Methane catalysis

Since the Industrial Revolution, human activities have significantly disrupted the natural cycle of materials, resulting in the emission of large quantities of greenhouse gases such as carbon dioxide, methane and nitrous oxide. Among these, methane (CH₄) is a major greenhouse gas, accounting for between 4 per cent and 19 per cent of the greenhouse effect, second only to CO₂ (which accounts for 55 per cent).

Methane is not only a greenhouse gas but also a green energy source, characterised by high calorific value and abundant reserves. Low-concentration methane accounts for a significant proportion of these reserves, such as coal seam gas and landfill gas.

Releasing methane into the atmosphere not only wastes resources but also exacerbates the greenhouse effect; therefore, the rational utilisation of low-concentration methane serves a dual purpose of energy conservation and environmental protection.

Catalysts can lower the ignition temperature of methane; this not only prevents environmental pollution from NOx produced by high-temperature flame combustion of methane but also enables more complete combustion of methane.

There are generally two categories of catalysts for catalytic combustion of methane: precious metals (such as Pd, Ru and Pt) and non-precious metals (such as perovskites, hexaluminates and composite oxides). To determine whether a catalyst possesses good catalytic combustion activity for methane, it is necessary to measure the concentration of methane before and after catalytic combustion.

Precious metals are the most active catalysts, exhibiting high catalytic combustion activity at low temperatures; consequently, they are widely used in methane catalytic combustion reactions. However, due to their poor high-temperature stability, they lose their activity at temperatures above 1,000 °C as the precious metal particles agglomerate, burn or evaporate. Furthermore, as precious metals are expensive, their application is subject to certain limitations.

Alumino-silicate compounds are characterised by high thermal stability, high strength and high resistance to thermal shock; they can be directly fabricated into honeycomb ceramic structures for use as supports in methane combustion. Perovskite-type composite oxide catalysts exhibit high catalytic activity for methane combustion due to their strong lattice oxygen activity and mobility, as well as their high thermal and chemical stability [5].

Qualitative and quantitative analysis of methane is typically carried out using gas chromatography or online mass spectrometry; both instruments have their own characteristics and are suited to different application requirements.

Online mass spectrometers offer analysis speeds in the millisecond range, ensuring dynamic and continuous online monitoring. This overcomes the time lag associated with gas chromatography, which requires analysis times of several minutes or even tens of minutes, making them suitable for applications such as catalytic methane combustion that demand high real-time performance. For the catalysts mentioned above, the activity of each catalyst can be determined by measuring the methane concentration before and after catalytic combustion using an online mass spectrometer.

By coupling an online mass spectrometer with a chemical adsorption analyser to analyse, in real time, the types and concentrations of gases at the analyser’s outlet, it is possible to determine the effects of material composition and calcination temperature on the physicochemical properties of the catalyst and its methane catalytic activity. This method offers advantages such as high resolution, good sensitivity, strong qualitative and quantitative capabilities, and speed,

It has now become the predominant method for catalytic laboratory analysis. The application of online mass spectrometers in the catalysis industry not only enables the qualitative and quantitative analysis of gases but also enhances the efficiency of catalytic experiments.

Catalyst Evaluation

The production process of ethylene oxide via the oxidation of ethylene involves the catalytic oxidation of ethylene to form ethylene oxide under the action of a silver catalyst.

In this process, trace amounts of ethylene dichloride (EDC) are added as a reaction regulator to improve the catalyst’s selectivity and activity.

During the evaluation of silver catalysts, the catalyst in the reaction system is highly sensitive to EDC; an excessive amount will cause catalyst poisoning and loss of activity, whilst too little will lead to ‘temperature runaway’ in the catalyst bed. Furthermore, when evaluating catalysts

process conditions that yield excellent performance, the EDC concentration in the reactor inlet gas is sometimes adjusted in real time according to the catalyst’s activity at different stages, to ensure the catalyst maintains good performance over the long term. This requires timely and accurate analysis of the EDC concentration in the inlet gas. Consequently, achieving rapid and accurate analysis of the EDC concentration in the reaction gas at the inlet of the micro-reactor is a crucial task in the evaluation of silver catalysts

Analytical method for the online determination of trace amounts of dichloroethane (EDC) in a reaction test apparatus. This method enables the online quantitative analysis of trace amounts of EDC in the inlet gas. Compared with offline chromatographic analysis, mass spectrometry offers faster analysis, facilitates real-time monitoring of EDC in the inlet gas, and eliminates errors in analytical results caused by the sampling process in offline chromatographic analysis.