Highly Active and Stable Ni/La-Doped Ceria Material for Catalytic CO2Reduction by Reverse Water-Gas Shift Reaction

[EN] The design of an active, effective, and economically viable catalyst for CO2 conversion into value-added products is crucial in the fight against global warming and energy demand. We have developed very efficient catalysts for reverse water-gas shift (rWGS) reaction. Specific conditions of the synthesis by combustion allow the obtention of macroporous materials based on nanosized Ni particles supported on a mixed oxide of high purity and crystallinity. Here, we show that Ni/La-doped CeO2 catalysts─with the "right"Ni and La proportions─have an unprecedented catalytic performance per unit mass of catalyst for the rWGS reaction as the first step toward CO2 valorization. Correlations between physicochemical properties and catalytic activity, obtained using a combination of different techniques such as X-ray and neutron powder diffraction, Raman spectroscopy, in situ near ambient pressure X-ray photoelectron spectroscopy, electron microscopy, and catalytic testing, point out to optimum values for the Ni loading and the La proportion. Density functional theory calculations of elementary steps of the reaction on model Ni/ceria catalysts aid toward the microscopic understanding of the nature of the active sites. This finding offers a fundamental basis for developing economical catalysts that can be effectively used for CO2 reduction with hydrogen. A catalyst based on Ni0.07/(Ce0.9La0.1Ox)0.93 shows a CO production of 58 × 10-5 molCO·gcat-1·s-1 (700 °C, H2/CO2 = 2; selectivity to CO > 99.5), being stable for 100 h under continuous reaction.We acknowledge the financial support of the Spanish Ministry of Science and Innovation (PID2021-123287OB-I00, PID2021-122477-OB-I00, PID2021-128915NB-I00, and RTI2018-101604-B-I00) and of the CSIC through the i-LINK 2021 program (LINKA20408). Financial support has also been received from AEI-MINECO/FEDER (Nympha Project, PID2019-106315RB-I00), “Comunidad de Madrid” regional government, and the European Structural Funds (FotoArt-CM project, S2018/NMT-4367). Authors also acknowledge financial support from the grant PLEC2021-007906 funded by MCIN/AEI/10.13039/501100011033 and the “European Union NextGenerationEU/PRTR”. We are grateful to ILL (France) for making all facilities available. This project also received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 832121. Computer time provided by the RES (Red Española de Supercomputación) resources at the MareNostrum 4 (BSC, Barcelona) node and the DECI resources at the BEM cluster of the WCSS based in Poland with the support from PRACE aislb is acknowledged

Adsorption and reaction of CO on (Pd–)Al2O3 and (Pd–)ZrO2: vibrational spectroscopy of carbonate formation

γ-Alumina is widely used as an oxide support in catalysis, and palladium nanoparticles supported by alumina represent one of the most frequently used dispersed metals. The surface sites of the catalysts are often probed via FTIR spectroscopy upon CO adsorption, which may result in the formation of surface carbonate species. We have examined this process in detail utilizing FTIR to monitor carbonate formation on γ-alumina and zirconia upon exposure to isotopically labelled and unlabelled CO and CO2. The same was carried out for well-defined Pd nanoparticles supported on Al2O3 or ZrO2. A water gas shift reaction of CO with surface hydroxyls was detected, which requires surface defect sites and adjacent OH groups. Furthermore, we have studied the effect of Cl synthesis residues, leading to strongly reduced carbonate formation and changes in the OH region (isolated OH groups were partly replaced or were even absent). To corroborate this finding, samples were deliberately poisoned with Cl to an extent comparable to that of synthesis residues, as confirmed by Auger electron spectroscopy. For catalysts prepared from Cl-containing precursors a new CO band at 2164 cm−1 was observed in the carbonyl region, which was ascribed to Pd interacting with Cl. Finally, the FTIR measurements were complemented by quantification of the amount of carbonates formed via chemisorption, which provides a tool to determine the concentration of reactive defect sites on the alumina surface

An immersion calorimetric study of the interactions between some organic molecules and functionalized carbon nanotube surfaces

