A spatial-resolved online MS study on OCM reaction catalyzed by Mn-Na2WO4/SiO2 system for radicals coupling mechanistic insight

doi:10.1016/S1872-2067(25)64694-8

Chinese Journal of Catalysis ›› 2025, Vol. 74: 167-176.DOI: 10.1016/S1872-2067(25)64694-8

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A spatial-resolved online MS study on OCM reaction catalyzed by Mn-Na₂WO₄/SiO₂ system for radicals coupling mechanistic insight

Ningxujin Ding^a, Danyu Wang^a, Shihui Zou^b, Jie Fan^b, Lyubov Alexandrovna Isupova^c, Junyu Lang^a^,^*(), Yong Yang^a^,^d^,^*()

^aSchool of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
^bKey Laboratory of Applied Chemistry of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou 310036, Zhejiang, China
^cBoreskov Institute of Catalysis SB RAS, Lavrentiev Ave. 5, Novosibirsk 630090, Russia
^dShanghai Key Laboratory of High-resolution Electron Microscopy, ShanghaiTech University, Shanghai 201210, China

Received:2025-01-07 Accepted:2025-03-18 Online:2025-07-18 Published:2025-07-20
Contact: *E-mail: yangyong@shanghaitech.edu.cn (Y. Yang), langjy@shanghaitech.edu.cn (J. Lang).
Supported by:
Ministry of Science and Technology of National Key R&D Program of China(2023YFB4005200);National Natural Science Foundation of China(22272107);National Natural Science Foundation of China(22072092);Analytical Instrumentation Center(SPST-AIC10112914);HPC Platform of ShanghaiTech University;Shanghai Key Laboratory of High-resolution Electron Microscopy (Shanghai Science and Technology Plan, No. 21DZ2260400), SPST, ShanghaiTech University

Abstract

Abstract:

Oxidative coupling of methane (OCM) is a catalytic partial oxidation process that directly converts methane into C₂ products. For this high temperature reaction, understanding the radical behavior through experimental investigation is important in correlating the catalytic activity and the products. In this work, a spatial resolution online mass spectrometry (MS) system was developed and applied to a Mn-Na₂WO₄/SiO₂ catalyzed OCM system. In addition to the residue gas analysis, the system obtained the distribution information of the reactants and products in the reactor. At various setting temperatures, all species online MS signals were collected at different positions, mapping the reaction activity covering parameters including temperature, time and space. The distribution behavior of the catalytic activity, selectivity, and apparent activation energy were kinetically analyzed. Selectivity and additional carbon balance analysis strongly supported the radical coupling model of OCM and indicated that after the catalytic bed layer, there is a significant length in the reactor (> 2 mm) filled with radicals. Based on the result, a designed new method by tuning the temperature field in the reactor was found effectively to improve the catalytic activity, especially the C₂ yield from 702 to 773 °C.

Key words: Oxidative coupling of methane, Mn-Na₂WO₄/SiO₂ catalyst, Online mass spectrometry, Spatial-resolved kinetic analysis, Radical coupling model

Ningxujin Ding, Danyu Wang, Shihui Zou, Jie Fan, Lyubov Alexandrovna Isupova, Junyu Lang, Yong Yang. A spatial-resolved online MS study on OCM reaction catalyzed by Mn-Na₂WO₄/SiO₂ system for radicals coupling mechanistic insight[J]. Chinese Journal of Catalysis, 2025, 74: 167-176.

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Figures/Tables 8

Fig. 1. Schematic diagram of the reaction device. Upper inset: the heated region of the catalytic bed with a Fe-Cr-Alloy spiral wire tightly winding around the tube together with the ceramic armored/isolated K-type thermocouple.

Fig. 2. The normalized average flow rate of CH4 (a), O2 (b), C2 (c), and COx (d) for every point (left scale) and the corresponding conversion and yield (right scale) at different temperature. 20 mg Mn-Na2WO4/SiO2, CH4:O2:Ar = 1:1:4, GHSV = 12 L·h-1·gcat-1.

Fig. 3. (a) Average ratio of ethylene to ethane for every point at 706, 754, 773, and 802 °C. (b) The normalized average flow rate of CH4, O2, C2H4, C2H6, CO, CO2 (left scale) and the corresponding C balance (right scale) for every point at 706 °C. 20 mg Mn-Na2WO4/SiO2, CH4:O2:Ar = 1:1:4, GHSV = 12 L·h-1·gcat-1.

Fig. 4. Spatial-resolved C balance deviation plot, with results obtained at 754, 773, and 802 °C overlapping together. Reaction conditions: 20 mg Mn-Na2WO4/SiO2, CH4:O2:Ar = 1:1:4, GHSV = 12 L·h-1·gcat-1.

Fig. 5. The average C2 selectivity for every point at 706, 754, 773 and 802 °C. (a) Ratio of C2 to methane conversion. (b) Ratio of C2 to total C products. Reaction conditions: 20 mg Mn-Na2WO4/SiO2, CH4:O2:Ar = 1:1:4, GHSV = 12 L·h-1·gcat-1.

Fig. 6. Spatial-resolved Arrhenius plots of CO2 (a) and C2H6 (b) from 0 to 6 mm, with CH4:O2:Ar = 1:1:4, GHSV = 12 L·h-1·gcat-1. The fitting curve for CO2 covers the temperature range from 706 to 802 °C, while that for C2H6 covers from 754 to 802 °C (Extension lines are indicated by dotted lines). (c)The corresponding apparent activation energy (Ea) of CO2 and C2H6 at different positions.

Scheme 1. Energy diagram of radical coupling model in gas phase.

Fig. 7. Spatial-resolved C2 yield, COx yield and C2 selectivity at different temperatures for diving setup (a) and constant setup (b). Note: C2 yield and COx yield are obtained by deducting the 0 mm product rate.

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A spatial-resolved online MS study on OCM reaction catalyzed by Mn-Na₂WO₄/SiO₂ system for radicals coupling mechanistic insight

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