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Applied Catalysis A, General (v.308, #1-232)
Oxidative steam reforming of methane under atmospheric and pressurized conditions over Pd/NiO–MgO solid solution catalysts by Mohammad Nurunnabi; Yuya Mukainakano; Shigeru Kado; Tomohisa Miyazawa; Kazu Okumura; Toshihiro Miyao; Shuichi Naito; Kimihito Suzuki; Ken-Ichiro Fujimoto; Kimio Kunimori; Keiichi Tomishige (pp. 1-12).
The effect of the Pd loading in NiO–MgO solid solution was investigated in oxidative steam reforming of methane under atmospheric and pressurized conditions. The small amounts of Pd addition on Ni0.2Mg0.8O can inhibit the oxidation of Ni species and the mixture can maintain the reforming ability at low W/ F conditions under atmospheric pressure, where Ni0.2Mg0.8O catalyst deactivated. In addition, Ni0.2Mg0.8O catalyst improved remarkably, gaining both high activity and excellent stability by the addition of small amounts of Pd under pressurized conditions. The deactivation rate was closely related to the amount of deposited carbon. Characterization results of TEM, TPR, EXAFS and FTIR suggest that Pd–Ni alloy particles are formed on Pd/Ni0.2Mg0.8O catalysts. The Pd–Ni alloy particles with a low ratio of Pd to Ni can play an important role in the high resistance to carbon deposition.
Keywords: Oxidative reforming; Steam reforming; Methane; Pd; NiO–MgO solid solution; Deactivation; Carbon deposition
Solid base catalysts obtained from hydrotalcite precursors, for Knoevenagel synthesis of cinamic acid and coumarin derivatives by E. Angelescu; O.D. Pavel; R. Bîrjega; R. Zăvoianu; G. Costentin; M. Che (pp. 13-18).
The goal of this paper was to study the synthesis of the cinamic acid, coumarin-3-carboxilic acid and their ethylesters by Knoevenagel condensation using the solid base catalysts obtained from calcined Mg–Al, Mg–Al+Ln (Ln=Dy, Gd) and Li–Al hydrotalcites, under solvent free conditions. Correlations between the basicity of the catalysts and the advancement degree in the pathway of the condensation reaction have also been investigated.
Keywords: Calcined hydrotalcites; Solid base catalysts for cinamic acid and coumarin derivatives synthesis
Carbon oxide hydrogenation over silica-supported iron-based catalysts by T. Herranz; S. Rojas; F.J. Pérez-Alonso; M. Ojeda; P. Terreros; J.L.G. Fierro (pp. 19-30).
A series of silica-supported iron samples has been prepared by the microemulsion technology. The samples were characterized by temperature programmed reduction (TPR), UV–vis spectroscopy, N2 adsorption isotherms, X-ray photoelectron spectra (XPS), SEM and transmission electron microscopy (TEM) microscopy and tested in the carbon monoxide and carbon dioxide hydrogenation reactions. Although all samples have similar composition and metallic loading, the preparation route was crucial for the actual nature of the samples, tuning also their catalytic performance. The main result of the preparation route was the extension of the degree of the interaction between the active phase and the support. As a consequence, samples where a metal–support interaction was promoted showed a lower reducibility and therefore a lower catalytic activity. The addition of Mn, Cu and K promoters improves the catalytic performance in carbon monoxide hydrogenation. The low activity of the samples in carbon dioxide hydrogenation is due to their low reverse water–gas shift activity.
Keywords: Supported iron catalysts; Microemulsion; Fischer–Tropsch; Metal–support interaction; Silica
Structure–activity correlations in thin film model catalysts: CO hydrogenation on Rh/VO x by Simon Penner; Bernd Jenewein; Di Wang; Robert Schlögl; Konrad Hayek (pp. 31-42).
The combination of (high-resolution) electron microscopy and electron diffraction was applied to study the structural and morphological alterations of a number of Rh/VO x-model systems upon oxidation and reduction, and to discriminate between different phenomena of metal–support interaction. Well-defined Rh particles (mean size 10–15nm) were grown epitaxially on NaCl(001) surfaces and subsequently covered by layers of VO x of varying thickness (0.07–25nm), prepared by reactive deposition of V metal in 10−2Pa O2. Most films were covered with a stabilizing layer of amorphous alumina. The resulting model catalysts were subjected to an oxidative treatment at 673K in O2 for 1h and to subsequent reduction in the temperature range 373–873K.While higher VO x exposures (mean VO x coverage≥3nm) favour the formation of crystalline V2O3 phases in partial epitaxial orientation to the Rh particles in the as-deposited state, lower exposures result in less ordered layers of cubic VO. Similarly, after a treatment in 1bar O2 at 673K the oxidation states of vanadium vary between V5+ and V2+, depending on the film thickness.Decoration of Rh by reduced VO x species was found to be the dominant feature of metal–support interaction upon reduction at low temperatures ( T<573K), whereas at increasing reduction temperature the formation of distinct Rh–V alloys (V3Rh5, Rh3V, V3Rh and VRh, respectively) was observed. On a “VO x/Rh/Al2O3� catalyst, prepared by depositing 1ML VO x prior to Rh deposition alloy formation was not detected, and decoration of the metal particles was the dominant effect of reduction at 673K. A counterpart to Rh/V “subsurface� or “surface� alloys, known to be formed on bulk Rh surfaces under similar conditions, could not be observed.
