Applied Catalysis A, General (v.525, #C)

Contents (iii-ix).

Facile synthesis of a ternary Pd-P-B nanoalloy: Enhanced catalytic performance towards ethylene glycol electrooxidation by Dan Chai; Wei Wang; Wenkui Dong; Yumao Kang; Yinjuan Dong; Ziqiang Lei (1-8).
Display OmittedIn this study, a carbon-supported Pd-P-B ternary catalyst (Pd-P-B/C) for ethylene glycol electrooxidation is prepared via a simple aqueous solution phase synthesis. Physical characterization reveals that phosphorus (P) and boron (B) atoms could modify the crystal structure of palladium (Pd) and lead to strong electronic interaction among P, B and Pd. Electrochemical results indicate that the Pd-P-B/C catalyst presents larger electrochemically active surface area, higher electrocatalytic activity and better stability compared to Pd/C and Pd-P/C. This may strongly depend on unique electronic and synergistic effects involved in this ternary nanoalloy. All results demonstrate that incorporating nonmetal P and B holds great promise to improve the performance of Pd in direct alcohol fuel cells.
Keywords: Metal-nonmetal alloy; Electronic modification; Pd based catalyst; Ethylene glycol electrooxidation;

Display OmittedThis article reports the synthesis and photocatalytic H2-generation of pristine and CdS-based hybrid photocatalysts. Acid-treated-multi-walled carbon nanotubes (a-MWCNTs) and colloids of the exfoliated two-dimensional MoS2 nanosheets were used for the preparation of binary CdS/a-MWCNTs and ternary CdS/MoS2/a-MWCNTs nanocomposites. Controlled exfoliation of as-synthesized bulk marigold flower-like MoS2 to few-layer MoS2 nanosheets shows a strong absorption and photoluminescence, indicating an indirect to direct bandgap transition. The visible-light photocatalytic H2-evolution performance of the ternary nanocomposites was superior to that of the binary and pure photocatalysts. Transient photocurrent results revealed that the ternary nanocomposite exhibits a maximum photocurrent density of 11.12 mA/cm2, which is 12 times higher than that of pristine CdS. This enhanced H2-generation performance and photocurrent response is attributed to the CdS/MoS2 heterojunction, which increases charge-separation efficiency of the composite. Furthermore, the presence of a-MWCNTs, as a co-catalyst/support, accounts for this excellent performance involving electron transfer from photoexcited CdS to MoS2 edges through a-MWCNTs; this transfer results in enhanced charge separation. This enhanced charge-separation efficiency and photostability was demonstrated using a suitable mechanism, which was evident from photocurrent measurements and photoluminescence data. In such ternary hybrids, metal co-catalysts showed H2-evolution activity with the following order: Pd > Ni > Au > Ag > Cu. This work further highlights the role of MoS2/CNTs p-n junction embedded in CdS which serves as a promising heterojunction that promoted hydrogen production.
Keywords: Few-layer MoS2; CdS; Heterojunction; Photocatalysis; H2 generation;

Display OmittedIn this study, NiK/yCexZr1-xO2-macroporous Al2O3 catalysts (y = 0, 10, 20, and 30; x = 0.73–0.92) were synthesized by dispersing different amounts of CexZr1-xO2 phase onto macroporous γ-Al2O3 as supports, and then subsequently impregnating Ni and K into the supports, which possessed advantageous properties, such as a high surface area, ordered macropores and high oxygen storage capacity. Moreover, the introduction of Ni and K metals into these supports created more oxygen vacancies in them. We applied these catalysts to the cracking of vacuum residue with steam. It was found that the variation of the liquid yield with the amount of CexZr1-xO2 phase showed a volcano pattern. The macropores in the supports played an important role in enhancing the diffusion of large molecules to the active sites, while the high oxygen storage capacity over the CexZr1-xO2 phase improved the oxidative cracking rate, thereby increasing the lighter oil fraction from the vacuum residue.
Keywords: CexZr1-xO2 phase; NiK/Al2O3; Macroporous; Vacuum residue; Catalytic cracking; Oxidative cracking;

Palladium supported on bis(indolyl)methane functionalized magnetite nanoparticles as an efficient catalyst for copper-free Sonogashira-Hagihara reaction by Mohammad Gholinejad; Abdollah Neshat; Fatemeh Zareh; Carmen Nájera; Mehran Razeghi; Abbas Khoshnood (31-40).
Display OmittedA novel heterogeneous catalyst based on palladium nanoparticles supported on 3,3′-bisindolyl(4-hydroxyphenyl)methane functionalized magnetite (Fe3O4) nanoparticles was synthesized, characterized and used as catalyst for Sonogashira-Hagihara reaction. The alkynylation of a variety of aryl iodides and aryl bromides with terminal alkynes was carried out at 60 °C under copper and phosphane-free conditions using N,N-dimethyl acetamide as solvent, DABCO as base and low Pd loadings (0.18 mol%) under air. In the case of aryl chlorides, the reaction was carried out at 120 °C in the presence of tetra-n-butylammonium bromide (TBAB) and 0.36 mol% of Pd catalyst. The heterogeneous palladium catalyst introduced in this study is recoverable by an external magnet and it can be used for seven consecutive runs without a significant loss in catalytic activity.
Keywords: Magnetic; Palladium; Nanoparticles; Sonogashira; Copper-free;

