Synergistic Effect in an Au−Ag Alloy Nanocatalyst:  CO Oxidation

Abstract

Au-Ag alloy nanoparticles supported on mesoporous aluminosilicate have been prepared by one-pot synthesis using hexadecyltrimethylammonium bromide (CTAB) both as a stabilizing agent for nanoparticles and as a template for the formation of mesoporous structure. The formation of Au-Ag alloy nanoparticles was confirmed by X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy, and transmission electron microscopy (TEM). Although the Au-Ag alloy nanoparticles have a larger particle size than the monometallic gold particles, they exhibited exceptionally high activity in catalysis for low-temperature CO oxidation. Even at a low temperature of 250 K, the reaction rate can reach 8.7 x 10(-6) mol.g(cat.)(-1).s(-1) at an Au/Ag molar ratio of 3/1. While neither monometallic Au@MCM-41 nor Ag@MCM-41 shows activity at this temperature, the Au-Ag alloy system shows a strongly synergistic effect in high catalytic activity. In this alloy system, the size effect is no longer a critical factor, whereas Ag is believed to play a key role in the activation of oxygen.

Understanding the synergistic effects of gold bimetallic catalysts

“…The resultant gold catalyst, with an average gold particle size of $5 nm, was only moderately active for low-temperature CO oxidation [63]. Assuming that Ag might be able to assist the activation of oxygen, Mou and co-workers further attempted to synthesize an Au-Ag@MCM catalyst using the same one-pot method [27]. The schematic synthesis procedure is shown in Fig.…”

“…The synthesis of Au-Ag and Au-Cu bimetallic NPs has led to great progress in the optical applications [55,56], while it has been less reported for the purpose of catalysis. Mou and Zhang's groups are among the first that reported synergistic effects of Au-Ag [27] and Au-Cu [21] in catalytic reactions.…”

“…Based on the chemical properties of the second metal, we can classify gold-based bimetallic catalysts into two types. The first type is Au-BM catalysts, where BM refers to base metals such as Cu [21][22][23][24][25][26], Ag [27][28][29][30][31][32][33][34][35], Co [36][37][38], and Ni [39][40][41], and the second type is Au-PGM catalysts, where PGM refers to platinum group metals such as Pt [42,43], Pd [44][45][46][47], Rh [48], and Ir [49]. This classification may not cover all the gold bimetallic catalysts, but it will facilitate understanding the synergistic effect between gold and the second metal in catalysis.…”

Development of novel supported gold catalysts: A materials perspective

“…For instance, Crooks and co-workers synthesized PdAu/TiO 2 using dendrimer-encapsulated alloy nanoparticles as the precursor, and found that the activities of the catalysts in CO oxidation followed the sequence PdAu/TiO 2 > Pd/TiO 2 > Au/TiO 2 [235]. Mou and coworkers synthesized AuAg/Al-MCM-41 catalysts via both a one-step approach [236][237][238][239] and a two step method [55], and demonstrated enhanced catalytic activity in CO oxidation associated with the alloyed silver. Zhang and co-workers used a similar two-step approach to prepare AuAg/SiO 2 [53], AuAg/Al 2 O 3 [53], AuCu/SBA-15 [240], and AuCu/silica gel [63] catalysts, and demonstrated their good performance in CO oxidation.…”

Using Gelatin as Protecting Agent and Organic Template to Synthesize Noble Metal Nanoparticles and Metal Nanoparticles@Mesoporous Silica for SERS and CO Oxidation Applications

“…Thus, the Au nanoparticles@mesoporous silica can be used as a highefficiency catalyst, particularly for CO oxidation. (13,14) The resulting Au nanoparticles@ mesoporous silica showed catalytic capability of CO oxidation. CO conversion rate increases with increasing reaction temperature and Au nanoparticle content (Fig.…”