Hydrothermal liquefaction of wheat straw in hot compressed water and subcritical water–alcohol mixtures

Hydrothermal liquefaction of lignocellulosic biomass (wheat straw) into bio-oil has been investigated under subcritical conditions (temperature up to 350 °C, pressure up to 200 bar) in water and water–alcohol mixtures using ethanol and isopropanol in a continuously operated tubular reactor. The effect of different reaction parameters such as temperature, pressure and water–alcohol ratio on the biomass conversion, cracking products yield and the higher heating value (HHV) of the received bio-oil was studied. The water–ethanol mixture was found to be a very reactive medium showing a complete biomass conversion and >30 wt% yield of high caloric oil (HCO). A maximum HHV of 28 MJ/kg for HCO was achieved. In addition, Ru (5 wt%) on H-Beta support was used as catalyst in a run with hydrogen in the feed showing deeper deoxygenation of reaction intermediates and highest HHV of the product oil (30 MJ/kg). This work demonstrated the usability of water–ethanol mixtures for an effective depolymerization of lignocellulosic biomass to bio-oils under subcritical reaction conditions with more than doubled HHV compared to the feedstock, in particular using a catalyst and the presence of hydrogen for further deoxygenation.     

Bio-oil production from Glycyrrhiza glabra through supercritical fluid extraction

Glycyrrhiza glabra was liquefied by ethanol and acetone in an autoclave under high pressure using potassium hydroxide or sodium carbonate as the catalyst, as well as without catalyst at various temperatures (250, 270 and 290 °C) for producing bio-oil. The experimental results show that the yield of the main liquefaction product (bio-oil) was influenced significantly by liquefaction parameters such as solvent type, and catalyst type and temperature. The results showed that the maximum bio-oil yield was obtained in acetone (79%) at 290 °C without catalyst. The products of liquefaction (bio-oil) were analysed and characterized using various methods including elemental analysis, Fourier transform infrared spectroscopy and gas chromatography–mass spectrometry. GC–MS identified 131 and 147 different compounds in the bio-oils obtained at 270 and 290 °C, respectively.     

Liquefaction of giant fennel (Ferula orientalis L.) in supercritical organic solvents: Effects of liquefaction parameters on product yields and character

Ferula orientalis L. stalks were liquefied in an autoclave in supercritical organic solvents (methanol, ethanol, 2-propanol, acetone and 2-butanol) with (NaOH, Na₂CO₃, ZnCl₂) and without catalyst at five different temperatures ranging from 240 °C to 320 °C. The amounts of solid (unconverted raw material), liquid (bio-oil) and gas produced, as well as the composition of the resulting liquid phase, were determined. The effects of various parameters such as temperature, solvent, catalyst and ratio of catalyst on product yields were investigated. The results showed that conversion highly depends on the temperature and catalyst. The highest bio-oil yield (53.97%) was obtained using acetone with 10% zinc chloride at 300 °C. The liquid products were extracted with benzene and diethyl ether. Some of selected liquid products (bio-oils) were analyzed by elemental, FT-IR and GC–MS. 126 different compounds were identified by GC–MS in the liquid products obtained in ethanol at 300 °C.     

Hydrodeoxygenation of vanillin over carbon nanotube-supported Ru catalysts assembled at the interfaces of emulsion droplets

Carbon nanotube supported ruthenium catalysts, assembled at the water/oil interfaces, show excellent activity and selectivity for the hydrodeoxygenation of the bio-oil model compound of vanillin under mild conditions (1 MPa, 150 °C). Based on a direct fluorescence image, the Ru/CNT catalysts are mainly distributed on the surface of the emulsion droplets, forming a Pickering emulsion. Simultaneous reaction and separation of the products are achieved in the constructed emulsions, which have great potential in the simplifications of the isolation and purification stages for bio-oil refining.     

