Showing papers in "Applied Catalysis A-general in 2010"

Ionic liquids and catalysis: Recent progress from knowledge to applications

Abstract: This review gives a survey on the latest most representative developments and progress concerning ionic liquids, from their fundamental properties to their applications in catalytic processes. It also highlights their emerging use for biomass treatment and transformation.

Biomass into chemicals: Conversion of sugars to furan derivatives by catalytic processes

Abstract: Recently, the production of furan derivatives from sugars has become exciting in chemistry and in catalysis studies, because it aids one of the major routes for achieving sustainable energy supply and chemicals production. 5-Hydroxymethylfurfural (5-HMF), 2,5-furan-dicarboxylic acid (2,5-FDCA) and 2,5-dimethylfuran (2,5-DMF) have been called the “sleeping giants” of renewable intermediate chemicals. 5-HMF is a dehydration product of hexoses and a potential substitute of petroleum-based building blocks of various polymers. 2,5-FDCA is derived from oxidative dehydration of hexoses and is considered as one of the top 12 compounds made from a sugar into a value-added chemical [T. Werpy, G. Petersen, Top Value Added Chemicals From Biomass, 2004. Available electronically at http://www.osti.gov/bridge ]. 2,5-DMF is produced through hydrogenation of HMF and is less volatile and of 40% higher energy density than ethanol. This review discusses mainly the catalytic routes for the synthesis of 5-HMF, 2,5-FDCA, 2,5-DMF and other furanic derivatives from sugars. Meanwhile, the possible reaction mechanism for the conversion of hexoses is discussed, and furthermore, some promising research orientations and advantageous catalysts are suggested based on the major problems encountered in the recent research.

Immobilisation of titanium dioxide onto supporting materials in heterogeneous photocatalysis: A review

Abstract: The aim of this review is to offer an overview of the evolution in the use of different anchors (supports) for the immobilisation of a semiconductor photocatalyst, which is titanium dioxide (TiO2). Several supports and immobilisation techniques that are commonly used for the removal of contaminants in wastewater are discussed. Generally, the immobilisation of a photocatalyst onto supporting material has largely been carried out via one of two major routes; physical (the thermal treatment method) route or chemical (the sol–gel method, chemical vapour deposition, electrodeposition, etc.) route. The benefits and drawbacks of various immobilisation techniques to obtain a high surface area TiO2 support are also discussed.

The advancements in sol–gel method of doped-TiO2 photocatalysts

Abstract: A critical review on the advancements in sol–gel method of doping TiO2 photocatalysts is provided Various sol–gel and related systems of doping were considered, ranging from co-doping, transition metal ions doping, rare earth metal ions doping to other metals and non-metals ions doping of TiO2 The results available showed that doping TiO2 with transition metal ions usually resulted in a hampered efficiency of the TiO2 photocatalyst, though in some few cases, enhancements of the photocatalytic activity of TiO2 were recorded by doping it with some transition metal ions In most cases, co-doping of TiO2 increases the efficiency of its photocatalytic activity The review reveals that there are some elemental ions that cannot be used to dope TiO2 because of their negative effects on the photocatalytic activity of the catalyst, while others must be used with caution as their doping will create minimal or no impacts on the TiO2 photocatalytic efficiency

Deoxygenation of vegetable oils over sulfided Ni, Mo and NiMo catalysts

Abstract: Deoxygenation of vegetable oils has a potential to become an important process for production of biofuels. The present work focuses on investigation of Ni, Mo, and NiMo sulfided catalysts prepared by impregnation in deoxygenation of rapeseed oil at 260–280 °C, 3.5 MPa and 0.25–4 h −1 in a fixed-bed reactor. The activity of the catalysts decreased in the order NiMo/Al 2 O 3 > Mo/Al 2 O 3 > Ni/Al 2 O 3 . The catalysts exhibited significantly different product distributions. The bimetallic NiMo catalysts showed higher yields of hydrocarbons than the monometallic catalysts at a given conversion. Apart from the various oxygenated product intermediates, NiMo/Al 2 O 3 yielded a mixture of decarboxylation and hydrodeoxygenation hydrocarbon products while Ni/Al 2 O 3 yielded only decarboxylation hydrocarbon products and Mo/Al 2 O 3 yielded almost exclusively hydrodeoxygenation hydrocarbon products. The effect of Ni/(Ni + Mo) atomic ratio in the range 0.2–0.4 on the activity and selectivity was not significant.

