Table 1. Comparison of Techniques for In Situ Imaging of Heterogeneous Catalysis.

Technique	Sample environment	Detection method	Characterizes	Detects reaction products?	Typical spatial resolutiona	Typical acquisition ratea	Requirements/limitations
STM	Vacuum	Tunneling current	Surface structure	If adsorbed on the surface	Atomic, 0.01 nm	Scan rates vary: 0.1–100 s for a 10 × 10 nm2 region	Requires clean, atomically flat surfaces
Gas & liquid-cell TEM	Electron-transparent cell in vacuum	Electron transmission/diffraction	Particle structure and morphology	When combined with GC or EELS	Atomic to nanoscale, 0.01–10 nm, depends on liquid thickness	8–150 frames/s for a region of 2.5 × 2.5 μm2 (low-res) to 25 × 25 nm2 (high-res)	Cells need high electron transparency; samples are subject to beam damage
SECM	In liquid, open to air	Electrochemical current	Charge-transfer rate	Detects rate of redox reactions	Nano- to microscale 0.05–10 μm	Scan rates vary from 30 nm/s to 10 μm/s	Primarily restricted to redox reactions
STXM	X-ray-transparent liquid cell	X-ray transmission	Distribution of elements and their oxidation states	No	Nanoscale 40–100 nm	Scan rates vary: 100 s to >1 h for a 1 × 1 μm2 region	Requires synchrotron radiation and specialized cell design
SMF	In liquid, open to air	Fluorescence	Number of product molecules generated	If they are fluorescent	Nanoscale 10–50 nm	10–70 frames/s for an 80 × 80 μm2 region	Requires samples and substrates with low fluorescence background

^aThe spatial resolutions and acquisition rates provided are based on representative examples. The resolution and either scan rate (for STM, SECM, and STXM) or frame rate (for TEM and SMF) will depend on the specific sample, reaction conditions, and instrument used.