Showing papers in "Applied Catalysis B-environmental in 2010"

The efficiency and mechanisms of catalytic ozonation

Abstract: Catalytic ozonation has recently gained significant attention as an effective process used for the removal of organics from water. Unfortunately, despite increasing research efforts in the field of catalytic ozonation and the introduction of new catalysts, the mechanisms of catalytic processes are still largely unknown. An understanding of the mechanisms of catalytic ozonation is vital in order to introduce this technique in water treatment at an industrial scale. Therefore, the main aim of this paper is to provide a short overview of catalytic processes, their recent advances and to identify major directions taken to understand mechanisms governing catalytic processes utilised in water and wastewater treatment. Catalytic ozonation is considered to belong to Advanced Oxidation Processes. However, the results published by several research groups indicate that not all catalytic processes utilise the power of hydroxyl radicals.

Catalytic oxidation of volatile organic compounds on supported noble metals

Abstract: Volatile organic compounds (VOCs) are toxic and mainly contribute to the formation of photochemical smog with a consequent remarkable impact to the air quality. A few techniques are available to reduce VOC emission, among them catalytic oxidation is suitable especially for highly diluted VOCs. The development of noble metals and transition metal oxides as catalysts for VOCs oxidation has been widely reported in the literature and the research field continues to be very active. Selection of catalytic materials for the abatement of organic pollutants is not easy because the activity depends on the specific molecule, on the reactions conditions and many parameters can affect the catalyst activity and resistance. The present review focus on the most used noble metals catalysts for oxidation of not halogenated VOC. The effects of metal salt precursor, chlorine poisoning, water inhibition, particle size dependence, nature of the support are discussed. The calculated reaction order with respect to VOC and oxygen as well as the proposed reaction mechanisms are addressed. Examples of the most recent catalytic systems reported in literature are also included.

Catalysts for methanol steam reforming—A review

Abstract: A large number of studies can be found in the literature regarding the production of new catalysts for methanol steam reforming. This work summarizes the latest developments on catalysts for this application and is divided in two main groups: copper-based and group 8–10 metal-based catalysts. In each section, the strategies proposed by several authors to enhance the performance of the catalysts are described. An overall comparison between the two groups shows that copper-based catalysts are the most active ones, while the 8–10 group catalysts present better results in terms of thermal stability and long-term stability. Very promising results were reported for both groups, enhancing the value of methanol as a hydrogen carrier for fuel cell applications.

Catalytic combustion of VOCs over a series of manganese oxide catalysts

Abstract: Catalytic combustion of volatile organic compounds (VOCs: benzene and toluene) was studied over manganese oxide catalysts (Mn3O4, Mn2O3 and MnO2) and over the promoted manganese oxide catalysts with alkaline metal and alkaline earth metal. Their properties and performance were characterized by using the Brunauer Emmett Teller (BET), temperature programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The sequence of catalytic activity was as follows: Mn3O4 > Mn2O3 > MnO2, which was correlated with the oxygen mobility on the catalyst. Each addition of potassium (K), calcium (Ca) and magnesium (Mg) to Mn3O4 catalyst enhanced the catalytic activity of Mn3O4 catalyst. Accordingly, K, Ca and Mg seemed to act as promoters, and the promoting effect might be ascribed to the defect-oxide or a hydroxyl-like group. A mutual inhibitory effect was observed between benzene and toluene in the binary mixture. In addition, the order of catalytic activity with respect to VOC molecules for single compound is benzene > toluene, and the binary mixture showed the opposite order of toluene > benzene.

Heterogeneous photo-Fenton oxidation with pillared clay-based catalysts for wastewater treatment: A review

Abstract: Due to their excellent properties, pillared clays (PILCs) have been widely used in several applications, particularly in catalysis. In this paper, their use in heterogeneous photo-Fenton-like advanced oxidation for wastewater treatment, employing either model/synthetic effluents or real streams, is reviewed. Particular attention is given to the effect that the main operating conditions have on process performance, namely wavelength of the light source and power, initial H2O2 or parent compound concentration, catalyst load, pH and temperature. Emphasis is also given to the type of catalyst used and its synthesis conditions (e.g. thermal aging or acid treatment). Several important technological aspects that should be accounted for in real practice are also discussed in detail, particularly the catalyst stability, the use of continuous-flow fixed-bed reactors, the mode of oxidant addition, the environmental impact/integration with biological processes and the possibility of using visible light instead of UV only. Then, some simple mechanistic studies reported are summarized, as well as modeling works.

