Spectroscopic Study on the Nature of Active Entities in Copper–Ceria CO-PROX Catalysts

Abstract

A series of oxidised copper-ceria catalysts with varying copper loadings and prepared by two different methods (impregnation of ceria and coprecipitation of the two components within reverse microemulsions) have been examined with the aim of determining the nature of active entities for the two main (CO and H 2 ) competing oxidation reactions that take place during preferential oxidation of CO in H 2 -rich streams over this type of catalysts. The analysis is mainly based on operando spectroscopic exploration by DRIFTS and XANES as well as in situ analysis by Raman. The results allow establishing a model of the catalytic behaviour of this type of catalysts which can provide keys to control their CO-PROX catalytic properties.

Promoting effect of AuCu alloying on Au-Cu/CeO2-catalyzed CO oxidation: A combined kinetic and in situ DRIFTS study

“…This suggests strong interaction between Cu and Ce [27], resulting in the presence of Cu 2+ species, as previously suggested by XPS results [4]. CO adsorption on Cu 2+ sites is indeed generally not observed [22,[24][25][26][27][28]63]. On the other hand, CuO/CeO 2 -R shows a weak band at 2114 cm À1 .…”

“…There is currently no available kinetic data on the AuCu-catalyzed CO oxidation and no available DRIFT study on the ceria-supported AuCu system. However, DRIFTS has proven useful for investigating the mechanism of the CO oxidation reaction on Au/CeO 2 [15][16][17][18][19][20], Cu/CeO 2 [21][22][23][24][25][26][27][28], and bimetallic AuCu [2,3,6,11] supported on ''inert" supports according to Schubert's classification of supports for gold-catalyzed CO oxidation [29], namely alumina and silica. For Cu/CeO 2 catalysts, CO oxidation rates were shown to correlate well with the formation of Cu + -CO [21,23] and to follow a Mars-Van Krevelen mechanism involving the redox properties of ceria in oxygen activation [26,30].…”

Characterization of Active Sites/Entities and Redox/Catalytic Correlations in Copper-Ceria-Based Catalysts for Preferential Oxidation of CO in H2-Rich Streams

“…On the other hand, the reaction mechanism under which this type of catalyst operates for CO oxidation has been proposed to be of a redox, generally speaking, of the Mars-van Krevelen [64,65], type [6]. This has been, indeed, demonstrated for the 1CuO/CeO 2 catalyst for which kinetic data are consistent with Mars-van J/mol and n = 0.09 [66]. In this respect, it becomes pertinent to enquire as to the nature of the active oxygen species involved in the reaction mechanism.…”

Recent Advances on the Rational Design of Non-Precious Metal Oxide Catalysts Exemplified by CuOx/CeO2 Binary System: Implications of Size, Shape and Electronic Effects on Intrinsic Reactivity and Metal-Support Interactions

“…A further increase in Cu content from 10 to 15 wt.% has been reported to reduce the catalytic activity, due to the large CuO x agglomerates on the catalyst surface [252]. It was revealed, by means of both ex situ and in situ characterization studies, that the desired CO oxidation process is related to partially reduced Cu + species, whereas, highly reduced copper species not strongly associated with CeO 2 favor the undesired H 2 oxidation [40,250,[265][266][267]. In view of this fact, extensive research efforts have been put forward to control the two competitive oxidation processes by appropriately adjusting the geometric and electronic interactions between copper and ceria through the above-described fine-tuning approaches.…”