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Applied Catalysis A, General (v.380, #1-2)
Potentiodynamic estimation of key parametric criterions and interrelating reversible spillover effects for electrochemical promotion by Jelena M. Jaksic; Diamantula Labou; Caslav M. Lacnjevac; Angeliki Siokou; Milan M. Jaksic (pp. 1-14).
Electrocatalytic potentiodynamic peaks are employed to assess diagnostic criterions in electrochemical promotion of catalysts (EPOC): The anodic HCHO oxidation by the spillover supplied primary oxide (Pt-OH), was investigated to estimate the relevance of catalytic peaks for the EPOC and the entire spillover effect of Pt-OH (figure), as well as its the UPD and OPD double layer charging properties. The figure shows partial charge capacity ( Q, mC) or reaction rate incremental changes for the anodic HCHO oxidation and the resulting dimensionless enhancement factor or faradaic efficiency ( Λ), calculated to display the EPOC effect.Electrocatalytic peaks from potentiodynamic spectra for relevant electrode reactions have been employed to assess decisive and most important diagnostic criterions and parameters in the electrochemical promotion of heterogeneous catalysts (EPOC) and electrocatalysts. More specifically, the anodic oxidation of formaldehyde by the spillover supplied primary oxide of Pt (Pt-OH), both of them proceeding simultaneously as the fast reversible electrode processes of rather high faradaic yields, was investigated to estimate the relevance of catalytic peaks in cyclic voltammetry for the electrochemical promotion. In the same sense, catalytic potentiodynamic peaks have been used to prove and assess the entire spillover (or effusion) effect both of H-adatoms and the primary oxide itself, too, otherwise decisive for some significant electrochemical oxidation processes, such as CO tolerance and kinetics in the cathodic oxygen reduction (ORR), including electrocatalytic features of the latter, as the one of most important electrode reactions in aqueous media. The UPD and OPD spillover double layer charging and discharging properties of the primary oxide (M-OH), interrelated with the interactive self-catalytic effect of dipole-oriented water molecules, has also been pointed out. There has also been inferred that altervalent hypo-d-oxides impose spontaneous dissociative adsorption of water molecules and pronounced membrane spillover transferring properties instantaneously resulting with corresponding bronze type (Pt/H xWO3) under cathodic, and/or its hydrated state (Pt/W(OH)6), responsible for Pt-OH effusion under anodic polarization, this way establishing reversibly revertible alterpolar features (Pt/H0.35WO3⇔Pt/W(OH)6) and substantially advanced electrocatalytic properties of these composite interactive electrocatalysts. Such nanostructured type electrocatalysts, even of mixed hypo-d-oxide structure (Pt/H0.35WO3/TiO2/C, Pt/H xNbO3/TiO2/C), have for the first time been synthesized by the sol–gel methods and shown rather high stability, distinctly pronounced electron conductivity and non-exchanged initial pure mono-bronze spillover and catalytic properties.
Keywords: Catalytic peak; Electrochemical promotion of catalyst (EPOC); NEMCA; Enhancement factor; Faradaic efficiency (; Λ; ); Effusion; Rate relaxation time; Turnover frequency; Primary oxide; Nanostructured tungsten (or niobium) bronze; Dipole spillover; Work function; Hypo-hyper-d–d-interelectronic bonding; Alterpolar electrocatalyst
Methanol steam reforming over bimetallic Pd–In/Al2O3 catalysts in a microstructured reactor by Yong Men; Gunther Kolb; Ralf Zapf; Martin O’Connell; Athanassios Ziogas (pp. 15-20).
Bimetallic Pd–In/Al2O3 catalysts wash-coated on microchannels were found to exhibit excellent methanol steam reforming activity, selectivity, and stability. High CO2 selectivity has been correlated with the active PdIn alloy phase, as confirmed by XRD measurements.Bimetallic PdIn catalysts have been investigated for methanol steam reforming within a microstructured reactor. The catalytic activity and CO2 selectivity were found to be markedly dependent on the Pd:In ratio as well as on metal loading. The high CO2 selectivity of Pd–In/Al2O3 catalysts has been ascribed to the PdIn alloy formation, whereas the metallic Pd without contact with indium is responsible for CO selectivity. The initial start-up properties of the Pd–In/Al2O3 catalyst were significantly improved in comparison with Pd/ZnO catalyst, allowing for a rapid attainment of the steady state. These findings illustrate that the catalyst surface dynamically changes depending on the reaction environment and undergoes a self-optimization induced by the reactants, and consequently the pre-reduction at elevated temperature is not necessary to achieve high CO2 selectivity.
Keywords: Microstructured reactor; Methanol; Fuel processor; Steam reforming; Supported catalyst; Palladium; Indium
The influence of lattice oxygen in titania on selective catalytic reduction in the low temperature region by Phil Won Seo; Sung Pill Cho; Sung Ho Hong; Sung Chang Hong (pp. 21-27).
