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Solid particle number vehicle exhaust measurements necessitate an aerosol conditioning system that removes efficiently volatile particles, does not create artifacts, and minimizes solid nucleation ...

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.

Within the general framework of investigating novel routes for solar hydrogen production, the idea of combining a solar centrifugal particle receiver with sulphur thermochemical cycles, involving SO3 dissociation to SO2 and O2 as key step, is pursued. In this perspective, the present work concerns the synthesis, development, evaluation and characterisation of particles suitable to operate as media for direct solar irradiation absorption, transfer and storage as well as catalysts for the SO3 dissociation reaction. Commercial bauxite-based proppants were modified to incorporate raw materials with elements known for their catalytic activity with respect to the SO3 dissociation, namely iron, copper, manganese and their combinations. The catalytic activity of such modified proppants was tested in fixed bed reactor test rigs at 850 °C and ambient pressure with concentrated liquid sulphuric acid as feedstock. Extensive screening tests complemented by physicochemical properties measurements before and after catalytic testing, identified systems that at 850 °C, 1 atm and Gas Hourly Space Velocity of 11,800 h−1 could achieve high SO3 conversions (60%, corresponding to 68% of equilibrium value) for over 125 h of continuous operation. This performance was achieved without degradation of their mechanical strength which, in fact exhibited a slight increase from 53 N in the fresh state to 55 N after long-term exposure to reaction conditions. However such systems were susceptible to colour alteration, affecting adversely their absorptance in the 1000–2500 nm wavelength range. Compositions with the best combination of properties are scheduled for large-scale synthesis and on-site testing in a pilot-scale solar receiver.

The present study provides a viable route to solar syngas production and conversion to fine chemicals using renewable energy sources and rendering CO2 a valuable reactant instead of a waste. It uses existing facilities and on-going breakthrough technological advancements from CO2 transportation to H2O/CO2 solar co-splitting for syngas formation to further conversion to either methanol or Fischer-Tropsch (FT) products. A full scale simulation of the overall chemical process is established, considering its subsections with respect to all relevant cost elements and operating expenses using appropriate cost correlations. Eight spanning routes of the CO2 superstructure are assessed for a real case of transporting compressed pure or mixtures of CO2 with a 130 kg/s capacity over a distance of 120 km from a power plant in Ptolemaida, Greece, operating with either natural gas or coal, and combining with water from an existing wastewater treatment facility in Thessaloniki, Greece. It is estimated that the choice of producing methanol requires an investment of ˜€7B and ˜€430 M/y to operate, while for FT-related plants it would cost >€3B to build and ˜€190 M/y to operate. Applying a standard feed-in tariff (FIT) value in terms of subsidization of the energy consumed by renewable sources boosts the expenditure resulting for the best case to a yearly net profit of ˜€500 M or ˜€100 M, for methanol or FT products, respectively. Other scenarios are also considered, including the best spanning route for the minimum FIT revenues by the break-even method, or the required carbon price without any subsidization of the proposed schemes.

A tutorial on the use of Side-Stream Reactor (SSR) technology is presented for screening different combustion engine particulate reduction technologies using small-scale filter segments in a well-controlled environment under realistic engine exhaust conditions. The testing examples include the evaluation of particulate filter flow resistance, soot loading, and soot oxidation (regeneration) performance.

A new technique is proposed for the assessment of aggregate morphology based on combined information of aerodynamic and mobility size distributions. Instead of formulating a complex inverse problem having aggregate morphology as unknown, the actual problem is separated to two stages. The aerodynamic distribution is determined directly by the electric low pressure impactor (ELPI) data whereas the morphology is independently assessed by matching the distribution arises from ELPI and from scanning mobility particle sizer (SMPS). The advantage of this approach is that it can estimate different fractal dimension for different aggregate size. The approach is applied to soot aggregates from three different diesel engines. In all cases, a non-monotonic behavior of fractal dimension versus aggregate size is observed. In particular, the fractal dimension initially decreases and then increases (passing through a minimum) as the mobility diameter increases.

Stringent regulation is endorsed to restrict global gaseous and particulate vehicle emissions by adapting advanced catalytic systems on the exhaust, incorporating costly platinum group metals (PGM) for oxidation catalysis. Porous silica and alumina particles are synthesized in the present work via a one-step aerosol spray route. The particles are doped with Pt, Ce and Na and are evaluated with respect to their pore size distribution, exhibiting surface areas between 6-269 m2/gr. The particles have been evaluated in a packed bed reactor with respect to NO oxidation in presence or absence of hydrocarbons (C2H4) in order to study the hydrocarbon inhibition effect on oxidation kinetics, showing higher conversion curves for higher surface area samples. The current work studies also the correlation between reactant accessibility to the in-pore Pt nanoparticles and catalytic activity by reaction kinetic model.

