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A fully characterized mesoporous silica prepared from industrial waste was impregnated with metals and applied as a green heterogeneous catalyst.

This study describes the use of succinylated twice-mercerized sugarcane bagasse containing adsorbed Cu 2+ or Ni 2+ ions from spiked aqueous solutions (2MSBA-Cu and 2MSBA-Ni) as heterogeneous catalysts for the catalytic oxidation of n -hexane and n -heptane in gas phase. To the best of our knowledge, this is the first study in which a spent adsorbent material based on lignocellulose biomass is used in the catalytic oxidation of volatile organic compounds. The adsorbent and spent adsorbent materials were characterized by FTIR, TGA and XRD. The amount of Cu 2+ and Ni 2+ adsorbed on 2MSBA was 0.49 and 2.49 mmol g −1 , respectively. The catalysts were active for total oxidation of n -hexane and n -heptane, even at low temperatures. 2MSBA-Cu exhibited higher catalytic activity than 2MSBA-Ni and surprisingly their performances were comparable or superior to those of some catalysts reported in the literature, including noble metal-based catalysts.

The production of biodiesel generates high amounts of glycerol as a byproduct. Thus, alternatives to reuse this byproduct need to be investigated. In this study, we evaluated the valorization of glycerol through a catalytic process with nickel/vanadium supported on γ-Al2O3 in different compounds, followed by the electrochemical characterization for energy storage of carbon-based materials (coke) produced during the catalytic reaction. The structural, morphological and compositional properties of the catalysts and carbon-based materials were investigated by X-ray diffraction, N2-physisorption, thermogravimetric analysis, Raman spectroscopy, inductively coupled plasma mass spectroscopy, scanning electron microscopy and high-resolution transmission electron microscopy. The glycerol reaction generated acrolein, dihydroxyacetone and methanol as main products. The addition of nickel to the catalyst increased the selectivity for methanol by ca. 44% for the catalytic cracking; while for the vapor reforming is observed a higher H2 production. The use of the coke residues for energy storage was investigated through cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. A maximum specific capacitance of 7.3 F g−1 at 3.75 mA g−1 was achieved, attributed to the high surface area, ease of access of the electrolyte ions to the entire surface of the electrode. This research reveals a zero-waste approach for the glycerol valorization reaction.

We describe herein the synthesis of MgNiO 2 nanoparticles employing a new one-dimensional system [MgNi(opba)] n ·9 n H 2 O, with opba standing for ortho -phenylenebis(oxamato), as precursor. The MgNiO 2 nanoparticles could be obtained after heat-treatment at 800 °C for 5 h under air atmosphere, which was responsible for the elimination of water and organic precursor material leading the formation of nanoparticles with average size of 40±9 nm. To this end, we first described the synthesis of [MgNi(opba)] n ·9 n H 2 O chain, which was obtained using a pre-synthetized Na 2 [Ni(opba)]·5H 2 O and Mg 2+ (molar ratio of 1:1) in aqueous media and then this chain was calcined to produce the desired MgNiO 2 nanoparticles. The obtained MgNiO 2 nanoparticles showed good catalytic performance towards ethanol decomposition achieving 100% of substrate conversion and producing acetaldehyde (56.8%) and hydrogen (24.8%) as the main gaseous products. Also, carbon based structures of great interest for technological applications, carbon nanotubes and onions were formed as valuable byproducts. Thus, we believe that our reported results may inspire the synthesis of catalysts with improved performances for applications in other gas-phase transformations.

This paper describes a systematic investigation on the synthesis of CeO2 supported on SiO2 by two different methods: (i) the in situ incorporation of CeO2 onto MCM-41 and (ii) wet impregnation. We were interested in investigating how the CeO2 preparation could influence their physicochemical properties and catalytic performances towards the benzene, toluene, and o-xylene (BTX) oxidation reactions. Our results showed that the catalytic performances were strongly dependent on the synthetic approach, in which the CeO2–MCM-41 material prepared by the in situ incorporation showed better BTX oxidation activities than the CeO2-based catalysts prepared by conventional wet impregnation. This result could be assigned to the higher specific surface area, better interaction between CeO2 and the support, improved Ce4+/Ce3+ redox process, and higher concentration of oxygen vacancies as enabled by the in situ approach. The influence of CeO2 content in the ordering of the SiO2 mesoporous structure was also demonstrated.

Made available in DSpace on 2018-12-11T17:20:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-01-01. Added 1 bitstream(s) on 2019-10-09T18:31:44Z : No. of bitstreams: 1 S1516-14392018000300037.pdf: 1978270 bytes, checksum: 13347cc24e2927c54c2c95e72ffb1d71 (MD5) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Calcium tungstate (CaWO4) crystals were prepared by microwave-assisted hydrothermal (MAH) and polymeric precursor methods (PPM). These crystals were structurally characterized by X-ray diffraction (XRD), N2 adsorption, X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) measurements. The morphology and size of these crystals were observed by field emission scanning electron microscopy (FESEM). Their optical properties were investigated by ultraviolet visible (UV-Vis) absorption and photoluminescence (PL) measurements. Moreover, these materials were employed as catalysts towards gas phase toluene oxidation reaction. XRD indicates the purity of materials for both preparation methods and MAH process produced crystalline powders synthesized at lower temperatures and shorter processing time compared to the ones prepared by PPM. FESEM images showed particles with rounded morphology and particles in clusters dumbbellslike shaped. PL spectra exhibit a broad band covering the visible electromagnetic spectrum in the range of 360 to 750 nm. XANES and EXAFS results show that preparation method does not introduce high disorders into the structure, however the H2-TPR results indicated that the catalyst reducibility is affected by the preparation method of the samples. Instituto de Física de São Carlos Universidade de São Paulo - USP Departamento de Física Instituto de Geociências e Ciências Exatas Universidade Estadual Paulista - Unesp Departamento de Química Universidade Federal de Santa Catarina - UFSC Departamento de Química Instituto de Ciências Exatas e Biológicas Universidade Federal de Ouro Preto - UFOP Departamento de Engenharias e Exatas Universidade Federal Do Paraná - UFPR Departamento de Física Instituto de Geociências e Ciências Exatas Universidade Estadual Paulista - Unesp FAPESP: 2013/07296-2 FAPESP: 2013/07909-4

