BUSCADOR RECOLECTA

In this study, we describe a very simple approach to the development of tailored mesoporosity in any nanostructured heteropolysalt with control over both the mesoporous volume and the pore size. This approach, which consists in the treatment of a solid microporous precursor with a basic agent, has been tested on the ammonium salt of the Keggin‐type [PMo12O40]3− heteropolyanion and constitutes a novel procedure for the preparation of mesoporous solids with no precedents. The results obtained in this study allow two main conclusions to be drawn: 1) the micro‐ and mesoporous structures in the heteropolysalt nanoparticles are independent from each other and 2) the development of mesoporosity in the solid material must be related to a process of alkaline degradation within the core of the nanocrystals that aggregate into the particles. These results afford valuable additional information to the present model of porosity that has been established for heteropolysalts., This work was financially supported by Generalitat Valenciana (grant PROMETEO2/2014/010) and Ministerio de Economía y Competitividad (grant CTQ2015‐64801‐R) through FEDER funds. S.R. acknowledges financial support from the program 'Ayudas para la Captación del Talento adscritas a los Institutos de Investigación de la Universidad Pública de Navarra' funded by a collaboration agreement between Universidad Pública de Navarra, Fundación Bancaria La Caixa and Fundación Bancaria Caja Navarra.

A series of materials based on the immobilization of the 12-tungstophosphoric heteropolyacid over zirconia supports have been prepared and applied as heterogeneous acid catalysts in the esterification of palmitic acid with methanol as a model reaction for the preliminary stage of the biodiesel production. The title materials have been obtained through the sol-gel method combined with a subsequent hydrothermal treatment at mild conditions, which affords catalysts with larger porosity and higher thermal and chemical stability under the esterification reaction conditions than other preparative approaches. Generating the zirconia support by hydrolysis of an alkoxyde precursor in the presence of the heteropolyacid leads to materials with homogeneously well-dispersed clusters, as well as to an increasing contribution of the tetragonal ZrO2 crystalline phase, a decreasing size of the nanoparticles and larger microporous volumes as the loading of the Keggin-type species increases. The 12-tungstophosphoric acid retains its catalytic activity in the esterification of palmitic acid with methanol at 60 °C upon immobilization over zirconia and conversions even higher than those observed under homogeneous conditions are obtained due to the active contribution of the support. The sample with a 30% mass percentage of heteropolyacid has been identified as the most efficient catalyst because it affords conversions above the 90% and shows the lower loss of activity over successive reaction runs among all of our materials. This loss of activity has been analyzed on the basis of the leaching of the catalyst and the fouling of the materials., This work was financially supported by Generalitat Valenciana through FEDER funds (grant PROMETEO2/2014/010) and by the Spanish Ministerio de Economía y Competitividad (grant CTQ2015-64801-R). S.R. acknowledges financial support from InaMat and from the program 'Ayudas para la Captación del Talento adscritas a los Institutos de Investigación de la UPNA' funded by a collaboration agreement with Obra Social la Caixa and Fundación Caja Navarra.

The oxidation of adamantane with hydrogen peroxide catalyzed by zirconia-supported 11-molybdovanadophosphoric acid is shown to be a suitable green route for the synthesis of adamantanol and adamantanone. This work evaluates how the catalyst activity and selectivity are affected by some of its preparative parameters, such as the method for supporting the catalytically active heteropoly acid over the zirconia matrix or the pretreatments applied to the resulting materials before being used as heterogeneous catalysts. Our results indicate that the most effective catalysts able to maintain their activity after several reaction runs are those prepared by following the sol-gel route, whereas the most selective catalysts are those obtained by impregnation methods. Moreover, the calcination temperature has also been identified as a relevant parameter influencing the performance of catalysts based on supported heteropoly acids. The increasing catalytic activity observed over several consecutive reaction runs has been attributed to the formation of peroxo derivatives of polyoxometalate clusters at the surface of the catalyst and their accumulation after each reaction cycle., Funding for this research was provided by: Generalitat Valenciana (grant No. PROMETE/2018/076); Ministerio de Economía, Industria y Competitividad (grant No. CTQ2015– 64801-R); Obra Social la Caixa, Fundación Caja Navarra and Universidad Pública de Navarra (contract to SR in the framework of the program ‘Captación de Talento’).

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.

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.