Solar Hydrothermal Liquefaction technology is a relatively novel and less developed area of solar fuels category. It enhances the circular economy by promoting both the environmental sustainability and the production of added value products, since its feedstock is comprised of organic waste and their water content that takes over the double role as reactant and catalyst. The present study focuses on the lab-scale screening of different organic waste in terms of their bio-oil production yield, with an immediate next step being the HTL system coupling with Concentrating Solar Technologies (CST). The relative lab-scale solar experiments will be carried out in APTL/CERTH's high flux solar simulator and solar furnace with the use of a dedicated batch reactor, while pilot-scale experiments will be performed in using a reactor coupled with a parabolic trough system. The feedstocks examined in the current work were peach stones, food waste and dairy waste processed in two different temperatures (300 and 350°C) and two initial pressures (1 and 20 bar) for a retention time of 30 minutes. Based on the findings, GC/MS analysis has shown that the main compounds of the bio-oil consisted of fatty acids, phenols and long-chain alkanes, whereas the primary gas-phase products (GC analysis) were CO2, CO, CH4, C2H4, C2H6, C3H8 and C3H6. Dairy waste had the highest bio-oil yield efficiency (up to 22 wt%), by employing dichloromethane as a solvent at a reaction temperature of 300°C and 1 bar initial N2 pressure. An increase of water/feedstock ratio by adding surplus water had a significantly positive effect on the bio-oil yield with an up to 98% increase.

This work is a first simplified approach on the exploitation of “direct” solar heat during on-sun operation, and stored solar-heat through thermochemical energy storage involving redox pair cycles during off-sun operation, for the production of solar hydrogen using concentrated solar energy. The coupling of the processes in a compact solar reforming–thermochemical heat storage system is conducted in terms of a lumped dynamic model; for the determination of the syngas composition in the reforming unit, thermodynamic equilibrium is assumed, while the required heat to facilitate the endothermic reforming reactions is provided by either solar heat (on-sun operation), or a combination of stored energy and an optimal linear profile of external heat provision (off-sun operation). The optimal heat management policy for the reduction or the oxidation step (during the solar heat storage and release process) ensures a steady H2 molar fraction for most of the operating time. It is revealed that the coupled scheme suggested is an in-principle viable option for sustainable H2 production, since reforming needs are entirely complemented by solar heat also supplying the required energy input for the storage unit, which in turn may provide almost 25% of the overall reforming energy needs under off-sun operation.

The present work relates to the synthesis of iron and iron oxide based particles via Aerosol Spray Pyrolysis; a continuous and scalable aerosol synthesis method. Different process parameters included the temperature of reactor synthesis, flow rate/type of carrier gas and post treatment temperature as well as precursor solution chemistry, concentration, solvent and reactant type and such parameters are evaluated with respect to their effect on the synthesized particles crystallinity, morphology, iron oxidation state and mean particle diameter of produced powders. Three different iron precursor sources are employed: chloride, nitrate and a dispersible gel derived from a steel industry byproduct. Iron nitrate and chloride aqueous solutions were sprayed at four different concentrations in order to evaluate the effect of the nature of the iron precursor salt on the main attributes of the particle synthesized. Particle diameter was calculated theoretically based on models from the literature describing nucleation at the droplet level, while mean diameter of the synthesized particles was experimentally measured on line at the exit of the reactor. Ex situ TEM characterization provided the necessary morphological data to elaborate on the mechanisms of produced particles formation and explain observed deviations from the theoretically calculated mean particle diameter values.

SSCI-VIDE+ING+FRM:NOG:YSC; International audience; In this study, a robust and efficient decentralized fuel processor based on the direct autothermal reforming (ATR) of biogas with a nominal production rate of 50 Nm3/h of hydrogen and a plant efficiency of about 65% was developed and tested. The ATR unit is composed of a structured catalyst support for the biogas reforming close coupled to a catalytic wall-flow filter to retain eventual soot particles.The performance of the conventional random foam and homogeneous lattice supports structures for the production of hydrogen from the ATR reaction was investigated. 15–0.05 wt%-Ni-Rh/MgAl2O4-SiSiC structured catalyst and LiFeO2-SiC monolith were selected for the conversion of biogas to hydrogen and for the syngas post-treatment process, respectively. For all the experiments, a model synthetic biogas was used and the catalytic activities were evaluated in three different experimental facilities: lab bench, pilot test rig and demonstration plant. High methane conversions (>95%) and hydrogen yields (>1.8) reached in the lab bench were also achieved in the pilot and demonstration plant operating at different GHSV.Results of duration test using a foam coupled to the filter has demonstrated that the pre-commercial processor is reliable while offering a satisfactory reproducibility and negligible pressure drop. A thermodynamic equilibrium and a cold gas efficiency of 90% were reached for an inlet temperature of 500 °C, O/C: 1.1 and S/C: 2.0, as predicted with the Aspen simulation.