NiFe/γ-Al2O3: A universal catalyst for the hydrodeoxygenation of bio-oil and its model compounds

NiFe bimetallic catalyst shows an excellent activity and selectivity for the hydrodeoxygenation (HDO) of three typical model compounds of bio-oil. The conversion of furfuryl alcohol, benzene alcohol and ethyl oenanthate is 100, 95.48 and 97.89% at 400 °C and the yield to 2-methylfuran, toluene and heptane is 98.85, 93.49 and 96.11% at 0.1 ml/min flow speed and atmospheric pressure. It indicates that the major reaction pathway is the cleavage of C–O rather than C–C. After the catalytic HDO of bio-oil over NiFe/Al₂O₃ catalyst, the heating value changes from 37.8 to 43.9 MJ/kg, the pH changes from 6.65 to 7.50.     

Promoting effect of rhenium on catalytic performance of Ru catalysts in hydrogenolysis of glycerol to propanediol

Ru/Al₂O₃, Ru/C and Ru/ZrO₂ catalysts were applied to the hydrogenolysis of glycerol to propanediol, and the effect of Re as an additive on the catalytic performance of Ru catalysts was examined. The catalyst systems were characterized by N₂ adsorption/desorption, XRD, TEM-EDX and XPS. The hydrogenolysis of glycerol was carried out under the conditions of 120–180 °C, 4–10 MPa hydrogen pressure and 4–8 h, and the conversion of glycerol varied from 18.7% to 29.7% over Ru/Al₂O₃, Ru/C and Ru/ZrO₂ catalysts. The reaction results indicate that Re possesses high promoting effect on the catalytic performance of Ru catalysts in glycerol hydrogenolysis.     

Hydroxyapatite as a novel support for Ru in the hydrogenation of levulinic acid to γ-valerolactone

Metal catalysts (Ru, Pt, Pd, Ni) supported on hydroxyapatite (HAP) were examined for the hydrogenation of levulinic acid to γ-valerolactone. Among these Ru supported on HAP exhibited 99% yield of γ-valerolactone at 70 °C and 0.5 MPa H₂ pressure. The Ru/HAP catalyst was characterized by various adsorption and spectroscopic techniques. The Ru/HAP catalyst was quite stable up to four recycles.     

Fast pyrolysis of chicken litter and turkey litter in a fluidized bed reactor

Disposal of poultry litter such as chicken litter and turkey litter is becoming a major problem in the USA poultry industry because of environmental pressures and health concerns. Poultry litters form wood chips, chicken litter (flock 1, flock 2 and broiler) and turkey litter were converted into bio-oil, gas and char in a fluidized bed reactor at the temperature ranges of 450–550 °C. The bio-oil yield of poultry litter was relatively low (15–30 wt%) compared to wood derived bio-oil (34–42 wt%). The gas yield was increased from 32 to 61 wt% with increasing reaction temperature, and char yield was between 22 and 45 wt% depending on age and reaction conditions. The higher heating value (HHV) of the poultry litter bio-oil were between 26 and 29 MJ/kg, whereas that of the bedding material (wood chips) was 24 MJ/kg. The dynamic viscosities of bio-oil were varied from 0.01 to 27.9 Pa s at 60 °C, and those of values were decreased with increasing shear rate.     

Pyrolysis of biomass in the presence of Al-MCM-41 type catalysts

Al-MCM-41 type mesoporous catalysts were used for converting the pyrolysis vapours of spruce wood in order to obtain better bio-oil properties. Four Al-MCM-41 type catalysts with a Si/Al ratio of 20 were tested. The catalytic properties of Al-MCM-41 catalyst were modified by pore enlargement that allows the processing of larger molecules and by introduction of Cu cations into the structure.Spruce wood pyrolysis at 500 °C was performed and the products were analysed with the help of on-line pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). In addition, thermogravimetry/mass spectrometry (TG/MS) experiments were applied for monitoring the product evolution under slow heating conditions (20 °C/min) from 50 to 800 °C.Levoglucosan is completely eliminated, while acetic acid, furfural and furanes become quite important among cellulose pyrolysis products over the unmodified Al-MCM-41 catalyst. The dominance of phenolic compounds of higher molecular mass is strongly cut back among the lignin products. Both the increase of the yield of acetic acid and furan and the decrease of large methoxyphenols are repressed to some extent over catalysts with enlarged pores. The Cu modified catalyst performed similarly to the catalyst with enlarged pore size in converting the pyrolysis vapours of wood, although its pore size was similar to the unmodified Al-MCM-41.     

