Chrysoula Pagkoura

Advanced Catalyst Coating Technology for Porous Substrates

The increasing demands and strict regulations in diesel emission control leads to an ever-increasing use of Diesel Particulate Filters (DPFs) in OEM applications. To accelerate the oxidation of soot particles collected in the DPF we have developed novel catalytic coatings with a variety of methods based on conventional and novel synthesis routes. The developed catalytic compositions exhibit significant direct soot oxidation as evaluated by reacting mixtures of diesel soot and catalyst powders in a thermogravimetric analysis apparatus (TGA). The catalyst compositions were further deposited on porous filter structures and were then evaluated on an engine bench with respect to their filtration efficiency, pressure drop behavior and soot oxidation activity under realistic conditions. Interestingly enough it is shown that the often-conflicting targets of high filtration efficiency, low pressure drop and high soot oxidation activity can be achieved simultaneously using the developed coating technologies.

Co3O4-based honeycombs as compact redox reactors/heat exchangers for thermochemical storage in the next generation CSP plants

Over the last years, several research groups have focused on developing efficient thermochemical heat storage (THS) systems, in-principle capable of being coupled with next generation high temperature Concentrated Solar Power plants. Among systems studied, the Co3O4/CoO redox system is a promising candidate. Currently, research efforts extend beyond basic level identification of promising materials to more application-oriented approaches aiming at validation of THS performance at pilot scale reactors. The present work focuses on the investigation of cobalt oxide based honeycomb structures as candidate reactors/heat exchangers to be employed for such purposes. In the evaluation conducted and presented here, cobalt oxide-based structures with different composition and geometrical characteristics were subjected to redox cycles in the temperature window between 800 and 1000°C under air flow. Basic aspects related to redox performance of each system are briefly discussed but the main focus lies on the evaluation of the segments structural stability after multi-cyclic operation. The latter is based on macroscopic visual observation and also supplemented by pre– (i.e. fresh samples) and post–characterization (i.e. after long term exposure) of extruded honeycombs via combined mercury porosimetry and SEM analysis.

Thermochemical storage for CSP via redox structured reactors/heat exchangers: The RESTRUCTURE project

The present work provides an overview of activities performed in the framework of the EU-funded collaborative project RESTRUCTURE, the main goal of which was to develop and validate a compact structured reactor/heat exchanger for thermochemical storage driven by 2-step high temperature redox metal oxide cycles. The starting point of development path included redox materials qualification via both theoretical and lab-scale experimental studies. Most favorable compositions were cobalt oxide/alumina composites. Preparation of small-scale structured bodies included various approaches, ranging from perforated pellets to more sophisticated honeycomb geometries, fabricated by extrusion and coating. Proof-of-concept of the proposed novel reactor/heat exchanger was successfully validated in small-scale structures and the next step included scaling up of redox honeycombs production. Significant challenges were identified for the case of extruded full-size bodies and the final qualified approach related to preparati...

Experimental proof of concept of a pilot-scale thermochemical storage unit

An efficient heat storage system, which allows disposal of the energy independently of the weather conditions, is a key factor on the development of Concentrated Solar Power (CSP). In this respect thermochemical heat storage could play an important role. Despite being still at early development stage, the number of recent studies dealing with thermochemical systems for high temperature storage shows that the interest on this topic is largely increasing. Among the reactive materials studied, certain multi-valent metal oxides seem to be a promising option, especially for air-operated CSP plants.

Solar Hydrogen Production

This chapter summarizes the current status of solar-aided hydrogen production technologies, with special emphasis on high temperature thermochemical concepts. The required high temperatures are achieved via concentrated solar irradiation through the respective systems, e.g., solar towers and solar dishes. Customized, efficient, and robust solar reactor concepts are important to ensure optimum coupling of the thermochemical phenomenon with the solar source. Of fundamental importance for such thermochemical processes is the development of active materials and key components. Some of the most studied and promising active materials are presented in this chapter along with their relevant advantages and challenges. Solar hydrogen (/fuels) production is found to constitute an in principle promising alternative and supplementary solution to currently employed renewables. Nevertheless, further development is required to increase solar-to-fuel efficiencies and to overcome long-term stability issues. Favorable solutions strongly depend on the identification of more active and robust materials as well as on the definition of solar reactor designs that will ensure optimum exploitation of solar irradiation.