Final Report Summary - FREECATS (Doped carbon nanostructures as metal-free catalysts)
Executive Summary:
FREECATS is primarily aimed at generating new fundamental knowledge and fostering new prospects and frontiers in the field of catalysis for the sustainable production of chemicals and commodities. New tailored metal-free catalytic architectures are designed and fabricated starting from nanoscale building blocks.
During the project a complete investigation on the influence of the synthesis parameters on the physical properties of N-CNTs has been accomplished. Development of organic functionalization as an alternative ex-situ approach to the hetero-decoration of carbon nanomaterials that allows an easy and precise control of the doping groups using mild reaction conditions has allowed, for the first time, to establish an unambiguous relationship between structure and catalytic activity for ORR paving the way to the design of more active catalysts. The development of a radically new scalable synthesis method starting from food residue for the production of N-doped carbon metal-free catalyst with controlled shape and size is demonstrated.
Direct CFD simulation of mixing in complex SiC foam structure using real structure models and comprehensive mechanistic models of oxidative dehydrogenation and catalytic ozonation on non-metallic catalysts have been obtained. Stability tests of ORR catalysts have been performed in a FC stack for 400 hours, and for CWAO in continuous flow for 100 hours.
Regarding AOPs, the screening tests with N-doped carbon materials using different target compounds revealed the positive effects of N-surface groups directly linked to the carbon nanotubes surface; SiC foams as structured catalysts presented a better catalytic performance than monoliths. The synthesis methods used for preparing the N-CNTs/SiC composite require the use of relatively low cost and non-toxic raw materials along with lower energy consumption for use in AOP processes. The life cycle study performed in the project also shows significant reduction in environmental impact due to replacement of noble metals.
Sustainability metrics were evaluated for the developed new catalytic processes and benchmarked against conventional (PGM) catalysts. The new ball-milled CNT catalyst outperforms PGM catalysts and clearly has a potential to replace the noble metal catalysts in both studied AOPs. An industrial CWAO plant was designed and on the basis of catalytic performances obtained during the project. The business plan for the AOP shows that the new metal-free catalyst developed in the FREECATS project may be applied in both Catalytic Ozonation (COZ) and Catalytic Wet Air Oxidation (CWAO) with positive cash-flow after two years of activity.
A 10-cell fuel cell stack was produced for demonstrating feasibility for ORR scale-up. The initial performance of the fuel cell MEAs featuring the new catalyst has been significantly improved by changing the technology of layer formation (spraying instead of roll-printing) and introducing pore-forming agents. Both measures improved the mass-transport by increasing the layer porosity. Based on the results, an economic and market application assessment of the new metal-free N-doped nanostructured carbon catalyst for ORR reaction in a PEM fuel cell has been performed. Fuel cell catalyst regarded as PGM replacement has to yield a similar fuel cell performance to PGM to be competitive in the market. The N-CNF catalytic material is still a promising ORR FC catalyst, and its development should be continued. It is likely that combining N-CNF and PGM in the catalysts should lead to significant reduction of PGM content in fuel cell catalysts.
The 6th International Symposium on Carbon for Catalysis, CARBOCAT-VI was hosted in 2014. A large number of publications in prestigious journals have been produced in the project, several with contributions from more than one FREECATS partner, demonstrating excellent collaboration. 6 PhD candidates and 21 post-doctoral fellows have been working in the project, with a good gender balance.
Project Context and Objectives:
The Freecats project was aimed at generating new fundamental knowledge and fostering new prospects and frontiers in the field of catalysis for the sustainable production of fine chemicals and commodities. Rethinking important noble metal-based catalytic processes in the light of new tailored metal-free catalytic architectures designed and fabricated starting from appropriate nanoscale building blocks, is the fundamental target of this research project.
The expanding global production and consumption of goods has created serious concern about problems related to the overall demand for critical materials. It is of paramount importance to avoid or minimise the consumption of scarce, difficult to explore or expensive materials.
Heterogeneous catalytic processes (particularly for oxidation reactions) are currently essentially based on the use of noble metals, and constitute an important part of the chemical industry.
Heterogeneous catalysis is nowadays considered as the backbone of the industrial chemistry with an approximate total turnover of about 14 billion US $ in 2007 (environment (44 %), chemistry industry (29 %) and refinery (27 %)) with a continuous growth of the solid catalysts market in the 5-8 %/year range. In 2009, global platinum sales totalled 193 tons with a following repartition: 48 % for jewellery industry, 23 % for the auto-catalyst industry, 18 % for other industries including catalysis,and about 11 % was used as investment.
The active phase recycling represents an option to recover part of these metals for its re-use in catalysis, however, such a recycling step is not straightforward and is generally cost intensive.
Therefore, the development of metal-free catalysts to replace precious metals can represent a real breakthrough in catalysis, particularly for those catalytic processes where a large amount of the active phase is needed (e.g. proton exchange membrane fuel cells - PEMFC, oxidation processes). This would avoid on a large scale the consumption of scarce and expensive metals.
Carbon nanomaterials, (i.e. nanotubes and nanofibers), have received an increasing scientific and industrial interest due to their unique physical and chemical properties, and are becoming more and more important as catalyst supports in the field of heterogeneous catalysis.
Their covalent “decoration” with foreign elements (chemical doping) can lead to a significant alteration of their intrinsic properties and, in turn, of their activity and selectivity in catalytic processes. Among these various doped carbon nanomaterials, the most studied are those containing nitrogen (nitrogen-doped carbon nanotubes: N-CNTs). Indeed, N-CNTs show many properties that are markedly different from their undoped counterparts.
