Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Applied Catalysis A, General (v.408, #1-2)
Methane reforming to synthesis gas over Ni catalysts modified with noble metals by Dalin Li; Yoshinao Nakagawa; Keiichi Tomishige (pp. 1-24).
Display Omitted► Addition of noble metals to Ni catalysts gives noble metal–Ni bimetallic particles. ► The structure of bimetallic particles is influenced by the preparation method. ► Noble metal–modified Ni catalysts show high performances by the synergetic effect. ► Activity, stability, hot spot, activation, and regeneration properties are improved.Nickel is an effective component for the steam reforming of methane in terms of the catalytic activity and the catalyst cost. When Ni catalysts are applied to dry reforming, oxidative reforming, and catalytic partial oxidation, it is necessary to add the properties of high resistance to oxidation, hot spot formation, and coke deposition, to the Ni catalysts. An efficient method for giving these properties while considering the catalyst cost is the modification of Ni metal particles with small amounts of noble metals. An important point is that preparation methods can affect the structure of noble metal–Ni bimetallic particles, which is connected to the catalytic performances. The additive effects of noble metals on the catalytic performances are summarized in terms of activity, suppression of Ni oxidation, carbon formation, self-activation, and sustainability in the daily startup and shutdown operations.
Keywords: Methane reforming, Synthesis gas, Ni catalyst, Noble metal, Ni oxidation, Hot spot, Carbon formation, Self-activation, Daily startup and shut down
Carbamazepine oxidation catalyzed by manganese porphyrins: Effects of the β-bromination of the macrocycle and the choice of oxidant by Dayse CarvalhoDa-Silva; Tatiana Cristina Oliveira Mac Leod; André Luiz de Faria; Joicy Santamalvina dos Santos; Maria Eliza Moreira Dai de Carvalho; Júlio Santos Rebouças; Ynara Marina Idemori; Marilda das Dores Assis (pp. 25-30).
Display Omitted► Mn-porphyrins can be used as cytochrome P450 models for carbamazepine oxidation. ► Extension of porphyrin β-bromination affects the catalytic outcome. ► 100% selectivity to the epoxide was achieved by using tert-butyl hydroperoxide. ► Mn-porphyrins are promising, bioinspired catalysts for the oxidation of drugs.Carbamazepine (CBZ), which is one of the most commonly prescribed antiepileptic drugs and also used in the treatment of trigeminal neuralgia and psychiatric disorders, is metabolized primarily by the cytochromes P450. A homologous series of β-brominated porphyrins derived from 5,10,15,20-tetrakis(4-carbomethoxyphenyl)porphyrinatomanganese(III) chloride, i.e., Mn(III)(Br xTCMPP)Cl ( x=0, 2, 4, 6, and 8), was investigated as cytochrome P450 models for CBZ oxidation in CH2Cl2 by iodosylbenzene, iodobenzene diacetate, tert-butyl hydroperoxide, meta-chloroperoxybenzoic acid, and hydrogen peroxide. Unlike previous studies on metalloporphyrin-based CBZ oxidation, which yielded CBZ epoxide (CBZ-EP) as the sole product, the Mn(III)(Br xTCMPP)Cl systems catalyzed both the oxidation of CBZ to CBZ-EP and the formation of the respective vicinal diol, CBZ-DiOH. The influence of β-bromination of the macrocycle and the choice of the oxidant on the catalytic properties of the Mn(III)(Br xTCMPP)Cl ( x=0, 2, 4, 6, and 8) series were examined. Some partially β-brominated Mn-porphyrins surpass the corresponding octabrominated analogue in efficiency and selectivity, but the extent by which the β-bromination affects the catalytic activity depends on the choice of oxidant. The selectivity for CBZ oxidation to yield the respective epoxide reached 100% or ∼94% by using tert-butyl hydroperoxide or hydrogen peroxide as oxygen donors, respectively.
Keywords: Manganese porphyrins; β-Halogenated porphyrins; Carbamazepine oxidation; Catalysis; Biomimetic models
Ni nanoparticles supported on microwave-synthesised hectorite for the hydrogenation of styrene oxide by Isabel Vicente; Pilar Salagre; Yolanda Cesteros (pp. 31-37).