Because oxygen is an essential component in standard SCR reactions, the ability to provide lattice oxygen is an important factor dictating catalytic activity. When the lattice oxygen in vanadia is exhausted, lattice oxygen in titanium can be supplied to vanadium; then the SCR reaction can continue to proceed and an oxygen bridge between vanadium and titanium can be formed.Vanadia/titania catalysts have various NOx conversion capabilities, which are dependent on the titania support, in selective catalytic reduction reactions with ammonia in the low temperature region. Because oxygen is an essential component in standard SCR reactions, the ability to provide lattice oxygen is an important factor dictating catalytic activity. Lattice oxygen can be provided to the reactants from a vanadia support as well as from a titania support. When the lattice oxygen in vanadia is exhausted, lattice oxygen in titanium can be supplied to vanadium; through this transfer of lattice oxygen, the SCR reaction can continue to proceed and an oxygen bridge between vanadium and titanium can be formed. Therefore, titania supports containing O/Ti mole ratios varying from 1.8 to 2.0 without vanadium deposition were adequate as SCR catalysts. In this work, the dual site mechanism was modified; based on these findings a more detail mechanism is suggested.
Keywords: SCR; Lattice oxygen; O/Ti mole ratio; Low temperature region
Peculiarities of oxidative coupling of methane in redox cyclic mode over Ag–La2O3/SiO2 catalysts by Jae Suk Sung; Ko Yeon Choo; Tae Hwan Kim; Alexander Greish; Lev Glukhov; Elena Finashina; Leonid Kustov (pp. 28-32).
Properties of Ag–La2O3/SiO2 catalysts in oxidative coupling of methane (OCM) carried out in redox cyclic mode were studied. Methane and air were injected as separate and alternating pulses, and the oxidative conversion of methane proceeded due to participation of mobile lattice oxygen of the catalysts. The figure shows a pulse feed circuit applied to the redox cyclic mode of OCM.Properties of Ag–La2O3/SiO2 catalysts in oxidative coupling of methane (OCM) carried out in redox cyclic mode were studied. Methane and air were injected as separate and alternating pulses, and the oxidative conversion of methane proceeded due to participation of mobile lattice oxygen of the catalysts. It was found that joint action of Ag and La2O3 in OCM could give considerable synergetic effect. Such catalysts as 3%Ag–10%La2O3/SiO2 and 6%Ag–10%La2O3/SiO2 exhibited high efficiency in the OCM reaction performed in the redox cyclic mode. In the case of 3%Ag–10%La2O3/SiO2, the yield of C2 hydrocarbons reached about 30% at C2 selectivity close to 60%. Active sites which were responsible for OCM reaction were generated during reduction of silver by the injected methane. OCM selectivity increased remarkably if a small amount of hydrogen was injected over the catalyst before the methane pulse.
Keywords: Oxidative coupling of methane; Redox cyclic mode; Lattice oxygen; Ag–La; 2; O; 3; /SiO; 2; catalyst; Synergetic effect
Design of active centers for bisphenol-A synthesis by organic–inorganic dual modification of heteropolyacid by Kenichi Shimizu; Soichiro Kontani; Soichiro Yamada; Go Takahashi; Takahito Nishiyama; Atsushi Satsuma (pp. 33-39).
The organic–inorganic dual modified heteropolyacid produced by Cs-ion change and immobilization of amino-mercapto compound shows comparable bisphenol-A yield to that of a conventional ion-exchange resin and higher turnover number and frequency.An effective design of solid acid catalysts for synthesis of bisphenol-A was investigated using organic–inorganic dual modification of heteropolyacids. Among various solid acids, partially Cs-ion exchanged tungstophosphate (Cs2.5H0.5PW12O40) showed the highest turnover frequency, i.e., the initial reaction rate per acid site. The acid strengths estimated by differential heat of ammonia adsorption showed that relatively moderate acid strength is optimum for the intrinsic activity of acid sites. Cs2.5H0.5PW12O40 was further modified by immobilization of mercapto compounds. The addition of 2-diethylamino-ethanethiol (DEAT) to Cs2.5H0.5PW12O40 significantly enhanced both activity and selectivity. When the ratio of DEAT and protonic acid site was unity, the designed catalyst showed comparable bisphenol-A yield and higher turnover number and frequency than those of a conventional ion-exchange resin. The high catalytic activity of the dual modified heteropolyacid is attributed to the microscopically designed active center composed of inorganic protonic acid coupled with immobilized organic thiol group.
Keywords: Heteropolyacid; Bisphenol-A; Cs-ion exchange; 2-Diethylamino-ethanethiol
Ni catalysts supported on modified ZnAl2O4 for ethanol steam reforming by Agustín E. Galetti; Manuel F. Gomez; Luis A. Arrúa; M. Cristina Abello (pp. 40-47).
