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CO2 - Loop for Energy storage and conversion to Organic chemistry Processes through advanced catalytic Systems

European Union Seventh Framework Programme
Focus on selected technologies for methane and methanol syntheses
 Home Newsletter 5 / April 2015
 

CEOPS upcoming events:

The CEOPS project will held 2 events in the frame of the upcoming E-MRS Spring Meeting 2015 at the Grand Palais in Lille, France.

CEOPS Summer School

  • Register now to CEOPS 1st Summer School !

This one day school on Carbon dioxyde recovery will be held on 10 May 2015, aiming for fruitful exchanges between students and teachers. The event is open to all categories of students, from Master to Post-docs. A financial support to attend the school is available.

Further information and the full programme are available 
here

Register before 30 April 2015
 here

Lille GP

  • Participate in the 2nd CEOPS workshop !

The 2nd CEOPS workshop, entitled "Carbon dioxide recovery and circular economy of carbon" will be held on 11 May 2015.
Scope of this one day symposium (combined with symposium A: Materials, mechanisms and devices in nano energy) is to discuss the current R&D situation, especially by considering the materials aspects in our E4F model for a future sustainable energy supply for the whole world. 

Further information and the full programme are available here 

 

Project coordinator:

Laurent BEDEL 
CEA-Grenoble - LITEN-DTBH 
38054 Grenoble Cedex 9 
France 
Tél: 33-4-38-78-57-20 
laurent.bedel@cea.fr  

 

 

The CEOPS project is focused on the development of advanced catalysts and processes for the conversion of CO2 to methane (pathway A), at the point of CO2 emission, and, after methane transportation, the direct conversion of methane to methanol (pathway B), at the final user facilities. Methane can be used as an easily storable and transportable carbon vector, which can be injected into the existing natural gas network. 

 


Specific advanced catalytic materials were developed and evaluated for each chemical pathway in order to overcome
the current limitations of thermal catalysis: catalyst ageing (Lewis acid) due to water adsorption (Lewis base) during the CO2 hydrogenation to CH4 and low CH4 conversion rate and selectivity in CH3OH during the methane direct conversion to methanol.

 

 

Three different promising electro-catalytic processes were evaluated as regards the CO2 conversion into methane and the direct conversion of methane into methanol: DBD (Dielectric Barrier Discharge) plasma catalysis, photo-activated catalysis and electro-catalytic reduction. 

 

Selection of processes & catalysts

The performances of the studied catalysts and processes have been benchmarked and the most efficient and durable scheme for both pathways have been selected on the basis of conversion rate, selectivity, electricity consumption and productivity.

The DBD plasma catalytic process was selected for methane production (pathway A) and the photo-catalytic process for methanol production (pathway B).

CO2 + 4H2 ↔ CH4 + 2H2O   (pathway A) 
CH4 + HO → CH3OH + H•  (pathway B)

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Noticeable results for Pathway A

Experimental set-up

DBD plasma catalysis was implemented in a fixed bed reactor at UPMC for mechanisms studies and in a fluidized bed reactor at CEA for performance assessment.
The fixed bed reactor at UPMC consists in two coaxial cylinders with od 8mm and id 3mm. A certain catalyst amount is packed in the annular space (gap of 2.5mm) which corresponds to a volume of 0.5ml.
The fluidized bed reactor at CEA is cylindrical with id 30mm. The volume of the reactor is about 50ml.
Sinusoidal high voltage current up to 14kV peak to peak is applied to the HV electrode of both reactors. At the reactor outlet, the exhaust gas is cooled in order to collect the water and the remaining gas phase is then analyzed by gas chromatography, FTIR and mass spectrometry.

Experiments

In the fixed bed configuration (UPMC), plasma-catalytic experiments were performed with mesoporous and zeolite based catalysts supplied by IREC and IST. A high dispersion of metals nanoparticles (Ni, Ru, Rh) and metal oxides (cerium oxides, zirconium oxides) lead to an optimum desorption of species from active sites and to a synergy with plasma (electro polarization of catalyst). Experiments were performed under stoichiometric conditions (inlet gas mixture of H2/CO2 = 80%-20%) at atmospheric pressure and from 120 to 420°C. A total gas flow rate of 200ml/min passed through the reactor, corresponding to a GHSV of 20000h-1. Typical voltage values of 10 to 14kV were applied for a frequency of 40kHz, corresponding to a power between 0.8 and 1.4W.
In the fluidized bed configuration (CEA), a commercial catalyst (Ni-γAl2O3) was tested. The experiments were carried out under stoichiometric conditions from atmospheric pressure to 5.5barabs, and from 250 to 335ºC. The total gas flow rate was varied from 2.5 to 10Nl/min, which corresponds to a GHSV of 2500-13000h-1. Typical voltage values of 4 to 12kV were applied for a frequency up to 3kHz, which corresponds to a maximum injected power of 50W.