Display Omitted► Total conversion and total selectivity to 2-phenylethanol with Ni/microwaved-hectorite. ► The use of microwaves for hectorite synthesis and its purity determined activity. ► Catalytic results were related to different NiO–hectorite interactions. ► Catalytic results were related to different amounts and accessibility of acid sites.Three hectorites were synthesised at different preparation conditions by aging with microwaves. One more hectorite was aged by conventional heating for comparison. Synthesized hectorites were used as supports of nickel nanoparticles for the catalytic hydrogenation of styrene oxide to obtain 2-phenylethanol. Ni/hectorite obtained by impregnation of a microwaved-synthesised hectorite with the highest nickel content (10wt%) resulted in high active, high selective to 2-phenylethanol and high resistant to deactivation catalyst. Catalytic results were related to the different NiO–hectorite interactions observed by TPR together with the accessibility to the acid sites present in the supports. Both factors mainly depended on the hectorite purity and the use of microwaves for hectorite synthesis.
Keywords: Hectorite; Microwaves; Hydrothermal treatment; Nickel nanoparticles, Styrene oxide; 2-Phenylethanol
CoZr/H-ZSM-5 hybrid catalysts for synthesis of gasoline-range isoparaffins from syngas by Xing Huang; Bo Hou; Jungang Wang; Debao Li; Litao Jia; Jiangang Chen; Yuhan Sun (pp. 38-46).
Display Omitted► Bifunctional CoZr/zeolite catalysts were prepared for Fischer–Tropsch synthesis. ► Hybrid catalysts had high selectivity towards gasoline and their isoparaffins. ► A relatively low methane selectivity was obtained. ► The catalyst performed superior stability during the long-term run.Different CoZr/H-ZSM-5 hybrid catalysts were prepared by a hydrothermal synthesis method, where H-ZSM-5 was enwrapped onto the Co-ZrO2 Fischer–Tropsch synthesis (FTS) catalyst. The catalysts were characterized by BET, XRD,27Al NMR, SEM, TEM, XPS, H2-TPR, NH3-TPD and IR techniques. The catalytic performance for the direct conversion of syngas to high-octane gasoline-range (C5–11) hydrocarbons was studied. Coke formation on the spent catalysts was measured by TGA. Compared with the base Co-ZrO2 catalyst or the physically mixed catalyst of Co-ZrO2 with H-ZSM-5, the reducibility of the hybrid catalyst was much lower due to the strong interactions of cobalt phase with zeolite and/or zirconia. The catalytic performance results showed that the as-prepared hybrid catalysts had high selectivity towards gasoline-range isoparaffins and relatively low methane selectivity in spite of the relatively low catalytic activity. The hybrid catalysts could effectively minimize the accumulation of carbonaceous deposits. The catalyst with aluminum isopropoxide as Al source exhibited excellent selectivity on the isoparaffin synthesis and relatively good stability.
Keywords: ZSM-5; Cobalt; Hybrid catalyst; Isoparaffin; Fischer–Tropsch synthesis
Heck reactions catalyzed by Pd(0)-PVP nanoparticles under conventional and microwave heating by Daniela de L. Martins; Heiddy M. Alvarez; Lúcia C.S. Aguiar; Octavio A.C. Antunes (pp. 47-53).
Display Omitted► Application of Pd(0)-PVP nanoparticles in Heck coupling reactions. ► Good conversions in short reaction time under MW or conventional heating. ► High turnover frequencies under MW with low loading of Pd(0)-PVP.Pd(0) nanoparticles stabilized by polyvinylpyrrolidone (Pd-PVP) with a diameter of 3–6nm in ethanol catalyzed Heck coupling of iodobenzene with different alkenes under microwave heating. Products were obtained in good yields (62–99%) and good selectivity to the E-isomers. Microwave heating proved to be superior to conventional heating, providing products in higher yields and selectivities in short times (12min).
Keywords: Nanoparticles; Heck coupling; Palladium; PVP; Polyvinylpyrrolidone; Microwave
Dimerisation of cyclooctene using Grubbs’ catalysts by Sandra M. Rountree; M. Cristina Lagunas; Christopher Hardacre; Paul N. Davey (pp. 54-62).
