Suchergebnisse

In this paper, the tolerance and stability versus SO2 of Ba0.9A0.1Ti0.8Cu0.2O3 (A = Sr, Ca, Mg) perovskite-type catalysts for NOx storage application have been analyzed at 400 °C. Characterization results show that only strontium and magnesium are introduced into the perovskite structure. From those data, it can be concluded that the incorporation of Sr into the Ba0.9Sr0.1Ti0.8Cu0.2O3 catalyst promotes the generation of new NOx adsorption active sites. On the contrary, for Ba0.9Mg0.1Ti0.8Cu0.2O3 catalyst, copper is segregated from the catalyst lattice to the surface due to the incorporation of magnesium into the B site of the perovskite. The partial substitution of barium in Ba0.9Sr0.1Ti0.8Cu0.2O3 and Ba0.9Mg0.1Ti0.8Cu0.2O3 catalysts increases the NOx Storage Capacity (460 and 415 μmol/g.cat. in saturation conditions, respectively), stability and tolerance versus SO2 compared to the raw BaTi0.8Cu0.2O3 perovskite. ; The authors thank Spanish Government (MINECO) and UE (FEDER Founding) (project CTQ2015-64801-R) and Generalitat Valenciana (project PROMETEO II/2018/076) for the financial support. V. Albaladejo-Fuentes thanks the University of Alicante for his Ph.D. grant.

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, the catalyst activity for NO oxidation promotes NO2 generation and the nitrate formation. ; This research was funded by Generalitat Valenciana (PROMETEO/2018/076 and Spanish Government (PID2019-105542RB-I00) and EU (FEDER Founding).

The activity for NO oxidation and for NO2-assisted diesel soot removal of a BaMn1−xCuxO3 (x = 0, 0.1, 0.2, 0.3) perovskite-type catalyst has been tested by Temperature Programmed Reaction (TPR) and isothermal experiments at 450 °C. Fresh and used catalyst characterization by ICP-OES, N2 adsorption, XRD, XPS, IR spectroscopy and H2-TPR was performed. Results showed that: (i) manganese is partially substituted by copper in the perovskite structure leading to the formation of a manganese-deficient perovskite with a new hexagonal structure, (ii) in BaMn1−xCuxO3 catalysts, manganese seems to be mainly Mn(III) and, as a consequence, the amount of oxygen vacancies increases gradually with the copper content and (iii) the presence of copper into the perovskite structure enhances the reducibility of the catalyst and increases the mobility of lattice oxygen. BaMn0.7Cu0.3O3 is the most active catalyst for NO2 generation and, consequently, shows the lowest T50% value, the highest CO2 selectivity, the best performance during TPR cyclic experiments, and the highest soot oxidation rate at 450 °C. This behavior is a result of the enhancement of the redox properties of the catalyst due to the replacement of Mn(III)/Mn(IV) by Cu(II) in the perovskite structure. ; The authors thank Spanish Government (MINECO project CTQ2015-64801-R), the European Union (FEDER) and the Generalitat Valenciana (Project PROMETEOII/2014/10) for the financial support. Vicente Albaladejo-Fuentes thanks the University of Alicante for his Ph.D. grant and Veronica Torregrosa-Rivero thanks SECAT for her "Introduction to Research" grant.

The effect of the synthesis method (hydrothermal and sol-gel) on the properties of BaTi0.8Cu0.2O3 perovskites as catalysts for NOx and soot removal has been analyzed. X-ray powder diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), ICP-AES, N2 adsorption at −196 °C, Raman spectroscopy, Field Emission Scanning Electron Microscopy (FESEM) and temperature programmed reduction with hydrogen (H2-TPR) have been used for catalysts characterization. To test their catalytic activity, NOx storage and soot combustion temperature programmed reaction tests have been carried out. The results allow to conclude that the synthesis method determines the position of copper on the perovskite structure and, therefore, the catalytic applications. When the hydrothermal method is used the copper is highly dispersed on the perovskite surface, obtaining a catalyst with a high activity for the NO to NO2 oxidation reaction, which can be used as oxidation catalyst for soot removal. Nevertheless, using the sol-gel method, copper is incorporated into the perovskite structure and, consequently, the catalyst presents a high NOx storage capacity. ; The authors thank the Spanish government (MINECO project CTQ2015-64801-R) for the financial support and Vicente Albaladejo Fuentes thanks the University of Alicante for his Ph.D. grant.