We describe herein the synthesis of solid Au@Pd and hollow AgPd nanoflowers displaying controlled sizes and compositions in order to investigate how their size, composition, and the presence of Au in the core of the nanoparticles influence their catalytic performance toward both liquid and gas-phase transformations. While the size and composition of Au@Pd and AgPd the nanoflowers could be controlled as function of growth time, their structure (solid or hollow) was dependent on the nature of the seeds employed for the synthesis, i.e., Au or Ag nanoparticles. Moreover, Au@Pd and AgPd nanoflowers were successfully supported onto commercial silica displaying truly uniform dispersion. The catalytic activities of Au@Pd and AgPd nanoflowers were investigated toward the 4-nitrophenol reduction and the benzene, toluene, and o-xylene (BTX) oxidation. The catalytic activities for the reduction of 4-nitrophenol decreased as follows: Au58@Pd42 > Au27@Pd73 > Ag20Pd80 and Ag8Pd92 > Au12@Pd88 > Ag38Pd62, suggesting that the Au core enhanced the catalytic activity relative to the hollow material when for Pd at.% was up to 80. Regarding the BTX oxidation, supported Au@Pd displayed higher catalytic activities than AgPd nanoflowers, also illustrating the role of the Au cores in the nanoflowers for improving catalytic performance. We believe these results may serve as a platform for the synthesis of Pd-based bimetallic nanomaterials that enable the correlation between these physical/chemical parameters and properties and thus optimized catalytic activities.

We described a versatile approach for the synthesis of Au/MCM-41, Pd/MCM-41 and Au-Pd/MCM-41 by the direct incorporation of the noble metals into the MCM-41 framework. The structural, textural and chemical properties were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), N2-adsorption (BET and BJH methods), H2-chemisorption, small angle X-ray scattering (SAXS), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The nanomaterials, being comprised of Au, Pd and Au-Pd nanoparticles and possessing high surface areas were applied as versatile and efficient catalysts in benzene, toluene and o-xylene (BTX) oxidation and in the steam reforming of ethanol for hydrogen production. The results revealed that the catalytic behavior in both processes was influenced by the experimental conditions and the nature of the catalyst employed. The Au-Pd/MCM-41 catalyst was the most active in the BTX total oxidation. On the basis of characterization data, it was proposed that the close contact between Pd and Au and the higher dispersion of Pd may be responsible for the enhanced activity of the bimetallic catalyst. However, the strong interaction between the noble metals did not improve the performance of the bimetallic catalyst in ethanol steam reforming, the Pd/MCM-41 catalyst being the most active and selective for hydrogen production.

Made available in DSpace on 2018-12-11T17:09:15Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-04-01 Barium molybdate and Barium tungstate are important materials due their photoluminescent properties and they also have catalysis and photocatalysis applications. In this work, powders of these compounds were prepared by microwave-assisted hydrothermal (MAH) method and polymeric precursor method (PPM) and their structural and optical properties were studied. Furthermore, these materials were employed as solid catalysts towards gas phase toluene oxidation reactions. X-ray diffraction confirms the purity of materials at both preparation methods and reveals a preferential growth when the powders are prepared by MAH due polymeric agents and processing using microwave, which was confirmed by Field emission scanning electron microscopy. Photoluminesce emission was attributed to the charge-transfer transitions within the [WO4]2- and [MoO4]2- complexes. The H2 Temperature-Programmed Reduction (H2-TPR), O2-chemisorption and extended X-ray absorption fine structure (EXAFS) results indicated that BaWO4 samples, compared with BaMoO4 samples, have higher oxygen mobility and oxygen vacancies that appear as key factors for the achievement of better catalytic performances. Instituto de Física de São Carlos Universidade de São Paulo USP Instituto de Geociências e Ciências Exatas Unesp - Universidade Estadual Paulista Departamento de Física Departamento de Física Centro de Ciências Exatas e Tecnologia Universidade Federal do Maranhão Departamento de Química Universidade Federal de Santa Catarina Instituto de Ciências Exatas e Biológicas Departamento de Química Universidade Federal de Ouro Preto Instituto de Geociências e Ciências Exatas Unesp - Universidade Estadual Paulista Departamento de Física

Benzene, toluene and xylene (BTX) are a particular class of volatile organic compounds, which are highly toxic pollutants. In this study, samples of gallium-containing mesoporous silica (MS-Ga7% and MS-Ga11%) were synthesized and their catalytic activity in the oxidation of BTX was investigated. The physicochemical characterization shows that the inclusion of gallium in the mesoporous silica structure leads to an increase in the number of oxygen vacancies in the structure of the MS-Ga system, which can result in an increase in the total and surface oxygen mobility. The results show the highest conversion for benzene (65%), with > 40% for toluene and > 28% for o-xylene. The high catalytic activity observed was attributed to a combination of several factors including a higher number of active sites (gallium and gallium oxide) being exposed, with a greater mobility of the active oxygen species on the surface of the catalyst promoting the catalytic activity.

