Effect of Fe/Co wt ratio on TiO2 supported catalysts for Fischer-Tropsch synthesis using syngas with H2/CO ratio < 2
| Autor: | M. Russo 1, M.L. Testa 1, V. La Parola 1, G. Pantaleo 1, R. Bal 2, A. M. Venezia 1 |
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| Jazyk: | angličtina |
| Rok vydání: | 2019 |
| Předmět: | |
| Zdroj: | EuropaCat 2019, Aachen, Germany, 18-23/08/2019 info:cnr-pdr/source/autori:M. Russo 1, M.L. Testa 1, V. La Parola 1, G. Pantaleo 1, R. Bal 2, A. M. Venezia 1/congresso_nome:EuropaCat 2019/congresso_luogo:Aachen, Germany/congresso_data:18-23%2F08%2F2019/anno:2019/pagina_da:/pagina_a:/intervallo_pagine |
| Popis: | The continuous depletion of conventional fossil fuel reserves and the concern about climate changes, enhanced by CO2 emission resulting from fossil fuel consumption, is driving nowadays a renewed interest in Fischer-Tropsch synthesis (FTS). Such gas-to liquid process is becoming particularly attractive when using bio syngas. This gas mixture, rich in CO and H2, derives indeed from biomass gasification and is characterized by a H2/CO ratio lower than the value of 2, appropriate for hydrocarbon syntheses [1]. In the present study, TiO2 supported cobalt catalysts are combined with iron, active in the water gas shift reaction (WGS), aiming to increase H2 in the synthesis reactor. To investigate the role of iron in different Fe/Co weight ratios, monometallic Co, Fe and bimetallic CoFe catalysts are prepared and tested in FTS. Structural and electronic properties of the obtained materials are investigated by XRD, TPR , XPS and TEM techniques. Mono metallic Co/TiO2 and Fe/TiO2 and two bimetallic catalysts (Co/Fe =1 and Co/Fe = 5) with a total metal loading of 12 wt% are synthetized by a microwave assisted co-precipitation procedure. The FTS tests are performed at 1atm in a fixed-bed flow reactor with reagent gas mixture of CO, H2 and He (CO:H2:He volume ratio of 1:1.7:2.3) using GHSV = 1.9 Lsyngas gcat-1 h-1 and a temperature range of 275-350 °C. Before test, the catalysts are reduced under H2 flow for 16 h at 350 °C. All the catalysts exhibit good CO conversion, due to the presence of highly dispersed Fe and Co nanoparticles favoured by the microwave assisted catalyst synthesis. In the bimetallic catalysts, as expected, the presence of iron enhances CO2 production and, as compared to the monometallic cobalt catalyst, it increases the selectivity to higher hydrocarbons. According to the structural characterization and to XPS results shown in Fig. 1, the better activity of the mixed 10Co2Fe/TiO2 catalyst can be related to the formation of metal carbides during reaction. Moreover, a direct correlation between catalyst reducibility and activity is clearly indicated by the TPR profiles shown in Fig. 2. High resolution TEM images evidence a mixture of amorphous and graphitic carbon over the spent catalysts, explaining some deactivation occurring during reaction. Overall, the results suggest that in order to have the desired FTS outcome, in terms of CO conversion and C5+ selectivity, it is important to play with the Fe/Co weight ratio. Indeed, a limited amount of Fe is beneficial because it provides an additional supply of H2 by the WGS reaction and at the same time it does not overwhelms the FTS reaction activated by cobalt. In virtue of this compromise the 10Co2Fe/TiO2 catalyst exhibits the best catalytic behavior. |
| Databáze: | OpenAIRE |
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