BaTi1−xCuxO3 perovskites have been prepared by the Pechini's sol-gel method and the effect of copper in the structural and physico-chemical properties of the perovskites and in the performance of the catalysts for NOx storage has been studied. XRD and Raman spectroscopy results indicate that all the copper containing catalysts present a distortion of the original tetragonal structure due to the incorporation of copper into the lattice. The XPS and H2-TPR results reveal that the copper catalysts, except for BaTiCu0,5 catalyst, present two copper species (with different electronic interaction with the perovskite) and active surface oxygen species. Additionally, it seems that the fraction of copper with a strong electronic interaction with the perovskite or incorporated into the perovskite structure increases with the copper content. The active sites created on the BaTi1−xCuxO3 perovskite surface bring to the catalysts activity for the NO to NO2 oxidation and for the NOx adsorption. The NOx storage capacity increases with the copper content and reaches a limit for the BaTiCu2 catalyst (300 μmol/g, at 420 °C) which is within the range of the values reported for the noble metal-based catalysts. ; The authors thank to Spanish Government (MINECO projectCTQ2012-030703) and to Generalitat Valenciana (project PROM-ETEOII/2014/010) for the financial support.

The effect of partial Ti substitution by Mn, Fe, Co, or Cu on the NOx storage capacity (NSC) of a BaTi0.8B0.2O3 lean NOx trap (LNT) catalyst has been analyzed. The BaTi0.8B0.2O3 catalysts were prepared using the Pechini's sol–gel method for aqueous media. The characterization of the catalysts (BET, ICP-OES, XRD and XPS) reveals that: i) the partial substitution of Ti by Mn, Co, or Fe changes the perovskite structure from tetragonal to cubic, whilst Cu distorts the raw tetragonal structure and promotes the segregation of Ba2TiO4 (which is an active phase for NOx storage) as a minority phase and ii) the amount of oxygen vacancies increases after partial Ti substitution, with the BaTi0.8Cu0.2O3 catalyst featuring the largest amount. The BaTi0.8Cu0.2O3 catalyst shows the highest NSC at 400 °C, based on NOx storage cyclic tests, which is within the range of highly active noble metal-based catalysts. ; This research was funded by Generalitat Valenciana (PROMETEO/2018/076 and Ph.D. grant ACIF 2017/221), Spanish Government (MINECO Project CTQ2015-64801-R) and EU (FEDER Founding).

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. ; This research was funded by the Generalitat Valenciana (PROMETEO/2018/076 and Ph.D. Grant ACIF/2017/221 for V.Torregrosa-Rivero), Spanish Government (MINECO Project CTQ2015-64801-R), and EU (FEDER Founding).

A series of BaFe1−xCuxO3 catalysts (x = 0, 0.1, 0.3 and 0.4) have been synthetized, characterized and used for soot oxidation in gasoline direct injection (GDI) exhaust conditions. The characterization of the catalysts (by BET, ICP-OES, XRD, XPS, H2-TPR and O2-TPD) reveals that copper is incorporated into the perovskite lattice leading to: (i) the distortion of the original hexagonal perovskite structure for the lowest copper content catalyst (BFC1) and the modification of the structure, from hexagonal to cubic, for the catalysts with higher copper content (BFC3 and BFC4), (ii) the generation of a BaOx–CuOx oxide as minority segregated phase for BFC4 catalyst, (iii) the increase in the amount of oxygen surface vacancies for BFC3 and BFC4 catalysts, and (iv) the decrease in the total amount of O2 released during O2-TPD experiments. All the BaFe1−xCuxO3 perovskites are active for soot oxidation under the highest demanding GDI exhaust conditions (regular stoichiometric GDI operation, i.e., 0% O2). The catalyst with the highest copper content (BFC4) shows the highest soot conversion, related to its largest amount of β-oxygen evolved, and, to the presence of a high amount of copper species (as BaOx–CuOx oxide) on its surface. ; The authors thank Generalitat Valenciana (PROMETEO/2018/076), Spanish Government (MINECO Project CTQ2015-64801-R) and UE (FEDER Founding) for the financial support. V. Torregrosa-Rivero thanks the Generalitat Valenciana for her Ph.D. Grant (ACIF 2017/221).