The present work aims to establish a methodology for the optimization of CO2 transportation networks by developing transportation levelized-cost functions for the mixture CO2:N2 (96:4%) within the ranges {25–2000 kg/s} and {50–2000 km}, locating the optimal solar cities (locations-sinks) to receive CO2 for further transformation into fine chemicals, and mapping the optimal routes which present the minimum transportation and utilization cost. Potential economies of scale of merging same-route sinks into a joint pipeline are scrutinized by selecting 17 CO2 sources from thermal power and combustion stations in the central EU region aggregating almost 3000 kg/s of CO2; these amounts are optimally allocated to 16 available sinks, which combine maximum solar capacity with the least distance to major ports. This study makes use of transport cost correlations, while the solar potential of the most promising solar cities is calculated in detail based on solar intensity databases and solar power plants cost assessment. Mixed-integer nonlinear programming (MINLP) techniques are incorporated in the optimization procedure under sinks capacity constraints. A major conclusion of this work is that for the mass flowrates considered and the sources locations chosen in the current study it is economically beneficial to transfer CO2 directly to the final sinks from the original sources rather than via intermediate sources. The MINLP formulation derives values of solar utilization cost of over €7B and transportation cost of over €2B per year covering transportation pipelines distances of 34,000 km: precise economic estimates of the proposed methodology regarding CO2 transportation and utilization might have significant implications on energy and environmental policy issues on European or global scale.

To prove the usefulness and achieve penetration of microporous ceramic membranes in gas separation applications of industrial interest, their behavior needs to be validated and predicted at relatively realistic conditions. In this respect, the present study employed hybrid silica (HybSi) membranes, modified by chemical vapor infiltration (CVI) in order to render them more selective to hydrogen in hydrogen/carbon dioxide binary mixtures, which are representative to effluent streams of methane or biogas steam reforming/water gas shift processes. Experimental studies with a single modified membrane exhibited high hydrogen permeance (1.5.10−7 mol.m−2.s−1.Pa−1, at 250 °C) and H2/CO2 permselectivity (H2/CO2 = 61.3, at 250 °C). Gas separation tests with binary gas mixtures revealed that high hydrogen purity values (>99%) can be reached at different process conditions. The mathematical model, also developed in this study in order to interpret the experimental results, can reliably predict hydrogen separation process performance over a wide range of operating conditions and also serve as a tool for subsequent optimum process engineering purposes.

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.

Experimental efforts have shown that thermo-chemical heat storage through cyclic hydration/dehydration of the CaO/Ca(OH)2 couple requires efficient CaO-based particles, in terms of both hydration capacity and structural robustness. Acknowledging the challenge caused by high fragmentation of pure CaO particles during multi-cyclic operation in bed reactors, the development of CaO-based materials with enhanced mechanical properties is essential. Promising results have been obtained for nearly spherical structured formulations using kaolinite as binder. The combination of natural limestone with 25 wt% kaolinite rendered mechanically strong materials with a hydration capacity of up to 50% compared to the maximum hydration capacity of pure CaO. These formulations remained intact and showed stable reactivity in the course of 10 hydration/dehydration cycles. In order to obtain valid conclusions for the suitability of these materials for the here suggested reaction scheme, examination upon multiple hydration/dehydration cycles was necessary. The current work is related to the assessment of CaO-kaolinite composite materials under three different evaluation protocols, as well as to the examination of their mechanical properties through crushing strength measurements and attrition tests. For most of the materials examined, more satisfactory results were obtained for hydration and dehydration reactions in vapor-rich atmosphere at 450 and 550 °C, respectively. Multi-cyclic evaluation (50–200 cycles) confirmed the initial findings of the 10-cycle tests. The final selected composition constituted a promising material for the suggested reaction scheme and was qualified as in-principle suitable for long-term operation in pilot scale units.

Solar driven hybrid sulfur-ammonia water splitting cycle (HySA) integrates a solar-photocatalytic hydrogen, H 2 , production step (H 2 sub-cycle) with a high-temperature solar thermochemical oxygen, O 2 , evolution step (O 2 sub-cycle), implementing efficient thermal energy storage as part of the cycle operation. Previous studies of the cycle omitted intermediate products, such as ammonium bisulfate, from the O 2 sub-cycle and, thus, neglected their potential impact on the cycle's chemistry. Also, there are discrepancies in reported literature for the thermodynamic properties of ammonium sulfate, (NH 4 ) 2 SO 4, and ammonium bisulfate, NH 4 HSO 4 . In this study, thermal analysis experiments were conducted in order to determine the phase transition temperatures and enthalpies, and the heat capacity temperature dependence of the ammonium sulfate, (NH 4 ) 2 SO 4, and ammonium bisulfate, NH 4 HSO 4 . Our experimentally determined values for these parameters agree well with the data reported in DIPPR Project 801 database. Moreover, an exploratory thermodynamic analyses was performed using AspenPlus © and FactSage © , that included all potential reaction products, in order to identify critical parameters for an optimum O 2 sub-cycle. A methodology is proposed and evaluated to mitigate AspenPlus © 's deficiency to handle solid phase changes. The thermodynamic analyses demonstrate that the NH 4 HSO 4 inclusion in the O 2 sub-cycle reduces the overall process energy requirements, and allows its use as an energy storage medium. Finally, we show that the use of molten salts, in combination with their interactions, significantly affects the efficiency and the operating conditions of the process, as well as the state of the mixtures.