Heterogeneous Fenton catalysts based on clays, silicas and zeolites

Abstract: This review focuses on the use of layered and porous aluminosilicates and layered double hydroxides as catalysts for the Fenton reaction. In the general sections of this review we present the elementary equations leading to the generation of hydroxyl radicals from H2O2 and the subsequent reactivity of this highly aggressive species. After justifying the advantages of using insoluble solids as heterogeneous catalysts, replacing soluble iron salts, we discuss the desirable features that should have an ideal Fenton catalyst and which are the parameters to be considered when ranking the efficiency of the materials. The main part of this review is focused on presenting the results reported up to late 2009 obtained using layered and porous aluminosilicates as heterogeneous catalysts. The structure of these materials is briefly presented to highlight the benefits and advantages of each type of solid with respect to their use as catalysts. When presenting the catalytic data, special emphasis is made on the missing data that would be useful to clarify, the relative efficiency and performance of the materials. In the final concluding remarks we stress again that the present situation needs to be clarified to draw solid conclusions on the relative performance and efficiency of the tested catalysts.

The role of lattice oxygen on the activity of manganese oxides towards the oxidation of volatile organic compounds

Abstract: A series of manganese oxides differing in the structure, composition, average manganese oxidation state and specific surface area have been used in the total oxidation of volatile organic compounds (VOC). Ethanol, ethyl acetate and toluene were chosen as models of VOC. Among the manganese oxides tested, cryptomelane (KMn8O16) was found to be very active in the oxidation of VOC. The performance of cryptomelane was significantly affected by the presence of other phases, namely, Mn2O3 and Mn3O4. Temperature-programmed experiments combined with X-ray photoelectron spectroscopy (XPS) show that the mobility and reactivity of the oxygen species were significantly affected, explaining the catalytic performances of those samples. Mn3O4 improves the catalytic performance due to the increase of the reactivity and mobility of lattice oxygen, while Mn2O3 has the opposite effect. These results show that there is a correlation between the redox properties and the catalytic performance of the manganese oxides. Temperature-programmed surface reactions (TPSR) after adsorption of toluene or ethanol, in addition to reactions performed without oxygen in the feed, show that lattice oxygen is involved in the VOC oxidation mechanism. The conversion level was found to be influenced by the type of VOC, the reactivity into CO2 increasing in the following order: Toluene

A review of the mechanisms and modeling of photocatalytic disinfection

Abstract: This paper is a review of the fundamental disinfection mechanisms of photocatalysis and the models used to fit the disinfection process. Photocatalysis is an attractive technology for water treatment largely due to its potential to utilize solar energy directly and achieve both disinfection and chemical detoxification. Many papers have been published on photocatalytic disinfection, but there is still considerable debate on disinfection mechanisms and a general lack of mechanistic models for the process. The fundamental photocatalytic disinfection mechanisms as they relate to the inactivation of bacteria are comprehensively surveyed here. The process of lipid peroxidation of membrane fatty acids, particularly polyunsaturated fatty acids, is gaining momentum in the literature. In recent papers, an increasing number of researchers are paying close attention to the products of lipid peroxidation. The mathematical models, empirical and mechanistic, used to fit the disinfection process have also been thoroughly reviewed. In this regard, most of the proposed models are empirical in nature and rooted in traditional chemical disinfection principles, which are often not representative of the heterogeneous photocatalytic process. The theoretical development of a mechanistic model for photocatalytic disinfection based on lipid peroxidation is explored with due consideration to the interaction between microbes and photocatalyst particles. The extensive literature on autooxidation of lipids in such fields as biology and medicine is informative to the development of the model.

Degradation of microcystin-LR using sulfate radicals generated through photolysis, thermolysis and e− transfer mechanisms

Abstract: This study explores the potential use of sulfate radical-based advanced oxidation technologies (SR-AOTs) for the degradation of the naturally occurring hepatotoxin, microcystin-LR (MC-LR). The generation of sulfate radicals was achieved by activation of the oxidants persulfate (PS) and peroxymonosulfate (PMS) through electrophilic transition metal cations (Ag+ and Co2+, respectively), radiation (UV 300 − has similar redox potential to hydroxyl radical (HO ), to the best of our knowledge, SR-AOTs have not been tested for the degradation of cyanotoxins. In this study, PMS was activated very efficiently with Co2+ at neutral pH and increasing catalyst concentration resulted in dramatic increase of the initial rates of degradation that reached a plateau for CCo(II) ≥ 1 mg. Based on the optimum pH conditions for each system, the efficiency order is Co2+/PMS > Fe2+/H2O2 ≫ Ag+/PS, which we believe is associated with the energy of the lower unoccupied molecular orbital of the oxidants. When UV (300 Since, the UV lamps used in the study emit light at a range of wavelengths (300

Pivotal role of fluorine in enhanced photocatalytic activity of anatase TiO2 nanosheets with dominant (0 0 1) facets for the photocatalytic degradation of acetone in air

