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Research results about the influence of BEA zeolite preliminary dealumination on the acid–base characteristics and catalytic performance of 1% Zn-BEA compositions in propane dehydrogenation with CO2 are presented. The catalyst samples, prepared through a two-step post-synthesis procedure involving partial or complete dealumination of the BEA specimen followed by the introduction of Zn2+ cations into the T-positions of the zeolite framework, were characterized using XRD, XPS, MAS NMR, SEM/EDS, low-temperature N2 ad/desorption, C3H8/C3H6 (CO2, NH3)-TPD, TPO-O2, and FTIR-Py techniques. Full dealumination resulted in the development of a mesoporous structure and specific surface area (BET) with a twofold decrease in the total acidity and basicity of Zn-BEA, and the formation of Lewis acid sites and basic sites of predominantly medium strength, as well as the removal of Brønsted acid sites from the surface. In the presence of the ZnSiBEA catalyst, which had the lowest total acidity and basicity, the obtained selectivity of 86–94% and yield of 30–33% for propene (at 923 K) exceeded the values for ZnAlSiBEA and ZnAlBEA. The results of propane dehydrogenation with/without carbon dioxide showed the advantages of producing the target olefin in the presence of CO2 using Zn-BEA catalysts. [ABSTRACT FROM AUTHOR]

Three series of zeolite catalysts Co all-silica and Co Al-containing zeolites beta were prepared for use in the selective oxidative dehydrogenation of propane to propylene. Two series of zeolite catalysts Co all-silica were prepared by a two-step postsynthesis method at pH = 2.5 and pH = 3.0–9.0, respectively, which allows the incorporation of cobalt into SiBEA zeolite in the form of isolated framework pseudo-tetrahedral Co(II) species. The incorporation of Co ions into vacant T-atom sites and their reaction with silanol groups were demonstrated by NMR and FTIR methods. The generation of Lewis acid sites without the formation of Brønsted sites was proved by FTIR using pyridine and CO as probe molecules. The state of cobalt in three series of prepared and calcined zeolite catalysts was characterized by DR UV-vis. This technique allowed to show that for low Co content (<2 wt.%) cobalt is present in the form of framework pseudo-tetrahedral Co(II) species. For higher Co content (>2 wt.%), both framework pseudo-tetrahedral and extra-framework octahedral Co(II) species are present. The Co Al-containing zeolite beta series prepared on non-dealuminated support shows the presence of extra-framework octahedral Co(II) only. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 contrast, for microporous catalysts, the dealumination did not play such a significant role and the relatively high activity is observed for both not dealuminated and dealuminated catalysts. The main liquid products of FTS on both mesoporous and microporous catalysts were C10-C14 isoalkanes and n-alkanes. The iso-/n-alkanes ratio for dealuminated zeolite catalysts was three times higher than that for not dealuminated ones, and was related to the presence of different kind of acidic sites in both zeolite catalysts. [ABSTRACT FROM AUTHOR]

Abstract: The effect of Co content on the catalytic activity of CoSiBEA zeolites in the selective catalytic reduction (SCR) of NO with ethanol is investigated. The Co x SiBEA zeolites (x =0.3, 0.7, 3.6 and 6.75Cowt.%) are prepared by a two-step postsynthesis method which allows to control the introduction of cobalt into zeolite and thus to obtain catalysts with specific Co sites. The nature of the active sites is characterized by XRD, diffuse reflectance UV–vis, H2-TPR and XPS. The catalytic activity of Co x SiBEA strongly depends on the nature and environment of Co species. Zeolites with isolated lattice tetrahedral Co(II) (Co0.3SiBEA and Co0.7SiBEA samples) are active in SCR of NO with ethanol with selectivity toward N2 exceeding 85% for NO conversion from 20 to 70%. When additional isolated extra-lattice octahedral Co(II) species appear (Co3.6SiBEA sample), the full oxidation of ethanol by dioxygen becomes a very important reaction pathway. In presence of additional cobalt oxides (Co6.75SiBEA sample), the activity and selectivity toward N2 substantially change and full oxidation of ethanol to CO2 is the main reaction pathway and full NO oxidation also takes place in the temperature range 550–775K. The lack of correlation between the activity in SCR of NO with ethanol and NO oxidation to NO2 suggests that the two reactions are more competitive than sequential. [Copyright &y& Elsevier]