Display Omitted► High selectivity (74%) and yield (60%) are obtained in the dimerisation of cyclooctene. ► Grubbs’ (1st and 2nd generation), Hoveyda–Grubbs’ and phosphonium catalysts are tested. ► Effect of varying solvent, catalyst loading and substrate concentration are analysed. ► Formation of trimer and tetramer compared to dimer studied, using dimer as substrate. ► Recyclability and immobilisation of catalysts are possible using ionic liquids.The dimerisation of cyclooctene (COE) to 1,9-cyclohexadecadiene, a molecule of interest to the fragrance industry, has been achieved using ruthenium catalysts in organic solvents with significantly better selectivities (47–74%) and yields (39–60%) than previously reported (34% and 30%, respectively). Grubbs’ first and second generation catalysts, the Hoveyda–Grubbs’ catalyst and a phosphonium alkylidene catalyst were tested in a range of organic solvents and ionic liquids (ILs), including 1:1 IL/dichloromethane mixtures and biphasic IL+pentane systems. The best results (74% selectivity, 60% yield) were obtained using Grubbs’ first generation catalyst in 1,2-dichloroethane. The formation of trimer, tetramer and other higher molecular mass products were found to be favoured at low catalyst loadings (<8.5mol%) and high concentration of cyclooctene (>0.77mM). Studies of metathesis reactions using 1,9-cyclohexadecadiene as substrate indicated that the monomer–dimer and monomer–trimer reactions are faster than the dimer–dimer reaction. The use of IL media allowed for the recyclability of the catalyst, although a drop in the yield of dimer generally occurred after the first run. Heterogeneized catalysts, where the IL-catalyst system was immobilised onto silica, resulted in fast reactions leading to poor yields of dimer.
Keywords: Metathesis; Cyclooctene; Grubbs’ catalysts; Ionic liquids; Dimerisation
Oxidation of methanol to formaldehyde on cation vacant Fe–V–Mo-oxide by Mariano Massa; Robert Häggblad; Staffan Hansen; Arne Andersson (pp. 63-72).
Display Omitted► Spinel-type Fe–V–Mo-oxide is selective for methanol oxidation to formaldehyde. ► The cations in the structure can change valence by forming cation vacancies. ► The oxidation states of the metals depend on the reaction conditions. ► Compared with the bulk, the surface is more oxidized. ► The catalyst is both phase stable and non-volatile in methanol oxidation.A spinel-type catalyst of the composition Fe2.50(1− z/3)V0.20(1− z/3)Mo0.30(1−z/3)□ zO4, where z is the number of cation vacancies (□), was prepared under reducing atmosphere. From the reduced sample a number of preoxidized samples were made by TPO treatment of the reduced material to different end temperatures ranging from 150 to 450°C. XRD shows that the spinel-type structure is maintained irrespective of the degree of preoxidation of the sample and the related increasing number of cation vacancies. The number of cation vacancies z increases from 0.12 for the most reduced sample up to 0.62 for the most oxidized sample. XANES data reveals that in the most reduced sample the cations are essentially Fe2+, Fe3+, V3+, Mo4+ and Mo5+ in the bulk, whereas the most oxidized sample has Fe3+, V4+ and Mo6+. XPS analysis shows that at the surface the metals are mainly in their highest oxidation state, i.e. Fe3+, V5+ and Mo6+. Irrespective of the degree of preoxidation of the catalyst, the same catalytic performance and composition of both the surface and the bulk are approached when the samples are used in methanol oxidation. Both the activity and the selectivity to formaldehyde increase initially with time-on-stream, and in parallel there is some enrichment of vanadium and molybdenum taking place at the surface. At steady state conditions the spinel-type catalyst gives a selectivity to formaldehyde of about 86% at high methanol conversion. Our results demonstrate that the spinel-type structure is flexible and stable at both reducing and oxidizing conditions, allowing the cations to change valence while maintaining the same basic structure type. Moreover, the spinel-type catalyst is stable towards volatilization.
Keywords: Fe–V–Mo-oxide; Spinel-type catalyst; Cation vacancies; XRD; XANES; XPS; Methanol oxidation; Formaldehyde
Immobilization of enzymes into self-assembled iron(III) hydrous oxide nano-scaffolds: A bio-inspired one-pot approach to hybrid catalysts by Martín G. Bellino; Alberto E. Regazzoni (pp. 73-77).
