BUSCADOR RECOLECTA

Carbon-ceramic composites (C/Cer) have been prepared by chemical vapor deposition of coal tar pitch onto clay substrates and characterized by thermogravimetric analyses, powder X-ray diffraction, Raman spectroscopy, and scanning and transmission electron microscopies (SEM and TEM). The study of the dc electrical conductivity, together with the determination of the Hall voltage sign, proves that such C/Cer composites are n-type semiconductors. Our results demonstrate that: 1) the mechanism of electrical conduction of C/Cer semiconductors proceeds through the pathways expected for amorphous solids (ie. variable-range hopping and heat-activated pathways at low and high temperatures, respectively); and 2) their transport properties are strongly dependent on the clay components, as evidenced by microscopy experiments., The authors would like to thank the financial support from Ministerio de Ciencia e Innovación (grant No. PID2019-105542RB-I00/AEI/10.13039/501100011033 ), the European Union (FEDER Funds), and Generalitat Valenciana (grant No. PROMETEO CIPROM/2021/70 ).

The aim of this research is an attempt to shed some light on the understanding of the nature of the active sites and the generated synergies in the copper/ceria-zirconia formulations for low temperature CO oxidation by means of the creation of copper entities with different physico-chemical nature. For this reason, several CuOx/ceria-zirconia catalysts, with different Cu contents and different methods to incorporate copper species, were synthesized. Focus was specially put in this case trying to link the results of CO oxidation catalytic tests with the CO-temperature programmed reduction profiles/approximate estimations and selected characterization parameters in order to find out correlations among catalysts' properties/reducibility and catalytic behaviors, especially those corresponding to the nature and roles of the different CuOx species in contact with ceria-based support on catalytic activity.

Results reveal a significant improvement in CO conversion compared to the ceria-zirconia support by adding a small amount of copper loading (as low as 0.5 %), emphasizing the paramount role of copper incorporated by the method of IWI. From 0.5 up to 2% of copper loading, an interesting increase gradual trend in activity and reducibility can be noted. It should be mentioned that all the catalysts obtained by this procedure are more catalytically active towards CO oxidation than 1%Pt/Al2O3 at low temperatures (T < 130 degrees C). CO-TPR results show that the reducibility of these catalysts is in line with their CO oxidation activity. The method of preparation has been revealed as a critical variable in the catalytic performance, and quite similar catalytic activities can be reached from different synthesis methods and different copper contents, due to the similar nature and type of CuOx species generated over the catalysts' surface, identified by the CO-TPR profiles and the rest of characterization data. Finally, IWI method seems to be the best one among those tested, thus combining superior areas of both alpha and beta contributions assigned on CO-TPR profiles, which seem to be critical in the interpretation of the catalytic behaviors.

The present work aims to assess the impact of morphology and reducibility on lanthanum-doped ceria nanocatalysts with controlled morphology on the NO oxidation reaction. Specifically, samples were prepared using a hydrothermal method incorporating lanthanum at varying molar concentrations (0, 5, 10, and 15 mol.%) into ceria with a controlled morphology (nanocubes and nanorods). The structural, compositional, and redox characterization of these catalysts has been performed via scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (X-EDS), inductively coupled plasma (ICP), hydrogen temperature-programmed reduction (H2-TPR), and oxygen storage capacity (OSC). NO oxidation catalytic tests were conducted, and the results were compared with estimated curves (obtained by considering the proportions of the corresponding components), which revealed the presence of a synergistic effect between lanthanum and ceria. The degree of enhancement was found to depend on both the morphology and the amount of lanthanum incorporated into CeO2. These findings may facilitate the optimization of features concerning ceria-based nanocatalysts for the removal of NOx emissions from exhaust gases., 16 páginas

