Decomposition of Al2O3-Supported PdSO4 and Al2(SO4)3 in the Regeneration of Methane Combustion Catalyst: A Model Catalyst Study

Niko M Kinnunen,Mika Suvanto,Teuvo Maunula,Ville H Nissinen,Matthew Keenan,Kauko Kallinen,Janne T Hirvi

doi:10.3390/catal9050427

Niko M Kinnunen, Mika Suvanto + Show 5 more

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https://doi.org/10.3390/catal9050427

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Abstract

Exhaust gas aftertreatment systems play a key role in controlling transportation greenhouse gas emissions. Modern aftertreatment systems, often based on Pd metal supported on aluminum oxide, provide high catalytic activity but are vulnerable to sulfur poisoning due to formation of inactive sulfate species. This paper focuses on regeneration of Pd-based catalyst via the decomposition of alumina-supported aluminum and palladium sulfates existing both individually and in combination. Decomposition experiments were carried out under hydrogen (10% H2/Ar), helium (He), low oxygen (0.1% O2/He), and excess oxygen (10% O2/He). The structure and composition of the model catalysts were examined before and after the decomposition reactions via powder X-ray diffraction and elemental sulfur analysis. The study revealed that individual alumina-supported aluminum sulfate decomposed at a higher temperature compared to individual alumina-supported palladium sulfate. The simultaneous presence of aluminum and palladium sulfates on the alumina support decreased their decomposition temperatures and led to a higher amount of metallic palladium than in the corresponding case of individual supported palladium sulfate. From a fundamental point of view, the lowest decomposition temperature was achieved in the presence of hydrogen gas, which is the optimal decomposition atmosphere among the studied conditions. In summary, aluminum sulfate has a two-fold role in the regeneration of a catalyst—it decreases the Pd sulfate decomposition temperature and hinders re-oxidation of less-active metallic palladium to active palladium oxide.

Highlights

Exhaust gas aftertreatment systems (ATSs) have been used since the 1950s to remove at least a portion of the exhaust gases emitted from internal combustion engines of vehicles [1]
Palladium is currently used as an active metal or as a promoter in almost all catalysts in vehicles exhaust gas ATSs, except in selective catalytic reduction (SCR) systems, which are commonly based on Fe- and Cu-promoted zeolites [4]
The Al2 O3 -supported PdSO4 /Al2 (SO4 )3 model catalysts were studied under various gas atmospheres in order to study their decomposition routes as well as their texture before and after each treatment

Summary

Introduction

Exhaust gas aftertreatment systems (ATSs) have been used since the 1950s to remove at least a portion of the exhaust gases emitted from internal combustion engines of vehicles [1]. Tight emission limits and durability requirements guide vehicle developers to implement regeneration procedures into the vehicle operation. Exhaust gas ATS catalysts consist of a support material, active metal(s), and promoter(s). Alumina as a support material for exhaust gas ATS catalysts has been known to be the best alternative owing to its good thermal stability and high surface area [2,3]. Palladium is currently used as an active metal or as a promoter in almost all catalysts in vehicles exhaust gas ATSs, except in selective catalytic reduction (SCR) systems, which are commonly based on Fe- and Cu-promoted zeolites [4].

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