Display OmittedCatalytic hydrogenation of aromatic compounds is of great interest due to environmental aspects and the wide range of industrial processes involving such reaction. In this context, the present work aims to study the influence of Pd or Pt addition on the performance of Ru/Al2O3 based catalysts for toluene hydrogenation in liquid phase. For this, catalysts were prepared by wet impregnation from chlorinated precursors and reduced in liquid phase by formaldehyde (H2CO). After impregnation, a part of the catalysts were activated ex situ at 573 K or in situ at 523 K under H2. The studied solids were characterized by N2 physisorption, SEM + EDX, TEM, XPS and TPR techniques. Catalytic tests were conducted in a slurry Parr reactor at 373 K under constant H2 pressure of 5 MPa. Results show that solids reduction by H2CO led to metallic species, while the activation treatments form oxides and decrease the catalytic activity. The initial reaction rate of non-activated monometallic catalysts follows the order: Ru/Al2O3  ≫ Pd/Al2O3  ≈ Pt/Al2O3. A synergistic effect on the activity of Ru/Al2O3 based catalysts is induced by the Pt addition.
Keywords: Noble metal; Alumina; Catalyst activation; Formaldehyde; Toluene hydrogenation;

Surfactant directed Ag1−xNix alloy nanoparticle catalysed synthesis of aromatic azo derivatives from aromatic amines by Mukesh Kumar; Kiran Soni; Geeta Devi Yadav; Surendra Singh; Sasanka Deka (50-58).
Display OmittedA bimetallic and multiply twinned Ag1−xNix (x = 0.2, 0.4, 0.6, 0.8) alloy nanoparticle (MTANP), for the first time has been explored as an efficient heterogeneous catalyst in the industrially important reaction conversion of aromatic amines to the symmetric or asymmetric azobenzenes by the activation of aerobic molecular oxygen. Here, we demonstrated that the as-synthesized and optimized Ag0.6Ni0.4 alloy NPs showed breakthrough in catalytic performance, enabling quantitative aromatic amine conversion and absolute selectivity in azobenzenes (100%) under aerobic green reaction conditions without using the environmentally unfriendly nitrites and any other hazardous materials. A high stability and recyclability of the catalyst are observed and investigated by several instrumental techniques. The key to the effective process is found to be size effect, electronic effect and structural defect, and the presence of surfactant at the surfaces of the AgNi MTANP catalyst.
Keywords: AgNi alloy nanoparticles; Oxygen activation; Aniline; Azobenzene;

Low-cost synthesis of size-controlled TS-1 by using suspended seeds: From screening to scale-up by Meng Liu; Zhonghua Chang; Huijuan Wei; Baojun Li; Xiangyu Wang; Yiqiang Wen (59-67).
Display OmittedThe synthesis of TS-1 zeolite with controllable crystal sizes has been successfully scaled up by using the suspension of nanosized S-1 as seed in a TPABr-template hydrothermal system. Even under poor stirring condition, the suspended seeds can be easily dispersed in the mixture of zeolite precursor. Therefore the synthesis shows a very good reproducibility when scaled up from 2 L to 500 L, and the crystal size of TS-1 zeolite can be exactly controlled and changed in a wide range by only changing seed amount. Using this TS-1 zeolite through large-scale synthesis as material, the catalyst was prepared by modification and used in propylene epoxidation. The yield of propylene oxide based on H2O2 and propylene reaches 96.5% and 64.3%, respectively, which is superior to that of nanosized TS-1. Though the TS-1 samples synthesized with dried nanosized S-1 seed are similar to the samples synthesized with suspended seeds on the lab scale, the synthesis process using dried seeds shows a low reproducibility on the large scale. This research also implies the low cost and high energy efficiency of the production of TS-1 by using suspended seeds in large-scale process.
Keywords: Suspended seeds; Stirring; Crystal size; Scale-up synthesis; Reproducibility;

