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Castro A.J.R.,Federal University of Ceará | Soares J.M.,Grande Rio University | Filho J.M.,Federal University of Ceará | Oliveira A.C.,Federal University of Ceará | And 2 more authors.
Fuel | Year: 2013

Porous iron-based catalysts with different promoters (Zr, Ti or Al) have been tested in oxidative dehydrogenation of ethylbenzene with CO2 for styrene production. The catalysts were characterized by X-ray diffraction (XRD), 57Fe-Mössbauer and Raman spectroscopy, temperature-programmed reduction (TPR) and N2 adsorption-desorption measurements, before and after the catalytic evaluation. The reactivity of ironbased catalysts toward styrene production was dependent on the structural and textural features of the solid as well as the nature of the promoter. α-Fe2O3 and rutile TiO2 present on FeTi were converted in situ into FeTiO3, Fe2TiO5 and FeTi2O5, and these phases revealed a high styrene yield (up to 50%) in the first stage of the reaction, but lower selectivity than that exhibited by their FeZr and FeAl counterparts. However, FeTi performed much better in terms of stability showing no tendency to sintering or phase transformation whereas the other solids suffered from hard carbon deposition. © 2013 Elsevier Ltd. All rights reserved.

Carvalho D.C.,Federal University of Ceará | Souza H.S.A.,Federal University of Ceará | Filho J.M.,Federal University of Ceará | Assaf E.M.,University of Sao Paulo | And 5 more authors.
RSC Advances | Year: 2014

The action of nanosized Pt-containing Al2O3 catalysts to avoid coking and sintering was studied in steam reforming of glycerol. The solids exhibited almost 100% conversion toward syngas produced at a suitable water to glycerol ratio. Depending on the promoter, a drastic drop in hydrogen yield was observed due to coking and sintering effects. Spent catalyst characterizations by Raman, HRTEM, XRD, TG and SEM-EDS as well as textural property techniques showed that coking, rather than sintering, was the main cause that determined the low hydrogen selectivity of nanosized Pt-containing Al2O3 with La2O3 or ZrO2. In contrast, coking did not cover the active sites of Pt-containing Al2O3 with MgO or CeO2. Thus, steam suppressed carbon deposition and improved the nanosized Pt/MgO-Al2O3 catalyst stability in the steam reforming of glycerol. © The Royal Society of Chemistry 2014.

Oliveira A.C.,Federal University of Ceará | Carvalho D.C.,Federal University of Ceará | De Souza H.S.A.,Federal University of Ceará | Filho J.M.,Federal University of Ceará | And 4 more authors.
Applied Catalysis A: General | Year: 2014

Mesoporous mixed oxides supports were impregnated with solutions of Pt or Ru compounds. The catalytic performance and stability were evaluated in dry reforming of methane. The catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, temperature programmed reduction (TPR), High-resolution transmission electron microscopy (HRTEM) and Transmission electron microscopy (TEM) analyses and Raman spectroscopy. Promoters such as MgO, ZrO2, CeO2 and La2O 3 were added to alumina support and exhibited distinct behaviour, when Ru or Pt was dispersed on these solids. Catalysts based on Pt-containing CeO2-Al2O3 showed a relatively high catalytic activity and stability compared to the other solids. The influences of the temperature and CH4/CO2 on the catalytic behaviour of the most active solids were also studied. The coking takes place due to carbonaceous deposition, but no significant loss of activity was observed during 24 h for some catalysts, which suggest the carbon species formed did not damage the solid. © 2014 Elsevier B.V. All rights reserved.

Guiselini C.,Federal Rural University of Pernambuco | Pandorfi H.,Federal Rural University of Pernambuco | Barros A.C.B.,CETENE | da Silva L.F.,Federal Rural University of Pernambuco | Neto S.P.O.S.,Federal Rural University of Pernambuco
Revista Brasileira de Engenharia Agricola e Ambiental | Year: 2013

This study aimed to analyse the global solar radiation, temperature and their effects on the growth and development of seedlings of sugarcane under acclimatization in two types of coverages in a protected environment. The study was conducted in the experimental area at the Center for Strategic Technologies in the Northeast - Igarassu, PE. The greenhouse was covered with white polyethylene and divided into two: one associated with the thermal reflector mesh and another associated with black mesh. The studied variables were: weather (solar radiation, air temperature) and biometric (stem length, stem diameter, leaf length, leaf number, plant height and leaf area). For biometric monitoring, 12 randomly selected trays with four tubes per tray per treatment were used. The experimental design was completely randomized, using the Tukey test (p <0.05) for comparison between means. The environment under thermal reflector mesh provided the best results for seedling development because of greater availability of solar radiation in the production environment.

