Oxidation of CO over gold supported on Zn-modified ceria catalysts

Abstract

A series of Zn-modified ceria solids were prepared by thermal decomposition of the corresponding metal propionates. The formation of segregated ZnO particles on the ceria surface is evidenced for these solids using X-ray diffraction; in addition to this the characterization data may allow discarding the formation of a ZnO-CeO 2 solid solution. On modifying with Zn, the reducibility of the ceria support is enhanced, being the highest reducibility the one obtained for the ZnO-CeO 2 solid having a 1:9 Zn:Ce atomic ratio (CeZn10). The activity of this solid in the CO oxidation reaction was the highest among the tested Zn-modified ceria solids. Therefore, catalysts containing 1 wt.% gold, supported on pure ceria and CeZn solids, were prepared, characterized and their catalytic activities tested.The Zn-modified gold catalyst is more active than the un-modified Au/CeO 2 catalyst in the oxidation of CO; this behavior is related to the higher metallic dispersion of gold on the CeZn support surface. However, the number of oxygen vacancies acting as nucleation sites for gold, is hardly modified in the Zn-modified ceria support and, therefore, the higher gold dispersion must be related to high electron density sites on the catalyst surface as a result of Au-Ce-Zn interaction, this improved gold dispersion results in higher activities for CO oxidation.

Gold supported on CuOx/CeO2 catalyst for the purification of hydrogen by the CO preferential oxidation reaction (PROX)

“…The tetragonalization of the cubic structure by the presence of Ce 3+ species may be confirmed by the broad and small signal centered at 279 cm -1 [51]. The promotion of the oxygen vacancies population by the inclusion of copper species is in good agreement with that widely established by different authors whose demonstrated that the doping of the cerium oxide results in the promotion of oxygen vacancies [14,37,40,52].…”

“…These results are in good agreement with previous reports where ceria-based catalysts loaded with 1 wt. % gold exhibited good performances in the TOX reaction [40,70].…”

“…From this result it can be inferred that the simultaneous reduction of copper and some Ce 4+ cations is produced at low temperature in the CeCu solid. In previous studies about the reducibility of the CeO 2 it has been widely established that the reduction of Ce 4+ at low temperature is occurring at the surface of the oxide from 400 to 500 °C [14,40], which agrees with the fact that the Ce 3+ reduced species are preferentially placed at the surface of the material in order to reduce the free Gibbs energy, as was discussed by Gellings et al [60]. However, the CeCu has exhibited the reduction of Ce 4+ species at temperatures below 300 °C, which would be confirming that the interaction between the copper species and the surface of the CeO 2 results in an easier reduction and stabilization of Ce 3+ species at low temperatures.…”

Au/CeO2 Catalysts: Structure and CO Oxidation Activity

“…It has been widely reported that the doping of the CeO 2 structure by the addition of one or more cations with a different nature, allows achieving mixed systems with improved oxygen exchange ability. Many different cations have been successfully used: Zr [11,50], Zn [17,51], Fe [52,53], Co [54], La [55,56], Eu [57], Gd [56], and Sm [58], among others. Taking into consideration the wide range of possible combinations between ceria and different cations, the different synthesis procedures that can be applied to obtain the mixed oxides, and the strict control of the variables required during the synthesis procedures, studies in the near future will be devoted to understanding the structural properties achieved for the obtained solids and to correlating them with their catalytic activity in the CO oxidation reactions, despite the large number of yet published papers in this topic many works.…”

Optimization and statistical analysis of Au-ZnO/Al2O3 catalyst for CO oxidation

“…In addition, presence of Au grows the oxygen vacancies on ZnO [34], also improves the catalysis reactivity. For calcination temperature, lower temperature can lead to smaller Au crystallites, which further lead to higher catalysis reactivity.…”