Abstract: Liquid-phase selective hydrogenation of acetylene is the key stage of GTL (‘gas-to-liquid’) technology for the natural or associated gas components converting to ethylene and/or to the high-octane components of motor fuel [1, 2]. Acetylene obtained by oxidative pyrolysis of natural (associated) gas is absorbed by selective solvent and converted to ethylene by hydrogenation on supported palladium catalysts. To increase of the process selectivity and the resistance of the samples to deactivation, palladium is modified by the second metal (elements of IB, IIB or IIIA subgroups). However, the literature data on the active component composition and structure influence for such systems on the catalytic properties in this process are limited to several patents [1, 2]. The aim of this work is to investigate the palladium and the modifier precursors reduction temperature (Tred) effect on the active component state and the catalytic properties of 0.5% Pd-M/C (M: Ag, Zn, Ga) (Pd:M = 1:1) in the liquid-phase hydrogenation of acetylene to ethylene. Carbon composite Sibunit (SBET = 325 m2/g) was used as a support. Samples of the catalysts were prepared by an incipient wetness impregnation with joint aqueous solution of palladium and modifier nitrates with following stages of drying and reduction in a hydrogen stream (3 h). Tred was varied from 200 to 500°C. Hydrogenation of the model gas mixture (4 % vol. C2H2 and 96 % vol. H2) was carried out at 55°C in N-methylpyrrolidone medium in the shaker-type flow reactor. The increasing of the Tred for Pd-M/C catalysts from 300 to 500°C leads to the decreasing in the catalytic activity but the selectivity is increasing (by 20-25%). According to results of the ethane hydrogenolysis on Pd/C samples, the decreasing in the catalytic activity is related to the drop in the surface palladium concentration due to the sintering of initial nanodispersed particles. Using the XRD SR and XAFS data, it was found that the increasing in hydrogenation selectivity for the samples prepared at 500°C is due to the formation of bimetallic PdZn, PdxGay and PdAg nanoalloys. It is lead to significant increase of the distance between neighboring atoms of palladium from 2.72 Å for Pd/C sample to 2.82 – 2.89 Å for the modified Pd-M/C catalysts, which is accompanied with a change in geometry of acetylene adsorption (predominantly in π-bonded state) and, possibly, lead to increasing of the target product yield [3]. The interaction of Pd and Ag occurs even at Tred = 300°C and bimetallic Pd0.12Ag0.88 and Pd0.52 Ag0.48 particles are formed. With the growth of the Tred to 500°C their composition is come near to the Pd0.57Ag0.43, which is accompanied by increasing in reaction selectivity from 43 to 58%. Transformation of the active component structure in Pd-Zn- and Pd-Ga-catalysts with the formation of bimetallic PdZn and Pd2Ga nanophases occurs at T = 500°C. Based on the analysis of the XAFS spectra, it is assumed that the PdZn particles have a «core-shell» structure where the palladium cores are coated by the layer of joint PdZn phase. Investigation of the Pd-Ga catalysts is complicated by the addiction of Ga to oxidize during the operating with the samples in air.

Cite: Glyzdova D.V. , Khramov E.V. , Smirnova N.S. , Vedyagin A.A. , Shlyapin D.A.
The Reduction Temperature Influence on the Active Component State and Catalytic Properties of Pd-M/Sibunit (M: Ag, Zn, Ga) in Liquid-phase Selective Hydrogenation of Acetylene
In compilation Catalysis: from science to industry: proceedings of V International scientific school-conference for young scientists, September 25-29, 2018, Tomsk. – "Ivan Fedorov" publishing., 2018. – C.94. – ISBN 9785917011325. РИНЦ

Identifiers:

Elibrary:

50436535

Citing: Пока нет цитирований