Effect of Crystallinity of Zeolite Beta on Physicochemical Properties and Performance of Cobalt Catalysts (original) (raw)
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Catalysts
Co-containing Beta zeolite catalysts prepared by a wet impregnation and two-step postsynthesis method were investigated. The activity of the catalysts was examined in Fischer-Tropsch synthesis (FTS), performed at 30 atm and 260 °C. The physicochemical properties of all systems were investigated by means of X-ray diffraction (XRD), in situ XRD, temperature programmed desorption of ammonia (NH3-TPD), X-ray Photoelectron Spectroscopy (XPS), temperature programmed reduction of hydrogen (TPR-H2), and transmission electron microscopy (TEM). Among the studied catalysts, the best results were obtained for the samples prepared by a two-step postsynthesis method, which achieved CO conversion of about 74%, and selectivity to liquid products of about 86%. The distribution of liquid products for Red-Me-Co20Beta was more diversified than for Red-Mi-Co20Beta. It was observed that significant influence of the zeolite dealumination of mesoporous zeolite on the catalytic performance in FTS. In contra...
Journal of Industrial and Engineering Chemistry, 2010
This work investigated reducibility of cobalt species in monometallic Co/NaY and bimetallic CoPt/NaY catalysts with various Co loading (1, 6 and 10 wt.%) and fixed Pt loading (1 wt.%). The form and environment of Co species after reduction was determined by X-ray absorption spectroscopy including X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies. The cobalt species in the mono-and bimetallic catalyst with Co loading of 1 wt.% was not reducible whereas those with Co loading of 6 and 10 wt.% were partially reduced. The extent of reduction increased with Co loading and enhanced by the presence of Pt. Catalytic performance for n-butane hydrogenolysis mono-and bimetallic catalysts were compared. The higher extent of Co reduction in 6CoPt/NaY and 10CoPt/NaY resulted in higher conversions than the monometallic counterpart. Sequential hydrogenolysis was favored on the monometallic catalysts because methane was the only product. The presence of Pt suppressed such reaction resulting in ethane and propane. The effect of Pt on such effect was most prominent in 6CoPt/NaY.
Carbon Monoxide Hydrogenation on Cobalt/Zeolite Catalysts
Journal of Porous Materials, 2005
The synthesis of hydrocarbons from catalytic hydrogenation of CO/H 2 was investigated over Co/zeolite catalysts at 1 atm, 493-553 K, H 2 /CO = 2, and GHSV = 1200. Various zeolites, such as NaA, NaX, NaY, KL and NaMordenite, were used as the supports. The catalysts were prepared by impregnation and were characterized by H 2 /CO chemisorption and temperature-programmed reduction (TPR). Based on TPD measurements, the CO/H 2 adsorption ratio can be used as an index for the extent of metal-zeolite interaction. The stronger the metal-zeolite interaction is, the higher the Co/H 2 adsorption ratio on metal is. The activity and selectivity of cobalt supported in zeolites were affected by complex factors such as framework structure, Si/Al ratio, and the complementary cations. The activity of the catalyst is in the order: Co/KL > Co/NaX > Co/NaY > Co/NaMordenite > Co/NaA. All of the Co/zeolite catalysts had a very high selectivity to C 2-C 4 olefins, which would decrease with increasing reaction temperature. Cobalt oxide supported in zeolite was difficult to reduce. Increasing the reduction temperature could increase the reducibility of cobalt and resulted in the increase of activity.
Cobalt-zeolite catalysts for the synthesis of hydrocarbons from CO and H2
Russian Chemical Bulletin, 1995
Catalysts prepared by mechanical mixing of high-silica zeolite ZSM-5 with cobalt oxide Co304, basic cobaltous carbonate, and cobaltous carbonate were studied. The nature of the cobalt compound introduced into the mixture affects the catalytic and physicochemical properties of the catalyst. The presence of Co304 in the sample (introduced as oxide or obtained by thermal decomposition of the carbonate) is favorable to the formation of aromatic compounds from CO and H 2. The use of cobaltous carbonates for the preparation of catalysts results in development of the porous structure of the catalyst. During preparation of samples, the mechanical treatment partially destroys the zeolite framework of the support.
Coal tar can be used as an alternative raw material for the production of liquid fuels, such as: gasoline and diesel through hydrogenation and cracking process. Hydrogenation and cracking process requires a catalyst which has metal components for hydrogenation reaction and acid components for cracking reaction. In this study, the Co/Zeolite Y and Co-Mo/Zeolite Y catalysts were prepared by impregnation and ion exchange methods. Characterizations of the catalysts were carried out by X-Ray Diffraction (XRD) and gravimetric acidity. The catalysts were tested for coal tar conversion to liquid fuel under various temperatures, amount of catalyst and hydrogen flow rates in a fixed bed flow reaction system. Liquid fuels products were analyzed by gas chromatography (GC). The XRD Spectra indicated that the addition of Co and Mo metals did not affect catalysts structure, however it alters the percentage of crystallinity. The addition of Co metal using impregnation method caused reduction in crystallinity, while the addition of Mo caused improvement of crystallinity. The Co-Mo/Zeolite Y catalyst with highest crystallinity was obtained by loading using ion exchange method. The addition of Co and Mo metals caused increasing acidity. However, the increasing composition of Co and Mo loaded on Zeolite Y catalyst decreased the yield of liquid fuels from coal tar. It can be concluded that the yields of liquid fuels and the composition of gasoline fractions from hydrocracking of coal tar were highly dependent on acidity of the catalyst.
