CO oxidation catalyzed by Au-Ag bimetallic nanoparticles supported in mesoporous silica

We report a novel Au - Ag bimetallic nanocatalyst supported on an acidic mesoporous aluminosilicate Au-Ag@APTS-MCM prepared by a two-step synthesis procedure, which is very active for low-temperature CO oxidation. Its catalytic activity is still quite appreciable after 1 year of storage under room conditions. The silane APTS [H₂N(CH₂)₃-Si(OMe) ₃] was used to surface functionalize mesoporous silica. The functionalized mesoporous silica was used to absorb the gold precursor AuCl ₄^- and silver precursor AgNO₃ to form gold-silver bimetallic nanoparticles inside the nanochannels after chemical reduction. The catalysts were activated by calcinations, followed with hydrogen reduction at 873 K. Using various characterization techniques, such as X-ray diffraction, UV-vis, transmission electrom microscopy, and X-ray absorption fine structure spectroscopy (EXAFS), we elucidated the structure and surface compositions. As compared with the previously reported Au-Ag@MCM, prepared by one-pot procedure, the new method yields smaller sizes of AuAg bimetallic nanoparticles (4-6 vs 20 nm). They exhibited higher activity in catalysis for low-temperature CO oxidation with high stability. Moreover, the catalyst is resistant to moisture over a long storage time. A synergetic effect in relative composition was also found. The EXAFS study shows that Ag predominantly resides on the surface of the bimetallic nanoparticle. This distribution helps to yield a catalyst that is very active in both CO and O₂ neighboring sites.