Keywords: Metal–support interaction; Rhodium; Vanadium; Alloy formation; Electron microscopy; Selected area electron diffraction
Structure–activity correlation in thin film model catalysts: CO hydrogenation on Rh/VO x by Bernd Jenewein; Simon Penner; Konrad Hayek (pp. 43-49).
The structure and morphology of thin film catalysts, consisting of well-defined Rh particles in contact with promoting and supporting vanadium oxides and subjected to oxidative and reductive treatments at elevated temperature, were correlated with the associated activity changes in CO hydrogenation. All systems exhibit a steady decrease of the catalytic activity with reduction temperature (373–823K), which is in part due to vanadia covering free metal surface area and in part to the formation of stable bulk alloy phases.By comparison with the results of electron microscopy, the initial decrease of catalytic activity (between 373 and 473K) is primarily caused by decoration of Rh particles by reduced VO x species. A strong decrease of catalytic activity after reduction above 573K is related the formation of distinct Rh–V alloys. A selectivity shift towards methane at high reduction temperatures goes along with this activity loss.
Keywords: Structure–activity correlation; Reduction; CO hydrogenation; Alloy formation; Vanadium; Rhodium
A new, aluminium oxy-hydrate supported NiAl skeleton catalyst by József Petró; László Hegedűs; István E. Sajó (pp. 50-55).
Starting with a 50–50wt.% nickel–aluminium alloy and using our procedure developed earlier an aluminium oxy-hydrate supported, finely dispersed NiAl intermetallic phase formed, which proved to be an active catalyst in liquid-phase hydrogenations. Its catalytic performance is very similar to that of the standard Raney®-Ni stored under water. It was found that, even after drying and storing in air for a year, this new catalyst preserved a significant amount of adsorbed hydrogen and its activity in hydrogenation reactions. Genesis of the new catalyst is discussed.
Keywords: Non-pyrophoric; Aluminium oxy-hydrate support; NiAl skeleton catalyst
Catalytic activity of versatile peroxidase from Bjerkandera fumosa in aqueous solutions of water–miscible organic solvents by Janina Rodakiewicz-Nowak; Anna Jarosz-Wilkołazka; Jolanta Luterek (pp. 56-61).
Versatile peroxidase (VP) from the white rot fungus Bjerkandera fumosa was isolated and purified by ion exchange and gel filtration chromatography. Its primary catalytic activity in oxidation of Mn(II) was studied in aqueous solutions in the presence of varying concentrations (up to 8M) of acetonitrile (MeCN), dimethylsulfoxide (DMSO), ethanol, and n-propanol. The observed maximum reaction rate values decreased with the addition of organic solvents in the order: MeCN< n-propanoln-propanol. This lead to various shapes of the specific activity constant values ( ks= Vmax/ KM) of VP in oxidation of Mn(II) in solutions of different organic solvents. KM values of typical organic substrates of enzymatic reactions increase with addition of organic solvents, due to unfavorable partitioning of substrates between the medium and the active center of the enzyme. In case of inorganic ions, the decrease of the medium polarity caused by addition of the organic solvent should lead to the enhancement of substrate binding by the enzyme due to the variation in the activity coefficient/solubility of the substrates in the studied systems, and therefore to the decrease of KM values. The results of our experiments confirm this expectation. To further support this thesis, the effect of ethanol on oxidation of 2,6-dimethoxyphenol catalyzed by VP in the presence of Mn(II) was also studied. The observed Vmax values were exponentially decreasing with the solvent concentration, while the KM versus ethanol concentration curve passed through a minimum. The later effect could be described by two exponential relationships (the one decreasing for Mn(II) and the other one increasing for 2,6-dimethoxyphenol).
Keywords: Versatile peroxidase; Organic solvent; Denaturation; Inorganic and organic substrate
MoVO-based catalysts for the oxidation of ethane to ethylene and acetic acid by Martial Roussel; Michel Bouchard; Khalid Karim; Saleh Al-Sayari; Elisabeth Bordes-Richard (pp. 62-74).
The influence of niobium and/or palladium in MoV0.4O x on both solid state chemistry and catalytic properties in the oxidation of ethane to acetic acid and ethylene is examined. Catalysts without molybdenum (VNb0.31Pd3e-4O x) are also studied for comparison. The structural properties of the precursors and of the catalysts obtained by calcination of precursors at 350 and 400°C are studied by X-ray diffraction, and by laser Raman and X-ray photoelectron spectroscopies. These properties depend on the presence or absence of niobium, and to a lesser extent, of palladium. Nb-free precursors and catalysts are heterogeneous mixtures of crystalline oxides, among which hexagonal and orthorhombic MoO3. The presence of Pd favors the instability of both precursors and catalysts. The catalysts are poorly active (conversion <4%), but they are mainly selective to acetic acid ( SAA max=61–73mol%) and to CO x (SCOx max=30−72mol%). The Nb-containing precursors without or with Pd are more stable, and the catalysts are made up of nanocrystalline particles of V, Nb-doped Mo5O14 and of V xMo1− xO3− x/2. They are active (conversion <15%) and very selective to ethylene and acetic acid ( Stot=90–96mol%). The surface being enriched with vanadium in most cases, the discussion deals with the relative role of Nb and Pd and their possible location in the identified oxides. Because no M1 and/or M2 oxides could be identified, synergistic effects between nanocrystals of (VMoNb)5O14 and V xMo1− xO3−0.5 x are proposed to account for the high catalytic performance of the multicomponent MoVNb(Pd) oxides.
