Catalyst Sheets Research Articles

EXPERIMENTAL INVESTIGATION OF PAR DEVICE FOR HYDROGEN RECOMBINATION IN REKO-4 FACILITY

The Fukushima accident has proved that passive safety systems in reactors are necessary to avoid hydrogen accumulation. One of these systems are PAR (passive autocatalytic recombiner) to remove the hydrogen gases inside the containment in case of an accident. This paper aims to investigate a PAR device with catalyst sheets to calculate the hydrogen consumption, determine the temperature distribution, and PAR performance in the test facility. Test series were carried out in the test facility REKO-4 under atmospheric pressure and natural flow conditions. For the test purposes, hydrogen between 2.0 and 6.0 vol.% was injected into the vessel with the volumetric flow, 1.9 m3/h. The first rise in the temperature of the PAR inlet was found after 100 seconds of first hydrogen injection, this result demonstrated that hydrogen consumption started. The results from the test series show that the PAR device can remove hydrogen and the PAR performance can be determined from the test results.

Constructing flexible and self-standing electrocatalyst for oxygen reduction reaction by in situ doping nitrogen atoms into carbon cloth

Nitrogen doped carbon materials have attracted tremendous attention as the promising candidates for platinum-based catalysts toward oxygen reduction reaction (ORR). Herein, we report a facile preparation of N-doped carbon cloth (Co-N-OCC) as a flexible and self-standing electrocatalyst toward ORR by calcining oxidized carbon cloth coated with cobalt ions in ammonia atmosphere. The pyridinic N, Co-N and pyrrolic N, related to ORR activity, are the dominant configurations of nitrogen with an atomic ratio of 42.27%, 25.36% and 20.29% in the catalyst. The resulting Co-N-OCC shows favorable ORR activity with an onset potential of 0.87 V vs. RHE, an electron transfer number of 3.57, and good methanol tolerance in alkaline electrolyte. Co-N-OCC catalyst sheets were directly assembled in zinc-air battery as catalyst and current collector of cathode. The ORR catalytic performance of Pt/C is further boosted in a zinc-air battery by using the Co-N-OCC sheet as an electrode substrate.

Visible light photoelectrocatalysis for wastewater treatment using bifacial N-TiO2/Graphene/Ho2O3/Titanium nanocomposite: Artificial neural network modeling and evaluation of ozone addition

In this paper, N-TiO2/Graphene/Ho2O3/Titanium bifacial nanocomposite electrode was prepared. First, the effect of Ho2O3 to N-TiO2 wt.% in the nanocomposite preparation matrix was investigated through studying visible light photoelectrocatalysis process in industrial wastewater decolorization. Characterizations of optimum catalyst were performed using DRS, XRD, SEM and EDX analyses. Then, the effect of operating variables i.e. catalyst dosage (electrode number(s)), wastewater pH, applied bias potential, visible light power and contact time on the extent of wastewater decolorization was investigated by the visible light photoelectrocatalysis process. It was observed that almost 80% wastewater decolorization was achieved using the photoelectrocatalysis at the optimum conditions by N-TiO2/Graphene/(10%) Ho2O3. Artificial neural network was used for model the photoelectrocatalysis process and determine the relative importance of investigated operating variables. It was also established that combination of photoelectrocatalysis with ozonation yielded 100% decolorization in 90 min and 96% COD removal in 270 min under the optimized conditions. Moreover, the catalyst sheet was enough stable to be used in all wastewater treatment experiments.

Wastewater Treatment from Batik Industries Using TiO2 Nanoparticles

Batik is cultural patterned fabric, and the this industries produce wastewater that can pollute the aquatic environment. Besides dyes, batik wastewater also contains synthetic compounds that are hard degraded, such as heavy metals, suspended solids, or organic compounds. In this study, photocatalitic membrane TiO2 coated plastic sheets have been used to degrade batik wastewater under solar exposure. A total of 8 pieces of catalyst sheets are added on 1000 ml of the waste, and managed to degrade 50.41% of the initial concentration during 5-days irradiation. In this study, several parameters of the water quality such as chemical oxygen demand (COD), biological oxygen demand (BOD), and total suspensed solids (TSS) of the wastewater were observed to be decreasing during photodegradation process. The catalyst sheet also is stable to be used repeatedly in wastewater treatment.

