Gold supported on metal-doped ceria catalysts (M=Zr, Zn and Fe) for the preferential oxidation of CO (PROX)

Abstract

A series of ceria oxides doped with 10 mol.% of Zr, Zn and Fe has been prepared by a pseudo sol-gel method throughout the thermal decomposition of the corresponding metallic propionates. With these supports, 1 wt.% gold catalysts were prepared by the deposition-precipitation method. All the solids were characterized by means of XRF, N 2 adsorption, XRD, Raman spectroscopy and SEM techniques and their catalytic activity towards preferential oxidation of CO (PROX) reaction tested. The results showed solid solution when doping with Zr and Fe and ZnO surface segregation in the case of Zn. We demonstrate that gold dispersion not only depends on the oxygen vacancy concentration but also on the nature of the doping agent. Finally, the catalytic activity was highly promoted by gold in all cases, being the doped gold catalysts more active than Au/CeO 2 at low temperature. 2 GRAPHICAL ABSTRACTThe doping CeO 2 with Zr, Zn and Fe was studied. Doping with Zr or Fe resulted in solid solution while doping with Zn resulted in the surface segregation of ZnO.The formation of oxygen vacancies is enhanced with Zr, remains constant with Zn and disappears on doping with Fe.

Synergy between gold and oxygen vacancies in gold supported on Zr-doped ceria catalysts for the CO oxidation

“…Pure CeO 2 presents two main signals that have been widely described for such oxide. The initial occurrence of the low temperature signal (centered at 470 °C in our case) is due to the surface reduction of Ce 4+ cations into Ce 3+ , while the high temperature signal (with maximum at 754 °C) is associated to Ce 4+ to Ce 3+ reduction in the bulk [8,29,30,56,57].…”

“…Then, during the calcination step, this order would be preserved by means of the slow decomposition of the propionates until consolidating the mixed oxide structure. According to that, the temperature and the rate for the calcination are relevant on determining No XRD signals associated with any gold crystalline phases were detected, which can be due to the low content of such metal or, more probably, to the high dispersion of the gold nanoparticles, as early reported for gold supported on modified ceria catalysts prepared by the same propionates decomposition method [8].…”

“…has been previously evidenced [8,36,37]. From these works, it can be inferred that the structural defects inserted by the doping agents create an energetic barrier that delays the crystallization of the mixed oxide framework.…”

“…As presented in recent works, a correct evaluation of the evolution of oxygen vacancies population in pure and doped cerium oxides must be carried out by comparing the area ratio of the oxygen vacancies band and the F 2g signal (Ov/F 2g ) [8,42,43] in order to reduce the possible influence of the particle size and other effects over the shape and intensity of the signals [8,43,46,47]. The Figure 5 inset shows how the population of oxygen vacancies increases with the Zr At.% in our materials.…”

“…Considering the relevance of the oxygen vacancies in the ionic mobility in ceria, several efforts have been devoted to increase the population of these defects and the doping with Zr has demonstrated to allow it [8][9][10][11]. The use of Zr as modifier of ceria has been widely reported not only by the improvement of the oxygen mobility but also for the enhancement of the thermal stability.…”