Abstract
Sheaf-like CeO2 (CeO2-S) in microscale was prepared by the hydrothermal method, and then etched with KOH aiming to obtain an imperfect fluorite structure (CeO2-SK) with high content of oxygen vacancies and oxygen mobility. With CeO2-S and CeO2-SK as supports respectively, a modified colloidal deposition method was employed to obtain Pd/CeO2 catalysts for being used in lean methane combustion. According to the inductively coupled plasma (ICP), N2 physisorption and scanning electron microscopy (SEM) results, the Pd supported catalysts are very similar in their Pd loading, surface area and morphologies. SEM and transmission electron microscopy (TEM) results revealed various nanorods exposed CeO2 (110) and (100) facets on Pd/CeO2-SK surface after KOH etching. Raman spectra and H2-temperature programmed reduction (H2-TPR) results indicated that Pd/CeO2-SK catalyst has a much higher content of catalytic active PdO species than Pd/CeO2-S catalyst. It was also found that the catalytic performance of Pd/CeO2 in lean methane combustion depends greatly upon the exposing crystal planes and oxygen vacancies content of sheaf-like CeO2, and Pd/CeO2-SK exhibits higher activity than Pd/CeO2-S. The larger amount of CeO2 (110) and (100) planes on Pd/CeO2-SK surface can enhance the formation of oxygen vacancies, active Pd species and migration of lattice oxygen, which all evidently improve the redox ability and catalytic activity of the Pd/CeO2-SK catalysts in lean methane combustion.
Highlights
A great amount of coal mine methane needs to be utilized owing to the huge annual output of coal in the world [1,2]
Many Pd/CeO2 catalysts with exceptionally high activities for CH4 combustion at low temperatures have been synthesized and investigated in that the synergistic interaction between palladium and CeO2 may result in higher catalytic performance of Pd species [19,20,21]
The as-made sheaf-like CeO2 was further etched with KOH to obtain an imperfect fluorite structure (CeO2-SK) with high content of oxygen vacancies as well as oxygen mobility, which can improve the activity of supported Pd catalysts in lean CH4 combustion at low temperatures
Summary
A great amount of coal mine methane needs to be utilized owing to the huge annual output of coal in the world [1,2]. Many Pd/CeO2 catalysts with exceptionally high activities for CH4 combustion at low temperatures have been synthesized and investigated in that the synergistic interaction between palladium and CeO2 may result in higher catalytic performance of Pd species [19,20,21]. Several reports have shown that the CeO2 morphology has great influence on the catalytic activity of palladium loaded catalysts This may be due to the fact that different shapes of ceria supports usually expose distinct ceria facets, which affects the palladium–CeO2 interaction. The as-made sheaf-like CeO2 was further etched with KOH to obtain an imperfect fluorite structure (CeO2-SK) with high content of oxygen vacancies as well as oxygen mobility, which can improve the activity of supported Pd catalysts in lean CH4 combustion at low temperatures. All of these are conducive to improving the economic benefits of its practical application
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