Reviewer Acknowledgment

Accidents at TMI, USA and Fukushima, Japan have emphasized the need for hydrogen mitigation during nuclear plant accidental conditions, especially during severe accidents which will be no power, massive hydrogen, high temperature, long-term operation, and poisoning environment. Passive autocatalytic recombiners with catalyst sheets are the promising way to deal with the situation in severe accidents. Here we report a new kind of catalyst sheets based on stainless steel supported Pd nanoclusters prepared by electroless deposition route. The catalyst sheets were characterised for morphology and composition of surface by SEM and EDS. The catalytic activity of the catalyst sheets has been evaluated under the conditions of higher temperature, long-term operation and poisoning environments. The catalyst sheets showed high activity and good stability either operating above 500 °C for 24 h or continuous operating for 25 days. For the obtained catalyst sheets after exposed to methanal, iodine vapor and BaSO4 aerosol respectively with corresponding concentrations higher than SA conditions, the start-up time for H2-O2 recombination reaction was less than 1 min and the catalytic efficiency was more than 90%. These results indicate the potential application of this type of catalyst sheets for hydrogen mitigation in severe accidents.

Supported Pd nanoclusters for the hydrogen mitigation application in severe accidents

Accidents at TMI, USA and Fukushima, Japan have emphasized the need for hydrogen mitigation during nuclear plant accidental conditions, especially during severe accidents which will be no power, massive hydrogen, high temperature, long-term operation, and poisoning environment. Passive autocatalytic recombiners with catalyst sheets are the promising way to deal with the situation in severe accidents. Here we report a new kind of catalyst sheets based on stainless steel supported Pd nanoclusters prepared by electroless deposition route. The catalyst sheets were characterised for morphology and composition of surface by SEM and EDS. The catalytic activity of the catalyst sheets has been evaluated under the conditions of higher temperature, long-term operation and poisoning environments. The catalyst sheets showed high activity and good stability either operating above 500°C for 24 h or continuous operating for 25days. For the obtained catalyst sheets after exposed to methanal, iodine vapor and BaSO4 aerosol respectively with corresponding concentrations higher than SA conditions, the start-up time for H2-O2 recombination reaction was less than 1 min and the catalytic efficiency was more than 90%. These results indicate the potential application of this type of catalyst sheets for hydrogen mitigation in severe accidents.

Batik Wastewater Treatment Using TiO2 Nanoparticles Coated on the Surface of Plastic Sheet

Batik is one of Indonesian cultures in the form of patterned fabric. As the rest of the coloring process, batik industries produce wastewater that can pollute the aquatic environment. Besides dyes, batik wastewater also contains synthetic compounds that are hard degraded, such as heavy metals, suspended solids, or organic compounds. In this study, TiO2 coated plastic sheets have been used to degrade batik wastewater under solar exposure. A total of 8 pieces of catalyst sheets are added on 1000ml of the waste, and managed to degrade 50.41% of the initial concentration during 5-days irradiation. In this study, several parameters of the water quality such as chemical oxygen demand (COD), biological oxygen demand (BOD), and total suspensed solids (TSS) of the wastewater were observed to be decreasing during photodegradation process. The catalyst sheet also is stable to be used repeatedly in wastewater treatment.

A First Orienting Investigation of the Interaction of Cable Fire Products with Passive Autocatalytic Recombiners