Catalysts
A goal of this work was to investigate the influence of the preparation procedure and activation conditions (reduction temperature and reducing medium: pure hydrogen (100% H2) or hydrogen-argon mixture (5% H2-95% Ar)) on the activity of Co-containing BEA zeolites in Fischer–Tropsch synthesis. Therefore, a series of CoBEA zeolites were obtained by a conventional wet impregnation (Co5.0AlBEA) and a two-step postsynthesis preparation procedure involving dealumination and impregnation steps (Co5.0SiBEA). Both types of zeolites were calcined in air at 500 °C for 3 h and then reduced at 500, 800 and 900 °C for 1 h in 100 % H2 and in 5% H2–95% Ar mixture flow. The obtained Red-C-Co5.0AlBEA and Red-C-Co5.0SiBEA catalysts with various physicochemical properties were tested in Fischer–Tropsch reaction. Among the studied catalysts, Red-C-Co5.0SiBEA reduced at 500 °C in pure hydrogen was the most active, presenting selectivity to liquid products of 91% containing mainly C7–C16 n-alkanes and iso...
Journal of Catalysis, 2005
The effect of cobalt precursor and pretreatment conditions on the structure of cobalt species in silica-supported Fischer-Tropsch (FT) catalysts was studied with a combination of characterization techniques (X-ray diffraction, UV-visible, X-ray absorption, X-ray photoelectron spectroscopies, DSC-TGA thermal analysis, propene chemisorption, and temperature-programmed reduction combined with in situ magnetic measurements). The catalysts were prepared via aqueous impregnation of silica with solutions of cobalt nitrate or acetate followed by oxidative pretreatment in air and reduction in hydrogen. It was found that after impregnation and drying cobalt exists in octahedrally coordinated complexes in catalysts prepared from cobalt nitrate or cobalt acetate. Decomposition of the octahedral complexes results in the appearance of Co 3 O 4 crystallites and cobalt silicate species. Cobalt repartition between crystalline Co 3 O 4 and the cobalt silicate phase in the oxidized samples depends on the exothermicity of salt decomposition in air and the temperature of the oxidative pretreatment. Co 3 O 4 crystallite is the dominant phase in the samples prepared via endothermic decomposition of supported cobalt nitrate. Significantly higher cobalt dispersion is found in the catalyst prepared via low-temperature cobalt nitrate decomposition. The uncovered enhanced cobalt dispersion is associated with lower cobalt reducibility. The high exothermicity of cobalt acetate decomposition leads primarily to amorphous, barely reducible cobalt silicate. A more efficient heat flow control at the stage of cobalt acetate decomposition significantly increases the concentration of easy reducible Co 3 O 4 in the oxidized catalysts and the number of cobalt metal active sites after reduction. The catalytic measurements show that FT reaction rates depend on the number of cobalt surface metal sites; a higher concentration of cobalt metal sites in the catalysts prepared from cobalt nitrate or with the use of soft cobalt acetate decomposition results in higher catalytic activity in FT synthesis. 2004 Elsevier Inc. All rights reserved.
Bioethanol Steam Reforming over Cobalt-Containing USY and ZSM-5 Commercial Zeolite Catalysts
Frontiers in Materials, 2020
The ethanol steam reforming (ESR) process over cobalt-based zeolitic catalysts, differing significantly in the structure, was comprehensively examined. The cobalt spinel phase (10 wt%) was deposited on the surface of USY and ZSM-5 zeolites (Si/Al ratio of 31). The catalysts were characterized in terms of their chemical (ICP) and phase composition (XRD), textural properties (low-temperature N 2 adsorption), morphology (STEM/EDX), and reducibility (H 2-TPR). The aforementioned characteristics were supplemented by the catalysts' acidity and redox properties investigations (quantitative FT-IR studies of pyridine and carbon monoxide adsorption). Catalysts' activity was evaluated in the ESR process at 500°C for various ethanol/water mixtures. Both catalysts exhibited 100% ethanol conversion, whereas their selectivity toward H 2 , CO 2 , and C 2 H 4 strongly depended on the applied ethanol-to-water molar ratio. Comparable selectivities observed for the 1 : 4 ratio were improved for the 1 : 9 ratio for both catalysts, as expected. For the ratio of 1 : 12, the significant difference in the reaction paths (the ethanol dehydration for CoUSY and the ethanol steam reforming for CoZSM-5) was explained by the cobalt reoxidation process facilitated by water molecules for the CoUSY. The superior overall performance of the CoZSM-5 catalyst in the ESR process, in comparison to CoUSY, also results from its almost three times enhanced accessibility of the cobalt species, as confirmed by the quantitative FT-IR studies of CO sorption. The microscopic studies also indicated a better dispersion of the cobalt phase supported on the ZSM-5 support. Thus, the structure of ZSM-5 zeolite assures higher cobalt active phase dispersion being more beneficial for the ESR process.
The Catalytic Performance of Ni-Co/Beta Zeolite Catalysts in Fischer-Tropsch Synthesis
Catalysts
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 s...