Kinetics of the sulfur oxidation on palladium: A combined in situ x-ray photoelectron spectroscopy and density-functional study

Abstract

We studied the reaction kinetics of sulfur oxidation on the Pd(100) surface by in situ high resolution x-ray photoelectron spectroscopy and ab initio density functional calculations. Isothermal oxidation experiments were performed between 400 and 500 K for small amounts (∼0.02 ML) of preadsorbed sulfur, with oxygen in large excess. The main stable reaction intermediate found on the surface is SO 4 , with SO 2 and SO 3 being only present in minor amounts. Density-functional calculations depict a reaction energy profile, which explains the sequential formation of SO 2 , SO 3 , and eventually SO 4 , also highlighting that the in-plane formation of SO from S and O adatoms is the rate limiting step. From the experiments we determined the activation energy of the rate limiting step to be 85 ± 6 kJ mol −1 by Arrhenius analysis, matching the calculated endothermicity of the SO formation.

Exploring the core level shift origin of sulfur and thiolates on Pd(111) surfaces

“…20 On this basis different surface structures have been proposed for the complex thiolate-S interface 15,21 starting with the (√3x√3) R30° S (√3 S) and (√7x√7) R19° S (√7 S) lattices, which are consistent with the estimated adsorbed S coverage and have also been observed by scanning tunneling microscopy on Pd(111), 22 and then including RS species to reach the total S content. 20 On this basis different surface structures have been proposed for the complex thiolate-S interface 15,21 starting with the (√3x√3) R30° S (√3 S) and (√7x√7) R19° S (√7 S) lattices, which are consistent with the estimated adsorbed S coverage and have also been observed by scanning tunneling microscopy on Pd(111), 22 and then including RS species to reach the total S content.…”

“…20 The employed PAW pseudopotential does not include spin-orbit effects, and only the uncoupled S 2p or 3d level is provided. 20 The employed PAW pseudopotential does not include spin-orbit effects, and only the uncoupled S 2p or 3d level is provided.…”

Detailed kinetic modeling of homogeneous H2SO4 decomposition in the sulfur–iodine cycle for hydrogen production

“…The three chemical reactions in the SI cycle are described as follows: Reaction (b) principally consists of a dehydration process at approximately 727 K and a catalytic decomposition process of SO 3 at approximately > 973 K. The former process produces gaseous SO 3 and H 2 O, whereas the latter process produces SO 2 In the SI cycle and hybrid sulfur cycle, the sulfuric acid decomposition section demanding the highest temperature and sulfuric acid concentration leads to the largest energy consumption. Previous studies [6,7] revealed that H 2 SO 4 is rapidly converted into SO 3 and H 2 O at 773 K [8]; however, the temperature needed for SO 3 to be converted into SO 2 focused on reaction (e). Sulfur trioxide electrolysis is conducted to reduce the maximum operating temperature to 773-823 K [8,9].…”

Ultrafast x-ray photoelectron spectroscopy in the microsecond time domain

“…4 With this improvement it became possible to study time-dependent surface processes in situ, i.e., to follow adsorption as function of time or reactions as function of temperature. This gain in time resolution not only opens the possibility to access the kinetics of surface reactions, 5,6 but also to greatly improve the output in measurement data per time. On top of that further improvements were achieved by new technological efforts: The development of new detectors and the operation of electron analyzers in the so called snapshot mode enable a time resolution of down to ∼100 ms in the case of analyzers with a CCD camera as detector, while times down to 1 ms are projected for delay line detectors 7 and other advanced detector designs.…”

“…8 As examples, we like to mention the detector from Bussat et al 9 and the company Omicron (128 channel stripe anode detector). The improved time resolution for XPS, and also for other X-ray based techniques, was used to study, e.g., surface reactions, 5, 10-13 giving insights to reaction intermediates and reaction kinetics, 6,14,15 a) Author to whom correspondence should be addressed. Electronic mail:…”