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Scientific Papers in SCI

2019


Extraordinary visible photocatalytic activity of a Co0.2Zn0.8O system studied in the Remazol BB oxidation


KarimTanji; J.A.Navio; Jamal Naja; M.C.Hidalgo; Abdellah Chaqroune; C.Jaramillo-Páez; Abdelhak Kherbeche
Journal of Photochemistry and Photobiology A: Chemistry, 382 (2019) 111877

ABSTRACT

Nanoparticles of CoxZn1-xO system with a nominal composition of x=0.2 were synthesized by the Solution Combustion Method (SCM). Structural and morphological studies as well as the chemical composition of the material were widely investigated by different techniques. Photocatalytic activity under UV and Visible illumination was studied by means of the Remazol Brilliant Blue dye (RBB) oxidation reaction. The effect of different experimental parameters, such as the initial dye concentration, photocatalyst mass, pH or hydrogen peroxide concentration on the RBB discoloration under UV irradiation was studied. Optimal experimental conditions were found to be a photocatalyst mass of 1 g.L-1, dye concentration of 20 mg.L-1 and solution pH of 11. Hydrogen peroxide addition was found to have no effect in the photocatalytic behavior of the material in the range of concentration studied (0 to 6•10-4 M). The optimal parameters were chosen to investigate the degradation of RBB under UV-illumination and just visible illumination. It was observed that the UV-photocatalytic property of pristine ZnO for the RBB removal was scarcely improved after cobalt-incorporation, whereas the effect of cobalt incorporation into ZnO greatly enhanced the RBB conversion under visible illumination. Even more interesting is that, under same experimental conditions, the visible efficiency of the Co-ZnO system is the same that the one showed under UV illumination, i.e. the system does not loose efficiency when illuminated only with visible light.


September, 2019 | DOI: 10.1016/j.jphotochem.2019.111877

Support effects on NiO-based catalysts for the oxidative dehydrogenation (ODH) of ethane


Delgado, D; Sanchis, R; Cecilia, JA; Rodriguez-Castellon, E; Caballero, A; Solsona, B; Nieto, JML
Catalysis Today, 333 (2019) 10-16

ABSTRACT

We report on the effect of NiO-support interactions on the chemical nature of Ni species in a series of supported NiO catalysts for the ODH of ethane. SiO2, TiO2-anatase, a high surface area TiO2 and a porous clay hetero-structure (PCH) with TiO2 and SiO2 pillars were used as supports, which led to a selectivity to ethylene in the range 30-90% over supported NiO catalysts. The catalysts were characterized by means of XRD, N-2-Adsorption, H-2-TPR, XPS and in situ (under H-2 reductive atmosphere) and ex situ XAS spectroscopy. The catalytic performance of supported materials is discussed in terms of their reducibility and specific reduction kinetics, but also taking into account the specific chemical nature of Ni species on each catalyst. The influence of the particle size and the presence of Ni and O vacancies on the catalytic performance in the ODH of ethane is inferred.


August, 2019 | DOI: 10.1016/j.cattod.2018.07.010

Au/Al2O3 - Efficient catalyst for 5-hydroxymethylfurfural oxidation to 2,5-furandicarboxylic acid


Megias-Sayago, C; Lolli, A; Ivanova, S; Albonetti, S; Cavani, F; Odriozola, JA
Catalysis Today, 333 (2019) 169-175

ABSTRACT

The catalytic activity of a simple Au/Al2O3 catalytic system prepared by the direct anionic exchange (DAE) method was evaluated in the selective 5-hydroxymethylfurfural (HMF) oxidation under mild conditions, using molecular oxygen as the oxidant. The influence of the HMF/NaOH ratio and reaction time on product yield and distribution were studied and discussed in detail. Extremely high activity and selectivity were observed in mild conditions, with 99% of 2,5-furandicarboxylic acid (FDCA) production at full HMF conversion after 4 h with the use of only 4 equivalents of NaOH at 70 degrees C. Catalyst viability and stability were verified by repeating the cycle up to five times. Changes in the nature of the support were also contemplated by introducing some ceria fraction, i.e. 20 wt%.