Solar-driven hybrid sulfur–ammonia water splitting cycle (HySA) is a promising technology for energy and environment applications. The advantage of the proposed cycle is the utilization of both solar photon and thermal radiation in a series of reaction steps from ambient temperature to less than 900 °C. It uses molten salts as reagents to control products of each step and as potential thermochemical energy storage. The use of a solar aerosol based reactor for the thermochemical steps of the cycle appears promising, therefore a particle model is required. Reliable thermodynamic data are necessary to develop an efficient conceptual particle model. Therefore, in this present study, we perform thermal analysis experiments and thermodynamic calculations for the related compounds and their reciprocal mixtures. Based on the experimental and numerical findings, we discuss the conceptual particle model according to the thermochemical steps of the hybrid sulfur–ammonia water splitting cycle.

This study aims at developing a kinetic model that can adequately describe solar thermochemical water and carbon dioxide splitting with nickel ferrite powder as the active redox material. The kinetic parameters of water splitting of a previous study are revised to include transition times and new kinetic parameters for carbon dioxide splitting are developed. The computational results show a satisfactory agreement with experimental data and continuous multicycle operation under varying operating conditions is simulated. Different test cases are explored in order to improve the product yield. At first a parametric analysis is conducted, investigating the appropriate duration of the oxidation and the thermal reduction step that maximizes the hydrogen yield. Subsequently, a non-isothermal oxidation step is simulated and proven as an interesting option for increasing the hydrogen production. The kinetic model is adapted to simulate the production yields in structured solar reactor components, i.e. extruded monolithic structures, as well.

Production of fuel-cell grade hydrogen via reforming of gaseous hydrocarbon fuels requires the design and implementation of efficient formulations, which incorporate high performance materials for the removal of undesired impurities; notably H2S. To this respect, the present study relates to the preparation and parametric evaluation of small-scale honeycomb structured flow-through reactors, coated with an in-house synthesized ZnO/CuO, 50%mol/50%mol, sorbent. Experimental tests involved quantification of the H2S trapping capacity and efficiency of the coated monoliths by monitoring the evolution of H2S concentration at the reactor outlet for known H2S feeds at the reactor inlet. The de-H2S performance of the coated monoliths was examined at reactor temperatures ranging from 160 °C to 400 °C, under two different synthetic mixtures containing a) 30%vol H2, 32%vol H2O, N2 balance and b) 30%vol H2, 32%vol H2O, 6.5%vol CO2, 4.5%vol CO, N2 balance. Space velocities at the reactor ranged from 20,000 to 60,000 h−1 for the experiments designed to examine trapping capacity and from 10,000 to 90,000 h−1 for the experiments designed to examine trapping efficiency. The breakthrough curves obtained proved that the particular formulation can provide a very efficient solution, particularly for the case of decentralized applications, for which system compactness is of prime importance. Total capture capacities up to a targeted H2S breakthrough value of 0.1 ppmv at the reactor outlet varied between 5 and 25 (gsulphur/100 × gsorbent). This value depended on reactor temperature and flow conditions, gas composition, monolith loading and monolith cell density.

Being a relatively new but quite promising field in CSP, thermochemical energy storage could be the next generation solution towards the implementation of baseload cost-effective solar thermal plants. The present work, taking place within the framework of EU-funded project PEGASUS, aims at synthesizing, shaping and experimentally evaluating the catalytic activity and main physicochemical attributes of Fe2O3−based particles. These particles can be exploited as both heat transfer fluid of the CSP plant and highly active catalysts for the key step of the SO3 dissociation reaction to produce SO2 and O2 in the framework of a solid sulfur thermochemical energy storage cycle. The experimental campaign takes place in a purpose-built setup used to evaluate the materials in a fixed bed reactor formulation at a temperature of 850°C and ambient pressure while concentrated liquid sulfuric acid (H2SO4) was used as feedstock. Based on the findings, pure Fe2O3 particles sintered at 950°C offered the most promising compromise between high SO3 conversion on the one hand and crushing strength value (i.e. a preliminary measure of thermomechanical stability) and particles’ color before and after exposure at reaction conditions on the other hand.

