Abstract
Octahedral molecular sieves (OMS-2) are an interesting form of manganese oxide with a 2 × 2 edge sharing tunnel structure and a cation positioned inside. Cryptomelane is an OMS-2 material with K+ cations within the crystalline tunnel and has been widely used in catalytic oxidation reactions, due to a mixed valency of Mn3+ and Mn4+ cations. Cryptomelane (K-OMS-2) can be modified by structural incorporation of various dopants and tunnel cations which can enhance the catalytic activity of the material. It also offers to be a promising alternative material for the low temperature emission control of combustion vehicles; particularly during cold start and low temperature conditions of diesel vehicles. In this work we used a one-pot sol–gel route to synthesize a range of manganese oxide based supports doped with Ce and CeZrO2, as alternative low temperature diesel oxidation catalysts. We have investigated the combination of manganese, ceria and zirconia in mixed oxide catalyst supports. The synthesized samples were loaded with 1 wt% Pt and their activity in the oxidation reactions of CO and C3H6, were compared with a commercial diesel oxidation catalyst with the same metal loading. The reductions in CO and C3H6 oxidation temperature T50 of 109 K and 81 K respectively was achieved compared to a commercial diesel oxidation catalyst.
Highlights
Ceria is the most plentiful rare earth metal on the planet and has been largely exploited for the effective use in catalytic redox reactions
All of the Ce/Mn samples proved to be amorphous with the exception of Ce[0.025]-Mn:60, which expressed the phases associated with Octahedral molecular sieves (OMS)-2
Peaks characteristic to a CeO2 are absent from the X-ray diffraction (XRD) pattern of Ce[0.025]Mn:60, suggesting that cerium is present in the form of cations, positioned inside the tunnel structure of OMS, rather than a free ceria phase
Summary
Ceria is the most plentiful rare earth metal on the planet and has been largely exploited for the effective use in catalytic redox reactions. One of the most common uses of ceria based materials is in automotive catalytic convertors They have been traditionally used as supporting materials in three-waycatalysts (TWC), diesel oxidation catalysts (DOC) and soot combustion [4, 29, 31]. The addition of zirconia to ceria has proved to increase the OSC compared to pure ceria This has been attributed to the structural defects which are imposed in the material by the addition of Zr4+, which has a smaller ionic radius than Ce4+. The introduction of zirconia to ceria, forming a mixed oxide material, has been
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