August, 2019 | DOI: 10.1016/j.cattod.2018.04.024

Natural abundance O-17 MAS NMR and DFT simulations: New insights into the atomic structure of designed micas


Pavon, E; Osuna, FJ; Alba, MD; Delevoye, L
Solid State Nuclear Magnetic Resonance, 100 (2019) 45-51

ABSTRACT

Combining O-17 Magic-Angle Spinning (MAS) NMR at natural abundance with DFT calculations is a promising methodology to shed light on the structure and disorder in tetrahedral sheets of designed micas with enhanced properties. Among brittle micas, synthetic mica is an important alternative to natural ones with a swelling sheet-like structure that results in many applications, by exploiting unique characteristics. Lowenstein's rule is one of the main chemical factor that determines the atomic structure of aluminosilicates and furthermore their properties. In the present article, O-17 MAS NMR spectroscopy is used to validate (or not) the agreement of the Lowenstein's rule with the distribution of Si and Al sites in the tetrahedral sheets of synthetic micas. O-17 MAS spectra of synthetic high-charged micas exhibit two regions of signals that revealed two distinguishable oxygen environments, namely Si-O-X (with X = Si, Al-tet , Mg) and Al-tet -O-Y (Y=Mg or Al-tet). DFT calculations were also conducted to obtain the O-17 chemical shift and other NMR features like the quadrupolar coupling constant, C-Q, for all of the oxygen environments encountered in the two model structures, one respecting the Lowenstein's rule and the other involving Al-tet -O-Al-tet and Si-O-Si environments. Our DFT calculations support the O-17 assignment, by confirming that Al-tet -O-3Mg and Al tet -O-Al tet oxygen environments show chemical shifts under 30 ppm and more important, with quadrupolar coupling constants of about 1 MHz, in line with the spectral observation. By quantifying the O-17 MAS NMR spectra at natural abundance, we demonstrate that one of the synthetic mica compositions does not meet the Lowenstein's rule.


August, 2019 | DOI: 10.1016/j.ssnmr.2019.03.006

Structural and compositional analysis of Co-based coatings after catalytic tests for the sodium borohydride hydrolysis


Beltran, AM
Materials Research Express, 6 (2019) art. 085511

ABSTRACT

The use of Co-based catalysts for the sodium borohydride hydrolysis for hydrogen production is a well-known process as a source of clean energy, although its mechanisms are still under discussion. With the aim of acquiring a deeper knowledge about this catalytic process, three different catalysts (Co, CoC and CoB) were deposited as a thin film layer by magnetron sputtering onto a polymeric membrane, used as a substrate and analyzed by advance transmission and scanning-transmission electron microscopy techniques (STEM). Structural and compositional characterizations, by electron energy loss spectroscopy (EELS), have been performed on the coatings before and after their use as catalysts on the sodium borohydride reaction for 90 min, to check the production of hydrogen. Results have shown the formation of CoxB nanoflakes and other Co-based compounds over the catalysts and related to their catalytic activity. Knowing the changes in the structure and composition of the catalysts is key to understanding their catalytic behavior, activity and durability. Among the analyzed catalysts, the Co-C presents better activity during the first cycles, which is related to a larger formation of CoxB.


August, 2019 | DOI: 10.1088/2053-1591/ab1e27

Exchange bias and two steps magnetization reversal in porous Co/CoO layer


Ovejero, JG; Godinho, V; Lacroix, B; Garcia, MA; Hernando, A; Fernandez, A
Materials & Design, 171 (2019) 107691

ABSTRACT

In this paper Co/CoO thick layers (hundreds of nanometers) of different porosity and oxidation degree were prepared in a magnetron sputtering deposition processby tailoring the DC sputtering power, as well as the process gas and target composition. The control of the synthesis parameters allowed the nanostructuration of the films with a singular distribution of closed pores and a controlled amount of CoO. We observed an exchange bias field of 2.8 KOe for porous Co/CoO composites, similar to Co/CoO bilayers but for coatings thicker than 300 nm. Besides, it was observed that the coating presents bistable magnetic features when cooled under zero field conditions as a result of the unusual exchange coupling.


