In situ absorption spectroscopy technology provides direct evidence for revealing reaction pathways, active sites, and kinetic mechanisms by real-time monitoring of the spectral characteristics of reactants, intermediates, and products during catalytic reactions, and has become one of the core tools for studying catalytic mechanisms.
1. Real time tracking of reaction intermediates to reveal reaction pathways
Catalytic reactions typically involve the generation and conversion of multi-step intermediates, and traditional offline analysis is difficult to capture these transient species. In situ absorption spectroscopy (such as UV Vis, IR, or Raman spectroscopy) can detect changes in the light absorption or vibration signal of the reaction system in situ, directly identifying the presence of intermediates. For example, in the photocatalytic CO ₂ reduction reaction, in situ UV Vis spectroscopy can monitor the characteristic absorption peaks of key intermediates such as COOH ⁻ and CO. Combined with density functional theory (DFT) calculations, the gradual conversion path from CO ₂ to CO in the reaction can be clarified, avoiding intermediate decomposition or misjudgment caused by offline sampling.
2. Locate active sites and optimize catalyst design
In situ spectroscopy technology can be combined with spatial resolution capabilities (such as visible light spectroscopy) to locate active sites in different regions of the catalyst surface. For example, in metal nanoparticle catalysts, in situ surface enhanced Raman spectroscopy (SERS) can display differences in the adsorption strength and product selectivity of reactants on specific crystal planes (such as Au {111}), thereby guiding catalyst morphology control (such as synthesizing nanoparticles with specific exposed crystal planes) to enhance activity. In addition, in situ X-ray absorption spectroscopy (XAS) can analyze changes in metal valence states and reveal the dynamic evolution of active sites in redox cycles.
3. Quantify reaction kinetics to guide process optimization
By continuously monitoring the changes in spectral signals over time, in-situ absorption spectroscopy can obtain kinetic parameters such as reaction rate constants and conversion frequencies. For example, in enzyme catalyzed reactions, in situ UV Vis spectroscopy can track substrate consumption and product generation curves, combined with fitting the Mie equation, to clarify the enzyme substrate binding constant (Km) and maximum reaction rate (Vmax), providing a basis for optimizing reaction conditions such as pH and temperature.
4. Combining multiple technologies to overcome the limitations of a single method
In situ absorption spectroscopy is often combined with mass spectrometry, chromatography, or electrochemical techniques to achieve multidimensional correlation analysis of "spectrum composition performance". For example, in electrocatalytic CO ₂ reduction, in-situ infrared spectroscopy combined with online gas chromatography can simultaneously monitor the generation of reaction intermediates (such as * COOH ⁻) and gas products (such as CO, H ₂), and construct a complete reaction network model.
Conclusion: In situ absorption spectroscopy, with its real-time, non-destructive, and high sensitivity, has become the "eye" of catalytic mechanism research, promoting the development of rational catalyst design and precise control of reaction processes, and providing key support for breakthroughs in green chemistry and energy conversion technology.