Optimizing the Catalytic Performance of Ba1-xCexMnO3 and Ba1-xLaxCu0.3Mn0.7O3 Perovskites for Soot Oxidation in Simulated GDI Exhaust Conditions.

Ba1-xCexMnO3 (BM-Cex) and Ba1-xLaxMn0.7Cu0.3O3 (BMC-Lax) perovskite-type mixed oxides were synthesized using the sol-gel method adapted for aqueous media with different values of x (0, 0.1, 0.3, 0.6) to estimate the effect of the degree of the partial substitution of Ba by Ce or La on the structure and properties that are relevant for their use as catalysts for gasoline direct injection (GDI) soot oxidation. The samples were deeply characterized by ICP-OES, XRD, XPS, N2 adsorption, H2-TPR, and O2-TPD, and their potential as catalysts for soot oxidation has been analyzed in various scenarios that replicate the exhaust conditions of a GDI engine. By comparing the catalytic performance for soot oxidation of the two tested series (BM-Cex and BMC-Lax) and in the two conditions used (100% He and 1% O2 in He), it could be concluded that (i) in the absence of oxygen in the reaction atmosphere (100% He), BMC-La0.1 is the best catalyst, as copper is also able to catalyze the soot oxidation; and (ii) if oxygen is present in the reaction atmosphere (1% O2/He), BM-Ce0.1 is the most-active catalyst as it presents a higher proportion of Mn(IV) than BMC-La0.1. Thus, it seems that the addition of an amount of Ce or La higher than that corresponding to x = 0.1 in Ba1-xCexMnO3 and Ba1-xLaxCu0.3Mn0.7O3 does not allow us to improve the catalytic performance of BM-Ce0.1 and BMC-La0.1 for soot oxidation in the tested conditions.

Improving the Catalytic Performance of BaMn0.7Cu0.3O3 Perovskite for CO Oxidation in Simulated Cars Exhaust Conditions by Partial Substitution of Ba.

The sol-gel method, adapted to aqueous media, was used for the synthesis of BaMn0.7Cu0.3O3 (BMC) and Ba0.9A0.1Mn0.7Cu0.3O3 (BMC-A, A = Ce, La or Mg) perovskite-type mixed oxides. These samples were fully characterized by ICP-OES, XRD, XPS, H2-TPR, BET, and O2-TPD and, subsequently, they were evaluated as catalysts for CO oxidation under different conditions simulating that found in cars exhaust. The characterization results show that after the partial replacement of Ba by A metal in BMC perovskite: (i) a fraction of the polytype structure was converted to the hexagonal BaMnO3 perovskite structure, (ii) A metal used as dopant was incorporated into the lattice of the perovskite, (iii) oxygen vacancies existed on the surface of samples, and iv) Mn(IV) and Mn(III) coexisted on the surface and in the bulk, with Mn(IV) being the main oxidation state on the surface. In the three reactant atmospheres used, all samples catalysed the CO to CO2 oxidation reaction, showing better performances after the addition of A metal and for reactant mixtures with low CO/O2 ratios. BMC-Ce was the most active catalyst because it combined the highest reducibility and oxygen mobility, the presence of copper and of oxygen vacancies on the surface, the contribution of the Ce(IV)/Ce(III) redox pair, and a high proportion of surface and bulk Mn(IV). At 200 °C and in the 0.1% CO + 10% O2 reactant gas mixture, the CO conversion using BMC-Ce was very similar to the achieved with a 1% Pt/Al2O3 (Pt-Al) reference catalyst.

Screening Ba0.9A0.1MnO3 and Ba0.9A0.1Mn0.7Cu0.3O3 (A = Mg, Ca, Sr, Ce, La) Sol-Gel Synthesised Perovskites as GPF Catalysts.

Ba0.9A0.1MnO3 (BM-A) and Ba0.9A0.1Mn0.7Cu0.3O3 (BMC-A) (A = Mg, Ca, Sr, Ce, La) perovskite-type mixed oxides were synthesised, characterised, and used for soot oxidation in simulated Gasoline Direct Injection (GDI) engine exhaust conditions. The samples have been obtained by the sol-gel method in an aqueous medium and deeply characterised. The characterization results indicate that the partial substitution of Ba by A metal in BaMnO3 (BM) and BaMn0.7Cu0.3O3 (BMC) perovskites: (i) favours the hexagonal structure of perovskite; (ii) improves the reducibility and the oxygen desorption during Temperature-Programmed Desorption (O2-TPD) tests and, consequently, the oxygen mobility; (iii) mantains the amount of oxygen vacancies and of Mn(IV) and Mn(III) oxidation states, being Mn(IV) the main one; and (iv) for Ba0.9A0.1Mn0.7Cu0.3O3 (BMC-A) series, copper is partially incorporated into the structure. The soot conversion data reveal that Ba0.9La0.1Mn0.7Cu0.3O3 (BMC-La) is the most active catalyst in an inert (100% He) reaction atmosphere, as it presents the highest amount of copper on the surface, and that Ba0.9Ce0.1MnO3 (BM-Ce) is the best one if a low amount of O2 (1% O2 in He) is present, as it combines the highest emission of oxygen with the good redox properties of Ce(IV)/Ce(III) and Mn(IV)/Mn(III) pairs.

Analyzing the Effect of Zr, W, and V Isomorph Framework Substitution on ZSM-5 and Beta Zeolites for Their Use as Hydrocarbon Trap.

