Magnesium-endowed exceptional hydrothermal stability of Pd/CeO2-ZrO2-Al2O3 catalyst for low-concentration methane combustion via two-step structure transformation

• Published in: Fuel (Guildford) 2024-11, Vol.376, p.132743, Article 132743
• Main Authors: Yang, Wenhu, Wu, Yang, Huang, Chengsong, Xu, Yang, Zhang, Yaliu, Wu, Bingcheng, Wang, Xingmei, Zhong, Lin, Wang, Jianli, Chen, Yaoqiang
• Format: Article
• Language: English
• Subjects: Hydrothermal stability; Magnesium promoter; Methane combustion; Palladium; Structure transformation
• ISSN: 0016-2361
• DOI: 10.1016/j.fuel.2024.132743

[Display omitted] •The two-step structure transformation of the Mg promoter enhanced the stability of the Pd/CeO2-ZrO2-Al2O3 catalyst.•Hydrothermal aging at 800 °C for 10 h slightly improved the activity of the Mg-modified catalyst.•The MgO resulting from the decomposition of Mg(NO3)2 transformed into MgAl2O4 during hydrothermal aging.•The strong electronic interaction between PdO and MgO resulted in more PdO-MgAl2O4 structures in the aged catalyst.•More PdO-MgAl2O4 structures compensated for the sintering-induced catalytic deactivation during aging. The Pd/Al2O3-based catalysts are highly effective for removing low-concentration methane (CH4), a strong greenhouse gas. The sintering of palladium (Pd) particles on the catalysts during long-term utilization causes catalytic deactivation. Magnesium (Mg) promoter would improve the hydrothermal stability of Pd/Al2O3-based catalysts by constructing PdO-MgAl2O4 structures on the catalyst surface. In this study, we report an innovative strategy wherein a two-step structure transformation of Mg promoter in a Mg-modified Pd/CeO2-ZrO2-Al2O3 (Pd/CZA) catalyst achieved exceptional hydrothermal stability of the catalyst. The Mg promoter in the form of MgAl2O4 spinel improved PdO reducibility, as indicated by TPR test results, resulting in a 15–17 °C decrease in the temperature of 90% CH4 conversion (T90) over the fresh catalyst. Conversely, the MgO impeded CH4 conversion and caused an increased T90 of 21 °C due to forming an electron-rich PdO, as evidenced by XPS and CO-FTIR test results. Accelerated hydrothermal aging (A) at 800 °C for 10 h induced a second structure transformation of MgO to MgAl2O4 in Pd/MgO-CZA catalyst to produce substantial PdO-MgAl2O4 structures, which compensated for the catalytic deactivation caused by the sintering of palladium particles, as demonstrated by XRD, HAADF-STEM, and CH4-TPR test results. As a result, the Pd/MgO-CZA-A exhibited a 13 °C decrease in T90 compared to Pd/MgO-CZA, achieving a T90 of 425 °C with reaction gases containing 10 vol% water vapor. This work provides valuable insights for enhancing the hydrothermal stability of Mg-modified Pd/Al2O3-based catalysts.