June, 2019 | DOI: 10.1016/j.matdes.2019.107691

2D compositional self-patterning in magnetron sputtered thin films


Garcia-Valenzuela, A; Alvarez, R; Rico, V; Espinos, JP; Lopez-Santos, MC; Solis, J; Siegel, J; del Campo, A; Palmero, A; Gonzalez-Elipe, AR
Applied Surface Science, 480 (2019) 115-121

ABSTRACT

Unlike topography patterning, widely used for numerous applications and produced by means of different technologies, there are no simple procedures to achieve surface compositional patterning at nanometric scales. In this work we have developed a simple method for 2D patterning the composition of thin films. The method relies on the magnetron sputtering deposition at oblique angles onto patterned substrates made by laser induced periodic surface structures (LIPSS). The method feasibility has been demonstrated by depositing SiOx thin films onto LIPSS structures generated in Cr layers. A heterogeneous and aligned distribution of O/Si ratios (and different Sin+ chemical states) along the LIPSS structure in length scales of some hundreds nm's has been proven by angle resolved X-ray photoelectron spectroscopy and a patterned arrangement of composition monitored by atomic force microscopy-Raman analysis. The obtained results are explained by the predictions of a Monte Carlo simulation of this deposition process and open the way for the tailored one-step fabrication of surface devices with patterned compositions.


June, 2019 | DOI: 10.1016/j.apsusc.2019.02.206

Microbiological induced carbonate (CaCO3) precipitation using clay phyllites to replace chemical stabilizers (cement or lime)


Morales, L; Garzon, E; Romero, E; Sanchez-Soto, PJ
Applied Clay Science, 174 (2019) 15-28

ABSTRACT

The objective of the present study is to develop a biotechnological tool for a new application of clay phyllites as stabilized materials in linear works replacing chemical stabilizer (e.g. cement or lime) by natural cement, formed by precipitated calcium carbonate generated by microorganisms of the Bacillaceae family (Bacilluspasteurii). Part of the development process conducting a chemical and mineralogical characterization and an examination of physical and hydromechanical properties. The results of this study show that the effect of bacteria on clay phyllites increases the calcium carbonate content, specific surface area and plasticity values. These increased values are caused by the addition of a non-plastic component to clay phyllites resulting in a more aggregated structure through the precipitation of calcium carbonate from the bacteria, ultimately filling the pores of this material. Microbiological treatments on clay phyllites tends to aggregate the original particles, creating aggregates that are partially associated with the formation of calcium carbonate. Said process is influenced by the curing and compaction procedures conducted on samples, which also cause breakage of carbonated structures formed during treatment. As a result of this breaking process of aggregates, some compaction energy is lost and the treated samples do not reach the maximum dry density of the natural state for the same level of compaction energy applied. Treated samples display a slightly larger friction angle with no cohesion, consistent with filling properties and denser condition. Compressibility is consistently lower than that of the natural state. Comparison of collapse data showsthat the occurrence and amount of collapse are controlled by the as-compacted dry density. It is also determined that higher compaction effort is even more effective than increasing the amount of bacteria introduced to stabilize the sample for the filling of pores (size ranges 3–50 μm) with calcium carbonate. However, the post-ageing compaction destroys the initial binding/cementation effect.


