Importance of Size and Contact Structure of Gold Nanoparticles for the Genesis of Unique Catalytic Processes

• Published in: Chemical reviews Vol. 120; no. 2; pp. 464 - 525
• Main Authors: Ishida, Tamao, Murayama, Toru, Taketoshi, Ayako, Haruta, Masatake
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 22.01.2020
• Subjects: Activation; Alcohols; Aldehydes; Bilayers; Catalysis; Catalysts; Catalytic activity; Cerium oxides; Clusters; Epoxidation; Gold; Hydrogenation; Lattice vacancies; Metal oxides; MOX; Nanoparticles; Oxidation; Oxides; Palladium; Platinum; Propylene oxide; Reaction mechanisms; Silicon dioxide; Titanium
• ISSN: 0009-2665; 1520-6890
• DOI: 10.1021/acs.chemrev.9b00551

Since the discovery of catalysis by Au nanoparticles (NPs), unique catalytic features of Au have appeared that are greatly different from those of Pd and Pt. In this Review, we aimed to disclose how the unique catalytic abilities of Au are generated with respect to (a) the contact structures between Au and its supports and (b) the size of the Au particles. For CO oxidation, the catalytic activity of Au on reducible metal oxides (MO x ) is strongly correlated with the amount of oxygen vacancies of the MO x surface, which play a key role in O2 activation. Single atoms, bilayers of Au, sub-nm clusters, clusters (1–2 nm), and NPs (2–5 nm) have been proposed as the active sizes of the Au species, which may depend on the type of support. For propylene epoxidation, the presence of isolated TiO4 units in SiO2 supports is important for the production of propylene oxide (PO). Au NPs facilitate the formation of Ti–OOH species, which leads to PO in the presence of H2 and O2, whereas Au clusters facilitate propylene hydrogenation. However, Au clusters can produce PO by using only O2 and water, whereas Au NPs cannot. For alcohol oxidation, the reducibility of the MO x supports greatly influences the catalytic activity of Au, and single Au atoms more effectively activate the lattice oxygen of CeO2. The basic and acidic sites of the MO x surface also play an important role in the deprotonation of alcohols and the activation of aldehydes, respectively. For selective hydrogenation, heterolytic dissociation of H2 takes place at the interface between Au and MO x , and the basic sites of MO x contribute to H2 activation. Recent research into the reaction mechanisms and the development of well-designed Au catalysts has provided new insights into the preparation of high-performance Au catalysts.