Ni/CeO2-ZrO2 catalysts for the dry reforming of methane

Abstract: Nickel catalysts supported on binary CeO 2 –ZrO 2 carriers (28–100% CeO 2 molar content) were prepared and evaluated regarding their catalytic performance for the CO 2 reforming of CH 4 (Dry Reforming of Methane, DRM). The textural and structural properties of catalysts and supports were studied in their calcined, reduced and used state by N 2 adsorption–desorption, XRD, UV–vis DRS, TPR, SEM–EDS and TPH. Zirconium improves the textural properties of the CeO 2 –ZrO 2 supports and the corresponding catalysts and enhances their textural stability under thermal reductive treatment. XRD analysis shows the formation of Ce x Zr 1− x O 2 solid solution for all Ce/(Ce + Zr) ratios. Considerable alterations in the electronic environment of the cations and increased lattice defects in the binary solid solutions were detected by UV–vis DR spectroscopy. A significant increase in the reducibility of both supports and catalysts is observed in the presence of Zr. Compared to the zirconia-free sample, the Ni/CeO 2 -ZrO 2 catalysts exhibited much higher activity for the title reaction, accredited to the increase of the surface concentration of the active sites. However, the amount of carbonaceous deposits is not straightforward related to the activity but depends on the Ce/Zr ratio. Among the zirconium containing catalysts, the zirconium-rich one exhibited the higher activity and the stronger resistance to the formation of carbonaceous deposits.

Biochar based solid acid catalyst for biodiesel production

Abstract: A promising catalyst based on a biomass pyrolysis by-product, biochar, has been developed for the production of biodiesel Two carbon-based solid acid catalysts were prepared by sulfonating pyrolysis char with concentrated or fuming sulfuric acids Prepared catalysts were studied for their ability to catalyze transesterification of vegetable oils and esterification of free fatty acids The catalyst sulfonated with the concentrated sulfuric acid demonstrated considerable conversion in free fatty acid esterification, while indicating limited transesterification activity Using the stronger sulfonating reagent, fuming sulfuric acid, resulted in much higher transesterification activity Further investigation of the latter catalyst was conducted to determine the effect of sulfonation time (5 and 15 h) and surface area on the transesterification reaction The surface area of the biochar was increased by chemical treatment using 10 M potassium hydroxide through porosity development The resulting four catalysts were compared for their catalytic activity Results showed the catalyst with the highest surface area and acid density to have the highest catalytic activity for the production of biodiesel from canola oil in the presence of methanol as the reagent Furthermore, the catalyst with the higher surface area indicated higher transesterification activity among the catalyst with similar acid densities The effects of alcohol to oil (A:O) molar ratio, reaction time and catalyst loading on the esterification reaction catalyzed by the sulfonated biochar were also investigated Free fatty acid (FFA) conversion increased with increasing A:O molar ratio, reaction time and catalyst loading The catalyst has a tremendous potential to be used in a process converting a high FFA feedstock to biodiesel

Reduction of Fe2O3 with hydrogen

Abstract: The reduction of Fe 2 O 3 with hydrogen was studied. The thermodynamic analysis of the process implied that temperature-programmed reduction of the oxide should proceed in three steps, i.e. Fe 2 O 3 → Fe 3 O 4 → “FeO” → Fe, at X H 2 O / X H 2 ratio over 0.35, but in two steps, i.e. Fe 2 O 3 → Fe 3 O 4 → Fe, below that value. The idea was verified by TPR and XRD studies. Generally, the examinations confirmed the suggestions. The reduction is three-step reaction at high X H 2 O / X H 2 ratio, but two-step reaction at low that ratio. Additionally, it was revealed that at extremely low X H 2 O / X H 2 ratio the TP reduction is a one-step reaction, i.e. Fe 2 O 3 → Fe.

Gas-phase dehydration of glycerol to acrolein catalysed by caesium heteropoly salt

Abstract: Caesium 12-tungstophosphate, Cs2.5H0.5PW12O40 (CsPW), possessing strong Bronsted acid sites is an active catalyst for the dehydration of glycerol to acrolein in the gas-phase process at 275 °C and 1 bar pressure. The initial glycerol conversion amounts to 100% at 98% acrolein selectivity, however, decreases significantly with the time on stream (∼40% after 6 h) due to catalyst coking, without impairing acrolein selectivity. Doping CsPW with platinum group metals (PGM) (0.3–0.5%) together with co-feeding hydrogen improve catalyst stability to deactivation, while maintaining high selectivity to acrolein. The enhancing effect of PGM was found to increase in the order: Ru ∼ Pt < Pd. The catalyst 0.5%Pd/CsPW gives 96% acrolein selectivity at 79% glycerol conversion, with a specific rate of acrolein production of 23 mmol h−1 gcat−1 at 275 °C and 5 h time on stream, exceeding that reported previously for supported heteropoly acids (5–11 mmol h−1 gcat−1 per total catalyst mass). Evidence is presented regarding the nature of acid sites required for the dehydration of glycerol to acrolein, supporting the importance of strong Bronsted sites for this reaction.

