Abstract: Ethylene is the most versatile petrochemical feedstock for the production of polyethylene, ethanol, ethylene oxide, ethylene glycol, styrene, dichloroethane, and many other chemical products. The process of hydrogenation of acetylene into ethylene can be used both to purify ethylene from an impurity of alkyne, which is formed at the stage of pyrolysis of crude oil while getting C2H4 [1], and for direct ethylene production from acetylene [2]. Most often, palladium-based metal systems are used as catalysts for the acetylene hydrogenation reaction due to their high catalytic activity. The efficiency of such catalysts is determined primarily by the dispersity and the electronic state of palladium, which depend on the strength of its interaction with the support and the acid-basic properties of the latter [3, 4]. Previously, we have showed the possibility of applying the sol-gel method including an aerogel approach to synthesize various nanocrystalline systems. Such materials possess both high specific surface area and uniform distribution of the active component, which is important for achieving appropriate performance in catalysis [5, 6]. In this work, a series of Pd/MgO catalysts was synthesized. The samples were identical in palladium content (1 wt.%) but different in the preparation method. Thus, an aerogel method, a sol-gel (SG) method, and an incipient wetness impregnation (IWI) method were used. The preparation procedures were followed by reduction in hydrogen at 500 °C for 3 h. Catalytic tests in the acetylene hydrogenation reaction were performed in a flow regime, in a stream of a gas mixture containing 4 vol.% C2H2 in hydrogen within the temperature range from 20 to 90 °C. Using transmission electron microscopy (TEM), it was shown that the palladium particles have a spherical shape and are uniformly distributed over the support. The average size of palladium particles depends on the synthesis method: the most dispersed particles (Dav = 2.0 – 2.2 nm) are formed in the case of sol-gel and impregnation methods. The aerogel-prepared samples contain palladium particles of ~ 8.0 nm in size. At the same time, the aerogel- prepared catalysts showed the highest activity: a 50% degree of acetylene conversion was observed already at 35 °C, while in the cases of SG- and IWI-prepared samples, such conversion values were achieved at noticeably higher temperatures of 49 and 65 °C, respectively. It was found that the maximum selectivity toward ethylene at 25 °C of about 60 – 70% is also characteristic of the aerogel-prepared sample (Fig. 1). As seen, the selectivity toward ethylene for the aerogel-prepared sample decreases by ~ 15% at temperatures above 60 °C, which is apparently caused by the diffusion limitations. Such behavior can be explained by the features of porous structure. Another reason is uniform distribution of the active component over the bulk of the catalyst’s granules when just a part of palladium particles is located on the outer surface. Thus, the aerogel-prepared Pd/MgO catalyst shows high activity in the acetylene hydrogenation reaction and appropriate selectivity toward ethylene at low temperatures.

Cite: Ilyina E.V. , Yurpalova D.V. , Shlyapin D.A. , Veselov G.B. , Shivtsov D.M. , Stoyanovskii V.O. , Vedyagin A.A.
Acetylene Hydrogenation over Pd/MgO Nanocrystalline system: Effect of the Synthesis Route on Catalytic Performance
The 8th Asian Symposium on Advanced Materials 03-07 Jul 2023