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Patino J.,CSIC - Institute of Materials Science | Gutierrez M.C.,CSIC - Institute of Materials Science | Carriazo D.,CSIC - Institute of Materials Science | Carriazo D.,Ikerbasque | And 4 more authors.
Journal of Materials Chemistry A | Year: 2014

Deep eutectic solvents (DESs) composed of resorcinol, 3-hydroxypyridine and tetraethylammonium bromide were used for the synthesis of hierarchical nitrogen-doped carbon molecular sieves. DESs played multiple roles in the synthetic process, as the liquid medium that ensures reagent homogenization, the structure-directing agent responsible for the achievement of the hierarchical structure, and the source of carbon and nitrogen for the solid sorbent obtained after carbonization. Thus, the synthesis offers an economy of reagents that emphasizes the green nature and low cost of conventional polycondensation. Interestingly, while macropores facilitated mass transport and access to the surface area, the combination of the molecular sieve structure and nitrogen functionalization provided, respectively, excellent CO2 adsorption capacities of up to 3.7 mmol g-1, and outstanding CO 2-N2 selectivities of up to 14.4 from single component gas data. Nonetheless, the CO2-N2 selectivity in the Henry law regime-representative of post-combustion flue-gas streams-of some of our carbons was particularly remarkable (e.g. 96), comparable to or even higher than those described for most recent carbons, and only surpassed by those of certain zeolites. This journal is © the Partner Organisations 2014. Source

Rosmaninho M.G.,Federal University of Minas Gerais | Tristao J.C.,Federal University of Minas Gerais | Moura F.C.C.,Federal University of Minas Gerais | Lago R.M.,Federal University of Minas Gerais | And 2 more authors.
Analytical and Bioanalytical Chemistry | Year: 2010

A series of bulk and Al2O3-supported perovskite oxides of the type LaMn1 - x - y Fe x Mo y O3 (x = 0.00-0.90 and y = 0.00-0.09) were synthesized by the citric acid complexation-gelation method followed by annealing in air at 800 °C. For all samples, the local environment and the chemical state and concentration of surface species were determined. Mössbauer spectra revealed the only presence of octahedral Fe3+ ions dispersed in the perovskite structure, however well-crystallized together with a poorly crystalline LaFeO3 phases were detected for larger substitutions (x = 0.90). A similar picture was obtained for Mo-loaded (y = 0.02 and 0.05) samples but a new phase most likely related to Fe3+ ions dispersed aside from the perovskite structure was found for larger substitutions (y = 0.09). Together with these structures, supported samples showed the presence of LaFeO 3 nanoparticles. Finally, photoelectron spectroscopy indicated that the chemical state and composition of the samples in the surface region (2-3 nm) approaches that of the bulk. For the unsupported substituted samples, iron (and molybdenum) enters into the perovskite structure while manganese tends to be slightly segregated. Moreover, in supported perovskites, a fraction of Mo and La atoms interact with the alumina surface. All these oxides were active in methane combustion and best performance was recorded for the Fe-rich composition (x = 0.9) in which both Mn3+ and Mo3+ ions were in the same proportion (y = 0.05). © 2009 Springer-Verlag. Source

Rasmussen S.B.,Institute Catalisis y Petroleoquimica ICP | Banares M.A.,Institute Catalisis y Petroleoquimica ICP | Bazin P.,National Engineering School of Caen | Due-Hansen J.,Technical University of Denmark | And 2 more authors.
Physical Chemistry Chemical Physics | Year: 2012

A monolithic vanadia-titania based catalyst has been subjected to studies with in situ FTIR spectroscopy coupled with mass spectrometry, during the SCR (Selective Catalytic Reduction) reaction. A device based on a transmission reactor cell for monolithic samples was constructed, dedicated to the study of surface species during reaction. After analysing the steady state SCR activity under industrially relevant conditions, NH 3 chemisorption phenomena as a function of temperature and the subsequent SCR reaction of NO + O 2 with chemisorbed ammonia and ammonium ion species were also investigated. The observations reported here serve as a demonstration of the great potential for the application of operando spectroscopy on monolithic systems. This cross disciplinary approach aims to identify reaction pathways, active sites, intermediate- and spectator-species for catalytic reactions under truly industrial conditions in a shaped monolithic catalyst based on monitoring chemical profiles along its channels. In particular, by demonstrating the feasibility of the approach using the technically challenging operando transmission FTIR spectroscopy methodology, we foresee easy future adaption of this approach with other surface or bulk sensitive techniques, e.g. Raman and UV-vis spectroscopy. © 2012 the Owner Societies. Source

