Showing papers in "Applied Catalysis A-general in 2014"

Production of green aromatics and olefins by catalytic cracking of oxygenate compounds derived from biomass pyrolysis: A review

Abstract: The concern for depletion of fossil fuels and their growing environmental threats necessitates to develop efficient techniques for utilization of biomass as an alternative fuel source which is renewable and environmentally safe. Catalytic cracking of biomass pyrolysis derived feedstock could be an economical process for production of high value added chemicals which are currently obtained from fossil fuels. However, promotion of reaction selectivity toward valuable chemicals is a great challenge in this process. Coke formation in catalytic cracking of biomass pyrolysis vapors/bio-oil is a competing reaction with production of valuable hydrocarbons like aromatics and olefins. Coke is one major undesired product of this process which its high yield is due to low hydrogen to carbon effective ratio of biomass and in turn low hydrogen content in hydrocarbon pool inside catalyst. Catalytic cracking of biomass pyrolysis vapors/bio-oil is a highly shape selective reaction with strong dependency on catalyst acidity and reaction conditions. This paper, for the first time, reviews the effects of catalyst properties and reaction conditions on reaction selectivity toward aromatics and olefins in catalytic cracking of biomass pyrolysis vapors/bio-oil and bio-oil model compounds.

Activity of solid acid catalysts for biodiesel production: A critical review

Abstract: a b s t r a c t Homogeneous acid catalysts received wide acceptability because of their fast reaction rates. However, postproduction costs incurred from aqueous quenching, wastewater and loss of catalysts led to the search for alternatives. Until recently, heterogeneous base catalyzed-biodiesel production also gained the atten- tion of most researchers. This was because the process minimized the problems of homogeneous catalysis in terms of catalyst regeneration and recycling in continuous processes. However, despite these advances, the ultimate aim of producing biodiesel at affordable cost is yet to be realized. Further, the process requires refined feedstocks which account for as high as 88% of the final production costs. Thus, the focus of many research efforts is towards the rational design and development of solid acid catalysts aimed at reduc- ing biodiesel production costs. Therefore, this study reviewed current literature on the activities and advantages of solid acid catalysts used in biodiesel production. It discussed in details how the prepara- tion method and prevailing reaction conditions affect the catalytic activity of the catalyst. The review concluded by suggesting way forward from the traditional trial-and-error method to a rational means of determining catalytic activities.

Catalytic fast pyrolysis of biomass with mesoporous ZSM-5 zeolites prepared by desilication with NaOH solutions

Abstract: This study investigated the effects of desilication of ZSM-5 zeolite on its catalytic properties in catalytic fast pyrolysis (CFP) of lignocellulosic biomass. A series of mesoporous ZSM-5 zeolites were prepared by desilication of a conventional microporous ZSM-5 zeolite with NaOH solutions of varying concentrations (0.1–0.5 M). The creation of mesopores improved the diffusion property of the desilicated ZSM-5 zeolites and their catalytic activity for cracking bulky oxygenates (e.g., syringols derived from the lignin component of biomass). Consequently, the desilicated zeolites produced more aromatic hydrocarbons (carbon yields of 26.2–30.2%) and less coke (39.9–41.2%) in CFP of beech wood than the parent microporous ZSM-5 (23.2% aromatics and 44.4% coke). The highest aromatic yield (30.2%) and lowest coke yield (39.9%) were obtained in CFP of beech wood with mildly desilicated zeolite treated with 0.3 M NaOH solution. However, desilication with a greater concentration, 0.5 M NaOH, decreased the aromatic yield to 26.2% due to a considerable loss of microporosity in the severely desilicated zeolite. The results indicate that carefully controlled desilication of zeolite can improve the conversion of lignocellulose to valuable aromatic hydrocarbons and decrease the formation of undesired coke, thus improving the product distribution in CFP of lignocellulose.

Recent development of mixed metal oxide anodes for electrochemical oxidation of organic pollutants in water

Abstract: Mixed metal oxides (MMOs) have been extensively employed for heterogeneous catalysis. In recent years, MMOs have received an intensive interest as anode materials for electrochemical treatment of wastewaters which contain recalcitrant organics. This review article gives an overview of the classification of MMO anodes systems, synthesis methods, characterization techniques, and recent advance of removing or alleviating various recalcitrant organic pollutants using MMO anodes, highlighting areas of consensus and currently unresolved issues. Practical issues pertinent to modification to the catalytic activities of MMO anodes are discussed, including nano- and microstructured deposits, doping and polymer composites. Electrogenerated reactive oxygen species (ROS) with MMO anodes and their determination by various techniques have also been reviewed. In addition, this article discusses several important factors which could affect the electrochemical oxidation of recalcitrant organics with MMO anodes, and critically identifies the shortcomings in current research including discrepant results and ambiguous conclusions. Finally, the challenges and possible improvement of MMO anodes for their future application are also proposed.

