Реферат: Semi-hydrogenation of alkyne to alkene is widely used to purify crude ethene containing a small amount of acetylene formed during the pyrolysis of petroleum feedstock. However, the depletion of oil reserves will greatly limit the possibility of its use in the future. Thus the alternative methods for producing ethylene from natural gas or coal through the stage of obtaining acetylene are being intensively developed [1, 2]. In both cases, ethylene is obtained by direct hydrogenation of acetylene on Pd-catalysts modified with Ag, Zn, Ga or other metals [3]. There is evidence that Pd-Co catalysts can also be promising systems for this process due to the possibility of forming bimetallic particles [4]. However, the influence of the active component state of such systems on their properties in the acetylene hydrogenation reaction has not been sufficiently studied. Therefore, the aim of this work was to study the modifying effect of Co on Pd in the Pd-Co/Sibunit catalysts and to establish the relationship between the active component state and catalytic properties in the process of acetylene hydrogenation to ethylene. Sibunit carbon mesoporous material was used as a catalyst support. Samples were prepared by incipient wetness impregnation method with joint aqueous solution of Pd(NO3)2 and Co(NO3)2. The catalysts were dried at 120°С and reduced in hydrogen at 500 – 700°С. The content of palladium in all samples was 0.5 wt.%. The Pd/Co molar ratio was varied from 1/0.5 to 1/2. The state of the active component was studied by XRD, XPS, TEM and EDX. Hydrogenation was carried out in a model gas mixture (4 vol.% C2H2 in a hydrogen) in a flow mode at atmospheric pressure at 25 – 95°C. The addition of small amounts of cobalt into the Pd/Sibunit catalyst (Pd/Co = 1/0.5) does not lead to a significant change in the catalytic properties, while an increase the concentration of cobalt to Pd/Co = 1/2 is accompanied by a decrease in catalytic activity and an increase in alkene selectivity. The yield of ethylene on Pd-Co(1:2)/Sibunit is 62%, which is 16 rel.% higher than the yield obtained on the Pd/Sibunit catalyst. According to TEM data, both samples contain spherical particles characterized by an approximately the same size distribution (dav = 4.2 nm). Consequently, the observed differences in catalytic properties are not due to the dispersion value, but due to the difference in the nature of the active component. According to in situ XRD analysis, the heating of Pd-Co/Sibunit in H2 at T ≥ 500°C leads to the formation of an fcc phase of the Pd(1-x)Cox solid solution enriched in Co. An increase in the reduction temperature to 700°C is accompanied by a gradual increase in the lattice parameter to 3.662 Å, which corresponds to a solid solution containing ~35 at.% of palladium. Pd-Co-catalysts reduced at 600 and 700°C exhibit lower activity, but the yield of the target product increases significantly to 66 and 68%, respectively. Based on the XPS results, it is assumed that the excellent selectivity of Pd-Co/Sibunit samples is due to a change in the electronic state of palladium under the modifying action of Co. Wherein the decrease in activity can be associated both with the presence of less active bimetallic sites and the partial blocking of the active component by a thin film of cobalt oxide identified by the EDX method.

Библиографическая ссылка: Glyzdova D.V. , Afonasenko T.N. , Prosvirin I.P. , Bukhtiyarov A.V. , Vinokurov Z.S. , Gerasimov E.Y. , Trenikhin M.V. , Shlyapin D.A.
Selective Hydrogenation of Acetylene over Pd-Co/Sibunit Catalysts: The Modifying Effect of Cobalt
VII International School-Conference for Young Scientists "Catalysis: from Science to Industry" 11-15 Oct 2022