Catalytic reaction pathways in liquid-phase deoxygenation of C18 free fatty acids

Abstract: The liquid-phase deoxygenation of stearic, oleic, and linoleic acids employing a 5 wt% Pd/C catalyst was investigated using on-line quadrupole mass spectrometry (QMS). Catalytic deoxygenation of stearic acid (SA) under He occurs primarily via decarboxylation; the liquid products are n-heptadecane and heptadecenes. On-line QMS revealed concomitant CO2 and H2 evolution which can explain the greater than expected heptadecene yields at low to intermediate conversions. After essentially complete SA conversion, hydrogenation of heptadecenes via hydrogen transfer from the dodecane solvent results in 98% n-heptadecane yield. The initial rate of SA decarboxylation under 10% H2 is lower than under He; however, by avoiding the formation of unsaturated products the reaction requires much less time to reach completion. The SA decarboxylation rate under 10% H2 is 6-fold slower in heptadecane than in dodecane. This apparent solvent effect is explained by the lower vapor pressure of heptadecane resulting in greater H2 inhibition of the decarboxylation reaction. Our results demonstrate that the unsaturated C18 free fatty acids, oleic and linoleic, must be hydrogenated to SA before decarboxylation can proceed at a significant rate. Oleic acid (OA) deoxygenation under He occurs very slowly and primarily via decarbonylation. In contrast, OA deoxygenation under 10% H2 occurs facilely via hydrogenation to SA followed by decarboxylation. Since hydrogenation is complete during heating to reaction temperature, the decarboxylation kinetics and product yields are not affected by the initial unsaturation of the reactant.

New catalytic route: Hydrogels as templates and reactors for in situ Ni nanoparticle synthesis and usage in the reduction of 2- and 4-nitrophenols

Abstract: Nickel nanoparticles inside poly(2-acrylamido-2-methyl-1-propansulfonic acid) (p(AMPS)) hydrogel were prepared by reduction of Ni(II) ions absorbed within hydrogel network. TEM images confirmed that in situ formed nickel particle in p(AMPS) hydrogel networks are about 100 nm. These nickel metal nanoparticles containing hydrogel-composites were utilized as catalysts and reaction media for the reduction reactions of aromatic nitro compounds, 2- and 4-nitrophenols with aqueous NaBH 4 . The reduction rate constants at four different temperatures (30, 40, 50 and 60 °C) and activation parameters were calculated. The activation energies ( E a ) for 4- and 2-nitrophenols are 25.70 and 38.69 kJ mol −1 , respectively. It was found that these types of hydrogel-composite catalyst systems can be used repetitively up to five times with 100% conversion and only with 25% reduction in the initial reduction rate.

Solar photodecolorization of methylene blue by CuO/X zeolite as a heterogeneous catalyst

Abstract: Semiconductor photocatalysis has proved to be an efficient method for decolorization and degradation of pollutants. In this study, a common semiconductor, CuO, as doped with synthetic zeolite NaX via wet impregnation of parent zeolite with Cu(NO 3 ) 2 aqueous solution was prepared. The potential of the obtained photocatalyst in decolorization of methylene blue (MB) dye under sunlight irradiation was studied. Characterization of parent zeolite NaX and prepared samples were studied using X-ray powder diffraction (XRD) patterns, infrared spectroscopy (FT-IR) spectra, diffuse reflectance spectroscopy (DRS), thermo analytical techniques (TG/DTG and DSC), SEM and BET methods. The active component value (CuO) on parent zeolite was also determined by atomic absorption spectroscopy (AAS) method on digested catalyst. The influence of experimental parameters on the dye photodecolorization process was studied and it was observed that photoreactivity of photocatalyst (CuO/X) varied with the amount of catalyst, initial dye concentration, pH of the dye solution, temperature, and active component value (CuO) loading. The role of zeolite NaX as a support was also investigated on decolorization rate. The optimal experimental conditions were determined as follow: catalyst amount; 1.0 g L −1 , concentration of the dye solution; 0.03 mM, pH of solution; 11, and active component value; 88 mg CuO per gram of the catalyst. Under these optimum conditions, the obtained decolorization efficiency for MB dye was 94%. The reusability of the intended catalyst was also investigated.