Keywords: Ethane oxidation; Acetic acid; Ethylene; MoVNbO; Pd dopant; Multicomponent catalyst; Synergistic effect
Performance of La2O3- or Nb2O5-added Pd/SiO2 catalysts in acetylene hydrogenation by In Young Ahn; Woo Jae Kim; Sang Heup Moon (pp. 75-81).
Pd catalysts promoted by La2O3 and Nb2O5, which were selected among metal oxides showing a strong metal-support interaction (SMSI), were tested for acetylene hydrogenation and their kinetic behaviors were compared with those of Pd-only and TiO2-added catalysts. The La2O3-added catalyst showed lower acetylene conversions but a higher ethylene selectivity and slower deactivation rates than the Pd-only catalyst. The improvement in ethylene selectivity and catalyst lifetime was significant, particularly when the catalysts were reduced at a temperature of 500°C. On the other hand, Nb2O5-added catalysts showed higher acetylene conversions as well as both improved ethylene selectivity and catalyst lifetime when compared with the Pd-only catalyst. In this case, the improved selectivity attained by reducing the catalyst at 500°C was significant when the reaction was conducted at low temperatures, i.e. 40°C and 50°C instead of 60°C.Based on the characterization of catalysts by temperature-programmed reduction (TPR), H2 chemisorption, and the temperature-programmed desorption (TPD) of ethylene, the La2O3 added to the catalyst modified the Pd surface in a manner similar to TiO2, which interacted strongly with Pd, both geometrically and electronically, after reducing the catalyst at 500°C. La2O3 interacted with Pd more strongly and, consequently improved catalyst performance to a greater extent than TiO2. Nb2O5 interacted with Pd similar to the other two oxides but also showed activity for hydrogenation, which contributed to the beneficial performance of Nb2O5-added catalysts: a higher activity for acetylene hydrogenation than that of Pd-only catalysts; remarkably low deactivation rates compared with the other catalysts.Among the three types of catalysts studied, La2O3-added catalysts that were reduced at 500°C showed the highest ethylene selectivity at a reaction temperature of 60°C. On the other hand, the Nb2O5-added catalysts showed the highest activity and longest catalyst lifetime due to the additional activity of Nb oxides for hydrogenation. Consequently, the former catalysts would be advantageous for use at high temperatures and the latter at low temperatures.
Keywords: Acetylene hydrogenation; Pd catalyst; La; 2; O; 3; Nb; 2; O; 5; SMSI; Ethylene selectivity; Deactivation
Steam reforming of dimethyl ether over ZSM-5 coupled with Cu/ZnO/Al2O3 catalyst prepared by homogeneous precipitation by Tomonori Kawabata; Hiromichi Matsuoka; Tetsuya Shishido; Dalian Li; Yan Tian; Tsuneji Sano; Katsuomi Takehira (pp. 82-90).
Steam reforming of dimethyl ether (DME) was carried out over combined solid acid/Cu-based catalysts. The reaction proceeded via a successive two-steps mechanism: hydrolysis of DME to methanol over solid acids, followed by steam reforming of methanol to produce H2 and CO2 over Cu-based catalysts. Effective hydrolysis catalysts were zeolites, among which ZSM-5 showed the highest activity as well as selectivity to methanol. When ZSM-5 was combined with Cu-based catalysts, a high yield of H2 production was obtained with Cu/ZnO/Al2O3 catalyst prepared by homogeneous precipitation (hp-) by urea hydrolysis. Moreover, the highest activity was obtained, when powders of both hp-Cu/ZnO/Al2O3 and ZSM-5 were kneaded in an agate mortar, pressed and sieved to the particles of composite catalysts. Either physical mixing of the particles of both catalysts or separate filling of ZSM-5 and hp-Cu/ZnO/Al2O3 resulted in the low activity, indicating that the closest packing of both active sites for DME hydrolysis and methanol steam reforming is required for DME steam reforming. As a Cu-catalyst in the composite catalysts, hp-Cu/ZnO/Al2O3 showed higher activity than hp-Cu/ZnO and moreover than that prepared by coprecipitation. It is likely that hp-preparation affords more finely dispersed Cu metal particles and moreover Al component stabilizes the finely dispersed Cu metal particles on the catalysts against sintering. The catalyst deactivation due to coke formation is discussed in connection with the analytical results of coke materials.