The present study relates to the preparation and evaluation of small-scale honeycomb structures as compact reactors/heat exchangers via exploitation of the cobalt/cobaltous oxide (Co3O4/CoO) cyclic reduction–oxidation (redox) heat storage scheme. The structures considered included in-house extruded monoliths (pure cobalt oxide and cobalt oxide/alumina composites) and commercial cordierite substrates coated with Co3O4. The samples were subjected to multi-cyclic redox operation under air flow, in the temperature range of 700–1000 °C. Reduction occurred during heating up to 1000 °C, while oxidation took place during cooling. Redox performance was evaluated on the basis of on-line oxygen release/consumption measurements, while continuous monitoring of imposed air flow reactor inlet/outlet temperatures facilitated the preliminary estimation of heat dissipation in the duration and after completion of the exothermic reaction (oxidation). For all samples, redox performance remained stable in the course of multi-cyclic exposure. In terms of heat transfer, there is strong indication that both composition and the geometry of the honeycomb are important. The pure Co3O4 extruded honeycomb exhibited the highest heat dissipation efficiency but suffered from severe deformation upon multi-cyclic operation. The addition of a small amount of alumina in the aforementioned composition (10% on the basis of total initial mass of oxides), particularly when combined with an increase of the honeycomb wall thickness, substantially improved macro-structural stability upon thermal/redox cycling. The Co3O4-coated cordierite monoliths showed essentially the same normalised redox performance with the pure Co3O4 extruded honeycomb, however the overall heat dissipation achieved was lower. Regarding the effect of redox cycling on the structural stability of studied formulations, pure Co3O4 samples exhibited notable swelling. In the case of the extruded body, this resulted to structural collapse while for the coated cordierite honeycomb, expansion of the coating layer led to partial channels blocking. Based on relevant morphological and structural post-analysis, it was concluded that formation of cobalt aluminate largely reduced swelling intensity.

The present work aims to establish a generic reforming reaction scheme to evaluate the performance of catalytic reforming systems with the aid of a one-dimensional heterogeneous dynamic model. The novelty of the numerical model stems from the direct inclusion of interphase (fluid-to-particle surface), intraparticle (within particle), and intrareactor heat and mass transport resistances under transient conditions. The developed model accounts for the multicomponent gas mixture physicochemical properties and correlations for calculating mass and heat transfer coefficients. Effective macroscopic properties within the particle are calculated by incorporating diffusivities and conductivities of the porous network characteristics accounting for Knudsen and molecular transport as well as tortuosity and porosity of the overall porous path. The industrial case of a steam-methane reforming multitubular reactor was studied as the most representative case of the generic reaction scheme, with all mass/energy resistances present under severe pressure and temperature conditions. It was shown that there are notable diffusional limitations within the particle, whereas there are also temperature and partial pressure gradients due to the heat and mass transport resistances in the particle film layer. It is further demonstrated that the proposed model can be utilized as a versatile design tool for catalytic reactor development and optimization.

The future stringent emission limits and fuel-saving requirements for non-road engines, in particular for the rail sector, require further research investments both on engine and after-treatment technologies. Therefore, the aim of this study is to identify, mainly on a literature data base, the most promising emerging engine technologies (waste heat recovery, turbocharging, etc.) and exhaust after-treatment systems (de-NOx catalyst systems, particulate filters, etc.) for improved fuel efficiency and emissions reduction of rail diesel engines. The considered technologies are currently from production series or under development mostly in the on-road research domain. The approach taken has been to gather available information and data from research and industry sources for the most promising emerging technologies of on-road heavy-duty (HD) engines. The collected data have been properly analyzed and elaborated in order to identify the most transferable data from road to the rail sector. The study is one of the results of a project carried out within the 7th European Framework program in which several academic and industrial partners have participated. Engine side and exhaust after-treatment system side technologies are discussed separately. The former takes into account quantitative data from the literature survey, mainly in terms of fuel efficiency benefits, and summarizes the evaluation in a return on investment calculation on the base of a reference rail engine cost. In the latter, essentially qualitative information has been collected. The analysis has been carried out by means of spider diagrams that are used to show the potential of the grouped after-treatment technologies in terms of pollutant emission reduction, size/weight reduction, technology maturity, and cost reduction. The results indicate that the emerging engine technologies are mostly about engine efficiency improvements, of which waste heat recovery shows the greatest potential in terms of fuel efficiency improvement. On the after-treatment system side, the integration of multiple after-treatment functionalities into a single device is particularly attractive for rail applications because it could significantly decrease space and weight requirements, as could the use of alternative to urea media for ammonia storage in the case of selective catalytic reduction (SCR) system functionalities.