Display Omitted► A simple bio-inspired one-pot enzyme immobilization procedure produces highly efficient hybrid biocatalysts. ► Texture of the self-assembled hybrid nanostructures determines their overall activity. ► Immobilized amylase is more active than the free enzyme at extreme conditions. ► The obtained hybrid catalysts are reusable, with no performance loss.A simple bio-inspired one-pot procedure for the immobilization of α-amylase into maturing hybrid iron(III) hydrous oxide nanostructures is described. The method resorts to the urease mediated decomposition of urea to induce the homogeneous precipitation of amylase-iron(III) hydrous oxide ensembles. Appropriate setting of the synthesis parameters, which control the shape and texture of the resulting hybrid nanostructures, is key to amylase entrapment. Highly efficient hybrid catalysts were prepared at the lowest urease concentration (0.5mg/mL), where spherical 100nm size hybrid iron(III) hydrous oxide ensembles formed; their amylase load depended on the enzyme concentration, in a michaelian fashion. Their specific activity is nearly that of free amylase. These catalysts are reusable, with no loss of performance, and substantially more active than the free enzyme at extreme pHs and temperatures. The high efficiency of the hybrid ensembles is ascribed to their open structure, high enzyme loading, and negligible amylase inactivation.
Keywords: Biocatalysts; α-Amylase; Immobilization; Hybrid nanoparticles; Iron (hydrous)oxide
Ethanol steam reforming over Ni/ZnAl2O4-CeO2. Influence of calcination atmosphere and nature of catalytic precursor by Agustín E. Galetti; Manuel F. Gomez; Luis A. Arrua; M. Cristina Abello (pp. 78-86).
.Display Omitted► The catalysts prepared from a nitrate solution produce lower amounts of carbon. ► The catalysts obtained under reductive atmosphere were the most stable with smaller activity losses. ► An ethanol conversion of 88% with an activity loss of 14% was obtained over the best catalyst.The hydrogen production from ethanol steam reforming has been studied over Ni/ZnAl2O4-CeO2 catalysts. The influence of calcination atmosphere and nature of catalytic precursor was analyzed. The impregnation of Ni was carried out from two different nickel salts: nitrate (Nt) and acetate (Ac). The catalysts were obtained from the precursor calcination under reductive and oxidative atmospheres. The catalysts obtained from nitrate salt impregnation were the most carbon resistance measured as mmolC/mol reacted C2H5OH, and those obtained under a reductive atmosphere were the most stable, as evidenced by smaller activity losses. The Ni(Nt)/ZnAl2O4-CeO2 obtained under reductive atmosphere was the most active (steady state ethanol conversion=88%) and stable (activity loss=14%) under mild reforming conditions (7.8% C2H5OH inlet concentration, H2O:C2H5OH molar ratio=4.9, reaction temperature=650°C andW/F=49gmin molC2H5OH−1). The hydrogen selectivity was 49% and the main C-containing products were CO2, CO and C2H4O.
Keywords: Ethanol steam reforming; Hydrogen production; Ni/ZnAl; 2; O; 4; -CeO; 2; catalysts
Effect of oxide support surface area on hydrogenation activity: Pt/Ni bimetallic catalysts supported on low and high surface area Al2O3 and ZrO2 by William W. Lonergan; Tiefeng Wang; Dionisios G. Vlachos; Jingguang G. Chen (pp. 87-95).
Display Omitted► Low-temperature 1,3-butadiene hydrogenation occurs on PtNi bimetallic catalysts supported on Al2O3 and ZrO2. ► Nature of oxide support influences hydrogenation activity. ► PtNi/HSA-ZrO2 is twenty times less active than PtNi/LSA-ZrO2. ► Characterization suggests low activity on PtNi/HSA-ZrO2 may be due to the SMSI effect.Catalyst characterization and batch reactor studies have been performed to better understand the effects of oxide support and support surface area on low-temperature 1,3-butadiene hydrogenation over supported PtNi bimetallic catalysts. The supports studied in this work are: α-Al2O3 (10–16m2/g), γ-Al2O3 (80–120m2/g), low surface area ZrO2 (20–30m2/g), and high surface area ZrO2 (100–200m2/g). Transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) were used to characterize the particle size and the extent of Pt–Ni bimetallic bond formation, respectively. The bimetallic catalysts supported on the two low surface area supports show larger metal nanoparticles; however, these catalysts also display greater extent of bimetallic bond formation, as characterized by the Pt LIII-edge EXAFS. After normalizing the hydrogenation rate constants for the two alumina-supported catalysts by the CO uptake values, the two rate constants appear very similar, suggesting that the bimetallic nanoparticles have similar structures on the alumina supports. In contrast, normalizing the hydrogenation rate constants for the two zirconia catalysts reveals that the catalyst supported on the high surface area zirconia is approximately twenty times less active, suggesting a strong metal-support interaction (SMSI) between the metal nanoparticles and the high surface area zirconia support.