Liquid phase catalytic transfer hydrogenation of furfural over a Ru/C catalyst

Abstract: Methyl furan production through catalytic transfer hydrogenation of furfural in the liquid phase has been investigated over a Ru/C catalyst in the temperature range of 120–200 °C using 2-propanol as a solvent. It has been found that furfural hydrogenation produces furfuryl alcohol, which undergoes hydrogenolysis to methyl furan. Small amounts of furan and traces of tetrahydrofurfuryl alcohol are also produced via furfural decarbonylation and furfuryl alcohol ring hydrogenation, respectively. Furfuryl alcohol can dimerize or produce ether with 2-propanol. The yield of methyl furan is enhanced with increasing reaction temperature and/or reaction time. Optimum results are attained after 10 h of reaction at 180 °C, where furfural conversion and methyl furan yield reach 95% and 61%, respectively, which is the highest reported yield in the liquid phase at temperatures lower than 200 °C. The reaction network has been investigated by analysing the evolution of reaction intermediates and products and by starting from furfuryl alcohol, methyl furan, and furan hydrogenation. Intermediates, as well as methyl furan, are produced faster when starting with furfuryl alcohol as the reactant, rather than furfural, indicating that initial hydrogenation of furfural to furfuryl alcohol is slow. Catalyst recycling experiments over spent Ru/C catalyst show that, although furfural conversion does not decrease significantly, furfuryl alcohol yield increases at the expense of methyl furan. The initial catalytic activity and selectivity are regained completely after catalyst regeneration. We show evidence that the active phase of the catalyst involves Ru and RuO x .

Fischer–Tropsch synthesis: A review of the effect of CO conversion on methane selectivity

Abstract: Methane is the least desired product for the Fischer–Tropsch synthesis so that it is of paramount importance to reduce methane selectivity in the FT process. Despite numerous efforts devoted to the reduction of methane selectivity, the effect of CO conversion on methane selectivity is still not well defined. For cobalt and ruthenium based catalysts, methane selectivity generally decreases monotonically with increasing CO conversion within the range 20–80%, while on iron catalysts, the methane selectivity is more influenced by its water–gas shift activity and potassium promotion. Methane selectivity remains more or less constant at conversion lower than 70% for potassium promoted iron catalysts. Pressure and temperature have a greater influence on methane selectivity for Co and Ru based catalysts. Pressure and temperature change the preference of the secondary reactions of primary olefins and tune methane selectivity at different CO conversions. An increased extent of olefin readsorption may compete with methyl intermediates for surface sites and hence reduce methane selectivity. Water seems to play an important role in determining the dependence of CH4 selectivity on CO conversion for the Co and Ru based catalysts by either inhibiting the hydrogenation reaction or by increasing the amount of surface carbon for chain growth. Choosing appropriate promoters and process conditions may reduce methane production.

A critical review on the recent progress of synthesizing techniques and fabrication of TiO2-based nanotubes photocatalysts

Abstract: One-dimensional titanium dioxide (TiO2)-based nanotubes have attracted great interest to be used as photocatalysts in the field of environmental applications. Three main approaches via template-assisted, electrochemical anodic oxidation and alkaline hydrothermal treatment used to prepare the nanostructured TiO2-based nanotubes are reviewed. The parameters that affect the formation of TiO2-based nanotubes via hydrothermal method such as phases and particle sizes of starting materials, types and concentrations of alkaline solution, temperature and duration of hydrothermal treatment, ultrasonication- and microwave-assisted hydrothermal synthesis, acid washing and calcination have been reviewed in details. This paper also discussed the possible crystal structure and formation mechanism of TiO2-based nanotubes via alkaline hydrothermal treatment. In addition, the recent research progress on the structural modification of TiO2-based nanotubes to be used as photocatalysts is summarized in this review. Modification strategies investigated include metal nanoparticles deposition, single- and co-doping of metal ions/non-metal ions, coupled with other semiconductors to form binary composites and hybrid with carbon nanomaterials.

Kinetics of hydrodeoxygenation of stearic acid using supported nickel catalysts: Effects of supports

Abstract: The hydrodeoxygenation of fatty acids derived from vegetable and microalgal oils is a novel process for production of liquid hydrocarbon fuels well-suited with existing internal combustion engines. The hydrodeoxygenation of stearic acid was investigated in a high pressure batch reactor using n-dodecane as solvent over nickel metal catalysts supported on SiO 2 , γ-Al 2 O 3 , and HZSM-5 in the temperature range of 533–563 K. Several supported nickel oxide catalysts with nickel loading up to 25 wt.% were prepared by incipient wetness impregnation method and reduced using hydrogen. The catalysts were then characterized by BET, TPR, H 2 pulse chemisorption, TPD, XRD, and ICP-AES. Characterization studies revealed that only dispersed nickel oxide was present up to 15 wt.% nickel loading on γ-Al 2 O 3 . The acidity of the supports depends on nickel loading of oxidized catalysts and increases with increasing nickel loading up to 15 wt.%. n-Pentadecane, n-hexadecane, n-heptadecane, n-octadecane, and l-octadecanol were identified as products of hydrodeoxygenation of stearic acid with n-heptadecane being primary product. The catalytic activity and selectivity to products for hydrodeoxygenation of stearic acid depends strongly on acidity of the supports. The maximum selectivity to n-heptadecane was observed with nickel supported γ-Al 2 O 3 catalyst. A suitable reaction mechanism of hydrodeoxygenation of stearic acid was delineated based on products distribution. The conversion of stearic acid was increased with increasing reaction time, nickel loading on γ-Al 2 O 3 , temperature, and catalyst loading. Complete conversion of stearic acid was accomplished with more than 80% selectivity to n-heptadecane at reasonable reaction temperature of 563 K after 240 min of reaction using 15 wt.% Ni/γ-Al 2 O 3 catalyst. An empirical kinetic model was also developed to correlate the experimental data.

