María Jesús Lázaro

Characterisation of tars from the co-pyrolysis of waste lubricating oils with coal

Abstract Pyrolysis of a lubricating oil waste with or without coal yields important quantities of valuable products such as C 1 –C 3 alkanes, C 2 –C 4 olefins and BTX. However, information on molecular structures of tars obtained is only available in terms of analyses in the GC–MS ranges. This range corresponds to an upper limit of approximately 300xa0u; aromatics of mass greater than 300xa0u do not normally elute from high-temperature GC columns. For this reason, an oil tar, a coal tar and a tar obtained by the co-pyrolysis of the coal and oil (50:50xa0wt%) have been characterised by an array of techniques: probe-mass spectrometry (probe-MS) (to extend the range of mass to 600xa0u); size exclusion chromatography (SEC) in 1-methyl-2-pyrrolidinone (NMP) solvent; matrix-assisted laser desorption ionisation-mass spectrometry (MALDI-MS); and UV-fluorescence spectroscopy (UV-F) to provide specific information on chemical structures of products. Thin-layer chromatography (TLC) was also carried out for three samples of tar (from oil, coal and mixed oil/coal) and fractions recovered from the plates were analysed by other techniques: SEC, UV-F and probe-MS. In addition, the proportion of the tars amenable to gas chromatography was determined; GC–MS was used to determine the main components of each tar within the GC range. In summary, it can be concluded that Samca coal tar is mainly formed by large polynuclear aromatic ring systems, as well as by heterocyclic structures and alkyl or heteroatom substituents. The tar from the coal/oil mixture is much more similar to the tar from oil than to the tar from coal, reflecting the synergy in the co-pyrolysis reaction.

Highly dispersed encapsulated AuPd nanoparticles on ordered mesoporous carbons for the direct synthesis of H2O2 from molecular oxygen and hydrogen.

AuPd nanoparticles (<3 nm) have been encapsulated on the pores of a nanostructured CMK-3 carbon prepared by a nanocasting procedure. This material has been shown to be an excellent catalyst for the direct synthesis of hydrogen peroxide from molecular hydrogen and oxygen.

Low cost catalytic sorbents for NOx reduction - 1. Preparation and characterization of coal char impregnated with model vanadium components and petroleum coke ash

Abstract Spanish coal, char and activated char doped with model vanadium components (V 2 O 5 and NH 4 VO 3 ) and petroleum coke ash (enriched in V, Fe, and Ni) were prepared and characterized as potential catalytic sorbents for NO x reduction. The phase-mineral and chemical composition, content and behavior (capture, retention, distribution, and redistribution) of transition metals, as well as morphogenesis, surface area, acid–base properties, surface active sites and oxidation–reduction transformations of the catalytic sorbents were characterized. It was found that minerals and phases such as anhydrite, calcite, clay minerals, pyrite, pyrrhotite, magnetite and fusinoid-type ingredients have a leading role for the behavior of loaded transition metals. Some original (pyrite, jarosite, shcherbinaite, coulsonite, trevorite, Ni oxide) and newly formed (pyrrhotite, magnetite, wuestite, hematite, paramontroseite, karelianite) Fe, V and Ni minerals in the catalytic sorbents are perspective redox indicators for the physicochemical conditions in such complex system. The data indicate that the V–Fe–Ni containing minerals dispersed onto and into the carbon support may be the most active catalytic sites. The preparation procedure that could provide the most favorable conditions for the production of effective and low cost catalytic sorbents for NO x reduction is also described.