Keywords: PtNi bimetallic catalysts; Hydrogenation; 1,3-Butadiene; Catalyst support effects
Cooperative effect of Ce and Pr in the catalytic combustion of ethanol in mixed Cu/CoMgAl oxides obtained from hydrotalcites by Alejandro Pérez; Mario Montes; Rafael Molina; Sonia Moreno (pp. 96-104).
Display Omitted► The enhanced catalytic activity has been explained in terms of the high surface area, reducibility and oxygen adsorption. ► The mixture of cobalt and copper in a 1:1 ratio leads to more active materials, showing a cooperative effect. ► The presence of Ce alone or combined with Pr, on the surface of the catalysts, notably favours the total oxidation of ethanol.The cooperative effect of Ce and Pr in the modification of mixed copper and cobalt oxide catalysts which were synthesized starting from the co-precipitation method of a hydrotalcite structure was evaluated in the catalytic combustion of ethanol. The solids were characterized by XRD, XRF, H2–TPR, O2–TPD and N2 adsorption. The greatest catalytic performance was associated with the increase in the oxygen storage capacity and reducibility in the solids that contain rare earth elements (Ce–Pr) and with the improvement in the specific surface area. Additionally, the high selectivity towards CO2, which is the principal product in total oxidation, demonstrates that the solids modified with Cu and/or Co and promoted with rare earth elements, are excellent catalysts in the total oxidation of ethanol, evidencing a cooperative effect among the metals.
Keywords: Cooperative effect; Hydrotalcite; Mixed oxide; Ethanol oxidation; VOCs
Performance evaluation of mesoporous host materials in olefin epoxidation using Mo(II) and Mo(VI) active species—Inorganic vs. hybrid matrix by Nuno U. Silva; Cristina I. Fernandes; Teresa G. Nunes; Marta S. Saraiva; Carla D. Nunes; Pedro D. Vaz (pp. 105-116).
Display Omitted► Mo complexes with two oxidation states suitable for epoxidation. ► Periodic mesoporous organosilicas (PMOs) were excellent epoxidation catalysts. ► Completely selective systems to octene and cyclooctene epoxides. ► PMOs and MCM-41 based catalysts are more active than homogeneous counterparts. ► Catalysts are effective under stoichiometric olefin/oxidant ratio.The [MoVIO2Cl2(thf)2] and [MoIII2(CO)3(MeCN)2] precursor complexes, were immobilized in a hybrid periodic mesoporous organosilicas (PMO)-type material. These new hybrid matrix materials were prepared in one pot synthesis, containing the bidentate N, N′-ligand ( glypy) in the material. In a second approach, the ordered mesoporous silica MCM- glypy was prepared using a tethered approach by a stepwise procedure. The metal complexes were grafted in both types of materials to obtain heterogeneous pre-catalysts. The modified materials have been characterized by powder X-ray diffraction, N2 adsorption, and solid-state CP MAS NMR (13C,29Si).All metal containing materials were tested as catalysts in epoxidation of 1-octene, cyclooctene and styrene with tert-butylhydroperoxide (TBHP) at 328K. Selectivity to octene and cyclooctene epoxides was complete. The new PMO materials described in this work are outstanding catalysts for any of the transformations described. In fact, cyclooctene selectivity based on TBHP consumption is found to be almost independent of the mol ratio attesting the efficiency of the catalysts. They are also effective under stoichiometric olefin/oxidant ratio. In addition, a mechanism for acid catalyzed benzaldehyde formation is proposed as well as the conversion of Mo(II) to Mo(VI) under catalysis.
Keywords: Epoxidation; MCM-41; Molybdenum; Periodic mesoporous organosilicas; Single-site catalyst
Dehydration of xylose over sulfated tin oxide catalyst: Influences of the preparation conditions on the structural properties and catalytic performance by Takeshi Suzuki; Toshiyuki Yokoi; Ryoichi Otomo; Junko N. Kondo; Takashi Tatsumi (pp. 117-124).
