Single Molecule Studies of Heterogeneous Catalysts

With the development of space and time resolution and detector sensitivity of microscopic equipment, it is possible to study a single site on heterogeneous catalysts since the concentration of probe molecules that responding to various properties of catalytic sites are down to nanomolar scale. The fluorescence data collected from the well-separated dye molecules can be interpreted to the properties of the interacting sites on the solid matrix. The improvement of fluorophores, which are originated in biochemistry and biochemical engineering, make the study of using single molecule spectroscopic (SMS) method to characterize solid catalysts promising, especially the ones that are sensitive to acid sites. The material under study is mesoporous silica synthesized by sol-gel method. Compared with other solid catalysts, this material can be modified with a wide variety of functional groups and the pore structure can be strictly ordered, providing a simple and well-defined system to study. With the SMS method and appropriate dye molecules, the active sites can be located and characterized by the fluorescence behaviors of the probes, and this resolution is difficult to achieve for conventional methods. In-situ characterization is also possible by using SMS method, and the reaction condition can be realistic without the requirement of high vacuum or conductive surface. The current work is to study the aligned mesoporous silica functionalized with sulfuric groups. A coumarin-based dye, which is low pH sensitive, is used to map the acid sites and obtain the acidity distribution on the solid matrix. To confirm the result, some conventional methods will also be used to verify the data and the data interpretation by SMS method. This work will indicate the potential of applying single molecule spectroscopic method for the characterization of heterogeneous catalysts.