Staining Makes Catalytic Sites Fluoresce

A fluorescence microscopy method can be used to image catalytically active regions of selectively stained industrial catalyst particles, according to a team of researchers in the Netherlands and the U.S. (Nat. Chem., DOI: 10.1038/nchem.1148). The method, which was developed to probe acidic functionality in solid catalysts, provides a new diagnostic imaging tool for monitoring catalyst aging and deactivation. Motivated by biological tissue staining methods, Inge L. C. Buurmans, Javier Ruiz-Martínez, and Bert M. Weckhuysen of Utrecht University, and coworkers selectively delivered the heterocyclic compound thiophene to acid sites in fluid catalytic cracking (FCC) catalysts, a workhorse petroleum refining catalyst. Commercial FCC catalysts are typically formulated as micrometer-sized particles of zeolite Y in a matrix of clay, alumina, and silica. Then by applying a thermal treatment, the team oligomerized thiophene at the zeolite acid sites to form fluorescent probe molecules at those catalytically active positions. They selectively treated the matrix with a different dye. In that way, the team was able to compare fluorescence signals from individual fresh catalyst particles with various aged and deactivated ones and develop a correlation between fluorescence intensity and catalytic cracking activity.