Chem. J. Chinese Universities ›› 2022, Vol. 43 ›› Issue (4): 20210816.doi: 10.7503/cjcu20210816

• Physical Chemistry • Previous Articles     Next Articles

Catalytic Methane Combustion over CeO2 Supported PdO and Ce1‒x Pd x O2‒δ Species

WANG Mingzhi, ZHENG Yanping, WENG Weizheng()   

  1. State Key Laboratory of Physical Chemistry of Solid State Surfaces,National Engineering Laboratory for Green Chemical Productions of Alcohols,Ethers and Esters,College of Chemistry and Chemical Engineering,Xiamen University,Xiamen 361005,China
  • Received:2021-12-03 Online:2022-04-10 Published:2022-01-15
  • Contact: WENG Weizheng E-mail:wzweng@xmu.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21872111);the National Key Research&Development Program of China(2020YFB0606401)

Abstract:

Pd/CeO2 catalysts containing mainly PdO and Ce1?x Pd x O2?δ species were prepared by modulating the deposition method of Pd species on CeO2. The Raman and XPS characterizations of the catalysts confirmed the presence of these two types of Pd species on the prepared catalysts. The characterization results of O2-TPD and H2-TPR showed that the Ce1?x Pd x O2?δ species with stronger interactions with CeO2 featured more stronger Pd—O bonds compared to the PdO species. The results of catalytic performance testing for the CH4 combustion reaction showed that, the Pd/CeO2 catalyst dominated with PdO species showed a good activity during the light off process with a T10 and T90 of 275 and 367 ℃, respectively, at a feed gas ratio of 1%CH4-4%O2-Ar and gaseous hourly space velocity(GHSV) of 60000 mL·gcat-1·h?1, while the catalysts dominated with Ce1?x Pd x O2?δ species possessed poor activity with T10 in excess of 420 ℃ under the same condition. The CH4-TPR characterization of the catalysts showed that the catalytic activity started to increase only when the PdO or Ce1?x Pd x O2?δ species started to be reduced by CH4 during the light off process. For the PdO species, the relatively weak Pd—O bonding allows the lattice oxygen on the Pd species to participate in the oxidation of CH4 at lower temperatures, and CeO2 support contributes to the reoxidation of the PdO x through oxygen migration, which in turn completes the process of catalysis by PdO/Pd0 cycle. The low activity of the ionic Ce1?x Pd x O2?δ should attribute to its strong Pd—O—Ce linkages which are difficult to be reduced by CH4 during the reaction. Furthermore, we prepared Pd/γ-Al2O3 catalysts by the same method using γ-Al2O3 as the support, and the characterization results further confirmed that the PdO species with weaker interaction with γ-Al2O3 are more easily be reduced by CH4 and thus exhibit better catalytic activity. It can be concluded that the reducibility of the oxidized Pd species on Pd/CeO2 by CH4 is one of the important factors determining the activity of the catalyst for the methane combustion reaction.

Key words: CeO2, Pd, CH4, Catalytic oxidation, PdO, Ce1?x Pd x O2?δ, Reducibility

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