In this work, several ceria-zirconia based catalysts with very low (and equimolar) metal contents were prepared, characterised and tested for the CO oxidation reaction (under lean and stoichiometric conditions), trying to emulate those conditions found in a diesel oxidation catalyst (DOC) system from a diesel engine and those encountered under gasoline exhaust (l ¼ 1). The metals chosen are Cu, Co, Ag and Pt (as a reliable benchmark). The results reveal enormous differences among reducibility and catalytic activity despite quite similar structural and textural properties of the catalysts, showing differences among dispersion (Ag-catalyst seems to present a low level of dispersion). This catalyst seems to be characterised, as well, by a strong electronic interaction between Ce and Ag centres which is suggested to yield an improved reducibility under H2-TPR conditions. Nevertheless, the order in catalytic activity (Cu > Ag > Co zPt>>support) seems not to follow the order found in reducibility and the Cu-catalyst seems to be the most active independently on the reaction conditions, yielding nearly overlapped CO oxidation catalytic curves. Interestingly, a strong correlation between the catalytic activity under the two conditions tested and the OSC values of the Ce0.8Zr0.2O2-supported metal catalysts is found. Therefore, OSC parameter measured at 150 C can be used as a relevant descriptor to evaluate the CO oxidation activity at low and medium conversions for the investigated catalysts, much better than the H2-TPR measurements.

In this work, a fundamental and systematic study was conducted, leading to a better understanding of the phenomena occurring on the catalyst’s surface during the NOx reduction process in NSR systems. For this purpose, ceria-based catalysts, with Cu in substitution of noble metal, have been synthesized and deeply characterized by means of XRF, XPS, in situ (XRD, Raman spectroscopy and DRIFTS), temperature-programmed reduction under H2 (H2-TPR) and under NO reaction (NO isothermal reaction + NO-TPR). The whole results show the key role of copper to promote the reducibility and the creation of oxygen vacancies, allowing a high NO consumption and fast kinetics of N2O and N2 formation, until the oxygen vacancies consumption takes place. The study of the surface reactions taking place in the formation of adsorbed NOx species and the oxygen vacancies consumption with NO uptake is complex; however, a hydroxyl consumption route is found to be involved. The reduction of NO provided higher levels of N2 at higher temperatures; also, a very high efficiency of the previously created oxygen vacancies was found for this process., The authors gratefully acknowledge the financial support of Generalitat Valenciana (PROMETEO/2018/076 project) and the Spanish Ministry of Science and Innovation (PID2019-105542RB-I00 project) and the UE-FEDER funding. Martínez-Munuera also acknowledges Spanish Ministry of Science, Innovation and Universities for the financial support through a FPU grant (FPU17/00603).

The aim of this research is an attempt to shed some light on the understanding of the nature of the active sites and the generated synergies in the copper/ceria-zirconia formulations for low temperature CO oxidation by means of the creation of copper entities with different physico-chemical nature. For this reason, several CuOx/ceria-zirconia catalysts, with different Cu contents and different methods to incorporate copper species, were synthesized. Focus was specially put in this case trying to link the results of CO oxidation catalytic tests with the CO-temperature programmed reduction profiles/approximate estimations and selected characterization parameters in order to find out correlations among catalysts’ properties/reducibility and catalytic behaviors, especially those corresponding to the nature and roles of the different CuOx species in contact with ceria-based support on catalytic activity. Results reveal a significant improvement in CO conversion compared to the ceria-zirconia support by adding a small amount of copper loading (as low as 0.5 %), emphasizing the paramount role of copper incorporated by the method of IWI. From 0.5 up to 2% of copper loading, an interesting increase gradual trend in activity and reducibility can be noted. It should be mentioned that all the catalysts obtained by this procedure are more catalytically active towards CO oxidation than 1%Pt/Al2O3 at low temperatures (T < 130 °C). CO-TPR results show that the reducibility of these catalysts is in line with their CO oxidation activity. The method of preparation has been revealed as a critical variable in the catalytic performance, and quite similar catalytic activities can be reached from different synthesis methods and different copper contents, due to the similar nature and type of CuOx species generated over the catalysts’ surface, identified by the CO-TPR profiles and the rest of characterization data. Finally, IWI method seems to be the best one among those tested, thus combining superior areas of both α and β contributions assigned on CO-TPR profiles, which seem to be critical in the interpretation of the catalytic behaviors., The authors gratefully acknowledge the financial support of Generalitat Valenciana (PROMETEO/2018/076 project) and the Spanish Ministry of Science and Innovation (PID2019-105542RB-I00 project) and the UE-FEDER funding. Martínez-Munuera also acknowledges Spanish Ministry of Science and Innovation for the financial support through a FPU grant (FPU17/00603).

