Hudson W. P. Carvalho

Karlsruhe Institute of Technology, Carlsruhe, Baden-Württemberg, Germany

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Publications (29)124.88 Total impact

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    ABSTRACT: A nanodispersed intermetallic GaPd2/SiO2 catalyst is prepared by simple impregnation of industrially relevant high-surface-area SiO2 with Pd and Ga nitrates, followed by drying, calcination, and reduction in hydrogen. The catalyst is tested for CO2 hydrogenation to methanol at ambient pressure, revealing that the intrinsic activity of the GaPd2/SiO2 is higher than that of the conventional Cu/ZnO/Al2O3, while the production of the undesired CO is lower. A combination of complementary in situ and ex situ techniques are used to investigate the GaPd2/SiO2 catalyst. In situ X-ray diffraction and in situ extended X-ray absorption fine structure spectroscopy show that the GaPd2 intermetallic phase is formed upon activation of the catalyst via reduction and remains stable during CO2 hydrogenation. Identical location-transmission electron microscopy images acquired ex situ (i.e., micrographs of exactly the same catalyst area recorded at the different steps of activation and reaction procedure) show that nanoparticle size and dispersion are defined upon calcination with no significant changes observed after reduction and methanol synthesis. Similar conclusions can be drawn from electron diffraction patterns and images acquired using environmental TEM (ETEM), indicating that ETEM results are representative for the catalyst treated at ambient pressure. The chemical composition and the crystalline structure of the nanoparticles are identified by scanning TEM energy dispersive X-ray spectroscopy, selected area electron diffraction, and atomically resolved TEM images.
    ACS Catalysis 09/2015; 5(10):5827-5836. DOI:10.1021/acscatal.5b01271 · 9.31 Impact Factor
  • Benjamin Mutz · Hudson W.P. Carvalho · Stefan Mangold · Wolfgang Kleist · Jan-Dierk Grunwaldt ·
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    ABSTRACT: The methanation of CO2 as a relevant strategy for energy storage has been studied by operando X-ray absorption spectroscopy under dynamic H2/CO2 and CO2 reaction atmospheres. A typical CO2 conversion of 81% was reached at 400 °C with a 23 wt.-% Ni/CaO–Al2O3 catalyst, yielding 80% of CH4. The operando XAS experiment under working conditions revealed pronounced structural changes, e.g., a fast bulk oxidation of the Ni particles after removal of H2 from the H2/CO2 (4:1) gas stream. A lower performance of the catalyst was observed in the subsequent methanation cycle due to the presence of a residual oxidized fraction of Ni.
    Journal of Catalysis 07/2015; 327. DOI:10.1016/j.jcat.2015.04.006 · 6.92 Impact Factor
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    ABSTRACT: Ni/Al2O3 catalysts were tested for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) as an important bio-based platform molecule for chemical products based on renewable feedstocks. The catalysts were prepared by wet impregnation, incipient wetness impregnation, precipitation, and flame spray pyrolysis; both the influence of different solvents (monovalent alcohols and water) as well as solvent free reaction conditions were screened in batch autoclaves. Whereas alcohols led to a number of side reactions that could only be suppressed by high hydrogen pressures (>20 bar), water as solvent resulted in a GVL selectivity of 100 %. The GVL yields reached 57%. Further improvement was achieved without any solvent, whereby the GVL yield increased to 92% at 100% LA conversion. Reuse of the Ni catalysts resulted in a significant drop in activity. The catalysts were thoroughly characterized by temperature programmed reduction (TPR), X-ray diffraction (XRD), linear combination analysis of X-ray absorption near edge structure (XANES) spectra and extended X-ray absorption fine structure (EXAFS). The results indicated that incorporated Ni2+ as present in flame-derived catalysts was less active for GVL synthesis compared to surface Ni particles as present in the wet impregnated catalyst.
    Applied Catalysis A General 05/2015; 502(1). DOI:10.1016/j.apcata.2015.05.007 · 3.94 Impact Factor
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    ABSTRACT: The structure of copper sites in Cu-SSZ-13 during NH3-SCR was unravelled by a combination of novel operando X-ray spectroscopic techniques. Strong adsorption of NH3 on Cu, its reaction with weakly adsorbed NO from the gas phase, and slow re-oxidation of Cu(I) were proven. Thereby the SCR reaction mechanism is significantly different to Fe-ZSM-5.
