effect of adding different catalysts to the DES system, including metal halides, water, solid acid catalyst, and certain oxides, on the production of furfural. Moreover, the challenges and perspectives of DES-assisted furfural synthesis in biorefinery systems are also discussed in this review.

Photocatalytic Oxidation of 5-Hydroxymethylfurfural Over Interfacial-Enhanced Ag/TiO2 Under Visible Light Irradiation.

Photocatalytic conversion of biomass-derived 5-hydroxyfurfural (HMF) to value-added 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) is an environmentally friendly process. Here, Ag nanoparticle (NP) supported on TiO2 (Ag/TiO2 ) materials with different interfacial structures were fabricated via incipient wetness impregnation. In the photocatalytic oxidation of 5-HMF to HMFCA, low-temperature reduction (473 K) on Ag/TiO2 could improve the photoinduced charge separation efficiency and promote the reaction due to the "enhanced" localized surface plasmon resonance (LSPR) effects achieved through strong metal-support interaction (SMSI). In particular, 2.5 % Ag/TiO2 -LTR exhibited superior performance with an HMFCA selectivity of up to 96.7 % under visible-light illumination. In contrast, the photocatalytic efficiency was greatly reduced when the reduction temperature increased to 773 K because of the encapsulation of Ag NPs by a thicker TiOx overlay, which significantly weakened visible-light harvesting. Overall, these findings offer an efficient methodology for designing interfacial enhanced plasmonic photocatalysts for the valorization of biomass.

Recent advances in the conversion of furfural into bio-chemicals through chemo- and bio-catalysis.

Furfural is a promising renewable platform molecule derived from hemi-cellulose, which can be further converted to fossil fuel alternatives and valuable chemicals due to its highly functionalized molecular structure. This mini-review summarizes the recent progress in the chemo-catalytic and/or bio-catalytic conversion of furfural into high-value-added chemicals, including furfurylamine, C6 carboxylic acid, i.e., furandicarboxylic acid, furfural alcohol, aromatics, levulinic acid, maleic acid, succinic acid, furoic acid, and cyclopentanone, particularly the advances in the catalytic valorization of furfural into useful chemicals in the last few years. The possible reaction mechanisms for the conversion of furfural into bio-chemicals are summarized and discussed. The future prospective and challenges in the utilization of furfural through chemo- and bio-catalysis are also put forward for the further design and optimization of catalytic processes for the conversion of furfural.

Aerobic Oxidation of 5-Hydroxymethylfurfural over Ag Nanoparticle Catalysts Stabilized by Polyvinylpyrrolidone with Different Molecular Weights.

The metal-support interaction (MSI) has a remarkable effect on the catalytic properties, but how to precisely modulate its degree remains a huge challenge. Herein, polyvinylpyrrolidone (PVP) with three different molecular weights (MWs) (24, 58, and 130 kDa) was used as a capping agent to fabricate Ag nanoparticles (NPs) supported on ZrO2. The physiochemical properties of the catalysts were characterized by X-ray diffraction (XRD), Transmission Electron Microscope (TEM), X-ray Photoelectron Spectroscopy (XPS), and Fourier transform infrared (FT-IR) techniques. The impacts of MSI on the catalytic activity and reaction kinetics for aerobic oxidation of 5-hydroxymethylfurfural (HMF) were investigated. The results showed that the introduction of PVP with various MWs could efficiently tailor the interfacial interactions and charge transfers (CT) among PVP, the support, and Ag NPs, thereby affecting the oxidation activity of HMF. The turnover number (TON) for HMF oxidation decreases in the order of unsupported colloidal Ag clusters > Ag/ZrO2 (58,000) > Ag/ZrO2 (130,000) > Ag/ZrO2 (24,000) > Ag/ZrO2. The reason for this large difference in the catalytic activity for HMF oxidation is that various MWs of PVP result in a change of MSI, thereby facilitating CT from PVP to Ag metal sites. This study offers a new strategy for modulating MSI by varying the MW of capping agents, thereby tuning the catalytic properties in the oxidation of HMF.