Display Omitted► Sulfated tin oxide is an effective catalyst for the dehydration of xylose to furfural. ► Sulfated tin oxide catalyst can be reused through the re-sulfation process. ► Both of Lewis and Brønsted acid sites collaborate to produce furfural.Various sulfated metal oxides were tested as solid acid catalyst for the dehydration of xylose to furfural under milder conditions. On the basis of our findings that sulfated tin oxide exhibited the highest catalytic activity, the effects of the content of SO42− group and the calcination temperature on the structural properties and catalytic performance were investigated, and the reusability of the sulfated tin oxide catalyst was evaluated. The acid property on the sulfated tin oxide catalyst was characterized by in situ FT-IR observations of the CO-adsorbed sample. Finally, the reaction mechanism of dehydration of xylose over the SO42−/SnO2 catalyst was considered.
Keywords: Sulfated metal oxides; Tin oxide; Dehydration of xylose
An atom-economic reaction for synthesis of 1-phenoxy-2-propanol over Al2O3/MgO by Yongbo Zhang; Bin Lu; Xiaoguang Wang; Jingxiang Zhao; Qinghai Cai (pp. 125-129).
Display Omitted► Al2O3/MgO as an effective catalyst. ► Catalyst for atom-economic synthesis of 1-phenoxy-2-propanol. ► Al2O3 supported on promotes catalytic activity. ► The catalytic activity is ascribed to base–acid balance.Al2O3/MgO materials with various Mg/Al molar ratios were prepared and characterized by XRD, FT-IR, SEM and BET analysis. These materials were used as catalysts for synthesis of 1-phenoxy-2-propanol (1-PhP) from phenol and propylene oxide as compared with some oxides, i.e. MgO, CaO, ZnO and Al2O3, etc. Al2O3/MgO with Al/Mg molar ratio of 1.5% exhibited outstanding catalytic performance with 98.2% conversion and 99.3% selectivity to 1-PhP at 120°C for 5h. This catalyst can be easily recovered and reused due to its heterogeneous catalytic nature.
Keywords: Al; 2; O; 3; /MgO composite; Propylene oxide; 1-Phenoxy-2-propanol; Propanediol phenyl ether
Theoretical studies on the reaction mechanisms of AlOOH- and γ-Al2O3-catalysed methanol dehydration in the gas and liquid phases by ZhiJun Zuo; Wei Huang; PeiDe Han; ZhiHua Gao; Zhe Li (pp. 130-136).
Display Omitted► DFT-COSMO method was used to examine DME synthesis from methanol dehydration. ► The activation energies of limiting step of DME synthesis over γ-Al2O3 is higher than that of over AlOOH. ► Liquid phase environment can influence γ-Al2O3 and AlOOH surfaces relaxation, surface energies and Mulliken charges. ► Liquid phase environment can influence adsorptive behavior and reactive path of DME synthesis over γ-Al2O3 and AlOOH surfaces.The influence of the liquid environment on the reaction mechanism in slurry reactors has not been fully investigated. In this work, dimethyl ether (DME) synthesis from methanol dehydration over γ-Al2O3 (110) and AlOOH (100) in liquid paraffin and in the gas phase is studied using density functional theory combined with the conductor-like solvent model. The liquid paraffin can influence surface relaxation, Mulliken charges, and adsorptive behavior of γ-Al2O3 and AlOOH. For DME synthesis, liquid paraffin does not influence the reaction path over the γ-Al2O3 surface, but influences its activation energy. Liquid paraffin influences the activation energy and also alters the reaction path of DME synthesis over AlOOH
Keywords: Density functional theory; AlOOH; γ-Al; 2; O; 3; Dimethyl ether; CH; 3; OH; Solvent effects
Palladium catalysts supported on N-functionalized hollow vapor-grown carbon nanofibers: The effect of the basic support and catalyst reduction temperature by Serap Sahin; Päivi Mäki-Arvela; Jean-Philippe Tessonnier; Alberto Villa; Sylvia Reiche; Sabine Wrabetz; Dangsheng Su; Robert Schlögl; Tapio Salmi; Dmitry Yu. Murzin (pp. 137-147).
