Quantum chemical study of NO reduction mechanism on Ag /Al2O3 catalysts

Authors

  • Ekaterina G. Ragoyja Belarusian State University, 4 Niezaliežnasci Avenue, Minsk 220030, Belarus https://orcid.org/0000-0002-8344-8438
  • Vitaly E. Matulis Belarusian State University, 4 Niezaliežnasci Avenue, Minsk 220030, Belarus https://orcid.org/0000-0001-9714-9087
  • Oleg A. Ivashkevich Research Institute for Physical Chemical Problems, Belarusian State University, 14 Lieninhradskaja Street, Minsk 220006, Belarus

Keywords:

nitrogen oxides reduction mechanism, DFT, SCR process, Ag/Al2O3 catalyst, silver clusters, activation barriers

Abstract

It was shown that N2O content among NO reduction products increases with an increase of the silver concentration in the catalyst because the nature of the catalytic centers changes and leads to a subsequent change in the mechanism of the reaction. Two reaction mechanisms were proposed and studied by means of quantum chemistry: a two-stage mechanism that proceeds via NO dimer formation on catalysts with high (above 2 wt. %) silver concentration and a parallel mechanism with isocyanates involved on catalysts with low (below 2 wt. %) silver concentration. It was demonstrated that on catalysts with high silver concentration mechanism that involves stepwise NO reduction via N2O to N2 is realised. Moreover, the final stage is complicated by the fact that formed intermediates and N2O are likely to desorb from the catalyst surface. In the case of catalysts with low silver concentration, the formation of both products (N2O and N2) proceeds in parallel and the lower activation barriers of the reaction leading to N2, as well as the thermodynamic profitability of its formation, lead to the predominance of the target product. The competition between the proposed mechanisms was studied in the case of catalytic centers represented by silver dimers. It was shown that activation barriers of reaction proceeding via NO dimer formation are lower than the corresponding barriers of the reaction with isocyanates involved, which confirms the prevalent realisation of the first process and the predominance of N2O among the final products. The obtained results explain the experimental data and are significant for further modelling of the mechanism of nitrogen oxides catalytic reduction considering the Al2O3 support.

Author Biographies

  • Ekaterina G. Ragoyja, Belarusian State University, 4 Niezaliežnasci Avenue, Minsk 220030, Belarus

    assistant at the department of analytical chemistry, faculty of chemistry

  • Vitaly E. Matulis, Belarusian State University, 4 Niezaliežnasci Avenue, Minsk 220030, Belarus

    PhD (chemistry), docent; associate professor at the department of inorganic chemistry, faculty of chemistry

  • Oleg A. Ivashkevich, Research Institute for Physical Chemical Problems, Belarusian State University, 14 Lieninhradskaja Street, Minsk 220006, Belarus

    academician of National Academy of Sciences of Belarus, doctor of science (chemistry), full professor; chief researcher at the laboratory for chemistry of condensed systems

References

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Published

2021-09-22

Issue

No. 2 (2021): Journal of the Belarusian State University. Chemistry

Section

Original Articles

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How to Cite

[1]
Ragoyja, E.G. et al. 2021. Quantum chemical study of NO reduction mechanism on Ag /Al2O3 catalysts. Journal of the Belarusian State University. Chemistry. 2 (Sep. 2021), 17–24. DOI:https://doi.org/10.33581/2520-257X-2021-2-17-24.