Abstract: Surface-fluorinated anatase TiO 2 nanosheets with dominant {0 0 1} facets were fabricated by a simple hydrothermal route in a Ti(OC 4 H 9 ) 4 -HF-H 2 O mixed solution. The atomic ratios of fluorine to titanium ( R F ) exhibit an obvious influence on the structures and photocatalytic activity of TiO 2 samples. In the presence of HF, TiO 2 nanosheets can be easily obtained. With increasing R F , the relative anatase crystallinity, average crystallite size, pore size and percentage of exposed {0 0 1} facets increase, contrarily, BET specific surface areas decrease. All fluorinated TiO 2 nanosheets exhibit much higher photocatalytic activity than Degussa P-25 TiO 2 (P25) and pure TiO 2 nanoparticles prepared in pure water due to the synergistic effect of surface fluorination and exposed {0 0 1} facets on the photoactivity of TiO 2 . Especially, at R F = 1, the fluorinated TiO 2 nanosheet exhibits the highest photocatalytic activity, and its photoactivity exceeds that of P25 by a factor of more than nine times.

Kinetics and mechanism of advanced oxidation processes (AOPs) in degradation of ciprofloxacin in water

Abstract: Fluoroquinolones and their metabolites are found in surface and ground waters, indicating their ineffective removal by conventional water treatment technologies. Advanced oxidation processes (AOPs) are alternatives to traditional water treatments. They utilize free radical reactions to directly degrade fluoroquinolones. This work reports absolute rate constants for the reaction of ciprofloxacin with several free radicals, OH, N 3 and SO 4 − as well as hydrated electrons. Pulsed radiolysis experiments showed that OH, N 3 and e aq − reacted quickly with ciprofloxacin, with bimolecular reaction rate constants of (2.15 ± 0.10) × 10 10 , (2.90 ± 0.12) × 10 10 and (2.65 ± 0.15) × 10 10 M −1 s −1 , respectively, while the SO 4 − radical appeared not to react with ciprofloxacin. Transient spectra were observed for the intermediate radicals produced by hydroxyl and azide radical reactions. Moreover, ciprofloxacin can be degraded rapidly using a typical advanced oxidation process, TiO 2 photocatalysis, with half-lives of 1.9–10.9 min depending upon pH values. Seven degradation products were elucidated by LC/MS/MS analysis, and the degradation mechanism of ciprofloxacin was also tentatively proposed by combining the experimental evidence with theoretical calculations of frontier electron densities. The calculations suggest that the addition of a hydroxyl radical to ciprofloxacin and photo-hole direct attack is two predominant reaction pathways.

Photocatalytic reduction of CO2 with H2O on mesoporous silica supported Cu/TiO2 catalysts

Abstract: Photoreduction of CO 2 to hydrocarbons is a sustainable energy technology which not only mitigates emissions but also provides alternative fuels. However, one of the largest challenges is to increase the overall CO 2 photo-conversion efficiency when water is used as the reducing reagent. In this work, mesoporous silica supported Cu/TiO 2 nanocomposites were synthesized through a one-pot sol–gel method, and the photoreduction experiments were carried out in a continuous-flow reactor using CO 2 and water vapor as the reactants under the irradiation of a Xe lamp. The high surface area mesoporous silica substrate (>300 m 2 /g) greatly enhanced CO 2 photoreduction, possibly due to improved TiO 2 dispersion and increased adsorption of CO 2 and H 2 O on the catalyst. CO was found to be the primary product of CO 2 reduction for TiO 2 –SiO 2 catalysts without Cu. The addition of Cu species, which was identified to be Cu 2 O by the XPS, markedly increased the overall CO 2 conversion efficiency as well as the selectivity to CH 4 , by suppressing the electron–hole recombination and enhancing multi-electron reactions. A synergistic effect was observed by combining the porous SiO 2 support and the deposition of Cu on TiO 2 . The peak production rates of CO and CH 4 reached 60 and 10 μmol g-cat −1 h −1 , respectively, for the 0.5%Cu/TiO 2 –SiO 2 composite that has the optimum Cu concentration; the peak quantum yield was calculated to be 1.41%. Deactivation and regeneration of the catalyst was observed and the mechanism was discussed. Desorption of the reaction intermediates from the active sites may be the rate limiting step.

Controllable synthesis of Bi2MoO6 and effect of morphology and variation in local structure on photocatalytic activities

Abstract: Highly crystalline orthorhombic Bi2MoO6 particles with high visible-light photocatalytic activity have been controllably synthesized via a facile hydrothermal process without adding any surfactant. The morphologies of Bi2MoO6 with nanosheet and microrod can be selectively obtained by adjusting the pH value of the reactant. The formation mechanisms of nanosheet and microrod structures were then discussed based on the H+ cations adsorption abilities on different crystal faces. The Bi2MoO6 samples prepared at acidic condition showed 12 times higher photocatalytic activity than that prepared at basic condition under visible-light irradiation. The reason for the big difference in the photocatalytic activities for the Bi2MoO6 samples obtained at different pH values were systematically studied based on their shape, size and the variation of local structure.