Display Omitted► Synthesis of basic N-functionalized vapor-grown carbon nanofibers. ► Introduction of Pd by sol immobilization. ► Characterization by various techniques, including adsorption microcalorimetry. ► Activity evaluated in synthesis of ( R)-1-phenylethyl acetate. ► Activity was highly dependent on the reduction procedure.The basic N-functionalized vapor-grown carbon nanofibers (N-VGCF) were synthesized by post-treating oxidized VGCFs in gaseous NH3 at high temperature (ammonolysis) prior to Pd addition by sol immobilization. The catalysts were characterized by nitrogen adsorption, hydrogen temperature programmed desorption, adsorption microcalorimetry and by SEM and TEM. Catalytic activity was evaluated in a model reaction, synthesis of ( R)-1-phenylethyl acetate starting from hydrogenation of acetophenone to racemic 1-phenylethanol over Pd supported on N-VGCFs, at 70°C under atmospheric hydrogen pressure in toluene, followed by acylation over an immobilized lipase in the same reaction pot. The main parameters investigated in this work were the role of the basic N-VGCF supports as well as the reduction procedure of the supported Pd catalysts (Pd-N-VGCF). The results revealed that the catalytic activity of the Pd-N-VGCF catalysts was highly dependent on the reduction procedure. The highest desired product yield, 35%, was obtained over a Pd-N-VGCF catalyst when the support was treated at 400°C with gaseous ammonia prior to Pd addition.
Keywords: Carbon nanofiber; Lipase; Hydrogenation; Pd
Photocatalytic decomposition of toluene by nanodiamond-supported TiO2 prepared using atomic layer deposition by Kwang-Dae Kim; Nilay Kumar Dey; Hyun Ook Seo; Young Dok Kim; Dong Chan Lim; Minyung Lee (pp. 148-155).
Display Omitted► TiO2 was deposited on nanodiamonds using atomic layer deposition. ► Photocatalytic decomposition of toluene was studied. ► TiO2/nanodiamonds are more tolerant towards deactivation than P-25 TiO2.The photocatalytic decomposition of toluene gas was investigated using TiO2 prepared by atomic layer deposition (ALD) on nanodiamond (ND) under UV irradiation. The photocatalytic activities of ND-supported TiO2 catalysts were compared with that of P-25. The photocatalytic activity of P-25 was rapidly decreased with time due to the accumulation of reaction intermediates formed on the surface as a result of partial oxidation of toluene. Comparing to P-25, deactivation of ND-supported TiO2 catalysts was less pronounced. It is suggested that ND surface facilitates total oxidation of toluene on TiO2 and reduces poisoning of TiO2 surface with time.
Keywords: Photocatalysis; Atomic layer deposition (ALD); Toluene decomposition; Deactivation; TiO; 2; Nanodiamond
Metal-doped carbon aerogels as catalysts for the aromatization of n-hexane by F.J. Maldonado-Hódar (pp. 156-162).
Display Omitted► The porosity of the carbon and the chemical nature of the metals can be adjusted. ► The aromatization ability of composites is regulated by the distribution of acid sites. ► The catalysts showed high selectivity and stability. ► The catalytic performance is enhanced by the interaction between phases.Metal (Cr, Mo, W) – doped carbon aerogels were synthesized from resorcinol–formaldehyde polymerization, characterized textural and chemically and used as aromatization catalysts. Catalytic performance depended on the thermal treatments applied to the samples and on the nature of the metal phases formed (pure carbon is inactive). Only cracking and aromatization reactions were detected and benzene was produced by dehydrogenation and direct 1–6 ring closure. The partial reduction of the metal oxides led to less acidic surfaces enhancing the aromatization versus cracking. Benzene selectivity of 60% without deactivation was obtained. However, when Ni and Co were reduced to the zero valence, strong interactions with the hexane led to a 100% selectivity to methane.
Keywords: Key words; n-Hexane aromatization; Carbon aerogels; Active phase; Acidity; Pre-treatments
Biomimetic simazine oxidation catalyzed by metalloporphyrins by Joicy Santamalvina dos Santos; Vinícius Palaretti; André Luiz de Faria; Eduardo José Crevelin; Luiz Alberto Beraldo de Moraes; Marilda das Dores Assis (pp. 163-170).