Magnesium aluminate particles were prepared from biopolymer (chitosan) and Al–Mg solutions by the metal–chitosan complexation method. The MgAl2O4 spinel obtained was used to prepare a Ni catalyst support. The Ni/MgAl2O4 (20% Ni, w/w) was evaluated as a catalyst in the methane decomposition reaction. The influence of the reaction temperature and the catalyst reduction temperature and time on the methane decomposition, as well as on the properties of the carbon produced, was investigated. The materials were characterized using XRD, SEM, TEM, TPR, TGA and Raman spectroscopy analyses. It was observed that the catalytic behavior was dependent on the reaction operating conditions employed. Under the operating conditions used in this study the carbon byproduct is mainly deposited as multi-walled nanotubes (MWNTs).

We report herein a systematic investigation on the effect of the size of silver (Ag) nanoparticles employed as starting materials over the morphological features and catalytic performances of AgPt nanoshells produced by a combination of galvanic replacement between Ag and PtCl6(2-) and PtCl6(2-) reduction by hydroquinone. More specifically, we focused on Ag nanoparticles of four different sizes as starting materials, and found that the outer diameter, shell thickness, and the number of Pt surface atoms of the produced nanoshells increased with the size of the starting Ag nanoparticles. The produced AgPt nanoshells were supported into SiO2, and the catalytic performances of the AgPt/SiO2 nanocatalysts toward the gas-phase oxidation of benzene, toluene, and o-xylene (BTX oxidation) followed the order: AgPt 163 nm/SiO2AgPt 133 nm/SiO2AgPt 105 nm/SiO2AgPt 95 nm/SiO2. Interestingly, bigger AgPt nanoshell sizes lead to better catalytic performances in contrast to the intuitive prediction that particles having larger outer diameters tend to present poorer catalytic activities due to their lower surface to volume ratios as compared to smaller particles. This is in agreement with the H2 chemisorption results, and can be assigned to the increase in the Pt surface area with size due to the presence of smaller NPs islands at the surface of the nanoshells having larger outer diameters. This result indicates that, in addition to the overall diameters, the optimization of the surface morphology may play an important role over the optimization of catalytic activities in metal-based nanocatalysts, which can be even more pronounced that the size effect. Our data demonstrate that the control over surface morphology play a very important role relative to the effect of size to the optimization of catalytic performances in catalysts based on noble-metal nanostructures.

In this paper, the results obtained in the methane decomposition reaction promoted by a Ni catalyst supported on MgAl 2 O 4 spinel are presented. The textural properties of the catalyst were investigated by X-ray diffraction (XRD), N 2 adsorption/desorption isotherms (BET and BJH methods), thermogravimetric (TGA) and temperature-programmed reduction (TPR) analysis. The influence of the operating conditions employed on the methane decomposition was studied. According to the results, it was found that a N 2 :CH 4 molar ratio of 7:1 and catalyst reduction temperature of 700 °C/1 h were the best conditions for methane decomposition. In addition, in the methane decomposition over Ni/MgAl 2 O 4 , multiwall carbon nanotubes were formed.

In this paper a novel and simple route for the preparation of magnesium aluminate (MgAl2O4) is proposed. The method was developed with the objective of obtaining a material with more porous structure and greater surface area compared with other spinel preparation methods, based on the formation of a metal–chitosan complex. The structural properties of the material were investigated by X-ray diffraction (XRD), N2 adsorption/desorption isotherms (BET and BJH methods), infra-red (IR) spectroscopy and thermogravimetric analysis (TGA). Through this route, porous MgAl2O4 powder with a high specific surface area was obtained at low temperature.

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T19:05:42Z No. of bitstreams: 1 S1516-14392012000200018.pdf: 775075 bytes, checksum: 34803fe25608a67b2c9586d3baba09a7 (MD5) Made available in DSpace on 2013-08-22T19:05:42Z (GMT). No. of bitstreams: 1 S1516-14392012000200018.pdf: 775075 bytes, checksum: 34803fe25608a67b2c9586d3baba09a7 (MD5) Previous issue date: 2012-04-01 Made available in DSpace on 2013-09-30T20:09:37Z (GMT). No. of bitstreams: 2 S1516-14392012000200018.pdf: 775075 bytes, checksum: 34803fe25608a67b2c9586d3baba09a7 (MD5) S1516-14392012000200018.pdf.txt: 23882 bytes, checksum: 5a40cc84bdda50d0295c49c9d0bc43f1 (MD5) Previous issue date: 2012-04-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T15:17:44Z No. of bitstreams: 2 S1516-14392012000200018.pdf: 775075 bytes, checksum: 34803fe25608a67b2c9586d3baba09a7 (MD5) S1516-14392012000200018.pdf.txt: 23882 bytes, checksum: 5a40cc84bdda50d0295c49c9d0bc43f1 (MD5) Made available in DSpace on 2014-05-20T15:17:44Z (GMT). No. of bitstreams: 2 S1516-14392012000200018.pdf: 775075 bytes, checksum: 34803fe25608a67b2c9586d3baba09a7 (MD5) S1516-14392012000200018.pdf.txt: 23882 bytes, checksum: 5a40cc84bdda50d0295c49c9d0bc43f1 (MD5) Previous issue date: 2012-04-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) In the present study, TiO2 nanopowder was partially coated with Y2O3 precursors generated by a sol-gel modified route. The system of nanocoated particles formed an ultra thin structure on the TiO2 surfaces. The modified nanoparticles were characterized by high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) analysis, Zeta potential and surface area through N2 fisisorption measurements. Bioethanol dehydration was used as a probe reaction to investigate the modifications on the nanoparticles surface. The process led to the obtainment of nanoparticles with important surface characteristics and catalytic behavior in the bioethanol dehydration reaction, with improved activity and particular selectivity in comparison to their non-coated analogs. The ethylene production was disfavored and selectivity toward acetaldehyde, hydrogen and ethane increased over modified nanoparticles. Universidade Federal de Ouro Preto Departamento de Química Universidade Estadual Paulista Departamento de Físico-Química Universidade Federal de São Carlos (UFSCar) Departamento de Química Universidade Federal de Santa Catarina Departamento de Química Universidade Federal de Pelotas Departamento de Química Analítica e Inorgânica Universidade Estadual Paulista Departamento de Físico-Química

