Fe-substituted 10Al2O3·2B2O3 as a multifunctional support for automotive Pd catalysts

Abstract

Partial substitution of various transition metals for Al in 10Al2O3·2B2O3 (Al20B4O36, 10A2B) was studied to use as a thermostable support for Pd catalysts. Fe-substitution afforded the formation of solid solutions in the range of x≤1.5 in FexAl20−xB4O36 (Fe-10A2B) without impurities. The DFT calculations confirmed that Fe-substitution was most likely to occur on the 5-coordinated Al site and predicted a shorter Fe–O distances of 1.84–2.05Å compared to 1.94 and 2.12Å in Fe2O3, in accordance with Fe-K edge EXAFS results. Fe-substitution improved the catalytic NO conversion in a rich region (A/F<14.6), because CO–H2O and subsequent NO–H2 reactions were accelerated. The redox between Fe3+ and Fe2+ in Fe-10A2B generated the oxygen storage capacity (OSC), which yielded an efficient buffering effect on air-to-fuel (A/F) fluctuation in a simulated exhaust gas stream with lean/rich perturbation. These results suggest that Fe-10A2B is expected to be used as a multifunctional support material for Pd catalysts in automotive three-way catalysts.