Nickel catalysts supported over ZnAl2O4 modified by Ce or/and Zr addition were studied in the steam reforming of ethanol under more severe reaction conditions. The catalysts were stable at 650°C during 35h in time on stream. The catalyst supported over CeO2–ZnAl2O4 was the most active and showed the highest hydrogen selectivity with an improved coking resistance.Nickel catalysts supported over ZnAl2O4 modified by Ce or/and Zr addition were studied in the steam reforming of ethanol under more severe reaction conditions such as a lower extent of feed dilution and lower space velocities. The catalysts were stable at 650°C during 35h in time on stream. The main reaction products were H2, CO2, CO, C2H4O and small amounts of CH4 and C2H4. The catalyst supported over CeO2–ZnAl2O4 was the most active and showed the highest hydrogen selectivity. The addition of ZrO2 decreased the activity and favored the CO production. The lowest degree of Ni2+ reduction over Ni/ZAZr could explain the worst performance of this system. Otherwise, the highest Ni2+ dispersion and the high oxygen mobility from ceria or from Ni–Ce boundary allowed a higher residual activity and an improved coking resistance.
Keywords: Ethanol steam reforming; Hydrogen production; Ni/ZnAl; 2; O; 4; catalysts
Effect of chemical etching by sulfuric acid or H2O2–NH3 mixed solution on the photocatalytic activity of rutile TiO2 nanorods by Eunyoung Bae; Naoya Murakami; Misa Nakamura; Teruhisa Ohno (pp. 48-54).
Rutile TiO2 nanorods synthesized by hydrothermal treatment were etched by addition of H2O2–NH3 or H2SO4 solution. New crystal faces were generated on rutile TiO2 nanorods by means of chemical etching. When treated with sulfuric acid, the end [(111) face] of the rutile TiO2 nanorod was gradually etched. The rutile TiO2 nanorod finally exposed (001) and (021) faces during prolonged treatment time.Rutile TiO2 nanorods synthesized by hydrothermal treatment were etched by addition of H2O2–NH3 or H2SO4 solution. The etched rutile TiO2 nanorods were characterized by TEM, SEM, XRD, and specific surface area measurements. New crystal faces were generated on rutile TiO2 nanorods by means of chemical etching. In the case of treatment with H2O2–NH3 solution, the shape of the rutile TiO2 nanorod changed to a sepal-like structure with reaction time. The dissolution of rutile TiO2 nanorod mainly proceeded along [001] direction. When treated with sulfuric acid, the end [(111) face] of the rutile TiO2 nanorod was gradually etched. The rutile TiO2 nanorod finally exposed (001) and (021) faces during prolonged treatment time. In both cases, rutile TiO2 nanorods were differently etched. The etched rutile TiO2 nanorod showed higher photocatalytic activity for degradation of toluene in gas phase than the original particles.
Keywords: Chemical etching; Photocatalyst; Rutile TiO; 2; Exposed crystal face; Photocatalytic activity
Solvent-free aerobic oxidation of benzyl alcohol over Pd monometallic and Au–Pd bimetallic catalysts supported on SBA-16 mesoporous molecular sieves by Yuanting Chen; Huimin Lim; Qinghu Tang; Yating Gao; Ting Sun; Qingyu Yan; Yanhui Yang (pp. 55-65).
Highly dispersed Au–Pd nanoparticles with substantially similar mean particle size were confined using SBA-16. These nanoparticles exhibited excellent catalytic activity in the solvent-free benzyl alcohol aerobic oxidation due to the synergetic effect of Au and Pd, while the size-dependent effect was excluded. The bimetallic nanoparticles were uniformly alloyed with Pd cluster-on-Au cluster structure.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 8667h−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.
Keywords: Benzyl alcohol oxidation; Gold; Palladium; Surface functionalization; SBA-16
Enhancement of activity of Ir catalysts for selective catalytic reduction of NO with CO by physical mixing with SiO2 by Tetsuya Nanba; Ken-ichi Wada; Shouichi Masukawa; Junko Uchisawa; Akira Obuchi (pp. 66-71).
The selective catalytic reduction of NO by CO (CO-SCR) over Ir–Ba/WO3–SiO2 was studied. Physical mixing of the Ir catalyst with SiO2, which is inert for CO-SCR, enhanced NO x conversion, and NO x conversion increased with increasing amounts of SiO2 in the physical mixture.The selective catalytic reduction of NO x by CO (CO-SCR) over Ir–Ba/WO3–SiO2 was studied. Physical mixing of the Ir catalyst with SiO2, which is inert for CO-SCR, enhanced NO x conversion, and NO x conversion increased with increasing amounts of SiO2 in the physical mixture. HNCO was formed over the physical mixture at low oxygen concentrations. The dependence of CO-SCR activity on contact time in 0.5% O2 suggested that HNCO was an intermediate species. In contrast, Ir catalysts that were not mixed with SiO2 exhibited only trace amounts of HNCO formation, even at low O2 concentrations. Temperature-programmed desorption of HNCO from non-mixed and mixed Ir catalysts, which were pretreated in H2 followed by H2O, revealed that the former had strong adsorption sites for NH3 formed by hydrolysis of HNCO, whereas the latter exhibited a smaller amount of these strong adsorption sites. The Ir catalyst showed high NH3 oxidation capacity under NH3-SCR conditions. The observed enhancement of CO-SCR activity over the mixed Ir catalyst was suspected to result from the decrease in the number of NH3 adsorption sites, which may have caused NH3 to be oxidized to NO.