Methane decomposition is an endothermic process. Therefore a high temperature increases the methane conversion and improves the carbon accumulation. Nevertheless at high temperature conditions a faster deactivation of catalyst is generally observed. To keep the stability of the catalyst, lower reaction temperatures can be used as well as methane dilution but the catalytic activity is lowered. The aim of the present work consists in the study of the catalytic properties of Ni–Pt supported over MgAl 2 O 4 for the selective conversion of methane into hydrogen and carbon nanotubes. The addition of a small amount of Pt to a nickel–MgAl 2 O 4 catalyst promotes the formation of carbon nanotubes with a significant selectivity to MWCNT. The interest of using a bimetallic (Pt–Ni) catalyst is to favour the reduction of the Ni precursor (and the formation of small nickel particles). For the catalyst that we prepared methane is mainly transformed into structured MWCNTs if the reduction is complete while graphitization is observed over partially reduced catalysts. A fine characterization of the catalyst surface after each step of the preparation and use is currently under investigation in order to progress in the relationships between the surface composition and the CNTs formation.

A simple method to prepare magnesium oxide catalysts for biodiesel production by transesterification reaction of soybean oil with ethanol is proposed. The method was developed using a metal–chitosan complex. Compared to the commercial oxide, the proposed catalysts displayed higher surface area and basicity values, leading to higher yield in terms of fatty acid ethyl esters (biodiesel). The deactivation of the catalyst due to contact with CO 2 and H 2 O present in the ambient air was verified. It was confirmed that the active catalytic site is a hydrogenocarbonate adsorption site.

γ-Alumina-supported 10, 20 and 33 wt.% nickel catalysts were prepared and used to investigate the decomposition of ethanol to hydrogen and carbon materials at 500 and 700 °C. It was verified that the ethanol conversion was complete for all nickel loadings at 500 and 700 °C. A low nickel loading (10 and 20%) favored the formation of the very stable spinel phase NiAl2O4, which has low activity in the production of solid carbon. The maximum hydrogen and carbon production was obtained using a nickel loading of 33%: more than 6 g of solid carbon per gram of catalyst (gC/gcat) was produced at 700 °C and 22.2 gC/gcat when the reaction was performed at 500 °C. At 500 °C, nanofibers were mainly formed, while at 700 °C the production of multiwalled nanotubes was favored. The selectivity in terms of the gaseous products was dependent on the nickel loading and temperature used. At high temperature the partial thermal decomposition of ethanol was favored leading, mainly, to the production of hydrogen, methane, and carbon monoxide. At 500 °C, there was the production of ethylene on the Al2O3 surface with low nickel loading. With high nickel loading (33%) ethanol decomposition to hydrogen and nanostructured carbon was favored

The increased preference for minimally processed vegetables has been attributed to the health benefits associated with fresh produce and the demand for ready-to-eat salads. In this paper, lettuce (Lactuca sativa L.) was evaluated for the effects of different cropping systems on the respiratory properties. Lettuce was packaged in low density polyethylene bags and stored in a refrigerator at 4 ºC. The concentration of carbon dioxide and oxygen inside the package was monitored during the storage at zero, three, six, eight, ten and twelve days by gas chromatography. Dry matter variation was measured gravimetrically up to day fourteen of storage. Values of respiratory rate for conventional lettuce increased from day 1 to 3 and remained low, while respiratory rate of the organic lettuce increased three-fold up to day 8, stabilizing at a high level. Variation in dry matter during storage also resulted from differences between the two cultivation systems. The highest content of dry matter was achieved by organic lettuce.

In the present study, TiO2 nanopowder was partially coated with Al2O3 precursors generated by a polymeric precursor method in aqueous solution. The system of nanocoated particles formed an ultra thin structure on the TiO2 nano- particle surfaces, where the particle is the core and the nanocoating (additive) is the shell. The nanocoating process led to the obtainment of nanoparticles with impor- tant surface characteristics and catalytic behavior in the bioethanol dehydration reaction, with improved activity and particular selectivity in comparison to their non-coated analogs. Ethylene production was disfavored and selectivity toward acetaldehyde, hydrogen and ethane increased with increasing Al2O3 content in the catalysts. It is important to highlight that the TiO2-Al2O3 catalysts presented sat- isfactory values of selectivity toward hydrogen, in spite of the deactivation observed during the period of the test.

