(691e) CH4 Steam Reforming on Pt+Pd/Al2O3 Monolith Catalyst: Impact of Mn0.5Fe2.5O4 Spinel Addition

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 [1]. The combination of lean/rich feed and spinel addition allows for improved CH₄ conversion [2]. 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.

References

[1] S. Golden, Z. Nazarpoor, M. Launois, R-F. Liu, P. Maram, Society of Automotive Engineering. SAE 2016-01-0933 (2016).

[2] S. B. Kang, K. Karinshak, P. W. Chen, S. Golden, M. P. Harold, Catalysis Today, 360 (2021) 284-293.