Solar photocatalytic activity of nano-ZnO supported on activated carbon or brick grain particles: Role of adsorption in dye degradation

Abstract: In precedent work, nano-ZnO was supported on activated carbon or brick grain particles using simple co-precipitation method. Successful formation of ZnO-activated carbon (ZnO-AC) and ZnO-brick grain particle (ZnO-BGP) nanocomposites was ascertained by various spectral techniques. Scanning electron microscope (SEM) images revealed that ZnO particles were highly dispersed in activated carbon/brick grain particles. The size of ZnO-AC and ZnO-BGP was found to be 70 and 80 nm, respectively. Both ZnO-AC and ZnO-BGP exhibited excellent adsorption and photocatalytic activity for malachite green (MG) and congo red dye (CR) degradation. The adsorption data for MG and CR removal followed pseudo second order kinetic model. The adsorption capacity followed the order: ZnO-AC > ZnO-BGP > ZnO. The effect of adsorption on photocatalysis was explored under different reaction conditions. Simultaneous adsorption and photocatalysis (A + P) exhibited promoting effect on dye degradation. While adsorption followed by photocatalysis (A − P) had retarding effect on dye removal. ZnO-AC/A + P system emerged as highly efficient for MG and CR degradation. The rate of photodegradation followed pseudo first order kinetics. Using ZnO-AC/A + P system, 99 and 92% of COD removal was attainted for MG and CR degradation, respectively. The oxidative degradation mainly occurred through hydroxyl radicals. The prepared nanocomposites possessed higher recyclability and could be easily separated from solution by sedimentation.

Enhancing the production of renewable petrochemicals by co-feeding of biomass with plastics in catalytic fast pyrolysis with ZSM-5 zeolites

Abstract: This study investigated catalytic fast pyrolysis (CFP) of a series of biomass (cellulose, lignin, and pine wood), plastics (low-density polyethylene (LDPE), polyethylene (PP), and polystyrene (PS)), and their mixtures with ZSM-5 zeolite. Co-feeding of cellulose with LDPE (mixing ratios of 4–1) produced much higher petrochemical (aromatics and olefins) yields (52.1–55.6 C%) and lower solid (coke/char) yields (22.6–10.9 C%) than those expected if there were no chemical interactions between the two feedstocks in co-feed CFP (37.4–39.2 C% and 25.0–15.9 C% for petrochemicals and solid, respectively, calculated by linear addition of the corresponding yields determined in CFP of cellulose and LDPE individually). This result indicates that cellulose and LDPE have a significant synergy that enhances the production of valuable petrochemicals and decreases the undesired coke in CFP. Similar synergy was also observed in co-feed CFP of pine wood and LDPE mixtures (mixing ratio of 2), which produced 49.5 C% petrochemicals and 19.5 C% solid residue. In comparison, CFP of pine wood and LDPE individually produced only 31.6 C% and 41.0 C% petrochemicals and 46.5 C% and 6.74 C% solid, respectively. This synergy, however, was less pronounced for the other combinations of biomass and plastics (cellulose/PP, cellulose/PS, and lignin/LDPE) tested in this study. The results suggest that the interactions between the primary pyrolysis products of cellulose and LDPE, especially Diels–Alder reactions of cellulose-derived furans with LDPE-derived linear α-olefins, play an important role in the synergy for petrochemical production and coke reduction in co-feed CFP. Co-feeding LDPE thus has great potential in improving the performance of CFP of natural lignocellulosic biomass, which usually contains a significant fraction (40–50 wt.%) of cellulose component.

Comparison of photocatalytic efficiency of supported CuO onto micro and nano particles of zeolite X in photodecolorization of Methylene blue and Methyl orange aqueous mixture

Abstract: The present study compares the photocatalytic decolorization ability of CuO as supported onto both micronized zeolite X (CuO/MX) and zeolite X nano-particles (CuO/NX) toward aqueous mixture of Methyl Orange (MO) and Methylene Blue (MB). Both photocatalysts were characterized by XRD, SEM, BET, FT-IR and DRS. The progress of the photodecolorization of the proposed mixture was monitored using UV–vis spectrophotometer. The decolorization of dyes was systematically studied by varying the experimental parameters in order to achieve maximum decolorization efficiency. Application of the Langmuir–Hinshelwood kinetics allowed calculating the photodecolorization rate constants. CuO/NX was more efficient than CuO/MX and also, MO was more degraded than MB. The reusability of the photocatalyts was also tested and the decolorization activities of 90% and 88% were respectively obtained for CuO/NX and CuO/MX after four recycles.

