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Applied Catalysis A, General (v.323, #)
Effect of nickel hexaaluminate mirror cation on structure-sensitive reactions during n-tetradecane partial oxidation by Todd H. Gardner; Dushyant Shekhawat; David A. Berry; Mark W. Smith; Maria Salazar; Edwin L. Kugler (pp. 1-8).
Reforming studies were conducted on nickel-substituted hexaluminate catalysts to reform liquid hydrocarbon fuels into H2-rich synthesis gas for fuel cell applications. The partial oxidation of n-tetradecane (I) and n-tetradecane containing 50ppmw sulfur as dibenzothiophene (II) were used as probe reactions to assess their performance and sulfur poisoning resistance. ▪Reforming studies were conducted on nickel-substituted hexaaluminate catalysts, ANi0.4Al11.6O19− δ (A=La, Sr and Ba), to reform liquid hydrocarbon fuels into H2-rich synthesis gas for fuel cell applications. The reaction conditions studied were the partial oxidation of n-tetradecane (I) and n-tetradecane with 50ppmw sulfur as dibenzothiophene (II). Hexaaluminate catalyst activity toward reaction conditions (I) and (II) as well as the surface Ni concentration and dispersion was shown to correlate with the type of mirror cation substituted into the lattice. The Ni surface concentration was determined by XPS to be 5.3, <0.1 and 0.7wt.% for LaNi0.4Al11.6O19− δ, BaNi0.4Al11.6O19− δ and SrNi0.4Al11.6O19− δ, respectively. SrNi0.4Al11.6O19− δ and BaNi0.4Al11.6O19− δ catalysts exhibited stable performance for reaction condition (I), while the loss in activity exhibited over time by LaNi0.4Al11.6O19− δ suggested site blocking by carbon deposition. Under reaction condition (II), additional activity loss was experienced by both LaNi0.4Al11.6O19− δ and SrNi0.4Al11.6O19− δ catalysts due to the presence of dibenzothiophene. However, LaNi0.4Al11.6O19− δ experienced more severe and partially reversible site blocking where SrNi0.4Al11.6O19− δ experienced a less severe loss of activity, selectivity and irreversible site blocking. The behavior observed in nickel-substituted hexaaluminate catalysts suggests that the different mirror cations influenced the coordination of Ni sites within the lattice and adsorption of hydrocarbons to the surface of the catalysts.
Keywords: Nickel; Hexaaluminate; Partial oxidation; Sulfur; Diesel; Fuel cell
Enhanced catalytic activity for butane isomerization with alumina-promoted tungstated mesoporous zirconia by Chi-Chau Hwang; Xiao-Rong Chen; She-Tin Wong; Chang-Lin Chen; Chung-Yuan Mou (pp. 9-17).
Alumina-promoted tungstated mesoporous zirconia (AW/m-ZrO2) catalysts were synthesized and tested on n-butane isomerization. They possess high catalytic activity and stability. The composition of acid sites on AW/m-ZrO2 catalysts calcined at different temperatures was then correlated to their catalytic performances. The unusually high catalytic activity was attributed to better dispersion of tungstate species on zirconia. ▪Mesoporous zirconia, synthesized from surfactant templating, was used to disperse alumina and tungstate as a catalyst (denoted as AW/m-ZrO2) for the isomerization of n-butane. At a relatively low temperature of calcination (700°C), the catalyst (AW/m-700) performed exceptionally well, both in maximum rate and stability, at a temperature of 250°C. This was lower than the temperature needed by other tungstated zirconia-based catalysts reported so far. This lower temperature of calcination leads to the presence of more Brönsted acid sites with higher acid strength. In comparison with the normal dense phase zirconia catalyst, AW/m-ZrO2 catalyst showed higher n-butane isomerization activity than the corresponding AW/d-ZrO2 catalyst, which has about the same surface area. The difference in catalytic activity was attributed to the higher degree of dispersion of tungstate on the surface of m-ZrO2.
Keywords: Tungstated zirconia; Alkane isomerization; Mesoporous zirconia; EXAFS; XPS; Surface acidity
Thin films of Co–B prepared by pulsed laser deposition as efficient catalysts in hydrogen producing reactions by N. Patel; G. Guella; A. Kale; A. Miotello; B. Patton; C. Zanchetta; L. Mirenghi; P. Rotolo (pp. 18-24).
Hydrogen generation by catalytic hydrolysis of sodium borohydride (NaBH4) is studied by using Co–B-based thin film catalyst synthesized by pulsed laser deposition (PLD) technique. Co–B nanoparticles, produced in the catalyst film after the laser ablation process, act as active centers producing significantly higher H2 generation rate than Co–B bulk powder. Films were deposited at different PLD set-up parameters in order to estimate the density of the nanoparticles and to understand the role of their size in the catalytic process. Cobalt has been found here to act as an efficient catalyst only when alloyed with boron which partially prevents cobalt oxidation. In particular we report that when used as suitable thin films, Co–B produces H2 with a maximum generation rate of about 3300ml/[ming catalyst]. ▪Hydrogen generation by catalytic hydrolysis of sodium borohydride (NaBH4) is studied by using Co–B-based thin film catalyst synthesized by pulsed laser deposition (PLD) technique. Co–B nanoparticles, produced in the catalyst film after the laser ablation process, act as active centers producing significantly higher H2 generation rate than Co–B bulk powder. Surface morphology was studied by using scanning electron microscopy and compositional analysis was established by using X-photoelectron and infrared spectroscopies. Films were deposited at different PLD set-up parameters in order to understand the possible role of size and density of the nanoparticles in the catalytic process. Cobalt has been found here to act as an efficient catalyst only when alloyed with boron which partially prevents cobalt oxidation. In particular we report that when used as suitable thin films, Co–B produces H2 with a maximum generation rate of about 3300ml/min per gram of catalyst.
Keywords: Hydrogen generation; Catalyst; Sodium borohydride; Nanoparticles; Cobalt boride
The influence of preparation variables on the performance of Pd/Al2O3 catalyst in the hydrogenation of 1,3-butadiene: Building a basis for reproducible catalyst synthesis by Tatjana Cukic; Ralph Kraehnert; Martin Holena; Daniel Herein; David Linke; Uwe Dingerdissen (pp. 25-37).