Results

In both configurations, CO2 hydrogenation led to the production of CH4, water and small amounts of CO. The amount of CO increased with temperature and was probably produced by the reverse water-gas shift (RWGS) reaction: CO2 + H2 → CO+H2O, an endothermic reaction occurring at higher temperatures.
In the case of thermal catalysis, CO2 conversion rates higher than 80% with a selectivity in methane higher than 95% were reached for a temperature >300°C.
In the case of plasma-assisted catalysis, an increase of CO2 conversion up to 80% was noticed especially at low temperature (<250°C) for an energy consumption of about 50kJ/mol with an electrical discharge. The higher the power injected in the plasma is, the higher is the CO2 conversion.

Conclusions

- Plasma ignition in the reactors leads to an electro-polarization in the pores of the catalyst and to the ionization of the gas reactants then to their activation and their dissociation on the surface of the catalyst.
- The applied high voltage can lead to a significant desorption of water from the support and especially at low temperature, which can limit carbon deposition and catalyst ageing.

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Noticeable results for Pathway B

Experimental set-up

The photocatalytic oxidation of methane tests were performed in a photochemical reactor of 500 mL volume, irradiated by means of an immersion lamp (medium pressure Hg) providing UVC-visible light. The temperature of the reaction was maintained at 55 ºC by a flow of cooling water. A water suspension of the photocatalyst (1 g·L-1) was maintained under magnetical stirring. A 20% CH4/He mixture was continuously sparged through the reactor. Prior to irradiation, the suspension was magnetically stirred in the dark for 30 min. After that, the lamp was turned on and gas samples were periodically analyzed by gas chromatography equipped with FID and TCD detectors.

Experiments

Different materials were used as catalysts for the photocatalytic path. Among these, mesoporous WO3, BiVO4 and V-impregnated zeolites (supplied by IST), besides some modified formulations (especially, La-WO3), were the most promising ones.
The reaction parameters were fixed for all the tests. The effect of some additives acting as electron, hole and/or ▪OH scavengers was also evaluated. Thus, Fe3+, IO3-, HCO3-, NO3- and NO2-, among others were tested.

Results

During the photocatalytic tests, CH3OH, C2H6 and CO2 were obtained as the main products. The reaction mechanism mainly proceeds through the generation of hydroxyl radicals (▪OH); these reactive species can be generated from the photocatalytic reaction of holes with water or hydroxide ions adsorbed on the surface of the catalyst. As these species are highly oxidizing, a close correlation between conversion and selectivity was found. In that sense, on the one hand, WO3/La leads to the best combination of both, because of the improved water adsorption associated to the active basic sites on the surface, which promote adsorbed-OH generation. On the other, BiVO4 is the most selective material, despite the lower conversion, because of the lower oxidizing power ascribed to its band potential. Finally, the desilicated β-zeolite (Si/Al= 12.5) exhibited interesting results in terms of methane conversion, despite its lower selectivity. The addition of vanadium, however, seems to improve the overall yield to methanol.
It was found that electron radical scavengers markedly improve the productivity; however, this enhancement leads to a lower CH3OH selectivity. On the other hand, radical scavengers as HCO3- and NO2-, due to the capture of hydroxyl radicals of the aqueous medium to produce less oxidizing species, promote a higher generation of methanol by inhibiting C2H6 formation and, in the case of nitrite species, importantly decreasing the process of total oxidation.

Conclusions

- The photoactivation of the catalyst and the later reaction of the formed holes with water or hydroxide ions on the surface leading to the formation of ▪OH radicals is the fundamental key for the conversion of methane to methanol.
- The inherent properties of the semiconductor determine the extent of the oxidation process. Therefore, having materials with less oxidizing potential (according to the band structure) as BiVO4 is a good alternative for assuring better selectivity values, at expenses of lower methane conversion.
- The better results obtained with mesoporous WO3-La indicates that controlling the surface of the photocatalyst is the best approach for enhancing the methanol yield. This material not only exhibits higher specific area but also increased basic sites on the acidic surface, which promotes the OHadsorption, thus increasing the selectivity in comparison to pure WO3. The optimal La-content has been found to be of 1%. Above this value, the catalyst exhibits higher reactivity, thus increasing the CO2 formation.

image_article_3.png 
 

Prospects

 

A prototype at a scale of m3.h-1 of sub systems A and B is under building. This prototype will integrate the selected schemes and will be validated in order to demonstrate the CEOPS proof of concept.

A test bench for the prototype evaluation was built-up at CEA. It aims to characterize both electro-catalytic reactors for the production of methane (pathway A) and methanol (pathway B). Both sub-systems will be connected to the test bench in order to assess the prototype performances.

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