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This work focuses on the investigation of the relationship between structure and oxidation behavior of particulate matter (PM) emitted from different diesel combustion systems. Commercially available graphite and carbon black materials were also studied as representing the soot with the lowest reactivity. An interpretation of the differences of soot oxidation between these materials is attempted based on the carbon morphology and microstructure; thus, various structural parameters, such as the average particle size, specific surface area, degree of nanostructural organization, average crystallite stacking height, fringe length, fringe tortuosity, and surface functional groups, have been opposed to the reactivity of the carbonaceous materials. Small structural differences were observed in between the carbonaceous samples which seem to directly affect the soot reactivity in terms of oxidation. Particulate matter composition (hydrogen-to-carbon ratio, ash content, and volatile matter) appears to have an impact on the soot reactivity.

Structured bodies from redox materials are a key element for the implementation of thermochemical cycles on suitable reactors for the solar H2O splitting. In the current work different configurations of nickel ferrite were investigated with respect to their performance in H2O splitting: i) powder, ii) disk, iii) honeycomb flow-through monoliths. The structured bodies were prepared via pressing and extrusion techniques. The performance of the different structures was affected significantly by differences in the structural characteristics. Alternative approaches involving casting techniques for the structuring of nickel ferrite porous bodies were also investigated. This work constitutes a preliminary attempt towards tuning such characteristics to achieve enhanced and cycle-to-cycle stable production yields.

Car brakes appears to be a significant atmospheric pollutant source, with a contribution to total non-exhaust traffic related PM10 emissions being estimated at approximately 55% in big cities and urban environments (Bukowiecki et al., 2009). Brake wear particle emissions of a minivan running on a chassis dynamometer were measured using a custom sampling system, positioned close to the braking system, under different initial speeds (30km/h and 50km/h), deceleration rates (0.5m/s2 , 1.5m/s2, 2.5m/s2) and ambient temperature (0°C, 15°C and 25°C). Braking from 50km/h to full stop, results in 40-100% more particles compared to 30km/h, depending on the deceleration rate. It was also found that only 9-50% of the total particles emitted, are released during the braking phase and therefore the most significant amount is released on the acceleration phase following. High brake pad temperatures, result in a bimodal distribution with the first peak being at 1μm and the second falling at the nanometer scale at 200 nm. The ambient temperature appears to have a negligible effect on the particle generation.

The Co 3 O 4 /CoO redox system has been recently proposed and is currently under consideration by several research groups as a promising thermochemical heat storage (THS) scheme to be coupled with high temperature Concentrated Solar Power plants. The present work is an investigation of cobalt oxide based honeycomb structures as candidate reactors/heat exchangers in relevant compact and efficient THS systems. The formulations studied included extruded bodies from pure cobalt oxide and two different cobalt oxide/alumina composites (i.e. 95/5 wt% and 90/10 wt%) as well as cobalt oxide-coated cordierite honeycombs with two different loadings (i.e. 28% and 65%). The structures were evaluated with respect to their redox performance in the course of 5 successive cycles in the temperature window of 800-1000 o C and under air flow. Based on measured oxygen evolution profiles, honeycombs from pure cobalt oxide and cobalt oxide-coated cordierites exhibited very similar normalized (i.e. μmol O 2 /g Co 3 O 4 ) redox performance. On the other hand, the addition of alumina had a moderately negative effect on normalized redox performance versus the two aforementioned formulations but contributed to the substantial increase of the honeycombs structural stability when compared to the extruded pure cobalt oxide monolith. The particular finding was based on performing, in a separate experimental setup, 10 redox cycles under idealized (i.e. no imposed loads) conditions. Pre- (i.e. fresh/calcined) and post-characterization (i.e. after 10 redox cycles) of extruded structures via mercury porosimetry revealed measurable decrease of bulk density and increase of mean pore size, indicating a net structure expansion/‘swelling’ effect.

Ce-based materials, that have been extensively investigated for catalytic applications, such as in automotive emission control and more specifically in the oxidation of diesel soot particles, were evaluated with respect to their performance on CO2 splitting. DFT calculations assisted towards the synthesis of two Zr-doped Ce-oxide formulations (Zr content: 20% and 40% respectively) via the LPSHS method. The materials were evaluated with respect to their CO2 splitting activity and compared with other Ce-Zr-based reference oxides. The most active materials were further evaluated under different CO2 splitting temperatures in the range of 800-1480oC in the course of successive redox cycles. The effect of thermal reduction temperature (T: 1480oC and 1600oC) on the most active material was also assessed. The Ce-based oxide formulation with the best performance (Ce0.8Zr0.2O2) was further investigated with respect to its activity towards H2O splitting. In addition, a porous flow-through structure consisting entirely of Ce0.8Zr0.2O2 was manufactured and the resulted body was also evaluated and compared to the respective powder in terms of its CO2 and H2O splitting ability.