Recent scientific reports have pointed out the possibility of using this material as metal-free catalyst in several demanding catalytic reactions. Recently, Gong et al. have synthesized N-CNT showing interesting ORR (Oxygen Reduction Reaction) activity and stability in alkaline conditions. It has been demonstrated that N-doped CNT exhibit enhanced catalytic activity compared to the traditional supported platinum catalyst. Recent reports even suggest that N-CNTs show comparable electrochemical activity and high stability compared to commercial Pt/C catalysts, and that N-doped graphene exhibit higher activity, stability and crossover tolerance than conventional platinum-based catalysts.
To substitute noble metals (platinum group metals and rare-earth elements) with these conceptually new, more cost-effective and eco-sustainable metal-free catalytic materials, Freecats obtains fundamental knowledge on the topics: 1. Density for doping of carbon nanostructures, 2. Stability of the doped materials, 3. Nature of the active sites, and 4. Flow patterns and behaviour of 3D structures in a reactor.
As the FREECATS project deals with the development of new metal-free catalysts, either in the form of bulk nanomaterials or in hierarchically organized structures both capable to replace
traditionally noble metal-based catalysts in catalytic transformations of strategic importance, three different cases have been selected. These case studies represent different scenarios, namely (i) a gas-solid reaction with high demand on heat transfer through the foam material, (ii) gas-vapour flow with potential for condensation inside the foam, and (iii) a gas-liquid-solid or liquid-solid reaction at close to ambient temperature. The requirements for optimal operation of the three different devices are very different. The common element is the need to connect the specific structure and materials of the foam with performance in mass and heat transfer. Each case has been selected for their contribution to fundamental understanding in the field of carbon nanostructures, their potential for
replacing PMG’s and their representation for other application domains due to their generic reactions: 1. Oxygen Reduction Reaction (ORR) in membrane fuel cells of one of our end-user
partners, 2. Oxidative Dehydrogenation of short-chain alkanes (ODH), 3. Advanced oxidation processes (AOP) in waste water treatments of one of our end-used partners.
Based on the three selected cases, FREECATS will rethink important metal-based catalytic processes in the light of new tailored metal-free catalytic architectures designed and fabricated starting from appropriate nanoscale building blocks. The approach used in the FREECATS proposal can be outlined in four main objectives:
1. Development of materials/catalysts:
The objective is to prepare nitrogen and boron-doped nanocarbons using an optimized and scalable procedure giving controllable nitrogen content presenting the following physical properties:
- High surface reactivity with an homogeneous dispersion of the dopant on the material surface
- Strong and stable interface with the macrostructured host matrix (SiC and C foam and cordierite monolith) at the targeted reaction conditions
- Efficient heat and electron transfer for the subsequence catalytic applications The main activities will be to prepare N/B/P-CNT samples, both in bulk form and supported on macroscopic foam/monolith host structures for initial screening and ranking. The materials will be extensively characterized at the different stages of preparation (after synthesis, after purification,
after functionalization, and also after catalytic tests). Specific attention will be given to surface characterization to be able to control the dopant dispersion and localization and on the purification
efficiency to remove the residual catalyst.
2. Hydrodynamics modelling regarding the catalyst physical properties and the process conditions.
The objective is to develop comprehensive process models for the three main case studies. The results will allow for determination of the optimum operation conditions. More concrete,
FREECATS aims to:
- To develop a detailed process model describing reactions, heat and mass transfer, and hydrodynamics with the foam structure as a parameter.
- To generate experimental data for model validation, specifically relating to heat transfer, mass transfer and foam structure.
3. Evaluation and lab-scale testing of the catalytic performance of the metal-free catalysts in the selected three cases and comparison with traditional noble or rare-earth metal-based systems:
- Oxygen reduction reaction (ORR) for use in proton exchange membrane fuel cells (PEMFC), using N-CNT
- Oxidative dehydrogenation of short chain alkanes (ODH) using P and B doped CNF.
- Advanced oxidation processes (AOP) for water and wastewater treatment: catalytic ozonation of organic micropollutants (COZ) and catalytic wet air oxidation (CWAO) using N-CNT
4. Process scale-up (i.e. laboratory micropilot plant setup), for the demonstration of the long-term stability of these metal-free nanocarbon catalysts.
The objective is to fully explore the different obstacles for scale-up step for a dedicated reaction.
- Scale-up the catalyst preparation up to ca. 1 kg of catalyst and micropilot plant setup with a structured reactor with size 3 x 8 inches.
- Validate performances expected from previous activities, namely lab scale testing and evaluation coupled with hydrodynamic modelling
- Generate technical data regarding catalyst scale-up (to full commercial scale), catalytic performances and durability, leading to a Technical, Economic and Ecologic assessment.
Project Results:
This description is attached as a separate pdf (STresults_foregrounds_FREECATS.pdf)
Potential Impact:
The results will allow more insights about the influence of the dopant loading on the physical and chemical properties of the composite materials, which could be exploited for other applications far beyond the scope of the present project.
Efficient catalytic processes require the development of a catalyst with high stability; this is one of the most important parameters in order to reduce the need for the cost-intensive catalyst replacement. The combination of the knowledge generated from the nitrogen loading and the stability of the catalyst under reaction conditions will allow us to perform optimization studies to find the most appropriate catalytic system for the targeted reactions. This fundamental knowledge will be further developed for building metal-free catalysts with applications far beyond the present project.