Keywords: Hydrogen production; Steam reforming; Dimethyl ether; Cu/ZnO/Al; 2; O; 3; Homogeneous precipitation; ZSM-5
Mesoporous H-AlMCM-41 supported NiO-MoO3 catalysts for hydrodenitrogenation of o-toluidine by S.J. Sardhar Basha; N.R. Sasirekha; R. Maheswari; K. Shanthi (pp. 91-98).
The mesoporous molecular sieve, H-AlMCM-41 (Si/Al=100) was synthesized hydrothermally and used as support for the preparation of series of sequentially impregnated NiO-MoO3 catalysts. Various amounts of MoO3 (12, 18, 24 and 30wt.%) along with of 7wt.% of NiO were loaded in order to optimize the MoO3 loading level for obtaining maximum HDN activity. These catalysts were well-characterized by physico-chemical techniques, such as X-ray diffraction (XRD), N2 adsorption–desorption, SEM, FT-Raman spectroscopy, UV–vis DRS and FT-IR spectra of CO adsorption and tested for hydrodenitrogenation (HDN) of o-toluidine. The change in dispersion with MoO3 loading was studied by FT-IR spectra of CO adsorbed samples. HDN activities of various NiO-MoO3 catalysts were evaluated and the activities are accounted in terms of physico-chemical characteristics of the catalytic materials. Catalyst with 7wt.% NiO-24wt.% MoO3 showed maximum HDN activity when compared to other catalysts and its enhanced activity due to the fine dispersion of MoO3 as well as due to formation of an additional Ni–Mo–O phase from AlMCM-41, as revealed by FT-IR of CO adsorption, FT-Raman and XRD studies.
Keywords: Hydrodenitrogenation (HDN); H-AlMCM-41; NiO-MoO; 3; FT-IR of CO adsorption; NiMoO; 4; phase
Activities of Pt/C catalysts prepared by low temperature chemical reduction methods by Jianhuang Zeng; Jim Yang Lee; Weijiang Zhou (pp. 99-104).
Carbon supported Pt nanoparticles were prepared in aqueous solutions by two methods: (1) room temperature NaBH4 reduction of H2PtCl6 with (Pt-1) or without (Pt-2) sodium citrate as the stabilizing agent and (2) microwave-assisted reduction of H2PtCl6 at boiling temperature using citrate as the reducing agent cum stabilizer (Pt-3 and Pt-4). The catalysts were characterized by X-ray diffraction, energy dispersive X-ray microanalysis and transmission electron microscopy, and their activities in room temperature methanol electrooxidation were evaluated by cyclic voltammetry and benchmarked against a commercial E-TEK catalyst with the same Pt loading. TEM showed smaller Pt particles if citrate was present in the synthesis, with average particle sizes of 4.0 and 2.2nm for Pt-1 and Pt-3, respectively. While the presence of citrate was generally beneficial to forming smaller and more uniform Pt nanoparticles, a large excess of citrate (H2Cyt−:PtCl62−=20:1) in the microwave synthesis had led to a decrease in catalytic activity. The microwave-synthesized Pt/C obtained using a smaller excess of citrate (H2Cyt−:PtCl62−=5:1) demonstrated the best mass activity, surpassing the performance of the commercial catalyst. In addition, a size effect was found in this study: with the decrease in the platinum particle size in the range of 2.2–4nm, the specific activity of Pt for room temperature methanol oxidation also decreased.
Keywords: Pt nanoparticles; Citrate; Microwave; Methanol oxidation; Size effect
Sonochemical synthesis of nanocrystallite Bi2O3 as a visible-light-driven photocatalyst by Lisha Zhang; Wenzhong Wang; Jiong Yang; Zhigang Chen; Wenqing Zhang; Lin Zhou; Shengwei Liu (pp. 105-110).
The synthesis of Bi2O3 by a simple sonochemical route is investigated. Surfactant polyvinylpyrrolidone (PVP) has strong effects on the grain sizes and morphologies of Bi2O3. Bi2O3 single crystallite with grain size of 40–100nm is obtained in the presence of 0.5g PVP. X-ray diffraction (XRD) pattern shows that the nanocrystallite Bi2O3 is monoclinic and has a high degree of crystallinity. Optical characterizations show that the nanocrystallite Bi2O3 presents the photoabsorption properties from UV light region to visible light shorter than 470nm and the band gap of the nanocrystallite Bi2O3 is 2.85eV. The photocatalytic performance of the nanocrystallite Bi2O3 is evaluated using methyl orange (MeO) as a model pollutant. The photocatalytic results show that such nanocrystallite Bi2O3 can effectively degrade 86% MeO within 100min under visible light illumination ( λ>400nm). The action spectrum of MeO degradation over nanocrystallite Bi2O3 further confirms that the photocatalytic reaction can be driven by visible light. The photocatalytic mechanism is also studied based on electronic structure calculations using density functional theory (DFT).
Keywords: Sonochemical synthesis; Nanocrystallite Bi; 2; O; 3; Photocatalytic; Visible light
Effect of aluminum modification on catalytic performance of Pt supported on MCM-41 for thiophene hydrodesulfurization by Yasuharu Kanda; Takao Kobayashi; Yoshio Uemichi; Seitaro Namba; Masatoshi Sugioka (pp. 111-118).