Passive autocatalytic recombiners (PARs) have been installed inside light water reactor containments in many countries to remove hydrogen and, thus, to mitigate the combustion risk during a severe accident (SA). Due to the challenging SA boundary conditions, PARs are exposed to several deactivation risks during operation, which may cause a reduction of the hydrogen removal capacity. Such a deactivation may occur through different mechanisms and could in principle affect the start-up behavior up to the full loss of catalytic activity. To assess the interaction of PARs with the products of cable fires, a set of PAR catalyst samples has been introduced to the atmosphere of cable fire tests performed at Institut de Radioprotection et de Sûreté Nucléaire (IRSN), France. The subsequent surface analyses performed at Forschungszentrum Jülich (Germany) reveal a significant amount of carbon, chlorine (a constituent of polyvinyl chloride), zinc, and antimony (a flame retardant) on all catalyst samples compared to reference samples. The subsequent performance tests confirm that all catalyst sheets suffer a significant start-up delay of between 17 and 45 min compared to the reference samples. However, after burning off the soot deposition, the catalyst samples reach full conversion capacity and show immediate start-up behavior in a subsequent test. The present results clearly demonstrate the adverse effect of cable fire products on the efficiency of hydrogen conversion in a PAR. To further understand and quantify the impact of cable fire products and to assess their relevance for SA scenarios, further experimental as well as theoretical investigations are required. In particular, the combined influence of cable fire products and humidity, which has intentionally been omitted in the present study, should be investigated in the future due to the possible corrosive impact on the catalyst as well as the influence of humidity on the nature of the soot deposition.

Start-up behaviour of a passive auto-catalytic recombiner under counter flow conditions: Results of a first orienting experimental study

A downward directed wall-near flow represents a typical thermal hydraulic condition inside the LWR containment during a severe accident. In order to efficiently remove hydrogen released into the containment, passive auto-catalytic recombiners (PARs) located close to the containment wall have to establish an internal upward directed chimney flow against this counter flow.In cooperation between RWTH Aachen and the Research Center Jülich, the effect of a downward directed flow on the PAR start-up has been investigated in the REKO-4 test facility at Jülich. The test series includes experiments with identical boundary conditions performed under counter flow conditions as well as in quiescent atmosphere as reference case.Under counter flow conditions, an earlier local start-up of the catalytic reaction on the upper edge of the catalyst sheets was observed. However, the establishment of full PAR operation required more time compared to the reference case. This delay is attributed to a partial inflow of the counter flow into the PAR outlet which interferes with the establishing of a chimney flow promoted by the exothermal catalytic reaction. Once a developed chimney flow inside the PAR is established, no negative effect on the PAR performance could be observed. As expected, the counter flow mixes immediately with the PAR outlet flow dissolving the characteristic plume of hot gases at the PAR outlet.

Optimization of a heterogeneous catalytic hydrodynamic cavitation reactor performance in decolorization of Rhodamine B: Application of scrap iron sheets

A low pressure pilot scale hydrodynamic cavitation (HC) reactor with 30L volume, using fixed scrap iron sheets, as the heterogeneous catalyst, with no external source of H2O2 was devised to investigate the effects of operating parameters of the HC reactor performance. In situ generation of Fenton reagents suggested an induced advanced Fenton process (IAFP) to explain the enhancing effect of the used catalyst in the HC process. The reactor optimization was done based upon the extent of decolorization (ED) of aqueous solution of Rhodamine B (RhB). To have a perfect study on the pertinent parameters of the heterogeneous catalyzed HC reactor, the following cases as, the effects of scrap iron sheets, inlet pressure (2.4–5.8bar), the distance between orifice plates and catalyst sheets (submerged and inline located orifice plates), back-pressure (2–6bar), orifice plates type (4 various orifice plates), pH (2–10) and initial RhB concentration (2–14mgL−1) have been investigated. The results showed that the highest cavitational yield can be obtained at pH 3 and initial dye concentration of 10mgL−1. Also, an increase in the inlet pressure would lead to an increase in the ED. In addition, it was found that using the deeper holes (thicker orifice plates) would lead to lower ED, and holes with larger diameter would lead to the higher ED in the same cross-sectional area, but in the same holes’ diameters, higher cross-sectional area leads to the lower ED. The submerged operation mode showed a greater cavitational effects rather than the inline mode. Also, for the inline mode, the optimum value of 3bar was obtained for the back-pressure condition in the system. Moreover, according to the analysis of changes in the UV–Vis spectra of RhB, both degradation of RhB chromophore structure and N-deethylation were occurred during the catalyzed HC process.

