New Frontiers in Gold Catalyzed Reactions

Abstract

BackgroundFor many years, gold has been regarded as a poor catalyst due to its chemical inertness towards reactive molecules such as oxygen and hydrogen. The interest in using gold in catalysis has increased during the last 20 years, since Haruta reported the surprisingly high activity in CO oxidation at low temperature for small (3-5 nm) gold particles supported on various oxides.Since then, gold nanostructured catalysts have attracted, rapidly growing attention, due to their potential applicability in various reactions of industrial and environment interest. The catalytic applications of gold have been, indeed, explored in several processes, such as NO removal, catalytic combustion of Volatile Organic Compound (VOC), hydrotreatment and chemical processing, and purification of hydrogen for fuel cell applications. Moreover, gold catalysts are, nowadays, employed as air-cleaning devices, for respiratory protection (gas masks), as sensors to detect individual poisonous or flammable gases, as well as deodorizers. Gold catalysts with low-temperature activity towards CO and hydrocarbons oxidation are suitable also for vehicles exhaust gas treatment, especially during the cold start period. Accordingly, at the end of 2007 the company Nanostellar announced the development of a diesel exhaust catalyst using a first catalytic component based on gold alloyed with palladium as the active component for CO oxidation. Nevertheless, despite the extensive recent efforts addressing the extraordinary catalytic behavior of gold nanoparticles, the attainment of the best performing supported gold catalyst is still a challenge and the origin of the structure sensitivity of Au catalytic activity is yet to be completely unravelled. The main reason for this is ascribed to the multiplicity of factors influencing the catalytic activity, including the size of the Au clusters, the oxidation state of gold, the nature of the support material, the Au-support interface, and the preparation method. The catalytic performances of gold nanoparticles have been correlated, in turn, with electronic (quantum size effect, oxidation state), structural and support (defects, perimeter interface) effects, but a OPEN ACCESS

Reducible Support Effects in the Gas Phase Hydrogenation of p-Chloronitrobenzene over Gold

“…The use of Au in hydrogenation reactions has been studied to a lesser extent, and the available literature has been compiled and assessed in reviews by Claus, Hashmi, and McEwan et al Work to date has largely focused on the conversion of carbon oxides, alkenes, alkynes, and α,β-unsaturated aldehydes and ketones. , Catalyst performance has shown a dependence on synthesis, Au particle size/shape, and support characteristics . Taking the latter, a range of catalytic responses has been observed for Au on different oxides. ,− The support can affect Au morphology and dispersion via surface interactions , where smaller (≤10 nm) Au particles exhibit electronic properties distinct from bulk Au . Moreover, the incorporation of Au is known to influence support reducibility, notably in the case of ceria (CeO 2 ) …”

Synthesis of Catalysts and Its Application for Low-Temperature CO Oxidation

“…The small Au particle size, narrow Au particle size distribution, and well Au dispersions on CoO -TiO 2 support play the key roles. The presence of CoO could stabilize the nano Au particles, resulting in high activity of the catalyst [20][21][22][23][24][25].…”