Effect of calcination temperature on morphology and photoelectrochemical properties of anodized titanium dioxide nanotube arrays

Abstract: Highly ordered TiO2 nanotube arrays (TNs) are prepared by electrochemical anodization of titanium foil in a mixed electrolyte solution of glycerol and NH4F and then calcined at various temperatures The prepared samples are characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy The photocatalytic activity is evaluated by photocatalytic degradation of methyl orange (MO) aqueous solution under UV light irradiation The production of hydroxyl radicals ( OH) on the surface of UV-irradiated samples is detected by a photoluminescence (PL) technique using terephthalic acid (TA) as a probe molecule The transient photocurrent response is measured by several on–off cycles of intermittent irradiation The results show that low temperatures (below 600 °C) have no great influence on surface morphology and architecture of the TNs sample and the prepared TNs can be stable up to ca 600 °C At 800 °C, the nanotube arrays are completely destroyed and only dense rutile crystallites are observed The photocatalytic activity, formation rate of hydroxyl radicals and photocurrent of the TNs increases with increasing temperatures (from 300 to 600 °C) due to the enhancement of crystallization Especially, at 600 °C, the sample shows the highest photocatalytic activity due to its bi-phase composition, good crystallization and remaining tubular structures With further increase in the calcination temperature from 600 to 800 °C, the photocatalytic activity rapidly decreases due to the vanishing of anatase phase, collapse of nanotube structures and decrease of surface areas

Activated carbon supported cobalt catalysts for advanced oxidation of organic contaminants in aqueous solution

Abstract: A heterogeneous cobalt catalyst was prepared by impregnation of cobalt ion on an activated carbon (AC) and used to activate peroxymonosulphate (PMS) for advanced oxidation of phenol in aqueous solution. The Co/AC catalyst was characterised by several techniques such as XRD, EDS, SEM, and TGA. It was found that Co2O3 was the major form of Co species and was homogeneously distributed on the activated carbon surface. Co/AC exhibited high activity in oxidation of phenol with sulphate radicals and 100% decomposition and 80% TOC removal could be achieved in 60 min at the conditions of 500 ml phenol solution of 25 ppm, 0.1 g catalyst and 1 g peroxymonosulphate. The catalyst also exhibited stable performance after several rounds of regeneration. Several operational parameters such as catalyst and oxidant amount, temperature on the rate of oxidation were found to influence the phenol oxidation.

TiO2 for water treatment: Parameters affecting the kinetics and mechanisms of photocatalysis

Abstract: The photocatalytic activity of TiO2 is the result of an interplay between a considerable number of parameters, e.g., phase composition, electronic structure, particle size, exposed surface area, degree of aggregation, mobility of charge carriers, presence of impurities, amount and kind of defects, adsorption of molecules from gas or aqueous phase, lateral interactions between adsorbed species, nature of solvent, etc. Furthermore, these parameters can be broadly subdivided into those that are intrinsic to the photocatalytic material, and those that are extrinsic being influenced by the surrounding environment and conditions. The specific function and influence of a given feature for the photocatalytic performance of a TiO2 sample is difficult to characterize since many of the before-mentioned parameters are strongly coupled. For example, while the degree of aggregation could be inherent to a given material, it is also simultaneously influenced by pH. The degree of aggregation can then influence adsorption of molecules, light scattering and photon adsorption, charge carrier dynamics etc. The plurality of variables driving the nature of the photocatalytic activity, presents a challenge when trying to understand the kinetics and mechanisms underlying photocatalytic processes. It is of primary importance to develop a method to understand and control these properties (or at least some of them). In this paper, we also discuss the relevance of quantum-integrated systems in which the local environment where the molecule is adsorbed is different from the “lonely” photocatalyst or the molecule in solution, and could be treated as a whole.