A methodology based on design of experiments, high-throughput experimentation and knowledge extraction was developed using the impregnation of Pd on Al2O3 as example to study the influence of a multitude of preparation variables other than composition on the catalyst performance in the 1,3-butadiene hydrogenation. The identified important preparation variables provide a basis to develop recipes for more controlled and reproducible catalyst synthesis. ▪A methodology based on design of experiments (DoE), high-throughput experimentation (HTE) and knowledge extraction was developed to study the influence of a multitude of preparation variables other than composition on the performance of supported catalysts. As an example, the methodology was applied to the impregnation of Pd on Al2O3 and its catalytic performance in the gas phase hydrogenation of 1,3-butadiene. From the experimental data of 90 differently synthesized catalysts, the relative importance of each preparation variable was assessed. Moreover, the experimental data were used to derive a non-linear regression model that predicts catalytic activity as a function of preparation variables. The model was validated successfully by additional experiments. The identified important preparation variables provide a good basis to develop recipes for more controlled and reproducible catalyst synthesis.
Keywords: Pd/Al; 2; O; 3; Butadiene hydrogenation; Preparation variables; Experimental design; High-throughput experimentation; Regression tree; Reproducibility of chemical recipes
Liquid-phase synthesis of isopropyl tert-butyl ether by addition of 2-propanol to isobutene on the oversulfonated ion-exchange resin Amberlyst-35 by Marc Pera-Titus; Marta Bausach; Javier Tejero; Montserrat Iborra; Carles Fité; Fidel Cunill; J. Felipe Izquierdo (pp. 38-50).
The selectivity and kinetics of the liquid-phase addition of 2-propanol to isobutene to give isopropyl tert-butyl ether (IPTBE) was investigated over the commercial oversulfonated ion-exchange Amberlyst-35 resin in the temperature range 60–90°C and 1.6MPa. Amberlyst-35 was found to be more active than Amberlyst-15 and medium-pore H-exchanged zeolites for carrying out the reaction.▪The selectivity and kinetics of the liquid-phase addition of 2-propanol to isobutene to give isopropyl tert-butyl ether (IPTBE) was investigated in a batch reactor over the commercial oversulfonated ion-exchange Amberlyst-35 resin in the temperature range 60–90°C and 1.6MPa for 2-propanol/isobutene initial ratios ranging from 0.5 to 3.0. The effect of the initial 2-propanol/isobutene molar ratio and temperature on isobutene conversion ( XIB), IPTBE yield ( YIPTBE/IB) and selectivity to dimers ( SIPTBE/DIM) and on the initial reaction rate of IPTBE formation ( r0IPTBE) was also evaluated. Amberlyst-35 was found to be more active than Amberlyst-15 and medium-pore H-exchanged zeolites for carrying out IPTBE synthesis. Experimental IPTBE formation rates can be successfully represented by two kinetic models derived from the LHHW and ER formalisms, where 2-propanol adsorbed on one active site reacts with isobutene, either adsorbed on one active site in the former model, or in liquid-state in the latter, to give IPTBE also adsorbed on one active site. The apparent activation energy found for both models was estimated to be 71+3kJmol−1.
Keywords: Isopropyl; tert; -butyl ether; 2-propanol; Isobutene; Etherification; Amberlyst-15; Amberlyst-35
Catalytic behavior of nickel nanoparticles stabilized by lower alkylammonium bromide in aqueous medium by M.L. Singla; Anjali Negi; Vikram Mahajan; K.C. Singh; D.V.S. Jain (pp. 51-57).
Heterogeneous synthesis of monodisperse nickel nanoparticles in aqueous medium carried out using cetyltrimethylammonium bromide and lower alkylammonium bromides. The particles were characterized using TEM, EDS, XRD, TGA–DSC and FTIR. The particles are spherical in shape, fcc with average diameter 15nm, stable in air up to 325°C. Nanoparticles have been used as a solid phase catalyst for the reduction of p-nitrophenol using hydrazine hydrate as reducing agent under different conditions. The reaction mechanism was monitored with UV–vis spectrophotometer. The particles were not poisoned after repeated use. ▪Heterogeneous synthesis of monodisperse pure nickel nanoparticles in aqueous medium has been carried out using cetyltrimethylammonium bromide and a lower alkylammonium bromide mixture of tetraethylammonium bromide and tetrabutylammonium bromide. The presence of cetyltrimethylammonium bromide alone results in the formation of a mixture of nickel hydroxide and nickel nanoparticles. The particles have been characterized using TEM, EDS, XRD, TGA–DSC and FTIR. The analysis showed that particles are spherical in shape, monodisperse, face-centered-cubic with average size about 15nm and are stable in air up to 325°C. The nanoparticles have been used as a solid phase catalyst for the reduction of p-nitrophenol in the presence of hydrazine hydrate as reducing agent at different temperatures under varying conditions. The reduction process has been monitored by UV–vis analysis. The present study showed that nanoparticles are not poisoned after their repeated use in reduction of p-nitrophenol to p-aminophenol. TEM analysis also confirms that nanoparticles are stable in the dispersed medium for longer times.
Keywords: Nickel nanoparticles; Lower alkylammonium bromide; Aqueous medium; p; -Nitrophenol; Catalysis; p; -Aminophenol
Generation of Brönsted acidity in AlMCM-41 by sulphation for enhanced liquid phase tert-butylation of phenol by Eng-Poh Ng; Hadi Nur; Ka-Lun Wong; Mohd Nazlan Mohd Muhid; Halimaton Hamdan (pp. 58-65).
Generation of Brönsted acidity in AlMCM-41 has been demonstrated by sulphation method. It was demonstrated that the sulphated AlMCM-41 was catalytically active towards liquid phase tert-butylation of phenol.▪AlMCM-41 mesoporous molecular sieve modified by impregnation with sulphuric acid in toluene possesses only Brönsted acid sites. The catalyst exhibits a high catalytic activity for tert-butylation of phenol with high selectivity to 2,4-di- tert-butylphenol in liquid phase.27Al MAS NMR study indicates that the modification of AlMCM-41 with sulphuric acid in toluene leaves only octahedrally coordinated Al species. The tetrahedrally coordinated Al species which exist before modification with sulphuric acid in toluene being dealuminated to form extraframework octahedrally coordinated Al species. The mesoporous structure of AlMCM-41 is retained after modification, but pore size decreases by ca. 3Å by the modification. The active sites are postulated on the basis of XRD, FTIR,27Al MAS NMR, TGA, BET analysis and FTIR-pyridine adsorption studies that –OSO3H bonded to octahedrally coordinated Al species.
