Preface

Heterogeneous catalysts are ubiquitous, typically including metal oxides, zeolites, and supported metal catalysts. They have found many applications in the synthesis of chemicals and materials, the conversion of fossil, hydrogen and biomass fuels, and the protection of environments. Supported metal catalysts are at the heart of heterogeneous catalysis. These catalysts include platinum, palladium, rhodium, and silver supported on oxide supports and have played key roles in many important chemical processes. For instance, platinum catalysts are useful for hydrotreating and complete oxidation, whereas palladium and rhodium are components in catalysts used for ablating car emissions, silver catalysts are useful in selective oxidation.

Gold was initially regarded as an inactive metal in catalysis. Gold catalysts prepared by traditional impregnation of HAuCl₄ followed by calcination usually have big gold particles, thus being inactive in reactions such as CO oxidation. However, in the 1980s, Haruta and co-workers in Japan have found that gold catalysts prepared by coprecipitation or deposition-precipitation have small gold nanoparticles and are highly active for CO oxidation. In the 1990s, Goodman and co-workers have discovered that the CO oxidation activity correlates nicely with the size of gold nanoparticles, being the highest when the size of gold nanoparticles is about 3 nm.

Since then, there have been a number of papers dealing with the synthesis of gold catalysts. Attention has been paid to the synthesis methods and synthesis details, including pH values during synthesis, gold loadings, aging temperature and duration, calcination conditions, and pretreatment conditions. These catalysts were often characterized by a number of techniques, such as X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), etc. CO oxidation has been chosen as a probe to compare the activity of different gold catalysts prepared. Often a “good” gold catalyst can exhibit high activity in CO oxidation well below room temperature.

As the research proceeds, there have been more papers reporting the application of gold catalysts in other reactions, such as selective oxidation or hydrogenation of organic molecules, elimination of other environmental pollutants in air and water, and purification of hydrogen fuel by selective oxidation of CO or the water-gas shift reaction. In addition, attention has been paid to the nature of active sites and reaction mechanisms. They can be studied by spectroscopic methods using supported catalysts under operando conditions, or using model catalysts such as single-crystal gold surfaces or gold nanoparticles supported on planer films. Finally, DFT calculations can help understand the nature of active sites and reaction mechanisms. These are really tough questions and the conclusions in different papers are often controversial due to different preparation details and properties of different catalysts.

Bond, Louis, and Thompson published an outstanding book “Catalysis by Gold” in 2006. That book summarized the various aspects of gold catalysis, and is particularly suitable for a new researcher of the field. Several years have passed by, and the field has undergone significant development. More and more new gold catalysts have been developed, and gold catalysts have found more applications in reactions other than CO oxidation. It is time-consuming to search through such a body of work, especially when new papers are published all the time.

The current book presents a collection of overviews, written by experts in the field, on the recent development of heterogeneous gold catalysts and catalysis. The first three chapters are devoted to the synthesis and design of new gold catalysts. Chapter 1 by Ma and Dai summarizes the several strategies for the design of new gold catalysts with enhanced thermal stability. Chapter 2 by Li and Jin overviews the synthesis, structure, thermal stability and catalytic applications of well defined gold nanoclusters and their supported forms. Chapter 3 by Murray and co-workers describes the preparation, characterization, and properties of nanocrystal superlattices as a new class of model materials for obtaining fundamental insights in catalysis.

The next four chapters are related to the application of gold catalysts in ablating environmental pollutants. In Chapter 4, Chen and Sasirekha summarize various metal oxide-based gold catalysts for preferential oxidation of CO in H₂ stream. In Chapter 5, Ivanova and co-workers review the development of various metal oxide-based gold catalysts for the water-gas shift reaction. In Chapter 6, Ma and Hao briefly summarize the application of gold catalysts in complete oxidation of CO, ethylene, and formaldehyde, as well as in the decomposition of ozone, N₂O, and NO. In Chapter 7, Zanella and co-workers review the modification of various semiconductors by gold nanoparticles for photocatalytic removal of water pollutants and for photocatalytic hydrogen production.

Chapters 8–11 are about the application of gold catalysts in the synthesis of chemicals via selective oxidation or hydrogenation. Han and co-workers summarize the application of heterogeneous gold catalysts in selective oxidation of alkanes, alkenes, alcohols, and aldehydes, and briefly introduce Fenton-like reaction and photocatalytic degradation. Zhong and co-workers furnish a long review on the application of heterogeneous gold catalysts for selective oxidation reactions. Simakova and Murzin concisely report the selective oxidation of biomass-derived secondary alcohols using gold catalysts. Finally, Keane and co-workers describe the selective hydrogenation of various organic substrates using supported gold catalysts.

Chapters 12–15 focus more on the fundamental aspects of heterogeneous gold catalysts and catalysis. Wu and Liotta summarize the interaction between gold and various reducible oxide supports, which is important for achieving high catalytic activity. Centeno and co-workers describe the oxygen vacancies presented in gold catalysts based on reducible and non-reducible supports, together with their role in oxidation catalysis. Wu and Overbury summarize their infrared spectroscopic study toward understanding nature of active sites and reaction mechanisms on gold catalysts based on non-reducible supports such as SiO₂, FePO₄, and LaPO₄. Finally, Huang summarizes their fundamental studies based on single crystalline and supported gold catalysts.

Overall, this book furnishes a diversified collection of overviews on various aspects of heterogeneous gold catalysts and catalysis. We wish to thank all the authors and publishing staff for their hard work.

Zhen Ma

Fudan University, P.R. China

Sheng Dai

Oak Ridge National Laboratory, TN, USA