The “holy grail” of solar chemistry and solar engineering, is the technical storage of solar energy into a more easily transformable and transportable form, namely an energy carrier such as H2. The two-step redox-based solar thermochemical H2O splitting cycle is considered to be among the most promising approaches for the production of H2 from entirely renewable sources (solar energy and water). In this redox cycle an active material is initially reduced thermally under inert atmosphere and at the next step it is oxidized from H2O producing H2. The materials that have been in the core of solar chemistry research are metal oxides such as ferrites, cerium oxides, perovskites, etc. The reactor types that are being investigated for the redox thermochemical splitting of H2O are either powder-particle reactors or structured reactors. In the current work Ni-ferrite and Ce-oxide structured into different monolithic bodies (honeycombs, foams) were evaluated w.r.t. their redox activity. Based on this investigation, the most promising structure was further scaled-up for the construction of the full-scale reactors of the HYDROSOL-PLANT solar plant installation.The “holy grail” of solar chemistry and solar engineering, is the technical storage of solar energy into a more easily transformable and transportable form, namely an energy carrier such as H2. The two-step redox-based solar thermochemical H2O splitting cycle is considered to be among the most promising approaches for the production of H2 from entirely renewable sources (solar energy and water). In this redox cycle an active material is initially reduced thermally under inert atmosphere and at the next step it is oxidized from H2O producing H2. The materials that have been in the core of solar chemistry research are metal oxides such as ferrites, cerium oxides, perovskites, etc. The reactor types that are being investigated for the redox thermochemical splitting of H2O are either powder-particle reactors or structured reactors. In the current work Ni-ferrite and Ce-oxide structured into different monolithic bodies (honeycombs, foams) were evaluated w.r.t. their redox activity. Based on this investigation,...

Redox-pair-based thermochemical cycles are considered as a very promising option for the production of hydrogen via renewable energy sources like concentrated solar energy and raw materials like water. This work concerns the synthesis of various spinel materials of the iron and aluminum families via combustion reactions in the solid and in the liquid-phase and the testing of their suitability as redox-pair materials for hydrogen production by water splitting via thermochemical cycles. The effects of reactants' stoichiometry (fuel/oxidizer) on the combustion synthesis reaction characteristics and on the products' phase composition and properties were studied. By fine-tuning the synthesis parameters, a wide variety of single-phase, pure and well crystallized spinels could be controllably synthesized. Post-synthesis, high-temperature calcination studies under air and nitrogen at the temperature levels encountered during solar-aided thermochemical cyclic operation have eliminated several material families due to phase composition instabilities and identified among the various compositions synthesized NiFe 2 O 4 and CoFe 2 O 4 as the two most suitable for cyclic water splitting – thermal reduction operation. First such thermochemical cyclic tests between 800 and 1400 °C with NiFe 2 O 4 and CoFe 2 O 4 in powder form in a fixed bed laboratory reactor have demonstrated capability for cyclic operation and alternate hydrogen/oxygen production at the respective cycle steps for both materials. Under the particular testing conditions the two materials exhibited hydrogen/oxygen yields of the same magnitude and similar temperatures of oxygen release during thermal reduction.

The present work describes the realisation and successful test operation of a 100 kW pilot plant for two-step solar thermo-chemical water splitting on a solar tower at the Plataforma Solar de Almeria, which aims at the demonstration of the feasibility of the process on a solar tower platform under real conditions. The process applies multi-valent iron based mixed metal oxides as reactive species which are coated on honeycomb absorbers inside a receiver–reactor. By the introduction of a two-chamber reactor it is possible to run both process concepts in parallel and thus, the hydrogen production process in a quasi-continuous mode. In summer 2008 an exhaustive thermal qualification of the pilot plant took place, using uncoated ceramic honeycombs as absorbers. Some main aspects of these tests were the development and validation of operational and measurement strategy, the gaining of knowledge on the dynamics of the system, in particular during thermal cycling, the determination of the controllability of the whole system, and the validation of practicability of the control concept. The thermal tests enabled to improve, to refine and finally to prove the process strategy and showed the feasibility of the control concept implemented. It could be shown that rapid changeover between the modules is a central benefit for the performance of the process. In November of 2008 the absorber was replaced and honeycombs coated with redox material were inserted. This allowed carrying out tests of hydrogen production by water splitting. Several hydrogen production cycles and metal oxide reduction cycles could be run without problems. Significant concentrations of hydrogen were produced with a conversion of steam of up to 30%.