    Chemical Communications 04/2015; 51(44). DOI:10.1039/C5CC01758K · 6.83 Impact Factor
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    ABSTRACT: A series of ceria-supported Rh and Pt catalysts was synthesized by flame spray pyrolysis for high temperature water gas shift (WGS) reactions in a membrane reactor. The structural and catalytic properties were compared with a Pt/CeO2 catalyst prepared conventionally by incipient wetness impregnation. BET results show that compared to conventionally prepared catalysts the specific surface area of the flame made catalysts is larger and decreases with increasing metal content. This is in line with X-ray diffraction (XRD) results uncovering a high nanocrystallinity of the ceria, whose crystallite size slightly increases with higher noble metal loading. Both Pt and Rh particles are not detected by XRD due to the small crystallite size. In fact, transmission electron microscopy (TEM) images of the flame made catalysts with high loading showed Pt and Rh particles with diameters of ca. 3 nm which remained stable after catalytic testing. X-ray absorption near edge spectra (XANES) at the Rh K- and Pt L3-edge showed that both Pt and Rh were in an oxidized state after preparation. In situ XANES during temperature programmed reduction in 5% H2/He indicated a lower reduction temperature than for the conventional Pt/CeO2 catalyst. Hence, Rh and Pt species are located on the surface of the CeO2 particles. Extended X-ray absorption fine structure (EXAFS) spectra provide further evidence for oxidized Rh, Pt before reduction and full reduction after activation in hydrogen, and small particle sizes in agreement with the TEM and XRD results. The catalytic activity measurements were performed at atmospheric pressure in two different gas mixtures by measuring CO conversion as a function of temperature. In all cases the Pt/CeO2 catalysts prepared by flame spray pyrolysis showed high catalytic activity and much higher selectivity than the Rh/CeO2 catalyst, where methane formation is observed above 300 °C. Furthermore, the reaction rate in terms of turnover frequencies is much higher on the Pt-based catalysts, which makes them promising candidates for high temperature WGS catalysts in membrane and microreactors.
    Applied Catalysis A General 02/2015; 504. DOI:10.1016/j.apcata.2015.01.047 · 3.94 Impact Factor
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    Applied Catalysis B Environmental 01/2015; 162:611. DOI:10.1016/j.apcatb.2014.07.030 · 7.44 Impact Factor
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    ABSTRACT: The effect of Ni catalysts promoted with Mg on catalytic activity and carbon deposition was investigated in acetic acid steam reforming. Acetic acid was chosen as representative compound for the steam reforming of bio-oil derived from biomass pyrolysis. In this study, nickel catalysts modified with Mg have been prepared by sequential impregnation method with 15 wt.% Ni and variable loadings of Mg (1-10 wt.%). The samples were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), high resolution transmission electron microscopy (HRTEM), specific surface area (BET) and temperature programmed reduction (TPR-H-2). Steam reforming of acetic acid was conducted in a fixed bed reactor at a temperature of 500 degrees C and 600 degrees C. Under reactive conditions, the 15Ni5Mg/Al catalyst proved to be superior to the other catalysts at 600 degrees C at which it presented an effluent gaseous mixture with the highest H-2 selectivity and reasonable low coke formation.
    Applied Catalysis B Environmental 11/2014; s 160–161(1):188–199. DOI:10.1016/j.apcatb.2014.05.024 · 7.44 Impact Factor
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    ABSTRACT: Hydrodeoxygenation of guaiacol over Pt-based catalysts was studied as a representative for phenolic compounds in pyrolysis oil. Screening of various Pt-based catalysts supported on different oxides and using different preparation methods resulted in 1% Pt/SiO2 and platinum supported on zeolites, such as 1% Pt/H-MFI-90, as the most promising catalysts in a temperature range up to 200 °C. Thereby conversions of 86 % and 100 % were received, respectively. Particularly, selectivities to cyclohexane above 90 % were achieved for 1% Pt/H-MFI-90.
    Applied Catalysis A General 10/2014; 490. DOI:10.1016/j.apcata.2014.10.043 · 3.94 Impact Factor
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    ABSTRACT: Die Effizienz von Polymerelektrolytmembran-Brennstoffzellen hängt stark von der Funktionalität der Elektrokatalysatoren ab, d. h. deren Aktivität und Stabilität. Wir beschreiben hier die Entwicklung eines Katalysators, der die typische Aktivität nanoskaliger Pt-Legierungen in der kathodischen Sauerstoffreduktion mit der exzellenten Stabilität eines nanostrukturierten Trägermaterials vereint. Aufgrund seiner hohen spezifischen Aktivität und großen aktiven Oberfläche zeigt der Katalysator eine ungewöhnliche massenbezogene Aktivität von 10 A mgPt−1. In beschleunigten Alterungstests behielt der Katalysator seine ursprüngliche Oberfläche und intrinsische Aktivität unter üblichen Betriebsbedingungen bei. Dieses exzellente Verhalten wird durch die raumbegrenzte Legierung der Nanopartikel in den Poren des Trägermaterials erreicht.