Effects of support identity and metal dispersion in supported ruthenium hydrodeoxygenation catalysts

Abstract: Substituted phenols are the most recalcitrant oxygenates in conventional pyrolysis oils and the dominant oxygenates in lower-oxygen content, formate-assisted pyrolysis oils (FAsP). Ru catalysts with a wide range of dispersion on carbon, silica, alumina, and titania supports were synthesized, characterized and evaluated for hydrodeoxygenation (HDO) activity using phenol as a model compound. Metal content, phase, and particle size were determined with ICP-OES, EXAFS/XANES, and CO pulse chemisorption, respectively. High dispersion of ruthenium on the supports converts more phenol to products. The majority of catalysts predominantly catalyze the hydrogenation (HYD) route typical of noble metal catalysts. A highly dispersed Ru/TiO2 catalyst shows unusually high selectivity toward direct deoxygenation (DDO) and outstanding activity. We suggest that the DDO pathway on titania involves a bifunctional catalyst, where hydrogen creates reduced titania sites, created by hydrogen spillover, that interact strongly with the phenol hydroxyl group.

Development of highly stable catalyst for methanol synthesis from carbon dioxide

Abstract: Zr-doped Cu-Zn-Zr-Al (CZZA) catalyst showed excellent performances for the methanol synthesis from carbon dioxide and hydrogen such as activity, selectivity and especially stability under mild conditions (such as 230 °C and 3.0 MPa). The catalyst showed excellent tolerance against water vapor. It was found that added alumina promoted the dispersion of Cu whereas it suppressed the reduction of copper oxide. On the other hand, added Zr promoted the catalytic activity of methanol synthesis from CO 2 and suppressed the inhibitive effect of water for the reaction as well as the catalyst deactivation. It was concluded that the methanol formation from CO 2 proceeds through two routes: one is the direct hydrogenation of CO 2 to methanol and another is the one which pass through the CO formation. The Zr-promoted catalyst gave methanol and CO at the selectivity ratio of 0.4 to 0.6, whereas the un-promoted catalyst gave only CO at the initial stage of the reaction. It was claimed that the doped Zr promote the in-situ reduction of oxidized Cu (which should be caused by the reaction with the co-product H 2 O) by H 2 to increase the content of reduced Cu (active site) and thus the catalyst activity. The promoted reductivity of the Zr-containing catalyst prevents the crystal growth of CuO x which cause the irreversible deactivation of catalyst.

Anisole hydrodeoxygenation over Ni–Cu bimetallic catalysts: The effect of Ni/Cu ratio on selectivity

Abstract: The activity and selectivity of model NiCu–SiO 2 catalysts with the high metal loading (90%) and various Ni content was studied in anisole hydrotreatment at 280 °C and a hydrogen pressure of 6 MPa in a batch reactor. To obtain the alloys with the homogeneous phase composition, the catalysts were prepared by simultaneous decomposition of metal salts with the subsequent stabilization with 10 wt% SiO 2 . The composition of the Ni y Cu 1− y alloy surface was estimated from the combination of XPS and XRD data. On the basis of obtained kinetic data, a reaction scheme of anisole conversion was proposed. The scheme includes two parallel routes, one of which leads to C ar O bond cleavage with the formation of benzene, which is then converted to cyclohexane (HDO route), while the second route leads to hydrogenation of the aromatic ring of anisole with the formation of methoxycyclohexane and cyclohexanol (HYD route). The experimental dependence of anisole conversion was described by the first-order kinetics with respect to the reagents. The effect of the surface composition of the active phase Ni y Cu 1− y on the specific catalytic activity was examined. According to the proposed reaction scheme, the dependence of the first-order rate constants for both routes on the nickel content in the active component of the catalysts was determined. The selectivities of both reaction routes of anisole conversion (HDO and HYD) were found to be independent of the Ni content except for the nickel-rich and copper-rich sides. The specific catalytic activity in the HDO route rises with an increase in the nickel content in the whole range of Ni loading.

Efficient aerobic oxidation of biomass-derived 5-hydroxymethylfurfural to 2,5-diformylfuran catalyzed by magnetic nanoparticle supported manganese oxide

Abstract: Magnetic fe3o4 supported mn3o4 nanoparticles (fe3o4/mn3o4) were prepared by the solvent thermal method, and its structure was characterized by xrd, xi's, tem, and ft-ir technologies the resulting fe3o4/mn3o4 nanoparticles could be used as an excellent heterogeneous catalyst for the aerobic oxidation of the biomass-derived model molecule 5-hydroxymethylfurfural into 2,5-diformylfuran (dff) under benign reaction conditions some important reaction parameters such as reaction temperature, catalyst amount, solvent, oxidant, and oxygen pressure were explored and high dff yield of 821% with hmf conversion of 100% were obtained in dmf under optimal reaction conditions more importantly, the catalyst could be readily separated from the reaction mixture by a permanent magnet, and recycled up to 6 times without the significant loss of its catalytic activity (c) 2013 elsevier bv all rights reserved

Dealuminated Beta zeolite as effective bifunctional catalyst for direct transformation of glucose to 5-hydroxymethylfurfural