Copper ferrite spinel oxide catalysts for palm oil methanolysis by Chuleeporn Luadthong; Pongtanawat Khemthong; Waraporn Nualpaeng; Kajornsak Faungnawakij (68-75).
Display OmittedCopper ferrite spinel oxide (CuFe2O4) samples with calcination temperatures ranging from 500 to 900 °C were synthesized using the sol-gel combustion method with citric-nitrate precursors. Each calcined sample was further characterized and carefully analyzed for its structure, morphology, porosity, magnetic property and reducibility. For the first time, the catalytic performance of the ferrite spinels was examined for palm oil methanolysis. The characterization results from X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) analyses revealed that the major part of the active species was divalent ions of Cu2+ and Fe2+ and that they played a crucial role in the activity of the considered spinel catalysts. The catalytic behaviors strongly depended on the crystallinity of spinel structures and operating parameters, such as the catalyst loading and methanol to oil molar ratio. The CuFe2O4 calcined at 700 °C was the most active and selective for methanolysis with palm oil. No activity decline was observed over the catalyst after it was reused for 5 cycles without any post-treatment. Easy and effective catalyst separation could be obtained when magnetization was applied to the magnetic spinel catalysts.
Keywords: Fatty acid methyl ester; Methanolysis; Copper ferrite spinel oxide; Sol-gel combustions; XAFS;

Display OmittedSpin-polarized density functional theory calculations have been performed to investigate the preferential mechanism of CH x (x  = 1–3) formation in Fischer-Tropsch synthesis on only the hexahedron Co( 10 1 ¯ 0 )-A and Co( 10 1 ¯ 0 ) surfaces. Our results show that CO hydrogenation to CHO is favored compared to CO direct dissociation and hydrogenation to COH on these two surfaces. Starting from C and CHO, we further seek out the optimal pathways of CH x formation, suggesting that CH x is mainly formed through H-assisted CO dissociation pathways on Co( 10 1 ¯ 0 )-A surface, in which CH is form via CHO dissociation, CH2 and CH3 are formed through CH2O with the direct and H-assisted dissociation, respectively; meanwhile, CH2 hydrogenation also contributes to CH3 formation; CH2 and CH3 are the surface abundant species on Co( 10 1 ¯ 0 )-A surface. However, on Co( 10 1 ¯ 1 ) surface, CH x species is formed through CO direct dissociation into C, followed by C successive hydrogenation, C and CH are the surface abundant species. Therefore, Co surface structure can affect the preferential formation pathways and the dominant existence form of CH x species. Moreover, CH3OH formation cannot compete with CH x formation on Co( 10 1 ¯ 0 )-A and Co( 10 1 ¯ 1 ) surfaces, considering both surfaces covering 63% of the total surface area exposed of hexahedron Co surfaces, which depends on the reaction conditions, particle size, catalyst support, carbon deposition and many other factors, the contribution to the overall CH x sources from Co( 10 1 ¯ 0 )-A and Co( 10 1 ¯ 1 ) surfaces even surpasses that of other hexahedron Co surfaces under the certain realistic conditions. As a result, the hexahedron Co surfaces exhibit high catalytic selectivity for CH x formation, and provide more CH x sources to participate into the F-T synthesis.
Keywords: Syngas; CH x formation; Cobalt; Methanol; Density functional theory;

Transfer hydrogenation of nitroarenes to arylamines catalysed by an oxygen-implanted MoS2 catalyst by Chaofeng Zhang; Zhixin Zhang; Xu Wang; Mingrun Li; Jianmin Lu; Rui Si; Feng Wang (85-93).
Display OmittedWe present an efficient approach for chemoselective synthesis of various functionalized arylamines from nitroarenes over an oxygen-implanted MoS2 catalyst (O-MoS2). The HRTEM, XRD, XPS, Raman, EXAFS and NH3-TPD characterizations show the existence of MoIVOx structure and abundant coordinative unsaturated (CUS) Mo sites in the 2D-layer structure of O-MoS2. In the transfer hydrogenation of nitroarenes with hydrazine hydrate, the MoIVOx structure works as the catalytic active center. The N2H4 selectively decomposes to the active hydrogen species in polar electronic states (Hδ− and Hδ+), which show high chemoselectivity toward the nitro reduction over C=C, C=C, and CN groups. The O-MoS2 catalyst can be recovered in a facile manner from the reaction mixture and recycled four times without any significant loss of activity.
Keywords: MoS2; MoOx; N2H4; Transfer hydrogenation; Nitro reduction;

Morphology-dependent performance of Co3O4 via facile and controllable synthesis for methane combustion by Zhiping Chen; Sheng Wang; Weigang Liu; Xiuhui Gao; Diannan Gao; Mingzhe Wang; Shudong Wang (94-102).
Display OmittedSpinel type cobalt oxide (Co3O4) nanocrystals were controllably synthesized with different morphologies (cubical, hexagonal and flower-like) via a facile hydrothermal method. The properties of the nanostructured Co3O4 were characterized by XRD, SEM, TEM, HRTEM and XPS techniques. The performance of the catalysts in methane combustion was evaluated under lean methane atmosphere. Superior catalytic activities for methane combustion were observed over these oxides. The performances seemed to depend on their morphologies. The catalytic activities of flower-like Co3O4 and hexagonal plate-like Co3O4 were comparable to those of noble metal catalysts due to the preferred exposure of more active {111} crystal plane. In case of cubical Co3O4 the {001} plane is the dominantly exposed crystal plane. The results may provide significant insights for the development of nanostructured metal oxide catalysts for the catalytic combustion of methane.
Keywords: Morphology-dependent; Cobalt oxide (Co3O4); Methane combustion;