Palladium nanoparticles supported on MOF-5: A highly active catalyst for a ligand- and copper-free Sonogashira coupling reaction

Abstract: Palladium nanoparticles supported on MOF-5 (Pd/MOF-5), have been prepared by a chemical method at room temperature. MOF-5 and Pd/MOF-5 were characterized by X-ray diffraction, N 2 sorption, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. The catalyst consists of highly dispersed palladium nanoparticles (about 3–6 nm) on MOF-5 with a high surface area (533 m 2 /g). It exhibits efficient catalytic activity for the Sonogashira coupling reaction between aryl iodides and terminal acetylenes without the assistance of ligand and copper.

Tuning of nitrogen-doped carbon nanotubes as catalyst support for liquid-phase reaction

Abstract: This work reports the synthesis of nitrogen-doped carbon nanotubes (N-CNTs) using a Chemical Vapor Deposition (CVD) process at temperature ranging from 600 °C to 850 °C and ethane/ammonia concentration (defined as a volume percentage of C 2 H 6 /(C 2 H 6 + NH 3 )) of 20–100% Several characterizations, ie XPS, SEM and TEM were done on the as-synthesized nitrogen-doped carbon nanotubes in order to get more insight about the influence of the synthesis conditions on the characteristics and properties of these N-CNTs Depending on the synthesis conditions, the atomic percentage of nitrogen in carbon nanotubes varied from 0 at% to about 55 at% The undoped carbon nanotubes (N-free CNTs) and two kinds of N-CNTs with different types of nitrogen incorporated species have been used as the supports for palladium in the liquid-phase hydrogenation of cinnamaldehyde The introduction of nitrogen atoms into the carbon matrix significantly modified the chemical properties of the support compared to the N-free carbon nanotube resulting in a higher metal dispersion N-CNTs exhibit much higher activity in the hydrogenation reaction compare to the undoped ones Nitrogen incorporation also strongly improved the selectivity towards the C C bond hydrogenation The results show that the type of nitrogen species incorporated in CNTs structure can also influence the catalytic activity Recycling test confirms the high stability of the catalyst as neither palladium leaching nor deactivation has been observed

Syntheses of 5-hydroxymethylfurfural and levoglucosan by selective dehydration of glucose using solid acid and base catalysts

Abstract: Selective dehydration of glucose, the most abundant monosaccharide, was examined using a solid acid catalyst individually or a combination of solid acid and base catalysts to form anhydroglucose (levoglucosan) or 5-hydroxymethylfurfural (HMF), respectively. Glucose was dehydrated to anhydroglucose by acid catalysis in polar aprotic solvents including N,N-dimethylformamide. Amberlyst-15, a strongly acidic ion-exchange resin, functioned as an efficient solid acid catalyst for anhydroglucose production with high selectivity. In the presence of solid base, aldose–ketose isomerization of glucose to fructose preferentially occurred by base catalysis, even in coexistence with the solid acid, resulting in successive dehydration of fructose to 5-hydroxymethylfurfural by acid catalysis with high yield in a one-pot reaction. A combination of Amberlyst-15 and hydrotalcite, an anionic layered clay, afforded high HMF selectivity under a moderate reaction temperature, owing to prevention of anhydroglucose formation.

Sulfated titania [TiO2/SO42−]: A very active solid acid catalyst for the esterification of free fatty acids with ethanol

Abstract: Sulfated titanias were prepared by using ammonium sulfate and sulfuric acid as sulfate precursors. Depending on the sulfation method, important effects on the acidity, textural properties as well as on activity were found. After ammonium sulfate was used, a large amount of S O linked to the titania surface was observed by FTIR spectroscopy. The acidity strength determined with Hammett indicators showed strong acidity in the sulfated samples. The FTIR-pyridine adsorption spectra evidenced the presence of Lewis and Bronsted acid sites in the catalysts sulfated with ammonium sulfate, while in the titania sulfated with sulfuric acid, only Lewis-type sites were observed. The sulfated titanias showed very high activity for the esterification of fatty acids with ethanol in a mixture of oleic acid (79%). Conversions up to 82.2% of the oleic acid and selectivity to ester of 100% were reached after 3 h of reaction at 80 °C. The results showed that sulfated titanias are promising solid acid catalysts to be used in the esterification of free fatty acids with ethanol.

