Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-I-17MECHANISM OF FORMATION OF ETHYLENE BY SELECTIVEHYDROGENATION OF ACETYLENE OVER CERIA SUPPORTEDGOLD CATALYSTYassine Azizi, Corinne Petit, Véronique PitchonLaboratoire des Matériaux, Surfaces et Procédés pour la Catalyse (LMSPC),UMR 7515 du CNRS 25 ECPM, 25 rue de Becquerel, 67087 Strasbourg, FranceEthylene is by far the basic petrochemical product most demanded with a production over130 millions tons per year worldwide. Industrially, ethylene is usually formed by pyrolysis ofhydrocarbons in the presence of steam. Acetylene is a by-product of ethylene production andacts as a poison for the catalyst used for the synthesis of polyethylene from ethylene, andshould therefore be removed by selective hydrogenation. There are several types of catalystssuitable for hydrogenation of acetylene and they are usually using palladium. However, thesecatalysts still need to be improved, as the problem of selectivity at higher temperature and ofoligomerization is not completely overcome. Gold has been found to be active for thehydrogenation of several reaction, such as acroleine, 1,3-butadiene, or even α,β insaturatedketones, but this propensity for hydrogenation has only rarely been studied for the alkynesmolecules.The present study was undertaken in an attempt to put in evidence the properties ofhydrogenation of gold on a support not yet reported in the literature, namely ceria in order topropose a mechanism of selective hydrogenation of acetylene. The choice of ceria was madebecause we are able, with a method of preparation developed in our group, to perfectly controlboth the deposition and the dispersion of gold, so that nanoparticules of 2 nm are obtained.The method of preparation is based upon the direct anionic exchange (DAE) of the goldspecies with the hydroxyl groups of the support, and was reported in a previous publication[1].The activity and selectivity has been measured between 30 and 400°C at differentH 2 /C 2 H 2 ratio (R), namely, 3, 5, 7, 10, 30 and 60. The selectivity towards ethylene is of 100%up to 300°C independently of the different C 2 H 2 /H 2 ratios. The conversion follows a volcanoshape trend for C 2 H 2 /H 2 ratio equal to 3, 5 or 7 with a deactivation above 300°C concomitantwith the loss of selectivity, i.e. with maxima at 300°C. For higher H 2 /C 2 H 2 ratio, i.e. 10, 30 or60, the conversion remains of 100%. The decrease of selectivity in C 2 H 4 is due to theformation of CH 4 , the formation of C 2 H 6 was never observed contrary to all the resultsreported, the literature, mainly on Pd, in.58