Abstract: To improve the catalytic performance of Beta zeolite in the direct transformation of glucose into 5-hydroxymethylfurfural (HMF), effects of calcination and steam treatment on the structure of Al atoms in the framework and acid properties of Beta zeolite were examined in detail 27Al MAS NMR measurement and IR observation revealed that a part of Si–O–Al bonds in the framework were cleaved to form Al species out of the * BEA framework during the treatments and these species showed Lewis acidity Especially, when the ammonium-type Beta was calcined over 700 °C or treated with steam (50 kPa in N2 balance) over 500 °C, the amount of Lewis acid sites was increased at the expense of Bronsted acid sites Thus prepared Beta zeolite catalysts having a sufficient amount of Lewis acid sites were found to be effective bifunctional catalysts in synthesis of HMF from glucose; for example, Beta zeolite prepared by the calcination at 750 °C showed 55% selectivity to HMF at 78% conversion of glucose We clarified the roles of Lewis and Bronsted acid sites on the Beta zeolite in the direct transformation of glucose to HMF Furthermore, the reaction mechanism for the isomerization of glucose was investigated by means of isotope experiment using deuterated glucose Finally, reusability of the Beta zeolite was also investigated

Methanation of carbon dioxide on metal-promoted mesostructured silica nanoparticles

Abstract: a b s t r a c t Metal-promoted mesostructured silica nanoparticles (MSN) have been studied for CO2 methanation under atmospheric pressure. In term of activities, high activity was observed on Rh/MSN, Ru/MSN, Ni/MSN, Ir/MSN, Fe/MSN and Cu/MSN at and above 623 K. However, on an areal basis, Ni/MSN was the most active catalyst, while Ir/MSN was the poorest catalyst. The catalysts have also been studied for elu- cidation of the role of each metal, MSN and metal/MSN in CO2 methanation by in situ FTIR spectroscopy studies. Firstly, CO2 and H2 was adsorbed and dissociated on metal sites to form CO, O and H atoms, followed by migration onto the MSN surface. The dissociated CO then interacted with oxide surfaces of MSN to form bridged carbonyl and linear carbonyl, while the presence of H atom facilitated the formation of bidentate formate. These three species could be responsible for the formation of methane. However, the bidentate formate species could be the main route to formation of methane. MSN support has been found to play an important role in the mechanism. MSN support served the sites for carbonyl species which act as precursors to methane formation. These results provided new perspectives in the catalysis, particularly in the recycling of CO2. © 2014 Elsevier B.V. All rights reserved.

Pd-grafted porous metal–organic framework material as an efficient and reusable heterogeneous catalyst for C–C coupling reactions in water

Abstract: Palladium nanoparticles (Pd NPs) have been grafted at the surfaces of a Co-containing metal–organic framework material MCoS-1. The Pd NPs grafted material Pd(0)/MCoS-1 has been characterized by HR TEM, XPS and EPR spectroscopic analyses. Pd(0)/MCoS-1 showed excellent catalytic activities in Suzuki–Miyaura cross-coupling reaction for the synthesis of a diverse range of biaryl organics in water. Sonogashira cross-coupling between terminal alkynes and aryl halides has also been carried out over this Pd-nanocatalyst in water without the addition of any Cu co-catalyst. In both reactions the catalyst is easily recoverable and can be reused for several times without appreciable loss of catalytic activity. No evidence of the leaching of Pd from the catalyst during the course of reaction has been observed, suggesting true heterogeneity in our catalytic systems.

Highly efficient reduction of 4-nitrophenol by heterostructured gold-magnetite nanocatalysts

Abstract: In this study, the catalytic reduction of 4-nitrophenol by heterostructured Au–Fe 3 O 4 nanocatalysts using NaBH 4 as the reducing agent was investigated under various environmental conditions. The electron behaviors at the interface of Au and Fe 3 O 4 nanoparticles were examined to elucidate the reaction mechanisms for 4-nitrophenol reduction. The transmission electron microscopic images show that the average particle size of Au–Fe 3 O 4 heterostructures increases slightly from 14 to 18 nm after phase transfer from oil phase to aqueous solution. The X-ray photoelectron and X-ray absorption near edge spectroscopic results show the electron flow from Au seeds to Fe 3 O 4 , resulting in the formation of positively charged Au surface to accelerate the catalytic reduction efficiency and rate of 4-nitrophenol. In addition, the reduction of 4-nitrophenol is a surface-mediated reaction and the catalytic efficiency and rate of 4-nitrophenol is highly dependent on the initial 4-nitrophenol concentration, pH, and reaction temperature. The increase in pH lowers the reduction efficiency and rate of 4-nitrophenol and a 2.4-fold decrease in the pseudo-first-order rate constant is observed when pH increases from 5 to 9. In addition, the Au–Fe 3 O 4 nanocatalysts show a good separation ability and reusability which can be repeatedly applied for complete reduction of 4-nitrophenol for at least six successive cycles without the loss of morphology and saturation magnetization. Results obtained in this study clearly demonstrate that the Au–Fe 3 O 4 heterostructures are excellent nanocatalysts which can be applied in heterogeneous catalysis, water treatment, and green chemistry.

