Abstract
ZrO2 and Ce0.8Zr0.2O2 mixed oxides were prepared and tested in the oxidation of carbon soot at different oxygen partial pressures and degrees of catalyst/soot contact to investigate their activity under typical gasoline direct injection (GDI) operating conditions. Under reductive atmospheres, generation of oxygen vacancies occurs in Ce0.8Zr0.2O2, while no reduction is observed on ZrO2. Both materials can oxidize carbon under high oxygen partial pressures; however, at low oxygen partial pressures, the presence of carbon can contribute to the reduction of the catalyst and formation of oxygen vacancies, which can then be used for soot oxidation, increasing the overall performance. This mechanism is more efficient in Ce0.8Zr0.2O2 than ZrO2, and depends heavily on the interaction and the degree of contact between soot and catalyst. Thus, the ability to form oxygen vacancies at lower temperatures is particularly helpful to oxidize soot at low oxygen partial pressures, and with higher CO2 selectivity under conditions typically found in GDI engine exhaust gases.
Highlights
The gasoline engine market, based on direct injection (DI) technology is growing rapidly, especially in relation to their better efficiency and lower CO2 emissions [1]
We have previously reported that soot oxidation over ceria-based catalysts is driven by two different ceria–zirconia oxidizes carbon at the soot catalyst interface; and (ii) the resulting vacancy or other coexisting phenomena, influenced amount active and oxygens that predominates in surface defects canone be the center for by thethe activation of of gassurface phase oxygen the formation of active oxygenoxygen rich atmosphere, and another related to the of the material that prevails species that contributes to oxidize soot on a parallel route
Ceria-based materials has been widely studied as a catalyst in diesel particulate filters, but their role and applicability in gasoline particulate filters, under oxygen-poor conditions, is still at the initial stage, and this preliminary work investigates their potential in soot oxidation at low oxygen partial pressure
Summary
The gasoline engine market, based on direct injection (DI) technology is growing rapidly, especially in relation to their better efficiency and lower CO2 emissions [1]. Due to the different operating conditions of a diesel engine and a GDI engine [3], it is not possible to transfer the technologies optimized and developed in the last twenty years for diesel particulate filters (DPF), but it is necessary to investigate in detail the mechanisms of soot accumulation and oxidation under typical GDI operating conditions [7]. As it happens for DPFs, the accumulation phase must necessarily be followed by a regeneration phase, in order to oxidize the accumulated soot and prevent an increased pressure drop [8]. The catalyst formulations developed for the DPFs cannot be directly transferred to the GDI engines, Catalysts 2020, 10, 768; doi:10.3390/catal10070768 www.mdpi.com/journal/catalysts
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