The interaction of organic chemicals with the surface of carbon nanotubes has been studied by immersion calorimetry revealing significant differences in the properties when these materials are modified thermally or chemically. Therefore, multiwall carbon nanotubes have been synthesized using a chemical vapour deposition procedure and subsequently aliquots were treated with HNO3 at reflux, maintaining the reaction during different times, in order to incorporate oxygen surface groups, or were treated at 2873 K under inert atmosphere. The aim of this thermal treatment is to eliminate structural defects of the carbon nanostructures and to graphitize the amorphous carbon phases. These features were confirmed by high-resolution transmission electron microscopy. The immersion in organic compounds, including toluene, methanol and methylcyclohexane, of all these carbon nanotubes samples reveals that the surface properties are remarkably modified. Thus, the formation of different types of interaction, depending on the surface, gives place to changes in the immersion enthalpies.E.C. gratefully acknowledges financial support from the Spanish Ministry of Science and Technology and from the CSIC, JAE postdoc programme. To J.M.D. Tascon of INCAR-CSIC, for having kindly provided the Raman spectra and the SEM micrographs, as well as for his valuable discussion of these data. This work was supported by the Spanish Government (project CTQ2011-29272-C04-01 and -03).Peer Reviewe

Catalizadores de Pd soportados en oxido de grafito y en sus derivados exfoliados aplicados en la hidrogenación de 1,3-butadieno

Trabajo presentado en el XXIV Congreso Iberoamericano de Catálisis, celebrado en Medellín (Colombia) del 14 al 19 de septiembre de 2014.Se prepararon dos series de catalizadores de Pd soportados sobre oxido grafitico y sus derivados exfoliados, empleando el método de intercambio y el método de impregnación, y se estudiaron en la reacción de hidrogenación del 1,3-butadieno. En la primera serie se redujeron las muestras a distintas temperaturas y sin exfoliar el oxido grafitico, y se observo un aumento en la actividad y selectividad hacia los productos deseados con la temperatura de reducción. En la segunda serie estudio la influencia de la etapa en la que tenía lugar la exfoliación del soporte sobre el comportamiento catalítico del Pd. Se consiguieron resultados optimizados de selectividad hacia butenos (98%) y en particular hacia el 1-buteno.Se agradece la financiación de este trabajo a cargo de los proyectos CTQ 2011-29272-C04-01 y 03 y del 2011/PUNED/0001.Peer Reviewe

Exploring the insertion of ethylenediamine and bis(3-aminopropyl)amine into graphite oxide

© 2014 The Author(s). Published by Taylor & Francis.The influence of ethylenediamine and bis(3-aminopropyl)amine insertion into graphite oxide using toluene and ethanol–water media was studied by elemental analysis, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetry, temperature-programmed desorption and diffuse reflectance infrared Fourier transform spectroscopy. In every case, amine was incorporated between the basal planes and on the edges of the material through different interactions with epoxy, hydroxyl, carboxyl and carbonyl groups resulting in new-layered materials. Results show that incorporation was homogeneous for ethylenediamine irrespective of the solvent and that the higher level of intercalation in non-polar media was probably a consequence of the inhibition of competitive reactions with the solvent. For bis(3-aminopropyl)amine, the higher reaction times required to obtain satisfactory degrees of intercalation in the non-polar solvent suggests that with this solvent the process is kinetically controlled for longer chain amines.The authors acknowledge the MICINN of Spain (Projects CTQ-2011-29272-C04-01 and -03) for financial support.Peer Reviewe

Green photo-oxidation of styrene over W-Ti composite catalysts

A series of WO3–TiO2 composite catalysts with variable quantities of tungsten was prepared by a single-pot microemulsion procedure and evaluated in the gas-phase selective photo-oxidation of the aromatic hydrocarbon styrene. Samples improve the performance of TiO2 by a factor ca. 3 and increase significantly the selectivity to valuable products (as styrene oxide) upon UV and, more importantly, sunlight-type excitation. Optimum performance in terms of both activity and selectivity was achieved under a sunlight-type renewable energy source. A complete structural (bulk and surface) and electronic characterization using Transmission Microscopy, X-ray diffraction (XRD), X-ray Photoelectron (XPS), Raman, and UV–visible spectroscopies and calorimetry with the help of the ammonia probe molecule was carried out. The study was able to detect and quantify the presence of different W entities as a function of the tungsten content of the catalysts. Three species were found to be present throughout the series; oligomeric W species and WO3 nanoparticles in close contact with anatase-TiO2 and non-contacting WO3 platelets. From a spectro-kinetic analysis carried out with the help of electron paramagnetic resonance (EPR), we provide evidence that these W-containing species play different roles in reaction. Activity and selectivity improvements with respect to the bare titania are intimately related with presence of oligomeric W species at anatase surfaces.A. Kubacka and M.J. Muñoz-Batista thank MINECO for support through, respectively, the postdoctoral, Ramón y Cajal” and predoctoral FPI programs. R.R. wants to acknowledge EU (Project no.UDA-POKL.04.01.01-00-029/10-00) for financial support of a stay at Madrid (ICP-CSIC). Financial support by MINECO is also acknowledged (project CTQ2010-14872/BQU).Peer Reviewe