Rasmussen S.B.,Institute Catalisis y Petroleoquimica ICP | Rasmussen S.B.,Technical University of Denmark | Perez-Ferreras S.,Institute Catalisis y Petroleoquimica ICP | Banares M.A.,Institute Catalisis y Petroleoquimica ICP | And 2 more authors.
ACS Catalysis | Year: 2013

Porosity is a factor affecting catalyst efficiency in pelletized form. This implies that care should be taken with uncritically relating activity measurements from transmission operando FTIR to final catalyst performance. If the pelletizing pressure is excessive, a destruction of the pore structure of, for example, support oxides might take place, which in turn affects the pore size distribution and the porosity of the catalyst, leading to the observation of lower activity values due to decreased catalyst efficiency. This phenomenon can also apply to conventional activity measurements, in the cases that pelletizing and recrushing of samples are performed to obtain adequate particle size fractions for the catalytic bed. A case study of an operando investigation of a V2O5-WO3/TiO2-sepiolite catalyst is used as an example, and simple calculations of the influence of catalyst activity and internal pore diffusion properties are considered in this paper for the evaluation of catalyst performance in, for example, operando reactors. Thus, it is demonstrated that with a pelletizing pressure of <1-2 ton/cm2, the pore structure is only negligibly altered, and small deteriorations of estimated catalyst efficiencies are observed for first-order kinetic constants lower than 100 mL/gs. However, if the operando study deals with highly active catalysts, it is necessary to consider efficiency losses. A simple procedure for evaluating efficiencies based on pellet dimensions and solid phase characteristics is proposed. The Thiele modulus is directly proportional to the thickness of the pellet, and, thus, inversely related to the catalyst efficiency. As a rule of thumb, we found that for catalytic constants below 100 mL/gs, the maximum thickness of the pellet pressed at 2 tons/cm 2 has to be as low as 80 μm to exhibit catalyst efficiencies above 90%. For catalysts with k' = 10 mL/gs, the value is 260 μm. This strongly underlines the importance of taking internal diffusion limitations into account when working with highly active catalysts. © 2012 American Chemical Society. Source

Lopez-Salas N.,CSIC - Institute of Materials Science | Gutierrez M.C.,CSIC - Institute of Materials Science | Ania C.O.,CSIC - National Coal Institute | Fierro J.L.G.,Institute Catalisis y Petroleoquimica ICP | And 2 more authors.
Journal of Materials Chemistry A | Year: 2014

Since the seminal work by Pekala in 1989, polycondensation of phenol derivatives with formaldehyde and subsequent carbonization has been one of the most used procedures for preparation of porous carbons. Nitrogen-doped carbons have also been obtained through this approach only by using nitrogen-rich precursors. The list of the most commonly used nitrogen-rich precursors includes melamine, urea, 3-hydroxypyridine, 3-aminophenol and lysine, and despite a few of them can be used in a single fashion, they typically need to be co-condensed with a second precursor. Nitrogen-rich precursors different from these ones have been used rarely because their molecular structure does not favor the nucleophilic substitution through which polycondensation takes place-e.g. p-nitrophenol. This is by no means a trivial issue because, on the one hand, these precursors cannot form a cross-linked network by themselves, and on the other hand, it may be difficult to encompass their different reaction kinetics when combined with more reactive precursors. This is also the situation for other precursors with an amphiphilic molecular structure that could be of interest to control the structure of the resulting porous carbons-e.g. 4-hexylresorcinol. In this work, we have used deep eutectic solvents composed of resorcinol, 4-hexylresorcinol, p-nitrophenol and choline chloride for the preparation of nitrogen-doped carbon monoliths with a hierarchical porous structure. Carbon conversions ranged from 64 to 50%-depending on the carbonization temperature-despite using three different carbon precursors for co-condensation and two of them were uncommon. The nitrogen content ranged from 4.9 to 3.0 wt%, revealing an excellent nitrogen-doping efficiency for p-nitrophenol when used in the form of DES. Finally, the use of 4-hexylresorcinol controlled the formation of a narrow microporosity that, in combination with the nitrogen functionalities, provided a remarkable CO2-sorption capability to the resulting carbons. This journal is © the Partner Organisations 2014. Source

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