Esterification of oleic acid with ethanol by 12-tungstophosphoric acid supported on zirconia

Abstract: Esterification of organic acids with alcohols produces an industrially important class of substances with a variety of applications. This work presents an impregnation route to support H3PW12O40 (H3PW) on zirconia (ZrO2) in acidic aqueous solution (HCl 0.1 mol L−1) at different ratios (5, 10, 15, 20, 25, 40 and 60 wt%), which were further applied in the esterification of oleic acid with ethanol. Impregnated samples calcined at 200 °C for 4 h were characterized by FTIR, FT-Raman, XRD, 31P MAS NMR and BET surface area. No decomposition of the Keggin anion structure was observed under these conditions. The XRD results, surface area determination and catalytic tests pointed out that H3PW was well dispersed over the support and only a monoclinic phase of the commercial ZrO2 was detected. An optimum reaction performance (88% of oleic acid conversion) was achieved at 20 wt% loading, 100 °C, 4 h reaction and 1:6 (acid:ethanol) molar ratio. A small leaching of 8 wt% of the initial mass of this catalyst (i.e., the actual loading was 18.4 wt%) was also observed at the end of reaction, which affects the reaction kinetics. Thermal stability studies of 20%H3PW/ZrO2 catalyst, determined by 31P MAS NMR, XRD and FT-Raman revealed that Keggin anion decomposition begins at ca. 500 °C, which was confirmed by the respective decrease of the catalytic activity. A preliminary study of recyclability indicated that a treatment of the spent catalyst involving a sequence of washing with n-hexane, drying at 100 °C and calcining at 300 °C for 4 h, recovered conversion values as high as 70%.

Solvent-free aerobic oxidation of benzyl alcohol over Pd monometallic and Au–Pd bimetallic catalysts supported on SBA-16 mesoporous molecular sieves

Abstract: Pd monometallic and Au–Pd bimetallic catalysts supported on surface-functionalized SBA-16 were prepared by a conventional adsorption method and were examined using X-ray diffraction, nitrogen physisorption, UV–vis spectroscopy, and high-resolution transmission microscopy. SBA-16 with the unique “super-cage” structure effectively controlled the formation of dispersed noble metal nanoparticles in the mesoporous channels. These confined nanoparticles with a narrow particle size distribution exhibited excellent catalytic activity in the solvent-free benzyl alcohol selective oxidation with molecular oxygen. Amine-functionalization remarkably improved the selectivity towards benzaldehyde. Au–Pd bimetallic catalysts showed enhanced catalytic performance compared to the Au and Pd monometallic catalysts. The highest turnover frequency of 8667 h −1 was achieved over a bimetallic catalyst with Au:Pd molar ratio of 1:5; this good catalytic activity can be maintained after five recycling runs. The characterization results of scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy revealed that the bimetallic catalyst was constructed of uniformly alloyed nanoparticles with Pd cluster-on-Au cluster structure. The synergetic effect between Au and Pd nanocluster was suggested to account for the better catalytic activity of bimetallic catalysts because the size-dependent effect can be ruled out due to the effective confinement of noble metal nanoparticles by SBA-16 mesostructure.

Zr-doped TiO2 for enhanced photocatalytic degradation of bisphenol A

Abstract: Zr ions were successfully incorporated into the bulk lattice of TiO2 by a multi-step sol–gel process. The doping of Zr ions in TiO2 lattice reached about 30%. The Zr-doped TiO2 photocatalysts exhibited much higher photocatalytic efficiency than pure TiO2 in the degradation of bisphenol A (BPA) under UV irradiation and complete mineralization of BPA was achieved. The higher photocatalytic activity of Zr-doped TiO2 was attributed to gradually upward shift of the conduction bands with increasing Zr content, thus resulting in a stronger reduction power of photogenerated electrons and contributing to the improved photoactivity. The effects of initial BPA concentration, irradiation intensity, initial solution pH and inorganic anions on the photocatalytic performance of Zr-doped TiO2 were studied. The photodegradation of BPA was found to be optimized under a basic condition at pH 9. The addition of PO43−and SO42− anions enhanced the photocatalytic reaction but NO3−and Cl− ions showed detrimental effects.

