Catalytic urea hydrolysis by composite metal oxide catalyst towards efficient urea-based SCR process: performance evaluation and mechanism investigation

Highlights

● Bimetallic oxide composite catalyst was designed for the urea-based SCR process.

● Surface chemical state and typical microstructure of catalyst was determined.

● Reaction route was improved based on intermediates and active site identification.

● TiO₂@Al₂O₃ presents an obvious promotion for urea hydrolysis.

Abstract

As a promising option to provide gaseous NH₃ for SCR system, catalytic urea hydrolysis has aroused great attention, and improving surface area and activity of catalysis are the crucial issues to be solved for efficient urea hydrolysis. Therefore, a composite metal oxide (TiO₂@Al₂O₃) catalyst was prepared by a simple hydrothermal method, with mesoporous alumina (γ-Al₂O₃) as substrate. The results verify the mesoporous structure and submicron cluster of TiO₂@Al₂O₃, with exposed crystal faces of (101) and (400) for TiO₂ and γ-Al₂O₃, respectively. The electronegativity difference of Ti⁴⁺ and Al³⁺ changes the charge distribution scheme around the interface, which provides abundant acid/base sites to boost the urea hydrolysis. Consequently, for an optimal proportioning with nano TiO₂ content at 10 wt.%, the hydrolysis efficiency can reach up to 35.2 % at 100 °C in 2 h, increasing by ~7.1 % than that of the blank experiment. ¹³C NMR spectrum measurements provide the impossible intermediate species during urea hydrolysis. Theoretical calculations are performed to clarify the efficient H₂O decomposition at the interface of TiO₂@Al₂O₃. The result offers a favorable technology for energy-efficiency urea hydrolysis.

Graphical abstract

Keywords

SCR / Urea hydrolysis / Catalytic / Water dissociation / Electronegativity

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Acknowledgements

The present study is supported by the Science and Technology Projects of China Huaneng Group Co., Ltd. (No. HNKJ21-H15), the National Natural Science Foundation of China (No. 22106084), and the Special Projects of China Postdoctoral Science Foundation (No. 2022T150350).

Author Contributions

Yuchen Li planned the project, carried out experiments and wrote the paper; Zhen Chen did the DFT calculation section and carried out experiments; Xiangyu Zhang, Kun Yang, Lidong Wang and Junhua Li analyzed data and reviewed the article. All the authors participated in discussion of the research.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s11783-023-1658-4 and is accessible for authorized users.

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