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J M C Bueno - One of the best experts on this subject based on the ideXlab platform.
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surface and structural features of pt ceo2 la2o3 al2o3 catalysts for partial oxidation and steam reforming of methane
Applied Catalysis B-environmental, 2011Co-Authors: Vanessa Bongalhardo Mortola, S Damyanova, Daniela Zanchet, J M C BuenoAbstract:Abstract Mixed xCeO2-yLa2O3-Al2O3 oxides (where x + y = 12 wt%) were prepared by sol–gel method. It was shown that the mixed oxides are suitable carriers for Supported Pt catalysts. The catalytic performances of the catalysts were evaluated in the reaction of stem methane reforming (SMR) and partial oxidation of methane (POM). The effect of the Support kind on the surface and structural properties, as well as on the redox and catalytic behavior of the catalyst was studied. It was shown that the coexistence of the Pt0/Ptδ+ and Ce4+/Ce3+ redox couples leads to the increase of the CH4 conversion and carbon resistance over Pt catalysts. The CeO2-containing catalysts showed the highest TOF CH 4 values in SMR in spite of the low metal dispersion that is related to the high capacity of the surface to carbon cleaning caused by the highest oxygen mobility at metal–Support Interface. The strong initial deactivation of alumina-Supported Pt catalyst in POM was related to Pt sintering.
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effect of ceo2 loading on the surface and catalytic behaviors of ceo2 al2o3 Supported pt catalysts
Applied Catalysis A-general, 2003Co-Authors: S Damyanova, J M C BuenoAbstract:Abstract Pt catalysts Supported on mixed CeO2-Al2O3 carriers with different CeO2 loading (0.5–10.3 wt.%) were prepared by wetness impregnation method. The catalysts were characterized by SBET, X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and thermogravimetric analysis (TG). It was shown that pretreatment temperature and the concentration of CeO2 in the Support influences significantly on the morphology of Pt. XRD showed the formation of nanocrystallites of Pt on the surface of alumina and low-loaded CeO2 (≤6 wt.%) samples at higher temperature of calcination (1073 K). Amorphous Pt was observed in all reduced samples. XPS spectra showed the presence of interaction between Pt and Ce, which leads to easy surface reduction of both, ceria and platinum, as revealed by TPR patterns. The effect of CeO2 loading on the catalytic behavior of Supported Pt catalysts in the reaction of CO2 reforming of CH4 was determined. Addition of cerium oxide results in improvement of catalytic performance for the reforming of methane with CO2. Pt catalyst with 1 wt.% of CeO2 exhibited the highest specific activity and stability, due to the increase in the metal–Support Interface area, caused by the higher Pt dispersion.
Fabio Souza Toniolo - One of the best experts on this subject based on the ideXlab platform.
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Pt nanoparticles embedded in CeO 2 and CeZrO 2 catalysts for biogas upgrading: Investigation on carbon removal mechanism by oxygen isotopic exchange and DRIFTS
Journal of CO2 Utilization, 2021Co-Authors: André Marinho, Raimundo Rabelo-neto, Florence Epron, Nicolas Bion, Fabio Noronha, Fabio Souza TonioloAbstract:This work investigated the effect of Pt nanoparticles embedded into CeO2 (Pt@CeO2) and CeZrO2 (Pt@CeZrO2) on the carbon removal mechanism for the dry reforming of methane, in comparison to impregnated Pt/CeO2. Morphological and structural characterization by TEM and Raman spectroscopy showed that Pt sintering is suppressed on both structures and the doping with Zr led to the CeZrO2 solid solution formation. A combination of TPR, oxygen isotopic exchange and DRIFTS measurements demonstrated that embedded Pt nanoparticles interact more strongly with ceria than Supported Pt, and as a consequence, reactive lattice oxygen becomes more abundant on the catalyst surface, promoting the mechanism of carbon gasification over Pt nanoparticle. The low availability of oxygen species on Pt/CeO2 resulted in higher carbon formation, as demonstrated by TPO analysis. Therefore, the Pt@CeO2 and Pt@CeZrO2 catalysts were more resistant to coke formation due to the higher presence of reactive oxygen species at the metal-Support Interface, promoting the balance between the rates of carbon formation and carbon gasification over Pt nanoparticle.
Angelos M Efstathiou - One of the best experts on this subject based on the ideXlab platform.
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low temperature water gas shift on pt ce1 xlaxo2 δ effect of ce la ratio
Applied Catalysis B-environmental, 2013Co-Authors: Klito C Petallidou, Angelos M EfstathiouAbstract:Abstract Pt nanoparticles (1.0–1.4 nm size) Supported on Ce1−xLaxO2−δ (x = 0.0, 0.2, 05, 0.8 and 1.0) carriers, the latter prepared by the citrate sol–gel method, were tested toward the water-gas shift (WGS) reaction in the 200–400 °C range. A deep insight into the effect of Ce/La atom ratio of Support chemical composition on the catalytic performance (CO conversion vs. temperature and stability) and kinetic rates of Pt-loaded catalysts was realized after employing HAADF/STEM, in situ Raman and DRIFT spectroscopies under different gas atmospheres, temperature-programmed surface reaction (TPSR) in He and O2/He gas atmospheres following WGS reaction, CO-TPD, in situ UV–vis/DRS, oxygen storage capacity measurements, and transient 18O-isotopic exchange studies followed by WGS reaction. It was found that doping of ceria with 20 at.% La3+ has increased significantly the catalytic activity of 0.5 wt% Pt/Ce0.8La0.2O2−δ solid in the 250–350 °C range, whereas addition of 50–80 at.% La3+ in ceria caused a negative effect on the CO conversion with respect to pure ceria. It was found that the Ce/La atom ratio in Ce1−xLaxO2−δ influences the catalytic site reactivity (k) along the Pt-Support Interface. The optimum La3+-dopant concentration of 20 at.% (Ce/La = 4/1) used in Pt/Ce0.8La0.2O2 compared to the worst one of 80 at.% (Pt/Ce0.2La0.8O2−δ, Ce/La = 1/4) correlates with (i) the higher specific kinetic rate per length of Pt-Support Interface (μmol CO cm−1 s−1), (ii) the higher concentration of oxygen vacant sites, (iii) the lower amount (μmol/g−1) of “carbon” accumulated during WGS and best stability with time on stream, (iv) the lower apparent activation energy (kcal mol−1) of WGS reaction, (v) the lower degree toward Pt oxidation (largest Pt2+/Pt4+ ratio), (vi) the lower Ce1−xLaxO2−δ Support energy band gap, and (vii) the lower mobility of surface lattice oxygen.
