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 , 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 . 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  . 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. 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
【会议名称】: Catalysis -a combination of science and technology
【会议组织】: Department of Chemistry, Nankai University,Tianjin 300071,CHINA;
【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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