The catalytic activities and properties of platinum supported on siliceous MCM-41 and Al-modified MCM-41, such as Al-incorporated MCM-41 (AlMCM-41) and alumina-modified MCM-41 (Al2O3-MCM-41), for the hydrodesulfurization (HDS) of thiophene were investigated. Al2O3-MCM-41 was prepared by an impregnation method using aluminum nitrate (Al(NO3)3·9H2O) aqueous solution. Pt/Al2O3-MCM-41 catalyst showed high and stable activity for HDS of thiophene and this activity was remarkably higher than that of a commercial CoMo/Al2O3 HDS catalyst. The catalysts were characterized by XRD, hydrogen adsorption, ammonia-TPD, 2-propanol dehydration, cumene cracking and FT-IR. Dispersion of platinum on Al2O3-MCM-41 was remarkably higher than on MCM-41 or on AlMCM-41. It was revealed that the acidity of Al2O3-MCM-41 was higher than that of MCM-41 or of AlMCM-41. Furthermore, it was observed that there exist Brønsted acid sites on Al-modified MCM-41. FT-IR spectra of thiophene adsorbed on Al-modified MCM-41 support indicates that thiophene molecules interact with Brønsted acid sites on Al-modified MCM-41. It was found that the HDS activity of Pt/quartz mixed mechanically with Al-modified MCM-41 catalyst was higher than that calculated. This suggests that there exists spillover hydrogen on supported Pt catalysts in the HDS of thiophene. Results revealed that the high activity of Pt/Al2O3-MCM-41 catalyst for HDS reaction is due to good harmony of high dispersion of Pt particles and Brønsted acidity of the support.
Keywords: Hydrodesulfurization; Thiophene; Supported Pt catalyst; Alumina modification; MCM-41
Kinetic study of the catalytic carbon dioxide reforming of methane to synthesis gas over Ni-K/CeO2-Al2O3 catalyst by A. Nandini; K.K. Pant; S.C. Dhingra (pp. 119-127).
The effect of reaction parameters on the catalytic activity of Ni-K/CeO2-Al2O3 catalyst for carbon dioxide (CO2) reforming of methane (CH4) was studied. The kinetic behavior of the Ni-K/CeO2-Al2O3 catalyst in the reforming reaction was investigated as functions of temperature and of partial pressures of CH4 and CO2. The apparent activation energy for CH4 and CO2 consumption, and H2 and CO production were 46.1±2.5, 46.2±2.4, 54.0±2.6 and 47.4±1.7kJ/mol, respectively, for the temperature range of 873–1073K. It was found that an increase of the H2 partial pressure leads to a continuous enhancement of the rate of CO formation, due to the simultaneous occurrence of the water–gas shift reaction. The rate of methane consumption is strongly affected by the partial pressure of methane. Variation of the CO2 partial pressure has a strong influence on the rate of methane consumption at low partial pressures of 0–0.1atm, while it is insensitive to CO2 partial pressure at high pressures. A mechanism of the CH4/CO2 reaction has been proposed based on the experimental results and literature review. Based on the mechanism, a kinetic model was developed, which was found to predict satisfactorily the kinetic measurements. CH4 activation to form CH x and CH xO decomposition are suggested to be the rate-determining steps of the CH4/CO2 reaction over the Ni-K/CeO2-Al2O3 catalyst.
Keywords: Methane carbon dioxide reforming; Kinetic; Ni-K/CeO; 2; -Al; 2; O; 3; catalyst
Direct oxidation of H2 to H2O2 over Pd-based catalysts: Influence of oxidation state, support and metal additives by V.R. Choudhary; C. Samanta; T.V. Choudhary (pp. 128-133).
The influence of oxidation state (reduced and oxidized), support (ZrO2, Ga2O3, CeO2, SiO2, H-β, ThO2, CeO2–ZrO2, BPO4 and Pd/Al2O3) and precious metal additives (Au, Pt, Rh and Ru) on the direct H2O2 synthesis has been investigated over Pd-based catalysts. For all the supports investigated herein, the oxidized Pd catalysts showed significantly superior H2O2 yields as compared to their reduced counterparts. The effect of the Pd oxidation state was found to be more important for determining the H2O2 yields than the particle size and surface area properties of the catalyst system. An excellent correlation was observed between the H2O2 selectivity and H2O2 decomposition activity of the oxidized Pd catalysts. The oxidized Pd catalysts showed almost an order of magnitude lower H2O2 decomposition activity than the reduced catalysts. The H2O2 yield in the H2 to H2O2 oxidation passed through a maximum with increase in the Au concentration. Although a similar effect was also observed in case of Pt, Au was found to be a superior promoter for the direct H2O2 synthesis process. Addition of Rh and Ru was found to be detrimental for the H2O2 yields; these results can be explained in terms of increased H2O2 decomposition activity and/or enhanced H2 to H2O reaction activity in their presence.