Da Silva A.F.,University of Pernambuco | Moura D.S.,University of Pernambuco | Gouveia-Neto A.S.,University of Pernambuco | Silva Jr. E.A.,University of Pernambuco | And 3 more authors.
Optics Communications | Year: 2011

In this report the optical properties and energy-transfer frequency upconversion luminescence of Er 3+/Yb 3+-codoped laponite-derived powders under 975 nm infrared excitation is investigated. The 75%(laponite):25%(PbF 2) samples doped with erbium and ytterbium ions, generated high intensity red emission around 660 nm and lower intensity green emission around 525, and 545 nm. The observed emission signals were examined as a function of the excitation power and annealing temperature. The results indicate that energy-transfer, and excited-state absorption are the major upconversion excitation mechanism for the erbium excited-state red emitting level. The precursor glass samples were also heat treated at annealing temperatures of 300 °C, 400 °C, 500 °C, and 600 °C, for a 2 h period. The dependence of the visible upconversion luminescence emission upon the annealing temperature indicated the existence of an optimum temperature which leads to the generation of the most intense and spectrally pure red emission signal. © 2011 Elsevier B.V.

De Sousa H.S.A.,Federal University of Ceará | Da Silva A.N.,Federal University of Ceará | Castro A.J.R.,Federal University of Ceará | Campos A.,CETENE | And 2 more authors.
International Journal of Hydrogen Energy | Year: 2012

Mesoporous alumina doped with CeO 2, MgO, ZrO 2 or La 2O 3 demonstrated that the solid structure influences on the deactivation behaviour of the catalysts in dry reforming of methane. Ni-containing phases such as CeO 2-Al 2O 3, CeAlO 3, MgAl 2O 4, NiAl 2O 4, ZrO 2-Al 2O 3 and La 2O 3-Al 2O 3 were formed, but did not impede coking on the solids. Only nickel species on a high surface area MgAl 2O 4 or NiAl 2O 4 exhibited elevated resistance to physical degradation and enhanced promoting effect to labile carbon formation. In this solid, the NiO nanoparticles included between the MgAl 2O 4 and NiAl 2O 4 layer were almost certainly accessible to methane and carbon dioxide molecules and the source supporting for the formation of such amorphous reactive carbon, graphite and carbon nanotubes, as well. © 2012 Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Carvalho D.C.,Federal University of Ceará | Pinheiro L.G.,Federal University of Ceará | Campos A.,CETENE | Millet E.R.C.,CETENE | And 6 more authors.
Applied Catalysis A: General | Year: 2014

Calcium hydroxyapatites (HAP) containing cobalt or copper were synthesized and catalytically evaluated in the dehydration of glycerol for valuable chemical intermediates production. The solids were characterized by chemical analysis, X-ray diffraction (XRD), Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy (SEM-EDS), acid-base measurements, Raman spectroscopy and nitrogen adsorption-desorption isotherms. Cobalt-containing HAPs had the characteristic hydroxyapatite (Ca10-x(HPO4)(PO 4)6-x(OH)2-xx(H2O)x) and monetite Ca(HPO4) phases, independently of the cobalt contents, being mesoporous materials. This was proven to be due to Ca2+ ions replaced by Co2+ ones in HAP structure; since the cobalt amount increased, a dispersion of nanosized cobalt species was suggested. Copper-containing hydroxyapatites showed the HAP and monetite phases. Increased copper contents provided the ionic exchange of Ca2+ by Cu 2+ and resulted in the libethenite (Cu2(OH)(PO 4)) phase formation as well as the deposition of CuO on solid surface. These solids possessing distinct morphologies had micro and mesopores and preserved the HAP and monetite phases, even increasing the copper content. The catalytic evaluation in the dehydration of glycerol was dependent on the content of the metals as well as the nature of the active phase. Generally, copper-containing samples were more active than those possessing cobalt, probably due to the either stable libethenite phase presence or great acidity of the formers. The catalytic performance of the solids with low copper contents showed the elevated selectivity to 1-hydroxyacetone and products from its dimerization-cyclysation reactions whereas samples possessing cobalt were selective to 1-hydroxyacetone and light products. © 2013 Elsevier B.V. All rights reserved.

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