Supported gold catalysts for CO oxidation: Effect of calcination on structure, adsorption and catalytic behaviour

Abstract

Adsorption behaviour and CO oxidation activity of and gold catalysts, prepared by TiO 2 -ZrO 2 -supported adsorption of gold colloids on the supports, have been investigated by pulse thermal analysis and di †use reÑectance FTIR spectroscopy. Structural investigations using transmission electron microscopy, X-ray di †raction and X-ray photoelectron spectroscopy showed that Au particles, mainly in the metallic state and with similar particle size distribution (2.0È3.0 nm), could be prepared on both supports, but the as-prepared samples contained carbonaceous impurities from the preparation procedure. Upon calcinations in 20 vol.% oxygen/He only slight sintering occurred up to 600 ¡C. Above 600 ¡C, the gold particles sintered on both supports. CO oxidation activity, studied by injection of CO pulses into an oxygen stream in the thermoanalyzer, depended strongly on the calcination temperature of the catalysts. Maximal activity was obtained for the catalysts calcined at 500 ¡C and 560 ¡C respectively. Catalysts calcined (Au/TiO 2 ) (Au/ZrO 2 ), at higher temperatures exhibited lower activity due to sintering of the gold particles. CO adsorption was found to be weak on both catalyst systems. No signiÐcant adsorption of and could be detected by pulse O 2 CO 2 thermal analysis. CO adsorption increased for catalysts calcined up to 200È400 ¡C. Calcination temperatures leading to maximal CO adsorption did not coincide with calcination temperatures a †ording maximal CO oxidation activity. Moreover, the removal of carbonaceous residues during calcination was found to be correlated to the activity. The results of the adsorption studies do not support a MarsÈvan Krevelen mechanism, where lattice oxygen would be involved. CO oxidation by the reaction of adsorbed CO with molecularly adsorbed oxygen seems more likely.

Insights into the reactivity of supported Au nanoparticles: combining theory and experiments

“…However, the similar turn over frequency found for the Au/TiO 2 and Au/MgAl 2 O 4 catalysts implies that such a support The absence of surface mediated oxygen transport in Au catalyzed CO oxidation is corroborated by isotope labeling studies of the CO oxidation reaction on Au/ TiO 2 and Au/Al 2 O 3 , which show that the CO 2 does not contain oxygen originating from the support [121]. Furthermore, the activities of a Au/TiO 2 , Au/Al 2 O 3 , Au/ZnO, and Au/ZrO 2 , catalysts do not follow the trend expected from the reducibility of the support [35,118,122]. A recent report of an active and stable LaPO 4 ) supported Au catalyst proves that non-oxidic supports can also be used [123], which further supports the idea that support-mediated oxygen transport does not necessarily contribute to the CO oxidation activity of Au catalysts.…”

FT-IR Spectroscopic Study of the Oxidation of Chlorobenzene over Mn-Based Catalyst

“…The result supports a Mars-van Krevelen mechanism, where lattice oxygen is involved in the oxidation process. 45,46 When gas-phase oxygen is present, formates and acetates are detected for TiO 2-Al 2 O 3 above 573 K, and for MnO x /TiO 2-Al 2 O 3 even at 473 and 573 K, and maleate species develop at 573 and 673 K. It is suggested that the oxidation of adsorbed chlorobenzene is enhanced due to the replenishment of lattice oxygen by gas-phase oxygen and MnO x is more active to the oxidation of adsorbed chlorobenzene.…”

Structure control of silica-supported mono and bimetallic Au–Pt catalysts via mercapto capping synthesis

“…8b, referring to the sample Au5, exhibits an additional high-frequency peak at 2117 cm À1 . Such peak is generally attributed to CO coordinated on neutral Au nanoparticles [34][35][36][37]. On the contrary, the assignment of the lowfrequency bands is quite controversial.…”

“…The derived phases and their relative percentages along with the corresponding particles sizes are listed in Table 1. At time zero, large platinum particles of 13 nm are formed along with smaller (3 nm) gold enriched alloyed particles with average composition Au 65 Pt 35 . By letting the solution rest for 1 day before introducing silica, we observe the segregation of pure gold and pure platinum with average particle sizes of 7 nm and 5 nm, respectively.…”

“…, which can be assigned to CO adsorbed on positively charged gold particles (Au + ) [34][35][36][37]. The presence of this band, which was not detected during the CO adsorption on the monometallic Au0 catalyst, according to literature, is due to formation of bimetallic AuPt particles [45,[48][49][50][51][52].…”