Photocatalysis fundamentals revisited to avoid several misconceptions

Abstract: Photocatalysis has presently become a major discipline owing to two factors: (i) the intuition of the pioneers of last 20th century and (ii) the mutual enrichment of scientists arising from different fields: photochemistry, electrochemistry, analytical chemistry, radiochemistry, material chemistry, surface science, electronics, and hopefully catalysis. Since heterogeneous photocatalysis belongs to catalysis, all the bases of this discipline must be respected: (i) proportionality of the reaction rate to the mass of catalyst (below the plateau due to a full absorption of photons); (ii) implication of the Langmuir–Hinshelwood mechanism of kinetics with the initial rate being proportional to the coverages θ in reactants;(iii) conversions obtained above the stoichiometric threshold defined as the maximum number of potential active sites initially present at the surface of a mass m of titania used in the reaction. In addition, one should respect photonics, with the photocatalytic activity, i.e. the reaction rate being (i) parallel to the absorbance of the photocatalyst and (ii) proportional to the radiant flux Φ. In every study, one should determine the quantum yield (QY) (or efficiency), which, although dimensionless, is a “doubly kinetic” magnitude defined as the ratio of the reaction rate r (in molecules converted/second) to the efficient photonic flux (in photons/second) received by the solid. This is an instantaneous magnitude directly linked to the parameters mentioned above, in particular to the concentration. It can vary from a maximum value of ca. 40% in pure liquid phase to very low values (10−2%) in diluted media (pollutants trace eliminations). To establish true photocatalytic normalized tests, the above recommendations must be observed with a real catalytic activity independent of non-catalytic side-reaction. In particular, dye decolorization, especially in the visible, provides an apparent “disappearance” of the dye, due to a limited stoichiometric electron transfer from the photo-excited dye molecule to titania, subsequently compensated by an additional ionosorption of molecular oxygen.The energetics of photocatalysis on TiO2, being based on the energy E of the photons, i.e. E ≥ 3.2 eV, enables one to produce OH radicals, the second best oxidizing agent. The decrease of energy E to the visible may be thermodynamically detrimental for the generation of such highly cracking and degrading species. Concerning solid state chemistry, it is now finally admitted that cationic doping is detrimental for photocatalysis. In conclusion, all these recommendations have to be addressed and experiments have to be operated in suitable conditions before claiming that one deals with a true photocatalytic reaction.

Direct hydrazine fuel cells: A review

Abstract: Low-temperature fuel cells operating on hydrazine fuel in acid and alkaline media comprise a promising class of new, non-conventional sources of energy. High battery performance is expected of hydrazine-based cells. The electrooxidation of hydrazine on the surface of different catalysts has been extensively studied recently. Examples of Direct Hydrazine Fuel Cells (DHFC) with anion or cation-exchange membranes show notable power densities. These aspects of DHFC development with analysis of future improvements in their performance based on changes such as an increase in catalytic activity, membrane type selection and MEA fabrication, are summarized in the present review.

Application of TiO2 photocatalysis for air treatment: Patents’ overview

Abstract: A review of patents on the application of titanium dioxide photocatalysis for air treatment is presented. A comparison between water treatment and air treatment reveals that the number of scientific publications dedicated to photocatalytic air treatment is significantly lower than the number of scientific manuscripts dedicated to photocatalytic water treatment, yet the situation is reversed upon comparing relevant patents. This indicates a growing interest in the implementation of photocatalysis for air treatment purposes, which surpasses that of water treatment. This manuscript analyzes the various patents in the area of air treatment, while differentiating between indoor air treatment and outdoor air treatment. Specific efforts were made to characterize the main challenges and achievements en-route for successful implementation, which were categorized according to mass transport, adsorption of contaminants, quantum efficiency, deactivation, and, no less important, the adherence and the long term stability of the photocatalyst.

Metal–support interactions in Pt/Al2O3 and Pd/Al2O3 catalysts for CO oxidation

Abstract: Platinum and palladium catalysts supported on γ-Al2O3 were studied by XRD, UV–vis DRS, HRTEM, TPR-H2, XPS together with measurements of their catalytic properties. The properties of the catalysts denoted as Pt(Pd)/Al2O3(X)-Y (X—the calcination temperature of support, °C; Y—the calcination temperature of catalyst, °C) were studied as a function of the temperatures used for calcination of the support and/or the catalyst in oxygen or in a reaction mixture of CO + O2. It was found that the deposition of Pt or Pd on γ-Al2O3 did not alter the structure of the support. Two types of the Pt and Pd particles were typically present on the γ-Al2O3 surface: individual particles with dimensions of 1.5–3 nm and agglomerates about 100 nm in size. In the catalysts calcined at relatively low temperatures (Pt/Al2O3(550)-450), platinum was present in the form of metal clusters. However, in the Pd/Al2O3(550)-450 catalyst, the palladium particles were almost completely decorated with a thin layer of an aluminate phase. These structures are not reduced in hydrogen in the temperature range of −15 to 450 °C, and are stable to treatment in a reaction mixture of CO + O2. Pd deposition on the γ-Al2O3-800 support was found to result in stabilization of the active component in two main forms, Pdo and PdO, with varying degrees of interaction due to the decoration effect. Calcination at the low temperature of 550 °C led to the formation of a so-called “core–shell structure”, where a palladium metal core is covered with a thin shell of an aluminate phase. Depending on the calcination temperature of the catalyst in the range of 450–1000 °C, the morphological form of the active component was converted from the “core-shell” state to a state consisting of two phases, Pdo and PdO, with a gradual decrease of the Pdo/PdO ratio, weakening the interaction with the support and the growth of palladium particles. Under the action of the reaction mixture, the Pd/Al2O3(800)-(450,600,800,1000) catalysts underwent changes in the Pdo/PdO ratio, which regulates the light-off temperature. After catalyst calcination at the highest temperature used in this study, 1200 °C, the palladium particles became much larger due to the loss of the palladium interaction with the support. Only the metal phase of palladium was observed in these catalysts, and their catalytic activity decreases substantially.