Keywords: Nitrogen oxide; Carbon monoxide; Iridium; Selective catalytic reduction; Tungsten oxide; Silica
Tuning of nitrogen-doped carbon nanotubes as catalyst support for liquid-phase reaction by Kambiz Chizari; Izabela Janowska; Matthieu Houllé; Ileana Florea; Ovidiu Ersen; Thierry Romero; Pierre Bernhardt; Marc Jacques Ledoux; Cuong Pham-Huu (pp. 72-80).
This work reports the synthesis of nitrogen-doped carbon nanotubes using a Chemical Vapor Deposition (CVD) process. The undoped CNTs and two kinds of nitrogen-doped CNTs (N-CNTs) with different types of nitrogen incorporated species have been used as palladium supports in the cinnamaldehyde hydrogenation. N-CNTs exhibit higher activity and selectivity in this hydrogenation reaction compare to the undoped ones.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 C2H6/(C2H6+NH3)) of 20–100%. Several characterizations, i.e. 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 0at.% to about 5.5at.%. 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 CC 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.
Keywords: Carbon nanotube; Nitrogen doping; Cinnamaldehyde hydrogenation; 3D TEM; XPS
Effect of solvent on hydrolysis and transesterification reactions on tungstated zirconia by Kanokwan Ngaosuwan; Xunhua Mo; James G. Goodwin Jr.; Piyasan Praserthdam (pp. 81-86).
This study found that hexane and a mixture of lauric acid (HLa) and hexane resulted in the highest catalytic activities on tungstated zirconia (WZ) for transesterification and hydrolysis, respectively, probably due to their non-polar and low kinematic viscosity inducing characteristics.The figure represents the effect of the use of solvents (33% of reaction mixture) on the catalytic activity of WZ for transesterification of TCp at 130°C.Using solvents has been found not only to overcome the miscibility problem in biodiesel synthesis but also makes it possible to obtain precise kinetic data. However, little is known about the effect of these solvents themselves on the reaction kinetics. This study explored solvent effects on the nature of the catalytic activity of the solid acid tungstated zirconia (WZ) for hydrolysis and transesterification of tricaprylin (TCp), two reactions that can occur during biodiesel synthesis, at 130°C and 12.2atm in a batch reactor using different solvents. It was found that hexane and a mixture of lauric acid (HLa) and hexane resulted in the highest catalytic activities for transesterification and hydrolysis, respectively, probably due to their non-polar and low kinematic viscosity inducing characteristics. Tetrahydrofuran (THF), in contrast, having a higher polarity, tended to reduce the activity for both hydrolysis and transesterification by competing for active sites on the WZ surface and being involved in side reactions with methanol.
Keywords: Solvent effect; Triglycerides; Tricaprylin; Hydrolysis; Transesterification; Tungstated zirconia; WZ; Biodiesel synthesis
Effects of acidity and microstructure on the catalytic behavior of cesium salts of 12-tungstophosphoric acid for oxidative dehydrogenation of propane by Jizhe Zhang; Miao Sun; Chuanjing Cao; Qinghong Zhang; Ye Wang; Huilin Wan (pp. 87-94).
The acidity and microstructure of Cs xH3− xPW12O40 catalysts, which change regularly depending on the Cs content in these samples, play important roles in determining the catalytic performances in ODH of C3H8. The best yield of C3H6 has been achieved over the Cs1.5H1.5PW12O40 catalyst, which possesses a larger amount of acid sites but lacks mesoporous structure.A series of Cs xH3− xPW12O40 ( x=0.9–3.0) samples with regularly dependent acidity values and gradually transformed microstructures was synthesized by a precipitation method. Along with the increase in Cs content in the Cs xH3− xPW12O40 samples, the concentration of acid sites decreased monotonically, and their morphologies changed gradually from compact large lumps to nano-sized particles. Mesoporous channels were formed probably because of the stacking of nanoparticles in the samples with x>2.1. When the Cs xH3− xPW12O40 samples were used as catalysts for oxidative dehydrogenation (ODH) of propane, higher conversions of propane were achieved over the catalysts with higher acidity. The formation of mesoporous structure improved propane conversion evidently. The best yield of propylene was achieved over the Cs1.5H1.5PW12O40 catalyst, which possessed a high concentration of acid sites and non-porous structure. Our studies demonstrate that not only the acidity but also the porous structure of the Cs xH3− xPW12O40 play key roles in the ODH of propane.