The understanding of the relationship between the nature of the doped nitrogen species and their catalytic performance, i.e. activity, selectivity and stability, is a key issue in the development of new metal-free catalytic systems and also for their optimization
The data collected from the project will allow us to develop novel structured reactor concepts with well controllable heat and mass transfer and chemical potential gradients with improved selectivity and also to allow a final economic, environmental and energy-efficiency assessment of the system with respect to further industrial development. The combined results obtained from the theoretical simulations and catalytic reactivity will enable one to understand and to control the characteristic of the heat and mass transfer within this structured reactor which can be further transferred to other catalytic processes, i.e. multi-phase reactors for one of the most demanding reactions like the Fischer-Tropsch synthesis reaction.
The project seeks to replace traditional noble metal-based catalysts processes of strategic importance. 3 different cases have been selected:
The Oxygen Reduction Reaction (ORR) mechanism still remains poorly understood. It is expected that the identification of the real mechanism will be helpful for developing a higher-performance catalytic system. Carrying out this reaction with carbon nanostructures, could replace the noble metals used in certain applications like PEMFC (polymer electrolyte membrane fuel cells), which could replace the combustion engines as the EC targets after 2050.
An economic and market application assessment of the new metal-free N-doped nanostructured carbon catalyst for ORR reaction in a PEM fuel cell has been performed using a case of 1 kW backup power unit. Capital and operating expenses combined for the projected lifetime of the system were compared and the assessment clearly shows that the performance and durability of the new catalyst must be improved to become competitive on the market. The key focus of FREECATS is on reduction in use of resources and replacement of noble metals. The results of the life cycle study indicate a significant reduction in environmental impacts due to removal of noble metals.
The conversion of alkanes into valuable olefins is of continuing interest with regard to the current technological restructuring of the petrochemical industry. Ethylene and propylene are economically very important commodities in polymer production and the demand of olefins is expected to grow further. FREECATS aims to replace the vanadium and platinum based catalysts with environmentally friendly ODH processes based on carbon nano-structured catalysts. Several consortium members have close collaboration with potential industrial end-users of this technology.
In advanced oxidation processes (AOPs), most of the original ozonation (OZ) and wet oxidation (WO) technologies are based on non-catalytic processes or homogeneous catalysts. The homogeneous catalysts represent a secondary source of pollution and a separation step of the catalyst is required. Pt-based materials and cerium oxide base materials are very active catalysts for these processes. However, besides the associated cost of the metals, deactivation are a major concern. Therefore, the use of carbon materials as catalysts should be considered as a cost/environmental effective option. Based on the strong indications that modified carbon-based catalysts have even larger potential for these reactions and can efficiently replace the metal-based catalysts, the FREECATS consortium has selected AOP as one of the tree cases since this is an emerging technology which may create increasing demand for PGM and rare-earth materials.
The introduction of noble metals on the surface of both CNTs (CNT-O and CNT-BM-M) led to a decrease of their performance as catalysts in ozonation of oxalic acid. In the case of CWAO the CNTs impregnated with platinum exhibit similar phenol removals as correspondent supports, but produce higher amounts of toxic intermediates. The rare earth metal based catalysts are shown to be clearly inferior in both studied AOP processes.
From an industrial point of view, the most viable and challenging industrial process was the CWAO. Regarding the support, the use of foams would represent a certain advantage vs monolith support (static mixer, pressure drop …). As a consequence, the reactor design has been described for a CWAO industrial process using beta SiC foams as a support. All the equipment needed to set up this plant and the P&ID have been described. Based on the data obtained in the WP4, a full industrial project of the CWAO technology was done. The project was performed in a 3D CAD software including piping, electrical and pneumatic project. Improvements to optimize the entire process have also been proposed.
The first stage of the process is the cutting of the polyurethane (PU) foam in the desirable dimensions. This cutting can be performed with a hot wire. The cutting machine is computer-controlled. Thus, through cutting software, the program required to create the desired PU foam is generated by the engineer and the data are transmitted to the hot wire via a controller. This technology is widely used to cut the PU foam and is available at SICAT facilities. For the designed reactor, the technologies are available at SICAT. From the foam production point of view, the challenging steps are the thermal treatment and the thickness of the pieces in order to obtain fully open cell foams. Regarding the thermal treatment, SICAT has developed a large expertise in producing SiC. As a consequence, a larger development up to industrial scale wouldn't be an issue.
Sustainability metrics data related to nitrogen-doped carbon nanofibres was performed by University of Cambridge using the data on the synthesis of carbon nanofibres provided by NTNU. In the FREECATS project the main objective was to eliminate noble metals from catalysts and develop new materials containing non-metal dopants, while retaining catalytic activity and selectivity. For environmental assessment of the impact of transition from noble metal to non-noble metal-based catalyst the most important consideration is the removal of all the impacts associated with mining and refining of noble metals and manufacture of noble metal-based catalysts. For this reason within FREECATS a new life cycle assessment case study was developed and compared directly with the previous case study. Here we compare manufacture of Pd-CNF/SMF (Pd deposited on carbon nanofibres, deposited onto sintered metal fibres) with the manufacture of N-CNF (nitrogen-doped carbon nanofibre) catalysts, produced by similar CVD methods. Evaluations were performed using UMBERTO life cycle assessment platform, using EcoInvent database and in-house developed inventories for the species not available in the database. The laboratory-scale composition of CO/NH3/H2 gas feed stream was scaled to the pilot set-up available at NTNU. The same pilot-scale set-up was used for the growth of the CNF/SMF support for the Pd-based catalyst and thus offers a good basis for comparison. LCA is best used as a comparative method, since absolute values of impacts are too inaccurate due to multiple assumptions used in developing life cycle inventories.