The volume expansion effect of amine during CO2 adsorption process: An experimental study combined with theoretical calculations.

The volume expansion effect of amine supported on mesoporous silica during CO2 adsorption process was found for the first time through well-designed experiments and was further confirmed by theoretical calculations. It was found that the residual pore volume of mesocellular silica foam (MCF) based solid amine sorbent (tetraethylenepentamine (TEPA) supported on MCF) gradually decreased with the increase of CO2 uptake. Moreover, the surface area, the average diameters of window and cell of MCF show a similar changing trend. This is due to the volume expansion effect of TEPA during CO2 adsorption process, i.e., the total volume of reaction products of TEPA and CO2 is larger than that of pure TEPA. The products are very sticky and almost lose the liquidity totally even at 80 °C. The sticky products and the volume expansion effect may increase the mass transfer resistance and are not beneficial to higher CO2 uptakes especially for solid amine sorbent with higher amine loading due to the decrease of pore size and the residual pore volume. DFT calculations based on simple models also indicate that the total volume of the generated products is much larger than that of unreacted amine, further confirming the volume expansion effect of amine during CO2 adsorption process. DFT calculations also indicate that the volume is even doubled in the presence of moisture. The volume expansion effect of solid amine sorbent found in this study may help to design the sorbent with high CO2 capture performance and less the mass transfer resistance.

Efficient Hydrogenation of Xylose and Hemicellulosic Hydrolysate to Xylitol over Ni-Re Bimetallic Nanoparticle Catalyst.

A disadvantage of the commercial Raney Ni is that the Ni active sites are prone to leaching and deactivation in the hydrogenation of xylose to xylitol. To explore a more stable and robust catalyst, activated carbon (AC) supported Ni-Re bimetallic catalysts (Ni-Re/AC) were synthesized and used to hydrogenate xylose and hemicellulosic hydrolysate into xylitol under mild reaction conditions. In contrast to the monometallic Ni/AC catalyst, bimetallic Ni-Re/AC exhibited better catalytic performances in the hydrogenation of xylose to xylitol. A high xylitol yield up to 98% was achieved over Ni-Re/AC (nNi:nRe = 1:1) at 140 °C for 1 h. In addition, these bimetallic catalysts also had superior hydrogenation performance in the conversion of the hydrolysate derived from the hydrolysis reaction of the hemicellulose of Camellia oleifera shell. The characterization results showed that the addition of Re led to the formation of Ni-Re alloy and improved the dispersion of Ni active sites. The recycled experimental results revealed that the monometallic Ni and the bimetallic Ni-Re catalysts tended to deactivate, but the introduction of Re was able to remarkably improve the catalyst's stability and reduce the Ni leaching during the hydrogenation reaction.

Efficient conversion of 5-hydroxymethylfurfural to high-value chemicals by chemo- and bio-catalysis.

5-hydroxymethylfurfural (HMF) is a very important versatile platform compound derived from renewable biomass. The functionalized molecule with an aldehyde group, a hydroxyl group and a furan ring provides great potential for the production of a wide variety of valuable chemicals. This review highlights the latest advances in the catalytic conversion of HMF into value-added chemicals by some important reactions including (1) aerobic oxidation of HMF into furan-based aldehydes and acids such as 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), 2,5-diformylfuran (DFF), and furandicarboxylic acid (FDCA), (2) reductive amination of HMF to amine, (3) the synthesis of aromatics by Diels-alder reaction followed by a dehydration reaction, (4) catalytic reduction of HMF into 2,5-bis(hydroxymethyl)furan (BHMF), and 2,5-dimethyl furan (DMF), (5) catalytic oxidation of HMF into maleic anhydride, and some other important transformations. The review mainly focuses on the recent progress in bio-catalytic, electrocatalytic, and heterogeneous catalytic transformation of HMF into high value chemicals over the past few years. Moreover, an outlook is provided to highlight opportunities and challenges related to this hot research topic.