Keywords: Cs salt of 12-tungstophosphoric acid; Acidity; Mesoporous structure; Oxidative dehydrogenation; Propane
Designing new V–Sb–O based catalysts on mesoporous supports for nitriles production by H. Golinska; E. Rojas; R. López-Medina; V. Calvino-Casilda; M. Ziolek; M.A. Bañares; M.O. Guerrero-Pérez (pp. 95-104).
Depending on the morphology and chemical composition of the support, method of active phase loading, and temperature of calcination, different Sb–V–O structures can be obtained, which modulates the activity, being possible the design of selective catalysts towards acrylonitrile or to acetonitrile.The effect of Sb/V molar ratio, textural morphology and chemical composition of the support on the catalytic behavior has been studied during acrylonitrile formation from both propane and glycerol, in the gas and in the liquid phase, respectively. Results nicely show that depending on the presence or absence of sodium cations, the method of Sb–V–O loading, and the calcination temperature, different Sb–V–O structures can be obtained at the catalyst surface. The nature of heteroatom included into mesoporous structure (Al or Nb) does not influence the type of crystal phases formed. Vanadium species remain in different oxidation states in such structures, which drastically affect the catalytic behavior so that it is possible to design catalysts towards high selectivity to acrylonitrile or to acetonitrile. In addition, the role of the niobium as dopant of these catalytic materials has been studied, and it is shown that in mesoporous materials, niobium is able to increase both activity and selectivity to N insertion.
Keywords: Mesoporous materials; Propane; Acrylonitrile; Acetonitrile; Ammoxidation; V-Sb-O catalysts
Tris(triorganosilyl)phosphites—New ligands controlling catalytic activity of Pt(0) complex in curing of silicone rubber by Ireneusz Kownacki; Bogdan Marciniec; Karol Szubert; Maciej Kubicki; Magdalena Jankowska; Helmut Steinberger; Sławomir Rubinsztajn (pp. 105-112).
New tris(triorganosilyl)phosphites synthesized by an efficient method were utilized for the preparation of new platinum complexes [Pt(η4-(H2CCHSiMe2)2O){P(OSiR3)3}]. The structures of two of them were determined by X-ray analysis. These new complexes proved to be very effective catalysts of silicones curing via hydrosilylation at elevated temperature. Moreover, the catalyzed silicone mixture had sufficiently long pot-life at room temperature.Applying novel and efficient method, new tris(triorganosilyl)phosphites were synthesized and further used for the preparation of new well-defined platinum complexes [Pt(DVTMDS){P(OSiR3)3}] (DVTMDS=(H2CCHSiMe2)2O, R3=Si7O9( iOct)7, iPr3, MePh2, Ph3, (O tBu)3, (OSiMe3)3) which were well characterized by spectroscopic methods. Structures of two platinum(0) complexes, [Pt{η4-(H2CCHSiMe2)2O}{P(OSiPh3)3}] (10) and [Pt{η4-(H2CCHSiMe2)2O}{P(OSi(O tBu3)3}] (11) were determined by X-ray analysis. The new complexes proved to be very effective catalysts of a cross-linking of silicones via hydrosilylation at elevated temperature with relatively short cure time and the enthalpy of network formation similar to that of Pt-Karstedt's/DAM (DAM=diallyl maleate) catalytic system. Additionally, the catalyzed silicone formulation had sufficiently long pot-life at room temperature.
Keywords: Hydrosilylation; Karstedt's catalyst; Platinum complexes; Silylphosphites; Curing; Silicones
The one-pot ethyl acetate syntheses: The role of the support in the oxidative and the dehydrogenative routes by Alexandre B. Gaspar; Flavia G. Barbosa; Sonia Letichevsky; Lucia G. Appel (pp. 113-117).
The dehydrogenative and oxidative routes for the one-pot ethyl acetate synthesis from ethanol were studied using physical mixtures of Cu/ZnO/Al2O3 or PdO/ m-ZrO2 with ZrO2. It was inferred that acetaldehyde and ethoxide condensation is very similar for both routes and occurs on the ZrO2 surface. The transport of acetaldehyde from the catalyst to the oxide is associated with the spillover phenomenon.Both the dehydrogenative and the oxidative routes for the one-pot ethyl acetate synthesis from ethanol were studied using physical mixtures of Cu/ZnO/Al2O3 or PdO/ m-ZrO2 with three different ZrO2. The characterization of these catalysts and oxides was carried out by N2 physisorption, pyridine adsorption, CO2 thermo desorption, dynamic light scattering and X-ray diffraction. It was inferred that the second step of the dehydrogenative and oxidative routes, i.e. acetaldehyde and ethanol or ethoxide condensation are very similar. Moreover, it could be verified that this condensation occurs on the ZrO2 surface and also that the basic properties of these oxides influence the catalytic behavior of the physical mixtures (Cu/ZnO/Al2O3+ZrO2 and PdO/ m-ZrO2+ZrO2). The transport of acetaldehyde from the dehydrogenative sites to the ZrO2 surface might be associated with the spillover phenomenon.
