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

Abstract

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.

The Basic Properties of Gold Nanoparticles and their Applications in Tumor Diagnosis and Treatment

“…For example, compared with spherical AuNPs, gold nanorods or gold nanostars are more suitable for photothermal therapy (PTT) or photodynamic therapy (PDT), because they can absorb near-infrared light (NIR) more efficiently [6]. Au clusters can produce propylene oxide (PO) by using only O 2 and water, whereas Au NPs cannot [7]. This will be covered in later paragraphs.…”

Gold catalysts containing interstitial carbon atoms boost hydrogenation activity

“…This complexity limits the correlation of the electronic structure with the catalytic properties, and industrial applications. It has been shown that there is no direct correlation between the number of cationic or anionic Au species and catalytic activity 20 .…”

A Review on Particle Size Effect in Metal‐Catalyzed Heterogeneous Reactions

“…[ 5‐6 ] One notable example in heterogeneous catalysis is Au‐catalyzed CO oxidation. [ 4,7 ] Several pioneer studies reported by Haruta et al . [ 8‐10 ] in late 1980s showed that gold NPs with a size of 3—5 nm deposited on reducible metal oxides such as Fe 2 O 3 , Co 3 O 4 , and TiO 2 were extraordinarily active for CO oxidation at a temperature as low as –73 °C, upturning the traditional view that Au is chemically inert in catalysis.…”

“…[ 8‐10 ] in late 1980s showed that gold NPs with a size of 3—5 nm deposited on reducible metal oxides such as Fe 2 O 3 , Co 3 O 4 , and TiO 2 were extraordinarily active for CO oxidation at a temperature as low as –73 °C, upturning the traditional view that Au is chemically inert in catalysis. [ 7 ] Tailoring the size of metal NPs is an effective and practical strategy for optimizing catalyst performance in industry, not only for the achievements of more efficient catalytic processes, but also for the conservation of precious metal resources. Accordingly, the particle size effect on heterogeneous metal catalysis has attracted tremendous interest from both fundamental science and industrial commercialization.…”