Highly dispersed Ni particles on Ru/NiAl catalyst derived from layered double hydroxide for selective CO methanation

In this communication, we report novel Ru/NiAl-layered double hydroxide derived catalysts for CO removal by selective CO methanation. The experimental results revealed that uncalcined Ru/NiAl catalyst shows the fine dispersion of the nickel particles and remarkably high activity to CO at wider operating temperature window ranging from 150 °C to 250 °C. This work shows promising potential in further application of selective CO methanation as deep CO removal process of fuel processors especially for polymer electrolyte membrane fuel cells (PEMFC).     

Efficient and selective conversion of glycidol to 1,2-propanediol over Pd/C catalyst

The present work deals with the catalytic hydrogenolysis of glycidol to 1,2-propanediol. Reactions were carried out in a closed steel reactor using noble metal based heterogeneous catalysts (Pd, Rh, Pt) under hydrogen pressure (1–8 bars) in the temperature range of 25–140 °C. Pd/C shows the highest glycidol conversion (96%) under solvent free conditions after 24 h with high selectivity to 1,2-propanediol (93%). The effect of the solvent was also investigated and it was demonstrated that ethanol reduces drastically oligomer production enhancing selectivity up to 99% with a significant reaction time reduction (6 h). The Pd/C catalyst shows high recyclability and could be reused several times (9 cycles) without losses in activity and selectivity.     

Addition effect of ruthenium on nickel steam reforming catalysts

Several Ni-based catalysts supported on a mixture of MgO, La₂O₃, and Al₂O₃ were prepared. The catalytic performance in the steam reforming of m-cresol was evaluated. In the investigation of the effect of Ru loading added to the Ni-catalyst, it was found that the presence of Ru strongly enhances the catalytic performance of the Ni-based catalyst when increasing Ru loading up to 2 wt%. Effect of Ni loading to the Ru-based catalyst system was also investigated. It was found that the addition of nickel to the Ru-based catalyst up to 15 wt% enhanced significantly the catalytic activity of the catalyst. The lifetime of the Ru–Ni catalysts in the reforming of m-cresol was further tested at 750 °C. In agreement with general observations of the use of Ni monometallic catalyst, deactivation of the catalyst due to the carbon deposition reaction already occurred in the reforming of the oxygenated compound. On the other hand, a reasonable high resistant on the carbon deposition in the reforming of m-cresol was given by the 2 wt% Ru–15 wt% Ni catalyst system. An effort in improving the strength of the catalyst support with this catalyst system was also conducted, and the catalyst showed significant increase in the stability of the reforming of oxygenated aromatic compound.     

Ammonolysis of ethanol on pure and zinc oxide modified HZSM-5 zeolites

Reaction between ethanol and ammonia have been studied on various zinc oxide modified HZSM-5 (Si/Al=225) catalysts under various conditions of temperature, C/N ratio of the reactants and their WHSV. Two pure zinc oxides were taken for the study. One was a highly active acidic form Z₁ and the other was a stoichiometric non acidic zinc oxide Z₂. The activity of the catalysts for ammonolysis reaction followed the order Z₂⪡Z₁⪡HZSM-5. However, for composite catalysts containing 10–40% Z₁ on HZSM-5, the activity increased synergistically and became maximum (∼81% conversion of alcohol) for the catalyst 40% Z₁/HZSM-5 and about 50% conversion for the catalyst 40% Z₂/HZSM-5. The products formed were mainly N-heterocycles. Some novel high molar mass N-heterocycles were also detected. The catalytic activity and product selectivity was crucially affected by the reaction conditions, particularly the effect of temperature; the optimum yield of the products was obtained at the catalyst temperature of 723 K, C/N ratio 0.3892 and WHSV of 2.5 h⁻¹.     

