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On the reactivity of cobalt and iron-based Fischer-Tropsch catalysts for the CO2 conversion into liquid fuels
No full textOn the synthesis and the catalytic performances of Co/g-Al2O3 eggshell catalysts for compact FT reactors
No full textCO2 hydrogenation to hydrocarbons over Co and Fe-based Fischer-Tropsch catalysts
Get PDFThe performances of representative Co-based and Fe-based Fischer-Tropsch catalysts have been comparatively investigated in the hydrogenation of CO and CO2. Over an un-promoted Co/γ-Al2O3 catalyst, CO2 is easily hydrogenated and its conversion rate is even faster than that of CO; however, the selectivities of the two processes are extremely different, with methane largely dominating the product distribution in the case of CO2 hydrogenation and long-chain hydrocarbons dominating the products pool during CO hydrogenation. As opposite to cobalt, CO2 hydrogenation rate over K-promoted 100Fe/10Zn/1Cu (at/at) catalysts is slower than that of CO, but the products are dominated by middle distillates when CO2 replaces CO in the feed. Such behaviors depend on the different adsorption strengths of CO and CO2, which affect the H/C atomic ratio on the catalyst surface. In the case of Fe-based catalyst, we have also found that the catalytic sites active in the chain growth process (iron carbides) are transformed into sites active in the hydrogenation reactions (iron oxides/reduced iron centers) at low CO partial pressures. Potassium has a key role in promoting the stability of chain growth sites, thus decreasing the secondary reactions of olefins
IS CO2 AN ALTERNATIVE TO CO FOR THE PRODUCTION OF SYNTHETIC FUELS? A STUDY ON COBALT AND IRON-BASED FISCHER-TROPSCH CATALYSTS
No full textTaking advantage of mass transfer limitations in egg-shell catalysts for intensified Fischer-Tropsch reactors
No full textOn the passivation of platinum promoted cobalt-based Fischer-Tropsch catalyst
Get PDFPassivation of reduced cobalt-based catalysts is required prior to air exposure due to the exothermicity of the Co metal oxidation, which may lead to a significant increase of the temperature of the catalyst resulting in its degradation and in a potential fire hazard. This work shows the results of the passivation process carried out on a Pt-promoted Co-based catalyst supported on stabilized alumina at different space velocities in the range of 5–50 Ncc/min/g cat and constant O 2 concentration of 1 vol.%. Increasing the O 2 flow fed to the reactor, the specific amount of O 2 consumed on the catalyst slightly decreases. Around 30% of Co metal particles are oxidized to CoO species in all the passivation treatments. These species are found to be much more reducible than the Co oxides species present on the calcined catalyst. Indeed, all the passivated catalysts are completely depassivated at a temperature which is significantly lower (300 °C) than that needed to fully reduce the calcined catalyst (400 °C). The temperature of the catalyst almost linearly increases with the increase of the O 2 feed flow. Indeed, an abrupt increase of the catalyst temperature is observed for high O 2 flows, resulting in a decrease of the Co° dispersion (i.e. increase of the average Co° crystallites size) after depassivation. This result is explained with the onset of sintering phenomena of the CoO species formed during passivation. The passivation treatment is found to be unsuitable for long-term catalyst protection, since a deep re-oxidation of the passivated catalyst is observed after two months of air exposure. The effectiveness of the catalyst passivation is eventually validated by running FT reactivity tests at industrially relevant process conditions. The activity of the calcined catalyst reduced in-situ at 400 °C is compared to that of the same catalyst reduced ex-situ at the same temperature, passivated at low O 2 flow and depassivated in-situ at 300 °C. Interestingly, similar stability and reactivity, expressed both in terms of activity and selectivity, are obtained
A novel preparation method for "small" eggshell Co/γ-Al2O3 catalysts: A promising catalytic system for compact Fischer-Tropsch reactors
No full textOPTIMAL DESIGN OF CO/AL2O3 EGGSHELL CATALYSTS FOR THE INTENSIFICATION OF COMPACT FISCHER-TROPSCH REACTORS
No full textTailoring the Properties of Co/Al2O3 Eggshell Catalysts for Compact Fischer-Tropsch Reactors
No full textExploiting the effects of mass transfer to boost the performances of Co/γ-Al2O3 eggshell catalysts for the Fischer-Tropsch synthesis
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