Keywords: Sulphation; AlMCM-41; Brönsted acid; tert; -Butylation; Phenol
Mass and heat transfer effects on the oxidative dehydrogenation of propane (ODP) over a low loaded VO x/Al2O3 catalyst by Benjamin Frank; Arne Dinse; Olga Ovsitser; Evgueni V. Kondratenko; Reinhard Schomäcker (pp. 66-76).
A low loaded VO x/Al2O3 catalyst (1.4wt.% V) was prepared by saturation-impregnation of a commercial γ-alumina support. The nature, distribution and redox properties of surface VO x species were investigated by means of in situ UV–vis and TPR tests as well as by O2 pulse experiments. Macroscopic structural properties of the catalyst were determined from XRD and BET (N2 physisorption) analysis including pore size distribution. It was found that propene selectivity in the oxidative dehydrogenation of propane with oxygen in the temperature range of 673–773K decreases with an increase in the size of the catalyst particles. Based on a simulation of intraparticle concentration and temperature profiles using developed intrinsic power-law kinetics, it was concluded that the dependence of propene selectivity on particle size is related to propene accumulation inside the particle pores and further oxidation. The kinetic evaluation indicated that total propene selectivity suffers exclusively from consecutive propene combustion to CO and CO2, whereas the reaction of propane with lattice oxygen of VO x species selectively yields propene. Moreover, the kinetic model in agreement with the experiment predicts an increase in propene selectivity with temperature. This is due to slightly higher activation energy of propene formation than its combustion. Since the measured effects were predicted quantitatively by the kinetic model, it, therefore, can be used for a precise design of extended microkinetic studies with this catalyst.A low loaded VO x/Al2O3 catalyst (1.4wt.%V) was prepared by saturation-impregnation of a commercial γ-alumina support. The nature, distribution and redox properties of surface VO x species were investigated by means of in situ UV–vis and TPR tests as well as by O2 pulse experiments. Macroscopic structural properties of the catalyst were determined from XRD and BET (N2 physisorption) analysis including pore size distribution. It was found that propene selectivity in the oxidative dehydrogenation of propane with oxygen in the temperature range of 673–773K decreases with an increase in the size of the catalyst particles. Based on a simulation of intraparticle concentration and temperature profiles using developed intrinsic power-law kinetics, it was concluded that the dependence of propene selectivity on particle size is related to propene accumulation inside the particle pores and further oxidation. The kinetic evaluation indicated, that total propene selectivity suffers exclusively from consecutive propene combustion to CO and CO2, whereas the reaction of propane with lattice oxygen of VO x species selectively yields propene. Moreover, the kinetic model in agreement with the experiment predicts an increase in propene selectivity with temperature. This is due to slightly higher activation energy of the ODP reaction compared to propene combustion. Since the measured effects were predicted quantitatively by the kinetic model, it, therefore, can be used for a precise design of extended microkinetic studies with this catalyst. ▪
Keywords: Vanadia; VO; x; /Al; 2; O; 3; Oxidative dehydrogenation of propane; ODP; Kinetic model; Mass transport limitation; Particle modelling
Catalytic ketonization over oxide catalysts by M. Gliński; A. Kozioł; D. Łomot; Z. Kaszkur (pp. 77-85).
Carboxylic acids were selectively reduced to aldehydes when their mixture with formic acid in the form of vapour had been passed over 20 wt.% MO2/Al2O3 catalysts (M = Mn, Ce or Zr). ▪Carboxylic acids were selectively reduced to aldehydes when their mixture with formic acid in the form of vapour had been passed over solid catalyst. The activities of 20 wt.% MO2/A catalysts, where M = Mn, Ce or Zr and A = Al2O3 have been studied in the mentioned reaction at the temperature range of 573–723 K. Hexanoic acid and its branched monomethyl and dimethyl isomers were used as substrates. For hexanoic acid reduction (HCOOH/C5H11COOH molar ratio 3) the following order of the maximum yield of aldehyde (in %) has been observed: Mn(58)> Ce(36)≫ Zr(5)> support(1). Ketonization of an acid into undecan-6-one was the main side reaction in the upper range of reaction temperatures. Small amounts of hexan-1-ol and methyl hexanoate have also been detected among reaction products. An increase in the molar ratio of HCOOH/C5H11COOH diminished the ketone formation. The reactivity of branched x-methylpentanoic (x=2, 3 and 4) acids in the reduction by formic acid depended strongly on the position of the substituent in the acid molecule and decreased in the following order: 4-methyl-> 3-methyl-> 2-methyl-. 2,2-Dimethyl- and 3,3-dimethylbutanoic acids were reduced to alkanals with very low yields (6%) even at the highest temperatures. The same order of reactivity of isomeric hexanoic acids has been observed in the homo-ketonization of pure acids. The MnO2/A catalyst has had a constant activity and selectivity in the reduction of hexanoic acid by formic acid. In the presence of HCOOH, methyl hexanoate was transferred below 673 K into hexanal and hexan-1-ol with 12 and 5% yields, respectively. Under the same conditions hexanal was reduced to hexan-1-ol with moderate yields (23%). Above 648 K, the ketonization of methyl hexanoate or hexanal took place and undecan-6-one was found to be the main product in both cases (94–96% at 723 K).It has been also shown that neither dihydrogen nor the products of the decomposition of formic acid can reduce hexanoic acid in the presence of the studied catalytic systems. The highest yields of hexanal (up to 3%) were reached at 673 K for the H2/C5H11COOH molar ratio equals 3. An increase in this ratio up to 15 resulted in an increase in the yield of hexanal up to 7%.A mechanism of the formation of an aldehyde in the reaction between formic and carboxylic acid has been proposed. It is assumed that a mixed formic-carboxylic anhydride is formed with its subsequent decarboxylation to an aldehyde.On the basis of XRD measurements of freshly prepared manganese catalyst, it was concluded that its active phase containsβ-MnO2 which is almost quantitatively reduced to MnO in contact with either formic or hexanoic acid or their mixture.
Keywords: Reduction of carboxylic acids by formic acid; Aldehydes; Manganese; Cerium and zirconium oxide catalysts
Synthesis and characterization of high-surface area tungsten carbides and application to electrocatalytic hydrogen oxidation by Yoshinori Hara; Noriko Minami; Hiroaki Itagaki (pp. 86-93).