June, 2019 | DOI: 10.1016/j.clay.2019.03.018

Multifunctional antimicrobial chlorhexidine polymers by remote plasma assisted vacuum deposition


Mora-Boza, A; Aparicio, FJ; Alcaire, M; Lopez-Santos, C; Espinos, JP; Torres-Lagares, D; Borras, A; Barranco, A
Frontiers of chemical science and engineering, 13 (2019) 330-339

ABSTRACT

Novel antibacterial materials for implants and medical instruments are essential to develop practical strategies to stop the spread of healthcare associated infections. This study presents the synthesis of multifunctional antibacterial nanocoatings on polydimethylsiloxane (PDMS) by remote plasma assisted deposition of sublimated chlorhexidine powders at low pressure and room temperature. The obtained materials present effective antibacterial activity against Escherichia coli K12, either by contact killing and antibacterial adhesion or by biocide agents release depending on the synthetic parameters. In addition, these multifunctional coatings allow the endure hydrophilization of the hydrophobic PDMS surface, thereby improving their biocompatibility. Importantly, cell-viability tests conducted on these materials also prove their non-cytotoxicity, opening a way for the integration of this type of functional plasma films in biomedical devices.


June, 2019 | DOI: 10.1007/s11705-019-1803-6

Preparation, characterization and photocatalytic degradation of Rhodamine B dye over a novel Zn3(PO4)2/BiPO4 catalyst


Naciri,Y.;Chennah,A.;Jaramillo-Páez,C.;Navío,J.A.;Bakiz, B.;Taoufyq,A.;Ezahri,M.;Villain,S.;Guinneton,F.;Benlhachemi,A.
Journal of Environmental Chemical Engineering, 7 (2019) 103075

ABSTRACT

In this work, a facile method was used to synthesize the Zn3(PO4)2/BiPO4 composite photocatalysts with different Bi contents followed by heat treatment at 900 °C for 3 h. The as-prepared samples were studied by a variety of characterization techniques including X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) combined with energy dispersive X-ray diffraction (EDX), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectroscopy (DRS). The UV–vis spectroscopy was used to analyze the evolution of Rhodamine B discoloration in presence of the synthesized phosphate photocatalysts. The XRD, SEM-EDX, TEM, DRS and XPS analyses confirmed the formation of heterojunction structure between both materials, during the process of co-precipitation and ulterior heat treatment. The photocatalytic tests showed that photocatalytic ability of the 70% Bi-Zn3(PO4)2 composites was higher than that of pure Zn3(PO4)2 and BiPO4 after 1 h of UV-illumination. The obviously enhanced photocatalytic activity of the 70% Bi-Zn3(PO4)2 sample could be mainly attributed to the formation of the heterojunction, accelerating the separation of photogenerated charge carriers. A plausible mechanism of the photocatalytic degradation of RhB on Zn3(PO4)2/BiPO4 composites is proposed. The reduction in the Chemical Oxygen Demand (COD) revealed the mineralization of dye along with color removal. Thus, it can be suggested that the 70% Bi-Zn3(PO4)2 can serve as a promising photocatalyst in the degradation of organic contaminants under UV light.


June, 2019 | DOI: 10.1016/j.jece.2019.103075

Phosphate-type supports for the design of WGS catalysts


Navarro-Jaen, S; Romero-Sarria, F; Centeno, MA; Laguna, OH; Odriozola, JA
Applied Catalysis B-Environmental, 244 (2019) 853-862

ABSTRACT

The importance of water availability during the WGS reaction has been extensively reported. Thus, the search of new supports able to interact with the water molecule is of great importance. In this work, a series of phosphate type supports containing Ce, Ca and Ti have been studied, demonstrating that water interaction with the support is closely related to the textural properties, surface composition and crystal structure of the solids. Additionally, DRIFTS results showed that different interaction mechanisms with the water molecule occur depending on the support. The system containing Ca dissociates the water molecule and interacts with it via the phosphate and Ca2+ ions. However, the Ce systems retain water in its molecular form, which interacts with the solids via hydrogen bonding with the phosphate groups. On the other hand, the Ti system experiences a loss of phosphorous, presenting a low degree of interaction with the water molecule. Additionally, the behavior of the supports with water has been successfully related to the WGS catalytic activity of the corresponding phosphate supported Pt catalysts.