    Angewandte Chemie 10/2014; 126(51). DOI:10.1002/ange.201406812
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    ABSTRACT: The efficiency of polymer electrolyte membrane fuel cells is strongly depending on the electrocatalyst performance, that is, its activity and stability. We have designed a catalyst material that combines both, the high activity for the decisive cathodic oxygen reduction reaction associated with nanoscale Pt alloys, and the excellent durability of an advanced nanostructured support. Owing to the high specific activity and large active surface area, the catalyst shows extraordinary mass activity values of 1.0 A mgPt−1. Moreover, the material retains its initial active surface area and intrinsic activity during an extended accelerated aging test within the typical operation range. This excellent performance is achieved by confined-space alloying of the nanoparticles in a controlled manner in the pores of the support.
    Angewandte Chemie International Edition 10/2014; 53(51). DOI:10.1002/anie.201406812 · 11.26 Impact Factor
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    ABSTRACT: An in-depth understanding of the active site requires advanced operando techniques and the preparation of defined catalysts. We elucidate here the mechanism of the selective catalytic reduction of NO by NH3 (NH3-SCR) over a Fe-ZSM-5 zeolite catalyst. 1.3 wt% Fe-ZSM-5 with low nuclearity Fe sites was synthesized, tested in the SCR reaction and characterized by UV-Vis, X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) spectroscopy. Next, this defined Fe-zeolite catalyst was studied by complementary high-energy-resolution fluorescence-detected XANES (HERFD-XANES) and valence-to-core X-ray emission spectroscopy (V2C XES) under different model in situ and realistic working (operando) conditions identical to the catalyst test bench including the presence of water vapor. In particular, this included the presence of water vapor which strongly influences the catalytic performance and the structure of the active centre. HERFD-XANES uncovered that the coordination (between 4 and 5), geometry (tetrahedral, partly 5-fold), and oxidation state of the Fe centres (reduced in NH3, partly in SCR mixture, slight reduction in NO) strongly changed. V2C XES supported by DFT calculations provided important insight into the chemical nature of the species adsorbed on Fe sites. The unique combination of techniques applied under realistic reaction conditions and the corresponding catalytic data unraveled the adsorption of ammonia via oxygen on the iron site. The derived reaction model supports a mechanism where adsorbed NOx reacts with ammonia coordinated to the Fe3+ site yielding Fe(2+) which reoxidation is slow.
    Journal of the American Chemical Society 08/2014; 136(37). DOI:10.1021/ja5062505 · 12.11 Impact Factor
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    Microscopy and Microanalysis; 08/2014
  • Hudson W. P. Carvalho · Celso V. Santilli · Valérie Briois · Sandra H. Pulcinelli ·
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    ABSTRACT: The radical trapping flame retardant mechanism of polymer-clay nanocomposites is frequently claimed to be responsible for improving the thermal stability of polymers. However it had never been demonstrated. Herein using in situ time-resolved X-ray Absorption Spectroscopy (XAS) we present experimental evidence that Fe3+ embedded in the clay can act as electron acceptors during polymer thermal decomposition. Therefore it contributes to improve the polymer thermal stability.