In analogy with W2N and WO3, WS2 and WP were found to undergo the CH4 carburization to produce α-WC. α-WC obtained from WS2 and W2N exhibited a high specific surface area compared with other routes. The introduction of a small amount of Pt into the WCs prepared in these ways contributed to a remarkable activity enhancement for the hydrogen electro-oxidation reaction.▪Tungsten carbides (WC) with different crystalline phases prepared from WO3 as the starting material showed electrocatalytic activity in the order of α-WC>β-WC1− x>β-W2C for the hydrogen oxidation reaction. α-WC obtained by methane carburizing of tungsten nitride (W2N), which was prepared from nitridation of WO3, produced much higher surface area than that from the direct carburization of WO3. We first found capable of carburize tungsten sulfide (WS2) and tungsten phosphide (WP) to produce α-WC though they require severe carburization reaction. In particular, α-WC obtained from WS2 exhibited a high specific surface area as well as α-WC by way of W2N. The XPS analysis revealed that the surface properties of α-WC are significantly dependent on the preparative methods. A large amount of graphite carbon was deposited on the surface of α-WC from direct carburization, whereas, there was far less on α-WC by way of W2N and WS2.The electrocatalytic activities of WCs obtained in these ways were greatly improved. The binary catalysts of WC promoted with Pt were evaluated in comparison with the current Pt catalyst. The introduction of a small amount of Pt onto the WC contributed to a remarkable anodic current enhancement. It turned out that the specific activity (activity based on the surface area of Pt metal) was higher than that of the commercial catalyst. It is concluded that the interaction Pt with α-WC enhance the utilization of Pt for the hydrogen electro-oxidation reaction.
Keywords: Hydrogen electro-oxidation; PEFC; Tungsten carbide; High-surface area
The effect of calcination time on the activity of WO3/Al2O3/HY catalysts for the metathesis reaction between ethene and 2-butene by Shengjun Huang; Shenglin Liu; Qingjun Zhu; Xiangxue Zhu; Wenjie Xin; Huijuan Liu; Zaochi Feng; Can Li; Sujuan Xie; Qingxia Wang; Longya Xu (pp. 94-103).
A series of WO3/Al2O3/HY catalysts were prepared by thermal spread method (i.e., calcination of physically mixed WO3, Al2O3 and HY zeolite) for the metathesis reaction between ethene and 2-butene to propene. The transformation of tungsten oxide species was studied by the characterization techniques of XRD, H2-TPR, UV-Vis, UV Resonance Raman, NH3-TPD and N2 adsorption–desorption techniques. The thermal spread effect during calcination results in the dispersion of bulk WO3 phase into microcrystallites on γ-Al2O3 surface, followed by a chemical transformation to the monomeric surface tungstate species via the involvement of Brönsted acid sites of HY zeolite. These monomeric surface tungstate species, identified by a characteristic Raman band at 970cm−1, are crucial for the metathesis activity. We suggest such activity related species are tetrahedrally coordinated. Moreover, it is found that there is an optimal calcination time for the formation of these WO42− species and further calcination causes the condensation to the polytungstate clusters, which are less active for the metathesis reaction. The optimized catalyst shows superior catalytic activity of metathesis reaction between ethene and 2-butene to propene at 453K with 2-butene conversion close to thermodynamic equilibrium value (∼64%).A series of WO3, Al2O3 and HY catalysts were prepared by the thermal spread method. A proportional correlation between tetrahedral tungsten oxide species and metathesis activities is observed, from which the structure of active sites precursors is confirmed. The optimized catalyst shows superior activity for the metathesis between ethene and 2-butene to propene at 453K with 2-butene conversion close to thermodynamic equilibrium value (∼64%).▪
Keywords: Metathesis; Tungsten oxide catalysts; γ-Al; 2; O; 3; HY zeolite; UV-Vis; UV Raman; Surface tungstate
Effect of Co addition for carburizing process of Ti-oxide/SiO2 into TiC/SiO2 by Yasuhiro Iwama; Nobuyuki Ichikuni; Kyoko K. Bando; Shogo Shimazu (pp. 104-109).
Lowering the carburization temperature of Ti-oxide into TiC down to 1173K could be achieved by the addition of Co. Co-promoted TiC/SiO2 catalysts were prepared by the temperature programmed reaction (TPR) method. Co–Ti/SiO2 precursors were prepared by use of the successive impregnation method (sc) and the co-impregnation method (co). Samples were characterized by X-ray absorption fine structure (XAFS) measurements and X-ray diffraction (XRD) results. The carburization degree of TiC was affected by the method of Co addition. The carburization degree of sc Co–TiC/SiO2 was better than that of co Co–TiC/SiO2. The activity of thiophene hydrodesulfurization reaction at 693K on sc Co–TiC/SiO2 was higher than that on co Co–TiC/SiO2. The HDS activity was related to the carburization degree of TiC. ▪Lowering the carburization temperature of Ti-oxide into TiC down to 1173K could be achieved by the addition of Co. Co-promoted TiC/SiO2 catalysts were prepared by the temperature programmed reaction (TPR) method. Co–Ti/SiO2 precursors were prepared by use of the successive impregnation method (sc) and the co-impregnation method (co). Samples were characterized by X-ray absorption fine structure (XAFS) measurements and X-ray diffraction (XRD) results. The carburization degree of TiC was affected by the method of Co addition. The carburization degree of sc Co–TiC/SiO2 was better than that of co Co–TiC/SiO2. The activity of thiophene hydrodesulfurization reaction at 693K on sc Co–TiC/SiO2 was higher than that on co Co–TiC/SiO2. The HDS activity was related to the carburization degree of TiC.
Keywords: TiC catalyst; XAFS; Co additive; Carburization
The hydrothermal synthesis of mesoporous TiO2 with high crystallinity, thermal stability, large surface area, and enhanced photocatalytic activity by Dong Suk Kim; Seung-Yeop Kwak (pp. 110-118).