Effect of silver doping on the TiO2 for photocatalytic reduction of CO2

Abstract: Pure TiO2 and various silver-enriched TiO2 powders were prepared by the sol–gel process controlled in the reverse micellar environment. The catalysts were tested in CO2 photocatalytic reduction and characterized by X-ray diffraction (XRD), nitrogen adsorption measurement and UV–vis. Methane and methanol were the main reduction products. The yield of methane and methanol increases when modifying the TiO2 by silver incorporation is caused by two mechanisms: up to 5% of Ag in TiO2 the Ag impurity band inside the TiO2 bandgap decreases the absorption edge and increases so the electron–hole pair generation, above 5% of Ag in TiO2 Ag metallic clusters are formed in TiO2 crystals with Shottky barrier at the metal–semiconductor interface, which spatially separates electron and holes and increases their lifetime (decreases probability of their recombination).

Production of advanced biofuels: Co-processing of upgraded pyrolysis oil in standard refinery units

Abstract: One of the possible process options for the production of advanced biofuels is the co-processing of upgraded pyrolysis oil in standard refineries. The applicability of hydrodeoxygenation (HDO) was studied as a pyrolysis oil upgrading step to allow FCC co-processing. Different HDO reaction end temperatures (230–340 °C) were evaluated in a 5 L autoclave, keeping the other process conditions constant (total 290 bar, 5 wt.% Ru/C catalyst), in order to find the required oil product properties necessary for successful FCC co-processing (miscibility with FCC feed and good yield structure: little gas/coke make and good boiling range liquid yields). After HDO, the upgraded pyrolysis oil underwent phase separation resulting in an aqueous phase, some gases (mainly CO2 and CH4), and an oil phase that was further processed in a Micro-Activity Test (MAT) reactor (simulated FCC reactor). Although the oil and aqueous phase yields remained approximately constant when the HDO reaction temperature was increased, a net transfer of organic components (probably hydrodeoxygenated sugars) from the aqueous phase to the oil phase was observed, increasing the carbon recovery in the oil product (up to 70 wt.% of the carbon in pyrolysis oil). The upgraded oils were subsequently tested in a lab scale catalytic cracking unit (MAT reactor), assessing the suitability of HDO oils to be used as FCC feed. In spite of the relatively high oxygen content (from 17 to 28 wt.%, on dry basis) and the different properties of the HDO oils, they all could be successfully dissolved in and co-processed (20 wt.%) with a Long Residue, yielding near normal FCC gasoline (44–46 wt.%) and Light Cycle Oil (23–25 wt.%) products without an excessive increase of undesired coke and dry gas, as compared to the base feed only. Near oxygenate-free bio-hydrocarbons were obtained, probably via hydrogen transfer from the Long Residue. In this way, we have demonstrated on a laboratory scale that it is possible to produce hydrocarbons from ligno-cellulosic biomass via a pyrolysis oil upgrading route. The much higher coke yields obtained from the catalytic cracking of undiluted HDO oil showed the importance of co-processing using a refinery feed as a diluent and hydrogen transfer source.

Electro-oxidation of glycerol at Pd based nano-catalysts for an application in alkaline fuel cells for chemicals and energy cogeneration

Abstract: Carbon supported Pd, Pt, Au and bimetallic PdAu and PdNi nano-catalysts with different compositions were synthesized. Their catalytic activity toward glycerol electro-oxidation was evaluated in alkaline medium. Physical and electrochemical methods where used to characterize the structure and the surface of the catalysts. It was shown that the PdxAu1−x/C catalysts were alloys, which present an increase of crystallite (XRD) and particle (TEM) sizes with increasing Au atomic fraction. Their surfaces were palladium rich whatever the Pd atomic ratio. The structure of the Pd0.5Ni0.5/C catalyst is much more difficult to understand, but it seems to be composed of a palladium phase in interaction with a Ni(OH)2 phase. The onset potential of glycerol oxidation is ca. 0.15 V lower on Pt/C than on Pd/C and Au/C. All PdxMe1−x/C catalysts presented lower onset potential than monometallic Au/C and Pd/C ones, but higher than Pt/C. For bimetallic catalysts, the order of activity at low potentials is: Pd0.3Au0.7/C > Pd0.5Au0.5/C > Pd0.5Ni0.5/C. Electrochemical experiments and in situ infrared spectroscopy measurements have shown that glycerol electro-oxidation mechanism is dependent on the catalyst, leading to different reaction products. Adsorbed CO species are detected on monometallic Pt and on Pd rich catalysts, but not on Au and Pd0.3Au0.7 catalysts, indicating that they are not able to break the C–C bond. The formation of hydroxypyruvate ion, which is a costly chemical product, is detected on pure gold catalyst.

