High‐temperature‐aging‐promoted Rh oxides on supported automotive exhaust catalysts

Abstract

Thermal decomposition of noble metal oxide phases formed during aging in air on industrially manufactured g-Al 2 O 3 -supported Rh catalysts was investigated. Some of the catalyst washcoats were modified by various stabilizers, promoters and oxygen storage components, such as La 2 O 3 , CeO 2 and Ce-Zr mixed oxide. In order to investigate the effect of aging, stabilizers and manufacturing method on the thermal stability of the noble metal oxide phases formed, a stepwise thermal decomposition in high vacuum (pressure <10 −7 Torr) was performed. X-ray photoelectron spectroscopy (XPS) was used to observe the changes in chemical state after each annealing cycle. Our results show marked differences in the rate of reduction between different Rh catalysts. Disposition of the Rh oxides towards reduction was also investigated by exposing the catalysts to 400 mbar of H 2 at 300 • C for 30 min. After 3 h of aging in air at 1000• C an irreducible rhodium oxide, which was identified to be either Rh 2 O 3 diffused into alumina or RhO 2 in intimate contact with the alumina surface, was formed regardless of the Ce-Zr mixed-oxide additive and manufacturing method of the catalyst.

Formation and Thermal Stability of Au2O3on Gold Nanoparticles: Size and Support Effects

“…2) at 300 K and ∼25% Au 3+ signal at 500 K. A similar size-dependent trend was observed by our group during the reduction of surface Pt-oxides (PtO and PtO 2 ) on Pt NPs supported on anatase TiO 2 powders . These results are also in agreement with data obtained by Suhonen et al on oxidized Rh clusters supported on different oxide powders, where faster reduction rates were measured for smaller clusters.…”

“…For example, there are reports indicating a slower decomposition rate of RhO x clusters when deposited on partially reduced Ce-Zr powders. 62 Here, the reducible oxide support is believed to act as a local supplier of oxygen, slowing down the metal oxide decomposition. This is, however, a different experimental system because, contrary to the case of Au on TiO 2 , where the enthalpy of formation of Au 2 O 3 is very high, Rh forms a much more stable oxide.…”

The effect of platinum on the reducibility of Rh oxides on CeZr modified alumina supported automotive catalysts

“…The formation of the reduction-resistive oxide phase is evident regardless of the presence of the Ce-Zr mixed oxide. 12 In the aged PtRh-CeZr-Al catalyst both Rh 3d and Pt 4d 5/2 peaks can clearly be resolved and the peak positions can be obtained by fitting. In the fitting procedure the relative widths and areas as well as the distance between the Rh 3d 5/2 and Rh 3d 3/2 synthetic components were constrained virtually to the same values as for the fresh samples.…”

XPS Study of Nanostructured Rhodium Oxide Film Comprising Rh4+ Species

“…Over the last 50 years, rhodium has demonstrated catalytic activity in many industrially important processes and thus attracted the attention of scientists. − The thorough investigation of catalytic activity of Rh species has been carried out using surface science and theoretical approaches on model systems − together with analysis of the powder catalytic systems. − However, many aspects of the catalytic action of rhodium still need to be clarified. In particular, most of the works are focused on the initial steps of the Rh oxidation, whereas the deep oxidation with formation of highly oxidized species is not usually analyzed.…”