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[Display omitted] • Doped Pt/mullite has excellent performance for NO oxidation. • The radius and valence differences of dopant ions induce oxygen vacancies. • Low temperature activity linked to oxygen vacancies and oxygen migration capacity. • The Pt/mullite interface are the key to the hydrothermal stability. • This simple doping method is also applicable to other mullite. Deep catalytic removal of nitrogen oxides is one of the widespread research topics, mainly limited by the low temperature activity and hydrothermal stability of the first step for NO oxidation. Oxygen vacancies (O v) and oxygen migration capacity play a crucial role in this challenge. Particularly, tuning the Mn-O coordination environment according to the radius and valence differences of dopant ions can increase O v , while accelerate oxygen migration by constructing Pt/mullite interfaces. Here, based on the hydrothermal stability of Pt/mullite to NO oxidation, we designed Mg2+- and Ba2+-doped catalysts. And the NO oxidation performance of the Mg2+-doped catalyst was significantly enhanced compared to the undoped catalysts (After hydrothermal aging, turnover frequency = 1.9 s−1 at 150 °C and activation energy = 21 kJ/mol). Meanwhile, all catalysts tested with simulated diesel exhaust and the NO oxidation performance showed essentially no decrease after 16 h of hydrothermal aging at 800 °C. Furthermore, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) demonstrated the O v content of doped catalysts increased significantly. In addition, O 2 temperature programmed desorption (O 2 -TPD) and Thermogravimetry (TG) proved that the oxygen migration capacity of doped catalysts was enhanced by several times. Notably, the simple doping method is general for the modification of other mullites and worthy of industrial application. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Doping ceria was favorable for NO oxidation due to more active oxygen. • Oxygen diffusion promoted the formation and transformation of nitrates. • Ce could anchor Pt, resulting in a better thermal-stability in NO oxidation. Abstract Catalytic NO oxidation is crucial in oxidizing soot and promoting NH 3 reduction during the emission eliminations of diesel vehicles by the modern after-treatment systems. To create more active oxygen species in favor of NO oxidation, ceria-modified monolithic Pt-based diesel oxidation catalyst was prepared by the step-impregnation method to improve its NO catalytic performance. Its NO maximum conversion was up to around 60% in the gas hourly space velocity of 60 kh−1. Experimental results suggested that the ceria addition could have a better dispersion due to the inhibition effect of platinum aggregation. Especially, it is found that more active oxygen and oxygen vacancies over the catalyst played a significant role in strengthening the interaction of NO molecule with catalyst surface, resulting in the formation and transformation of more bridging/chelating nitrates confirmed by in situ FTIR studies. After thermal ageing, the catalyst with ceria addition still enabled a excellent NO catalytic performance, up to 50% NO maximum conversion. It would be proposed that active oxygen from the interaction bewteen ceria and Pt improved its NO catalytic activity and thermal-stability. [ABSTRACT FROM AUTHOR]

To stabilize Pt, Magnesium-modified SiO 2 -Al 2 O 3 materials was used to impregnate with Pt, which could strengthen the bonding effect between Pt and Mg. Before and after aging, both showed a higher dispersion. High valence state of Pt in fresh modified catalyst was unfavorable of NO oxidation, indicating that the valence state of Pt was the leader factor in fresh catalytic performance. While for the aged Mg-modified sample, its reaction temperature of 30% NO conversion lowered by around 30 °C. The Pt stabilization via interacting with Mg derives a relation that the variation of Pt valence state and its exposed sites played a significant role in fresh and aged catalytic NO activity, respectively. [ABSTRACT FROM AUTHOR]

For diesel oxidation catalyst (DOC), the sintering and oxidation of active Pt0 nanoparticles leads to severe deactivation during long-term operating condition. Here, we have synthesized SiO 2 -modified Pt/SiO 2 -Al 2 O 3 (Pt-SiAl@Si) catalysts, and this silica coating layer not only can inhibit the migration of precious metals through physical isolation, but also restrain Pt0 oxidation by interfacial electron interaction between Pt and acid sites (Si-OH-Al). Before and after hydrothermal aging, the maximum NO conversion of Pt-SiAl@Si decreased slightly by 5%, showing excellent durability. TEM and CO chemisorption unveiled that no obvious differences in Pt size between fresh and aged Pt-SiAl@Si. 1H NMR and NH 3 -DRIFTS confirmed that Pt-SiAl@Si possessed more Brönsted acid sites (Si-OH-Al). And the Pt−acid sites interface caused more active Pt0 by the electronic effect. This bifunctional overcoating allows a wide application in other catalytic materials for various reactions. [Display omitted] • The SiO 2 overlayer of Pt-SiAl@Si is bifunctional. • SiO 2 shell as a physical barrier has an ability to retard sintering of Pt nanoparticles. • Pt-acid sites interfaces arising from interaction between SiO 2 shell and support enhanced the oxidation-resistance of Pt0. • The increased acidity of catalyst promoted the fast desorption and decomposition of nitrate species, facilitating NO oxidation. [ABSTRACT FROM AUTHOR]

Pt/SiO 2 -Al 2 O 3 (Pt/SA) is commonly used as diesel oxidation catalysts (DOC) in industry, but it could be seriously deactivated caused by H 2 O at long-term high temperature. In this paper, the inhibition mechanism of water on Pt/SA for NO oxidation was studied. The fresh Pt/SA (Pt/SA-F) was treated in an air flow with/without 10% H 2 O at 700 °C for 10 h to obtain the hydrothermally/thermally aged catalysts named as Pt/SA-HA and -A, respectively. NO oxidation tests showed that Pt/SA-HA had lower activity than Pt/SA-A. A series of characterizations proved H 2 O didn't affected Pt states and support structure as they were similar over two aged catalyst. 1H NMR and In-situ DRIFTS testified that water deactivation was a result of the acidity loss of catalysts, which inhibited the decomposition and desorption of reaction intermediate, finally resulting in bad NO oxidation activity. [Display omitted] • H 2 O inhibition mechanism at hydrothermal aging on Pt/SiO 2 -Al 2 O 3 for NO oxidation was investigated. • H 2 O leaded to the loss of Brönsted acid sites (like-bridge Al-OH-Si). • The loss of acid sites induced by H 2 O suppressed decomposition of nitrate species resulting in low NO activity. [ABSTRACT FROM AUTHOR]