Keywords: Zirconia; Ethyl acetate; Condensation; Ethanol; One-step synthesis
Transformation of 1-butene over AlSBA-15 synthesized at different conditions of pH and hydrolysis by V. Sazo; C.M. López; G. Gonzalez; A. Arregui; M.E. Gomes; C. Urbina (pp. 118-124).
The catalytic transformation of 1-butene has been carried over AlSBA-15 catalysts synthesized by adding an aluminium salt, before (BH) or after (AH) silica source hydrolysis at pH 0–4.5. Hydrolysis affected the distribution and strength of the acid sites. The highest 1-butene skeletal isomerization efficiency (SIE) and Al incorporation was obtained over catalysts synthesized at pH 4.5.In the present work a detailed study of the effect of pH, in the range of 0–4.5, over the mesostructure of SBA-15 and catalytic transformation of 1-butene has been carried out. Also, the effect of silica source hydrolysis on the Al incorporation at different pH was studied varying the order of addition of an aluminium salt, before and after hydrolysis. The samples were characterized by SEM, TEM, ICP and N2 adsorption. The materials showed a highly ordered hexagonal mesostructure for all the pH range studied. A decrease in particle size with increase of pH was observed. Al incorporation was favoured as pH increased; the highest incorporation was obtained at pH 4.5. An important effect of hydrolysis on Al incorporation was observed depending of metal incorporation. Hydrolysis had also an effect on the distribution and strength of the acid sites. The materials with the highest skeletal isomerization selectivity were those synthesized at pH 4.5.
Keywords: AlSBA-15; 1-Butene; Skeletal isomerization; Synthesis; Hydrolysis
Tandem hydroformylation-acetalization of para-menthenic terpenes under non-acidic conditions by Camila G. Vieira; José G. da Silva; Cristiano A.A. Penna; Eduardo N. dos Santos; Elena V. Gusevskaya (pp. 125-132).
α-Terpinene, γ-terpinene, terpinolene, and limonene can be selectively transformed in corresponding diethylacetals in ethanol solutions containing [Rh(COD)(OMe)]2 and triphenylphosphine or tris( O-tbu-phenyl)phosphite under mild non-acidic conditions through the hydroformylation and consecutive one-pot acetalization of primarily formed aldehydes. One to three main fragrance para-menthenic acetals account for 70-90% of the mass balance for each substrate.Rhodium-catalyzed tandem hydroformylation/acetalization of a series of para-menthenic terpenes, i.e., α-terpinene (1), γ-terpinene (2), terpinolene (3), and limonene (4), has been studied in ethanol solutions in the presence of PPh3 or P(O- o-tBuPh)3 as auxiliary ligands. Limonene gives a corresponding acetal in high yields in both systems. The reaction with conjugated diene 1 occurs in the presence of PPh3 at a reasonable rate giving aldehydes and acetals only as minor products. On the other hand, non-conjugated dienes 2 and 3 has showed an extremely low reactivity in the Rh/PPh3 system. The use of P(O- o-tBuPh)3 not only remarkably accelerates the hydroformylation of all four substrates but also increases significantly the acetalization activity of the catalytic system. With the Rh/P(O- o-tBuPh)3 system, the mixtures of fragrance acetals have been obtained from substrates 1–3 in excellent combined yields, with two or three main acetals accounting for 70-85% of the mass balance for each substrate. The process is performed under mild conditions and in the absence of acid co-catalysts. The hydroformylation of all substrates in ethanol solutions was found to be much faster than in toluene.
Keywords: Acetalization; Hydroformylation; Monoterpenes; Rhodium
Some features of acetylene hydrogenation on Au-iron oxide catalyst by A.Sárkány; Z. Schay; K. Frey; É. Széles; I. Sajó (pp. 133-141).
Au/FeO x catalysts supporting Au particles of 2.5, 3.3, 3.5 and 7.5nm in average is highly selective in semi-hydrogenation of acetylene (H2/C2H2=140, 1100ppm C2H2) in the 323–473K temperature range and the ethane formation selectivity is less than 1% at 100% C2H2 conversion. The hydrogenation is accompanied with oligomer formation, the C4+ selectivity is typically 2–4%. Hydrogen treatment at T>573K brings about modification of the Au–FeO x interface. Appearance of Fe0 and AuFe particles significantly increased the hydrogenation activity but decreased the semi-hydrogenation selectivity.Hydrogenation of acetylene has been investigated on Au-iron oxide catalysts containing 4.5, 3.0, 5.6wt% Au prepared by deposition–precipitation (DP) with urea, adsorption of Au sol (SA) and by co-precipitation (CP) of HAuCl4 and Fe(NO3)3, respectively. The latter method produced Au particles supported on 2-line ferrihydrite (Fe5HO8·4H2O). Au/iron oxide catalyst precursors (Au/α-Fe2O3 and Au/2-line ferrihydrite) were characterized by BET, TGA, TPR and XRD, and the Au particle size by TEM measurements. The TPR measurements confirm the ease of transformation of 2-line ferrihydrite to magnetite (Fe3O4) and that the formation of magnetite from α-Fe2O3 depends strongly on the size of the gold and the supporting oxide particles. Particle size effect of gold has been investigated in semi-hydrogenation of acetylene. Temperature of hydrogen treatment has been observed to play a crucial role in the activity and ethylene selectivity. Au/FeO x samples hydrogen treated at 353–473K prior to introduction of the reactants (H2:C2H2=140, 0.11% C2H2) show very limited over-hydrogenation (ethane formation is less than ≈1%) and 2–4% selectivity of oligomer (C4+) formation at 353–473K. Hydrogen treatment of the samples at T>573K but lower than the wüstite (FeO) stability point (≈843K) resulted in partial reduction of Fe3O4 and formation of Fe0. The shift of Au(111) XRD line to higher 2 Θ provided evidence for the incorporation of Fe0 into the Au particles. Modification of the Au/Fe2O3 perimeter and appearance of Fe0 co-catalyst and Fe–Au ensembles on the surface increased the hydrogenation activity but decreased the selectivity of ethylene formation.