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the influence of reaction temperature on the chemical structure and surface concentration of active nox in h2 scr over pt mgoceo2 ssitka drifts and transient mass spectrometry studies
Journal of Catalysis, 2008Co-Authors: Petros G Savva, Angelos M EfstathiouAbstract:Abstract Steady-state isotopic transient kinetic analysis (SSITKA), transient isothermal, and temperature-programmed surface reaction in H 2 (H 2 -TPSR) techniques coupled with online mass spectroscopy (MS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were used to study essential mechanistic and kinetic aspects of the selective catalytic reduction (SCR) of NO with the use of H 2 under strongly oxidizing conditions (H 2 -SCR) over a novel Pt/MgO CeO 2 catalyst. The main focus was to study and report for the first time the effects of reaction temperature on the chemical structure and surface concentration of the active NO x intermediate species thereby formed. The information obtained is essential to understanding the volcano-type profile of the catalyst activity versus reaction temperature observed here and also reported previously. In the present work, two active NO x intermediate species identified by SSITKA-DRIFTS were found in the nitrogen-reaction path toward N 2 and N 2 O formation, one species located in the vicinity of the Pt CeO 2 Support Interface region (nitrosyl [NO + ] coadsorbed with a nitrate [NO − 3 ] species on an adjacent Ce 4+ O 2− site pair) and the second located in the vicinity of the Pt MgO Support Interface region. The chemical structure of the second kind of active NO x species was found to depend on reaction temperature. In particular, the chemical structure was that of bidentate or monodentate nitrate (NO − 3 ) at T 200 ° C and that of chelating nitrite (NO − 2 ) at T > 200 ° C . The concentration of the active NO x intermediates that lead to N 2 formation was found to be practically independent of reaction temperature (120–300 °C) and significantly larger than 1 equivalent monolayer of surface Pt ( θ NO x = 2.4 – 2.6 ). The former result cannot be used to explain the volcano-type behavior of the catalytic activity versus the reaction temperature observed; alternative explanations are explored. The H-spillover process involved in the H 2 -SCR mechanism was found to be limited within a Support region of about a 4–5 A radius around the Pt nanoparticles ( d Pt = 1.2 – 1.5 nm ).
David Mitlin - One of the best experts on this subject based on the ideXlab platform.
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titanium oxynitride interlayer to influence oxygen reduction reaction activity and corrosion stability of pt and pt ni alloy
Chemsuschem, 2015Co-Authors: Xuehai Tan, Liya Wang, Beniamin Zahiri, Alireza Kohandehghan, D S Karpuzov, Elmira Memarzadeh Lotfabad, Michael Eikerling, David MitlinAbstract:A key advancement target for oxygen reduction reaction catalysts is to simultaneously improve both the electrochemical activity and durability. To this end, the efficacy of a new highly conductive Support that comprises of a 0.5 nm titanium oxynitride film coated by atomic layer deposition onto an array of carbon nanotubes has been investigated. Support effects for pure platinum and for a platinum (50 at %)/nickel alloy have been considered. Oxynitride induces a downshift in the d-band center for pure platinum and fundamentally changes the platinum particle size and spatial distribution. This results in major enhancements in activity and corrosion stability relative to an identically synthesized catalyst without the interlayer. Conversely, oxynitride has a minimal effect on the electronic structure and microstructure, and therefore, on the catalytic performance of platinum-nickel. Calculations based on density functional theory add insight with regard to compositional segregation that occurs at the alloy catalyst-Support Interface.
Xenophon E Verykios - One of the best experts on this subject based on the ideXlab platform.
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influence of structural parameters on the reaction of low temperature ethanol steam reforming over pt al2o3 catalysts
Catalysis Today, 2015Co-Authors: Marios Kourtelesis, Paraskevi Panagiotopoulou, Xenophon E VerykiosAbstract:Abstract The effect of mean metal crystallite size on activity and selectivity of Pt/Al 2 O 3 catalysts under conditions of ethanol steam reforming at low temperatures was investigated. It was found that catalytic activity is strongly influenced by metal crystallite size. Normalized turnover frequency (TOF divided by the length of the perimeter of the metal–Support Interface) increases by three orders of magnitude with increasing platinum crystallite size from 0.9 to 16.8 nm. Reaction is initiated by dehydrogenation of ethanol over the Pt surface, a reaction which is significantly enhanced over large Pt crystallites. Evidence is provided that the active sites for ethanol/adsorption dehydrogenation are platinum terrace sites of multiple Pt atoms, and that this may be the key step for ethanol reforming at low temperatures.