Well-defined spherical mesoporous TiO2 was prepared from a poly(ethylene glycol)-poly(propylene glycol)-based triblock copolymer and titanium isopropoxide mixed with 2,4-pentanedione by using a simple sol–gel approach in aqueous solution. Hydrothermal treatment was performed to increase the crystallinity, thermal stability, surface area, and photocatalytic activity of the mesoporous TiO2. The hydrothermally treated mesoporous TiO2 materials were found to have a high crystallinity with a nanocrystalline anatase structure even in the as-synthesized state, whereas untreated materials were found to have an amorphous or semicrystalline phase prior to calcination at 300°C. The surface area of hydrothermally treated mesoporous TiO2 was found to exceed 395m2g−1, whereas the areas of the untreated materials were less than 123m2g−1. The pore size distributions of the hydrothermally treated mesoporous TiO2 materials were found to be narrower than those of untreated materials; the average pore size increased from 5.7 to 10.1nm with increases in the calcination temperature. The photocatalytic activity of hydrothermally treated mesoporous TiO2 is significantly higher than the activities of untreated materials, with a maximum decomposition rate that is three times faster than that of a commercial TiO2, P25. The high photocatalytic activity of mesoporous TiO2 is due to the large surface area and high crystallinity with a nanocrystalline anatase that is induced by the hydrothermal treatment.The hydrothermal synthesis of mesoporous TiO2 with high crystallinity, thermal stability, and large surface was synthesized. The photocatalytic activity is higher than that of commercial TiO2 induced by the high crystallinity, large surface area, and small crystallite anatase. ▪
Keywords: Mesoporous TiO; 2; Hydrothermal treatment; High crystallinity; Surface area; Photocatalytic activity
Decomposition of cyclohexyl hydroperoxide over transition metal-free zeolite H-beta by Zhiqiang Sun; Jie Xu; Zhongtian Du; Wei Zhang (pp. 119-125).
Cyclohexyl hydroperoxide, a key intermediate in the cyclohexane autoxidation for the manufacture of cyclohexanone and cyclohexanol, was decomposed over transition metal-free zeolite H-beta. The CHHP decomposition efficiency reached 191mmolg−1h−1, which is almost equal to that over 5% Ru/Al2O3 under the same conditions. The highest combined yield of cyclohexanol and cyclohexanone reached 84.6mol% at 125°C. Elevation of reaction temperature can increase the activity and selectivity to cyclohexanone. Correlating study between the catalytic activity and the acidity reveals that the medium strength Brönsted acid sites of H-beta are the main active centers for the decomposition reaction.Cyclohexyl hydroperoxide was decomposed over transition metal-free zeolite H-beta, the CHHP decomposition efficiency reached 191mmolg−1h−1, which is almost equal to that over 5% Ru/Al2O3 under the same conditions. The highest combined yield of cyclohexanol and cyclohexanone reached 84.6mol% at 125°C. The medium strength Brönsted acid sites of H-beta are the main active centers for the decomposition.▪
Keywords: Cyclohexyl hydroperoxide; Zeolite; H-beta; Decomposition
La-promoted Na2WO4/Mn/SiO2 catalysts for the oxidative conversion of methane simultaneously to ethylene and carbon monoxide by Jingjing Wu; Haili Zhang; Song Qin; Changwei Hu (pp. 126-134).
A series of La-promoted 5wt% Na2WO4/2wt% Mn/SiO2 catalysts were prepared by varying the impregnation sequence and the concentration of La promoter, and their catalytic performance for the oxidative conversion of methane was investigated in a micro-quartz-tube reactor. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was found that the existence of Mn ions was in favor of the dispersion of La species on the catalyst, and the addition of La promoter could increase the dispersion of Na2WO4, which enriched the amount of surface oxygen species connected with the metal atoms. This oxygen species was found to be active for the oxidative coupling of methane to C2 hydrocarbons. The selectivity and yield of C2 hydrocarbons with a C2H4/CO ratio of 1/1 reached the optimized value of about 56% and 25%, respectively, at 800°C, over the 5wt% Na2WO4/2wt% La–2wt% Mn/SiO2 catalyst prepared by co-impregnation of La and Mn.The oxygen species connected to metals over La-promoted 5wt% Na2WO4/2wt% Mn/SiO2 catalysts were found to be the active oxygen species for the oxidative coupling of methane to C2 hydrocarbons. The selectivity and yield of C2 hydrocarbons with a C2H4/CO ratio of 1/1 reached about 56% and 25%, respectively, under optimized conditions. ▪
Keywords: Oxidative coupling of methane; La-promoted Na; 2; WO; 4; /Mn/SiO; 2; catalyst; Surface oxygen species
Rational design of the carbon nanofiber catalysts for oxidative dehydrogenation of ethylbenzene by Tie-Jun Zhao; Wei-Zhen Sun; Xiong-Yi Gu; Magnus Rønning; De Chen; Ying-Chun Dai; Wei-Kang Yuan; Anders Holmen (pp. 135-146).
Synthesized carbon nanofibers with different graphitic sheet orientations in respect to the fiber axis have been used as a platform for the rational catalyst design for oxidative dehydrogenation of ethylbenzene. Effects of the properties of carbon nanofibers such as the amount of basic groups, the crystallinity, and the ratio between the prismatic area and the basal plane area on the catalyst activity and selectivity have been addressed. ▪The rational design of the carbon nanofiber catalysts for oxidative dehydrogenation of ethylbenzene (ODE) has been discussed based on a reviewed reaction mechanism. The synthesized carbon nanofibers with systematically varied graphitic platelet orientations have been used as a model system for the rational catalyst design, in respect to the carbon nanofiber properties such as the amount of basic groups, the crystallinity, and the ratio between the prismatic area and the basal plane area. Well defined carbon nanofibers have been synthesized by hydrocarbon or carbon monoxide decomposition on the sub-iron group catalysts and at selected preparation conditions. The catalytic test in a fixed bed reactor at a temperature of 400°C shows that the stable activity and selectivity can be obtained on the well-defined carbon nanofibers catalysts. Removing the residual metal in carbon nanofibers does not evidently influence the catalytic behavior whereas the lower conversion of ethylbenzene can be observed on the high-temperature treated carbon nanofiber samples. No clear evidences are found for the catalytic behavior being related to the surface area and graphitization degree of carbon nanofibers. The basic oxygen-containing groups are identified as the active sites by TPD–MS and a special method suggested by Boehm. The ratio between the prismatic surface area and the basal area has been identified as the most important parameter for the rational catalyst design. The fish-bone catalysts CNF 20 seems to be the best catalyst in the samples studied in the present work, due to the large number of basic edge groups, the optimum ratio between the prismatic and basal plane area. It can result in a delicate balance in the redox catalytic cycle. As a consequence, the formation of CO2 can be reduced.