Nanoparticles (NPs), due to their increased application and production, are being released into the environment with unpredictable impact on the physiology of marine organisms, as well as on entire ecosystems and upcoming effects on human health. The aim of the present study was to evaluate and compare the oxidative responses of the mussel Mytilus galloprovincialis after exposure to iron oxide NPs and to iron oxide NPs incorporated into zeolite for 1, 3 and 7 days. Our results showed that both effectors induced changes on animal physiology by causing oxidative stress in hemocytes of exposed mussels compared to control animals. This was shown by the significant increase in reactive oxygen species (ROS) production, protein carbonylation, lipid peroxidation, ubiquitin conjugates and DNA damage. In addition an increase in prooxidant levels as measured by the prooxidant-antioxidant balance (PAB) assay was observed in exposed mussels' hemolymph. The results show that ROS, DNA damage, protein and lipid oxidation, ubiquitin conjugates and PAB could constitute, after further investigation, reliable biomarkers for the evaluation of pollution or other environmental stressors. In addition, more studies are needed in order to ensure the safety of these NPs on various biomedical applications, since it is critical to design NPs that they meet the demands of application without causing cellular toxicity.

A mobile laboratory unit (MOBILAB) with on-board instrumentation (Scanning Mobility Particle Sizer, SMPS; Ambient NOx analyzer) was used to measure size-resolved particle number concentrations (PNCs) of quasi-ultrafine particles (UFPs, 9–372 nm), along with NOx, in road microenvironments. On-road measurements were carried out in and around a large Greek urban agglomeration, the Thessaloniki Metropolitan Area (TMA). Two 2-week measurement campaigns were conducted during the warm period of 2011 and the cold period of 2012. During each sampling campaign, MOBILAB was driven through a 5-day inner-city route and a second 5-day external route covering in total a wide range of districts (urban, urban background, industrial and residential), and road types (major and minor urban roads, freeways, arterial and interurban roads). All routes were conducted during working days, in morning and in afternoon hours under real-world traffic conditions. Spatial classification of MOBILAB measurements involved the assignment of measurement points to location bins defined by the aspect ratio of adjacent urban street canyons (USCs). Source apportionment was further carried out, by applying Positive Matrix Factorization (PMF) to particle size distribution data. Apportioned PMF factors were interpreted, by employing a two-step methodology, which involved (a) statistical association of PMF factor contributions with 12 h air-mass back-trajectories ending at the TMA during MOBILAB measurements, and (b) Multiple Linear Regression (MLR) using PMF factor contributions as the dependent variables, while relative humidity, solar radiation flux, and vehicle speed were used as the independent variables. The applied data analysis showed that low-speed cruise and high-load engine operation modes are the two dominant sources of UFPs in most of the road microenvironments in the TMA, with significant contributions from background photochemical processes during the warm period, explaining the reversed seasonal variation of UFP concentrations, compared to those observed in cities across Northern Europe. It was also demonstrated that town planning exerts a profound effect on the mitigation of traffic emissions.

The thermal reduction step of substituted ferrites (MFe2O4 where M = Fe, Ni, Co, Gd) and doped ceria (MxCe1-xO2, where M = Ce, Zr, Hf and x = 0.25) in two-step thermochemical cycles for H2O and CO2 splitting is investigated within the DFT+U framework. This thermal reduction step is described as the oxygen vacancy formation energy (reduction enthalpy), i.e. the energy required to create an oxygen vacancy in the crystal lattice. Oxides with a lower oxygen vacancy creation energy are easier to reduce. A Bader charge analysis of the reduction mechanism is carried out providing the charge distribution of the bulk and reduced ions, enabling interrelations of the substitute ions and the resulting reduction energies. Based on the approach presented here, interesting solar fuels producing materials are CoFe2O4, NiFe2O4 and Hf0.25Ce0.75O2.

