Studio della reazione di conversione di N2O catalizzata da film di ossido di ferro.

Responsabili di progetto

Letizia Savio, Mikolaj Lewandowski

Accordo

POLONIA - PAS (NUOVO ACCORDO) - Polish Academy of Sciences/Polska Akademia Nauk

Bando

CNR-PAN 2017-2019

Dipartimento

Ingegneria, ICT e tecnologie per l'energia e i trasporti

Area tematica

Ingegneria, ICT e tecnologie per l'energia e i trasporti

Stato del progetto

Nuovo

Proposta di ricerca

Climate changes and greenhouse effects are among the most worrying environmental problems of our century.
Nitrous oxide (N2O) is the largest stratospheric-ozone-depleting substance and the third anthropogenic greenhouse gas after CO2 and CH4 [1,2]. It is emitted by both natural and anthropogenic sources. The latter ones, including the biological transformation of nitrogen fertilizers, biomass burning and combustion of fossil fuels, have rapidly increased in the last 60 years and are predicted to almost double by 2050. Therefore, control of N2O emission is a subject of high environmental impact.

Among the possible strategies for N2O abatement, the catalytic decomposition of N2O to nitrogen and oxygen is an option when concentrated N2O emissions are produced (e.g. from fossil fuels combustion and chemical industry). Such process occurs on different catalysts, as noble-metal-supported catalysts, metal oxides and zeolite-based catalysts [2].
Metal oxides are an important and widely employed category of solid catalysts, due to their low cost combined with characteristics such as excellent redox properties, thermal stability and good catalytic activity [3]. Now it is well established that N2O decomposes on metal oxides through a redox-type mechanism. The process involves dissociative chemisorption of the reactant on surface active sites (most probably oxygen vacancies) followed by N2 desorption and recombination of adsorbed O atoms to gaseous O2 or by molecular O2 release through the direct interaction of N2O with adsorbed oxygen. The key role of surface oxygen mobility and active sites is evident.

Iron oxides are widely used in many technological fields due to their unique electronic, magnetic and catalytic properties, combined with low cost and non-toxicity. In catalysis, they are employed in oxidation, hydrogenation, desulfurization and other reactions [4]. Ultrathin iron oxide films grown on platinum substrates exhibit superior catalytic activity in CO oxidation reaction [5] and in O2 and NO dissociation. Their activity derives from electron transfer effects allowed by the work function of the film and the electron affinity of the reacting gas molecule. Raw iron oxides are not among the most common single oxides exploited for N2O decomposition but, since N2O has similar electron affinity to NO, ultrathin FeO(111)/Pt(111) are believed to be promising candidates for N2O conversion. The aim of the present project is to verify this assumption. We also underline that the design of new efficient materials for N2O adsorption may lead to the future development of N2O gas sensors, currently not available on the market [6].

Therefore we propose to investigate the N2O decomposition reaction on thin iron oxide films grown on Pt(111) to unravel the mechanisms at the basis of this process. The problem will be faced from the complementary points of view of catalysis (in ambient pressure conditions to test the efficiency of the catalyst - experiments to be performed in Poznan) and of surface science (under highly controlled ultrahigh vacuum conditions, to unravel the single steps leading to the final products - to be done in Genova). The general picture coming out can lead to the comprehension of the isolated steps of relevant catalytic processes and to the improvement of next generation catalysts and, possibly, gas sensors.

The Genoa team has a longstanding experience in the study of gas-surface interaction with the methods of surface science [7]. It will take advantage of a low temperature scanning tunnelling microscopy (LT-STM) apparatus and of a second ultra-high vacuum (UHV) chamber for photoemission and vibrational spectroscopy (XPS and HREELS). Both apparatuses can be coupled to a supersonic molecular beam (SMB), which simulates the high-energy tail of the Boltzmann distribution and thus allows to overcome possible energy barriers. In addition, the dynamics of the gas-surface interaction can be measured using the retarded reflector method of King&Wells (KW) [8] by suitably combining the SMB with a quadrupole mass spectrometer.
The Polish team has experience in studies of structure and properties of ultrathin (FeO) and thin (Fe3O4, Fe2O3) iron oxide films grown on single crystal supports (e.g. Pt(111), Ru(0001), Ag(111)). The structure is investigated with surface science methods (STM, LEED, AES, XPS) while the catalytic properties are analysed in a high pressure catalytic reactor combined with a gas chromatography system for real-time monitoring of the reactions. The team leader, Dr. Mikolaj Lewandowski, got his PhD at the Fritz-Haber-Institut der Max-Planck-Gesellschaft in Berlin, Germany - one of the world's leading scientific institutes for catalysis- investigating CO oxidation reaction over ultrathin iron oxide films.
Both research groups will benefit from the unique combination of equipment and expertise. This combination is also the key for successful realization of the project. Staff exchange will allow the Polish partner to gain knowledge and expertise on SMB experiments, while the Italian partner will gain knowledge and expertise on high-pressure gas chromatography studies. The groups have not cooperated so far, though they have already discussed and identified some common interests. Thus, this project will be a starting point for the establishment of a long-term collaboration to be prosecuted by writing future joint research projects.

[1] M. Strokal, C. Kroeze, Curr. Opin. Environ. Sustainability 910, 108 (2014)
[2] M. Konsolakis, ACS Catal. 5, 6397 (2015)
[3] X. Yao, C. Tang, F. Gao, L. Dong, Catal. Sci. Technol. 4, 2814 (2014)
[4] J. W. Geus, Appl. Catal. 25, 313 (1986)
[5] Y.N. Sun, Z.H. Qin, M. Lewandowski, E. Carrasco, M. Sterrer, S. Shaikhutdinov, H.J. Freund, J. Catal. 266, 359 (2009)
[6] Alter company, Poland, private communication, 2016.
[7] L. Vattuone et al., Angew. Chemie Int. Ed. 48, 4845 (2009)
[8] D.A. King, M.G. Wells, Surface Sci. 29, 454 (1972)

Obiettivi della ricerca

The aim of the project is to unravel the mechanisms at the basis of the catalytic N2O conversion reaction over supported ultrathin iron oxide films.
The main goals of the project include:
1/ Determination of the adsorption properties of N2O on ultrathin iron oxide films - important both from the point of view of catalytic reactions, as well as for future development of N2O gas sensors.
Are there adsorption barriers? Which are the active adsorption sites?
2/ Determination of catalytic activity of ultrathin iron oxide films in N2O conversion reaction at various reaction temperatures and pressures in presence of O2.
Which are the optimal conditions for the reaction to occur?
3/ Determination of the reaction mechanisms in situ.
Can we identify the single reaction steps by UHV studies? Which are the intermediate reaction products? Which is the desorption temperature of the final products? Does oxygen co-adsorption change the reaction dynamics?
4/ Dissemination of the results.
Results will be presented in form of communications at national/international workshops and conferences and joint publication in highly-ranked scientific journals (JCR list). It is expected that the project will result in a minimum of two scientific publications, one lead by each partner.

Ultimo aggiornamento: 03/01/2025