    RSC Advances 12/2013; 3(45):22830. DOI:10.1039/c3ra44388d · 3.84 Impact Factor
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    ABSTRACT: Poly(methylmetacrilate)-maghemite (PMMA-gamma-Fe2O3) hybrid material was studied by the electron stimulated ion desorption (ESID) techniques coupled with time-of-flight mass spectrometry (TOF-MS) and theoretical investigation about its fragmentation. Moreover, atomic force microscopy was utilized to characterize the morphology before and after ionic desorption. ESID results indicated differences of pattern fragmentation for different compositions of hybrid material in comparison with neat PMMA. Theoretical studies suggest that kinetics effects can take place in the fragmentation process and electrostatic contributions were important in the stabilization of PMMA on maghemite after the grafting process.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 08/2013; 117C:276-283. DOI:10.1016/j.saa.2013.08.029 · 2.35 Impact Factor
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    ABSTRACT: The XAS/WAXS time-resolved method was applied for unraveling the complex mechanisms arising from the evolution of several metastable intermediates during the degradation of chlorine layered double hydroxide (LDH) upon heating to 450 °C, i.e., Zn2Al(OH)6·nH2O, ZnCuAl(OH)6·nH2O, Zn2Al0.75Fe0.25(OH)6·nH2O, and ZnCuAl0.5Fe0.5(OH)6·nH2O. After a contraction of the interlamellar distance, attributed to the loss of intracrystalline water molecules, this distance experiences an expansion (T > 175–225 °C) before the breakdown of the lamellar framework around 275–295 °C. Amorphous prenucleus clusters with crystallo-chemical local order of zinc-based oxide and zinc-based spinel phases, and if any of copper-based oxide, are formed at T > 175–225 °C well before the loss of stacking of LDH layers. This distance expansion has been ascribed to the migration of ZnII from octahedral layers to tetrahedral sites in the interlayer space, nucleating the nano-ZnO or nano-ZnM2O4 (M = Al or Fe) amorphous prenuclei. The transformation of these nano-ZnO clusters toward ZnO crystallites proceeds through an agglomeration process occurring before the complete loss of layer stacking for Zn2Al(OH)6·nH2O and Zn2Al0.75Fe0.25(OH)6·nH2O. For ZnCuAl(OH)6·nH2O and ZnCuAl0.5Fe0.5(OH)6·nH2O, a cooperative effect between the formation of nano-CuO and nano-ZnAl2O4 amorphous clusters facilitates the topochemical transformation of LDH to spinel due to the contribution of octahedral CuII vacancy to ZnII diffusion.
    Chemistry of Materials 07/2013; 25(14):2855–2867. DOI:10.1021/cm401352t · 8.35 Impact Factor
  • Hudson W.P. Carvalho · Ana F. Suzana · Celso V. Santilli · Sandra H. Pulcinelli ·
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    ABSTRACT: The structure and the thermodegradation behavior of both poly(methyl methacrylate)-co-poly(3-tri(methoxysilyil)propyl methacrylate) polymer modified with silyl groups and of intercalated poly(methyl methacrylate)-co-poly(3-tri(methoxysilyil)propyl methacrylate)/Cloisite 15A™ nanocomposite have been in situ probed. The structural feature were comparatively studied by Fourier transform infrared spectroscopy (FTIR), 13C and 29Si nuclear magnetic resonance (NMR), and small angle X-ray scattering (SAXS) measurements. The intercalation of polymer in the interlayer galleries was evidenced by the increment of the basal distance from 31 to 45 Å. The variation of this interlayer distance as function of temperature was followed by in situ SAXS. Pristine polymer decomposition pathway depends on the atmosphere, presenting two steps under air and three under N2. The nanocomposites are more stable than polymer, and this thermal improvement is proportional to the clay loading. The experimental results indicate that clay nanoparticles play several different roles in polymer stabilization, among them, diffusion barrier, charring, and suppression of degradation steps by chemical reactions between polymer and clay. Charring is atmosphere dependent, occurring more pronounced under air. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers
    Polymer Engineering and Science 06/2013; 53(6). DOI:10.1002/pen.23364 · 1.52 Impact Factor
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    ABSTRACT: In this study, the short-and long-range chem-ical environments of Cu dopant in TiO 2 photocatalyst have been investigated. The Cu-doped and undoped TiO 2 spec-imens were prepared by the sol–gel approach employing CuSO 4 Á5H 2 O and Ti(O-iPr) 4 precursors and subjecting the dried gels to thermal treatment at 400 and 500 °C. The photocatalytic activity, investigated by methylene blue degradation under sunlight irradiation, showed a signifi-cantly higher efficiency of Cu-doped samples than that of pure TiO 2 . The X-ray diffraction results showed the pres-ence of anatase phase for samples prepared at 400 and 500 °C. No crystalline CuSO 4 phase was detected below 500 °C. It was also found that doping decreases the crys-tallite size in the (004) and (101) directions. Infrared spectroscopy results indicated that the chemical environ-ment of sulfate changes as a function of thermal treatment, and UV–vis spectra showed that the band gap decreases with thermal treatment and Cu doping, showing the lowest value for the 400 °C sample. X-ray absorption fine struc-ture measurements and analysis refinements revealed that even after thermal treatment and photocatalytic assays, the Cu 2? local order is similar to that of CuSO 4 , containing, however, oxygen vacancies. X-ray photoelectron spec-troscopy data, limited to the near surface region of the catalyst, evidenced, besides CuSO 4 , the presence of Cu 1? and CuO phases, indicating the active role of Cu in the TiO 2 lattice.
