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Investigating the Catalytic Active Sites of Mo/HZSM-5 and Their Deactivation During Methane Dehydroaromatization

52 Pages Posted: 7 Oct 2020 Publication Status: Published

See all articles by Ning Wang

Ning Wang

King Abdullah University of Science and Technology - Advanced Membranes and Porous Materials (AMPM) Center

Xinglong Dong

King Abdullah University of Science and Technology - Advanced Membranes and Porous Materials (AMPM) Center

Lingmei Liu

King Abdullah University of Science and Technology - Advanced Membranes and Porous Materials (AMPM) Center

Dali Cai

Tsinghua University - Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology

Jianjian Wang

Chongqing University - Multi-scale Porous Materials Center

Yilin Hou

Tsinghua University - Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology

Abdul-Hamid Emwas

King Abdullah University of Science and Technology - Imaging and Characterization Core Lab

Jorge Gascon

King Abdullah University of Science and Technology - KAUST Catalysis Center (KCC)

Yu Han

King Abdullah University of Science and Technology - Advanced Membranes and Porous Materials Center

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Abstract

Molybdenum supported on zeolite HZSM-5 (Mo/HZSM-5) is the most studied catalyst for methane dehydroaromatization (MDA). However, the nature of its catalytic active sites and their deactivation mechanisms remain unclear and controversial. Here we report new insights into this system, on the basis of advanced characterization and a rational design of experiments. We find that it is the size of the HZSM-5 crystal that determines the form and location of the catalytic active molybdenum carbide (MoCx) species, and thus the performance of Mo/HZSM-5; we also find that MoCx sites are preferentially deactivated over acid sites, when supported on nano-sized HZSM-5. These findings lead us to develop an “encapsulation” strategy, which effectively reconciles the deactivation rates at the MoCx sites and the acid sites, enabling a full utilization of both sites, and consequently leading to a 10-fold increase in catalyst lifetime and aromatics yield. Our results indicate that MoCx particles formed outside the micropores of HZSM-5, which are traditionally considered detrimental to the reaction, can serve as active sites for MDA, provided that they are properly protected from direct exposure to coke deposition. These findings allow us to design control experiments to answer an open question whether the acid sites, in addition to promoting the dispersion of Mo species, play a catalytic role in the MDA reaction, and the results show that acid sites are indeed essential for the conversion of methane.

Keywords: Methane dehydroaromatization, Zeolite, Electron Microscopy

Suggested Citation

Wang, Ning and Dong, Xinglong and Liu, Lingmei and Cai, Dali and Wang, Jianjian and Hou, Yilin and Emwas, Abdul-Hamid and Gascon, Jorge and Han, Yu, Investigating the Catalytic Active Sites of Mo/HZSM-5 and Their Deactivation During Methane Dehydroaromatization. Available at SSRN: https://ssrn.com/abstract=3689779 or http://dx.doi.org/10.2139/ssrn.3689779
This version of the paper has not been formally peer reviewed.

Ning Wang

King Abdullah University of Science and Technology - Advanced Membranes and Porous Materials (AMPM) Center ( email )

Saudi Arabia

Xinglong Dong

King Abdullah University of Science and Technology - Advanced Membranes and Porous Materials (AMPM) Center ( email )

Saudi Arabia

Lingmei Liu

King Abdullah University of Science and Technology - Advanced Membranes and Porous Materials (AMPM) Center ( email )

Saudi Arabia

Dali Cai

Tsinghua University - Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology ( email )

Beijing, 100084
China

Jianjian Wang

Chongqing University - Multi-scale Porous Materials Center

Shazheng Str 174, Shapingba District
Chongqing 400044, Chongqing 400030
China

Yilin Hou

Tsinghua University - Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology

Beijing, 100084
China

Abdul-Hamid Emwas

King Abdullah University of Science and Technology - Imaging and Characterization Core Lab ( email )

Thuwal 23955- 6900
Thuwal, 4700
Saudi Arabia

Jorge Gascon

King Abdullah University of Science and Technology - KAUST Catalysis Center (KCC)

Thuwal 23955- 6900
Thuwal, 4700
Saudi Arabia

Yu Han (Contact Author)

King Abdullah University of Science and Technology - Advanced Membranes and Porous Materials Center ( email )

Saudi Arabia

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