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Structure Features and Evolution of Cobalt Catalyst Supported on Carbon Nanotubes in Fischer-Tropsch Synthesisтезисы доклада
- Авторы: Chernyak S.A., Suslova E.V., Ivanov Anton S., Maslakov K.I., Egorov A.V., Savilov S.V., Lunin V.V.
- Сборник: Catalyst Design: From Molecular to Industrial Level. 5th International School-Conference on Catalysis for Young Scientists (May 20-23, 2018, Moscow, Russia) [Electronic resource] : Abstracts / Boreskov institute of Catalysis SB RAS
- Тезисы
- Год издания: 2018
- Место издания: BIC Novosibirsk
- Первая страница: 98
- Последняя страница: 99
- Аннотация: The increase of the cost of oil extraction makes the conversion of natural gas, coal, and biomass into hydrocarbons, alcohols and ethers one of the main trends in natural fuel processing industry. This process, also known as Fischer-Tropsch synthesis (FTS), is based on the catalytic conversion of synthesis gas into more valuable hydrocarbons, alcohols and ethers on iron or cobalt-containing catalysts. Comparing to iron catalysts, the advantages of cobalt systems are their increased time stability and lower process pressure and temperature. The properties of carbon nanotubes (CNTs) favour their use as a catalyst support for FTS. The chemical inertness of CNTs, their structural rigidity, high thermal conductivity, tuneable surface properties and localization of catalyst particles distinguish them from oxide or other carbon-based supports [1]. In this work we investigate the FTS on cobalt catalysts supported on CNTs and transformations of metal and support at different stages of catalyst life cycle: fabrication, reduction and catalytic reaction. For this purpose, pristine CNTs were functionalized to the different degrees with oxygen-containing groups. It was found that the stability of catalysts to sintering is determined by the geometry of the support surface, while the homogeneity of both Co distribution and its dispersion depends on the degree of functionalization of the support [1-3]. TEM, XPS, Raman spectroscopy, and low temperature nitrogen sorption were used to control the structure of both supports and catalysts. The activity of Co/CNT catalysts loaded with 15 wt.% of Co linearly depended on the metal dispersion in the dCo range of 4–25 nm, which confirms the absence of interaction of the catalyst with the support, even in the case of CNTs containing a large number of functionalities. Despite the selectivity to C5+ hydrocarbons was found to be lower for samples with dCo of about 4 nm than that for the catalysts with dCo larger than 5 nm, the highest yield of this fraction was observed in the case of smaller particles. Thus, the total amount of surface Co plays a more significant role in the formation of condensed hydrocarbons than the quality of the active centres. At the same time, in the case of simultaneously low Co content and a high degree of surface functionalization, the formation of metal particles smaller than 3 nm with the amorphous structure was observed revealing the metal-support interaction at the stage of catalyst preparation. Further studies showed the absence of FTS activity over this catalyst and the formation of carbon shells around amorphous Co particles. TEM images of Co catalyst supported on oxidized CNTs are shown in Fig.1. To investigate the support evolution Co was washed from the catalyst after annealing, reduction and FTS. It was found that the annealing and reduction significantly change the structure of CNTs which results in the increase of the SBET and total pore volume. The change in the composition and content of functional groups was thoroughly studied It was found that about 70% of oxygen had been removed by the beginning of the FTS. The methanation of CNTs during reduction was demonstrated by TEM (Fig.2). Nitrogen-doped CNTs were also studied as a support for Co catalysts in the FTS.
- Добавил в систему: Черняк Сергей Александрович