The present work concerns the synthesis of various single and mixed oxide materials and their study as catalysts for the sulfuric acid dissociation reaction via which the production of SO2 and O2 is achieved. This is the most energy intensive step of sulfur-based thermochemical cycles for the production of hydrogen. Commercial (i.e. FeO, Fe3O4 ,F e2O3, CuO, Cr2O3, g-Al2O3, Pt/g-Al2O3) and in-house binary and ternary compositions of the CueFeeAl system as well as FeeCr mixed oxide materials prepared by the Solution Combustion Synthesis (SCS) technique were comparatively tested. The materials were studied in

The present study deals with Aerosol Spray Pyrolysis (ASP) synthesis of two families of nanostructured redox materials targeted to two different environmental applications: transition-metal-doped ferrites and base metal-doped cerium oxide, used for hydrogen production through solar-assisted water splitting and for catalytic soot oxidation, respectively. The synthesized powders were characterized with respect to their phase composition, morphology and particle size distribution by XRD, SEM and TEM analysis, which have shown their nanostructured character. Doped ferrites were evaluated, with respect to their hydrogen production activity from water dissociation, in an in-house built water-splitting testing rig. ASP materials proved to be very active water splitters demonstrating higher water conversion and hydrogen yields than materials of the same composition synthesized through Solid State Synthesis (SSS), with material performance depending on the dopants’ kind and stoichiometry. Base metal-doped cerium oxides were evaluated with respect to their direct soot oxidation activity, via Thermogravimetric Analysis (TGA), as well as on a diesel engine bench under realistic conditions. It was found that doping improves their activity and that they enhance soot oxidation at lower temperatures compared to materials synthesized through Liquid Phase Self-propagating High temperature Synthesis (LPSHS).

The increasing need for controlled diesel engine emissions and the strict regulations in the abatement of diesel exhaust products lead to an ever increasing use of Diesel Particulate Filters (DPFs) in OEM applications. The periodic regeneration of DPFs (oxidation of soot particles) demands temperatures that rarely appear during engine operation. It is therefore necessary to employ direct or indirect catalytic measures. In the present work, the development and synthesis via aerosol-based routes, of nanostructured base metal oxides for direct soot oxidation, along with their characterization and their evaluation in engine exhaust is described. The synthesized powders were characterized with respect to their phase composition and morphology. XRD, SEM and TEM analysis have shown the nanostructured character of the powders, while Raman spectroscopy was employed for the preliminary characterization of the materials surface chemistry. The catalytic activity of the materials on soot oxidation was evaluated via thermogravimetric analysis (TGA). It was found that they have increased soot oxidation activity at lower temperatures than materials synthesized through a liquid phase route (Liquid Phase Self-propagating High temperature Synthesis, LPSHS). Powders with best catalytic activities were deposited on porous filter structures and were subsequently tested on an engine bench for the evaluation of their catalytic activity under realistic conditions.