The comparative life cycle assessment performed here is a cradle-to-gate evaluation that was designed to reveal the contribution of raw materials on the environmental impacts from the process. In this case the new LCA case study for the nitrogen doped carbon nanofibres shows the significant reduction in the impacts compared to the metal-based catalyst. This illustrates the significance of eliminating noble metals in catalysts not only from the point of view of cost and availability, but also from the point of view of environmental impact of technology. The performance of the catalysts and end-of-life have not been evaluated, since the long-term catalyst performance data were only available at the end of the project. The up-scale of catalyst manufacture and first commercial implementation that are likely to follow from the FREECATS project will provide the necessary data for evaluation of in-use and end-of-life environmental performance of the new catalysts.
The key focus of the project is on reduction in resource use and elimination of the use of scarce materials, such as noble metals. This is completely supported by the results of the life cycle study, which shows the significant reduction in environmental impacts due to removal of noble metals.
FREECATS results are disseminated through publications, conference contributions, and our website (www.freecats.eu). In turn these activities will facilitate exchange of information between the FREECATS consortium and potential end-users of the materials and processes – other than those already involved in the project and with the wider community. A large dissemination event was organised in Trondheim in June 2014: The 6th International Symposium on Carbon for Catalysis, CARBOCAT-VI. An impressive number of publications and presentations have emerged from the project work. Plans have been drawn up to commercially exploit the catalyst technology developed within the project and possible markets, prices and distributors.
The list of publications and presentations that have emerged from the project work is impressive. The full list is available in the participant portal. All partners have had significant contributions to the overall dissemination activities. However, most of the scientific publications are produced by the academic partners. Some of the partners have produced an impressive list of publications during the course of the project. Several publications also have contributions from more than one FREECATS partner, which demonstrates the excellent teamwork and value-added collaboration in the project. Several joint publications are in progress and will be published after the end of the project. In addition to the scientific publications a large number of conference presentations promoting FREECATS results have also been achieved.
6 PhD candidates are being educated within the project framework at UPORTO, NTNU and CSIC. In addition, 21 post-doctoral fellows have been working in the project at CSIC, CNR, CNRS, UCAM, UP, Warwick and NTNU. They will be ambassadors and dissemination vectors of the knowledge built in FREECATS. It is also important to observe that the gender balance among the PhD/postoc candidates is relatively good; 11 female, 16 male. Several master projects (5) have also been carried out in collaboration with FREECATS.
Based on the results obtained from WP4 and WP5, Adventech defined two models for the studied CWAO unit with different capacities. The two chosen capacities take into account the usual industry needs where this technology could be applied. These two models were used in developing a business plan. The business plan for the AOP using the new developed metal-free catalyst has been produced in this task (deliverables D6.3 and D6.4). The business plan includes the assessment of costs of goods sold and materials consumed, the prevision of sales and services provision. Sales and costs of goods were estimated and projected in a timeline of 6 years after FREECATS project. Sales grow were also estimated taking into account the actual inquiries that Adventech receive for this product line and assuming also a price grow rate of 3%. Services associated to both models of CWAO were also considered. These plans allowed the determination of the income statement and the forward estimates, as well as the cash-flow evolution during the five years from 2016. From these business and financial plan it was possible to conclude that the project is profitable, with positive cash-flow after two years of activity.
The new metal-free catalyst developed under the FREECATS project may be used in both Catalytic Ozonation (COZ) and Catalytic Wet Air Oxidation (CWAO). The main advantages of the use of the FREECATS catalyst are the absence of expensive metals, lower cost and equivalent efficiency. As outlined in WP5, the metal-free structure of the new catalysts avoid the fluctuation on price caused by the frequent variation in price of rare earth metals and PGM commonly used in these kind of conventional catalysts. The treatment of wastewater an end-of-line technology in an industry layout, which means that the wastewater treatment unit is of the last equipments installed in new industrial plants. This leads to long delays between the commercial contract and the effective installation of the treatment unit. The variation in price of conventional metal based catalyst cause cash flow problems and even some significant losses in large installations. The lower cost of the new catalyst associated to equivalent efficiency improves the competitive edge of both AOP’s technologies. The business plan presented in FREECATS is based on two different models of the CWAO technology with different capacities of treatment. The capacities of each model were selected according the previous experience of Adventech in the treatment of industrial wastewater.
In addition, the requirements needed for the new N-CNT catalyst to be competitively commercialised for the FC stack is highlighted. When the performance of the novel N-CNF catalyst in PEM fuel cells was obtained, and initial work to improve it was performed (see D 3.2) the commercial plan for exploitation of these results was still unclear. But the later tests in the stack (D 4.7) and the market application assessment performed after (D 5.3) led us to the following conclusions:
• The assessment clearly shows that the performance and durability of the new catalyst must be improved for it to become competitive on the market
• A more general conclusion was made: any fuel cell catalyst aimed as a platinum or Pt-group metal replacement has to yield a similar fuel cell performance (even with much higher loading) to be competitive on the market, at least in the situation where platinum is still available
• The N-CNF catalytic material is still a promising ORR FC catalyst, and its development should be continued especially because of the limited platinum resources and their inevitable depletion with the growth of the fuel cell industry. It may also be that a combining N-CNF and PGM in the catalysts can lead to significant reduction of PGM content in fuel cell catalysts.
Due to the reasons above a decision was made not to patent the use of this catalyst in fuel cells yet and work instead on improving the catalyst.
