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THE CONVERSION OF SYNGAS ON Fe MnO (1): Effects of Metal Modification on The Product Distribution


Fe/Mn oxide is potential catalyst for selective production of short chain olefmes in FT-synthesis. Lee and Ponec have summerized the effects of loading ions to metaloxide catalysts on the product distribution of CO-hydrogenation [1], They sugested that Rh, Pd oxides as catalysts for FT-Synthesis lead to produce more alcoholic products, while Cu/ZnO and Pd oxide to methanol and Ni, Fe to the production of hydrocabons. In this paper the catalytic properties of metal modified Fe/MnO catalysts were investigated in order to observe the selectivity of C_2-C_4 olefins and the activity of CO hydrogenation compared with unloaded Fe/MnO. The results are discussed in combination with XPS surface studies.rnThe Fe/Mn oxide (Fe/Mn=1/4) was prepared by continuous co-precipitation and the promotorions (1%K, 1%Cu, 1%Co, 1%Pd, 1%Rh in mol%) were loaded by impregnating the calcined Fe/Mu oxide precursor. The exact composition of all catalysts were determined by AAS and XPS. The catalytic reactions were carried out in a fixed bed tubular microreactor, at 543K, 11bar. The GHSV was held constant at 215/h. The gaseous products were analysed online by a Carle AGC 111 gaschromatograph with 4 columns. The liquid effluent was separated and then analysed by a Perkin-Elmer Sigma 2B capillary-gaschromatograph. The catalysts were reducted at 400℃ with H_2 for 24 hr before reaction started. The results are summerized in Table 1.rnAn increase in CO-conversion was resulted with the promotors except for K-containing one. The K~+ led to a light decrease in CO conversion. The product distribution was also changed. The catalysts with potassium had lower C-1 -C_4 selectivity than K-free catalysts,rnexcept for Rh-Fe/MnO, in which a great amount of CH_4 was found. K~+ led to an increase in the average molecular weight of the products, as was mentioned in literature [2]. The selectivity to C_2-C_4 olefines was affected differently by the promotors. The highest selectivityrnwas found with 1%Cu-(28%) and followed by 1%Co-Fe/MnO(25%). In contrast to thisrn1%Pd- and 1%Rh-Fe/MnO had a negative effect on the production of olefmes because of their strong hydrogenation ability. Only 1% olefines were found over l%Pd- and almost nothing over 1%Rh-Fe/MnO. The unmodified Fe/MnO is itself a good catalyst for the production of short chain olefines (21 %), but the conversion of CO over it is limited. The addition of potassium could not increase the selectivity to olefines but obviously increased the ratio of C_2-rnC_4 olefines to C_2-C_4 paraffines. The selectivity ratio varied from 0 (1%Rh) to 3.96(1%K).rnKoelbel and Dry et al sugested by measuring the adsorption heat that the addition of alkali metal to Fe catalyst can intensify the CO adsorption at the surface. This conducted a poor hydrogenation function of the catalyst [3] [4]. It can also be proved by the strong coke formation that will be mentioned later.rnThe XPS-studies were performed for all catalysts after calcination, reduction and reaction. After reaction, the Fe-content at the surface reduced strongly, only about 10% lefl from the original 20% percent. In contrast, the Mn -content increased 5%-10%. The Fe is composed of Fe~(3+), Fe~(2+) and Fe~o in various ratio after in situ reduction. The content of Fe~o was most favoured by the addition of Pd and Rh. It has been sugested by Grzybek et al.[5] that the initial activity of the catalysts is correlated with the amount of Fe~o, that has been also proved by our present work.......

【作者名称】: Naijia Guan
【作者单位】: Department of Chemistry, Nankai University,Tianjin 300071,CHINA
【关 键 词】: FT-synthesis, Fe/MnO, olefins, activity, selectivity, XPS
【会议名称】: Catalysis -a combination of science and technology
【期刊论文数据库】: [DBS_Articles_01]
【期刊论文编号】: 100,827,754
【摘要长度】: 3,495
【会议地点】: Tianjin(CN);Tianjin(CN)
【会议组织】: Department of Chemistry, Nankai University,Tianjin 300071,CHINA;
【会议时间】: 1995
【上篇论文】: 外文会议 - CO-OPERATION IN COMPLEX, SELF-ORGANISING, INFORMATIONGENERATING SYSTEMS
【下篇论文】: 外文会议 - GENERAL SYSTEMS ESSENTIALS: AN INTRODUCTORY COURSE FOR A MODERN GENERALIST CURRICULUM

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