HycycleS was a cooperation of nine European partners and further non-European partners and aimed at the qualification and enhancement of materials and components for key steps of solar and nuclear powered thermochemical cycles for hydrogen generation from water. The focus of HycycleS was the decomposition of sulphuric acid (H2SO4) which is the central step of the sulphur-based family of those processes. Emphasis was put on materials and components for H2SO4 evaporation, decomposition, and sulphur dioxide separation. The suitability of materials and components was demonstrated by decomposing H2SO4 and separating its decomposition products in scalable prototypes. Silicon Carbide (SiC) turned out as the material of choice for the components facing the most corrosive environment of the process: the sulphuric acid evaporator and decomposer. Candidate catalysts for the high temperature reduction of sulphur trioxide have been screened and analysed. Cr-Fe mixed oxide (Fe 0.7Cr1.3O3) was the most promising material among the ones examined. Based on the use of the highlighted construction and catalyst materials prototype decomposers have been developed and tested. The successful fabrication and testing of a large size heat exchanger/reactor prototype composed of SiC plates shows promise with respect to its use for H2SO4 decomposition in the SI and HyS cycle. A solar specific decomposer prototype was developed, realised and successfully tested on sun in a solar furnace. A novel approach of using dense oxygen transport membranes, made from complex ceramics, for oxygen removal from the H 2SO4 decomposition product in order to shift the equilibrium in favour of increased decomposition was investigated. The membranes stability and suitability for carrying out this separation was investigated experimentally. Parallel to this, a conventional oxygen separator, a low-temperature wet scrubbing system, was investigated as well. Scale-up scenarios of components and of the process were addressed. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Solar methane dissociation appears as a possible route toward a hydrogen-based economy. The competitiveness of the process strongly depends on the carbon black properties and economic value. At CNRS-PROMES, a 50 kW tubular solar reactor was developed to produce carbon black and hydrogen from methane. The reaction was carried out in a graphite receiver crossed by seven graphite tubes heated up by concentrated solar radiations at the 1 MW CNRS solar furnace. The temperatures ranged between 1608 K and 1928 K and the methane flow-rates varied from 10.5 to 21 NL/min. Total methane dissociation was reached with hydrogen yield higher than 80% and the carbon yield was drastically affected by the acetylene by-product. The carbon samples were analysed in detail and their properties were compared to a commercial conductive grade carbon black. Transmission electron microscopy showed primary particles of 10–70 nm diameter. The crystallinity of the samples was characterised by Raman spectroscopy. It was also possible to correlate the specific surface area with the reaction temperature and with the concentrations of residual methane and of the acetylene by-product. The resistivity and the structure of the agglomerates were determined by simultaneous measurements of the conductivity and the density under compression.

Within the framework of the recent trend to identify efficient ways of producing solar syngas (CO/H 2 ), the two-step redox based solar thermochemical water dissociation cycle, already employed at a semi-pilot scale for the renewable production of H 2 , can be modified to include CO 2 and/or combined CO 2 /H 2 O splitting. The present work relates to Ni-ferrite, as candidate redox material to be employed in Concentrated Solar Power (CSP)-aided thermochemical processes for CO 2 and CO 2 /H 2 O splitting for the renewable production of CO and syngas respectively. The mixed oxide was synthesized via the Self-propagating High temperature Synthesis (SHS) method and subsequently calcined under air at 1400 o C for 1 h. Upon calcination, the material obtained the single phase spinel structure. The material was tested, in the form of powder and as a small cylinder-shaped porous structured body, in a lab-scale fixed bed reactor. The experimental protocol involved a thermal activation step of the material for 1 h at 1400 o C under N 2 flow, the CO 2 or CO 2 /H 2 O splitting step at 1100 o C for 30 min, which resulted in the production of CO or CO/H 2 respectively and the thermal reduction step under N 2 at 1400 o C for 30 min. The effect of CO 2 concentration in the feed gas (4%-100%) was investigated in two-cycle experimental runs. In addition, a preliminary durability test was conducted under pure CO 2 flow for 8 consecutive splitting and thermal reduction steps. Co-feeding of H 2 O and CO 2 was also conducted for two different compositions; 8%H 2 O/4% CO 2 /N 2 and 16%H 2 O/8% CO 2 /N 2 ). The porous structured body showed somewhat lower yield, in terms of CO 2 splitting, compared to the powder.

The present work relates to the investigation of cobalt and manganese oxide based compositions as candidate materials for the storage of surplus energy, available in the form of heat, generated from high temperature concentrated solar power plants (e.g. solar tower, solar dish) via a two-step thermochemical cyclic redox process under air flow. Emphasis is given on the utilization of small structured monolithic bodies (flow-through pellets) made entirely from the two aforementioned oxides. As compared to the respective powders, and in addition to the natural advantage of substantially lower pressure drop that monolithic structures can offer, this study demonstrated that structured bodies can also improve redox kinetics to a measurable extent. Cobalt oxide was found to be superior to manganese oxide both from an estimated energy density and from a redox reactions kinetics point-of-view. Among the redox conditions studied, the optimum reduction-oxidation operating window for the former oxide was determined to be in the range of 1000-800 °C, while for the latter material no clear conclusion was drawn with reduction reaching its maximum extent at 1000 °C and oxidation occurring in the range of 500-650 °C. In both cases, no significant degradation of redox performance was observed upon cyclic operation (up to 10 cycles), however manganese oxide showed notably slower oxidation kinetics.