Structure and Energy Profile of the Skeletal Nickel Surface According to the Small-Angle X-Ray Diffraction and Adsorptio
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cture and Energy Profile of the Skeletal Nickel Surface According to the Small-Angle X-Ray Diffraction and Adsorption Calorimetry Data V. V. Kuznetsova, T. Yu. Osadchayaa, A. V. Afineevskiia, D. A. Prozorova,*, M. V. Lukina, and D. N. Smirnovab a Ivanovo
State University of Chemical Technology, Ivanovo, 153000 Russia Open Joint-Stock Company, Ivanovo, 153021 Russia *e-mail: [email protected]
b Ivkhimprom
Received October 5, 2018; revised September 7, 2020; accepted September 17, 2020
Abstract—A systematic study of the surface of Raney nickel-based pyrophoric catalysts by small-angle X-ray diffraction analysis was carried out for the first time. The parameters of the crystallites constituting the active catalyst surface were determined. A correlation between the surface structure and the activity of skeletal nickel for the liquid-phase hydrogenation reactions was demonstrated. The effect of treatment of Ni–Al alloy with sodium hydroxide and hydrogen peroxide on the catalyst particle size and on the course of the hydrogenation reaction was revealed and substantiated. The X-ray diffraction data on the catalyst surface structure and the adsorption calorimetry data were correlated with the skeletal nickel activity parameters. Keywords: liquid-phase hydrogenation, nickel catalyst, catalyst activity, small-angle X-ray diffraction analysis, catalyst particle size
DOI: 10.1134/S1070363220090327 INTRODUCTION Skeletal nickel catalyst. Today, the properties of a catalyst are generally regarded as being determined by the physicochemical properties of the entire catalytic system. In particular, the activity, selectivity, and operational stability of a catalyst obviously depend not only on its chemical nature but also on the mechanism of the reaction being accelerated [1]. For heterogeneous catalysts, of decisive importance are the main physical characteristics: specific surface area, chemical composition, and porosity [2]. Therefore, most studies on metal- and metal oxidebased catalysts aim primarily to examine the physical characteristics of the metal surface and to develop ways for increasing the number of active surface sites as determined by the specific surface area [2–4]. One way to increase the active surface area of a catalyst is to use of skeletal or porous metal catalysts. Such catalysts are traditionally prepared by pyrometallurgical methods or by mechanical alloying of an inert component with a catalytically active metal. Removing the inert component under controlled conditions allows obtaining systems with desired adsorption properties. By changing the
conditions of mechanical pretreatment of the initial alloy it is possible to vary the catalytic activity of the finished catalyst [3, 5, 6]. Skeletal nickel, or Raney nickel, was the most-used skeletal catalyst in the 20th century [7], with skeletal cobalt and skeletal copper being used in some applications as well [8]. In such systems the original alloy typically contains 40–60 wt % [2, 4, 9] chemically active metal; the optimal composition is determined by the
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