Display OmittedA Ni nanosheet-coated FeCrAlloy monolith catalyst was successfully prepared using a deposition-precipitation-based “Korea Institute of Energy Research” (KIER) coating method, which provides a uniform coating of highly dispersive Ni catalyst on the metal substrate. The newly developed monolith catalyst showed a higher Ni dispersion and surface area on the substrate as compared to a washcoated monolith catalyst. The Ni nanosheet-coated monolith catalyst exhibited high activity and long-lasting stability at a high space velocity of GHSV = 15,000 h−1 during a natural gas steam reforming reaction for H2 production. This is mainly attributed to the fact that the uniform and highly dispersed Ni nanosheet catalyst improves the availability of surface active metal sites on the metal substrate.
Keywords: Ni nanosheet; Catalyst coating; Monolith; Steam reforming; Hydrogen production;

Maximum electrocatalytic oxidation performance for formaldehyde in a combinatorial copper-palladium thin film library by Isabella Pötzelberger; Cezarina Cela Mardare; Wolfgang Burgstaller; Achim Walter Hassel (110-118).
Display OmittedFormaldehyde electrocatalytic oxidation with an optimum activity at Cu-7.5 at.% Pd was found by screening along the entire compositional spread using the flow-type scanning droplet cell microscopy. Thin film combinatorial libraries were deposited by sputter co-deposition. The crystallographic properties, surface microstructure and contact potential difference were investigated along the compositional spread using X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning kelvin probe (SKP) and on define points by X-ray photoelectron spectroscopy (XPS). The electrocatalytic oxidation was determined as a function of the Pd concentration along the thin film combinatorial libraries. The entire compositional spread (2.4–38.5 at% Pd) showed the suitability for being implemented in the formaldehyde detection, which was evidenced by cyclic voltammetric measurements. The maximum response was obtained at a Pd content of 7.5 at.% (E SHE  = −0.35 V) with a current density value of 1.81 mA cm−2. In the same compositional region, the most prominent drop in the contact potential difference values measured by SKP was present. The results were explained based on a synergistic effect of Pd concentration, surface properties and different electron density. Also, a good stability and reproducibility of the values were achieved, indicating the suitability of this material as catalyst for formaldehyde oxidation, e.g. in a sensor.
Keywords: Copper-palladium; Combinatorial material library; Thin film; Formaldehyde; Electrocatalytic oxidation;

Display OmittedPd/Al2O3 catalysts were synthesized via one-pot evaporation-induced self-assembly and hydrothermal methodology, and the conventional impregnation method. XRD, N2 adsorption-desorption and TEM showed that the one-pot synthesized catalyst, especially evaporation-induced self-assembly one (EISA-Pd/Al2O3) possesses the large specific surface area, ordered mesopores with the narrow pore size distribution and well-dispersed Pd particles encapsulated inside the mesopores of Al2O3. Catalytic hydrogenation of 2-ethyl-anthraquinone (EAQ) to form anthrahydroquinone at 0.3 MPa and 70 °C showed that EISA-Pd/Al2O3 exhibits superior performance, with the improvement of 50% in the selectivity and 82% in the activity compared with the impregnated catalyst. The high selectivity is due to the increased electron density of Pd particles and lower amount of acid sites measured by NH3-TPD, which had an inhibitory effect on the formation of the by-product and degradation products. The high activity could be ascribed to the higher proportion of linear carbonyls which has a positive correlation with low-coordinated Pd atoms, characterized by in situ FTIR. DFT calculations revealed that the high activity of the defective Pd surface with low-coordinated Pd atoms is due to the larger adsorption energy and longer length of carbonyl bond of EAQ adsorbed on it than on the perfect Pd surface.
Keywords: Pd/Al2O3 catalysts; One-pot synthesis; Low-coordinated Pd; Hydrogenation; 2-Ethyl-anthraquinone;