The release of nitrogen during the combustion of coal chars: the role of volatile matter and surface area

Abstract The effect of pyrolysis conditions on the release of nitrogen during char combustion was investigated. A fluidized bed pyrolysis unit was used to produce several chars at different temperatures and pressures from a Spanish coal. In this way, a number of chars differing in volatile matter and specific surface area were obtained. Gas evolution profiles of CO, CO 2 , NO and N 2 from temperature-programmed char combustion were recorded by a thermogravimetric analyser linked to a quadrupole mass spectrometer. The NO evolution profiles show two zones whose intensity depends on the volatile matter and specific surface of the chars. These zones of NO release are attributed to two different nitrogen sources. The fraction of the total nitrogen char released as NO depends on the volatile matter and the specific surface of the chars. The higher the volatile matter and the lower the surface area, the higher the NO/N ratio, i.e. the fraction of the char nitrogen that is released as NO. The nitrogen released as NO + N 2 accounts for nearly all the nitrogen in chars of low surface area and high volatile matter. This is not the case for the chars of high specific surface and low volatile matter, showing that other nitrogen species, probably N 2 O, are formed during oxidation of such chars. The results are discussed on the basis of the mechanisms proposed in the literature for NO release that involve primary NO formation and subsequent reduction to N 2 and N 2 O by CO and char carbon.

Towards new generation fuel cell electrocatalysts based on xerogel–nanofiber carbon composites

Xerogel–nanofiber carbon composites (XNCCs) have been easily synthesized by using a Ni catalyst supported on carbon xerogel (CXG), growing randomly oriented carbon nanofibers (CNFs) within the coralline-like structure of the xerogel (CXG). This novel composite combines the advantages of xerogel and fiber nanostructures. The interactions between these phases as well as their effect as a support on Pt electrocatalysts for the oxygen reduction reaction (ORR) have been investigated. Platinum catalysts supported on different XNCCs (varying in terms of CXG and CNF contents) as well as on bare CXG and CNFs have been synthesized using a microemulsion route. They have been characterized in terms of structure, morphology and porosity and investigated for the ORR in a half-cell configuration. The catalyst supported on the XNCC with a 44% CNF content shows the best electrochemical behavior. This catalyst formulation leads to a catalytic activity 5 times higher than that obtained on a Vulcan-based catalyst at low overpotential and 2.5 times higher at large overpotential. Accelerated degradation tests also show better stability for the composite support-based catalyst. Compared to bare CNF and CXG supports, a stabilization effect is envisaged by the presence of highly graphitic CNFs within the composite structure.

On the importance of the structure in the electrical conductivity of fishbone carbon nanofibers

Carbon nanofibers (CNFs) have a remarkable electrical conductivity resulting highly attractive for different applications such as composites or electronics due to their high quality/price ratio. Although it is known that their graphitic character provides a high conductivity, very little is known about the influence of the nanofibers structure on that property. In this study, CNFs characterized by different physical properties are prepared at diverse synthesis temperatures within a range (550–750xa0°C) in which significant structural and dimensional changes are accomplished and homogeneous nanofiber growth takes place. The electrical conductivity is determined on the powdery as-grown materials modifying the compaction degree by applying pressure. Because of a combination of structural features, the apparent electrical conductivity increases with synthesis temperature of CNFs, ranging from 50xa0Sxa0m−1 for the worst conducting CNFs at a low compaction degree (25xa0% of solid volume fraction) to 3xa0×xa0103xa0Sxa0m−1 for the best conducting CNFs at a high compaction degree (60xa0% of solid volume fraction). Further analysis is carried out applying the percolation theory to analyze the experimental data and the results suggest that both the orientation of the graphenes and the filament diameter distribution play a determining role in the intrinsic electrical conductivity with values in the interval 1.5xa0×xa0103 to 1.3xa0×xa0104xa0Sxa0m−1. These intrinsic values of electrical conductivity are found between one and two orders of magnitude higher than that of the powder, highlighting the also important effect of porosity.

