| The catalyst is consists of three parts:active metal,promoters and supports.Therefore,in order to prepare the high-efficiency ruthenium catalyst for ammonia synthesis,and study the mechanism of ammonia synthesis catalyst.We must systematically study the relationship between catalyst activity and ruthenium loading,the mechanism of alkali promoters,and the graphitization of carbon support.In this paper,various measurements were applied to investigate the structure-activity relationship between physicochemical properties and activities of ruthenium based ammonia synthesis catalysts.And we systematically studied the preparation of graphitic carbon by catalytic graphitization and its application as a support of ruthenium based catalyst for ammonia synthesis,the promoter effect of alkali on Ru/C ammonia synthesis catalyst and the effects of ruthenium loadings on the stability of carbon-supported ruthenium based catalyst.The main conclusions in this thesis are as follows:(1)The graphitic carbon was prepared by heating of carbon in the presence of Fe(NO3)3 or/and KOH at low temperature.It was shown that the co-presence of Fe(NO3)3 and KOH not only enhances the graphitization degree and total surface area of carbons,but also increases the amount of carbon defects and surface oxygen groups.The presence defects and surface oxygen groups decreases the strongly adsorbed hydrogen,and thus the as-obtained carbon-supported Ru catalysts would show excellent ammonia synthesis rates.(2)Under the same reaction conditions,all Li-promoted Ru catalysts show similar ammonia synthesis rates.While Ru catalysts with high K loading exhibits slightly higher activity than the sample promoted with fewer K(8K).On the other hand,the catalytic activities of Cs-promoted Ru catalysts increase with the increase in Cs content in the range of 7 to 40 wt.%.It is clear that in the M/Ru molar ratios range of 2.0-3.2,the ammonia synthesis rates increase and rank in the order of Cs>K>Li.All Ru particles with a narrow size distribution in the range of 1.0-3.0 nm were finely dispersed on the surface of carbon support.Therefore,it can conclude that the effect of the alkali promoters on the catalytic activity is not result from changing the Ru particle size.(3)The peaks corresponding to graphitic carbon intensity decrease with the increase of Ru loading,plausibly a result of partial plugging of carbon pores by K promoter and a larger amount of Ru metal.The Ru particle sizes increase with increasing Ru loading.While the initial activities of Ru catalysts all increase with increasing Ru loading up to a certain value and then decrease upon further increasing Ru content for Ru/AC and Ru/AC-H catalysts.For Ru/AC catalysts,the highest initial activity is obtained for the sample with about 10wt.%Ru.Heat treatment at 500? leads to the more severe deactivation for Ru/AC-H catalysts with high Ru loading.This paper is helpful to search a new method of graphitization of carbon in the low temperature and find the relationship between the properties of carbon and the performance of catalyst.From this paper we investigate the promoter effect of alkalis(Li,K and Cs)on Ru/C catalyst using in ammonia synthesis,and systematically review the Ruthenium loading effects on the properties of Ru catalyst for ammonia synthesis. |
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