The gadolinium-doped ceria nanorods (Gd0.2Ce0.8O2−x) were synthesized by hydrothermal treatment. It was shown that the use of microwave heating during hydrothermal treatment decreases the treatment time required to obtain gadolinium-doped ceria nanorods and that oriented attachment is the dominant mechanism responsible for anisotropic growth. It was clear that Gd0.2Ce0.8O2−x nanorods were more catalytically active than commercial CeO2 in the ethanol reforming reaction.

article i nfo Two different routes to obtain SnO2 nanoparticles, undoped and doped with rare earth metals (Eu or Pr), are described herein. The first route was based on the polymeric precursor method that led to the obtainment of SnO2 nanoparticles dispersed in amorphous silica. The second route was simply the impregnation with SnCl4 aqueous solution of SiO2-CaO glass microparticles functionalized with hydroxyl ( � OH) groups. The materials were characterized by N2 physisorption, XRD, EDS and TEM analyses. We also present the results of catalytic experiments involving the nanocrystalline composites in ethanol steam reforming. The catalytic properties of the undoped composites with SnO2 supported on SiO2-CaO glass differ from their doped analogues, however, they were both selective towards ethylene formation, in contrast to the doped composite obtained by the polymeric precursor method.

Al2O3, MgO, SiO2 and ZnO-supported nickel catalysts were prepared and evaluated in the ethanol steam reforming for hydrogen production. It is shown that the catalytic behavior can be influenced depending on the experimental conditions employed and chemical composition of the catalyst.

Made available in DSpace on 2013-08-28T14:11:27Z (GMT). No. of bitstreams: 1 WOS000257381500004.pdf: 420516 bytes, checksum: 80fedd1e0e678afcf73e354f6f6206d7 (MD5) Made available in DSpace on 2013-09-30T19:07:39Z (GMT). No. of bitstreams: 2 WOS000257381500004.pdf: 420516 bytes, checksum: 80fedd1e0e678afcf73e354f6f6206d7 (MD5) WOS000257381500004.pdf.txt: 24246 bytes, checksum: 4b097b5d491f64187cc016a34c5a1d51 (MD5) Previous issue date: 2008-05-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T14:17:49Z No. of bitstreams: 2 WOS000257381500004.pdf: 420516 bytes, checksum: 80fedd1e0e678afcf73e354f6f6206d7 (MD5) WOS000257381500004.pdf.txt: 24246 bytes, checksum: 4b097b5d491f64187cc016a34c5a1d51 (MD5) Made available in DSpace on 2014-05-20T14:17:49Z (GMT). No. of bitstreams: 2 WOS000257381500004.pdf: 420516 bytes, checksum: 80fedd1e0e678afcf73e354f6f6206d7 (MD5) WOS000257381500004.pdf.txt: 24246 bytes, checksum: 4b097b5d491f64187cc016a34c5a1d51 (MD5) Previous issue date: 2008-05-01 Nanoparticles of tin oxide, doped with Ce and Y, were prepared using the polymeric precursor method. The structural variations of the tin oxide nanoparticles were characterized by means of nitrogen physisorption, carbon dioxide chemisorption, X-ray diffraction, and X-ray photoelectron spectroscopy. The synthesized samples, undoped and doped with the rare earths, were used to promote the ethanol steam reforming reaction. The SnO2-based nanoparticles were shown to be active catalysts for the ethanol steam reforming. The surface properties, such as surface area, basicity/base strength distribution, and catalytic activity/selectivity, were influenced by the rare earth doping of SnO2 and also by the annealing temperatures. Doping led to chemical and micro-structural variations at the surface of the SnO2 particles. Changes in the catalytic properties of the samples, such as selectivity toward ethylene, may be ascribed to different dopings and annealing temperatures. Univ Estadual Paulista, Inst Quim Araraquara, Dept Bioquim Tecnol Quim, BR-14801907 Araraquara, SP, Brazil Univ Fed Santa Catarina, Dept Quim, BR-88040900 Florianopolis, SC, Brazil Univ Fed Ceara, Dept Quim Analit & Fis Quim, BR-60451970 Fortaleza, CE, Brazil Univ Fed Pelotas, Dept Quim Analit & Inorgan, BR-96010900 Capao do Leao, RS, Brazil Univ Fed São Paulo, Dept Quim, BR-13560905 Sao Carlos, SP, Brazil Univ Estadual Paulista, Inst Quim Araraquara, Dept Bioquim Tecnol Quim, BR-14801907 Araraquara, SP, Brazil

This paper describes aspects of the catalytic properties of nanometric pure and rare earth (RE = La or Ce)-doped SnO2 powders, synthesized by a chemical route known as the modified polymeric precursor route (MPPR). Methanol oxidation was chosen as the probe reaction. It was verified that using up to 1 mol% of dopant no detectable influence was found, however changes in the reaction profile were observed with higher concentrations (5 mol%). The nature of dopant was also found to play an important role in the route of the reaction. Ce-doped samples exhibited high methanol conversion even at low temperatures. On the other hand, La-doped samples seem to have a delayed reaction, exhibiting significant conversion only at temperatures higher than 350 °C.

