Mechanism visualization of nanocluster catalysis via in situ mass spectrometry.

Visualizing catalytic reaction processes and elucidating their mechanisms continue to pose substantial challenges in the field of catalysis. A comprehensive understanding is often hindered by the inherent heterogeneity of most catalysts and the scarcity of tools capable of correlating structure with activity at atomic resolution. Here, we describe the potency of paper spray ionization mass spectrometry to study molecularly defined nanoclusters in catalytic reactions. We identified key reaction intermediates and tracked their evolution during the reduction of 4-nitrophenol and Suzuki-Miyaura cross-coupling reactions. Critical information about the rate-determining step, the dynamics of active sites, and the catalyst evolutions was obtained, which is difficult to acquire using conventional techniques prevalent in heterogeneous catalysis research. Moreover, we uncovered reaction mechanisms distinct from those previously reported. The approach presented here is expected to play an important role in decoding the "black box" of catalytic reaction processes.