Catalytic hydroconversion of tricaprylin and caprylic acid as model reaction for biofuel production from triglycerides

Abstract: There is strong interest in the production of fuels from triglycerides of biological origin. In this work tricaprylin (TC) and caprylic acid (CA) were used as model compounds to study the catalytic hydroconversion process of triglycerides to acyclic aliphatic hydrocarbons. Supported metal and metal oxide catalysts, such as palladium on activated carbon (Pd/C), and promoted molybdena–alumina (Ni,Mo/γ-Al2O3) were used. The reaction was found to proceed in consecutive steps: hydrogenolysis (HYS) of TC to CA and propane, followed by hydrodeoxygenation (HDO) of the CA intermediate. The overall reaction rate was governed by the rate of the HDO reaction. Two distinct HDO routes were distinguished: (i) hydrodecabonylation and (ii) reduction of oxygen. Over Pd/C the prevailing reaction route of CA hydroconversion was the decarbonylation giving mainly C7 alkane and CO, whereas the HDO over the Ni,Mo/γ-Al2O3 catalysts proceeded in consecutive H2 addition and dehydration steps giving predominantly C8= alkenes, C8 alkanes and water. In reaction route (ii) alcohol and traces of aldehyde were detected as acid-to-alkane intermediates. Results suggest that reaction route (i) passes through formic acid intermediate that, in the presence of H2, rapidly decomposes to CO and H2O.

A comparative study of “standard”, “fast” and “NO2” SCR reactions over Fe/zeolite catalyst

Abstract: In order to elucidate the contributions of standard (NO2/NOx = 0%), fast (=50%) and NO2 (=100%) SCR reactions under conditions where they occur simultaneously, the NOx conversion rate and N2O production rate over Fe/zeolite were investigated while varying both NO2/NOx ratio and temperature, in small increments. The NOx conversion rate decreased in the following order: fast SCR > NO2 SCR > standard SCR, although after excluding the contribution of N2O production, the order was changed to fast SCR > standard SCR > NO2 SCR. When the fast SCR conversion was subtracted from the total NOx conversion, the remaining “apparent” conversion of standard SCR (NO2/NOx 50%), was independent of NO2/NOx ratio. This indicates that standard or NO2 SCR progressed once fast SCR was completed. N2O production reached a maximum at ca. 250 °C and was determined responsible for NO2 SCR. At temperatures below 200 °C, the NOx conversion behaviors of fast and NO2 SCR changed drastically; the fast SCR conversion dropped suddenly with decreasing temperature, and the NO2 SCR conversion went through a minimum and then began to increase with no N2O production.

Deep oxidation of volatile organic compounds using ordered cobalt oxides prepared by a nanocasting route

Abstract: Ordered Co 3 O 4 with high surface area (until 173 m 2 /g) has been successfully obtained through a nanocasting route using mesoporous KIT-6 silica as a hard template and tested in the deep oxidation of a series of representative volatile organic compounds (VOCs): propane as a model of short chain alkane and toluene as a model of monoaromatic hydrocarbon. It has been demonstrated that the catalytic activity for VOC deep oxidation is very elevated and its catalytic stability at moderate temperatures very good. However, the role of the ordered structure in the catalytic performance does not seem to be beneficial. The enhanced catalytic activity has been explained in terms of both the high surface area and the presence of oxygen vacancies. In the present work we show for the first time the catalytic behaviour of a nanocasted cobalt oxide for the elimination of different VOCs.

Methane dry reforming with CO2: A study on surface carbon species

Abstract: Methane dry reforming with a mixture of 29% CO 2 and 71% CH 4 over 8 wt% NiMgAl 2 O 4 in a plug flow reactor with temperature programmed mode has been investigated. It was established that in sequential reactions the catalyst was deactivated due to graphite like carbon deposit measured by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) while by X-ray photoelectron spectroscopy (XPS) only Ni–carbide was observed. The discrepancy found by XPS and TEM can be explained by the different types of carbon species, i.e. it is assumed that after the first reaction mostly carbide is deposited, whereas after several subsequent reactions the carbon on the surface is graphitized forming carbon nanotubes (TEM). Addition of 0.5 wt% gold to NiMgAl 2 O 4 improves the catalytic activity and on gold containing bimetallic catalyst the formation of nanotubes is vanished. The results are interpreted by the formation of non-crystalline NiC x which – depending on the conditions – is transferred to graphitic carbon species.

