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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.

Esta tesis doctoral se ha centrado en el diseño y la síntesis de óxidos inorgánicos con estructura macroporosa altamente activos en la combustión de carbonilla y el control de emisiones de NOx mediante el ciclo NSR. Estos materiales, que incluyen óxidos mixtos de estroncio y titanio, óxidos de cerio, praseodimio y lantano, con y sin cobre en su composición, han sido estudiados para entender la relación entre las propiedades físico-químicas de los materiales y su comportamiento catalítico, de modo que se puedan diseñar catalizadores óptimos para cada aplicación.

PrOx and CuO/PrOx catalysts have been prepared with conventional (Ref) and three dimensionally ordered macroporous (3DOM) structures, and the effect of the structure on soot combustion has been studied. It has been demonstrated that the 3DOM structure significantly improves the catalytic combustion of soot with O2. The activity follows the trend PrOx-3DOM > CuO/PrOx-3DOM ∼ CuO/PrOx-Ref ≫ PrOx-Ref, which is explained considering two aspects: the production of active oxygen and its transfer from catalyst to soot. FESEM microscopy, N2 adsorption, Hg porosimetry and He density show that the 3DOM catalysts have ordered macroporosity with pores of 80 nm in diameter, which favors the carbon–catalyst contact. In addition, the 3DOM catalysts present higher surface density of active oxygen (Oads), which follows the trend CuO/PrOx-3DOM > PrOx-3DOM ∼ CuO/PrOx-Ref > PrOx-Ref. Consequently, the PrOx-3DOM catalyst combines a good production of active oxygen and an efficient transfer to soot, making it the most active catalyst to accelerate soot combustion. In contrast, PrOx-Ref is the least active since it is the least efficient in producing and transferring active oxygen. The impregnation of copper with the conventional support (CuO/PrOx-Ref) enhances the production and transfer of active oxygen, improving the activity with respect to PrOx-Ref. However, CuO blocks the porosity of the 3DOM support, hindering the contact with soot. Soot combustion is accelerated in the presence of NOx due to the production of NO2. This NO2, once produced, is mostly readsorbed on the surface of the catalysts producing active oxygen that must be transferred to soot. For this reason, the porosity of the catalysts also plays a relevant role during combustion with NOx/O2 because it affects the transfer of active oxygen produced by NO2 to soot.

The effect of the LnOx support has been studied for Ni‐based CO2 methanation catalysts. 10 wt. % nickel catalysts with LaOx, CeO2 and PrOx supports have been prepared, characterized by N2 adsorption, XRD, XRF, TG‐MS (N2‐TPD and H2‐TPR) and XPS, and have been tested for CO2 methanation. The catalytic activity follows the trend Ni/CeO2 > Ni/PrOx >> Ni/LaOx, all catalysts being very selective towards CH4 formation. The activity depends both on the nature of the catalytic active sites and on the stability of the surface CO2 and H2O species. Ni/CeO2 is the most active catalyst because (i) the Ni2+‐ceria interaction leads to the formation of the highest population of active sites for CO2 dissociation, (ii) the reduced Ni0 sites where H2 dissociation takes place are the most electronegative and active, and (iii) the stability of surface CO2 and H2O species is lowest. Ni/LaOx achieves lower activity because of the strong chemisorption of H2O and CO2, which poison the catalyst surface, and because this support is not able to promote the formation of highly active sites for CO2 and H2 dissociation. The behavior of Ni/PrOx is intermediate, being slightly lower to that of Ni/CeO2 because the formation of active sites is not so efficient and because the stability of chemisorbed CO2 is slightly higher.

CeO2 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 CeO2-3DOM catalyst produces more active oxygen upon O2 chemisorption than the counterpart CeO2-Ref catalyst, and this active oxygen is transferred more efficiently to soot due to the macroporous structure. CeO2-3DOM and CeO2-Ref also accelerate the oxidation of NO to NO2, and their activity is equal. However, CeO2-3DOM utilizes NO2 more efficiently than CeO2-Ref for soot combustion. NO2 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 NO2. In ceria catalysts with a conventional structure, the main role of NO2 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 NO2, that is, NO2 contributes to active oxygen production and the 3DOM structure allows its efficient transference to soot.

The synthesis and use for soot combustion of praseodymium oxide with three-dimensionally ordered macroporous (3DOM) structure is described. This novel PrOx-3DOM catalyst is presented as an improved novel metal-free alternative to CeO2 as soot combustion catalyst. The PrOx-3DOM catalyst presents a well-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 PrOx regarding CeO2, ameliorate the active oxygen production and its transfer to soot particles, improving the soot combustion with O2. In addition, the higher ability of PrOx to oxidize NO to NO2, improves the soot combustion in a higher extent than CeO2 in presence of NOx. The catalytic activity of PrOx-3DOM after several soot combustion cycles is also confirmed.