This paper presents the development of an on-line pre-concentration system to determine cadmium(II) in aqueous samples. The analyte was trapped in a mini-column filled with Al(2)O(3) in the form of macro-spheres obtained by the mixture of Al(NO(3))(3).9H(2)O(aq) and chitosan dissolved in acetic acid. The mixture was dropped into an NH(4)OH aqueous solution under rigorous agitation using a peristaltic pump, the macro-spheres were separated from alkaline solution and dried, and finally were submitted to thermal treatment. The pre-concentration system was linear between 1.0 and 100 microg L(-1), with a linearity of 0.999, sensitivity of 3.58 x 10(-3)L microg(-1) and enrichment factor of 21.9. The limits of detection and quantification were 0.08 microg L(-1) and 0.28 microg L(-1), respectively. The repeatability was between 2.6 and 5.9%. Recovery tests were carried out with a real aqueous sample.

The organic polymer chitosan was used as the polymeric precursor for the synthesis of Ni/CeO2 nanocomposite catalysts. The materials were characterized by N2 physisorption, H2 chemisorption, AA, XRD, TGA, TPR, SEM and TEM analyses. The catalysts provide very good reactivity in ethanol steam reforming compared to the conventional Ni/CeO2 catalyst prepared by the impregnation method using a commercial support. High hydrogen selectivity (>75%) was obtained on Ni/CeO2 catalysts by operating at a temperature range of 325–500 °C and a H2O/C2H5OH molar ratio of 3. It was verified that the catalytic behavior could be influenced depending on the experimental conditions employed.

Since their discovery carbon nanotubes (CNT) have attracted much attention due to their singular physical, mechanical and chemical properties. Catalytic chemical vapor deposition (CCVD) of hydrocarbons over metal catalysts is the most promising method for the synthesis of CNT, because of the advantages of low cost and large-scale production and the relatively low temperature used in the process, compared to the other methods (laser ablation and discharge between graphite electrodes). In this study, CNT were synthesized by CCVD using Ni supported on SiO2 as a catalyst. The carbon deposited in the reaction was analyzed by Raman spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effects of reaction temperature and Ni loading on the carbon nanotube formation were evaluated. The catalyst with 5% Ni favored high yield of CNT at lower temperature, with abundant “multi-walled carbon nanotubes” (MWNTs) at 625 °C, while single-walled carbon nanotubes (SWNTs) and MWNTs were obtained at 650 °C. With an increase in the reaction temperature a marked decrease in the yield of CNT was observed, probably due to the sintering of the catalyst. The catalyst with 1% Ni gave SWNTs with a high degree of order at all reaction temperatures, but in low quantity.

In this work, a simple but powerful method for controlling the size and surface morphology of AgAu nanodendrites is presented. Control of the number of Ag nanoparticle seeds is found to provide a fast and effective route by which to manipulate the size and morphology of nanoparticles produced via a combined galvanic replacement and reduction reaction. A lower number of Ag nanoparticle seeds leads to larger nanodendrites with the particles' outer diameter being tunable in the range of 45-148 nm. The size and surface morphology of the nanodendrites was found to directly affect their catalytic activity. Specifically, we report on the activity of these AgAu nanodendrites in catalyzing the gas-phase oxidation of benzene, toluene and o-xylene, which is an important reaction for the removal of these toxic compounds from fuels and for environmental remediation. All produced nanodendrite particles were found to be catalytically active, even at low temperatures and low metal loadings. Surprisingly, the largest nanodendrites provided the greatest percent conversion efficiencies.

We describe the synthesis of AgPt hollow nanodendrites employing Ag nanospheres as seeds by combining a galvanic replacement reaction between Ag and PtCl62− and PtCl62− reduction to Pt in the presence of hydroquinone. AgPt hollow nanodendrites comprised of several Pt islands ≈6 nm in diameter could be obtained in only 15 s following the addition of PtCl62− to a suspension containing Ag nanospheres, and their size and composition could be tuned as a function of the growth time. The synthesis could be scaled up by 100 folds, which enabled us to uniformly support the AgPt nanostructures onto commercial silica. The AgPt nanodendrites displayed good catalytic activities for both the 4-nitrophenol reduction and the BTX oxidation reactions. The results presented herein may inspire the synthesis of noble metal nanostructures displaying attractive features for catalysis, such as hollow interiors, ultrathin walls, and uniform dispersion over solid supports (solid supported catalysts).

This paper presents the synthesis of Al 2 O 3 and Ni-doped Al 2 O 3 spherical catalysts, developed by our group, with porous structures and high surface areas. The catalytic activity of the materials obtained was evaluated in the catalytic decomposition of methane, which is an attractive method for CO/CO 2 -free production of hydrogen, particularly for fuel cell applications. The catalysts were shown to be active and stable in relation to the catalytic decomposition of methane reaction. After the catalytic tests, characterization of the deposited carbon was carried out by transmission electron microscopy, scanning electron microscopy and Raman spectroscopy. The analyses indicated the presence of single-walled nanotubes (SWNTs) and multiwalled nanotubes (MWNTs). It was observed that the catalytic behaviour and the form of carbon produced depend on the characteristics of the sites present on the catalyst surface and on the operational conditions employed.

The biopolymer Chitosan was used as polymeric precursor for the synthesis of Ni:CeO2 nanocomposite catalysts. Evidences for the formation of a hybrid polymer, of the Ce-citrate complex and the chitosan by polyesterification reaction, was provided by 13 C NMR and Raman spectroscopy. After the heat-treatment of the hybrid polymer at several temperatures, the materials were characterized by N2 physisorption, H2 and CO2 chemisorption, XRD, EDX, TEM and Raman analyses. The results show that the presence of residual carbon has a positive influence on the samples properties. It was found that residual carbon contributes to a high surface area and to direct formation of Ni metal during the pyrolysis in N2 atmosphere. In addition, due to the presence of residual carbon, the catalytic performance in CO2 reforming of CH4 indicated an enhanced stability and coking resistance of the catalysts. # 2006 Elsevier B.V. All rights reserved.

