Preparation and Comparison of Supported Gold Nanocatalysts on Anatase, Brookite, Rutile, and P25 Polymorphs of TiO₂ for Catalytic Oxidation of CO

Abstract

Nanosized anatase (< or = 10 nm), rutile (< or = 10 nm), and brookite (approximately 70 nm) titania particles have been successfully synthesized via sonication and hydrothermal methods. Gold was deposited with high dispersion onto the surfaces of anatase, rutile, brookite, and commercial titania (P25) supports through a deposition-precipitation (D-P) process. All catalysts were exposed to an identical sequence of treatment and measurements of catalytic CO oxidation activity. The as-synthesized catalysts have high activity with concomitant Au reduction upon exposure to the reactant stream. Mild reduction at 423 K produces comparably high activity catalysts for every support. Deactivation of the four catalysts was observed following a sequence of treatments at temperatures up to 573 K. The brookite-supported gold catalyst sustains the highest catalytic activity after all treatments. XRD and TEM results indicate that the gold particles supported on brookite are smaller than those on the other supports following the reaction and pretreatment sequences.

Ultrastable Gold Nanocatalyst Supported by Nanosized Non-Oxide Substrate

“…Surprisingly, Au/LaPO 4 -H was activated strongly, while both Au/ LaPO 4 -M and Au/TiO 2 -R were deactivated. The latter observation is consistent with previous reports [14,15,54] showing that Au catalysts on oxide supports can be readily deactivated through sintering induced by calcination at high temperature (e.g., 500 8C). The calcined Au/LaPO 4 -H unexpectedly reached the specific rate of 0.66 mol CO g Au À1 h À1 (50 % conversion) at a temperature as low as À71 8C, whereas 41 and 6 8C were required for Au/LaPO 4 -M and Au/TiO 2 -R to reach this specific rate, respectively ( Figure 2).…”

Probing Oxide Reduction and Phase Transformations at the Au-TiO2 Interface by Vibrational Spectroscopy

“…S2 in Supplementary Information), brookite and gold [50], as well as Magnéli-type TiO 2 phases [51,52] display diffraction reflexes between 40° and 45° 2θ. Crystalline gold should only have one signal in this region, though, and it is usually only seen for much higher loadings and larger particles [50]. Due to the absence of any other strong diffraction peaks, or potentially the overlap with those of anatase, we cannot assign those small peaks unambiguously to a certain titania phase by XRD alone.…”

Titania‐Supported Gold Nanoparticles Catalyze the Selective Oxidation of Amines into Nitroso Compounds in the Presence of Hydrogen Peroxide

“…Forc omparison, Au/P25 catalyst was also preparedi nasimilar procedure to Au/MTA, but depositing1wt %g old on commercially available TiO 2 Degussa P25 NPs (particle size~20-30 nm). [21] TheA ul oadingso ft he samples was determined by elemental X-ray analysis (EDS).…”

“…70/30 wt %), in agreement with previous studies. [21,22] Theh erein presented catalytic protocol arose while studyingt he oxidation of aryl amines by hydrogen peroxide (H 2 O 2 )i nt he presence of metal oxide catalysts.P recedenti st he first work by Kosswing who investigated the transformation of aniline into azoxybenzene on Ti IV substancesu sing tBuOOH. [16a] Later on, Tu el and co-worker studied the oxidation of aniline with H 2 O 2 and tert-butyl hydroperoxide (tBuOOH) in the presence of various titanium silicalite catalysts.H oweveri nt hese reactions am ixture of nitrosobenzene and azoxybenzene was observedw ith the latter as the major one at late reactiont imes.…”