MOF-5 as an efficient heterogeneous catalyst for Friedel–Crafts alkylation reactions

Abstract: A highly porous metal-organic framework (MOF-5) was synthesized by a solvothermal method, and used as an efficient heterogeneous acid catalyst for Friedel–Crafts alkylation reactions. The solid acid catalyst was characterized using a variety of different techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), atomic absorption spectrophotometry (AAS), and nitrogen physisorption measurements. Quantitative conversion was achieved under mild conditions without the need for an inert atmosphere. The MOF-5 catalyst could be facilely separated from the reaction mixture, and could be reused several times without significant degradation in catalytic activity. Furthermore, no contribution from homogeneous catalysis of active acid species leaching into reaction solution was detected.

Synthesis of CNT-supported cobalt nanoparticle catalysts using a microemulsion technique: Role of nanoparticle size on reducibility, activity and selectivity in Fischer–Tropsch reactions

Abstract: The influence of cobalt particle size on catalyst performance in Fischer–Tropsch synthesis (FTS) has been investigated using inert carbon nanotube (CNT)-supported catalysts. The catalysts were produced by the core reverse micelle reactions with cobalt particles of various sizes (3–10 nm). It has been shown that particle size is proportional to the water-to-surfactant ratio (3–10) used for the catalyst preparation. Very narrow particle size distributions have been produced by the microemulsion technique and at relatively high loading (Co 10 wt%). Selectivity and activity were found to be dependant on cobalt particle size. The FTS rate increases from 0.36 to 0.44 g HC/gcat./h and the C5+ selectivity increases from 89 to 92.5 wt% with increasing the average cobalt particle size from 2–3 to 9–10 nm, respectively. According to TEM analysis, small Co particles (2–6 nm) are mostly confined inside the CNTs where influence of its electron deficiency in the inside surface has changed the commonly expected catalyst's structure-sensitive results. Finally, the CNT-supported cobalt nanoparticles synthesized by the proposed microemulsion technique increased the CO conversion by 15% compared to those prepared by incipient wetness impregnation.

Hydrodeoxygenation of oleic acid and canola oil over alumina-supported metal nitrides

Abstract: Nitrides of molybdenum, tungsten and vanadium supported on γ-Al 2 O 3 were prepared by temperature-programmed reaction with NH 3 and tested as catalysts for hydrodeoxygenation of oleic acid and canola oil at 380–410 °C and 7.15 MPa H 2 . The molybdenum nitride catalyst was found superior to the vanadium and tungsten nitrides for catalytic hydrotreating of oleic acid in terms of fatty acid conversion, oxygen removal and production of normal alkanes (diesel fuel cetane enhancers). The supported molybdenum nitride favoured the hydrodeoxygenation of oleic acid to n-C 18 H 38 three times out of four compared to decarbonylation and decarboxylation. A 450-h long hydrotreating test performed at 400 °C and 8.35 MPa H 2 with Mo 2 N/Al 2 O 3 and canola oil, indicated that oxygen removal exceeded 90% over the duration of the experiment and that the yield of middle distillate hydrocarbons (diesel fuel) ranged between 38 and 48 wt% (based on liquid feed).

Selective hydrogenolysis of glycerol to 1,3-propanediol over a Pt/WO3/TiO2/SiO2 catalyst in aqueous media

Abstract: SiO2-supported Pt/WO3/TiO2 catalysts were prepared; they were found to be more active and selective than the Pt/WO3/TiO2 catalyst for glycerol hydrogenolysis to 1,3-propanediol in a slurry batch reactor. The influences of catalyst component, reaction medium, reaction temperature, H2 pressure and reaction time on glycerol hydrogenolysis over the Pt/WO3/TiO2/SiO2 catalyst were investigated. XRD, TEM, NH3-TPD and Py-IR characterization were employed to reveal the roles of WO3 and TiO2 in the performance of the Pt based-catalysts. XRD patterns and TEM images showed that the presence of TiO2 species in the catalyst favored the dispersion of platinum. The weak Bronsted acid sites formed by addition of WO3 to the catalyst were concluded to play a key role in selective formation of 1,3-propanediol, based on the results of NH3-TPD and Py-IR characterization.