Hydrogen production from ethanol steam reforming over Rh/CeO2 catalyst

Hydrogen production from ethanol steam reforming over an Rh/CeO₂ catalyst was investigated with a stoichiometric feed composition. Ethanol was entirely converted to hydrogen and C₁ products (CO, CO₂, CH₄) at 400 °C due to the remarkable C–C bond cleavage capacity of Rh species. The Rh/CeO₂ catalyst exhibited stable activity and selectivity without the obvious deactivation during 70 h on stream test. Structural analysis of the aged catalysts indicated that the strong interaction between Rh and ceria support efficiently inhibited Rh particles sintering (stable at around 2 nm) and coke formation to guarantee catalyst stability.     

Pt-CeO2/C anode catalyst for direct methanol fuel cells

In order to develop a cheaper and durable catalyst for methanol electrooxidation reaction, ceria (CeO₂) as a co-catalytic material with Pt on carbon was investigated with an aim of replacing Ru in PtRu/C which is considered as prominent anode catalyst till date. A series of Pt-CeO₂/C catalysts with various compositions of ceria, viz. 40 wt% Pt-3–12 wt% CeO₂/C and PtRu/C were synthesized by wet impregnation method. Electrocatalytic activities of these catalysts for methanol oxidation were examined by cyclic voltammetry and chronoamperometry techniques and it is found that 40 wt% Pt-9 wt% CeO₂/C catalyst exhibited a better activity and stability than did the unmodified Pt/C catalyst. Hence, we explore the possibility of employing Pt-CeO₂ as an electrocatalyst for methanol oxidation. The physicochemical characterizations of the catalysts were carried out by using Brunauer Emmett Teller (BET) surface area and pore size distribution (PSD) measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques. A tentative mechanism is proposed for a possible role of ceria as a co-catalyst in Pt/C system for methanol electrooxidation.     

Ammonia synthesis on magnesia supported ruthenium catalysts with mesoporous structure

Mesoporous Ru/MgO catalysts for ammonia synthesis were prepared by sol–gel method with concurrently decomposing Ru carbonyl complex. The catalytic properties were characterized mainly by means of nitrogen adsorption isotherm, hydrogen chemisorption, X-ray diffraction, and transmission electron microscopy. The detailed observation of decarbonylation behavior on the catalysts prepared under various conditions revealed that the carbonyl complex acted as an effervescent reagent to form a mesoporous structure with radius of 1–9 nm on MgO support. Furthermore, both specific surface area and metal dispersion tended to increase with increasing the Ru carbonyl complex concentration. The best ammonia formation rate was consequently observed on the Ru/MgO catalyst (Ru: 7.1 wt%) with high surface area (290 m²/g) of this series.     

Deactivating species in the transformation of crude bio-oil with methanol into hydrocarbons on a HZSM-5 catalyst

A study has been carried out by using different techniques (TPO, FTIR, Raman, ¹³C NMR, GC/MS of the coke dissolved in CH₂Cl₂) on the nature of the coke deposited on a HZSM-5 catalyst modified with Ni in the transformation of the crude bio-oil obtained by flash pyrolysis of lignocellulosic biomass (pine sawdust) into hydrocarbons. The reaction system has two steps in-line. In the first one, the components of crude bio-oil derived from the pyrolysis of biomass lignin are polymerized at 400 °C. In the second one, the remaining volatile oxygenates are transformed into hydrocarbons in a fluidized bed catalytic reactor at 450 °C. The reaction has been carried out with different bio-oil/methanol mass ratios in the feed (from 100/0 to 0/100). Co-feeding methanol significantly attenuates coke deposition, and the nature of the coke components varies according to the bio-oil/methanol ratio in the feed. When bio-oil is co-fed, the coke deposited on the catalyst has a significant content of oxygenates and oxo-aromatics and consists of two fractions, identified by temperature programmed oxidation, corresponding to external and internal coke in the zeolite crystals. The fraction of external coke is soluble in CH₂Cl₂, with a high content of oxygenates and oxo-aromatics, and is generated by polymerization of products derived from biomass lignin pyrolysis activated by the zeolite acid sites. The fraction of coke retained within the zeolite crystals is partially insoluble and is formed by several routes: from the intermediates in the transformation of both methanol and bio-oil oxygenates into hydrocarbons; by evolution of the other coke fraction; from the hydrocarbons (with high aromatics content) in the reaction medium.     