Keywords: H; 2; O; 2; Direct synthesis; Decomposition; Pd catalysts; Metal additives; Oxidation state; Supports
Ni(Co)-Mo-W sulphide unsupported HDS catalysts by ex situ decomposition of alkylthiomolybdotungstates by R. Huirache-Acuña; M.A. Albiter; C. Ornelas; F. Paraguay-Delgado; R. MartÃnez-Sánchez; G. Alonso-Nuñez (pp. 134-142).
Ni(Co)-Mo-W sulphide unsupported hydrodesulphurization (HDS) catalysts were prepared by ex situ decomposition of trimetallic (Ni-Mo-W) precursors. The precursors were synthesized by reaction of the tetraalkylammonium thiomolybdotungstates salts, (R4N)4MoWS8 (where R=H, methyl, propyl) with an aqueous solution of Ni(Co)Cl2·6H2O in order to give molar ratios of Ni/[Ni+(Mo+W)]=0.5 and Co/[Co+(Mo+W)]=0.3. A new method by the ex situ activation was used. First, the precursors were treated in a stainless steel vessel of 45mL volume at 523K for 2h under argon atmosphere. Subsequently, the respective thiosalt was decomposed under a reductive atmosphere of H2S/H2 (15vol.% H2S) from room temperature to 673K, dwell of 2h at 673K. All catalysts were tested in the HDS of dibenzothiophene (DBT) and characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD) and BET specific surface area measurements.The ex situ activation method used in this work leads to catalysts with a wide distribution of specific surface areas (from 11.4 to 60.6m2/g), mesoporous structure with pore size ranging from 18 to 45Å and type IV adsorption–desorption isotherms of nitrogen, poorly crystalline structures with different morphology and high catalytic activities in the HDS of dibenzothiophene (DBT).
Keywords: Ex situ activation; Ni(Co)-Mo-W sulphide; Tetraalkylammonium thiomolybdotungstates salts
Methane activation on superacidic catalysts based on oxoanion modified zirconium oxide by Ruth. L. Martins; Martin Schmal (pp. 143-152).
A series of metal promoted catalysts was prepared by impregnation of metal precursor solutions on oxoanion modified zirconias (sulfated, molybdated and tungstated), well recognized, in the literature, for their ability in catalyzing the isomerization of light alkanes at low temperatures. Structural characterization and nature of surface active sites were attempted to explain the methane activation reaction on these catalysts. Although Lewis and Brönsted acid sites were observed on the oxoanion modified zirconias, as detected by infrared of pyridine adsorption, the methane activation occurred only when promoted with specific metals, such as Fe-Mn, Co-Mn, Al, Ni and Cu, for sulfated zirconias, and Ni for molybdated and tugstated zirconias. The results obtained suggest different kinds of active surface sites, depending on the oxoanion present and thus different mechanisms could be proposed for the methane activation reaction. It was suggested that on metal promoted sulfated zirconias, methane was converted into ethane by an acid catalyzed mechanism, more specifically, by SOH groups as proton donors. On NiO promoted molybdated and tungstated zirconias, methane was not simultaneously converted into ethane but only after an induction period. The XRD patterns of tugstated zirconias after the reaction with methane, showed only reflections at 2 θ=42.6°, 53.8° and 77.6°, characteristics of nickel on zero oxidation state. Although these reflections were absent for Ni promoted molybdated zirconias, these catalysts were black in color after reaction. TPR experiments using CH4 as reduction gas gave support to the proposal for a mechanism catalyzed by metal for the methane conversion into ethane on Ni promoted molybdated and tungstated zirconias.
Keywords: Superacid catalysts; Oxoanion modified zirconia; Methane activation
Keggin heteropolyacid-based catalysts for the preparation of substituted ethyl β-arylaminocrotonates, intermediates in the synthesis of 4-quinolones by L. Pizzio; G. Romanelli; P. Vázquez; J. Autino; M. Blanco; C. Cáceres (pp. 153-160).
Catalysts based on tungstophosphoric and molybdophosphoric acids supported on SiMCM-41 and amine-functionalized SiMCM-41 were obtained. They were characterized by FT-IR and31P NMR spectroscopies, and their acidity was determined by potentiometric titration with n-butylamine. The undegraded Keggin structure was observed when the heteropolyacids (HPA) are supported on SiMCM-41, and there was a partial degradation to a lacunar species on the amine-functionalized carrier. Also, the acidity of the latter catalysts was lower. The supported Keggin heteropolyacid catalysts are used for the preparation of different substituted ethyl β-arylaminocrotonates, intermediates in the synthesis of 4-quinolones, from substituted anilines and ethyl acetoacetate. The products were obtained with high selectivity. The effect of the different nature of the aniline substitutes was observed. For this Conrad–Limpach reaction, the activity of the prepared catalysts agrees with the different characteristics of the supported heteropolyacids, the yield being higher for the SiMCM-41 supported catalysts.
Keywords: Keggin HPA; SiMCM-41; Amine-SiMCM-41; Catalysts; Conrad–Limpach reaction; Substituted anilines; Ethyl acetoacetate; Ethyl β-arylaminocrotonates
Improvement in the catalytic performance of In-mordenite through preferential growth on metallic monoliths by Juan M. Zamaro; MarÃa A. Ulla; Eduardo E. Miró (pp. 161-171).
