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Preparation, Characterization and Catalytic Activity on Ni-Fe/γ-Al2O3 Bimetallic Catalyst for CO Methanation

Author: WangNing
Tutor: ZhaoYongXiang；ZhangJianPing
School: Shanxi University
Course: Physical and chemical
Keywords: bimetallic catalysts Ni-Fe/γ-Al2O3 CO methanation
CLC: O643.36
Type: Master's thesis
Year: 2010
Downloads: 491
Quote: 2
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Abstract


Researchers expressed their great interests over CO methanation because of its important practical value in many ways. For example, it is used for the removal of a small amount of CO in H2-rich gases, improvement of the calorific value of city gas and the study on avoiding generation of methane in F-T synthesis. Especially, its application in synthesis of the substitute natural gas through coke oven gas or the low quality coal has become very important and attracted a great attention in academia and industry.The high-temperature Ni-based catalyst (280-450℃) is commonly used in the methanation process of a small amount of CO in process gases. Although the catalyst shows the high catalytic activity, the reaction has the equipment requirement, the high cost in operation, the high energy consumption and the low security. Low temperature methanation can provide useful information for development of methanation catalyst which has the moderate equipment requirement, low cost in operation, small energy consumption and high security. In order to increase its catalytic activity and achieve the purpose of low-temperature methanation, choosing the suitable metal or several metals in preparation process of catalyst is a practicable and feasible way. In addition, investigating the effect of metal or metals on the catalytic activity of catalyst has important theoretical and practical significance.The adding of the second metal to bimetallic catalyst, the two metals also have an interaction between the metal including the metal and support interaction, which can change the structure of the catalyst. Alloys were observed in most of the bimetalic catalysts as the active species owning to alloys have special electronic effects and surface structure. So bimetallic catalysts for catalytic hydrogenation, catalytic cracking reactions show a better activity and selectivity, and widely used in many fields of chemical production process. In this paper, a series of Ni/γ-Al2O3、Fe/γ-Al2O3、Ni-Fe/γ-Al2O3 catalysts were prepared by the wet impregnation method. The catalytic activity for CO methanation was investigated in a fixed-bed continuous-flow microreactor. Then the the structure and surface property of the catalysts were investigated via the N2-physisorption、XRD, H2-TPR, H2-TPD and CO-TPD characterizations. Meanwhile, CO methanation reaction mechanism was discussed by the TPSR technique and in-situ DRIFTS. By comparing the changes of structure and surface property of the catalysts as well as TPSR and DRIFTS differences of CO adsorption and methanation reaction over the monometal catalysts and the bimetallic catalyst, the reasons for increase of the catalytic activity of the Ni-Fe/γ-Al2O3 catalyst were given. The main results are as follows:1. From the investigation of the Ni/γ-Al2O3、Fe/γ-Al2O3 and Ni-Fe/γ-Al2O3 catalysts, the 6Ni-4Fe/γ-Al2O3 catalyst has the lowest light-off temperature (180℃) and completely conversion temperature (220℃), and shows the highest catalytic activity.2. Characterizations results show that the alloy formation in bimetallic catalyst has little effect on the texture of the catalysts, but the dispersion of active species in the 6Ni-4Fe/γ-Al2O3 catalyst is obviously promoted. In addition, the addition of the second component iron causes the formation of the Ni-Fe alloy, which decreases the interaction between active species and the support. The moderate interaction improves the dispersion degree and the reduction degree of active species, and then results in more active active species and stronger adsorption ability for H2 and CO.3. From TPSR and in-situ DRIFTS investigation of CO adsorption and methanation reaction over the catalysts, it is found that the addition of the second component iron change the CO methanation reaction mechanism on Ni-Fe/γ-Al2O3 bimetallic catalyst, the breaking of C-0 bond over on the Ni/γ-Al2O3 and 6Ni-4Fe/γ-Al2O3 catalysts is quite different. Ni/γ-Al2O3 catalyst is via multi-hydrogen carbonyl hydride but 6Ni-4Fe/γ-Al2O3 catalyst is via direct breaking in CO methanation reaction. Meanwhile, combined with the characterizations of the structure and surface properties, the formation of alloy leads to more active species, stronger adsorption ability for CO and H2 and in the presence of H2, the formation of a new active carbon species at lower temperature over the Ni-Fe/γ-Al2O3 catalyst, which is the reason for increase of the catalytic activity for CO methanation.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalyst
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