CO oxidation over Au/TiO2 catalyst: Pretreatment effects, catalyst deactivation, and carbonates production

Abstract

a b s t r a c tA commercially available Au/TiO 2 catalyst was subjected to a variety of thermal treatments in order to understand how variations in catalyst pretreatment procedures might affect CO oxidation catalysis. Catalytic activity was found to be inversely correlated to the temperature of the pretreatment. Infrared spectroscopy of adsorbed CO experiments, followed by a Temkin analysis of the data, indicated that the thermal treatments caused essentially no changes to the electronics of the Au particles; this, and a series of catalysis control experiments, and previous transmission electron microscopy (TEM) studies ruled out particle growth as a contributing factor to the activity loss. Fourier transform infrared (FTIR) spectroscopy showed that pretreating the catalyst results in water desorption from the surface, but the observable water loss was similar for all the treatments and could not be correlated with catalytic activity. A Michaelis-Menten kinetic treatment indicated that the main reason for deactivation is a loss in the number of active sites with little changes in their intrinsic activity. In situ FTIR experiments during CO oxidation showed extensive buildup of carbonate-like surface species when the pretreated catalysts were contacted with the feed gas. A semi-quantitative infrared spectroscopy method was developed for comparing the amount of carbonates present on each catalyst; results from these experiments showed a strong correlation between the steady-state catalytic activity and amount of surface carbonates generated during the initial moments of catalysis. Further, this experimental protocol was used to show that the carbonates reside on the titania support rather than on the Au, as there was no evidence that they poison Au-CO binding sites. The role of the carbonates in the reaction scheme, their potential role in catalyst deactivation, and the role of surface hydroxyls and water are discussed.

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

“…6) and agree with DRIFTS measurements showing formation and build-up of carbonates, carboxylates, hydroxycarbonyls/formates, and bicarbonates on Au/TiO 2 during CO oxidation [6,9,18,19,25]. The point whether the carbonates reside on the gold [19], on the support [9,18,27], on the Au-TiO 2 border [6], or on both the Au and the support [28] is still in debate. Our SIMS data demonstrating an intense emission of molecular ions…”

“…Deactivation of the catalyst was suggested to occur due to reduction of oxidized gold species (which were claimed to be the most active sites for CO oxidation) to metallic gold [3,4], sintering of Au nanoparticles (irreversible) [6,15,18], dehydroxylation of the support during the reaction (assuming that OH groups were involved in the oxidation pathway) [23,24], and accumulation of carbonate-like species (carbonate  2 3 CO , formate  2 HCO and carboxylate O-CO groups) at the active sites [6,9,19,25,27,28]. In our work, some sintering, dehydroxylation and build-up of surface carbonate-like species occurred in the catalyst (DP1) already after 1 h on stream, although no deactivation was observed ( Fig.…”

Controlling activity and selectivity using water in the Au-catalysed preferential oxidation of CO in H2

“…Catalyst deactivation is similarly important in PROX, and water may prevent the deposition of carbonates, which poison CO oxidation 8,40,41 . Long-term activity and selectivity plots are shown in Fig.…”

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

“…However, it is likely that the carbonates formed as consequence of CO 2 formation preferably saturate those electron-rich sites: CO 2 is a Lewis acid that preferably adsorbs to Lewis basic sites. In this respect, the poisoning effect of carbonates in CO oxidation on Au/TiO 2 is well known, and increased carbonate formation has been observed after reducing pretreatments [69].…”