May, 2019 | DOI: 10.1016/j.apcatb.2018.12.022

Coupling of WO3 with anatase TiO2 sample with high {001} facet exposition: Effect on the photocatalytic properties


Lara, M.A.; Jaramillo-Páez, C.; Navío, J.A.; Sánchez-Cid, P.; Hidalgo, M.C.
Catalysis Today, 328 (2019) 142-148

ABSTRACT

A highly faceted {001} TiO2 catalyst was hydrothermally synthesized by using Ti(IV)-isopropoxide precursor with aqueous HF addition. WO3 was synthesized by following a reported method. Coupled TiO2-WO3 samples were synthesized by adding the corresponding amount of WO3 to fluorinated TiO2 gel followed by a hydrothermal treatment. Additionally the synthesized systems were characterized by using X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy (DRS) and N2-adsorption (BET) for specific surface area determination. The photocatalytic activity of the single and coupled oxides was measured by means of three model reactions: the photo-oxidation of phenol (as a colourless substrate) and methyl orange (as a dye) and the photoreduction of Cr(VI) as K2Cr2O7. The coupling of WO3 with a highly faceted {001} TiO2 makes it possible to optimize the photocatalytic properties of the faceted material. In fact, {001} faceted TiO2 by itself presents a substantial improvement with respect to commercial TiO2(P25), as it can implement its photoactivity after the incorporation of WO3 with promising results, which can reduce the limitations of TiO2 in terms of its photoactivity, taking advantage of a higher percentage of solar radiation.


May, 2019 | DOI: 10.1016/j.cattod.2018.11.012

BixTiyOz-Fe multiphase systems with excellent photocatalytic performance in the visible


Zambrano, P.; Navío, J.A.; Hidalgo, M.C.
Catalysis Today, 328 (2019) 136-141

ABSTRACT

New photocatalysts based on bismuth titanates doped with iron with outstanding visible photocatalytic activity were prepared by a facile hydrothermal method followed by incipient wetness impregnation. The starting material was composed by three phases; majority of Bi20TiO32 closely interconnected to Bi4Ti3O12 and amorphous TiO2. Fe doping increased the already very high visible activity of the original material. The high visible activity showed by these materials could be ascribed to a combination of several features; i.e. low band gap energy value (as low as 1.78 eV), a structure allowing a good separation path for visible photogenerated electron-holes pairs and a relatively high surface area. Fe doping could be acting as bonding paths for the bismuth titanates phases, and the amount of Fe on the surface was found to be a crucial parameter on the photocatalytic activity of the materials. Visible activity of the best photocatalyst was superior to UV-Activity of commercial TiO2 P25 used as reference in same experimental conditions.


May, 2019 | DOI: 10.1016/j.cattod.2018.11.032

Liquid switchable radial polarization converters made of sculptured thin films


Oliva-Ramirez, M; Rico, VJ; Gil-Rostra, J; Arteaga, O; Bertran, E; Serna, R; Gonzalez-Elip, AR; Yubero, F
Applied Surface Science, 475 (2019) 230-236

ABSTRACT

A radial polarization converter is a super-structured optical retarder that converts a conventional linearly polarized light beam into a structured beam with radial or azimuthal polarization. We present a new type of these sophisticated optical elements, which is made of porous nanostructured sculptured single thin films or multilayers prepared by physical vapor deposition at an oblique angle. They are bestowed with an axisymmetric retardation activity (with the fast axis in a radial configuration). In particular, a Bragg microcavity multilayer that exhibits a tunable transmission peak in the visible range with a retardance of up to 0.35 rad has been fabricated using this methodology. Owing to the highly porous structure of this type of thin films and multilayers, their retardance could be switched off by liquid infiltration. These results prove the possibility of developing wavelength dependent (through multilayer optical design) and switchable (through vapor condensation or liquid infiltration within the pore structure) radial polarization converters by means of oblique angle physical vapor deposition.