The present study relates to the preparation of mixed calcium oxide–alumina compositions as candidate materials for a cyclic thermochemical hydration–dehydration scheme at moderate to high temperatures (e.g. 400–600 °C) that can offer the possibility of short and long term energy storage, particularly suitable for concentrated solar power installations. The synthesized materials were assessed in terms of their cyclic hydration–dehydration performance in the temperature range of 200–550 °C. Acknowledging the fact that the particular thermochemical scheme has been identified to result in substantial cycle-to-cycle fragmentation of pure CaO particles which is detrimental to particle reactor bed concepts, one of the main purposes of using Al as additive is related to materials structural enhancement. To this respect, preliminary studies related to macro-structural integrity assessment were also conducted. In addition, the performance of synthesized material is compared to the one of natural lime (benchmark material). The additive content spanned over a wide range of Ca/Al molar ratios, namely from 95/5 to 52/48, while two different calcium oxide precursors, i.e. calcium nitrate and calcium acetate, were employed. Fresh and hydrated compositions were characterized in-detail with respect to their physicochemical properties in order to correlate different behaviors with certain attributes of the materials. Synthetic materials, both calcium nitrate and calcium acetate derived, favored the formation of Ca/Al mixed phases. The latter led to materials with higher surface areas and, for a given Ca/Al ratio, resulted to higher hydration/dehydration performance. Mixed oxides, although capable of being hydrated at ambient temperature, did not participate in the reaction scheme at temperatures ⩾200 °C and thus presence of such phases resulted in considerable decrease of hydration/dehydration capacity versus the one of natural lime. On the other hand, the presence of such mixed compositions improved, albeit not dramatically, macro-structural integrity. A relatively good combination of hydration–dehydration performance with better-than-natural lime structural integrity was achieved for the mixed materials with a Ca/Al molar ratio equal to 89/11 and 81/19 molar ratio. The Ca-precursor used in these materials slightly affected their cyclic performance with the ex-CaN ones presenting better behavior.

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 “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,...

The present work is an experimental investigation of commercial diesel fuel liquid desulfurization via adsorption under mild conditions. The sorbent employed was a commercial high surface area activated carbon (AC), and studies involved both laboratory- and pilot-scale experiments performed in dedicated fixed-bed setups. Under laboratory-scale conditions, maximum sulfur removal measured exceeded 90%, while according to breakthrough curves the total sulfur content remained below 2 ppmw for up to 20–22 mL of processed diesel per gram of sorbent. Process scaling-up by a factor of 15 showed a moderate negative effect, with the respective breakthrough fuel amount (total sulfur ≤2 ppmw) being ∼15–17 mL processed fuel/g sorbent. Several sorbent regeneration strategies were studied under laboratory-scale conditions. The one with the highest restoration of initial (i.e., fresh state) AC performance involved heating under vacuum (200 mbara) up to 200 °C and subsequent washing of the material with a binary organic s...

Catalysts for direct soot oxidation in catalyzed diesel particulate filters (CDPFs) consist typically of various mixed oxide compositions (frequently with CeO2 as the dominant component) that assist soot oxidation by enhancing the supply of oxygen from the catalyst to the soot. Apart from the composition, the material morphological characteristics may also contribute to the catalytic activity and this is the motivation for the present study. Different CeO2 nanoparticle catalysts have been obtained employing aerosol-based synthesis (ABS) and sol–gel methods. The obtained catalyst particles have been characterized with respect to their physical and morphological properties as well as with respect to their catalytic soot oxidation activity. The results have been analyzed with the aid of a multi-population kinetics model where soot is found to consist of three fractions reacting with different activation energies, namely 120, 180, and 240 kJ/mol. The occurrence of these three fractions is attributed to the formation of distinct families of surface oxygen complexes (SOCs) on the carbon surface which are subsequently gasified and hence cause soot oxidation, in agreement with accepted mechanisms of soot oxidation in the literature. The CeO2 nanoparticles oxidize catalytically all three fractions of soot, but with different “enhancement factors,” while the activation energies during catalytic oxidation remain the same. A comparison of the catalytic pre-exponentials to those of plain soot shows, in most cases, enhancements, which for some catalysts, can be up to ∼4.5, 6.5, and 2 times larger than those of plain soot, reflecting the relative capacity of the catalyst to generate more of the respective SOCs. The developed approach provides a more detailed but tractable way to describe soot oxidation (plain and catalytic), which can be readily incorporated into simulations of actual emission control systems to increase their reliability.

The EU emission standards for new rail diesel engines are becoming more stringent: stage IV emission targets have just come into effect, while stage V is in under considerations. Both exhaust gas recirculation (EGR) and selective catalytic reduction (SCR) technologies can be used to reduce nitric oxide (NOx) emissions, while the PM emission control requires a diesel particulate filter (DPF). The use of SCR requires on-board storage of urea, while the use of DPF needs to take into account its impact on engine efficiency performance. Both of these technologies require specific studies when applied to the rail engines; in particular, it becomes necessary to evaluate the engine performance trade-offs in order to evaluate how these technologies can be utilized efficiently in rail applications in order to meet current and future emission standards. The present study assesses the application of these technologies in diesel railcars on a quantitative basis using one- and three-dimensional numerical simulation tools. In particular, the study considers a 560-kW railcar engine with the use of different technology combinations for NOx reduction: SCR or EGR + DPF, and EGR + DPF + SCR. The NOx and PM emission performances are evaluated over the C1 homologation cycle and, in the case of the DPF, over an approximated railcar driving cycle as well. Several BSNOx targets were considered: 2 g/kWh, 1 g/kWh, and 0.4 g/kWh. Simulation results indicate that EGR + DPF + SCR-based solution is necessary to achieve stage IV emission limits for the 560-kW engine. On the other hand, SCR-based solutions have the potential to go beyond the stage IV NOx limit through scaling up the size of the SCR device and the on-board urea storage.