Evaluation of the performance of Ni/La2O3 catalyst prepared from LaNiO3 perovskite-type oxides for the production of hydrogen through steam reforming and oxidative steam reforming of ethanol

Abstract: This paper studies the performance of LaNiO3 perovskite-type oxide precursor as a catalyst for both steam reforming and oxidative steam reforming of ethanol According to results of temperature-programmed desorption of adsorbed ethanol and by carrying out diffuse reflectance infrared Fourier transform spectroscopy analyses of ethanol steam reforming, ethanol decomposes to dehydrogenated species like acetaldehyde and acetyl, which at moderate temperatures, convert to acetate by the addition of hydroxyl groups Demethanation of acetate occurs at higher temperatures, leading to a steady state coverage of carbonate Catalyst deactivation occurs from the deposition of carbon on the surface of the catalyst Both thermogravimetric and scanning electron microscopy analyses of postreaction samples indicate that lower reaction temperatures and lower H2O/EtOH ratios favor the deposition of filamentous carbon However, less carbon formation occurs when the H2O/EtOH ratio is increased Increasing reaction temperature or including O2 in the feed suppresses filamentous carbon formation

Promotional effect of La2O3 and CeO2 on Ni/γ-Al2O3 catalysts for CO2 reforming of CH4

Abstract: The CO 2 reforming reaction of CH 4 was conducted by using a Ni-based catalyst prepared by the co-impregnation method. The properties of the catalysts and the carbon deposition performance on the catalyst surface were surveyed by XRD, TPR, TG-DTA, and SEM. The results showed that the activity of the Ni/γ-Al 2 O 3 catalyst with Ni loading of 10% was higher than that of those with other Ni loadings. However, the Ni/γ-Al 2 O 3 catalyst was not stable in the continuous reaction due to a large amount of carbon deposition on the catalyst surface. Although the activity of Ni/γ-Al 2 O 3 with the La 2 O 3 and CeO 2 as promoters was not obviously increased, the carbon deposition on Ni/γ-Al 2 O 3 with La 2 O 3 and CeO 2 as promoters was greatly suppressed in the CO 2 reforming reaction of CH 4 . The amount of carbon deposition on the 10%Ni/3%CeO 2 –3%La 2 O 3 –γ-Al 2 O 3 catalyst was reduced 76.2% compared with the 10%Ni/γ-Al 2 O 3 catalyst, due to alkaline function and dispersion enhancement of La 2 O 3 –CeO 2 , as well as the electronic interactions between CeO 2 and Ni. The results of SEM showed that the moss-like carbon on the 10%Ni/γ-Al 2 O 3 catalyst was not easily gasified with CO 2 and Ni particles, which would result in the catalyst deactivation. On the other hand, the filamentous carbon on the 10%Ni/3%CeO 2 –3%La 2 O 3 –γ-Al 2 O 3 catalysts could be eliminated readily by gasifying with CO 2 . Because of the suppression in the sintering of Ni particles and the dominant formation of the reactive filamentous carbon on the Ni-based catalyst that included La 2 O 3 and CeO 2 promoters, 10%Ni/3%CeO 2 –3%La 2 O 3 –γ-Al 2 O 3 catalyst showed stable activity in the continuous CO 2 reforming reaction of CH 4 at 1073 K and atmospheric pressure.

CO2 photoreduction using NiO/InTaO4 in optical-fiber reactor for renewable energy

Abstract: The photocatalytic reduction of CO2 into fuels provides a direct route to produce renewable energy from sunlight. NiO loaded InTaO4 photocatalyst was prepared by a sol–gel method. Aqueous-phase CO2 photoreduction was performed in a quartz reactor to search for the highest photoactivity in a series of NiO/InTaO4 photocatalysts. Thereafter, the best NiO/InTaO4 was dip coated on optical fibers and calcined at 1100 °C. A uniform NiO/InTaO4 layer of 0.14 μm in thickness was observed on the optical fiber. An optical-fiber photoreactor, comprised of ∼216 NiO/InTaO4-coated fibers, was designed to transmit and spread light uniformly inside the reactor. The UV–vis spectra of powder InTaO4 as well as NiO loaded InTaO4 prepared via the same procedure indicated that both photocatalysts could absorb visible light. XRD confirmed that InTaO4 was in single phase. Vapor-phase CO2 was photocatalytically reduced to methanol using the optical-fiber reactor under visible light and real sunlight irradiation in a steady-state flow system. The rate of methanol production was 11.1 μmol/g h with light intensity of 327 mW/cm2 at 25 °C. Increasing the reaction temperature to 75 °C increased the production rate to 21.0 μmol/g h. Methanol production rate was 11.30 μmol/g h by utilizing concentrated sunlight which was comparable to the result of using artificial visible light. The quantum efficiencies were estimated to be 0.0045% and 0.063% in aqueous-phase and optical-fiber reactors, respectively, per gram NiO/InTaO4 photocatalyst. The quantum efficiency increased due to the superior light-energy utilization of NiO/InTaO4 thin film in the optical-fiber reactor