Preparation,characterization and catalytic activity studies of CeO2–K diesel soot oxidation catalysts loaded on porous Al2O3 substrate using water-immiscible solvent

CeO₂–K catalysts supported on porous alumina substrate have been prepared by using a novel water-immiscible solvent. The advantage of this method is to load the catalyst onto the filter surface by one-time coating and prevent depositing the catalyst into the porous structure of support materials. The catalytic activities of the supported catalysts were evaluated by TPR system and the results showed that the pure CeO₂ displayed a poor catalytic activity for soot oxidation, while the addition of K element into CeO₂ would result in the formation of CeO₂–K solid solution and significant enhancement of catalytic activity. Nevertheless, the variation of K content had a limited effect on soot ignition temperature. The catalyst with a Ce:K molar ratio of 1:2 exhibited an ignition temperature of about 330 °C and the oxidation rates of about 0.16 and 0.28 mg min⁻¹ cm⁻² at temperatures of 370 and 390 °C, respectively.     

Catalytic effects of ferric chloride and sodium hydroxide on supercritical liquefaction of thistle (Cirsium yildizianum)

Cirsium yildizianum stalks were liquefied in organic solvents under supercritical conditions with and without catalyst in a cylindrical reactor at temperatures of 260, 280 and 300 °C. The effects of liquefaction temperature, catalyst type and solvent on product yields were investigated. The liquid products (bio-oils) were extracted with diethyl ether and benzene using an extraction procedure. The liquid yields in supercritical methanol, ethanol and acetone were found to as 45.66%, 49.34% and 60.05% in the non-catalytical runs at 300 °C, respectively. The highest conversion (liquid + gaseous products) was obtained in acetone with 10% ferric chloride at 300 °C in the catalytic runs. The produced liquids at 300 °C were analyzed and characterized by elemental, GC–MS and FT-IR. 85, 79 and 60 different types of compounds were identified by GC–MS obtained in methanol, ethanol and acetone, respectively. The liquid products were composed of various organics including aromatics, nitrogenated and oxygenated compounds.     

Influence of CeO2 morphology on the catalytic oxidation of ethanol in air

Nano-CeO₂ catalysts of different shapes were synthesized at different hydrothermal crystallization temperatures from an alkaline aqueous solution. X-ray diffraction (XRD), transmission electron microscope (TEM), and H₂ temperature-programmed reduction (H₂-TPR) were used to study the synthesized nano-CeO₂ catalyst samples. The catalytic properties of the prepared nano-CeO₂ catalysts for the catalytic oxidation of ethanol in air were also investigated. TEM analysis showed that CeO₂ nanorod and nanocube catalysts have been synthesized at hydrothermal crystallization temperatures of 373 K and 453 K, respectively. XRD results showed that the synthesized nano-CeO₂ catalysts have similar cubic fluorite structures. H₂-TPR results indicated that CeO₂ nanorod and nanocube catalysts exhibit different reduction behaviors for H₂ and that the nanorod catalyst has better low-temperature reduction performance than the nanocube catalyst. Ethanol catalytic oxidation results indicated that oxidation and condensation products (including acetaldehyde, acetic acid, CO₂, and ethyl acetate) have been produced from the prepared catalysts. The ethyl acetate and acetic acid can be ignited by ethanol at low temperature on the CeO₂(R) catalyst to give low catalytic combustion temperature for ethyl acetate and acetic acid molecules. CeO₂ nanorods gave ethanol oxidation conversion rates above 99.2% at 443 K and CO₂ selectivity exceeding 99.6% at 483 K, while CeO₂ nanocubes gave ethanol oxidation conversion rates of about 95.1% until 508 K and CO₂ selectivity of only 93.86% at 543 K. CeO₂ nanorod is a potential low-cost and effective catalyst for removing trace amounts of ethanol to purify air.