The Influence of Yttrium Stabilized Zirconia as Support of Copper-Ceria Systems on their Catalytic Properties in the Pro
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THE INFLUENCE OF YTTRIUM STABILIZED ZIRCONIA AS SUPPORT OF COPPER-CERIA SYSTEMS ON THEIR CATALYTIC PROPERTIES IN THE PROX PROCESS G. R. Kosmambetova
UDC 54ci4.478.1/.02
It is shown that with the same quantitative composition of the copper-ceria-zirconia catalyst, varying only the structural and dimensional characteristics of the yttrium stabilized zirconia (YSZr), it is possible to improve the activity and selectivity of the catalyst and expand the «temperature window» of its effective operation. It has been established that the low surface area of YSZr support, due to the high degree of agglomeration of its nanoparticles, contributes to the formation of a larger number of interaction zones of copper and cerium oxides that are active sites of the process of selective oxidation of CO in hydrogen (PROX – Preferential CO oxidation).
Keywords: yttrium stabilized zirconium dioxide, oxide copper-cerium catalysts, PROX process.
High activity and selectivity of the copper-cerium catalysts in the selective oxidation of CO in hydrogen (PROX process is preferential CO oxidation) is associated with a synergistic effect due to the contact of active sites: activation of CO on Cum+ (m = 1, 2) and the presence of a nearby oxygen activation center Cen+ (n = 3, 4) in the composition of nonstoichiometric cerium dioxide [1, 2]. As a result of the interaction of copper and cerium oxides, both components are easily reduced and oxidized, thus providing high performance (activity and selectivity) of the oxide copper-cerium catalysts in the PROX process [3]. The oxygen vacancies generated as a result of this interaction act as the oxygen activation sites, accelerating the CO oxidation stage. The presence of copper in various oxidation states was detected in the copper-cerium catalysts using the X-ray photoelectron spectroscopy [4]. The formation of zones of CuO and CeO2 interfacial interaction was confirmed by DRIFTS and XANES methods [5]. It should be noted that the high dispersion of copper and cerium oxides contributes to the synergistic effect [6]. In particular, it is known that the ability of cerium dioxide to accumulate oxygen from the gas phase is directly related to the size of its particles [7]. One of the effective supports capable of stabilizing the highly dispersed state of cerium dioxide is yttrium stabilized zirconia (YSZr) [8]. Reducing the size of nanoparticles to the nanometer range improves the functional properties of YSZr, which is related not only to the size but also to a certain way of organizing particles into agglomerated nanosystems and the formation of grain boundaries [9]. Such structures may be characterized by a small size of crystallites, while having a low specific surface area. This study presents an analysis of the influence of structural and dimensional characteristics of YSZr as a support of the copper-cerium catalysts on their catalytic properties in the PROX process and the oxidation reactions of CO and hydrogen.
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