Conversion of cellulose to hydrocarbon fuels by progressive removal of oxygen

Abstract: We report a catalytic process to convert cellulose into liquid hydrocarbon fuels (diesel and gasoline), using a cascade strategy to achieve the progressive removal of oxygen from biomass, allowing the control of reactivity and facilitating the separation of products. The process starts with the deconstruction of solid cellulose in an aqueous solution of sulfuric acid yielding an equi-molar mixture of levulinic acid and formic acid. The formic acid in this mixture can then be used (upon decomposition to H2 and CO2) to reduce levulinic acid to γ-valerolactone (GVL) in the sulfuric acid solution over a Ru/C catalyst. The formation of GVL allows strategies for the separation and recycling of the sulfuric acid used in the cellulose deconstruction step. This GVL product, with residual amounts of sulfur, can be upgraded to 5-nonanone with high yields (90%) in a single reactor by using a dual catalyst bed of Pd/Nb2O5 plus ceria-zirconia. The 5-nonanone product is hydrophobic and separates spontaneously from water, yet possesses a functional group that can be used to control the structure and molecular weight of hydrocarbon fuel components formed in downstream catalytic upgrading treatments.

A soft hydrogel reactor for cobalt nanoparticle preparation and use in the reduction of nitrophenols

Abstract: Bulk poly(2-acrylamido-2-methyl-1-propansulfonic acid) (p(AMPS)) hydrogels were prepared by irradiation of an aqueous solution of AMPS in the presence of crosslinker and photoinitiator. These p(AMPS) hydrogel networks were utilized for in situ cobalt nanoparticle synthesis by reduction of metal ions absorbed into the hydrogel network with a reducing agent, i.e., NaBH4. TEM images confirmed that Co particles are about 100 nm in size. The hydrogel network with embedded Co nanoparticles was utilized as a catalyst in the reduction of 4-nitrophenol (4-NP) and 2-nitrophenol (2-NP) in aqueous media in the presence of an excess amount of NaBH4. The kinetics of the reduction reaction under different reaction conditions was investigated to determine the activation parameters. Activation energies are 27.8 kJ mol−1 and 39.3 kJ mol−1 for 4-NP and 2-NP, respectively. It was found that hydrogel–Co composites were 99% active after 5 days storage.

S-doped α-Fe2O3 as a highly active heterogeneous Fenton-like catalyst towards the degradation of acid orange 7 and phenol

Abstract: S-doped α-Fe2O3 (α-Fe2O3/S) was synthesized with ferrous sulfate and Na2S2O3 via a hybrid hydrothermal-calcination treatment. The crystal phase, special surface area, morphology of the α-Fe2O3/S as well as the chemical state of the sulfur were studied by X-ray diffraction (XRD), scanning electro microscopy (SEM), Raman spectrum and X-ray photoelectron spectroscopy (XPS). The Fenton and photo-Fenton reactivities of the α-Fe2O3/S were tested by degrading acid orange 7 (AO7) and phenol. Although α-Fe2O3/S showed little Fenton reactivity in the dark, it had an excellent heterogeneous Fenton reaction under either UV or visible irradiation, while other α-Fe2O3s were still kept inactive. S element was found to dope into α-Fe2O3 in the forms of FeS or FeS2 in α-Fe2O3/S. The doped S element promotes the photo-Fenton reaction of α-Fe2O3/S via two roles: retarding the recombination of photogenerated charge carriers and promoting the electron transfer between the peroxide species and iron ions at the interface.

Highly valuable chemicals production from catalytic upgrading of radiata pine sawdust-derived pyrolytic vapors over mesoporous MFI zeolites

Abstract: The catalytic upgrading of pyrolytic vapors derived from radiata pine sawdust was carried out over mesoporous MFI zeolite synthesized using an amphiphilic organosilane. Its catalytic activity was compared with those of conventional HZSM-5 and mesoporous material from HZSM-5 (MMZZSM-5). The effect of gallium incorporation into mesoporous MFI zeolite on the product distribution and chemical composition of bio-oil was also investigated. The catalysts synthesized were characterized using ICP, XRD, N2-sorption, NH3-TPD, and H2-TPR methods. After catalytic upgrading, products were analyzed by GC–TCD, GC–FID, GC–MS, and Karl Fischer titration. The mesoporous MFI zeolite exhibited the best activity in deoxygenation and aromatization during the upgrading of pyrolytic vapors. In particular, mesoporous MFI zeolite showed high selectivity for highly valuable aromatics, such as benzene, toluene, and xylenes (BTX), even though it decreased the overall organic fraction of the bio-oil. The incorporation of gallium into the mesoporous MFI zeolite increased both the organic fraction of the bio-oil and resistance to coke deposition. Moreover, the selectivity for BTX aromatics was enhanced when the appropriate amount of gallium was introduced.

