Study on MnO2-supported noble metal catalysts for CO catalytic oxidation at low temperature
A series of MnO2-supported noble metal catalysts(Pd/MnO2、Ru/MnO2、Ag/MnO2 and Pt/MnO2)with a noble metal loading of 3.0％were synthesized by redox precipitation.The catalytic oxida-tion ability of CO followed the order:3.0％Pd/MnO2＞3.0％Ru/MnO2＞MnO2＞3.0％Ag/MnO2＞3.0％Pt/MnO2.To understand the relationship between activity and textures of the catalysts,characterization techniques such as HRTEM/HAADF-STEM,XRD,Raman,H2-TPR,O2-TPD and XPS were em-ployed to analyze the particle size of noble metals,crystal structure,defection structure,low-tempera-ture reducibility,active oxygen species and elemental composition of the catalysts.The tests indicated that the support of Ag or Pt simply promoted the low-temperature reducibility of MnO2.However,Ag and Pt on the catalyst surface were rapidly reduced by CO,leading to partial deactivation.In contrast,supporting Pd or Ru not only enhanced low-temperature reducibility but also created abundant surface chemisorption oxygen species.The superior CO catalytic oxidation ability of 3.0％Pd/MnO2 and 3.0％Ru/MnO2 was attributed to the combined effect of low-temperature reducibility and abundant surface chemisorption oxygen species.The 3.0％Pd/MnO2 catalyst exhibited a lower reduction temperature and a greater abundance of surface chemisorption oxygen species,enabling complete oxidation of a 1％CO/4％O2 reaction gas mixture at 10 ℃(GHSV=40 000 mL/(g·h)).It was speculated that the CO cata-lytic oxidation mechanism of 3.0％Pd/MnO2 followed the Langmuir-Hinshelwood(L-H)model.
Pd/MnO2CO oxidationCatalystLow temperature reducibilityChemisorbed oxygen species
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