This work explored different ways of obtaining metallic monoliths coated with mordenite by hydrothermal synthesis. The results demonstrate that while direct synthesis favored the growth of ZSM5 instead of mordenite, the mordenite structure could only be obtained after seeding the support with crystals. Secondary synthesis showed great flexibility and possibilities of achieving different coating properties. Seed size and concentration, agitation and number of synthesis runs could be manipulated in order to change the microstructural characteristics. In most cases, the mordenite coatings were dense, thin films with high intergrowth. Additionally, the orientation of the zeolite crystals was so privileged that the channels in the b direction were perpendicular to the support whereas the channels in the c direction were parallel to it. This preferential orientation could be the main reason for the improved NO x SCR activity of the In-mordenite monoliths if compared to the powder catalysts.
Keywords: Mordenite; Hydrothermal synthesis; Metallic monolith; SCR of NO; x; with CH; 4
Intermediate species generated from halogenated manganese porphyrins electrochemically and in homogeneous catalysis of alkane oxidation by Geraldo Roberto Friedermann; Matilte Halma; Kelly Aparecida Dias de Freitas Castro; Flávio Luiz Benedito; Fábio Gorzoni Doro; Sueli Maria Drechsel; Antonio Salvio Mangrich; Marilda das Dores Assis; Shirley Nakagaki (pp. 172-181).
This paper reports the intermediate species of six different manganese porphyrins of first, second and third generation obtained by electrolysis and homogeneous chemical oxidation catalysis of cyclohexane. In order to understand some of the electrochemical processes and transitions involved, studies focused on coupling techniques involving electro-generated species and UV–vis and EPR spectroscopy methods applied to characterize the species formed in situ. Homogenous catalysis for cyclohexane oxidation showed that Mn-second-generation porphyrins are better catalysts than the other classes, and also have the most catalyst recovery, with lower destruction of the catalyst during the run. For all porphyrins, it was possible to observe various intermediate species such as Mn(II), Mn(IV) and radicals. Only for the third-generation porphyrin was it possible to observe a radical species during electro-reductive procedures with SEC–EPR spectroscopy.
Keywords: Porphyrin; EPR; Electrochemistry; Oxidation; Catalysis
Reforming reactions of acetic acid on nickel catalysts over a wide temperature range by A.C. Basagiannis; X.E. Verykios (pp. 182-193).
Catalytic steam reforming of bio-oil, a liquid derived from pyrolysis of biomass, may be a viable process of renewable hydrogen production. Acetic acid is one of the major constituents of bio-oil, and for this reason, it is used as a model compound to study its reaction network under steam reforming conditions over Al2O3 and La2O3, and Ni catalyst supported on La2O3/Al2O3 carrier, employing transient and steady-state techniques. It is found that acetic acid interacts strongly with the Al2O3 carrier and less strongly with La2O3. Decomposition reactions as well as the ketonization reaction take place, especially at intermediate temperatures. In the presence of Ni, catalytic activity is shifted toward lower temperatures. Nickel promotes steam reforming reactions and retards the rate of carbon deposition onto the catalyst surface. It is also found that carbon formation is affected by reaction temperature, the HAc/H2O ratio and catalyst composition. Carbon deposition is favoured at low reaction temperatures and at high HAc/H2O ratio.
Keywords: Steam reforming; Hydrogen production; Bio-oil; Acetic acid; Nickel catalysts; Temperature programmed reaction; Temperature programmed desorption
Sustainability of Ni loaded Mg–Al mixed oxide catalyst in daily startup and shutdown operations of CH4 steam reforming by Takenori Ohi; Takeshi Miyata; Dalin Li; Tetsuya Shishido; Tomonori Kawabata; Tsuneji Sano; Katsuomi Takehira (pp. 194-203).
Daily startup and shutdown (DSS) operations using several purge gases were applied for Ni-loaded Mg(Al)O periclase catalyst to test the sustainability in steam reforming of CH4. Thirteen wt% Ni loaded Mg(Al)O catalysts were prepared by using Mg(Ni)–Al hydrotalcite as the precursor with varying Mg/Al ratios. H2O/N2 (100/25mlmin−1), O2/N2 (40/10mlmin−1) and CO2/H2O/N2 (40/15/25mlmin−1) were tested as the purge gas in imitation of steam, air and spent gas, respectively. Use of air as the purge gas resulted in a quick deactivation of all Ni loaded catalysts due to the oxidation of Ni metal on the catalyst surface. Spent gas was the most inert for the DSS operation causing no significant deactivation of Ni loaded catalysts. Steam, the most convenient purge gas for DSS operation of PEFC, revealed evident deactivation depending on the (Mg+Ni)/Al ratio in Ni/Mg(Al)O catalysts; use of the (Mg+Ni)/Al ratio of 3/1 resulted in a quick deactivation with steam purge, although this ratio was the most profitable for the steady state operation with the Ni/Mg(Al)O catalysts. The most stable operation was achieved with the ratio of 6/1 in steam as the purge gas. The deactivation took place mainly by the oxidation of Ni metal by steam as the purge gas during the DSS operation between 200 and 700°C. It is likely that Mg(Al)O on the Ni/Mg(Al)O catalysts was hydrated by steam to form Mg(OH)2 on the catalyst surface, resulting in the oxidation of Ni metal finely dispersed on Mg(Al)O periclase.