In this study, we describe a very simple approach to the development of tailored mesoporosity in any nanostructured heteropolysalt with control over both the mesoporous volume and the pore size. This approach, which consists in the treatment of a solid microporous precursor with a basic agent, has been tested on the ammonium salt of the Keggin-type [PMo12O40]3− heteropolyanion and constitutes a novel procedure for the preparation of mesoporous solids with no precedents. The results obtained in this study allow two main conclusions to be drawn: 1) the micro- and mesoporous structures in the heteropolysalt nanoparticles are independent from each other and 2) the development of mesoporosity in the solid material must be related to a process of alkaline degradation within the core of the nanocrystals that aggregate into the particles. These results afford valuable additional information to the present model of porosity that has been established for heteropolysalts., This work was financially supported by Generalitat Valenciana (grant PROMETEO2/2014/010) and Ministerio de Economia y Competitividad (grant CTQ2015-64801-R) through FEDER funds. S.R. acknowledges financial support from the program “Ayudas para la Captación del Talento adscritas a los Institutos de Investigación de la Universidad Pública de Navarra” funded by a collaboration agreement between Universidad Pública de Navarra, Fundación Bancaria la Caixa and Fundación Bancaria Caja Navarra.

A series of materials based on the immobilization of the 12-tungstophosphoric heteropolyacid over zirconia supports have been prepared and applied as heterogeneous acid catalysts in the esterification of palmitic acid with methanol as a model reaction for the preliminary stage of the biodiesel production. The title materials have been obtained through the sol-gel method combined with a subsequent hydrothermal treatment at mild conditions, which affords catalysts with larger porosity and higher thermal and chemical stability under the esterification reaction conditions than other preparative approaches. Generating the zirconia support by hydrolysis of an alkoxyde precursor in the presence of the heteropolyacid leads to materials with homogeneously well-dispersed clusters, as well as to an increasing contribution of the tetragonal ZrO2 crystalline phase, a decreasing size of the nanoparticles and larger microporous volumes as the loading of the Keggin-type species increases. The 12-tungstophosphoric acid retains its catalytic activity in the esterification of palmitic acid with methanol at 60 °C upon immobilization over zirconia and conversions even higher than those observed under homogeneous conditions are obtained due to the active contribution of the support. The sample with a 30% mass percentage of heteropolyacid has been identified as the most efficient catalyst because it affords conversions above the 90% and shows the lower loss of activity over successive reaction runs among all of our materials. This loss of activity has been analyzed on the basis of the leaching of the catalyst and the fouling of the materials., This work was financially supported by Generalitat Valenciana through FEDER funds (grant PROMETEO2/2014/010) and by the Spanish Ministerio de Economia y Competitividad (grant CTQ2015-64801-R). S.R. acknowledges financial support from InaMat and from the program “Ayudas para la Captación del Talento adscritas a los Institutos de Investigación de la UPNA” funded by a collaboration agreement with Obra Social la Caixa and Fundación Caja Navarra.

Two series of ceria-praseodymia catalysts with varying composition have been systematically investigated in the oxidation of soot under inert atmosphere in order to find out its potential utilization in Gasoline Particulate Filters for GDI engines. The samples have been widely characterized by XRD, Raman spectroscopy, TEM, FESEM, XPS, N2 adsorption at −196 °C and O2-TPD. The praseodymium incorporation onto the ceria enhances the oxygen mobility in the subsurface/bulk of the sample favoring higher O2 released amounts under inert atmosphere. The intermediate compositions can promote more accentuated O2 emissions at moderate temperatures (up to 500 °C). The efficiency of the own active oxygen species released from the catalyst to oxidize soot under inert atmosphere, even under loose contact mode, has been well demonstrated. The pathways of the mechanism taking place seem to be dependent on the temperature and mainly on the type of contact among soot and catalyst. Under loose contact conditions and low-medium temperatures, the O2 freshly emitted from the catalyst can oxidize soot more efficiently than a diluted O2-gas stream. Conversely, under more severe conditions (higher temperature or tight contact conditions), the soot acts as a “driving force” and the own lattice oxygen species can be transferred directly towards soot surface in an efficient way., The authors gratefully acknowledge the financial support of Generalitat Valenciana (PROMETEO/2018/076), MINECO (CTQ2015-64801-R) and the UE (FEDER funding). Also, JCMM acknowledges Spanish Ministry of Science, Innovation and Universities for the financial support through a FPU grant (FPU17/00603).

