SOx storage materials under Lean-Rich cycling conditions--Part II: influence of Pt, H2O, and cycling time.
The role of Pt and the influence of the reaction conditions during lean-rich cycling experiments were studied on a second generation SOx trapping material. The combination of the Generalized 2-D Correlation Analysis, 2-D Sample-Sample Correlation Analysis, and Factor Analysis using the MCR-ALS technique was applied to identify the reactive species. Transient surface sulfate species were formed under oxidative reaction conditions (lean mode) and decomposed under reducing reaction conditions (rich operation mode). The reduction of this species was identified to be the main contribution to the SO2 release observed under dynamic flow conditions. Pt facilitates the formation of sulfates but also catalyzes the reduction of the transient surface sulfate species leading to a higher amount of SO2 released under rich conditions. In the presence of water, this effect was diminished, which was found to be mainly a result of the suppressed formation of surface sulfate species caused by the faster transport of SO2 into the bulk phase of the SOx trapping component (BaCO3). Increasing the time under reducing conditions in the cycles leads to an enhanced reduction of the surface during rich conditions. The presence of water did not influence the bulk type species. It is proposed that for effective SO2 storage materials, strong SOx adsorption sites on the surface, the presence of water, and a short time under reducing conditions are essential.
Dathe
Hendrik
H
Technische Universität München, Department of Chemistry, Lichtenbergstrasse 4, D-85747 Garching, Germany.
Haider
Peter
P
Jentys
Andreas
A
Lercher
Johannes A
JA