High‐Resolution Single‐Turnover Mapping Reveals Intraparticle Diffusion Limitation in Ti‐MCM‐41‐Catalyzed Epoxidation

Abstract

Shedding light on catalysis: For the first time, transport phenomena and their influence on catalysis are directly observed for individual catalytic particles by single‐turnover mapping using high‐resolution fluorescence microscopy. The Thiele modulus could be measured with just one experiment, proving the existence of diffusional limitations for the Ti‐MCM‐41 catalyzed epoxidation of a fluorescent reporter molecule (see picture; TBHP=tert‐butylhydroperoxide).

Fragmentation patterns of boron‐dipyrromethene (BODIPY) dyes by electrospray ionization high‐resolution tandem mass spectrometry

“…In recent years, heterogeneous catalyst epoxidations have risen strongly in popularity . A specific feature of these reactions, in particular in the homogeneous phase, is the presence of a co‐agent in large excess.…”

“…In recent years, heterogeneous catalyst epoxidations have risen strongly in popularity. [16] A specific feature of these reactions, in particular in the homogeneous phase, is the presence of a co-agent in large excess. The concentrations of the substrate molecules in the micromolar range are required for detection by fluorescence spectroscopy.…”

Copper nanoparticle heterogeneous catalytic ‘click’ cycloaddition confirmed by single-molecule spectroscopy

“…In our strategy here, we apply the nascent area of single-molecule techniques to establish if catalysis is truly heterogeneous. Further, for those cases where improving the heterogeneous nature of the reaction is desirable, single-molecule-single nanoparticle studies can be a powerful tool for catalyst optimization [27][28][29][36][37][38][39] .…”

“…While examples to determine the phase of the catalyst remain rare, discerning the active regions of catalysts has been the focus of a number of recent single-molecule catalysis reports. Hofkens and co-workers 29,30 utilized single-molecule techniques to map the catalytic activity of zeolites and mesoporous materials. Single-molecule techniques have also been used to observe crystal-face-dependent catalysis of layered double hydroxides 31 , and face-dependent catalysis of gold nanoparticles [32][33][34] and has also been the subject of recent reviews [35][36][37][38] .…”

“…In this study, we combine mole scale reactions with singlemolecule studies utilizing total internal reflection fluorescence microscopy (TIRFM), an effective tool in studying heterogeneous nanoscale catalyst surface dynamics and reactivity 27,[29][30][31][32][33][34][35][36][37][38][39][40][41] . The success of TIRFM as a single-molecule technique hinges on the generation of an evanescent wave at the glass-sample interface that only allows irradiation of the sample within approximately 100 nm from the glass support surface 42 .…”