For stoichiometric natural gas vehicles (NGV) emission control, a four-way catalyst containing platinum group metal (PGM) and spinel is used to simultaneously convert CH4, CO, NOx and other hydrocarbons. Spinel oxides (AB2O4) have been reported to be excellent oxygen storage materials and can reduce the required PGM loading. The combination of lean/rich feed and spinel addition allows for improved CH4 conversion. Our recent work includes the investigation of the role of water and spinel in reducing atmospheres. Flow experiments, post-reaction characterizations and density functional theory (DFT) were used to examine the catalyst activity on methane steam reforming (MSR).Dual-layer PGM+spinel (30/100/25) and PGM-only (30/100a) monolith catalysts [30 g PGM/ft3 monolith, 100 g spinel (25% on Al2O3)/L or 100 g Al2O3/L monolith] were provided by CDTi Inc. Flow experiment results with lean/rich feed reveal O2 depletion at temperature above 350oC, suggesting that MSR becomes the primary pathway for the remaining ~20% CH4 conversion (Figure 1). Figure 2 shows full CH4 conversion by 475oC in the MSR reaction over PGM-only catalyst. However, MSR activity is inhibited by spinel addition. Enrichment of Mn and Fe species was observed near the surface PGM layer of the PGM+spinel catalyst from SEM-EDS analyses (Figure 3) and DRIFTS data, indicating possible metal migration and encapsulation of the PGM active sites. DFT calculated results also indicate favorable metal and/metal oxide layer formation on the PGM layer. Our study provides fundamental and practical insight into the CH4 abatement in rich conditions at high temperatures, which paves the path for optimizing catalyst formulation and operation of NGV emission control.

CH4 steam reforming on Pt+Pd/Al2O3 monolith catalyst: impact of Mn0.5Fe2.5O4 spinel addition

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.