Design of surface sites for the selective hydrogenation of 1,3-butadiene on Pd nanoparticles: Cu bimetallic formation and sulfur poisoning

Modifications to the selectivity during partial hydrogenation of butadiene over graphite supported Pd nanoparticle catalysts may be achieved by at least three methodologies: (1) by changing the structure of the surface ensembles that constitute the active surface sites by the incorporation of another metallic component, such as Cu in the present case, (2) by self-poisoning of the surfaces by strongly adsorbed carbonaceous intermediates, or carbon deposits, which are very sensitive to the presence of excess hydrogen in the feed during reaction, and (3) by anchoring a sulfur containing compound over the Pd surfaces. A detailed analysis of the selectivity variations yielding 1-butene, cis- or trans-2-butene and undesired butanes is presented in these three cases, and the catalytic data are related to the characterization data of these materials; transmission electron microscopy was used to determine the size of the nanoparticles and X-ray photoelectron spectroscopy to obtain the surface analysis composition. The latter indicates that some electronic modifications on Pd take place.Financial support of the Spanish government by projects CTQ2011-29272-C04-01 and -03 is recognized.Peer Reviewe

Improved performance of carbon nanofiber-supported palladium particles in the selective 1,3-butadiene hydrogenation: Influence of carbon nanostructure, support functionalization treatment and metal precursor

Two types of commercial carbon nanofibers with different graphitic structure, Pyrograph PR24-HHT (NFHHT) and PR24-PS (NFPS) were chemically modified to introduce oxygen groups or SO3H-containing species on their surface. Incorporation of these surface groups was confirmed by temperature programed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Palladium catalysts using these modified supports and PdCl2 as precursor were prepared, and subsequently tested in the partial hydrogenation of 1,3-butadiene under conditions of excess hydrogen. The effect of using a different Pd precursor (PdSO4) was also studied. All the prepared catalysts were characterized by transmission electron microscopy to determine the Pd nanoparticle sizes and by X-ray photoelectron spectroscopy to obtain the surface composition and the oxidation state characteristics of the Pd surface species. The carbon nanofiber structure seems to determine the Pd particle size and morphology, probably due to different metal–support interaction. Selectivities to butenes higher than 95% were obtained with the catalysts prepared on SO3H-modified supports or with the PdSO4 precursor, while over-hydrogenation to butane took place over the Pd on oxidized supports. Catalytic activity–structure correlations have been derived and it is proposed that the catalytic behaviour depends on the type of sulfur species, functional group or adsorbed residual sulfur. Furthermore, variations in 1-butene selectivity and 2-butene trans/cis ratio between the two series of catalysts were also detected and ultimately related to the different nanostructure of the carbon nanofiber.Financial support of the Spanish government by projects CTQ2011-29272-C04-01 and CTQ2011-29272-C04-03 is recognized.Peer Reviewe

Selective 1,3-butadiene hydrogenation by gold nanoparticles deposited & precipitated onto nano-carbon materials

Graphene oxide and multiwall carbon nanotubes (CNTs) were chemically modified by treatment with urea and subsequent annealing at different temperatures. These materials were used as supports for gold nanoparticles and the resulting samples have been applied as catalysts in the 1,3-butadiene partial hydrogenation reaction. The supports and catalysts were exhaustively characterized. It was shown that urea treatments modified the graphene surfaces and the morphology of CNTs, in both cases with incorporation of significant amounts of different nitrogen surface groups. The presence of these groups on few layered graphene or on CNT surfaces modifies the gold precipitation–deposition process during catalyst preparation, giving place to different amounts of incorporated gold on the various supports. The obtained catalytic results suggested that the partial hydrogenation requires limited availability of hydrogen, and for this the migration through adsorbed species between the metal and support to initiate the hydrogenation, probably by a spillover mechanism, seems to be a required step. In general intramolecular selectivity is structure-sensitive meanwhile catalytic activity is not structure-sensitive, as evidenced when the gold nanoparticle sizes are decreased.E C gratefully acknowledges nancial support from the Spanish Ministry of Science and Technology and from the UNED postdoc programme. This work was supported by the Spanish Government (project CTQ 2011-29272-C04-01and 03).Peer Reviewe