Keywords: Au–iron oxide; Ferrihydrite; Acetylene hydrogenation; Au particle size; Selectivity
Kinetic of adsorption and of photocatalytic degradation of phenylalanine effect of pH and light intensity by L. Elsellami; F. Vocanson; F. Dappozze; E. Puzenat; O. Païsse; A. Houas; C. Guillard (pp. 142-148).
Amino acids, simpler molecules constituting microorganisms, are found behind filtration process and are at the origin of odorous compounds after chlorination. Our objective is to contribute to a better understanding of the efficiency of photocatalytic treatment for removing them by studying their kinetics of adsorption on TiO2 and of photocatalytic degradation under different pH and light intensities and the intermediate products. TOC disappeared (a) and evolution of nitrate and ammonium (b) as a function of irradiation time.Phenylalanine (Phe) was chosen to study the TiO2 photocatalytic degradation of amino acids, which are at the origin of the formation of odorous compounds after chlorination. The photocatalytic degradation has been investigated in aqueous solutions containing TiO2 suspensions as photocatalyst, in order to assess the influence of various parameters, such as adsorption, initial concentration, pH and radiant flux on the photocatalytic process. Results showed no correlation between dark adsorption and photocatalytic degradation. A multilayer kinetic was observed in the dark with a monolayer corresponding to less that 1% of OH covered, whereas Langmuir–Hinshelwood model seems to modelize the photocatalytic disappearance of Phe. However, even if the form of the curve is similar to L–H model, the degradation of phenylalanine is not a kinetic of L–H as we could plan it by considering the adsorption of the phenylalanine in the dark. The study of the mineralization of carbon and nitrogen showed that nitrogen atoms were predominantly photoconverted into NH4+ and a total mineralization of nitrogen and carbon seems occur. The identification of the by-products by LC–MS reveal mono- and di-hydroxylation and nitrogen–carbon (N–C) cleavage.The effect of pH showed an increase of adsorption under acid pH but a decrease of disappearance rate. The more efficient degradation was found at basic pH. The evolution of hydroxylated compounds of phenylalanine as a function of conversion revealed the presence of more hydroxylated compounds at natural pH and at basic pH compared to acid pH suggesting a modification of mechanism with solution pH. The effect of the radiant flux evaluated under different initial concentration of phenylalanine allowed us to determine that k increases by increasing the radiant flux, whereas K decreases or remains constant from about a value of 3.5mW/cm2. The disappearance rate as a function of radiant flux has been showed to reach a maximal value corresponding to a maximal quantum yield of 1.6%.
Keywords: Phenylalanine; Adsorption; Photocatalysis; Kinetic; By-products; pH; Radiant flux
The effect of preparation conditions on the properties of high-surface area Ni2P catalysts by Rui Wang; Kevin J. Smith (pp. 149-164).
The addition of citric acid (CA) to precursor metal and phosphate salt solutions produces an amorphous precursor after calcination, rather than crystalline NiO and Ni2P4O12 that was observed in the absence of CA, and the amorphous material yields high surface area Ni2P (∼220m2/g) when reduced above 600°C. The high surface area Ni2P favored the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) by the hydrogenation route.The effect of preparation conditions on the properties of unsupported, high surface area Ni2P catalysts, prepared by adding citric acid (CA) to precursor metal salt solutions prior to drying, calcination and temperature-programmed reduction (TPR), is reported. The highest Ni2P surface area (∼220m2/g) was obtained from a precursor solution with a P/Ni mole ratio of 2 and a CA/Ni mole ratio of 2 that was dried, calcined at 500°C and reduced in H2 at 650°C. Adding CA to the precursor salt solution is shown to yield amorphous precursors after calcination, rather than crystalline NiO and Ni2P4O12 that was observed in the absence of CA, and the amorphous material yielded high surface area Ni2P when reduced at temperatures above 600°C. The high surface area Ni2P favored the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) by the hydrogenation route, although some direct-desulfurization was observed on catalysts reduced at lower temperature in which significant metaphosphate species were identified.
