(628d) Enhanced CH4 Conversion over Pt+Pd/Al2O3 + Mn0.5Fe2.5O4 Spinel Catalyst: Impact of Oxygen Storage Material

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]. A current focus in our group is to investigate the impact of spinel on CH₄ conversion. Dynamic oxygen storage capacity (DOSC), temporal analysis of products (TAP) and flow experiments are used to provide mechanistic insight into the contribution of spinel.

Dual-layer [“30/100”: 30 g PGM/ft³ monolith, 100 g spinel (25% on Al₂O₃)/L monolith], single-layer (30/0, 0/100) monolith catalysts and several powder samples were provided by CDTi for flow experiments and DOSC measurements. The powder mixture of PGM and spinel (PGM#spinel) simulated the dual-layer sample, whereas the metalized spinel sample had close contact between PGM and spinel.

Figure 1 shows the combination of lean/rich feed modulation and spinel addition allowed for improved CH₄ conversion [2]. The enhancement is due in part to the high DOSC of PGM#spinel. DOSC comparison on PGM#spinel and metalized spinel suggests PGM proximity to spinel is detrimental, Figure 2. Spinel addition also limits steady-state CH₄ conversion above 500ËšC, Figure 1. This is tentatively attributed to differences in reforming activity, which dominates at high CH₄ conversion with O₂ depletion. TAP experiments are used to resolve the mechanistic intricacies between oxygen storage, oxidation and reforming.

Our study provides fundamental and practical insight into the function of spinel on CH₄ conversion, 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. Kang, K. Karinshak, P.W. Chen, S. Golden, M.P. Harold (in press), Catalysis Today, (2020).