Abstract: High selectivity for the target product is one of the main requirements for modern catalysts. One of the approaches to increase the acetylene hydrogenation selectivity to ethylene is the application of catalysts containing bimetallic particles as an active component [1]. Pd-Zn catalysts are of particular interest. Palladium, interacting with zinc, can form both solid solutions and ordered intermetallic compound PdZn. Zinc atoms in the bimetal structure “dilute” neighboring palladium atoms, effectively isolating them from each other, so active centers are formed on the catalyst surface [2–4]. Since the structure of active sites, determined by the method of synthesis, plays an important role in achieving the specified parameters of the catalytic process, the goal of this work was to establish the correlation between the method of synthesis of supported Pd-Zn catalysts, the structure of the active component, and the catalytic properties in the gas-phase hydrogenation of concentrated acetylene mixtures with hydrogen. Carbon material Sibunit was used as a catalysts support. The choice of the support was stipulated, first of all, by absence of strong surface acid sites responsible for acetylene oligomerization [5]. In addition, Sibunit, in contrast to traditional oxide supports (for example, Al2O3), is not able to interact with the modifier (Zn) to form various compounds (for example, spinels), which should increase the likelihood of contact between palladium and zinc precursors to form bimetallic nanoparticles [6]. The samples were obtained by an incipient wetness impregnation method by varying the sequence of palladium (Pd(NO3)2) and modifier (Zn(NO3)2) precursors deposition. At the first stage, one of the precursors was deposited, then the sample was dried at 120°С (3 h), and reduced in a hydrogen stream at 500°С (3 h). At the next stage the second precursor was added, followed by drying and heat treatment under the same conditions. Also one more bimetallic Pd-Zn sample was prepared by co-deposition of palladium and zinc nitrates, drying at 120°C (3 h), and reduction in H2 at 500°C (3 h). The palladium and zinc contents were 0.5 and 0.31 wt.%, respectively. Catalytic tests were carried out in flow reactor, in a stream of gas mixture containing 4 vol.% C2H2 and 96 vol.% H2 at 25-95 °C. The obtained catalysts were studied using a set of instrumental methods (EXAFS, XRD, TEM). It was found that the sequential addition of palladium and zinc precursors with an intermediate stage of reduction in hydrogen flow ensures the closest contact between the metals. As a result, dispersed (dav = 5.3 nm) intermetallic PdZn particles with a tetragonal structure are predominantly formed, which, as can be assumed, provide a high ethylene selectivity up to 74%.

Cite: Yurpalova D.V. , Afonasenko T.N. , Khramov E.V. , Trenikhin M.V. , Shlyapin D.A.
Effect of synthesis methods on the structure and properties of Pd-Zn/Sibunit catalysts for acetylene hydrogenation
6 International School-Conference on Catalysis for Young Scientists "Catalyst Design: From Molecular to Industrial Level" 16-19 May 2021