FREECATS is primarily aimed at generating new fundamental knowledge and fostering new prospects and frontiers in the field of catalysis for the sustainable production of chemicals and commodities. New tailored metal-free catalytic architectures are designed and fabricated starting from nanoscale building blocks.
During the project a complete investigation on the influence of the synthesis parameters on the physical properties of N-CNTs has been accomplished. Development of organic functionalization as an alternative ex-situ approach to the hetero-decoration of carbon nanomaterials that allows an easy and precise control of the doping groups using mild reaction conditions has allowed, for the first time, to establish an unambiguous relationship between structure and catalytic activity for ORR paving the way to the design of more active catalysts. The development of a radically new scalable synthesis method starting from food residue for the production of N-doped carbon metal-free catalyst with controlled shape and size is demonstrated.
Direct CFD simulation of mixing in complex SiC foam structure using real structure models and comprehensive mechanistic models of oxidative dehydrogenation and catalytic ozonation on non-metallic catalysts have been obtained. Stability tests of ORR catalysts have been performed in a FC stack for 400 hours, and for CWAO in continuous flow for 100 hours.
Regarding AOPs, the screening tests with N-doped carbon materials using different target compounds revealed the positive effects of N-surface groups directly linked to the carbon nanotubes surface; SiC foams as structured catalysts presented a better catalytic performance than monoliths. The synthesis methods used for preparing the N-CNTs/SiC composite require the use of relatively low cost and non-toxic raw materials along with lower energy consumption for use in AOP processes. The life cycle study performed in the project also shows significant reduction in environmental impact due to replacement of noble metals.
Sustainability metrics were evaluated for the developed new catalytic processes and benchmarked against conventional (PGM) catalysts. The new ball-milled CNT catalyst outperforms PGM catalysts and clearly has a potential to replace the noble metal catalysts in both studied AOPs. An industrial CWAO plant was designed and on the basis of catalytic performances obtained during the project. The business plan for the AOP shows that the new metal-free catalyst developed in the FREECATS project may be applied in both Catalytic Ozonation (COZ) and Catalytic Wet Air Oxidation (CWAO) with positive cash-flow after two years of activity.
A 10-cell fuel cell stack was produced for demonstrating feasibility for ORR scale-up. The initial performance of the fuel cell MEAs featuring the new catalyst has been significantly improved by changing the technology of layer formation (spraying instead of roll-printing) and introducing pore-forming agents. Both measures improved the mass-transport by increasing the layer porosity. Based on the results, an economic and market application assessment of the new metal-free N-doped nanostructured carbon catalyst for ORR reaction in a PEM fuel cell has been performed. Fuel cell catalyst regarded as PGM replacement has to yield a similar fuel cell performance to PGM to be competitive in the market. The N-CNF catalytic material is still a promising ORR FC catalyst, and its development should be continued. It is likely that combining N-CNF and PGM in the catalysts should lead to significant reduction of PGM content in fuel cell catalysts.
The 6th International Symposium on Carbon for Catalysis, CARBOCAT-VI was hosted in 2014. A large number of publications in prestigious journals have been produced in the project, several with contributions from more than one FREECATS partner, demonstrating excellent collaboration. 6 PhD candidates and 21 post-doctoral fellows have been working in the project, with a good gender balance.
Project Context and Objectives:
The Freecats project was aimed at generating new fundamental knowledge and fostering new prospects and frontiers in the field of catalysis for the sustainable production of fine chemicals and commodities. Rethinking important noble metal-based catalytic processes in the light of new tailored metal-free catalytic architectures designed and fabricated starting from appropriate nanoscale building blocks, is the fundamental target of this research project.
The expanding global production and consumption of goods has created serious concern about problems related to the overall demand for critical materials. It is of paramount importance to avoid or minimise the consumption of scarce, difficult to explore or expensive materials.
Heterogeneous catalytic processes (particularly for oxidation reactions) are currently essentially based on the use of noble metals, and constitute an important part of the chemical industry.
Heterogeneous catalysis is nowadays considered as the backbone of the industrial chemistry with an approximate total turnover of about 14 billion US $ in 2007 (environment (44 %), chemistry industry (29 %) and refinery (27 %)) with a continuous growth of the solid catalysts market in the 5-8 %/year range. In 2009, global platinum sales totalled 193 tons with a following repartition: 48 % for jewellery industry, 23 % for the auto-catalyst industry, 18 % for other industries including catalysis,and about 11 % was used as investment.
The active phase recycling represents an option to recover part of these metals for its re-use in catalysis, however, such a recycling step is not straightforward and is generally cost intensive.
Therefore, the development of metal-free catalysts to replace precious metals can represent a real breakthrough in catalysis, particularly for those catalytic processes where a large amount of the active phase is needed (e.g. proton exchange membrane fuel cells - PEMFC, oxidation processes). This would avoid on a large scale the consumption of scarce and expensive metals.
Carbon nanomaterials, (i.e. nanotubes and nanofibers), have received an increasing scientific and industrial interest due to their unique physical and chemical properties, and are becoming more and more important as catalyst supports in the field of heterogeneous catalysis.
Their covalent “decoration” with foreign elements (chemical doping) can lead to a significant alteration of their intrinsic properties and, in turn, of their activity and selectivity in catalytic processes. Among these various doped carbon nanomaterials, the most studied are those containing nitrogen (nitrogen-doped carbon nanotubes: N-CNTs). Indeed, N-CNTs show many properties that are markedly different from their undoped counterparts.
