Facile synthesis of Ag-CuO/SBA-15 for aerobic epoxidation of olefins with high activity

An efficient 'structure-property' catalyst Ag-CuO/SBA-15 for aerobic epoxidation of olefins was designed and prepared via a simple grinding method, which provided a dynamic assembly driving force to push the precursors into the channels step by step. Partial melting on the precursor particles surface is necessary for synthesizing the Ag-CuO/SBA-15 catalysts. During the thermal grinding process, the partial melting Cu(NO₃)₂ first adhered on AgNO₃ particles surface because the N of AgNO₃ possess stronger interaction with Cu(NO₃)₂ than OH- of SBA-15, then the mixture of melting precursors on AgNO₃ particles surface were sucked into the channels of SBA-15 step by step. Finally, high dispersion of both Ag and CuO nanoparticles were formed in the SBA-15 channels after calcination. The interaction between Ag and CuO, which was characterized by high-resolution transmission electron microscopy, UV-vis and x-ray powder diffraction, enhances the catalytic activity of the catalysts, giving high conversion and selectivity to the epoxides. The reaction mechanism is as follows, the solvent xylene molecule was first oxidized on the Ag surface to form methyl-benzaldehyde (R1), and then moved to the CuO surface to form the peroxidic radical (R2), the peroxidic radical attacked the trans-stilbene C=C bonds on the CuO surface to obtain the epoxides. This synergistic effect shows high activity toward the epoxidation of trans-stilbene.

Digestive-Ripening-Facilitated Nanoengineering of Diverse Bimetallic Nanostructures

From an ingenious methodology for obtaining monodispersity, digestive ripening has advanced to become an outstanding solution-based synthesis route to realizing various bimetallic heterostructures. This feature article attempts to provide an overview of the various facets of the codigestive ripening process and the array of heterostructures that could be achieved by this technique. We briefly discuss the mechanism of digestive ripening in the case of monometallic elements and use that understanding to elucidate the mechanism of the less well established codigestive ripening strategy for designing bimetallic nanostructures. The systems studied by our group in the past decade for the fabrication of diverse heterostructures are highlighted in this article. The exploitation of digestive ripening to realize monodisperse bimetallic nanostructures by several other groups is also featured. In addition to digestive ripening agents, the significance of tuning various reaction parameters and its consequences on the final structure and morphology have also been discussed. Additionally, efforts based on theoretical studies to gain insight into the factors which dominate the mechanism of the digestive ripening process have also been covered. This article is a contribution to the understanding of the codigestive ripening methodology and a demonstration of its tremendous potential in achieving the desired bimetallic heteronanostructures.