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    ABSTRACT: Mn-incorporated Fe3O4 photocatalysts were prepared by a simple co-precipitation method. Photocatalytic discoloration of Methylene Blue (MB) was used to evaluate the performance of these catalysts. The DSC results have shown that the insertion of Mn into Fe3O4 lattice has increased converting Fe3O4 to γ-Fe2O3. This is accompanied by a decrease of surface area and of crystallinity, as detected by XRD. The analysis of the chemical environment by XPS has shown that Mn2+ replaces Fe2+ preferentially in the octahedral sites while Mn3+ replaces Fe3+ of inverse spinel sites. The Mn-incorporated samples were significantly more efficient in MB discoloration assisted by UVA irradiation and H2O2. It was also found that ascorbic acid prevents H2O2 decomposition, by scavenging preferentially OOH radicals produced at Mn sites. Finally, the results reported here can contribute for a better comprehension of the activity of composite catalysts and the design of efficient systems for discoloration of organic pollutants.
    Materials Science and Engineering B 01/2013; 181(1). DOI:10.1016/j.mseb.2013.11.008 · 2.17 Impact Factor
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    Hudson W.P. Carvalho · Ana P.L. Batista · Peter Hammer · Teodorico C Ramalho ·
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    ABSTRACT: In this work the effect of doping concentration and depth profile of Cu atoms on the photocatalytic and surface properties of TiO(2) films were studied. TiO(2) films of about 200 nm thickness were deposited on glass substrates on which a thin Cu layer (5 nm) was deposited. The films were annealed during 1s to 100°C and 400°C, followed by chemical etching of the Cu film. The grazing incidence X-ray fluorescence measurements showed a thermal induced migration of Cu atoms to depths between 7 and 31 nm. The X-ray photoelectron spectroscopy analysis detected the presence of TiO(2), Cu(2)O and Cu(0) phases and an increasing Cu content with the annealing temperature. The change of the surface properties was monitored by the increasing red-shift and absorption of the ultraviolet-visible spectra. Contact angle measurements revealed the formation of a highly hydrophilic surface for the film having a medium Cu concentration. For this sample photocatalytic assays, performed by methylene blue discoloration, show the highest activity. The proposed mechanism of the catalytic effect, taking place on Ti/Cu sites, is supported by results obtained by theoretical calculations.
    Journal of hazardous materials 12/2010; 184(1-3):273-80. DOI:10.1016/j.jhazmat.2010.08.033 · 4.53 Impact Factor
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    ABSTRACT: In this work, we study the effect of doping depth profile on the photocatalytic and surface properties of TiO2 films. Two thin film layers of TiO2 (200nm) and Co (5nm), respectively, were deposited by physical evaporation on glass substrate. These films were annealed for 1s at 100 and 400°C and the Co layer was removed by chemical etching. Atomic force microscopy (AFM) phase images showed changes in the surface in function of thermal treatment. The grazing-incidence X-ray fluorescence (GIXRF) measurements indicated that the thermal treatment caused migration of Co atoms to below the surface, the depths found were between 19 and 29nm. The contact angle showed distinct values in function of the doped profile or Co surface concentration. The UV–vis spectra presented a red shift with the increasing of thermal treatment. Photocatalytical assays were performed by methylene blue discoloration and the higher activity was found for TiO2–Co treated at 400°C, the ESI-MS showed the fragments formed during the methylene blue decomposition.
    Journal of Materials Science 10/2010; 45(20):5698-5703. DOI:10.1007/s10853-010-4639-5 · 2.37 Impact Factor

Publication Stats

215 Citations
124.88 Total Impact Points


  • 2013-2015
    • Karlsruhe Institute of Technology
      • Institute of Technical and Polymer Chemistry
      Carlsruhe, Baden-Württemberg, Germany
    • SOLEIL synchrotron
      Gif, Île-de-France, France
  • 2008-2013
    • São Paulo State University
      • • Institute of Chemistry
      • • Department of Physics and Chemistry
      San Paulo, São Paulo, Brazil
  • 2007-2009
    • Universidade Federal de Lavras (UFLA)
      • Departamento de Química
      لفراس, Minas Gerais, Brazil