Keywords: Carbon nanofibers; Oxidative dehydrogenation of ethylbenzene; Selectivity; Rational design
Hydrogen production by sequential cracking of biomass-derived pyrolysis oil over noble metal catalysts supported on ceria-zirconia by Eduard Emil Iojoiu; Marcelo Eduardo Domine; Thomas Davidian; Nolven Guilhaume; Claude Mirodatos (pp. 147-161).
Hydrogen production from biomass-derived pyrolysis oil is performed using a cracking/regeneration sequential process. Pt/and Rh/Ce0.5Zr0.5O2 catalysts are comparatively studied, both leading to efficient H2 production and ensuring a good control of carbon deposition and combustion. The use of supported monolith instead of powder catalyst enhances H2 productivity and stability by decreasing side-products formation and improving soots gasification.▪Conversion of crude pyrolysis bio-oil for H2 production is investigated using a sequential process which alternates (i) cracking reaction steps, during which the bio-oil is converted to syngas and carbon stored on the catalyst and (ii) regeneration steps allowing to combust coke under an air flow. The performances of Pt and Rh catalysts supported on ceria-zirconia in powder form or deposited on cordierite monoliths are comparatively studied. From these data and calculated thermodynamic equilibrium, the co-existence of thermal and catalytic processes is demonstrated. A stable hydrogen productivity up to ca. 18mmol of H2g−1 of bio-oil (∼50% H2 in the gas stream) with a minimized methane formation (ca. 6%) is obtained with the monolith configuration. Both Pt and Rh-based catalysts allow a good control of carbon formation, the coke being fully combusted during the regeneration step. Slow deactivation phenomena and selectivity changes along time on stream, mostly observed for platinum powder samples, are related to changes in catalyst structure and to the peculiar role of oxygen stored in the zirconia-ceria support. The heat balance evaluation of the sequential cracking/regeneration cycle shows that the process could be auto-thermal, i.e., minimizing the energy input, being competitive with conventional steam-reforming process under the same operating temperature.
Keywords: Hydrogen production; Pyrolysis bio-oil; Catalytic cracking and steam reforming; Pt; Rh; Ceria-zirconia; Monolith
Identification of key parameters for the selective growth of single or double wall carbon nanotubes on FeMo/Al2O3 CVD catalysts by Emmanuel Lamouroux; Philippe Serp; Yolande Kihn; Philippe Kalck (pp. 162-173).
The successive organometallic chemical vapor deposition of metallic molybdenum and then iron from their carbonyl precursors at 220°C on γ-alumina results in the formation of a bi-layered film on the alumina surface. These catalysts might be active for the selective synthesis of single or double wall carbon nanotubes from methane at 900°C provided that (i) a fine tuning of the activation step is performed and (ii) the gas phase composition is carefully controlled. The negative influence of nitrogen on the selectivity towards SWCNT and DWCNT has been evidenced. Addition of hydrogen is harmful to SWCNT growth, whereas a low partial pressure of hydrogen is necessary to grow selectively DWCNT. These results can be rationalized in terms of kinetics of reduction of the active catalytic species. Based on XRD, Raman spectroscopy, XPS, FESEM/EDX and TEM analyses, a general pathway for SWCNT formation on the FeMo/Al2O3 CVD catalysts is proposed that involves the active mixed FeMoO4 oxide phase.OMCVD Fe–Mo/Al2O3 catalysts might be active for the selective synthesis of single or double wall carbon nanotubes from methane at 900°C provided that a fine tuning of the activation step is performed and that the gas phase composition is carefully controlled. ▪
Keywords: Carbon nanotubes; Chemical vapor deposition; Iron molybdenum catalysts
Epoxidation of cyclooctene with hydroperoxy sultams catalyzed by molybdenum boride by O. Makota; J. Wolf; Yu. Trach; B. Schulze (pp. 174-180).
The hydroperoxy sultams have been investigated in epoxidation reaction of cyclooctene catalyzed by MoB. It was shown hydroperoxides can function as the epoxidation agents. The high epoxides yields were observed in the case of hydroperoxy sultams with chlorine atoms.▪The hydroperoxy sultams (HPS) have been investigated in catalytic epoxidation reaction of cyclooctene. We have found that HPS can function as the epoxidation agents in the presence of molybdenum boride MoB as a catalyst. The reaction was sensitive to steric as well as electronic factors. The high epoxides yields were observed in the case of hydroperoxy sultams with chlorine atoms and especially favorable was hydroperoxide structure with α-position of chlorine atom to bond of nitrogen with aromatic ring.
Keywords: Catalyst; Epoxidation; Hydroperoxide; Hydroperoxy sultam; Molybdenum boride
Catalytic activity and performance of LSM cathode materials in single chamber SOFC by B. Morel; R. Roberge; S. Savoie; T.W. Napporn; M. Meunier (pp. 181-187).
The catalytic activity of symmetrical LSM cells operated under single chamber SOFC conditions was investigated. The oxidation reactions over electrodes sintered at 1100 and 1200°C were studied. The effect of any combustion was followed through electrochemical impedance spectroscopy. A LSM1100 electrode deposited on a Jülich half-cell was studied and proves to reach better performance at 600°C than at 700°C.▪The catalytic activity of symmetrical LSM (La0.8Sr0.2MnO3) cells operated under single chamber solid oxide fuel cell (SC-SOFC) conditions was investigated for methane-to-oxygen ratios Rin between 1 and 2. The oxidation reactions over electrodes sintered at 1100°C (LSM1100) and 1200°C (LSM1200) were studied, and the effect of any combustion was followed through electrochemical impedance spectroscopy (EIS). The activity of the LSM1100 electrode increases with temperature. Above 700°C, the conversion of the oxygen species may exceed 30%. As a consequence, oxygen depletion is occurring and a low frequency semicircle in the EIS spectra becomes predominant. An increase of the sintering temperature to 1200°C leads to a decrease in the catalytic activity. A LSM1100 electrode deposited on a Jülich half-cell proves to reach better performance at 600°C than at 700°C. On such complete cells, however, the catalytic combustion becomes much more complex than on a LSM cathode alone. We are thus proposing a comprehensive parameter, Rout, that is summarizing the processes inside the single chamber reactor.