Keywords: CH; 4; reforming; H; 2; production; Daily startup and shutdown operation; PEFC; Ni/Mg(Al)O catalyst; Mg–Al hydrotalcite
An improved solid phosphoric acid catalyst for alkene oligomerization in a Fischer–Tropsch refinery by Johannes H. Coetzee; Thomas N. Mashapa; Nicolaas M. Prinsloo; Johann D. Rademan (pp. 204-209).
An improved solid phosphoric acid catalyst has been developed for the oligomerization of C3–C5 alkenes, an important reaction for the refining of Fischer–Tropsch products. Catalyst particle strength is found to be the controlling design parameter when using a solid phosphoric acid catalyst for this application. The crushing strength is controlled by the relative amounts of the silicon ortho- and pyrophosphate phases present. The effect of the silicon ortho- to pyrophosphate ratio on the final catalyst was investigated by variation of key catalyst preparation parameters, namely: H3PO4 concentration, impregnation and calcination temperature and water addition. An improved catalyst with respect to crushing strength and hence lifetime, was prepared using an acid concentration of 115% H3PO4, an impregnation temperature of 220°C and a calcination temperature of 420°C. Water addition during calcination was found to be detrimental. Based on these findings, a new commercial catalyst was formulated which requires no binders. Comparative tests using commercial conditions showed a 30% increase in catalyst lifetime when compared to catalysts previously available.
Keywords: Oligomerization; Solid phosphoric acid; Fischer–Tropsch synthesis
Selective CO oxidation over carbon-coated Pt/SiO2-TiO2 particles by Tao Zheng; Yong-Rong Dong; Norikazu Nishiyama; Yasuyuki Egashira; Korekazu Ueyama (pp. 210-215).
Carbon-coated Pt/SiO2-TiO2 catalyst was synthesized by vapor infiltration of furfuryl alcohol into porous SiO2-TiO2 particles, followed by carbonization at 1000°C under N2 atmosphere. At the elevated temperature of 1000°C, the Pt particles on the uncoated SiO2-TiO2 particles aggregated and the micropores and macropores of the uncoated SiO2-TiO2 particles disappeared. Further, a phase transformation of TiO2 from anatase to rutile was complete at 1000°C. On the other hand, the aggregation of Pt and SiO2-TiO2 particles and the phase transformation of TiO2 were partly suppressed for the carbon-coated Pt/SiO2-TiO2 particles. The carbon-coated catalyst showed a high activity and high selectivity for CO oxidation in excess H2, due to selective adsorption and diffusion of CO through the carbon layer. This work demonstrates that reactant selectivities (CO/H2) in oxidation can be enhanced by a combination of catalyst particles with an adsorption-selective layer.
Keywords: Pt/SiO; 2; -TiO; 2; Carbon coating; CO oxidation; Vapor infiltration; Thermal stability
Acylation of veratrole over promoted SZ/MCM-41 catalysts: Influence of metal promotion by A. Breda; M. Signoretto; E. Ghedini; F. Pinna; G. Cruciani (pp. 216-222).
Acylation of veratrole with acetic anhydride over sulphated zirconia (SZ) supported on MCM-41 catalysts (SZ/MCM-41) was investigated. In order to study the effect of metal oxides promotion on catalytic activity of the systems, modified SZ/MCM-41 catalysts were synthesized by addition of small amount of Ga and Fe oxides. The catalysts were characterized by N2 adsorption, X-ray diffraction and TPO-MS analyses. Sulphate content was determined by ion exchange chromatography. The effect of the veratrole/acetic anhydride ratio and reaction temperature on the reaction activity were studied.
Keywords: Veratrole; Acylation; SZ/MCM-41
Dehydration of 1-pentanol to di- n-pentyl ether catalyzed by a microporous ion-exchange resin with simultaneous water removal by J. Tejero; C. Fité; M. Iborra; J.F. Izquierdo; R. Bringué; F. Cunill (pp. 223-230).
A good selectivity, more than 90%, and an excellent yield can be achieved in the DNPE synthesis by 1-pentanol dehydration at 130–155°C using a gel-type acidic resin. It is the result of shifting the equilibrium point to DNPE formation through the removal of the formed water during the chemical reaction by distillation and reflux of the organic phase. Alkenes have been obtained as byproducts with selectivities ranging from 5 to 10% in the final product. A kinetic model in terms of compound activities describes satisfactorily the kinetic data. It is based on a mechanism in which the rate-determining step is the surface reaction between two adjacent adsorbed 1-pentanol molecules. The activation energy obtained for the dehydration reaction is 115kJmol−1.From the operation point of view, it has been proved that 1-pentanol dehydration can be successfully tracked by a calorimetric reactor equipped with a Fourier transform mid-infrared (FTIR) probe.
Keywords: 1-Pentanol; Di-; n; -pentyl ether; Diesel fuel; Alcohol dehydration