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The individual and simultaneous removal of NOx by Storage and Reduction with H2 (H2‐NSR) and combustion of soot have been studied for La and CuLa catalysts. The NOx storage capacity of pure lanthanum oxide is improved either by copper addition or by using a colloidal crystal hard template for the synthesis of a macroporous structure. Although the NOx storage capacity of the CuLa macroporous material is around ten times lower regarding conventional PtBa catalysts, the kinetics of the H2‐NSR cycles are fast enough to allow high NOx removal (until 90 % removal). Lanthanum oxide catalyst prepared with uncontrolled structure has no activity for soot combustion, but the activity increases for a macroporous counterpart prepared using the colloidal crystal template because the macroporous structure improves the soot‐catalyst contact and allows the nitrogen‐oxygen surface groups yielded upon NOx chemisorption to oxidize soot. The soot combustion activity of lanthanum catalysts is also enhanced upon copper loading, because copper improves the NO2‐assisted soot combustion mechanism and favors the chemisorption of NOx, enhancing soot oxidation by nitrogen‐oxygen surface species. Finally, it is demonstrated that the simultaneous removal of NOx by H2‐NSR and soot combustion can be carried out with a CuLa catalyst at 450 °C. The simultaneous removal does not affect the combustion of soot and only has a small effect in NOx removal. [ABSTRACT FROM AUTHOR]

CeO 2 catalysts have been prepared with conventional (Ref) and three dimensionally order macroporous (3DOM) structures, and the effect of the structure on the soot combustion mechanism has been studied in detail. Isotopic exchange experiments showed that the CeO 2 -3DOM catalyst produces more active oxygen upon O 2 chemisorption than the counterpart CeO 2 -Ref catalyst, and this active oxygen is transferred more efficiently to soot due to the macroporous structure. CeO 2 -3DOM and CeO 2 -Ref also accelerate the oxidation of NO to NO 2 , and their activity is equal. However, CeO 2 -3DOM utilizes NO 2 more efficiently than CeO 2 -Ref for soot combustion. NO 2 has two roles in the soot combustion mechanism: i) reacts with soot and ii) is chemisorbed on ceria and produces active oxygen, which is more oxidizing than NO 2 . In ceria catalysts with a conventional structure, the main role of NO 2 is the direct oxidation of soot, because active oxygen has restrictions to be transferred from catalyst to soot due to the poor soot-catalyst solid-solid contact. However, the 3DOM structure improves the transfer of active oxygen, and therefore, an additional benefit is obtained from NO 2 , that is, NO 2 contributes to active oxygen production and the 3DOM structure allows its efficient transference to soot. [ABSTRACT FROM AUTHOR]

Graphical abstract A novel three dimensionally ordered macroporous PrO x catalyst, which outperforms the activity of Ceria, has been prepared and tested for soot combustion. This novel catalyst combines high active oxygen production with enhanced transfer of such active oxygen to soot due to the improved solid-solid soot-catalyst contact. Highlights • A novel three dimensionally ordered macroporous (3DOM) PrOx catalyst was prepared. • The soot combustion activity of 3DOM PrO x was compared with 3DOM Ceria and conventional (Ref) catalyst. • 3DOM PrOx is more active for soot combustion than 3DOM ceria. • PrOx is more easily reducible than CeO 2 and 3DOM structure favours that reducibility. • PrOx presents higher ability to oxidize NO to NO 2 than CeO 2 improving the activity. Abstract The synthesis and use for soot combustion of praseodymium oxide with three-dimensionally ordered macroporous (3DOM) structure is described. This novel PrO x -3DOM catalyst is presented as an improved noble-metal-free alternative to CeO 2 as soot combustion catalyst. The PrO x -3DOM catalyst presents a defined 3DOM structure with high macropores volume, which significantly enhances the solid-solid soot-catalyst contact. This enhanced contact, together with the improved reducibility of PrO x regarding CeO 2 , ameliorate the active oxygen production and its transfer to soot particles, improving the soot combustion with O 2. In addition, the higher ability of PrO x to oxidize NO to NO 2 , improves the soot combustion in a higher extent than CeO 2 in presence of NO x. The catalytic activity of PrO x -3DOM after several soot combustion cycles is also confirmed. [ABSTRACT FROM AUTHOR]

[Display omitted] • The shape of a Ce 0.5 Pr 0.5 Ox soot combustion catalyst was tunned (Nanoparticles, NP, and macroporus, MS). • An hybrid-shape catalyst was prepared combining NP and MS. • The macropores of MS Ce 0.5 Pr 0.5 Ox are large enough to disperse Ce 0.5 Pr 0.5 Ox NP. • The hybrid catalyst decreased soot combustion by ca. 100 °C even after an aging process. • NP provide high activity and MS structure, high thermal stability and improved soot-catalyst contact. A Ce 0.5 Pr 0.5 Ox soot combustion catalyst has been shaped combining this material prepared in two different structures (nanoparticles and MS-macroporous) in a single active phase. Nanoparticles, prepared by reversed microemulsion method, provide high activity to the hybrid material, and the MS structure, obtained by a hard template synthesis method, provides high thermal stability and improved soot-catalyst contact. Ce 0.5 Pr 0.5 Ox nanoparticles present high surface area (148 m2/g; 5 nm) and improved redox properties with regard to other Ce 0.5 Pr 0.5 Ox structures, and the macropores size of MS Ce 0.5 Pr 0.5 Ox are large enough (around 100 nm) to properly disperse Ce 0.5 Pr 0.5 Ox nanoparticles inside and also to host soot particles, creating a high reactive catalyst environment. As a result, the as prepared Ce 0.5 Pr 0.5 Ox hybrid catalyst, mixed in loose-contact mode with soot, decreased soot combustion by ca. 100 °C with regard to the uncatalyzed reaction, and thermal aging at 800 °C only decreased this difference to ca. 75 °C. The as-prepared counterpart hybrid catalyst obtained dispersing pure ceria nanoparticles on pure ceria MS support was also active for soot combustion, but the activity was almost lost completely upon thermal aging due to ceria sintering. [ABSTRACT FROM AUTHOR]

[Display omitted] • PrO x nanoparticles (10 nm; 81 m2/g) have been synthesized and tested in soot combustion. • Three morphological architectures were analysed: nanoparticles, 3DOM and uncontrolled structure. • PrO x nanoparticles reached the highest activity compared to other structured PRO x and CeO 2 catalysts. • PrO x nanoparticles kept high activity after aging at 800 °C. • CeO 2 catalysts suffer almost total deactivation upon aging. PrO x nanoparticles (10 nm; 81 m2/g) were synthesized and analysed as soot combustion catalyst in comparation with other reference materials including CeO 2 nanoparticles and PrO x and CeO 2 catalysts with three dimensionally ordered (3DOM) and without controlled structure. PrO x nanoparticles reached the highest activity; T50 decreases from 603 °C (uncatalysed combustion) to 494 °C. This high activity can be attributed to the high surface area/low crystal size, which enhances the soot catalyst contact, and to the improved reducibility. PrO x nanoparticles kept high activity (T50 = 520 °C) after aging at 800 °C, being significantly more active than aged PrO x catalysts with 3DOM and uncontrolled structure and also significantly more active than all aged CeO 2 catalysis which suffer almost total deactivation upon aging. In all cases, PrO x catalysts are more active than CeO 2 counterpart materials with the same structure and thermal history, and this applies to nanoparticles, 3DOM and uncontrolled structures. [ABSTRACT FROM AUTHOR]