Keywords: Single chamber SOFC; LSM cathode; Methane conversion; Impedance; Cell performance
Structural and surface features of PtNi catalysts for reforming of methane with CO2 by B. Pawelec; S. Damyanova; K. Arishtirova; J.L.G. Fierro; L. Petrov (pp. 188-201).
The surface and catalytic properties of bimetallic PtNi catalysts supported on ZSM-5 in the reaction of methane reforming with CO2 was studied. It was shown that the presence of a small amount of Pt (0.3–0.5wt%) in bimetallic PtNi catalysts affects the surface and catalytic performances towards the CO2 reforming of methane. Addition of Pt leads to easy reduction of nickel oxide species and a better dispersion of nickel metal particles at ≤6wt% Ni due to the contact between nickel and platinum. The latter is revealed by the higher stability of the catalysts as it is shown in the figure. ▪The effect of Ni content (1–12wt%) on the surface and catalytic behavior of bimetallic PtNi catalysts supported on ZSM-5 for reforming of methane with CO2 was studied. The properties of the catalysts, before and after exposure to reaction conditions, were investigated employing N2 adsorption–desorption isotherms, XRD, TGA/DTA, FTIR spectroscopy of framework vibrations, DRIFT spectroscopy of adsorbed CO, XPS and TPR. It was shown that addition of a small amount of Pt (0.5%) to Ni catalyst leads to formation of small nano-sized NiO particles and easy reduction of NiO. It was found that the amount of Ni precursor plays an important role on the surface and catalytic properties of bimetallic catalysts. The improvement of catalytic activity and stability observed for bimetallic catalyst was attributed to an increase of the nickel metallic dispersion caused by an intimate contact between nickel and platinum at Ni-loading of 6wt%.
Keywords: Dry reforming; Bimetallic catalysts; Nickel; Platinum; Coke; Characterization
Generation of hydrogen peroxide via the selective reduction of oxygen by hydrazine sulfate over Br-promoted Pd/Al2O3 catalyst in an aqueous medium at ambient conditions by V.R. Choudhary; Prabhas Jana; Chanchal Samanta (pp. 202-209).
The in situ generation of H2O2 via the selective reduction of O2 by hydrazine sulfate (in an aqueous medium) has been thoroughly investigated over the Br-promoted Pd(or PdO)/Al2O3 catalyst. The influence of the following factors have been addressed in this study: (a) Br concentration (in the reaction medium or incorporated in the catalyst); (b) reaction conditions (viz. reaction time, temperature); (c) concentrations of reducing agent and phosphoric acid in the reaction medium. Decomposition of N2H4 (from N2H4·H2SO4) and its reaction with H2O2 under similar reaction conditions (in the absence of O2) have also been studied. H2O2, which is an intermediate product of the O2 reduction, is involved in further consecutive reactions. It can be converted to water via its decomposition and/or reaction with the unconverted N2H4. In the presence of Br promoter, the later (reaction with unconverted N2H4) is more dominant. Both the consecutive reactions are drastically retarded in the presence of protons and Br promoter. A plausible reaction mechanism has been proposed for illustrating the role of the protons and Br promoter in the selective formation of H2O2 in the O2 reduction process. In situ generation of H2O2 with high selectivity/yield can be accomplished by the reduction of molecular oxygen by the hydrazine from hydrazine sulfate over brominated Pd/Al2O3 catalyst in an acidic aqueous medium under or close to ambient conditions.▪
Keywords: Hydrogen peroxide; Hydrazine sulfate; Pd/Al; 2; O; 3; catalyst; Brominated Pd/Al; 2; O; 3; catalyst; Oxygen reduction; In situ; H; 2; O; 2; generation
tert-Butylation of toluene with isobutylene over zeolite catalysts: Influence of water by G. Kostrab; M. Lovič; I. Janotka; M. Bajus; D. Mravec (pp. 210-218).
tert-Butylation of toluene with isobutylene in the liquid phase was studied over large pore zeolite catalysts (H-MOR CBV 21A with Si/Al=10.5 and H-BEA CP 814E with Si/Al=12.5) and over cerium modified parent zeolite H-MOR with 2wt.% of cerium. The influence of catalyst and different amount of added water on tert-butylation of toluene with isobutylene as alkylating agent on catalytic activity and para-selectivity was studied. H-MOR was slightly more active than H-BEA when tert-butylation of toluene with isobutylene in the liquid phase was carried on in the absence of water (45% and 40% conversion of toluene, respectively) at 180°C after 8h with para-selectivity for both catalysts near 68%. When different amount of water was added to the reaction mixture (0–200mmol) the maximum conversion increased significantly in the case of both catalysts H-MOR and H-BEA and it was obtained at 120mmol of water/40mmol of toluene. At optimum amount of added water (120mmol/40mmol of toluene) the conversion over H-MOR and H-BEA of toluene reached 60% and 66% respectively which is maximum at given reaction conditions. Maximum constant para-selectivity for both catalysts was near 90% (93% for H-MOR and 90% for H-BEA respectively for maximum amount of added water (200mmol/40mmol of toluene)). The positive influence of optimal amount of added water on catalytic activity and para-selectivity in tert-butylation of toluene with isobutylene in the liquid phase over H-MOR and H-BEA is shown in this paper. para-Selectivity increased monotonically within studied range of added water. The influence of water on coke deposits on catalysts was demonstrated by TGA analyses which clearly demonstrated that added water has inhibition effect on carbon deposition. tert-Butylation of toluene with isobutylene over shape-selective zeolite catalysts H-MOR and H-BEA can be an ecofriendly process for industrial preparation of 4- tert-butyltoluene which is important intermediate product for fine chemicals.
Keywords: Alkylation; tert; -Butylation; Zeolites; Isobutylene; 4-; tert; -Butyltoluene; para; -Selectivity; Water; TGAAbbreviations; TO; toluene; TBA; tert; -butanol; IB; isobutylene; TBTO; tert; -butyltoluenes; X; TO; conversion of TO; S; 4-TBTO; selectivity; =; (4-TBTO/∑TBTO); ×; 100
Promoters state and catalyst activation during ammonia synthesis over Ru/C by Ilenia Rossetti; Francesca Mangiarini; Lucio Forni (pp. 219-225).