Construction of graphite/TiO2/nickel foam photoelectrode and its enhanced photocatalytic activity by Jialin Jia; Dong Li; Xiuwen Cheng; Jiafeng Wan; Xiujuan Yu (128-136).
Display OmittedGraphite/TiO2/nickel foam photoelectrode was constructed through a modified sol-gel method, followed by coating procedure. Morphology, structure and optical property of the as-prepared photoelectrode was characterized via transmission electron microscopy (TEM), scanning electrons microscopy (SEM), X-ray photoelectron microscopy (XPS), X-ray diffraction (XRD) and UV–vis diffuse reflection spectroscopy (DRS). Results indicated that nickel foam framework was partly covered by graphite/TiO2 and the crystallite sizes of anatase TiO2 were found to be about 10 nm. C elements were incorporated into the lattice of TiO2 nanoparticles through replacing titanium atom. Graphite/TiO2/nickel foam photoelectrode showed the enhancement of light absorption in entire UV–vis regions. Besides, the photoelectrochemical performances of the graphite/TiO2/nickel foam electrode were studied by transient photocurrent response (TPR), open circuit voltage (OCV) and electrochemical impedance spectroscopy (EIS). Moreover, photodecomposition properties of the electrode were evaluated by the generation of hydroxyl (•OH) radicals, photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of methyl orange (MO). The graphite/TiO2/nickel foam electrode revealed high transient photogenerated current of 0.054 mAcm−2, open circuit photovoltage of −0.32 mVcm−2, yield of •OH radicals, PC activity of 85.1% and PEC activity of 99.8% for removal of MO. The improved PEC efficiency could be mainly ascribed to the coupled graphite, nickel foam support and applied bias voltage, which could not only enhance the UV–vis light absorption, but also accelerate the charges separation and transfer.
Keywords: TiO2; Graphite; Nickel foam; Photoelectrode; Photoelectrocatalysis;

Display OmittedFour monomeric titanium(IV) dichloride complexes of amine-bis(phenolate) ligands having an extra donor arm (2a–2d) and one oxo-bridged complex 3 were successfully synthesized in the reaction of TiCl4 with a sodium salt of the appropriate ligand, and they were characterized by 1H NMR spectroscopy. The ligands had either a dimethylamino side‐arm donor and t-Bu substituents on both (1a) and one (1d) phenolate rings or a diisopropylamino side-arm donor and t-Bu (1b) and t-Bu along with OMe (1c) phenolate substituents. All complexes upon activation with [Ph3CB(C6F5)4] and MAO were used to catalyze polymerization of 1-octene (in liquid monomer) into poly(1-octene). Their activities as well as product microstructures were found to be highly dependent on the structure of the diamine-bis(phenolate) ligand. The catalytic activities of the complexes towards 1-olefin polymerization decreased in the following order: 2a  >>  2b  >  2c  >  2d. The polymers produced were atactic or isotactic with the [mmmm] pentad content varied from about 4 up to 90%. The highest isotacticity was exhibited by poly(1-octene) synthesized by 2d. The catalytic activities increased and polymer molecular weight decreased with the increasing reaction temperature. Moreover, catalyst 2a/Al(iBu)3Ph3CB(C6F5)4 was used in the bulk polymerization of other α-olefin and it was found that the monomer conversion decrease in the order: 1-octene > 1-decene > 1-dodecene > 1-hexene >> 4-methyl-1-pentene.
Keywords: Titanium complex; Diamine-bis(phenolate) ligand; Ziegler-Natta polymerization; Poly(1-octene); Microstructure;

Influence of pretreatment atmospheres on the performance of bimetallic Au-Pd supported on ceria-zirconia mixed oxide catalysts for benzyl alcohol oxidation by Carol M. Olmos; Lidia E. Chinchilla; Alberto Villa; Juan J. Delgado; Huiyan Pan; Ana B. Hungría; Ginesa Blanco; Jose J. Calvino; Laura Prati; Xiaowei Chen (145-157).
Display OmittedMonometallic Au, Pd and bimetallic Au-Pd catalysts supported on a Ce0.62Zr0.38O2 mixed oxide have been synthesized by the sol-immobilization method. An in-depth Scanning-Transmission Electron Microscopy (STEM) study has been performed to reveal the structural and chemical nature of the metal nanoparticle system present in these catalysts. Attention has been paid both to the evolution of the particle size distribution and the degree of Au-Pd interaction as a function of the treatment used to activate the catalysts. This characterization work has been complemented by results coming from other macroscopic techniques like Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES), N2 physisorption, Temperature Programmed Oxidation (TPO) or X-ray Photoelectron Spectroscopy (XPS). The whole set of characterization data evidences the intrinsic structural complexity of this type of bimetallic systems, in which a fraction of monometallic Au, monometallic Pd and bimetallic nanoparticles of varying compositions coexist. This picture, which clearly contrasts with other much more homogeneous situations described in previous literature on bimetallic catalysts, also indicates the requirement of combining both atomic scale and macroscopic techniques to understand the structure of these catalysts.Concerning catalytic performance, a synergistic effect between Au and Pd has been observed in the selective oxidation of benzyl alcohol on ceria-zirconia. Moreover, the catalytic activity of these bimetallic Au-Pd catalysts is higher than that on other commonly used supports, such as activated carbon or carbon nanotubes. The treatments in oxidative and inert atmospheres at 250 °C improve the catalytic activity with respect to the fresh, un-pretreated, catalyst. Subsequent reduction of the oxidized bimetallic catalyst leads to an activity similar to that of the fresh catalyst, which is reduced at room temperature with H2 bubbles.
Keywords: Selective oxidation of benzyl alcohol; Bimetallic catalyst; Au; Pd; Ceria-zirconia; Thermal treatment;

