Abstract
The influence of nickel introduction on the catalytic performance of cobalt micro- and mesoporous Beta zeolite catalysts in Fischer–Tropsch Synthesis was studied. Catalysts containing 3 wt% of nickel and 10 wt% of cobalt were prepared by co-impregnation and sequential impregnation and comprehensively characterized by XRD, XPS, NH3-TPD, TPR-H2 and TEM EDX techniques. Neither the dealumination of Beta zeolite nor the incorporation of Co and Ni affected its structure, as shown by XRD and BET investigations. The presence of nickel results in the decrease in the temperature of the cobalt oxide reduction, evidenced by TPR-H2 and the increase of CO conversion. Among all the tested catalysts, the best catalytic properties in FTS showed that based on microporous dealuminated zeolites with a very high CO conversion, near 100%, and selectivity to liquid products of about 75%. In case of dealuminated samples, the presence of Ni decreased the selectivity to liquid products. All catalysts under study showed high resistance to deactivation during the whole time of synthesis (24 h). The very high stability of nickel-cobalt based Beta catalysts was probably due to the hydrogen spillover from metallic nickel particles to cobalt oxides, which decreased re-oxidation of the active phase, sintering and the creation of the carbon on the catalyst surface. Moreover, the presence of Ni on the surface of cobalt-based Beta catalysts could obstruct the formation of graphitic carbon and, in consequence, delay the deactivation of the catalyst.
Highlights
As a result of oil resources reduction, the development and optimization of the alternative fuels production is becoming a very important challenge
Different types of Mi-Ni3.0 Co10 AlBeta and Me-Ni3.0 Co10 SiBeta zeolite catalysts were prepared by conventional wet impregnation and the two-step post-synthesis method, respectively, where “Mi” stands for microporous, “Me” for mesoporous, “Ni3.0 ” for 3.0 wt% of nickel, “Co10 ” for 10 wt% of cobalt, “AlBeta” for aluminated Beta zeolite and “SiBeta” for dealuminated Beta zeolite
The suspensions were stirred during 24 h at room temperature and the separation of the solids from the fraction of suspension was performed in an evaporator under the vacuum of a membrane pump for 2 h in air at 60 ◦ C
Summary
As a result of oil resources reduction, the development and optimization of the alternative fuels production is becoming a very important challenge. The application of zeolite materials as catalysts support in FTS process seems to be justified These materials possess many specific properties like highly developed specific surface area, the presence of micro- and mesopores, which may improve the metal dispersion inside of micro- and mesoporous channels and allow for obtaining of smaller cobalt crystallites. The application of the two-step postsynthesis method for the preparation of catalysts allows for a decrease of catalysts acidity and results in the formation of a smaller amount of carbon deposition in comparison to classical oxide-supported catalysts This promising result encourages the continuation of this investigation and of making attempts to improve the activity and selectivity towards gasoline on CoBeta zeolite catalysts [14,15].
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