Higher H2 and O2 uptakes have been observed during reduction and chemisorption, respectively, on Cs- and K-promoted samples supported on graphitised carbon, at difference with samples promoted with Ba or supported on active carbon. This indicates that alkaline promoters reduction under the ammonia synthesis conditions is favoured by the formation of graphite intercalation compounds. The efficacy of catalyst activation depends on the nature of Ru precursor.▪Carbon-supported, promoted Ru-based catalysts for ammonia synthesis proved to be interesting substitutes for the traditional Fe-based ones. A debate recently arose on the active state of promoters, mainly Cs and Ba, and on the effect of the latter on Ru active sites. In the present work a set of Ba-, Cs- and K-promoted samples has been characterised by various techniques. Higher H2 and O2 uptakes have been observed during reduction and chemisorption, respectively, on Cs- and K-promoted samples supported on graphitised carbon. No evidence of this has been observed with samples supported on active carbon. This is in line with the hypothesis of alkaline promoters partial reduction under the ammonia synthesis conditions, favoured by the formation of graphite intercalation compounds. Furthermore, some suggestions are here introduced on the beneficial role of Ba, especially in increasing the support resistance to methanation. Finally, the efficacy of catalyst activation was found to depend on the nature of Ru precursor. Indeed, a prolonged activation at relatively high temperature is usually needed with chloride precursors, to remove the counterion, a poison for the catalyst, whereas less dramatic conditions are required for different precursors, such as nitrosylnitrate.
Keywords: Ammonia synthesis catalyst; Intercalation compounds; Temperature programmed reduction; Alkali metals reduction
Influence of cobalt precursor and fuels on the performance of combustion synthesized Co3O4/γ-Al2O3 catalysts for total oxidation of methane by U. Zavyalova; P. Scholz; B. Ondruschka (pp. 226-233).
A series of nanosized Co3O4/γ-Al2O3 catalysts have been prepared using a combination of wetness impregnation and subsequent combustion synthesis (CS) in self-propagating mode. Alumina impregnated with various cobalt precursors and fuels, and respective as-burnt combustion-synthesized catalysts were characterised by TGA-DTA, IR-spectroscopy, N2 adsorption–desorption, XRD, SEM/EDX and TEM, and tested in the total oxidation of methane. The observed influence of the initial precursors cobalt acetate, mixtures of cobalt acetate/cobalt nitrate, and mixtures of cobalt nitrate wit fuels such as urea, citric acid, glycine, and glycerine on the catalytic performance correlates well with their combustion behaviour. Catalysts obtained with the combustion method at the highest velocities and the lowest temperatures during the synthesis were found to have the highest activity (complete conversion of methane at 400–425°C). After two days of catalytic performance in the reaction, no considerable deactivation of combustion-synthesized catalysts was observed and their particle size remained about twice less in comparison with the sample prepared by cobalt nitrate thermal decomposition.Combination of wetness impregnation and combustion method in self-propagating mode was used for synthesis of nanosized Co3O4/γ-Al2O3 catalysts with high activity in total oxidation of methane. Catalytic performance of obtained catalysts correlates well with combustion behaviour of Co precursor and fuels. Complete conversion of methane with the Co3O4/Al2O3 catalysts synthesized from mixtures Co acetate/Co nitrate and Co nitrate/glycine was achieved at 400–425°C. ▪
Keywords: Combustion synthesis; Nanosized supported catalyst; Co; 3; O; 4; /Al; 2; O; 3; Methane oxidation
Reduced anatase on silica as a support for a Ziegler catalyst by Jose Luis de Souza; Fabio Fabri; Regina Buffon; Ulf Schuchardt (pp. 234-241).
Reduced anatase TiO2 is used as an alternative support for TiCl4, leading to good results in the polymerization of ethylene and propylene with isotacticity above 80%. With the purpose of increasing the amount of active sites and the productivity, a catalytic system with a high surface area was developed. The amount of supported TiO2 was, on average, 13mg TiO2 (gSiO2)−1. The content of active titanium was 23μmol Ti(III) (gcat)−1. The catalyst was tested in the polymerization of ethylene in the liquid and in the gas phase, leading to productivities of 140 and 120g PE (gcat)−1, respectively. The polymers presented a melting point of 137°C, molar masses around 3000kgmol−1 and crystallinities between 49 and 69%. ▪Reduced anatase TiO2 is used as an alternative support for TiCl4, leading to good results in the polymerization of ethylene and propylene with isotacticity above 80%. However, due to the low concentration of active sites, approximately 1wt% of active titanium, the system leads to low productivity. With the objective of increasing the amount of active sites and the productivity, a catalytic system with a high surface area was developed. The synthesis consists in the chemical vapor deposition, known as Atomic Layer Epitaxy (ALE), of TiCl4 onto a silica surface. The deposited titanium is then transformed into anatase by heating between 300 and 500°C. The synthesis of the catalyst is carried out by chemical reduction of the oxide with n-butyl lithium and heterogenization of TiCl4. The amount of supported TiO2 was, on average, 13mg TiO2 (gSiO2)−1. The content of active titanium was 23μmol Ti(III) (gcat)−1. Two resonance peaks for Ti(III) ( g=1.98 and g=1.96) in the EPR spectrum suggest the presence of two different active species on the catalyst surface. The catalyst was tested in the polymerization of ethylene in the liquid and in the gas phase, leading to productivities of 140 and 120g PE (gcat)−1, respectively. The polymers presented a melting point of 137°C, molar masses around 3000kgmol−1 and crystallinities between 49 and 69%.
Keywords: Reduced anatase; Silica support; Atomic layer epitaxy; Ethylene polymerization; Ziegler catalyst
Heteropolyacid: An efficient and eco-friendly catalyst for the synthesis of 14-aryl-14 H-dibenzo[ a, j]xanthene by Mostafa Mohammadpour Amini; Mozhdeh Seyyedhamzeh; Ayoob Bazgir (pp. 242-245).
A simple and efficient catalytic procedure for the synthesis of 14-aryl-14 H-dibenzo[ a, j]xanthene is reported. Tungsten heteropoly acid catalysts are used both in bulk or supported on silica gel under solvent-free conditions at 100°C. Good yields and short reaction time are advantages of this new method.▪A simple and efficient catalytic procedure for the synthesis of 14-aryl-14 H-dibenzo[ a, j]xanthene is reported. Tungsten heteropoly acid catalysts are used both in bulk or supported on silica gel under solvent-free conditions at 100°C. Good yields and short reaction time are advantages of this new method.
Keywords: Heteropolyacid; Xanthene; Solvent-free; Naphthol; Recyclable catalyst