Display Omitted► Metalloporphyrins have efficiently catalyzed the persistent herbicide simazine. ► Metalloporphyrins can mimic the in vivo action of cytochrome P450 for simazine oxidation. ► Dehalogenated products predominate, although one chlorinated product is also observed. ► Dechlorination or dealkylation pathways occur through different intermediate species.The metalloporphyrin-mediated simazine oxidation was investigated, in order to evaluate whether metalloporphyrins were good biomimetic models for the oxidation of this herbicide. The commercially available second-generation metalloporphyrins: 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin metal(III) chloride, [M(TDCPP)]Cl; 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin metal(III) chloride, [M(TFPP)]Cl; and 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin metal(III) chloride, [M(TMPyP)]Cl5 (metal=Fe or Mn), and the oxidants iodosylbenzene (PhIO), hydrogen peroxide, and 3-chloroperoxy benzoic acid ( m-CPBA) were employed in this study. Results demonstrated that these metalloporphyrins can mimic both the in vivo and in vitro action of cytochrome P450 for simazine oxidation, with formation of the dechlorinated metabolites OEET and OEAT mainly, as well as production of two other unknown compounds, identified by HPLC/mass spectrometry as ODET and ODDT. Among the systems, [Fe(TDCPP)]Cl/ m-CPBA was the most efficient for simazine oxidation, giving up to 49% total conversion. Although hydrogen peroxide did not afford the best results (about 14% simazine conversion), it can be considered the most efficient oxidant from the point of view of toxicity, because it leads to less toxic products, namely OAAT and OEAT. The effect of some reaction conditions was investigated, and product evolution as a function of time was also monitored. Based on these results, simplified reaction mechanisms have been proposed.
Keywords: Simazine; Cytochrome P450 models; Metalloporphyrins; Herbicide metabolism, Biomimetic catalysis
Epoxidation of styrene with molecular oxygen over binary layered double hydroxide catalysts by Beena Tyagi; Ulka Sharma; Raksh Vir Jasra (pp. 171-177).
Display Omitted► Mg/Co–Al binary LDH solid base catalysts for styrene epoxidation with O2 in DMF. ► Significant affect of cation molar ratio on catalytic activity. ► Highest activity shown by cation molar ratio (Mg/Co:Al) of 3:1. ► Co–Al LDH showed higher activity and reusability than Mg–Al LDH. ► Activity increased by increasing DMF amount.Binary layered double hydroxides (LDHs) of Mg–Al and Co–Al having varied cation molar ratio were studied for the catalytic epoxidation of styrene with molecular O2 as an oxidant and DMF as a solvent. The effect of various reaction variables, reconstruction and reuse of LDH samples on the catalytic activity was evaluated. The cation molar ratio of LDH as well as concentration of DMF significantly affected the catalytic activity. The highest styrene conversion was observed with LDH having cation molar ratio (Mg/Co:Al) of 3:1. Mg–Al LDH showed highest styrene conversion of 85% with 80% styrene oxide selectivity and Co–Al LDH sample exhibited highest styrene conversion of 97% with 83% oxide selectivity at 100°C after 4h.
Keywords: Epoxidation; Styrene; Molecular oxygen; Binary LDH; Hydrotalcite
Preparation and characterization of low-temperature nano-crystalline cubic molybdenum carbides and insights on their structures by G. Vitale; M.L. Frauwallner; C.E. Scott; P. Pereira-Almao (pp. 178-186).
Display Omitted► Conversion of ammonium heptamolybdate (AHM) and sucrose to α-Mo2C at 673K was achieved. ► XRD simulations suggests the formation of carbon vacancies in the prepared α-Mo2C. ► Prepared α-Mo2C is active for the low temperature hydrogenation of toluene.Direct conversion of precursors formed by drying mixtures of ammonium heptamolybdate (AHM) and sucrose solutions to nano-crystalline cubic molybdenum carbides by temperature-programmed reaction (TPR) with H2 has been studied at low temperature (673K). The precursors prepared with AHM and sucrose were able to produce nano-crystalline domains of cubic molybdenum carbide which seemed to show carbon vacancies affecting the intensity of the signals (200) and (220) of the X-ray powder diffraction patterns. The number of carbon vacancies was affected by the time the precursor spent at 673K; the longer the time at this temperature, the higher the carbon vacancies observed by reduction of the intensity of the (200) signal of the X-ray diffraction pattern. The nano-crystalline molybdenum carbides prepared showed activity for the hydrogenation of toluene at 473K to selectively produce methyl-cyclohexane.
Keywords: α-Mo; 2; C; Carbon vacancies; Toluene hydrogenation; XRD