Recent scientific reports have pointed out the possibility of using this material as metal-free catalyst in several demanding catalytic reactions. Recently, Gong et al. have synthesized N-CNT showing interesting ORR (Oxygen Reduction Reaction) activity and stability in alkaline conditions. It has been demonstrated that N-doped CNT exhibit enhanced catalytic activity compared to the traditional supported platinum catalyst. Recent reports even suggest that N-CNTs show comparable electrochemical activity and high stability compared to commercial Pt/C catalysts, and that N-doped graphene exhibit higher activity, stability and crossover tolerance than conventional platinum-based catalysts.
To substitute noble metals (platinum group metals and rare-earth elements) with these conceptually new, more cost-effective and eco-sustainable metal-free catalytic materials, Freecats obtains fundamental knowledge on the topics: 1. Density for doping of carbon nanostructures, 2. Stability of the doped materials, 3. Nature of the active sites, and 4. Flow patterns and behaviour of 3D structures in a reactor.
As the FREECATS project deals with the development of new metal-free catalysts, either in the form of bulk nanomaterials or in hierarchically organized structures both capable to replace
traditionally noble metal-based catalysts in catalytic transformations of strategic importance, three different cases have been selected. These case studies represent different scenarios, namely (i) a gas-solid reaction with high demand on heat transfer through the foam material, (ii) gas-vapour flow with potential for condensation inside the foam, and (iii) a gas-liquid-solid or liquid-solid reaction at close to ambient temperature. The requirements for optimal operation of the three different devices are very different. The common element is the need to connect the specific structure and materials of the foam with performance in mass and heat transfer. Each case has been selected for their contribution to fundamental understanding in the field of carbon nanostructures, their potential for
replacing PMG’s and their representation for other application domains due to their generic reactions: 1. Oxygen Reduction Reaction (ORR) in membrane fuel cells of one of our end-user
partners, 2. Oxidative Dehydrogenation of short-chain alkanes (ODH), 3. Advanced oxidation processes (AOP) in waste water treatments of one of our end-used partners.
Based on the three selected cases, FREECATS will rethink important metal-based catalytic processes in the light of new tailored metal-free catalytic architectures designed and fabricated starting from appropriate nanoscale building blocks. The approach used in the FREECATS proposal can be outlined in four main objectives:
1. Development of materials/catalysts:
The objective is to prepare nitrogen and boron-doped nanocarbons using an optimized and scalable procedure giving controllable nitrogen content presenting the following physical properties:
- High surface reactivity with an homogeneous dispersion of the dopant on the material surface
- Strong and stable interface with the macrostructured host matrix (SiC and C foam and cordierite monolith) at the targeted reaction conditions
- Efficient heat and electron transfer for the subsequence catalytic applications The main activities will be to prepare N/B/P-CNT samples, both in bulk form and supported on macroscopic foam/monolith host structures for initial screening and ranking. The materials will be extensively characterized at the different stages of preparation (after synthesis, after purification,
after functionalization, and also after catalytic tests). Specific attention will be given to surface characterization to be able to control the dopant dispersion and localization and on the purification
efficiency to remove the residual catalyst.
2. Hydrodynamics modelling regarding the catalyst physical properties and the process conditions.
The objective is to develop comprehensive process models for the three main case studies. The results will allow for determination of the optimum operation conditions. More concrete,
FREECATS aims to:
- To develop a detailed process model describing reactions, heat and mass transfer, and hydrodynamics with the foam structure as a parameter.
- To generate experimental data for model validation, specifically relating to heat transfer, mass transfer and foam structure.
3. Evaluation and lab-scale testing of the catalytic performance of the metal-free catalysts in the selected three cases and comparison with traditional noble or rare-earth metal-based systems:
- Oxygen reduction reaction (ORR) for use in proton exchange membrane fuel cells (PEMFC), using N-CNT
- Oxidative dehydrogenation of short chain alkanes (ODH) using P and B doped CNF.
- Advanced oxidation processes (AOP) for water and wastewater treatment: catalytic ozonation of organic micropollutants (COZ) and catalytic wet air oxidation (CWAO) using N-CNT
4. Process scale-up (i.e. laboratory micropilot plant setup), for the demonstration of the long-term stability of these metal-free nanocarbon catalysts.
The objective is to fully explore the different obstacles for scale-up step for a dedicated reaction.
- Scale-up the catalyst preparation up to ca. 1 kg of catalyst and micropilot plant setup with a structured reactor with size 3 x 8 inches.
- Validate performances expected from previous activities, namely lab scale testing and evaluation coupled with hydrodynamic modelling
- Generate technical data regarding catalyst scale-up (to full commercial scale), catalytic performances and durability, leading to a Technical, Economic and Ecologic assessment.
Project Results:
This description is attached as a separate pdf (STresults_foregrounds_FREECATS.pdf)
Potential Impact:
The results will allow more insights about the influence of the dopant loading on the physical and chemical properties of the composite materials, which could be exploited for other applications far beyond the scope of the present project.
Efficient catalytic processes require the development of a catalyst with high stability; this is one of the most important parameters in order to reduce the need for the cost-intensive catalyst replacement. The combination of the knowledge generated from the nitrogen loading and the stability of the catalyst under reaction conditions will allow us to perform optimization studies to find the most appropriate catalytic system for the targeted reactions. This fundamental knowledge will be further developed for building metal-free catalysts with applications far beyond the present project.
