Free radicals and reactive intermediates

Free radicals are species containing unpaired electrons and exhibiting highly reactive chemical properties; whilst they are present in large quantities during combustion, pyrolysis and catalysis, they are extremely difficult to capture—they have short lifetimes and low concentrations, and often react and disappear during conventional sampling and chromatographic separation. Typical examples include the methyl radical (·CH₃), the peroxymethyl radical (CH₃OO·), acetylene (CH₂=C=O) and formaldehyde (HCHO).

The New Source ProC series and ProC-1C system list the ‘detection of unstable intermediate products such as free radicals, formaldehyde and ketones’ as a core capability, and provide specific examples: in the methane oxidation-coupling (OCM) reaction, reactive intermediates such as the methyl radical, peroxymethyl radical and formaldehyde can be captured and detected in situ; in the methanol-to-olefins (MTH) reaction, they can directly capture formaldehyde and observe its dynamic changes from the induction phase to the deactivation phase; in research on the production of olefins from synthesis gas, they have confirmed that acetylene is a key intermediate in the formation of low-carbon olefins. These intermediates are precisely the most critical—and also the most difficult to observe directly—aspects of catalytic mechanism research.

This detection is achieved through two technical approaches. Firstly, photoionisation produces virtually no fragments, enabling the intermediates to be directly identified in their molecular ion form without being broken down into fragments that are difficult to trace. Secondly, in-situ sampling techniques such as ‘molecular beam sampling’ allow gas from the reaction zone to rapidly enter the ionisation region in the form of a molecular beam, thereby shortening the transport time and suppressing reactions en route, thus ‘freezing’ transient species. Combined with sampling at the second scale (a sampling frequency of 30,000 Hz) and high-efficiency ion lenses, the instrument is able to complete ionisation and recording before the intermediates have disappeared.

This is precisely why in situ mass spectrometry is regarded as “one of the most powerful methods for detecting reactive intermediates in the gas phase”. For researchers investigating reaction mechanisms, observing reactive intermediates means being able to distinguish between “direct conversion of reactants into products” and “gradual transformation via a key intermediate”, thereby guiding catalyst design and the optimisation of reaction conditions. The description of the New Ceyuan ProC-1C cites research examples involving systems such as FTO, OCM and MTH, and notes that the relevant findings have been published in journals such as *Science*—its value lies not in the instrument itself, but in its ability to transform ‘invisible reaction processes’ into interpretable spectra and time curves.