A new and simple method to prepare Al2O3 and Ni/Al2O3 spherical catalysts for hydrogen production by steam reforming of ethanol is proposed. The present method was developed using a biopolymer (chitosan) and Al solution. A hybrid spherical compound of aluminum hydroxide and the biopolymer is formed. Through polymer elimination by thermal treatment, porous spheres with a high specific surface area and large pore volume are obtained. The Ni/Al2O3 spheres showed a high catalytic activity in ethanol steam reforming and hydrogen selectivity at temperatures between 450 and 650 °C. In all cases no CO was detected indicating that the Ni/Al2O3 spheres could be considered as a good choice for hydrogen production from ethanol steam reforming for fuel-cell applications.

A new and simple method to prepare alumina containing mainly mesopores is described. This alumina has a high surface area (464 m2/g) and a large pore volume ranging from about 0.35 to 0.65 cm3/g. The present method was developed using a biopolymer (chitosan) and Al solution. The Al–chitosan solution was added to NH4OH solution in the form of drops. A hybrid macrosphere compound of aluminum hydroxide and organic polymer is formed. Through polymer elimination by thermal treatment, porous Al2O3 spheres with a high specific surface area are obtained. The Ni-impregnated Al2O3 spheres showed a high catalytic activity and stability for dry reforming of methane at 650 °C and a CH4 / CO2 = 1 molar ratio.

Sulfated TiO 2 was prepared by a single-step sol–gel method, in which the hydrolysis and sulfation occur in the same step, varying some conditions of the preparation method. The characterization was carried out by thermogravimetric analysis, infrared absorption spectroscopy, Raman spectroscopy, pyridine adsorption infrared spectroscopy for the determination of the Bronsted acid sites/Lewis acid sites ratio, determination of the specific surface area (BET method), average pore diameter (BJH method) and catalytic activity in the n -hexane isomerization reaction. In the infrared spectra it was verified that the sulfate is coordinated to the titanium in a chelate form, while in the Raman spectra it was observed that the samples are in an anatase crystalline form. Catalytic tests of the n -hexane conversion at 100 and 200 °C were carried out. At 100 °C, it was observed that the selectivity for isomerization and catalytic stability are higher than at 200 °C, however, at 100 °C the conversion is lower than at 200 °C. Among the structural and textural properties investigated, it was found that the samples which had greater average pore diameters and a higher Bronsted acid sites/Lewis acid sites ratio were the ones which showed greater catalytic activity.

Ni, Al and/or Mg-based materials with high surface area and pore volume were prepared. The synthesis method was based on a modification of the polymeric precursor technique. It is well known that the temperature of pyrolysis and the material’s composition play an important role in the surface area (which, in this study, lay in the range of 46–404 m 2 /g) and in the sample’s porosity. The method produced promising results in terms of Ni particle size. H 2 chemisorption revealed that Ni nanoparticles (in the range of 2.3–39.8 nm) were obtained. This is known to be an important property of materials with catalytic applications. The presence of residual carbon after pyrolysis, which was determined by elementary analysis (CHN), indicated that carbon may be essential in the synthesis of materials with an excellent potential for catalytic applications.

Ultrafine particles of tin oxide, doped with the rare earths Ce, Y and La respectively, were prepared using the polymeric precursor method. The novel application of nanostructured tin oxide, undoped and doped, to the CC bond formation of an α,β-unsaturated compound (methyl vinyl ketone; MVK) is presented. The promotion of SnO2 by rare earths results in a large increase in the catalytic activity and basicity (total basic sites). The catalytic behavior observed in SnO2 samples suggests that the control of the catalytic activity and the selectivity of the products takes place by the segregation of a layer of a rare earth compound, with the increase of the heat-treatment temperature. The structural variations of the ultrafine particles were characterized by means of BET, XRD, CO2 chemisorption and Raman.

This paper discusses the influence of the presence of a second dopant (Pt or Pd) on the SnO 2·Ce matrix. The characteristics of the material and the catalytic activity of oxidizing methanol were evaluated. Two routes were used to prepare the SnO2·5 mol% Ce·1 mol% NM (NM = Pt or Pd). Transmission electronic microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and chromatographic assays were used to study the samples. Almost no changes in the morphology were detected when the samples were prepared by the impregnation route. In contrast, preparation by the chemical route (modified polymeric precursor (MPP) route) revealed crystallite growth and CeO2 segregation. No sample showed any metallic cluster, but all the samples containing noble metal displayed a very marked catalytic property, suggesting significant activity even at room temperature. The products formed were CO 2 and water, representing a competitive advantage from the standpoint of environmental protection. © 2003 Elsevier B.V. All rights reserved.

Nanoparticle catalysts based on SnO2 were processed by two different methods, viz.the polymeric precursor and high-energy mechanical milling. The sample morphology and catalytic performance in the aldol condensation between methanol and acetone were modified by the processing and rare earth doping.