Nanostructured Ce0.7Mn0.3O2−δ and Ce0.7Fe0.3O2−δ solid solutions for diesel soot oxidation

Abstract: Nanostructured Ce 0.7 Mn 0.3 O 2− δ (CM) and Ce 0.7 Fe 0.3 O 2− δ (CF) solid solutions were prepared by a facile coprecipitation method and evaluated for soot oxidation. The structural, morphological, and surface properties were investigated by various techniques, namely, XRD, ICP-OES, BET surface area, SEM-EDX, TEM-HRTEM, UV–vis DRS, Raman, FT-IR, XPS, H 2 -TPR, and TGA-DTA. XRD and TEM results confirmed formation of nanocrystalline solid solutions with the incorporated Mn and/or Fe cations in the ceria lattice. SEM studies ensured nanoparticle nature of Ce–Mn–O and Ce–Fe–O solid solutions with homogeneous distribution. ICP-OES and EDX analysis confirmed actual amount of metal loadings in the respective catalysts. UV–vis DRS and Raman results revealed the formation of more oxygen vacancies, which lead to the creation of more surface active species (Ce 4+ /Ce 3+ and O*). XPS results revealed that the doping of Mn and/or Fe into the ceria lattice makes some Ce 4+ transferred into Ce 3+ in order to maintain the electrical neutrality, thereby facilitate the reduction of Ce 4+ → Ce 3+ and the formation of oxygen vacancies. TPR results showed that the mixed oxides reduce at lower temperatures than pure ceria. This observation confirmed that there is a synergetic interaction between Ce–O and M–O (M = Mn, Fe). The catalytic activity of CM and CF samples towards soot oxidation has been evaluated under tight contact conditions and compared with the well-established CeO 2 –ZrO 2 (CZ) catalyst. Among the investigated catalysts, the Mn and/or Fe doped ceria solid solutions showed improved catalytic activity. The order of activity is as follows: CM > CF > CZ > C. Further, the CM and CF catalysts were found to be thermally quite stable compared to pure ceria. In particular, the CM sample exhibited superior catalytic activity ( T 50 = ∼665 K) and thermal stability towards soot oxidation.

Enhanced sunlight photocatalytic performance over Nb2O5/ZnO nanorod composites and the mechanism study

Abstract: Highly effective Nb 2 O 5 /ZnO nanorods (NRs) were synthesized via a hydrothermal–precipitation method and characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Brunauer–Emmett–Teller (BET) surface area analysis and photoluminescence (PL) spectroscopy. Under natural sunlight irradiation, Nb 2 O 5 /ZnO NR composites degraded phenol efficiently and displayed much higher photocatalytic activity than those of pure ZnO, commercial Nb 2 O 5 and Degussa P25. Mineralization and intermediates detection upon phenol degradation under natural sunlight, fluorescent light and UV irradiation were systematically studied. The results showed that phenol was almost completely mineralized under sunlight irradiation over the Nb 2 O 5 /ZnO NRs, while 26.1 and 40.7% of organic carbons were removed under fluorescent light and UV irradiation, respectively that could be associated with the formation of muconic acids and others resulting aromatic ring products. PL analysis suggested that 2 at% Nb 2 O 5 /ZnO NRs had the lowest electrons and holes recombination rate and revealed good degradation and mineralization efficiencies after 4 times of cycle experiments. Terephthalic acid-photoluminescence (TA-PL) probing test and radical scavenger experiments revealed that hydroxyl radicals were the predominant oxidative species while the hole and superoxide anion radical could be negligible. It was worth nothing that the possible transfer process of photogenerated charge carriers based on the band structures of Nb 2 O 5 and ZnO NRs was also proposed.

Influence of support on the aerobic oxidation of HMF into FDCA over preformed Pd nanoparticle based materials

Abstract: Here, the preparation and evaluation of supported nanoparticle based catalytic material is reported. Polyvinylpyrrolidone (PVP) stabilized palladium nanoparticles with a mean particle size of 1.8 nm were synthesized in ethylene glycol and subsequently deposited onto different metal oxide supports (TiO2, γ-Al2O3, KF/Al2O3, and ZrO2/La2O3). The prepared catalysts were applied to the aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) in aqueous solution at atmospheric pressure (T = 90 °C, pO2 = 1 bar) and compared regarding their catalytic performance and stability. The highest FDCA yield (>90%) was obtained for the Pd/ZrO2/La2O3 catalysts which additionally showed a relatively stable catalytic performance when the material was reused. Various characterization methods including XRD, TEM, XPS, and AAS were applied to obtain information about the Pd NP before and after utilization in HMF oxidation. For the Pd/TiO2 the least changes in Pd NP structure were observed after using the material in HMF oxidation. This was attributed to a stronger interaction between the Pd NP and the TiO2 support compared to other supports used in the studies.