Kinetic modeling of levulinic acid hydrogenation to γ-valerolactone in water using a carbon supported Ru catalyst by A.S. Piskun; H.H. van de Bovenkamp; C.B. Rasrendra; J.G.M. Winkelman; H.J. Heeres (158-167).
Display Omittedγ-Valerolactone (GVL) is considered a very interesting green, bio-based platform chemical with high application potential for the production of both biofuels and biobased chemicals. In this contribution, we report a kinetic study on the hydrogenation of levulinic acid (LA) to 4-hydroxypentanoic acid (4-HPA) and the subsequent intramolecular esterification to GVL in water using Ru/C (3 wt.% Ru) as the catalyst in a batch set-up. A large number of experiments was performed in a temperature range of 343–403 K, a hydrogen pressure range from 30 to 60 bar and initial LA concentrations between 300 and 2500 mol m−3. Experimental data, supported by calculation, indicate that intra-particle diffusion of LA and hydrogen affect the overall reaction rate and as such a heterogeneous model with both reaction and diffusion was used to model the data. The hydrogenation reaction of LA to 4-HPA was modelled using a Langmuir-Hinshelwood type expression whereas the reaction of 4-HPA to GVL was modelled as an equilibrium reaction occurring in the bulk of the liquid, catalyzed by a Brönsted acid, in this case LA and 4-HPA. A good fit between experiments and model was observed. The results were compared to a kinetic model without considering mass transfer and diffusion limitations.
Keywords: Levulinic acid; Hydrogenation; Ruthenium catalyst; Kinetic modelling; Batch set up;

Silica material variation for the MnxOy-Na2WO4/SiO2 by M. Yildiz; Y. Aksu; U. Simon; T. Otremba; K. Kailasam; C. Göbel; F. Girgsdies; O. Görke; F. Rosowski; A. Thomas; R. Schomäcker; S. Arndt (168-179).
Display OmittedThe oxidative coupling of methane (OCM) is one of the best methods for the direct conversion of methane. Among the known OCM catalysts, MnxOy-Na2WO4/SiO2 is a promising candidate for an industrial application, showing a high methane conversion and C2 selectivity, with a good stability during long-term catalytic activity tests. In the present study, some results have been already published and discussed briefly in our previous short communication. However, we herein investigated comprehensively the influence of various silica support materials on the performance of the MnxOy-Na2WO4/SiO2 system in the OCM by means of ex situ and in situ XRD, BET, SEM and TEM characterization methods and showed new results to reveal possible support effects on the catalyst. The catalytic performance of most MnxOy-Na2WO4/SiO2 catalysts supported by different silica support materials did not differ substantially. However, the performance of the SBA-15 supported catalyst was outstanding and the methane conversion was nearly twofold higher in comparison to the other silica supported catalysts at similar C2 selectivity as shown before in the communication. The reason of this substantial increase in performance could be the ordered mesoporous structure of the SBA-15 support material, homogeneous dispersion of active components and high number of active sites responsible for the OCM.
Keywords: Oxidative methane coupling; OCM; MnxOy-Na2WO4/SiO2; Silica support material variation; Mesoporous silica; SBA-15;

On the detectability limits of nickel species on NiO/γ-Al2O3 catalytic materials by Gabriella Garbarino; Paola Riani; Antonia Infantes-Molina; Enrique Rodríguez-Castellón; Guido Busca (180-189).
Display OmittedNiO/Al2O3 mechanical mixtures and impregnated catalytic materials have been prepared and analysed by XRD, DR-UV–vis-NIR, skeletal FT-IR, XPS, FE-SEM techniques. The presence of the carcinogenic and easily reducible NiO phase (bunsenite) is detected by XRD, DR-vis and DR-NIR with a sensitivity limit well lower than 1000 ppm, which is the lower limit by law to classify a NiO-containing waste, such as spent catalysts, as dangerous. This species is also observed by XPS and FE-SEM with a similar sensitivity limit. Hardly reducible surface dispersed Ni2+ species are also observed by DR-vis with a sensitivity limit lower than 1000 ppm. A surface spinel-like phase, with a composition NixAl2O3+x, with x ≤ 0.25 is formed at higher loadings, and is distinguished from the highly dispersed Ni2+ species using IR and XRD. This defective surface spinel like species can be distinguished from stoichiometric bulk NiAl2O4 by applying DR-NIR spectroscopy. The stoichiometric bulk nickel aluminate phase NiAl2O4 (which is also classified as carcinogenic) does not form from γ-Al2O3 or δ-Al2O3 and nickel species at temperatures up to 1073 K.
Keywords: Nickel-alumina catalysts; Spent catalysts; Toxicity of spent catalysts; Dispersion of nickel; Alumina; Surface spinel;