Ceria-based catalysts, with Cu in substitution of noble metals, were studied in a vertical microreactor system under isothermal conditions, where NOx was previously stored, followed by the reduction step conducted under H2. The possible remaining ad-NOx species after the reduction stage, were investigated by Temperature Programmed Desorption in He. In situ DRIFTS was used as a complementary technique for the analysis of the surface species formation/transformation on the catalysts’ surface. Catalysts containing both Ba and Cu were found to be selective in the NOx reduction, producing N2 and minor amounts of NH3 during the reduction step, as well as NO. The different ceria-based formulations (containing copper and/or barium) were prepared and tested at two different temperatures in the NOx reduction (NSR) processes. Their catalytic activities were analyzed in terms of their compositions and have been useful in the elucidation of the possible origin and relevant pathways for NOx reduction product formation, which seems to involve the oxygen vacancies of the ceria-based materials (whose generation seems to be promoted by copper) during the rich step. The scope of this work involves an interdisciplinary study of the impact that catalysts’ formulations (noble metal-free) have on their LNT performance under simulated conditions, thus covering aspects of Materials Science and Chemical Engineering in a highly applied context, related to the development of control strategies for hybrid powertrains and/or the reduction of the impact of cold-start emissions., This research was funded by the financial support from the Generalitat Valenciana (PROMETEO/2018/076 project) and the Spanish Ministry of Science and Innovation (PID2019-105542RB-I00 project) and the UE-FEDER funding. J.C.M.-M. also acknowledges Spanish Ministry of Science and Innovation for the financial support through an FPU grant (FPU17/00603).

In order to improve the catalytic formulations for soot removal in after-treatment emission control technologies for gasoline and diesel engine vehicle, an isotopic study was approached using transitory labeled oxygen response method over model catalysts that allows the unraveling of soot oxidation mechanism. Ce-based materials promote oxygen exchange associated with the high population of lattice oxygen species (O2-) denoted as OI type. The incorporation of praseodymium produces a Pr3+ enrichment that decrease the energy for oxygen release and increase oxygen mobility through surface and subsurface oxygen centers (OII type) depending on the synthesis procedure. For PtBaK catalyst, OIII species are responsible for oxygen exchange. Gas-solid reaction between soot and gas phase molecular oxygen is responsible for direct uncatalyzed soot oxidation. For ceria containing catalysts, low-temperature soot removal takes place through the intervention of lattice atomic species and superoxide species. For DPNR model catalyst, PtBaK/Al2O3, the soot elimination occurs with the intervention OIII type centers. In the presence NO, the assisted and cooperative mechanism due to NO2 and the intervention of the adsorbed nitrate species on the trimetallic catalyst enhances soot removal capacity., MCR acknowledges the postdoctoral fellowship obtained from the University of Malaga. MCR, CH, MAL and LJA want to thank the financial support of CTQ 2017-87909R project. MCR also want to thank the University of Alicante for the financial support for the internship (INV19-07). JCMM and AGG gratefully acknowledge the financial support of Generalitat Valenciana (PROMETEO/2018/076 project) and the Spanish Ministry of Science, Innovation and Universities (PID2019-105542RB-I00 project) and the UE-FEDER funding. JCMM also acknowledges Spanish Ministry of Science, Innovation and Universities for the financial support through a FPU grant (FPU17/00603).

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., This research was funded by Generalitat Valenciana (PROMETEO/2018/076 and Spanish Government (PID2019-105542RB-I00) and EU (FEDER Founding).