Selective hydrogenation of acetylene in excess ethylene using Ag- and Au–Pd/SiO2 bimetallic catalysts prepared by electroless deposition

Abstract: Selective hydrogenation of acetylene in excess ethylene has been investigated for a series of Ag- and Au–Pd/SiO2 bimetallic catalysts having incremental surface coverages of Ag and Au on the Pd surface. The catalysts were prepared by electroless deposition and characterized by atomic absorption spectroscopy and selective chemisorption. Both Ag- and Au–Pd/SiO2 catalysts showed increased selectivity of acetylene conversion to form ethylene, rather than ethane, at high coverages. The catalyst performance results suggest that at high coverages of Ag or Au on Pd, that result in small ensembles of Pd sites, acetylene is adsorbed as a π-bonded species that favors hydrogenation to ethylene. At low coverages, where ensemble sizes of contiguous Pd surface sites are much larger, acetylene is strongly adsorbed as a multi-σ-bonded species which preferentially forms ethane, lowering the selectivity to ethylene. Both kinetic analyses and the calculated turnover frequencies of acetylene conversion and ethane formation were consistent with the above explanation. The similar performance trends for Ag- and Au–Pd/SiO2 suggest that the bimetallic effect for these catalysts is geometric and not electronic in nature.

Enhanced catalytic performances of Ni/Al2O3 catalyst via addition of V2O3 for CO methanation

Abstract: Highly active and coking resistant Ni-V2O3/Al2O3 catalysts were prepared by co-impregnation method for CO and CO2 methanation. The influence of vanadium oxide addition on catalyst structure, distribution and reducibility of Ni species, morphology and surface characteristics, was investigated in detail. Compared to the catalyst without vanadium, the Ni-V2O3/Al2O3 catalysts showed significant improvement in the activity, thermal stability, and resistance to coke formation in CO methanation. In addition, these catalysts also showed high activities for CO2 methanation at both atmospheric and 2.0 MPa pressures. It was found that Ni3V2O8 was formed during the calcination of the Ni-V2O3/Al2O3 catalysts, which led to the formation of smaller Ni particle sizes (ca. 3.0 nm) as compared to the case without vanadium oxide addition. The higher catalytic activity over the Ni-V2O3/Al2O3 catalysts for CO methanation was mainly due to the larger H-2 uptake, the higher Ni dispersion as well as the smaller metallic Ni nanoparticles. The oxidation-reduction cycle of V2O3 could increase the oxygen vacancies, which enhanced the dissociation of CO2 by-product and generated surface oxygen intermediates, thus preventing carbon deposition on the Ni particles in CO methanation. (C) 2014 Elsevier B.V. All rights reserved.

Esterification of levulinic acid with ethanol over sulfated Si-doped ZrO2 solid acid catalyst: Study of the structure–activity relationships

Abstract: Esterification of levulinic acid with ethanol to produce ethyl levulinate was examined by using sulfated Si-doped ZrO 2 solid acid catalysts with enlarged surface areas and the relationships between the structural properties and catalytic performances were investigated. Structures of the catalysts were verified by XRD, nitrogen physisorption, FE-SEM, UV–vis and FTIR measurements. Acidity of the catalysts that substantially affect the catalytic activity was evaluated by NH 3 -TPD measurement. Incorporation of Si atom into the lattice structure of ZrO 2 (up to 30 mol% Si per Zr atom) afforded high-surface-area SiO 2 -ZrO 2 mixed oxides, and their sulfated forms provided increased numbers of sulfate anions and the associated acid sites. Several distinct correlations were found between the structural properties/acidities and catalytic activities, which suggested that (i) the number of accessible active acid sites and (ii) the accessibility of the organic reactants to the active sites play crucial roles in determining the overall activity. Among the catalysts tested, sulfated Si-doped ZrO 2 with optimum Si content (5.0–10 mol% Si per Zr) was found to be the best catalyst, the activity of which was far superior to that of the conventional sulfated ZrO 2 . In addition, direct conversion of cellulosic sugars (glucose and fructose) into levulinate esters was also examined, in view of their practical applications in acid-catalyzed biomass conversion processes.

Molecular size- and shape-selective Knoevenagel condensation over microporous Cu3(BTC)2 immobilized amino-functionalized basic ionic liquid catalyst

Abstract: A novel molecular size- and shape-selective catalyst, microporous metal-organic framework HKUST-1 immobilized amino-functionalized basic ionic liquid (ABIL-OH), was synthesized by facile impregnation and activation. Characterizations and catalytic results revealed that the catalytically active species ABIL-OH could be confined in well-defined HKUST-1 nanocavities via Cu NH2 coordination bond. The resulting ABIL-OH/HKUST-1 heterogeneous catalyst showed comparable catalytic activity and enhanced selectivity in liquid phase Knoevenagel condensation, and it could be recovered conveniently and reused at least 5 times without significant loss of its catalytic efficiency. Moreover, ABIL-OH/HKUST-1 catalyst demonstrated distinct size- and shape-selective properties for discrimination of reactants in Knoevenagel condensation. It was supposed that diffusion kinetics of reactants might be controlling step and play a more important role than the nature of the substituents in the confined microenvironment.