May, 2019 | DOI: 10.1016/j.apsusc.2018.12.200

Hydrophobicity, Freezing Delay, and Morphology of Laser-Treated Aluminum Surfaces


Rico, VJ; Lopez-Santos, C; Villagra, M; Espinos, JP; de la Fuente, GF; Angurel, LA; Borras, A; Gonzalez-Elipe, AR
Langmuir, 35 (2019) 6483-6491

ABSTRACT

Until recently, superhydrophobicity was considered as a hint to predict surface icephobicity, an association of concepts that is by no means universal and that has been proven to depend on different experimental factors and material properties, including the actual morphology and chemical state of surfaces. This work presents a systematic study of the wetting and freezing properties of aluminum Al6061, a common material widely used in aviation, after being subjected to nanosecond pulsed IR laser treatments to modify its surface roughness and morphology. All treated samples, independent of their surface finishing state, presented initially an unstable hydrophilic wetting behavior that naturally evolved with time to reach hydrophobicity or even superhydrophobicity. To stabilize the surface state and to bestow the samples with a permanent and stable hydrophobic character, laser-treated surfaces were covered with a thin layer of CFx prepared by plasma-enhanced chemical vapor deposition. A systematic comparison between freezing delay (FD) and wetting properties of water droplets onto these plasma-/polymer-modified laser-treated surfaces that, under conditions where a heterogeneous nucleation mechanism prevails, surface morphology rather than the actual value of the surface roughness parameter the key feature for long FD times. In particular, it is found that surface morphologies rendering a Cassie-Baxter wetting regime longer FDs than those characterized by a Wenzel-like wetting state. It is that laser treatment, with or without additional coverage with thin CFx coatings, affects wetting and ice formation behaviors and might be an efficient procedure to mitigate icing problems on metal surfaces.


May, 2019 | DOI: 10.1021/acs.langmuir.9b00457

Amber imitation? Two unusual cases of Pinus resin-coated beads in Iberian Late Prehistory (3rd and 2nd millennia BC)


Odriozola, CP; Cordero, JAG; Daura, J; Sanz, M; Martinez-Blanes, JM; Aviles, MA
PLOS ONE, 14 (2019) e0215469

ABSTRACT

A group of beads from the artificial cave of La Molina (Lora de Estepa, Sevilla) and Cova del Gegant (Sitges, Barcelona) were made from a biogenic raw material and intentionally covered by a layer of resin. This is the first time this type of treatment has been documented on elements of adornment in the Late Prehistory of the Iberian Peninsula. The composition and nature of the coatings are analysed and the symbolic role of such alterations and imitations of prehistoric adornments is discussed.


May, 2019 | DOI: 10.1371/journal.pone.0215469

Surface nickel particles generated by exsolution from a perovskite structure


Aguero, FN; Beltran, AM; Fernandez, MA; Cadus, LE
Journal of Solid State Chemistry, 273 (2019) 75-80

ABSTRACT

LaAl1-xNixO3 (with x = 0.05 and 0.2) perovskite oxides were successfully synthesized and its behavior under reduction atmosphere was studied. HRTEM and STEM studies, coupled to HAADF and EDX detection, allowed to evidence the Ni exsolution process to the surface of the solid and to build nano-catalytic centers. The size of these centers is independent of the reduction conditions in the range studied. The high specific surface of the raw material, its porosity and the structure defects could be responsible of the low temperature at which the exsolution process starts. The content of Ni dopants allows the control of Ni centers size on the surface and the synthesis method provides Ni-nanoparticles strongly anchored to the resultant support.


May, 2019 | DOI: 10.1016/j.jssc.2019.02.036

3D core-multishell piezoelectric nanogenerators


A. Nicolas Filippin; Juan R.Sanchez-Valencia; Xabier Garcia-Casas; Victor Lopez-Flores; Manuel Macias-Montero; Fabian Frutos; Angel Barranco; Ana Borras
Nano Energy, 58 (2019) 476-483