Here we describe a new chemical route for obtaining highly dispersed nanometric Ni particles embedded in different matrices based on Al2O3, MgO, and TiO2 and in the heterogeneous matrices CeO2-doped Al2O3 and MgO-doped Al2O3. The synthesis method is based on a modification of the polymeric precursor method. The Ni nanoparticles (particles in the range of 1-40 nm) were obtained in a single process, without the use of an external reducing agent (hydrogen atmosphere).

The carbon dioxide reforming of methane was carried out over nickel catalysts supported on the gamma-Al2O3/CeO2 system prepared by wet impregnation. With the increase of the CeO2 weight in the catalyst, a higher stability was observed in the catalytic activity, together with an excellent resistance to carbon deposition and a better Ni dispersion. The catalysts were characterized by means of surface area measurements, TPR, H2 chemisorption, XRD, SEM, EDX, XPS and TEM. An interaction between Ni and CeO2 was observed to the Ni/CeO2 sample after activation in a H2 atmosphere above 300 ºC. Such behavior has a significantly influence on the catalytic activity.

Nickel nanoparticles supported on amorphous silica ceramic matrix were synthesized by the polymeric precursor method. The nanostructure was characterized by NMR, BET, XRD, SEM, TEM, and flame atomic absorption spectrometry techniques. It was observed a dependence of the crystallite size on the thermal annealing, under a N2 atmosphere. The materials presented a high catalytic activity and selectivity upon the beta-pinene hydrogenation reaction. The magnetic hystereses were also correlated with the morphology of the processed material.

Here we describe a new route to synthesize ultrafine rare earth doped and undoped tin oxide particles for catalytic applications. The catalytic behavior observed in SnO2 samples suggests the control of the catalytic activity and the selectivity of the products by the segregation of a layer of a rare earth compound with the increase of the heat-treatment temperature. The ultrafine particles were characterized by means of BET, XPS, TEM, XRD and Rietveld refinement. It was demonstrated that the effects of the dopant on the methanol decomposition reaction and on the H2 selectivity were correlated with the segregation of a rare earth layer on the tin oxide samples.

Neste trabalho são apresentados os procedimentos de preparação de materiais cerâmicos de SiO2, SnO2 e Al2O3 e, também, suas propriedades catalíticas nas reações de reforma do metano e do metanol. As análises dos resíduos de carbono, após testes catalíticos, sugerem que a modificação estrutural dos catalisadores pode minimizar os efeitos de sua desativação. This work presents the procedures for preparing SiO2, SnO2 and Al2O3 ceramic materials and also their catalytic properties for the reforming reactions of methane and methanol. The analyses of the carbonaceous residues suggest that the structural modification of the catalyst can minimize the deactivation effect upon them.

Here we describe a new route for the synthesis of nanometric Ni particles embedded in a mesoporous silica material with excellent potential for catalytic applications. Mesoporous silica with a surface area in the range of 202-280 m2/g, with narrow pore size distribution and Ni nanoparticles (particles in the range of 3-41 nm) were obtained in a direct process. A different approach was adopted to process such a nanocomposite. This new approach is based on the formation of a polymer with the silicon oxianion and nickel cation chelated to the macromolecule structure and on the control of the pyrolysis step. The CO/CO2 atmosphere resulting from the pyrolysis of the organic material promotes the reduction of the Ni citrate.

Cobalt catalysts supported on γ-alumina, ceria and γ-alumina-ceria, with 10 or 20%wt of cobalt load, prepared by the wet impregnation method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission transmission electron microscopy (FETEM), N2 adsorption-desorption isotherms (BET/BJH methods), energy-dispersive X-ray spectroscopy (EDX), X-ray photoemission spectroscopy (XPS), O2-chemisorption and temperature programmed reduction (TPR) were used to promote the oxidation of volatile organic compounds (n-hexane, benzene, toluene and o-xylene). For a range of low temperatures (50-350 °C), the activity of the catalysts with a higher cobalt load (20% wt) was greater than that of the catalysts with a lower cobalt load (10% wt). The Co/γ-Al2O3-CeO2 catalytic systems presented the best performances. The results obtained in the characterization suggest that the higher catalytic activity of the Co20/γ-Al2O3-CeO2 catalyst may be attributed to the higher metal content and amount of oxygen vacancies, as well as the effects of the interaction between the cobalt and the alumina and cerium oxides.

In this study we prepared a WO3-based catalyst to investigate its catalytic activity in the total oxidation of the volatile organic compounds known as benzene, toluene and xylene (BTX). For a range of low temperatures (50-450oC) the only reaction products were CO2 and H2O. The results for the catalyst characterization suggested that the high catalytic activity could be attributed to the effects of a strong metal interaction, which is possibly originated from the small lattice parameter difference between the (111), (020) and (002) lattice planes and the presence of W4+, W5+ and W6+ species on the surface of the catalyst which react with active oxygen species.

The aim of this study was to reduce the emissions of organic compounds, such as BTX (benzene, toluene and xylenes), due to their toxicity and adverse effects on the environment. In this regard, catalysts (SiO2(1-x)Cux) were developed which exhibit high catalytic activity for converting BTX compounds to CO2 and H2O, and which do not require the use of solvents and materials detrimental to the environment, with low production cost and good reproducibility. Cu (from copper(II) nitrate) was loaded (2.99; 5.01; 10.01 and 19.97 wt.%) onto supports (SiO2) by wet impregnation. The study was carried out within the temperature range of 50-350 oC. The catalysts described in this paper have high catalytic activity in the total oxidation of BTX. The conversion of benzene in this study exceeded 85% at 150 oC.