Generation of reductive Zn species over Zn/HZSM–5 catalysts for n–pentane aromatization by Sikarin Tamiyakul; Tawan Sooknoi; Lance L. Lobban; Siriporn Jongpatiwut (190-196).
Display OmittedThe effects of hydrogen treatment on Zn/HZSM–5 catalysts to the evolution of zinc species and their activity in n-pentane aromatization were studied. By heating Zn/HZSM–5 catalysts under inert atmosphere, most of zinc species appeared as (ZnOH)+. The XPS and IPA–TPD results showed that using H2 as a treatment gas, the hydrodehydroxylation of (ZnOH)+ generated (ZnH)+ species with the recovery of some Brønsted acid sites. It was found that under the hydrogen atmosphere, the H2 molecule was dissociated on this Zn species and generated the H2-chemisorbed Zn species. Compared with HZSM-5 catalyst, the presence of (ZnOH)+ species improved the aromatics selectivity from 11% to 22%. Nevertheless, after pre-treating Zn/HZSM–5 with H2, the formation of H2-chemisorbed Zn species remarkably increased the BTX aromatics selectivity to 31%. It was found that the H2-chemisorbed Zn species was not stable in the absence of H2 however it could be regenerated upon H2 treatment.
Keywords: Zn/HZSM–5; (ZnOH)+; (ZnH)+; Pentane; Brønsted acid; Aromatics;

Display OmittedThe deactivation of a Pd-Ag/α-Al2O3 catalyst (2.5 mm in diameter, containing 0.03 wt.% Pd and 0.18 wt.% Ag) with egg-shell distribution was studied for acetylene selective hydrogenation. The reaction was performed in a fixed bed reactor using C2H2/C2H4/H2 feed mixture (1:67.5:1.5 molar ratio). The long-term deactivation behaviour of the catalyst was studied by differential method of analysis using appropriate power law kinetics for the main reaction and catalyst decay. Based on the analysis of model results, it was proposed that the catalyst deactivation proceeded in two stages. The initial stage (Stage I) was relatively short (<20 h) and characterized by rapid catalyst deactivation, followed by second stage (Stage II) of much slower deactivation rate exhibiting a deactivation rate constant one order of magnitude smaller than Stage I. It was attributed to the dual role of carbonaceous deposits on catalyst that exhibited sequential activation and deactivation effects. The TG and FT-IR analysis of the spent catalyst revealed formation of aliphatic (soft) coke after about 100 h on stream.
Keywords: Acetylene hydrogenation; Pd-Ag/α-Al2O3; Catalyst deactivation; Coke formation;

Modifying Hopcalite catalyst by SnO2 addition: An effective way to improve its moisture tolerance and activity for low temperature CO oxidation by Yang Liu; Yao Guo; Honggen Peng; Xianglan Xu; Yuanyuan Wu; Cheng Peng; Ning Zhang; Xiang Wang (204-214).
Display OmittedTo improve the water tolerance and activity of traditional Hopcalite catalyst, a series of CuMnOx catalysts with a typical Hopcalite composition, but with part of the Mn element replaced by Sn were prepared and evaluated for low temperature CO oxidation. It is revealed that with suitable Sn replacement, both the moisture tolerance and activity of the catalysts have been evidently enhanced. The best performance is achieved with 8.5 wt% Sn addition. With the incorporation of Sn, the morphologies of the catalysts were changed accompanying the formation of a larger amount of intra-particle mesopores, thus resulting in catalysts with much higher surface area. In addition, more active oxygen species has been formed in the catalysts, as evidenced by H2-TPR, O2-TPD and XPS results. Furthermore, the catalyst surface has more exposed Cu2+ cations, thus having stronger ability to adsorb CO molecules. Most importantly, FTIR and H2O-TPD results have testified that the addition of SnO2 can significantly suppress the adsorption of H2O molecules on the surface of the catalysts, hence improving their water resistance at low temperature dramatically. In conclusion, these are believed to be the major reasons accounting for the remarkably improved moisture tolerance as well as activity for Hopcalite catalysts by SnO2 addition.
Keywords: Hopcalite catalyst; SnO2 modification; Moisture tolerance; Improved activity; CO oxidation;