The present study deals with the mechanical properties of structured reactors/heat exchangers, for high temperature heat storage via the cobalt oxide cyclic redox scheme. Two different structures (i.e. honeycomb and perforated block) and two different compositions (i.e. 100% cobalt oxide and 90 wt% cobalt oxide – 10 wt% aluminium oxide) were evaluated. During thermal cycling in the range of 800-1000 o C, different loads were applied to the sampleswhile monitoring their length variation. The integrity of the samples was assessed after every cycle. It was found that mechanical strength was substantially improvedupon addition of 10 wt% aluminium oxide. The cobalt oxide/alumina composite presented lower maximal expansion during cycling and exhibited higher integrity, already after one thermal cycle. Another important result is that, for both the honeycomb and the perforated block, the load decreases the over-all sample net expansion. Moreover, the perforated block exhibited lower expansion and better mechanical strength as compared to the honeycomb. Due to the better chemical performance expected to be achieved by the honeycomb structure, a compromise between these two structureshas to be chosen (e.g. honeycomb structure with thicker walls). The results are used for building a thermochemical storage system prototype, implemented for the first time in an existing concentrated solar power facility (STJ).

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.

A methodology is introduced, the Collision Rate Method (CRM), to calculate the friction coefficient of power-law aggregates across the entire momentum-transfer regime. The friction coefficient is calculated via the ratio of two fictitious particle-aggregate collision rates evaluated in the continuum and slip-flow regimes. The effective collision rates are obtained from the numerical solution of the Laplace equation with Robin boundary condition. The methodology was justified by comparing the slip correction factor of straight-chains composed of up to 50 spherical monomers with literature results. We determined the validity of the CRM to lie in an extended slip-flow regime, the maximum monomer Knudsen number being 2. We calculated the adjusted-sphere radius, the radius of a sphere with the same slip correction factor as the chain, in slip flow. We found it to be weakly dependent on flow conditions, as specified by the carrier-gas mean free path, a dependence that leads to a weak effect on calculated slip correction factors. The CRM was combined with the Adjusted-Sphere Method to extend its validity to all Knudsen numbers. Excellent agreement of calculated, straight-chain, slip correction factors with literature values was obtained for monomer Knudsen numbers up to 100. Various characteristic length scales, geometric (equivalent volume radius, radius of gyration) and dynamic (equivalent hydrodynamic and mobility radii), were calculated.

The influence of geometric properties and particle size on mobility properties of fractal-like aggregates was studied in the mass and momentum-transfer transition regimes. Two methodologies were investigated. The Collision Rate Method (CRM) that determines the slip correction factor through the ratio of two fictitious Brownian particle-aggregate effective collision rates, and the Adjusted Sphere Method (ASM) that assumes the existence of a virtual, flow-independent adjusted sphere with the same slip correction factor as the aggregate over the entire transition regime. The simulated fractal-like aggregates were synthetic as they were generated via a cluster–cluster agglomeration algorithm. The CRM was used to calculate the adjusted-sphere radius of various aggregates: we found it to be weakly dependent on the monomer Knudsen number for Kn greater than 0.5. Numerical expressions for the aggregate orientationally-averaged projected area and the adjusted-sphere radius are proposed. Both expressions depend on geometric, non-ensemble averaged quantities: the radius of gyration and the number of monomers. The slip correction factor and the mobility radius of DLCA and RLCA aggregates were calculated using the ASM: for a given number of monomers, fractal dimension and prefactor, and Knudsen number their values were approximately constant (averaged over aggregate realizations). A fractal-like scaling law based on the mobility radius was found to hold. The mobility fractal dimension and prefactor were determined for different aggregates. The hydrodynamic radius, proportional to the friction coefficient, and the dynamic shape factor of DLCA and RLCA aggregates were also calculated.

This study aims at developing a kinetic model that can adequately describe solar thermochemical water and carbon dioxide splitting with nickel ferrite powder as the active redox material. The kinetic parameters of water splitting of a previous study are revised to include transition times and new kinetic parameters for carbon dioxide splitting are developed. The computational results show a satisfactory agreement with experimental data and continuous multicycle operation under varying operating conditions is simulated. Different test cases are explored in order to improve the product yield. At first a parametric analysis is conducted, investigating the appropriate duration of the oxidation and the thermal reduction step that maximizes the hydrogen yield. Subsequently, a non-isothermal oxidation step is simulated and proven as an interesting option for increasing the hydrogen production. The kinetic model is adapted to simulate the production yields in structured solar reactor components, i.e. extruded monolithic structures, as well.