Isomerization of glucose into fructose by environmentally friendly Fe/ß zeolite catalysts.

Herein, the environmentally friendly Fe/ß zeolite for glucose isomerization to fructose in aqueous media was reported for the first time. The effects of various reaction conditions including reaction temperature, reaction time, catalyst dosage, etc. on the isomerization reaction over Fe/ß zeolite were studied in detail. Under the optimized conditions, yield of fructose higher than 20% were obtained. Moreover, the Fe/ß zeolite catalysts were stable and remained constant catalytic activity after five consecutive runs. The possible active Fe species for isomerization of glucose in Fe/ß zeolite is also discussed.

One-pot catalytic conversion of cellulose into polyols with Pt/CNTs catalysts.

A series of Pt nanoparticles supported on carbon nanotubes (CNTs) were synthesized using the incipient-wetness impregnation method. These catalysts were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscope (TEM) techniques. The characterization results indicate that the Pt nanoparticles were highly dispersed on the surface of the CNTs, and the mean size was less than 5 nm. These catalysts were utilized to convert cellulose to hexitol, ethylene glycerol (EG), and 1,2-propylene glycol (1,2-PG) under low H2 pressure. The total yields were as high as 71.4% for EG and 1,2-PG using 1Pt/CNTs as the catalyst in the hydrolytic hydrogenation of cellulose under mild reaction conditions.

From molecular fragments to crystals: a UV Raman spectroscopic study on the mechanism of Fe-ZSM-5 synthesis.

The nucleation process of iron-exchanged zeolite Fe-ZSM-5, from the assembly of distorted tetrahedrally coordinated iron species and silicate rings in the precursor to the final Fe-ZSM-5 crystals, as well as variations in the coordination environment of iron, were studied by UV resonance Raman spectroscopy and complementary techniques.The entire sequence of crystallization events of Fe-ZSM-5 was monitored by UV Raman spectroscopy in combination with HRTEM, UV/Vis spectroscopy, X-ray diffraction patterns, and periodic DFT calculations. Fe-ZSM-5 was synthesized by an organic-free method to avoid signal interference from the organic template in Raman spectra. Framework iron atoms with resonance Raman bands at 516, 1115, and 1165 cm(-1), and a Raman band at 1016 cm(-1) are detected for Fe-ZSM-5. In the early stage of Fe-ZSM-5 synthesis, the precursor contains iron atoms in distorted tetrahedral coordination and five- and six-membered silicate rings. Nucleation by aggregation of the precursor species was monitored by UV Raman spectroscopy based on the resonance Raman effect, and confirmed by periodic DFT calculations. Evolution of iron species on the surface and in the bulk phase was monitored by UV Raman spectroscopy with excitation at 244 and 325 nm, as well as HRTEM. Nucleation takes place first in the core of the amorphous particles, and crystalline nuclei with Fe-ZSM-5 structure are formed in the core by consuming the amorphous shell. Finally the amorphous particles are completely transformed into Fe-ZSM-5 crystals.

Iron-functionalized Al-SBA-15 for benzene hydroxylation.

For the first time an ordered mesoporous silica (Fe-Al-SBA-15) with catalytically active isolated Fe surface species for the hydroxylation of benzene with nitrous oxide is prepared by introduction of Fe3+ in the synthesis gel of Al-SBA-15.

Enhancement of alpha-oxygen formation and N2O decomposition on Fe/ZSM-5 catalysts by extraframework Al.

The concentration of alpha-oxygen which can oxidize methane to methanol and benzene to phenol at RT, increases linearly with the amount of introduced extraframework Al on Fe/ZSM-5 catalysts prepared by solid-state exchange of FeCl3 and AlCl3 with H-ZSM-5.