Keywords: Catalyst; Hydrodesulfurization; Nickel phosphide; 4,6-Dimethyldibenzothiophene; Citric acid; Catalyst preparation; Catalyst characterization
Biomass to chemicals: Rearrangement of β-pinene epoxide into myrtanal with well-defined single-site substituted molecular sieves as reusable solid Lewis-acid catalysts by Olalla de la Torre; Michael Renz; Avelino Corma (pp. 165-171).
Zr-Beta is found to be an active and selective catalyst for the epoxide rearrangement of β-pinene oxide into myrtanal in acetonitrile solvent. The catalyst with Lewis-acid centers can be used in a batch reactor or in a fixed-bed continuous-flow reactor and it can be recycled for several times without loss of activity or selectivity.The epoxide rearrangement of β-pinene oxide into myrtanal was studied in the presence of solid Lewis-acid catalysts. Different metals such as Zr, Sn, Ti, Nb, Ta, Al, and Ga have been incorporated within network positions of zeolite Beta by isomorphous substitution. The materials have been characterized by powdered X-ray diffraction (XRD), IR spectroscopy and by in situ IR spectroscopy on adsorbed molecules (cyclohexanone and pyridine). Among the studied catalysts Zr-Beta gave the best selectivity (up to 94%) in acetonitrile as solvent at practically complete conversion. In this epoxide rearrangement the solvent has to be selected to balance the competitive adsorption of the product. Product desorption is enhanced with acetonitrile which results in a selectivity increase with only a small penalty on the rate of reaction. Zr-Beta has been reused in the batch mode and in a fixed-bed reactor for several times and analysis of the reused catalyst indicated that Zr-Beta is a robust catalyst for the epoxide rearrangement. Leaching of the metal or crystal degradation has not been detected.
Keywords: Beta zeolite; Epoxide rearrangement; Heterogeneous catalysis; Solid Lewis acid
CO2 photoreduction using NiO/InTaO4 in optical-fiber reactor for renewable energy by Zhen-Yi Wang; Hung-Chi Chou; Jeffrey C.S. Wu; Din Ping Tsai; Guido Mul (pp. 172-177).
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. An optical-fiber photoreactor, comprised of ∼216 NiO/InTaO4-coated fibers, was designed to transmit and spread light uniformly inside the reactor. Methanol production rate was 11.30μmol/gh by utilizing real concentrated sunlight.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 0.14μm 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 11.1μmol/gh with light intensity of 327mW/cm2 at 25°C. Increasing the reaction temperature to 75°C increased the production rate to 21.0μmol/gh. Methanol production rate was 11.30μmol/gh 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.
Keywords: CO; 2; Photocatalytic reduction; InTaO; 4; Optical fiber reactor; Renewable energy
H2–O2 promoting effect on photocatalytic degradation of organic pollutants in an aqueous solution without an external H2 supply by Zizhong Zhang; Xuxu Wang; Jinlin Long; Zhengxin Ding; Xianliang Fu; Xianzhi Fu (pp. 178-184).
A cooperative photocatalyst composed of Pt/TiO2 and a water-splitting catalyst such as NiO/NaTaO3:La exhibited efficient activity for the degradation of organic compounds in an aqueous solution under UV light irradiation. The activity was enhanced because the water molecules can be facilely transformed into the active oxygen species H2O2 andOH radical over Pt/TiO2 through the assistance of water splitting into H2 on NiO/NaTaO3:La.To fabricate the H2–O2 promoting effect systems for quicker degradation of organic pollutants without an external H2 supply, we replace pure Pt/TiO2 photocatalyst by a cooperative catalyst composed of Pt/TiO2 and some assistant catalysts with water-splitting ability. When the cooperative catalysts were used for the photooxidation of organic pollutants under UV light irradiation, enhanced activities were observed for salicylic acid and phenol removal, except for formate, as compared to pure Pt/TiO2 catalyst. For different metal oxides as the assistant catalyst, an increase in the activity depended on their ability to promote H2 release. The fluorescence spectroscopy and photometric techniques combind with GC–MS were applied to investigate the cooperative system. Results revealed that more hydroxyl radical (OH) and hydrogen peroxide (H2O2) were formed from the H2O molecules over a cooperative catalyst. A photodegradation mechanism of organic pollutants on a cooperative catalyst is proposed.
Keywords: Pt/TiO; 2; Photocatalysis; Degradation; Cooperative catalyst; H; 2; -promoting effect
Comments on “NO2− adsorption onto denitration catalysts” [Appl. Catal. A 363 (2009) 81–85]
by Francisco Ruiz-Beviá; Maria J. Fernandez-Torres (pp. 185-185).
Reply to the comments on “NO2− adsorption onto denitration catalysts”
by Akane Miyazaki; Toru Asakawa; Ioan Balint (pp. 186-186).