When Catalysis Research Meets Online Mass Spectrometry: How In Situ Analysis Is Changing Our Understanding of Reaction Mechanisms

There is a saying in the field of catalysis research: offline analysis studies the ‘outcome of the reaction’, whilst online analysis captures the ‘process of the reaction’. The difference between the two may lead to entirely different conclusions regarding the mechanism in certain fast-reacting systems.

In recent years, in situ characterisation schemes that couple online mass spectrometers with catalytic reactors have become an important tool in research into heterogeneous catalysis, photocatalysis and thermocatalysis. The core logic of this approach is to direct gaseous products from the reactor outlet into the mass spectrometer’s sample introduction system via the shortest possible tubing, and to continuously acquire mass spectrometry data at intervals of a few seconds, thereby obtaining real-time kinetic curves of reactant consumption and product formation.

Time-resolved catalysis: from discrete sampling to continuous tracking

Traditional methods of catalytic mechanism research—such as sampling at fixed time intervals followed by offline chromatographic analysis—face a ceiling in terms of temporal resolution. For an intermediate product with a half-life of only a few tens of seconds, if the sampling interval is five minutes, traces of this intermediate may never be detected.

The full-spectrum parallel acquisition capability of time-of-flight mass spectrometers (TOF-MS) is ideally suited to such scenarios. The ProC-1C in-situ catalysis/pyrolysis mass spectrometry analysis system, developed by Hefei Xinceyuan Instrument Technology Co., Ltd., combines a micro-catalytic reactor with a dual-field reflection TOF-MS detection unit. It supports continuous, on-line, full-component analysis of the gas exiting the reactor under various experimental modes, including programme temperature ramping, isothermal reactions or pulsed injection.

The analytical logic of this system stands in stark contrast to the traditional “end-point sampling” method. In temperature-programmed desorption (TPD) experiments, the system can record mass spectrometry signals at a rate of one frame per second or every few seconds throughout the entire heating process, generating continuous temperature–signal intensity spectra; in pulsed chemical adsorption experiments, changes in gas composition following each pulse can be visualised in real time. This density of data results in a substantial improvement in the accuracy of kinetic parameter fitting.

The Unique Value of the Photoionisation Source

In catalytic reactions, particularly hydrocarbon conversion reactions, the product mixture often contains saturated hydrocarbons, alkenes and aromatic hydrocarbons simultaneously—these three types of compounds produce extensive overlapping fragment peaks in traditional electron impact (EI) sources, posing difficulties for mass spectrometric analysis.

The vacuum ultraviolet photoionisation (PI) sources employed in the ProC-1C and ProC-1/ProC-2 series offer distinct performance in this regard. With VUV photon energies of approximately 10.0–10.6 eV—close to the ionisation energies of most organic molecules—they produce very few, if any, fragment peaks. For isomers with similar molecular weights but different structures, photionisation mass spectrometry primarily yields molecular ion peaks, with fragment peak abundances far lower than those observed in EI source spectra. This ‘soft ionisation’ characteristic enables mixtures of reaction products to be directly distinguished into molecular weight signals of different components without the need for chromatographic separation, thereby significantly simplifying the data analysis process for online analysis.

From a research tool to an industrial process analysis instrument

The role of online mass spectrometers is evolving from that of purely laboratory-based research tools to that of online process analysers in the chemical and petrochemical industries. In scenarios such as catalytic cracking units in oil refineries, the outlets of gasifiers in coal chemical plants, and the headspace of reactors in the fine chemicals sector, real-time monitoring of changes in gas composition is not only necessary for process optimisation but also an essential requirement for safe production.

The ProC-1 and ProC-2 online time-of-flight mass spectrometers offer different configuration options in this regard, covering a wide range of applications from millisecond-scale kinetic tracking in laboratories to long-term online monitoring in industrial settings. The core competitive advantage of these products lies in combining the high acquisition rate of TOF-MS with the low fragmentation characteristics of the PI source—the synergistic value of these two features is particularly evident in scenarios requiring rapid identification of unknown components or the differentiation of isomers.

Technological Trends: In-situ, Online, Real-time

In a sense, the history of analytical chemistry is a history of ever-increasing analytical speed. From gravimetric analysis to titrimetric analysis, from chromatography to mass spectrometry, and from offline to online—each step has shortened the time between ‘sampling’ and ‘obtaining results’.

In-situ catalytic mass spectrometry systems have compressed this interval to the order of seconds or even shorter time scales. For research into catalytic mechanisms, this means progressing from “comparing pre- and post-reaction states” to “dynamic tracking during the reaction process”; such a shift in the research paradigm often has a more far-reaching impact than improvements in individual technical metrics.

Information Summary

Hefei Xinceyuan Instrument Technology Co., Ltd. – Catalytic Analysis Products:

• ProC-1C In-situ Catalysis/Pyrolysis Mass Spectrometry Analysis System (Catalytic Reactor–TOF-MS Coupling, supporting TPD/TPR/Pulsed Chemical Adsorption modes, etc.)

• ProC-1 / ProC-2 Online Time-of-Flight Mass Spectrometers (Dual-Field Reflection TOF-MS + PI Photoionisation Source)

• ProC-1S Multi-component Dynamic Flue Gas Analysis System

Core technologies: Photoionisation (PI, soft ionisation with low fragmentation), dual-field reflection time-of-flight mass spectrometry (high resolution). Official website: https://www.neo-source.com.cn/