The understanding of the relationship between the nature of the doped nitrogen species and their catalytic performance, i.e. activity, selectivity and stability, is a key issue in the development of new metal-free catalytic systems and also for their optimization
The data collected from the project will allow us to develop novel structured reactor concepts with well controllable heat and mass transfer and chemical potential gradients with improved selectivity and also to allow a final economic, environmental and energy-efficiency assessment of the system with respect to further industrial development. The combined results obtained from the theoretical simulations and catalytic reactivity will enable one to understand and to control the characteristic of the heat and mass transfer within this structured reactor which can be further transferred to other catalytic processes, i.e. multi-phase reactors for one of the most demanding reactions like the Fischer-Tropsch synthesis reaction.
The project seeks to replace traditional noble metal-based catalysts processes of strategic importance. 3 different cases have been selected:
The Oxygen Reduction Reaction (ORR) mechanism still remains poorly understood. It is expected that the identification of the real mechanism will be helpful for developing a higher-performance catalytic system. Carrying out this reaction with carbon nanostructures, could replace the noble metals used in certain applications like PEMFC (polymer electrolyte membrane fuel cells), which could replace the combustion engines as the EC targets after 2050.
An economic and market application assessment of the new metal-free N-doped nanostructured carbon catalyst for ORR reaction in a PEM fuel cell has been performed using a case of 1 kW backup power unit. Capital and operating expenses combined for the projected lifetime of the system were compared and the assessment clearly shows that the performance and durability of the new catalyst must be improved to become competitive on the market. The key focus of FREECATS is on reduction in use of resources and replacement of noble metals. The results of the life cycle study indicate a significant reduction in environmental impacts due to removal of noble metals.
The conversion of alkanes into valuable olefins is of continuing interest with regard to the current technological restructuring of the petrochemical industry. Ethylene and propylene are economically very important commodities in polymer production and the demand of olefins is expected to grow further. FREECATS aims to replace the vanadium and platinum based catalysts with environmentally friendly ODH processes based on carbon nano-structured catalysts. Several consortium members have close collaboration with potential industrial end-users of this technology.
In advanced oxidation processes (AOPs), most of the original ozonation (OZ) and wet oxidation (WO) technologies are based on non-catalytic processes or homogeneous catalysts. The homogeneous catalysts represent a secondary source of pollution and a separation step of the catalyst is required. Pt-based materials and cerium oxide base materials are very active catalysts for these processes. However, besides the associated cost of the metals, deactivation are a major concern. Therefore, the use of carbon materials as catalysts should be considered as a cost/environmental effective option. Based on the strong indications that modified carbon-based catalysts have even larger potential for these reactions and can efficiently replace the metal-based catalysts, the FREECATS consortium has selected AOP as one of the tree cases since this is an emerging technology which may create increasing demand for PGM and rare-earth materials.
The introduction of noble metals on the surface of both CNTs (CNT-O and CNT-BM-M) led to a decrease of their performance as catalysts in ozonation of oxalic acid. In the case of CWAO the CNTs impregnated with platinum exhibit similar phenol removals as correspondent supports, but produce higher amounts of toxic intermediates. The rare earth metal based catalysts are shown to be clearly inferior in both studied AOP processes.
From an industrial point of view, the most viable and challenging industrial process was the CWAO. Regarding the support, the use of foams would represent a certain advantage vs monolith support (static mixer, pressure drop …). As a consequence, the reactor design has been described for a CWAO industrial process using beta SiC foams as a support. All the equipment needed to set up this plant and the P&ID have been described. Based on the data obtained in the WP4, a full industrial project of the CWAO technology was done. The project was performed in a 3D CAD software including piping, electrical and pneumatic project. Improvements to optimize the entire process have also been proposed.
The first stage of the process is the cutting of the polyurethane (PU) foam in the desirable dimensions. This cutting can be performed with a hot wire. The cutting machine is computer-controlled. Thus, through cutting software, the program required to create the desired PU foam is generated by the engineer and the data are transmitted to the hot wire via a controller. This technology is widely used to cut the PU foam and is available at SICAT facilities. For the designed reactor, the technologies are available at SICAT. From the foam production point of view, the challenging steps are the thermal treatment and the thickness of the pieces in order to obtain fully open cell foams. Regarding the thermal treatment, SICAT has developed a large expertise in producing SiC. As a consequence, a larger development up to industrial scale wouldn't be an issue.
Sustainability metrics data related to nitrogen-doped carbon nanofibres was performed by University of Cambridge using the data on the synthesis of carbon nanofibres provided by NTNU. In the FREECATS project the main objective was to eliminate noble metals from catalysts and develop new materials containing non-metal dopants, while retaining catalytic activity and selectivity. For environmental assessment of the impact of transition from noble metal to non-noble metal-based catalyst the most important consideration is the removal of all the impacts associated with mining and refining of noble metals and manufacture of noble metal-based catalysts. For this reason within FREECATS a new life cycle assessment case study was developed and compared directly with the previous case study. Here we compare manufacture of Pd-CNF/SMF (Pd deposited on carbon nanofibres, deposited onto sintered metal fibres) with the manufacture of N-CNF (nitrogen-doped carbon nanofibre) catalysts, produced by similar CVD methods. Evaluations were performed using UMBERTO life cycle assessment platform, using EcoInvent database and in-house developed inventories for the species not available in the database. The laboratory-scale composition of CO/NH3/H2 gas feed stream was scaled to the pilot set-up available at NTNU. The same pilot-scale set-up was used for the growth of the CNF/SMF support for the Pd-based catalyst and thus offers a good basis for comparison. LCA is best used as a comparative method, since absolute values of impacts are too inaccurate due to multiple assumptions used in developing life cycle inventories.