The occurrence of Cannizzaro reaction over Mg-Al hydrotalcites by Oleg Kikhtyanin; Estera Lesnik; David Kubička (215-225).
Display OmittedMg-Al mixed oxides and reconstructed hydrotalcites prepared from mixed oxides by rehydration attract much attention as solid basic catalysts for organic reactions, such as aldol condensation. Therefore, the understanding of parameters that govern their catalytic performance is of great importance. Cannizzaro reaction in the presence of mixed oxide and reconstructed HTC as basic catalysts was used as a model reaction to characterize both catalytic systems and to understand their behavior in aldol condensation. The performance of the samples was investigated in the conversion of aqueous furfural mixture using stirred batch reactor operating at T = 50 °C. The properties of both initial samples and catalysts after reaction were studied by different physico-chemical methods, such as XRD, DRIFT and TGA. It was shown that both mixed oxide and reconstructed HTC possessed poor activity in the conversion of dried furfural proving the importance of water presence for the reaction to take place. Addition of water to the reaction mixture resulted in growth of the yield of both furfuryl alcohol and furoyl furoate as reaction products. Furoic acid was not identified by GC analysis, but the interaction of the acid with the basic sites of catalysts was confirmed by DRIFT and TGA analyses indicating that at optimum reaction conditions, most of the basic sites were involved in the formation of furoate species. The formation of the surface furoate species influenced the behavior of the basic catalysts in aldol condensation of furfural and acetone. It allows concluding that the occurrence of Cannizzaro reaction should be taken into account when considering the behavior of basic catalysts in organic reactions with furfural as a reactant.
Keywords: Basic catalysis; Cannizzaro reaction; Mg-Al hydrotalcite; Mixed oxide rehydration; Aldol condensation;

Bimetallic PtCu core-shell nanoparticles in PtCu/C electrocatalysts: Structural and electrochemical characterization by Vasiliy V. Pryadchenko; Vasiliy V. Srabionyan; Alexander A. Kurzin; Natalia V. Bulat; Darya B. Shemet; Leon A. Avakyan; Sergey V. Belenov; Vadim A. Volochaev; Ivo Zizak; Vladimir E. Guterman; Lusegen A. Bugaev (226-236).
Display OmittedComposite metal-carbon electrocatalysts PtCu/C containing core-shell bimetallic PtCu nanoparticles were synthesized by sequential chemical reduction of Cu (II) and Pt (IV) in carbon suspension, prepared on the basis of ethylene glycol–water solvent. The characterization of “as prepared” and obtained after the acid treatment PtCu nanoparticles was performed by TEM, XRD, Pt L 3- and Cu K-edge extended X-ray absorption fine structures (EXAFS). The technique and computational code were proposed for visualization of components distribution over the volume of cluster, which represents the mean bimetallic nanoparticle, according to the values of structural parameters derived from EXAFS. By this technique, the cluster models of PtCu nanoparticles before and after acid treatment, reflecting the character of components’ distribution, were generated. The study of electrochemical performances of the obtained PtCu/C electrocatalyst revealed the similar oxygen reduction reaction (ORR) activity and increased durability compared to commercial Pt/C electrocatalyst E-TEK 20.
Keywords: Voltammetric cycling; Electrochemical performance; Atomic structure; TEM; XRD; EXAFS; Cluster modeling; Oxygen reduction reaction;

Effective and selective oxidation of 2-butanol over Mn supported catalyst systems by Kandasamy Prabu; Marimuthu Prabu; Ashok Kumar Venugopal; Aswathy Thareparambil Venugopalan; W.V.Y. Sai Sandilya; Chinnakonda S. Gopinath; Thirumalaiswamy Raja (237-246).
Display OmittedOxidation of alcohols to their corresponding aldehydes/ketones is an important reaction in industries as well as in academic perspective. Selective oxidation (Selox) of alcohols like methanol, ethanol and propanol are well studied in literature; however, alcohols like butanol, pentanol, octanol is a challenging task. Selective oxidation of 2-butanol to methyl ethyl ketone (MEK) is an important reaction due to its wide range of applications. Herein, we demonstrated the selective oxidation of 2-butanol to MEK over Mn supported on different oxide supports. A series of MnxOy-Al2O3 (MA), MnxOy-CeO2 (MC), MnxOy-ZrO2 (MZ) and MnxOy-SiO2 (MS) catalysts were prepared by co-precipitation followed by hydrothermal method. As synthesised catalysts were characterised by various physico-chemical characterisation techniques. It was found that the presence of Mn3O4 species in MA and MZ catalysts is responsible for maximum catalytic activity towards 2-butanol oxidation. MA catalyst conferred a maximum 2-butanol conversion of 51% and 88% selectivity towards MEK. XPS analysis revealed that Mn in MA catalyst exists in +2 and +3 oxidation states and responsible for 2-butanol oxidation. Moreover it was found that the acidity of the catalyst also plays an important role in catalytic activity.
Keywords: Selective oxidation; 2-Butanol; Methyl ethyl ketone; Mn based catalysts;