Oxidation of CO on Gold Supported Catalysts Prepared by Laser Vaporization: Direct Evidence of Support Contribution

Abstract

Gamma-Al2O3, ZrO2, and TiO2 gold supported model catalysts have been synthesized by laser vaporization. Structural characterization using Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy experiments have shown that the gold clusters deposited on the different supports have similar distribution of size centered around 3 nm and are in the metallic state. However, X-ray photoemission measurements also indicate lower binding energies than the usual Au 4f(7/2) at 84.0 eV for both alumina and titania supported catalysts, indicating a modification of the electronic structure of the metal. One has taken benefit of these features to study the influence of the nature of the support toward CO oxidation activities without being hindered by particle size or gold oxidic species effects. By comparing the activities of the different catalysts, it is concluded that the nature of the support directly affects the activity of gold. The following tendency is observed: titania and zirconia are superior to alumina as supports, titania being slightly better than zirconia. From XPS and activity results we can conclude that the existence of negatively charged clusters is not the key point to explain the high activity observed for Au/ZrO2 and Au/TiO2 catalysts and also that metallic Au is the major catalytically active phase. Hence, due to their very nature, titania and to a less extent zirconia should participate to the catalytic process.

XPS/ToF-SIMS Characterization of TiO$_{2}$ Supported Au Nanoparticles: Effect of Catalytic CO Oxidation

“…2 and 3, a, after catalytic reaction a further decrease of the Au 4f BE in the used catalyst occurred as compared with the fresh one, with the total negative shift with respect to the bulk Au amounting to 0.45  0.05 eV for DP1 and 0.41  0.03 eV for DP2. This observation is in agreement with other works [6,7,18] reporting a similar shift of the Au 4f spectrum toward lower binding energies for Au/TiO 2 catalysts used in the CO oxidation reaction. The additional negative shift of the Au 4f line in the used catalyst may result a b c Fig.…”

“…The data on the chemical and electronic state of gold nanoparticles in different catalysts used in the CO oxidation as determined by the Au 4f binding energy are rather contradictory, although they clearly indicate that formation and modification of the particles' electronic state strongly depend on the nature of support. For the Au/TiO 2 system, in which gold was in a metallic state, the reaction of CO oxidation was observed to cause an appreciable shift of the Au 0 4f peak to lower binding energies as compared to the fresh catalyst [6,7]. A similar negative shift of the Au 4f and Au 4d lines was also reported for an Au/Al 2 O 3 catalyst used in the CO oxidation [8].…”

“…Conversely, in works [7,9] no significant shift of the Au 4f line was detected for Au/Al 2 O 3 and Au/TiO 2 catalysts after CO oxidation. Also, the position of the Au 4f line was noted to remain practically unaffected in the used Au/ZrO 2 [7,10] and Au/MnO x [11] catalysts.…”

Mechanistic Study into the Direct Epoxidation of Propene over Gold/Titania Catalysts

“…7 The attention to these catalysts has not diminished, as is evidenced by the number of reports published by many groups over the last year. [8][9][10][11][12][13][14][15][16][17][18][19][20] Despite all of this attention, the mode of operation of these catalysts is still under discussion, especially for the epoxidation of propene. Both gold and titania seem to be a necessity for a catalyst to be able to epoxidize propene.…”

Gold, an alternative to platinum group metals in automobile catalytic converters

“…It was also shown that the catalyst preparation technique has a significant impact on the performance of GNPs catalysts, and hence, research has focussed on the use of various techniques to prepare supported GNPs such as coprecipitation [41], chemical vapour deposition [50], impregnation [51], grafting [52], photo-deposition [53], physical mixing [54], low-energy cluster beam deposition [55], adsorption of Au colloids on metal oxides [56] and ion-exchange [57]. In general, GNP catalysts prepared with the deposition-precipitation technique exhibited the highest activity [41].…”