Development of Alternated Catalyst Layer Structure for PEM Fuel Cells

A novel alternated catalyst layer structure (ACLS) has been developed for fuel cell applications. Sputtering process was applied directly on commercial gas diffusion layer (GDL) by depositing catalyst-forming material and pore-forming material alternately in a nanometer- scale and then removing the pore-forming material. The main physical features of the ACLS are (1) carbon-free and support-free (2) a large amount of void layers/pores, (3) sheet-like catalyst with extended surface and compressed lattice, and (4) a large amount of <111> crystalline planes parallel to catalyst sheet surface. Such characteristics make the ACLS a promising candidate for the PEM cathode application. In this report, some basic evaluation results of the ACLS cathode are presented. Electrochemical surface area (ECSA) evaluations showed that the typical ACLS exhibited a value of 15~30 m2/g and had a high Pt utilization efficiency. For oxygen reduction reaction activity (ORR), the measurement on 5 cm2 fuel cell membrane electrode assemblies showed that an ACLS with 5 nm-thick Pt sheets could increase mass activity 1.5 times and specific activity 3.5 times compared to the commercial Pt/C. Cathode potential at high current densities was evaluated by H2/O2 single-cell test. An ACLS with a Pt loading of 0.07 mg/cm2 demonstrated performance comparable to that of a commercial Pt/C with 0.2 mg/cm2 Pt loading. Excellent durability of the ACLS was also confirmed.

Selective oxidation of benzyl alcohol using RuHAp-containing sheet composites

Ru-containing hydroxyapatite (RuHAp) powder was successfully impregnated into sheet composites using a papermaking technique, and its catalytic efficiency was investigated. The RuHAp powder was homogeneously scattered over the fiber-mix networks that had been tailored within the catalyst sheet. RuHAp-containing sheets demonstrated superior performance to RuHAp beads for the selective oxidation of benzyl alcohol to benzaldehyde in a batch reaction process and the efficiency was equivalent to that of RuHAp powder. Catalytic performance was also evaluated in a continuous fixed-bed column reactor and RuHAp sheets showed higher oxidation efficiency than both RuHAp powder and beads. The porous structure of composites seemed to improve the effective transport of benzyl alcohol to RuHAp surfaces which were immobilized within the sheets, resulting in enhanced catalytic performance.

Ensuring the long-term functionality of passive auto-catalytic recombiners under operational containment atmosphere conditions—An interdisciplinary investigation

In order to sustain the structural integrity of the containment and other safety relevant components i.e. to avoid a detonation of the hydrogen-air mixture generated during a severe accident in light water reactors, passive auto-catalytic recombiners (PAR) are used for hydrogen removal in many European nuclear power plants (NPP). In 1999, the German NPP Emsland (KKE) was equipped with 58 PAR of AREVA design as an internal accident management measure for a beyond-design accident. Since that time the recombiners are in a stand-by state. As the catalyst elements are exposed to various airborne substances during normal plant operation their function is controlled periodically by testing selected catalyst sheets in a specially designed device. Under the conservative test conditions during this procedure some catalyst sheets showed a delayed responding behavior. First internal analysis gave indication of a beginning fouling on the catalytic surface. The aim of a precautionary investigation performed in cooperation between KKE, Forschungszentrum Juelich and RWTH Aachen University was to characterize the composition of the fouling and to correlate it with potential sources within the containment. In the framework of the investigation the reports of the periodic inspections were analyzed and appropriate sample sheets were selected from the installation. These samples were subjected to a comprehensive chemical surface analysis in order to identify effects like thermal sintering, poisoning or a blocking of the catalytic surface ( Baerns, M., 2004. Basic Principles in Applied Catalysis, Springer Verlag). Along with the chemical analysis the catalytic activity of the samples was assessed in several test series in order to correlate the chemically quantified deposition on the catalyst samples with the characteristics of the start-up and the steady-state performance of the recombination reaction. In a final step, possible sources of the fouling were analyzed with regard to their possible contribution to the phenomena. According to the results achieved, measures have been implemented at KKE in order to optimize procedures and to enhance the performance of the PARs.

