Observing Single‐Atom Catalytic Sites During Reactions with Electrospray Ionization Mass Spectrometry

Abstract

Single‐atom catalysts (SACs) have become a prominent theme in heterogeneous catalysis, not least because of the potential fundamental insight into active sites. The desired level of understanding, however, is prohibited due to the inhomogeneity of most supported SACs and the lack of suitable tools for structure–activity correlation studies with atomic resolution. Herein, we describe the potency of electrospray ionization mass spectrometry (ESI‐MS) to study molecularly defined SACs supported on polyoxometalates in catalytic reactions. We identified the exact composition of active sites and their evolution in the catalytic cycle during CO and alcohol oxidation reactions performed in the liquid phase. Critical information on metal‐dependent reaction mechanisms, the key intermediates, the dynamics of active sites and even the stepwise activation barriers were obtained, which would be challenging to gather via prevailingly adopted techniques in SAC research. DFT calculations revealed intricate details of the reaction mechanisms, and strong synergies between ESI‐MS defined SAC sites and electronic structure theory calculations become apparent.

Electrothermal Water‐Gas Shift Reaction at Room Temperature with a Silicomolybdate‐Based Palladium Single‐Atom Catalyst

“…While XPS suggested electron transfer from Pd 1 /CsSMA to PMA in solution, this includes the possibility of the transfer of an oxygen vacancy [34] . After the reaction, the m / z peak determined by electrospray ionization mass spectrometry (ESI‐MS, Figure 4d) near 1825.55 can be fitted by two individual peaks centered at 1824.56 and 1826.57, corresponding to the {H 2 PO 4 [Mo VI O 3 ] 12 } − and {H 4 PO 4 [Mo VI O 3 ] 10 [Mo V O 3 ] 2 } − species, respectively.…”

The Opportunities and Challenges in Single‐Atom Catalysis

“…Consequently, insight into the reaction mechanisms is essential for the design of highly active SACs with suitable supports. Furthermore, though the micro‐environment of catalytic center can be controlled in some extent, the reaction‐driven structural transformation cannot be neglected [38] . There are still debates about the oxidation state, or the accurate number of metal ions in the active sites under working conditions [39] .…”

Panoramic Mechanistic Insights into Hydrogen Production via Aqueous-Phase Reforming of Methanol Catalyzed by Ruthenium Complexes of Bis-N-Heterocyclic Carbene Pincer Ligands

“…With the best-performing complex C7 , mechanistic studies were carried out. In addition to the commonly used spectroscopic techniques/methods, including nuclear magnetic resonance (NMR) analysis of the reaction mixture, kinetic isotope effect (KIE) experiments, gas chromatographic analyses of the product mixture, and density functional theory (DFT) calculations of reaction free–energy profiles, our mechanistic studies rely heavily on the use of high-resolution electrospray ionization-mass spectrometry (HRESI-MS), a sensitive technique capable of providing valuable information on the identity of the many intermediates that are often hard to detect by any other means; ,,− its power and usefulness in helping deriving catalytically active species and putting forth plausible reaction mechanisms have recently been demonstrated in the recent works by us and other researchers. ,,,− …”