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).

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 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).

The semiconductive and redox properties of different Ce1-xPrxO2-δ systems with x = 0, 0.2, 0.5, 0.8 and 1 were investigated by in situ electrical conductivity measurements and correlations with their catalytic behavior in the total oxidation of methane and the CO-PROX process were attempted. Thus, the electrical conductivity of the Ce1-xPrxO2-δ oxides was measured as a function of temperature and oxygen partial pressure, and was followed with time during sequential exposure to air and different gaseous mixtures containing CH4, CO or H2, in conditions close to those of their catalytic applications. All the solids showed both electronic and ionic conductivities, the total conductivity increasing continuously with the value of x. CeO2 appeared to be of n-type, while all the Pr-containing materials were p-type semiconductors in air. They kept their semiconductivity type under different gaseous atmospheres, except for Ce0.8Pr0.2O2-δ mixed oxide which switches from p-type to n-type passing through an NDC-like (Negative Differential Conductivity) state in the presence of CO and H2. The catalytic behavior of the Ce1-xPrxO2-δ oxides, which function during the catalytic oxidation reactions via a heterogeneous redox mechanism, was discussed for both processes studied in correlation with the electrical conductivity results., A. G.-G. and J.C. M.-M. gratefully acknowledge the financial support of Generalitat Valenciana (PROMETEO/2018/076), MINECO (CTQ2015-64801-R) and the UE (FEDER funding). J.C. M.-M. also acknowledges Spanish Ministry of Education, Culture and Sports for the financial support through a FPU grant (FPU17/00603).

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).

The oxidation of adamantane with hydrogen peroxide catalyzed by zirconia-supported 11-molybdovanado­phospho­ric acid is shown to be a suitable green route for the synthesis of adamantanol and adamantanone. This work evaluates how the catalyst activity and selectivity are affected by some of its preparative parameters, such as the method for supporting the catalytically active heteropoly acid over the zirconia matrix or the pretreatments applied to the resulting materials before being used as heterogeneous catalysts. Our results indicate that the most effective catalysts able to maintain their activity after several reaction runs are those prepared by following the sol-gel route, whereas the most selective catalysts are those obtained by impregnation methods. Moreover, the calcination temperature has also been identified as a relevant parameter influencing the performance of catalysts based on supported heteropoly acids. The increasing catalytic activity observed over several consecutive reaction runs has been attributed to the formation of peroxo derivatives of polyoxometalate clusters at the surface of the catalyst and their accumulation after each reaction cycle., Funding for this research was provided by: Generalitat Valenciana (grant No. PROMETE/2018/076); Ministerio de Economía, Industria y Competitividad (grant No. CTQ2015–64801-R); Obra Social la Caixa, Fundación Caja Navarra and Universidad Pública de Navarra (contract to SR in the framework of the program ‘Captación de Talento’).

The effect of Ce/Pr ratio on ceria-praseodymia on structural and surface properties is studied. The catalytic activity towards soot combustion under NOx/O2 and O2/N2 atmospheres is also evaluated, together with the NO oxidation activity to NO2. CexPr1-xO2-δ compositions (x = 0.8, 0.5 and 0.2) have been prepared along with ceria and praseodymia. Catalysts were prepared by co-precipitation. The Ce0.5Pr0.5O2-δ composition, was also prepared by nitrate calcination. Ceria-praseodymia mixed oxides yield reduction profiles shifted to lower temperatures, higher NO oxidation activities to NO2 and improved catalytic activities for soot combustion with respect to pure ceria. Ce0.5Pr0.5O2-δ was the most active one. Under NOx/O2, it has greater soot combustion activity if it is prepared by nitrate calcination. However, under O2/N2, the co-precipitation method is more favorable because of the better dopant insertion achieved in the ceria lattice, which seems to lead better oxygen mobility on the surface and in the bulk oxide., The authors gratefully acknowledge the financial support of Generalitat Valenciana (PROMETEO/2018/076 project) and the Spanish Ministry of Economy and Competitiveness (CTQ2015-64801-R project) and the UE-FEDER funding. J.C.M.M. also acknowledges Spanish Ministry of Science, Innovation and Universities for the financial support through a FPU grant (FPU17/00603).