| Summary: | SSCI-VIDE+ING+APN:NOG:YSC:FRM International audience 1.IntroductionSynthetic fuels and base chemicals can be obtained from both fossil and renewable sources through the conversion of synthesis gas (“syngas”, a mixture of carbon oxides and H2) [1]. The nature of the reaction mechanism of the Fischer-Tropsch synthesis over cobalt-based catalysts is still a debate, as well as the nature of the active sites [2,3]. IR-based techniques are useful in investigating syngas conversion because CO is both a reactant and a molecular probe often used to characterize metal surfaces. We recently reported that the most active cobalt sites were likely those associated with the formation of bridged CO(ads), which are thought to be located at the particle edges or steps [4]. This conclusion was reached by noting that the poisoning of cobalt by chloride affected more bridged CO(ads) than linear CO(ads) [4].We report herein an operando diffuse reflectance FT-IR spectroscopy (DRIFTS) study in which the hydrogenation of CO is monitored on Co and Sn-Co catalysts. Sn-modified cobalt catalysts were synthesized to obtain similar poisoning effects, using an element less volatile than chlorine. Sn does not adsorb CO at the temperatures investigated, so the carbonyl band observed in the region 2100-1700cm-1 by FT-IR could be attributed to CO adsorbed only on cobalt atoms.2.ExperimentalA 15 wt.% Co/Al2O3 catalyst used for the CO hydrogenation was prepared with the method reported by Shi et al.[5]. Commercial reagents of Co(NO3)2.6H2O, γ-alumina and citric acid were used. Two Sn-modified catalysts were prepared by adding tin (according to a yet undisclosed method) on the as-prepared 15 wt.% Co/Al2O3 catalyst, with Co/Sn molar ratios equal to 60 and 120. The hydrogenation of CO was performed using a modified high temperature DRIFT cell described in [4]. The reactor effluent was quantified using a 2m-pathlength FT-IR gas cell. The low mass of catalyst (30 mg) used in the reactor enabled to maintain low conversion and to operate essentially ...
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