This work evaluates the effect on the adsorption and desorption kinetics of propene and toluene (used as probe molecules for vehicle cold-start emissions) of the isomorph framework substitution of Zr, W, and V on commercial ZSM-5 and beta zeolites. TG-DTA and XRD characterization data indicated that: (i) Zr does not modify the crystalline structure of the parent zeolites, (ii) W develops a new crystalline phase, and (iii) V causes the breakdown of the zeolite structure during the aging step. The CO2 and N2 adsorption data revealed that the substituted zeolites present a narrower microporosity than pristine zeolites. As a consequence of all these modifications, the modified zeolites feature different adsorption capacity and kinetics of HCs, so, different hydrocarbon trapping ability than pristine zeolites. However, a clear correlation is not observed between the changes in the porosity/acidity of zeolites and the adsorption capacity and kinetics, which depends on: (i) the zeolite (ZSM-5 or BEA), (ii) the hydrocarbon (toluene or propene), and (iii) the cation to be inserted (Zr, W, or V).

Tailoring the Composition of BaxBO3 (B = Fe, Mn) Mixed Oxides as CO or Soot Oxidation Catalysts in Simulated GDI Engine Exhaust Conditions.

Mixed oxides with perovskite-type structure (ABO3) are promising catalysts for atmospheric pollution control due to their interesting and tunable physicochemical properties. In this work, two series of BaxMnO3 and BaxFeO3 (x = 1 and 0.7) catalysts were synthesized using the sol-gel method adapted to aqueous medium. The samples were characterized by µ-XRF, XRD, FT-IR, XPS, H2-TPR, and O2-TPD. The catalytic activity for CO and GDI soot oxidation was determined by temperature-programmed reaction experiments (CO-TPR and soot-TPR, respectively). The results reveal that a decrease in the Ba content improved the catalytic performance of both catalysts, as B0.7M-E is more active than BM-E for CO oxidation, and B0.7F-E presents higher activity than BF for soot conversion in simulated GDI engine exhaust conditions. Manganese-based perovskites (BM-E and B0.7M-E) achieve better catalytic performance than iron-based perovskite (BF) for CO oxidation reaction due to the higher generation of actives sites.

Improving the Performance of BaMnO3 Perovskite as Soot Oxidation Catalyst Using Carbon Black during Sol-Gel Synthesis.

A series of BaMnO3 solids (BM-CX) were prepared by a modified sol-gel method in which a carbon black (VULCAN XC-72R), and different calcination temperatures (600-850 °C) were used. The fresh and used catalysts were characterized by ICP-OES, XRD, XPS, FESEM, TEM, O2-TPD and H2- TPR-. The characterization results indicate that the use of low calcination temperatures in the presence of carbon black allows decreasing the sintering effects and achieving some improvements regarding BM reference catalyst: (i) smaller average crystal and particles size, (ii) a slight increase in the BET surface area, (iii) a decrease in the macropores diameter range and, (iv) a lower temperature for the reduction of manganese. The hydrogen consumption confirms Mn(III) and Mn(IV) are presented in the samples, Mn(III) being the main oxidation state. The BM-CX catalysts series shows an improved catalytic performance regarding BM reference catalyst for oxidation processes (NO to NO2 and NO2-assisted soot oxidation), promoting higher stability and higher CO2 selectivity. BM-C700 shows the best catalytic performance, i.e., the highest thermal stability and a high initial soot oxidation rate, which decreases the accumulation of soot during the soot oxidation and, consequently, minimizes the catalyst deactivation.

NOx Storage on BaTi0.8Cu0.2O3 Perovskite Catalysts: Addressing a Feasible Mechanism.

The NOx storage mechanism on BaTi0.8Cu0.2O3 catalyst were studied using different techniques. The results obtained by XRD, ATR, TGA and XPS under NOx storage-regeneration conditions revealed that BaO generated on the catalyst by decomposition of Ba2TiO4 plays a key role in the NOx storage process. In situ DRIFTS experiments under NO/O2 and NO/N2 show that nitrites and nitrates are formed on the perovskite during the NOx storage process. Thus, it seems that, as for model NSR catalysts, the NOx storage on BaTi0.8Cu0.2O3 catalyst takes place by both "nitrite" and "nitrate" routes, with the main pathway being highly dependent on the temperature and the time on stream: (i) at T < 350 °C, NO adsorption leads to nitrites formation on the catalyst and (ii) at T > 350 °C, the catalyst activity for NO oxidation promotes NO2 generation and the nitrate formation.

BaFe1-xCuxO3 Perovskites as Active Phase for Diesel (DPF) and Gasoline Particle Filters (GPF).

BaFe1-xCuxO3 perovskites (x = 0, 0.1, 0.3 and 0.4) have been synthetized, characterized and tested for soot oxidation in both Diesel and Gasoline Direct Injection (GDI) exhaust conditions. The catalysts have been characterized by BET, ICP-OES, SEM-EDX, XRD, XPS, H2-TPR and O2-TPD and the results indicate the incorporation of copper in the perovskite lattice which leads to: i) the deformation of the initial hexagonal perovskite structure for the catalyst with the lowest copper content (BFC1), ii) the modification to cubic from hexagonal structure for the high copper content catalysts (BFC3 and BFC4), iii) the creation of a minority segregated phase, BaOx-CuOx, in the highest copper content catalyst (BFC4), iv) the rise in the quantity of oxygen vacancies/defects for the catalysts BFC3 and BFC4, and v) the reduction in the amount of O2 released in the course of the O2-TPD tests as the copper content increases. The BaFe1-xCuxO3 perovskites catalyze both the NO2-assisted diesel soot oxidation (500 ppm NO, 5% O2) and, to a lesser extent, the soot oxidation under fuel cuts GDI operation conditions (1% O2). BFC0 is the most active catalysts as the activity seems to be mainly related with the amount of O2 evolved during an. O2-TPD, which decreases with copper content.