ABSTRACT

The thin film configuration presents obvious practical advantages over the 1D implementation in energy harvesting systems such as easily manufacturing and processing, and long-lasting and stable devices. However, ZnO-based piezoelectric nanogenerators (PENGs) generally rely on the exploitation of single-crystalline nanowires because of their self-orientation in the c-axis direction and ability to accommodate long deformations resulting in high piezoelectric performance. Herein, we show an innovative approach to produce PENGs by combining polycrystalline ZnO layers fabricated at room temperature by plasma-assisted deposition with supported small-molecule organic nanowires (ONWs) acting as 1D scaffolds. Such hybrid nanostructures present convoluted core-shell morphology, formed by a single-crystalline organic nanowire conformally surrounded by a poly-crystalline ZnO shell and combine the organic core mechanical properties with the ZnO layer piezoelectric response. In a step forward towards the integration of multiple functions within a single wire, we have also developed ONW-Au-ZnO nanoarchitectures including a gold shell acting as inner electrode achieving output piezo-voltages up to 170 mV. The synergistic combination of functionalities in the ONW-Au-ZnO devices promotes an enhanced performance generating piezo-currents one order of magnitude larger than the ONW-ZnO nanowires and superior to the thin film nanogenerators for equivalent and higher thicknesses.


April, 2019 | DOI: 10.1016/j.nanoen.2019.01.047

Effect of support oxygen storage capacity on the catalytic performance of Rh nanoparticles for CO2 reforming of methane


Yentekakis, IV; Goula, G; Hatzisymeon, M; Betsi-Argyropoulou, I; Botzolaki, G; Kousi, K; Kondarides, DI; Taylor, MJ; Parlett, CMA; Osatiashtiani, A; Kyriakou, G; Holgado, JP; Lambert, RM
Applied Catalysis B-Environmental, 243 (2019) 490-501

ABSTRACT

The effects of the metal oxide support on the activity, selectivity, resistance to carbon deposition and high temperature oxidative aging on the Rh-catalyzed dry reforming of methane (DRM) were investigated. Three Rh catalysts supported on oxides characterized by very different oxygen storage capacities and labilities (gamma-Al2O3, alumina-ceria-zirconia (ACZ) and ceria-zirconia (CZ)) were studied in the temperature interval 400-750 degrees C under both integral and differential reaction conditions. ACZ and CZ promoted CO2 conversion, yielding CO enriched synthesis gas. Detailed characterization of these materials, including state of the art XPS measurements obtained via sample transfer between reaction cell and spectrometer chamber, provided clear insight into the factors that determine catalytic performance. The principal Rh species detected by post reaction XPS was Rh, its relative content decreasing in the order Rh/CZ(100%) > Rh/ACZ(72%) > Fth/gamma Al2O3(55%). The catalytic activity followed the same order, demonstrating unambiguously that Rh is indeed the key active site. Moreover, the presence of CZ in the support served to maintain Rh in the metallic state and minimize carbon deposition under reaction conditions. Carbon deposition, low in all cases, increased in the order Rh/CZ < Rh/ACZ < Rh/gamma-Al2O3 consistent with a bi-functional reaction mechanism whereby backspillover of labile lattice O2- contributes to carbon oxidation, stabilization of Rh and modification of its surface chemistry; the resulting O vacancies in the support providing centers for dissociative adsorption of CO2. The lower apparent activation energy observed with CZ-containing samples suggests that CZ is a promising support component for use in low temperature DRM.


April, 2019 | DOI: 10.1016/j.apcatb.2018.10.048

Operando Spectroscopic Evidence of the Induced Effect of Residual Species in the Reaction Intermediates during CO2 Hydrogenation over Ruthenium Nanoparticles


Navarro-Jaen, S; Szego, A; Bobadilla, LF; Laguna, OH; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Chemcatchem, 11 (2019) 2063-2068

ABSTRACT

In this work, we present a highly active catalyst based on Ru nanoparticles dispersed on alumina, which showed an unexpected activity for CO2 methanation. This exceptional catalytic behavior was attributed to the presence of residual species that remained on the surface after synthesis. Furthermore, through Operando DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) measurements it was demonstrated that these remaining species provoked an induced effect on the nature of the surface intermediates spectroscopically observed, and consequently on their mechanistic role during the pathway of the CO2 hydrogenation to methane.


April, 2019 | DOI: 10.1002/cctc.201900101

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