In heterogeneous catalysis gas (or liquid)-solid catalyst reactions take place at the atomic level at elevated temperatures. Understanding and control of complex catalytic reactions on the atomic scale are crucial for the rational development of improved catalysts and processes. The development of the first atomic resolution environmental (scanning) transmission electron microscope (E(S)TEM) is described (1-6) including for the direct visualisation of reacting individual atoms in gas-solid reactions in the working state in real time (3-6), opening up striking new opportunities for studies of catalysis at the atomic level.  Our development of the atomic resolution ETEM (2) is now used globally.  Benefits of the in-situ studies include new knowledge, improved and more environmentally beneficial technological processes for healthcare and renewable energy as well as better or replacement mainstream technologies in the chemical and energy industries.

Examples include heterogeneous catalysis of biomass conversion into bioenergy and water gas shift (WGS) reaction (employing carbon monoxide and water) which is the basis of heterogeneous catalysis important in the generation of clean hydrogen energy for fuel cells, transportation fuels and in ammonia manufacture (7). Potential supported noble metal catalysts are examined for low temperature WGS catalysis (Fig.1) and compared with reaction data and modelling. The in-situ observations in WGS have revealed the formation of clusters of only a few noble metal atoms resulting from single atom dynamics and the catalytic effect of low coordination surface sites.  The new insights have important implications for applications of nanoparticles in chemical process technologies including for transportation fuels and emission control.

References

1. P.L. Gai, et al: Science 267 (1995) 661.
2. E.D. Boyes and P.L. Gai, Ultramicroscopy  67 (1997)219.
3. P.L. Gai and E.D. Boyes, Microscopy Research and Tech. 72 (2009) 153.
4. E.D. Boyes, M. Ward, L. Lari and P.L. Gai, Ann. Phys. (Berlin) 525 (2013) 423.
5. P.L. Gai, L. Lari, M. Ward and E.D. Boyes, Chemical Physics Letters, 592 (2014) 355.
6. E.D. Boyes and P.L. Gai, Comptes Rendus Physique, 15 (2014) 200.
7. P.L. Gai, K. Yoshida, M R Ward, M Walsh, E D Boyes, et al : Catal. Sc. Tech.  2015:  DOI: 10.1039/c5cy01154j
8.Email :  pratibha.gai@york.ac.uk  

Acknowledgements

We thank the EPSRC (UK) for the strategic critical mass research grant EP/J018058/1.

Figures:

Dynamic ceria supported gold nanocatalyst in CO+H2O environment (WGS) shows faceted gold single crystal NP in [110] with atomically clean {111} surfaces. The NP stops sintering, suggesting a lower surface energy configuration is reached. Time resolved real time ETEM atomic images in WGS video sequences: after (e) 6.8 sec; (f) 8.35 sec; (g) 14.3 sec and (h) 37 sec. Once this lower energy configuration is achieved Au NPs do not grow even after a long periods of reaction. But movements of atomic species (clusters and atoms) were observed in other areas in the water-gas shift reaction.

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