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Study On The Catalytic Oxidation Of Formaldehyde And Carbon Monoxide Over MnO_x-based Mixed Oxides

Posted on:2010-11-29Degree:MasterType:Thesis
Country:ChinaCandidate:X S LiuFull Text:PDF
GTID:2121360278968325Subject:Physical chemistry
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MnOx and Mn-based composite oxides is known to be efficiently catalysts due to their multiple chemical states. In this thesis, a series of MnOx-CeO2 composite oxides were prepared using a modified co-precipitation method, CuxCe1-xO2-δ and MnxCe1-xO2-δ solid solution were prepared using a modified citrate sol-gel method, and CuO/OMS-2 were prepared using an impregnation method. The samples were characterized by XRD,Raman,H2-TPR,in situ DRET,SEM,and XPS techniques. The catalytic performances of MnOx-CeO2 composite oxides, CuxCe1-xO2-δ and MnxCe1-xO2-δ solid solutions were tested for the HCHO and CO oxidation, the catalytic performance of CuO/OMS-2 were tested for the CO oxidation. 1 Preparation of Mn(Cu)xCe1-xO2-δsolid solution with high surface area and itsapplication for HCHC,CO oxidationMn(Cu)xCe1-xO2-δcatalysts were prepared using a modified citrate sol-gel method, with a molar ratio of Ce:Cu = 9:1. The precursor was heated in N2 at 800℃, and then the intermediate mixture was calcined in air at 400℃. The specific surface areas of the Ce0.9Cu0.1O2-δ and Ce0.9Mn0.1O2-δcatalysts were 105 and 112 m2/g, respectively, which were much larger than those prepared by the normal citrate sol-gel method. Raman results indicated that a higher concentration of oxygen vacancies was obtained on the Ce0.9Cu0.1O2-δ catalyst compared to the Ce0.9Mn0.1O2-δ. In situ DRIFTS results evidenced the chemisorption of CO on the Ce0.9Cu0.1O2-δ catalyst, but there was no chemisorption of CO on the Ce0.9Mn0.1O2-δ catalyst. For CO oxidation, the Ce0.9Cu0.1O2-δ had higher activity than the Ce0.9Mn0.1O2-δ, due to the higher concentration of oxygen vacancies and the strong chemisorption of CO on the catalyst. CO-TPR results implied that the surface lattice oxygen of Ce0.9Mn0.1O2-δ is more active than that of the Ce0.9Cu0.1O2-δ. For HCHO oxidation the Ce0.9Mn0.1O2-δ showed slightly higher activity than the Ce0.9Cu0.1O2-δ, due to the fact that the lattice oxygen in the Ce0.9Mn0.1O2-δ is more easily reducible than that in the Ce0.9Cu0.1O2-δ.2 A Comparative study of HCHO and CO catalytic oxidation on MnOx-CeO2 composite oxidesA series of MnOx-CeO2 composite oxides with different Mn contents were prepared using Mn(NO3)2, KMnO4 and Ce(NO3)3 as precursors by a modified co-precipitation method, taking KOH as the precipitator. Their catalytic activities for HCHO and CO oxidation were much higher than those prepared by other method. The activity of MnOx-CeO2 catalysts for the HCHO oxidation increased with Mn content in the catalyst, and the most active catalyst was the pure MnOx. For the CO oxidation, the activity increased with Mn content in the catalyst up to 50%, but with further increasing Mn content the activity declined. In order to compare the intrinsic reaction activities of these catalysts, reaction rates of the MnOx-CeO2 catalysts normalized by the Mn content for HCHO and CO oxidation were calculated. It was found that the addition of CeO2 slightly enhanced the activity for the HCHO oxidation. However the addition of CeO2 remarkably enhanced the reactivity for CO oxidation. The enhancement of reactivity for HCHO oxidation was due to the activation of the lattice oxygen species in MnOx by the addition of CeO2. And the remarkable enhancement of reactivity for CO oxidation by the addition of CeO2 was due to the active oxygen species generated on the CeO2 surface.3 Synthesis and catalytic performance of OMS-2 molecular sieve and CuO/OMS-2 catalysts for CO oxidationManganese oxide octahedral molecular sieve (OMS-2) were synthesized using MnSO4 and KMnO4 as precursors by the reflux method under acidic conditions. CuO/OMS-2 catalysts were prepared by impregnation method and calcined in air at 400℃. Their catalytic activities for CO oxidation were tested. SEM observation shows that OMS-2 molecular sieve is nanorods. According to the X-ray diffraction results, the material was a manganese oxide octahedral molecular sieve with the cryptomelane type structure. The TG-DTA result showed thermal stability up to 500℃. Cu supported on OMS-2 showed higher activity for CO oxidation compared to the pure OMS-2, due to the active oxygen species generated on the catalysts surface. The activity of CuO/OMS-2 was much higher than other Cu-based catalysts, which was supposed that the strong interaction between the finely dispersed CuO and higher oxidation state MnOx.
Keywords/Search Tags:Mn(Cu)0.1Ce0.9O2-δ Solid Solution, MnOx-CeO2 Composite Oxides, HCHO Catalytic Oxidation, CO Catalytic Oxidation, OMS-2 Molecular Sieve
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