Visible-light sensitive cobalt-doped BiVO4 (Co-BiVO4) photocatalytic composites for the degradation of methylene blue dye in dilute aqueous solutions

Abstract: A series of visible-light sensitive Co-BiVO4 photocatalysts were synthesized by heteronuclear complexing method using diethylenetriamine pentaacetic acid (DTPA) as the chelating agent. The photocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM). UV-vis diffuse reflectance spectroscopy (DRS), and Raman spectroscopy. Results indicated that all Co-BiVO4 photocatalysts had a crystal structure of monoclinic scheelite. Loading BiVO4 with cobalt did not alter the crystal structure of the composites. Cobalt was present as oxides and was deposited on the surface of larger BiVO4 particles. The oxidation state of cobalt varied with its content in Co-BiVO4. The photocatalytic activity of Co-BiVO4 was studied by the decolorization of methylene blue (MB). BiVO4 containing 5% (molar wt) of cobalt exhibited the greatest photocatalytic activity with a 85% of MB removal versus 65% by pure BiVO4 in 5 h. Factors such as pH, initial MB concentration, electrolytes, and irradiation conditions that may affect the photodegradation of methylene blue were studied. High pH and low initial MB concentration resulted in fast photocatalytic reaction. Electrolytes, especially those capable of scavenging hydroxyls, can inhibit MB degradation. The stability of the photocatalysts was confirmed using reclaimed Co-BiVO4 in three successive runs. There was no loss of photocatalytic ability in three successive runs each of which lasted for 6h with BM removal remained high at >90%. Results demonstrated clearly that Co-BiVO4 was stable and resistant to photocorrosion during the photocatalytic oxidation of organic compounds such as methylene blue. (C) 2010 Elsevier B.V. All rights reserved.

Hydrodeoxygenation of 2-ethylphenol as a model compound of bio-crude over sulfided Mo-based catalysts: Promoting effect and reaction mechanism

Abstract: The hydrodeoxygenation of 2-ethylphenol was carried out under 7 MPa of total pressure and at 340 °C in a fixed-bed reactor over unpromoted Mo/Al2O3 catalyst and over two promoted catalysts (CoMo/Al2O3 and NiMo/Al2O3). For all experiments, dimethyldisulfide was added to the feed to maintain the sulfidation state of the catalysts. On these sulfided catalysts, the transformation of 2-ethylphenol is considered to proceed by three pathways: (1) prehydrogenation of the aromatic ring followed by a dehydration reaction leading to a mixture of alkenes (1-ethylcyclohexene and 3-ethylcyclohexene) and after hydrogenation leading to ethylcyclohexane (HYD pathway); (2) direct cleavage of the Csp2–O bond leading to ethylbenzene (DDO pathway); (3) disproportionation and isomerization reactions leading to oxygenated products (phenol, isomers of 2-ethylphenol and diethylphenols) and their deoxygenated products (ACI pathway). The production of those oxygenated compounds mainly involved the support acidity. The presence of nickel and cobalt allowed an increase of the deoxygenation rate. Nickel only promoted the HYD pathway whereas cobalt promoted both the HYD and DDO pathways. Consequently, the DDO/HYD selectivity was very dependent on the catalyst used. The highest DDO/HYD selectivity was obtained for CoMo/Al2O3. Sulfur vacancies are proposed as active sites for both deoxygenation pathways of 2-ethylphenol, although other active sites (e.g. brim sites) could be involved to explain that the HYD pathway was always predominant. For both deoxygenation pathways, two probable mechanisms are described. The adsorption mode of the molecule most likely determines the deoxygenation route.

Significant photocatalytic enhancement in methylene blue degradation of TiO2 photocatalysts via graphene-like carbon in situ hybridization

Abstract: Graphene-like carbon/TiO2 photocatalysts were prepared via a facile in situ graphitization approach. The introduction of graphene-like carbon to TiO2 effectively enhanced its photocatalytic activity. A graphene-like carbon/TiO2 photocatalyst with a monolayer carbon shell (0.468 nm) showed the highest photocatalytic activity which is about 2.5 times as high as that of pristine TiO2 (P25) under UV light irradiation. The mechanism of the enhanced photocatalytic activity is based on the synergetic effect between graphene-like carbon and TiO2. The synergetic effect caused a rapid photoinduced charge separation and decreased the possibility of recombination of electron–hole pairs, which increased the number of holes participated in the photooxidation process and enhanced the photocatalytic activity.