Comparison between single atoms and clusters of platinum supported on γ-Al2O3 in CO oxidation
Résumé
Noble metals are used as catalysts for numerous chemical reactions. However, due to their rarity and high price, their decreased usage or substitution by inexpensive metals is strongly desired. A way to save metals while possibly improving the catalytic performance is to increase metal dispersion up to the single-atom limit. The recent development of aberration-corrected scanning transmission electronic microscopy facilitated the development of so-called single-atom catalysts (SACs) [1]. On the respective performances of SACs and nanoparticulate catalysts, the literature is controversial. In particular, for CO oxidation on Pt/Al2O3, single Pt atoms have been found intrinsically active [2] or, in contrast, inactive [3].
.
In this work, Pt/γ-Al2O3 catalysts were prepared by incipient wetness impregnation followed by an oxidative and/or a reductive thermal treatment. It was shown that the treatment atmosphere and the Pt loading are decisive for controlling the Pt dispersion [4]. At intermediate Pt loading, operando experiments using diffuse reflectance infrared spectroscopy and X-ray absorption spectroscopy showed that Pt atoms gradually aggregate into subnanometric clusters throughout CO oxidation cycles, making the catalyst more active [5]. Here, from the comparison of the initial CO oxidation activities of catalysts composed of Pt single atoms, clusters (size < 2 nm), or nanoparticles (> 2 nm), it is consistently demonstrated that single atoms are less efficient than clusters and nanoparticles. The kinetics and mechanism of CO adsorption and oxidation on the different types of catalysts will be discussed in this contribution.
References
[1]S. Mitchell, E. Vorobyeva, J. Pérez‐Ramírez, Angew. Chem. Int. Ed. 57 (2018) 15316–15329.
[2]M. Moses-DeBusk, M. Yoon, L.F. Allard, D.R. Mullins, Z. Wu, X. Yang, G. Veith, G.M. Stocks, C.K. Narula, J. Am. Chem. Soc. 135 (2013) 12634–12645.
[3]K. Ding, A. Gulec, A.M. Johnson, N.M. Schweitzer, G.D. Stucky, L.D. Marks, P.C. Stair, Science 350 (2015) 189–192.
[4]C. Dessal, A. Sangnier, C. Chizallet, C. Dujardin, F. Morfin, J.L. Rousset, M. Aouine, M. Bugnet, P. Afanasiev, L. Piccolo, Nanoscale 11 (2019) 6897-6904.
[5]C. Dessal, T. Len, F. Morfin, J.L. Rousset, M. Aouine, P. Afanasiev, L. Piccolo, ACS Catal. 9 (2019) 5752-5759.