Photocatalytic activity of rubber sheet impregnated with TiO2 particles and its recyclability

The preparation of rubber sheet impregnated with titanium dioxide particles is presented. This method is simple and low cost based on the use of commercial TiO2 powder directly mixing with rubber latex (60% HA) and distilled water. The morphology and roughness of the sheet surface increased with increasing amount of distilled water. Sheet impregnated with anatase (Imp-An) showed uniform, small grains with dense structure and well surface coverage more than one with P25 (Imp-P25). Their photocatalytic activities were evaluated using methylene blue (MB) as a model organic dye compound. These impregnated sheets could degrade MB solution under UV-light irradiation. Comparing with the commercial TiO2 samples in powder form (anatase from Carlo Erba and Degussa P25) the efficiencies of photocatalytic degradation of MB fall in the decreasing order as: P25 (powder) > anatase (Carlo Erba) (powder) > Imp-An sheet > Imp-P25 sheet. However, the impregnated sheet has an advantage over the loose powder that the catalyst sheet can be recovered after used and can be reused.

Preparation of porous sheet composite impregnated with TiO2 photocatalyst by a papermaking technique

Titanium dioxide (TiO2) powder-containing sheet composites, called TiO2 sheet, were prepared by a papermaking technique, and their photocatalytic efficiency was investigated. The TiO2 powders were homogeneously scattered over the fiber-mix networks tailored within the catalyst sheet. Under UV irradiation, the TiO2 paper could decompose p-hydroxyacetophenone (p-HAP), although the degradation efficiency by the TiO2 sheet was lower than that by the TiO2 powder. Scanning electron microscopy revealed that coverage of the TiO2 particles inside the sheet by alumina binder which was used to improve the sheet strength caused the deterioration of the photocatalytic performance. Internal addition of alumina binder made the TiO2 sheet porous and such a TiO2 sheet exhibited high photocatalytic performance equivalent to that of TiO2 powder. The porous structure of TiO2 sheet might contribute to effective transport of p-HAP to the surface of TiO2 particles inside the sheet, resulting in high degradation performance. In addition, TiO2 sheet prepared using TiO2 sol showed higher photocatalytic efficiency than TiO2 powder and it was indicated that the porous sheet structure might provide suitable conditions for TiO2 catalysis for photodecomposition.

Photocatalytic Degradation of Toluene Using a Novel Flow Reactor with Fe‐doped TiO2 Catalyst on Porous Nickel Sheets¶

ABSTRACTA novel continuous‐flow photocatalytic reactor was designed to decompose toluene by using porous nickel sheets that were coated with a Fe‐doped TiO2 catalyst. While locating the UV lamp at the central axis, the catalyst sheets were located along the inner wall and positioned vertically with an equal space of 50 mm along the reactor. This geometry ensures better use of UV light, and a zigzag flow pattern of gas between the vertically located sheets provides for better mass transfer. The X‐ray diffraction, scanning electron microscope and electric field‐induced surface photovoltage spectra characterizations showed that Fe3+ ions were embedded effectively and distributed evenly throughout the TiO2 crystal lattice and an optimum molar ratio of Fe:Ti was 0.007. The reactor was used to investigate the factors that affect toluene degradation. The results showed that inlet toluene concentration, relative humidity and gas flow rate significantly affect toluene decomposition. The conversion decreases as inlet concentration increases. Degradation efficiencies of more than 95 % can be achieved provided that the toluene concentration is kept below 3200 mg/m3. The conversion is affected little when oxygen content exceeds 21%. The optimal relative humidity is 25%. From the experimental data, a rate constant k of 131 mg/(m3.min) and Langmuir adsorption coefficient K of 0.0175 m3/mg were obtained.

Photocatalytic Degradation of Toluene Using a Novel Flow Reactor with Fe-doped TiO2 Catalyst on Porous Nickel Sheets¶

A novel continuous-flow photocatalytic reactor was designed to decompose toluene by using porous nickel sheets that were coated with a Fe-doped TiO2 catalyst. While locating the UV lamp at the central axis, the catalyst sheets were located along the inner wall and positioned vertically with an equal space of 50 mm along the reactor. This geometry ensures better use of UV light, and a zigzag flow pattern of gas between the vertically located sheets provides for better mass transfer. The X-ray diffraction, scanning electron microscope and electric field-induced surface photovoltage spectra characterizations showed that Fe3+ ions were embedded effectively and distributed evenly throughout the TiO2 crystal lattice and an optimum molar ratio of Fe:Ti was 0.007. The reactor was used to investigate the factors that affect toluene degradation. The results showed that inlet toluene concentration, relative humidity and gas flow rate significantly affect toluene decomposition. The conversion decreases as inlet concentration increases. Degradation efficiencies of more than 95% can be achieved provided that the toluene concentration is kept below 3200 mg/m3. The conversion is affected little when oxygen content exceeds 21%. The optimal relative humidity is 25%. From the experimental data, a rate constant k of 131 mg/(m3.min) and Langmuir adsorption coefficient K of 0.0175 m3/mg were obtained.