Sulfur poisoning of Ni-based anodes for Solid Oxide Fuel Cells in H/C-based fuels

Abstract: The present review is mainly dealing with the latest progress on sulfur poisoning of Solid Oxide Fuel Cell anodes, which in particular operate under reforming conditions. In general, sulfur seems to poison the electrochemical interface and at the same time or even faster blocks the catalytically active sites that are responsible for the H/C conversion, leading finally to the cells’ degradation. Worldwide research effort has focused on the development of efficient and tolerant anode materials against carbon deposition and/or sulfur poisoning and one viable approach has been through targeted modifications of the traditional Ni-based anode cermets. In this respect, the review comprises a brief description of anode materials that are less prone to carbon deposition, but the main interest is focused on the studied sulfur tolerant cermets. The latter have been classified into four groups, depending on whether the examined anode feed comprises H2S in H2 or H/Cs plus H2S fuels, while there is also discrimination between Ni-free and Ni-based anode materials. Finally, the main part of the discussion focuses on the published studies regarding the effect of sulfur on the reforming activity and consequently on the electrochemical performance of H/C fueled Ni-based SOFCs.

Functionalized phosphonium-based ionic liquids as efficient catalysts for the synthesis of cyclic carbonate from expoxides and carbon dioxide

Abstract: A series of novel functionalized phosphonium-based ionic liquids (FPBILs) were synthesized by a simple method, and first evaluated as catalysts for the synthesis of cyclic carbonates through the cycloaddition of CO2 to epoxides in the absence of co-catalyst and solvent. The FPBILs perform well in the cycloaddition reaction, especially the carboxyl-functionalized one. Over [Ph3PC2H4COOH]Br, the yield of propylene carbonate is 97.3% (TOF = 64.9 h−1) at 130 °C and 2.5 MPa in 3 h. The synergistic effects of polarization induced by hydrogen bonding and nucleophilic attack of Br−anion account for the excellent performance. Furthermore, the FPBILs with moderate methylene chain length show superior catalytic activity. It is because they have both strong acidity and weak electrostatic interaction between phosphonium cation and halide anion. The strong acidity facilitates the ring-opening of epoxyl, and the weak electrostatic interaction enhances the nucleophilic attack capability of Br−. It is envisaged that the metal- and solvent-free process has high potential for the catalytic conversion of CO2 into value-added chemicals.

Catalytic performance of supported nanosized cobalt and iron–cobalt mixed oxides on MgO in oxidative degradation of Acid Orange 7 azo dye with peroxymonosulfate

Abstract: Cobalt and mixed iron–cobalt oxides immobilized on MgO and their bulk analogues were prepared and their catalytic behavior in advanced oxidation of Acid Orange 7 (AO7) in aqueous solution using sulfate radical was investigated. The catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Mossbauer spectroscopy. Results showed that nanostructured oxide materials having spinel structure were obtained with good dispersion on the surface of MgO in the case of supported compounds. The performance of the as-prepared nanocatalysts in the activation of peroxymonosulfate (PMS) to generate sulfate radicals for degradation of AO7 was studied. It was found that the spinel oxides loaded on MgO are far more efficient for heterogeneous PMS activation than the unsupported ones, resulting in much faster AO7 removal rate. Complete degradation of 50 mg/L AO7 (>99%) could occur within a short duration of 10 min (for Co/MgO) to 25 min (for CoFe 2 /MgO) by using very low catalysts concentration of 0.15 g/L. The supported catalysts were also found more active than the homogeneous Co(II) ions and physical mixtures of corresponding bulk oxide and MgO. Kinetic studies showed that heterogeneous oxidation of AO7 in supported catalyst/PMS systems followed first order kinetics. The effect of several operational parameters, such as catalyst loading, PMS concentration, and pH on the AO7 degradation kinetics and removal efficiency was investigated. The catalysts studied presented stable performance during three runs of reuse with minor Co and Fe leaching even under acidic condition. Quenching studies by using ethanol and tert -butyl alcohol as radical scavengers were conducted which indicated that sulfate radicals are the primary reactive species responsible for the AO7 degradation. Results obtained reveal that the as-prepared catalysts could be potentially used in advanced oxidation technologies for organic dyes removal in water.

Effects of linker substitution on catalytic properties of porous zirconium terephthalate UiO-66 in acetalization of benzaldehyde with methanol

Abstract: A family of isoreticular metal-organic frameworks (MOFs), based on the UiO-66 structure, were synthesized from the two linker ligands containing electron-donating NH 2 -groups (2-amino-benzenedicarboxylic acid (H 2 N-H 2 BDC)) and electron-withdrawing NO 2 -groups (2-nitro-benzenedicarboxylic acid (O 2 N-H 2 BDC)). The catalytic performance of these materials was investigated with a combination of physicochemical and catalytic approaches in acetalization of benzaldehyde with methanol. The investigation of basicity and Lewis acidity was done by IR spectroscopy using CDCl 3 and 5-nonanone as probe molecules, respectively. The combination of physicochemical and catalytic investigations demonstrates that acid–base and catalytic properties of these materials depend on amount and type of functional groups presented in the linker units. Insertion of electron-donating NH 2 -groups into linker ligand leads to increase in the strength of basic sites in contrast to electron-withdrawing NO 2 -groups. The strength of Lewis acid sites decreases in order of UiO-66-NO 2 > UiO-66 > UiO-66-NH 2 , that leads to the decrease in their catalytic activity in acetalization of benzaldehyde with methanol in the same order.