Low cost catalytic sorbents for NOx reduction. 2. Tests with no reduction reactives

Abstract Coal, char and activated char doped with model vanadium compounds (V 2 O 5 and NH 4 VO 3 ) and petroleum coke ash, PCA, (main metal components: V, Fe and Ni) have been tested as catalytic sorbents for NO reduction without the addition of a reduction reactive. The sorbents prepared have shown to be active for NO reduction at temperatures higher than 350xa0°C. The most efficient sorbents are those obtained from unactivated chars and doping with model vanadium compounds or PCA does not upgrade significantly their behaviour. On the other hand, for the samples prepared from activated char, an improvement of the reduction efficiency is observed after impregnation with model vanadium compounds or PCA. SSA of the samples does not play a relevant role on the NO reduction efficiency while surface chemistry significantly affect the samples’ behaviour: higher the CO 2 /CO ratio determined by TPD, higher the NO reduction efficiency of the sample. Slightly higher NO conversions are observed for the samples loaded with pure compounds but PCA is perspective for producing catalyst doped activated carbons.

Platinum Ruthenium Catalysts Supported on Carbon Xerogel for Methanol Electro‐Oxidation: Influence of the Catalyst Synthesis Method

A high surface area, highly mesoporous carbon xerogel was synthesised and used as a support in the preparation of platinum–ruthenium catalysts by different synthetic routes. The platinum–ruthenium carbon xerogel catalysts were physico‐chemically characterised and used for the chemical electro‐oxidation of methanol. The synthetic routes pursued included: 1)u2005impregnation with metal chloride precursors and reduction with two different reducing agents: sodium borohydride and formic acid; 2)u2005a microemulsion‐based method and 3)u2005a sulfite complex method, which led to catalysts with different physico‐chemical features that strongly influence their catalytic behaviour towards methanol oxidation. The electro‐oxidation of methanol was found to depend on both the crystal size and the extent of active phase reduction as well as on the platinum concentration on the catalyst surface, which were maximised for the impregnation method and reduction with formic acid.

Spectroelectrochemical Study of Carbon Monoxide and Ethanol Oxidation on Pt/C, PtSn(3:1)/C and PtSn(1:1)/C Catalysts

PtSn-based catalysts are one of the most active materials toward that contribute ethanol oxidation reaction (EOR). In order to gain a better understanding of the Sn influence on the carbon monoxide (principal catalyst poison) and ethanol oxidation reactions in acidic media, a systematic spectroelectrochemical study was carried out. With this end, carbon-supported PtSnx (x = 0, 1/3 and 1) materials were synthesized and employed as anodic catalysts for both reactions. In situ Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS) indicate that Sn diminishes the amount of bridge bonded CO (COB) and greatly improves the CO tolerance of Pt-based catalysts. Regarding the effect of Sn loading on the EOR, it enhances the catalytic activity and decreases the onset potential. FTIRS and DEMS analysis indicate that the C-C bond scission occurs at low overpotentials and at the same potential values regardless of the Sn loading, although the amount of C-C bond breaking decreases with the rise of Sn in the catalytic material. Therefore, the elevated catalytic activity toward the EOR at PtSn-based electrodes is mainly associated with the improved CO tolerance and the incomplete oxidation of ethanol to form acetic acid and acetaldehyde species, causing the formation of a higher amount of both C2 products with the rise of Sn loading.

N-Doped Carbon Xerogels as Pt Support for the Electro-Reduction of Oxygen

Durability and limited catalytic activity are key impediments to the commercialization of polymer electrolyte fuel cells. Carbon materials employed as catalyst support can be doped with different heteroatoms, like nitrogen, to improve both catalytic activity and durability. Carbon xerogels are nanoporous carbons that can be easily synthesized in order to obtain N-doped materials. In the present work, we introduced melamine as a carbon xerogel precursor together with resorcinol for an effective in-situ N doping (3–4 wt % N). Pt nanoparticles were supported on nitrogen-doped carbon xerogels and their activity for the oxygen reduction reaction (ORR) was evaluated in acid media along with their stability. Results provide new evidences of the type of N groups aiding the activity of Pt for the ORR and of a remarkable stability for N-doped carbon-supported Pt catalysts, providing appropriate physico-chemical features.