Adsorption of sulfur dioxide and the interaction of coadsorbed oxygen and sulfur on Pt(111)

Astegger, St.; Bechtold, E.

doi:10.1016/0039-6028(82)90098-x

Cited by 90 publications

(35 citation statements)

References 16 publications

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“…Figure 7 shows a comparison of the 64 amu desorption following adsorption at 160 K of (i) 0(A) and SO2 alone and (ii) in the presence of C3H8. In the absence of C3H8 two 64 amu desorption states are observed at 370 K and 550 K. This high temperature state is coincident with a peak in the 80 amu spectrum ( Figure 7A) and is ascribed to SO3, in agreement with previous workers [19]. Following reaction with C3H8, (Figure 7B) substantial changes in the 64 amu TPR occur: the 550 K state is attenuated and a new state at 420 K appears.…”

supporting

confidence: 80%

Short-Chain Alkane Activation

Wilson

Hardacre

Lambert

1996

ACS Symposium Series

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SO 2 chemisorption on oxygenated Pt(111) enormously enhances the dissociative chemisorption and subsequent combustion of propane. This activation of the metal surface is induced by an adsorbed sulfoxy species which is formed > 220 K. In the absence of adsorbed SO 2 the sticking probability of propane is immeasurably small. However in the presence of SO 2 , the precursor-mediated initial sticking probability rises from ~0.02 at 300 K to ~ 0.15 at 160 K. XPS and HREELS measurements identify the active species as SO4 2-, and also demonstrate the consumption of SO 4 during the oxidation reaction. Coincident CO 2 and SO 2 formation suggest decomposition of a complex reaction intermediate: this is supported by isotope experiments involving CO adsorption onto SO 2 / 18 O2 precovered Pt(111). Propane oxidation over sulphated AlO X films on Pt (111) is also reported, with increased activity for submonolayer oxidised Al films being observed compared to clean Pt(111).The activation of short chain alkanes is often the rate limiting step in catalytic oxidation of hydrocarbons [1]. In particular, the slow oxidation of alkanes, namely propane and methane, is a technological problem faced by the automotive exhaust catalyst industry [2]. Reactor studies of Pt/Al203 and Pt-Rh/Al203/Ce02 catalysts have shown that the inclusion of SO2 in the gas feed significantly promotes the oxidation of propane [3,4], whilst inhibiting reactions of CO, NO and propene. It has also been observed that in the presence of SO2, the activity of Pt/Al203 catalysts for propane oxidation becomes independent of Pt loading. In the absence of SO2, the activity usually increases with Pt loading, a result which suggests the formation of different active sites on inclusion of SO2 in the gas feed. Infra-red analysis of these catalysts following exposure to O2 and SO2, indicates the presence of S04^" on the support, which is thought to be involved in the activation process. Enhanced C-H bond dissociation is often attributed to catalyst acidity [5]; for example homogeneous Pt(III) solutions display increased oxidative capacity in the presence of sulphuric acid.

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supporting

confidence: 80%

Short-Chain Alkane Activation

Wilson

Hardacre

Lambert

1996

ACS Symposium Series

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“…[14][15][16][17] This enabled us to investigate the oxidation of small amounts of sulfur with oxygen present on the surface in large excess, which simplifies the kinetic analysis and makes it possible to determine the activation energy of the rate-determining step.The information on sulfur oxidation is rather limited in the literature. Early TPD studies [18,19] on Pt(111) yielded no information on surface intermediates, and consequently only an apparent activation energy was derived. [19] Theoretical calculations [20] indicate that at the oxygen saturation limit S is oxidized to SO x (x = 1-4) and the total energy increases with x, but no information on the activation energy of the ratelimiting step is available.…”

mentioning

confidence: 99%

“…The information on sulfur oxidation is rather limited in the literature. Early TPD studies [18,19] on Pt(111) yielded no information on surface intermediates, and consequently only an apparent activation energy was derived. [19] Theoretical calculations [20] indicate that at the oxygen saturation limit S is oxidized to SO x (x = 1-4) and the total energy increases with x, but no information on the activation energy of the ratelimiting step is available.…”

mentioning

confidence: 99%

Sulfur Oxidation on Pt(355): It Is the Steps!

et al. 2009

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Platinum catalysts are frequently used in catalytic converters in cars [1][2][3] and also in oil refineries. [4][5][6] The catalysts' active sites are subject to deactivation through poisoning by sulfur (or sulfur oxides), which are common impurities in fuels. [1][2][3][4][5][6][7][8] These active sites are thought to be defects, such as step or kink sites, which are omnipresent on the surface of the highly dispersed catalyst nanoparticles. Adsorbed sulfur modifies the electronic properties of the catalyst surface, which leads to a decrease of chemical and catalytic activity. [9][10][11] The key step to regain catalyst activity is the removal of the sulfur atoms from the catalyst surface, for example by exposing it to molecular oxygen, thereby oxidizing the adsorbed sulfur, and then removing the resulting SO x species from the surface. The mechanism, the chemical nature of the intermediates formed, and the specific role of defects in this process are unknown for the most part. This lack of insight is exists, because the relevant information can be obtained directly only by in situ methods, which allow a quantitative determination of the surface species or intermediates on the timescale of seconds. However, up to now there have been only very few studies for the direct measurement of kinetic parameters such as activation energies. [12,13] In most cases kinetic parameters are determined by temperature-programmed desorption (TPD), where only the desorbing species are detected. Since important reaction intermediates can thereby easily be missed, the correct determination of kinetic parameters can be hampered.Herein we present the first in situ study of sulfur oxidation on a model catalyst surface, namely stepped Pt(355). We have clearly identified the steps as active sites and determined the activation energy directly. The Pt(355) surface has (111) terraces five atom rows wide, and monatomic steps with (111) orientation. The role of the steps is elucidated by comparison to data obtained on a flat Pt(111) surface. Using synchrotron radiation, we were able to measure high-resolution XP spectra in situ during adsorption and while heating the sample with short measuring times. Owing to the high resolution, different surface species could be identified and analyzed quantitatively and site selectively in a time-dependent fashion, also for very low adsorbate coverages. [14][15][16][17] This enabled us to investigate the oxidation of small amounts of sulfur with oxygen present on the surface in large excess, which simplifies the kinetic analysis and makes it possible to determine the activation energy of the rate-determining step.The information on sulfur oxidation is rather limited in the literature. Early TPD studies [18,19] on Pt(111) yielded no information on surface intermediates, and consequently only an apparent activation energy was derived. [19] Theoretical calculations [20] indicate that at the oxygen saturation limit S is oxidized to SO x (x = 1-4) and the total energy increases with x, but no information on the a...

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“…When enough sulfur has been removed that openings begin to appear in the sulfur layer, the reaction rate accelerates dramatically. This highly nonlinear behavior, which has also been reported in single-crystal studies, [56][57][58] explains the abrupt reappearance of the sensor response after two hydrogen/oxygen cycles following sulfur exposure in Fig. 8.…”

Section: Removal Of Adsorbed Sulfur With Hydrogen and Oxygenmentioning

confidence: 56%