The influence of promoters (Zr, La, Tb, Pr) on the catalytic performance of CuO-CeO2 systems for the preferential oxidation of CO in the presence of CO2 and H2O

Abstract

CuO supported on CeO2 and Ce0.9X0.1O2, where X is Zr, La, Tb or Pr, were synthesized using nitrate precursors, giving rise ceria based materials with a small particle size which interact with CuO species generating a high amount of interfacial sites. The incorporation of cations to the ceria framework modifies the CeO2 lattice parameter, improving the redox behavior of the catalytic system. The catalysts were characterized by X-ray Diffraction (XRD), High-resolution Transmission Electron Microscopy (HRTEM), Raman spectroscopy, thermoprogrammed reduction with H2 (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The catalysts were tested in the preferential oxidation of CO under a H2-rich stream (CO-PROX), reaching conversion values higher than 95% between 115-140 ºC and being the catalyst with 6 wt.% of Cu supported on Ce0.9Zr0.1O2 (sample 6CUZRCE) the most active catalyst. The influence of the presence of CO2 and H2O was also studied simulating a PROX unit, taking place a decreasing of the catalytic activity due to the inhibitor effect both CO2 and H2O.

Catalytic Behaviour of CuO-CeO2 Systems Prepared by Different Synthetic Methodologies in the CO-PROX Reaction under CO2-H2O Feed Stream

“…This value was obtained considering the theoretical amount of CuO set in each H2-TPR. The H2 quantification from TPR profiles reveals that H2 consumption of all catalysts is higher than theoretical (Table 2), indicating the simultaneous reduction of CuO species and the surface of the CeO2 [24,26,27,32]. In fact, a relationship can be established between the CeO2 particle size and its H2-consumed/H2-theoretical ratio.…”

“…In this sense, Cu + species are the ones involved in the adsorption of CO in the CO-PROX reaction [40,44]. Finally, the absence of a band at 919 eV discards the presence of Cu 0 species [26].…”

“…The structural parameters of CeO2, determined by the Rietveld method, show that all samples maintained the typical cell parameter of CeO2 (a = 5.415 Å) [26], so the formation of Ce1−xCuxO2 solid solutions must be discarded. The SEM images of the CuO-CeO2 catalysts obtained from several synthetic methods are summarised in Figure 2.…”

“…CeO2-CuO catalyst was synthesised following the procedure described by Cecilia et al [26]. Briefly, the precursor Ce(NO3)3·6H2O (99.99%, Aldrich, St. Louis, MO, USA) was calcined to 500 °C at a rate of 10 °C·min −1 , maintaining this temperature for 2 h. The copper-containing catalyst was prepared by incipient wetness impregnation of the supports with a solution of copper(II) nitrate (99.99%, Aldrich) and the solid dried overnight at 60 °C and calcined for 4 h at 400 °C.…”

Separation of Light Liquid Paraffin C5–C9 with Cuban Volcanic Glass Previously Used in Copper Elimination from Water Solutions

“…In the same way, the chemical composition on its surface was determined by XPS, reaching a Cu content of 0.6% ( Table 2). The Cu 2p core level spectrum displays a main peak at about 932.8 eV, which is ascribed to Cu 2+ species in the form of CuO, while the other contribution, located at about 935.2 eV, is assigned to the shake-up satellite, which is typical of bivalent cations [52]. From the atomic concentrations, a slight decrease of the Mg and Ca species on its surface can be observed, which could indicate partial leaching of these species or deposition of the Cu species in these zones.…”