The comparative life cycle assessment performed here is a cradle-to-gate evaluation that was designed to reveal the contribution of raw materials on the environmental impacts from the process. In this case the new LCA case study for the nitrogen doped carbon nanofibres shows the significant reduction in the impacts compared to the metal-based catalyst. This illustrates the significance of eliminating noble metals in catalysts not only from the point of view of cost and availability, but also from the point of view of environmental impact of technology. The performance of the catalysts and end-of-life have not been evaluated, since the long-term catalyst performance data were only available at the end of the project. The up-scale of catalyst manufacture and first commercial implementation that are likely to follow from the FREECATS project will provide the necessary data for evaluation of in-use and end-of-life environmental performance of the new catalysts.
The key focus of the project is on reduction in resource use and elimination of the use of scarce materials, such as noble metals. This is completely supported by the results of the life cycle study, which shows the significant reduction in environmental impacts due to removal of noble metals.
FREECATS results are disseminated through publications, conference contributions, and our website (www.freecats.eu). In turn these activities will facilitate exchange of information between the FREECATS consortium and potential end-users of the materials and processes – other than those already involved in the project and with the wider community. A large dissemination event was organised in Trondheim in June 2014: The 6th International Symposium on Carbon for Catalysis, CARBOCAT-VI. An impressive number of publications and presentations have emerged from the project work. Plans have been drawn up to commercially exploit the catalyst technology developed within the project and possible markets, prices and distributors.
The list of publications and presentations that have emerged from the project work is impressive. The full list is available in the participant portal. All partners have had significant contributions to the overall dissemination activities. However, most of the scientific publications are produced by the academic partners. Some of the partners have produced an impressive list of publications during the course of the project. Several publications also have contributions from more than one FREECATS partner, which demonstrates the excellent teamwork and value-added collaboration in the project. Several joint publications are in progress and will be published after the end of the project. In addition to the scientific publications a large number of conference presentations promoting FREECATS results have also been achieved.
6 PhD candidates are being educated within the project framework at UPORTO, NTNU and CSIC. In addition, 21 post-doctoral fellows have been working in the project at CSIC, CNR, CNRS, UCAM, UP, Warwick and NTNU. They will be ambassadors and dissemination vectors of the knowledge built in FREECATS. It is also important to observe that the gender balance among the PhD/postoc candidates is relatively good; 11 female, 16 male. Several master projects (5) have also been carried out in collaboration with FREECATS.
Based on the results obtained from WP4 and WP5, Adventech defined two models for the studied CWAO unit with different capacities. The two chosen capacities take into account the usual industry needs where this technology could be applied. These two models were used in developing a business plan. The business plan for the AOP using the new developed metal-free catalyst has been produced in this task (deliverables D6.3 and D6.4). The business plan includes the assessment of costs of goods sold and materials consumed, the prevision of sales and services provision. Sales and costs of goods were estimated and projected in a timeline of 6 years after FREECATS project. Sales grow were also estimated taking into account the actual inquiries that Adventech receive for this product line and assuming also a price grow rate of 3%. Services associated to both models of CWAO were also considered. These plans allowed the determination of the income statement and the forward estimates, as well as the cash-flow evolution during the five years from 2016. From these business and financial plan it was possible to conclude that the project is profitable, with positive cash-flow after two years of activity.
The new metal-free catalyst developed under the FREECATS project may be used in both Catalytic Ozonation (COZ) and Catalytic Wet Air Oxidation (CWAO). The main advantages of the use of the FREECATS catalyst are the absence of expensive metals, lower cost and equivalent efficiency. As outlined in WP5, the metal-free structure of the new catalysts avoid the fluctuation on price caused by the frequent variation in price of rare earth metals and PGM commonly used in these kind of conventional catalysts. The treatment of wastewater an end-of-line technology in an industry layout, which means that the wastewater treatment unit is of the last equipments installed in new industrial plants. This leads to long delays between the commercial contract and the effective installation of the treatment unit. The variation in price of conventional metal based catalyst cause cash flow problems and even some significant losses in large installations. The lower cost of the new catalyst associated to equivalent efficiency improves the competitive edge of both AOP’s technologies. The business plan presented in FREECATS is based on two different models of the CWAO technology with different capacities of treatment. The capacities of each model were selected according the previous experience of Adventech in the treatment of industrial wastewater.
In addition, the requirements needed for the new N-CNT catalyst to be competitively commercialised for the FC stack is highlighted. When the performance of the novel N-CNF catalyst in PEM fuel cells was obtained, and initial work to improve it was performed (see D 3.2) the commercial plan for exploitation of these results was still unclear. But the later tests in the stack (D 4.7) and the market application assessment performed after (D 5.3) led us to the following conclusions:
• The assessment clearly shows that the performance and durability of the new catalyst must be improved for it to become competitive on the market
• A more general conclusion was made: any fuel cell catalyst aimed as a platinum or Pt-group metal replacement has to yield a similar fuel cell performance (even with much higher loading) to be competitive on the market, at least in the situation where platinum is still available
• The N-CNF catalytic material is still a promising ORR FC catalyst, and its development should be continued especially because of the limited platinum resources and their inevitable depletion with the growth of the fuel cell industry. It may also be that a combining N-CNF and PGM in the catalysts can lead to significant reduction of PGM content in fuel cell catalysts.
Due to the reasons above a decision was made not to patent the use of this catalyst in fuel cells yet and work instead on improving the catalyst.
