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 [H 2 N(CH 2 ) 3 -Si(OMe) 3 ] was used to surface functionalize mesoporous silica. The functionalized mesoporous silica was used to absorb the gold precursor AuCl 4and silver precursor AgNO 3 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 O 2 neighboring sites.

A new class of potential magnetic resonance imaging contrast agents with nanosized mesoporous silica as the metal carrier is reported. Gadolinium-incorporated mesoporous silicas were synthesized by using longchain surfactant as a template. The products were characterized with X-ray powder diffraction, nitrogen adsorption-desorption isotherms, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, 29 Si-MAS NMR, and proton relaxivity. The materials showed much higher relaxivities, r 1 and r 2 , than Gd-DTPA. The particles are nanosized and can enter cells easily. This is a completely novel biomedical application of mesoporous silica materials.