Photocatalytic Degradation of Toluene Using a Novel Flow Reactor with Fe-doped TiO2 Catalyst on Porous Nickel Sheets

A novel continuous-flow photocatalytic reactor was designed to decompose toluene by using porous nickel sheets that were coated with a Fe-doped TiO2 catalyst. While locating the UV lamp at the central axis, the catalyst sheets were located along the inner wall and positioned vertically with an equal space of 50 mm along the reactor. This geometry ensures better use of UV light, and a zigzag flow pattern of gas between the vertically located sheets provides for better mass transfer. The X-ray diffraction, scanning electron microscope and electric field-induced surface photovoltage spectra characterizations showed that Fe3+ ions were embedded effectively and distributed evenly throughout the TiO2 crystal lattice and an optimum molar ratio of Fe:Ti was 0.007. The reactor was used to investigate the factors that affect toluene degradation. The results showed that inlet toluene concentration, relative humidity and gas flow rate significantly affect toluene decomposition. The conversion decreases as inlet concentration increases. Degradation efficiencies of more than 95% can be achieved provided that the toluene concentration is kept below 3200 mg/m3. The conversion is affected little when oxygen content exceeds 21%. The optimal relative humidity is 25%. From the experimental data, a rate constant k of 131 mg/(m3.min) and Langmuir adsorption coefficient K of 0.0175 m3/mg were obtained.

High-throughput Evaluation of Catalytic Activity by Infrared Thermography

Carbon nanotubes grown perpendicularly on a silicon substrate were used as supports of fine platinum particles. Activity for catalytic combustion of hydrogen on the catalyst sheets was evaluated rapidly by the use of infrared imaging thermography. The thermographic image of the catalysts during hydrogen combustion reveals that platinum contents and conditions in preparation of catalysts, such as heat treatment temperatures or solvents used, affects the catalytic activity. The infrared thermography has therefore been shown to be a technique in evaluating catalytic activity.

Introduction by the Guest Editors

In order to sustain the structural integrity of the containment and other safety relevant components i.e. to avoid a detonation of the hydrogen-air mixture generated during a severe accident in light water reactors, passive auto-catalytic recombiners (PAR) are used for hydrogen removal in many European nuclear power plants (NPP). In 1999, the German NPP Emsland (KKE) was equipped with 58 PAR of AREVA design as an internal accident management measure for a beyond-design accident. Since that time the recombiners are in a stand-by state. As the catalyst elements are exposed to various airborne substances during normal plant operation their function is controlled periodically by testing selected catalyst sheets in a specially designed device. Under the conservative test conditions during this procedure some catalyst sheets showed a delayed responding behavior. First internal analysis gave indication of a beginning fouling on the catalytic surface.The aim of a precautionary investigation performed in cooperation between KKE, Forschungszentrum Juelich and RWTH Aachen University was to characterize the composition of the fouling and to correlate it with potential sources within the containment.In the framework of the investigation the reports of the periodic inspections were analyzed and appropriate sample sheets were selected from the installation. These samples were subjected to a comprehensive chemical surface analysis in order to identify effects like thermal sintering, poisoning or a blocking of the catalytic surface (Baerns, M., 2004. Basic Principles in Applied Catalysis, Springer Verlag). Along with the chemical analysis the catalytic activity of the samples was assessed in several test series in order to correlate the chemically quantified deposition on the catalyst samples with the characteristics of the start-up and the steady-state performance of the recombination reaction. In a final step, possible sources of the fouling were analyzed with regard to their possible contribution to the phenomena. According to the results achieved, measures have been implemented at KKE in order to optimize procedures and to enhance the performance of the PARs.