The preferential oxidation of CO in H2-rich mixtures has been studied using Ce0.8Zr0.2O2-supported Cu catalysts containing increasing amounts of copper [1 wt% (Cu1/CZ), 2 wt% (Cu2/CZ) and 4 wt% (Cu4/CZ)]. The oxide support was prepared by co-precipitation and the copper was incorporated using the wetness impregnation method. The catalysts were characterized using N2 adsorption, XRD, STEM-XEDS, H2-TPR, H2 chemisorption and XPS techniques. In particular, the complementarity of electron microscopy and hydrogen chemisorption techniques was found to be very useful for elucidating one of the most challenging properties of copper catalysts, namely their dispersion. The results show that the Cu1/CZ catalyst is the most active in the CO-PROX reaction at low temperatures (<125 °C), despite having a lower copper content. The results are discussed and correlated with the textural properties of the catalysts and with parameters such as metal dispersion and the binary interfacial active sites., The authors gratefully acknowledge financial support from the Generalitat Valenciana (PROMETEO/2018/076 project), the Spanish Ministry of Science and Innovation (PID2019-105542RB-I00 and MAT2017-87579-R projects) and UE-FEDER. J.C. Martínez-Munuera also acknowledges the Spanish Ministry of Science and Innovation for financial support through an FPU grant (FPU17/00603).

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., This research was funded by the Generalitat Valenciana (PROMETEO/2018/076), Spanish Government (PID2019-105542RB-I00) and the EU (FEDER Founding).

A series of BaMn0.7Cu0.3O3 solids were prepared by a modified sol-gel method in which carbon black (VULCAN XC-72R), and different calcination temperatures (BMC3-CX, where X indicates the calcination temperature) have been used. The fresh and used catalysts were characterized by ICP-OES, XRD, XPS, FESEM, TEM, O2-TPD and H2-TPR. The presence of a carbon black during sol-gel synthesis of BMC3 mixed oxide allows diminishing the calcination temperature needed to achieve the perovskite structure, but it hinders the formation of the BaMnO3 polytype. The use of low calcination temperatures during synthesis reduces the sintering effects, and the mixed oxides present lower particle size, slightly higher BET surface areas and macropores with lower diameter than BMC3. The distribution of copper in BMC3-CX catalysts depends on the calcination temperature and copper insertion into the perovskite structure is promoted as the calcination temperature increases. All BMC3-CX catalysts are active for NO to NO2 and NOx-assisted soot oxidation processes, but only BMC3-C600 and BMC3-C700 show higher catalytic activity than BMC3 reference catalyst. BMC3-C600 presents the best performance as it features a high amount of surface copper and oxygen vacancies that increase during reaction. The comparison between the performance of the two best catalysts of the BM-CX series (BM-C700) and the BMC3-CX series (BMC3-C600) suggests that the unique advantage of using copper in the modified sol-gel synthesis is an additional decrease of 100 °C in the calcination temperature used for the synthesis of the best catalyst, which is 700 °C for BM-CX and 600 °C for BMC3-CX., This research was funded by Spanish Government (PID2019-105542RB-I00) and EU (FEDER Founding).

Mixed oxides with perovskite-type structure (ABO3) present interesting physico-chemical properties to be used as catalyst for atmospheric pollution control. In this work, a series of CuX/Ba0.7MnO3 catalysts (being x: 0, 4, 8 and 12 wt%) has been synthesized, characterized and tested for CO oxidation reaction. All the catalysts were active for CO oxidation in the two reactant mixtures tested: low CO mixture (0.1% CO and 1% O2 in He) and near stoichiometric mixture (1% CO and 1% O2 in He). Copper-free perovskite is the most active catalyst in the less demanding conditions (0.1% CO and 1% O2), as it presents the highest amount of oxygen vacancies working as active sites. However, at higher CO concentrations (1% CO in near stoichiometric mixture), copper-containing catalysts were more active than the perovskite support because, due to the saturation of the oxygen vacancies of perovskites, CuO seems to participate as active site for CO and O2 activation. Cu4/Ba0.7MnO3 and Cu12/Ba0.7MnO3 are more active than Cu8/Ba0.7MnO3 catalyst, since they present a larger amount of active sites on surface. These two copper-containing catalysts present a high stability and recyclability during the reaction at 300 °C in an ideal near stoichiometric mixture (1% CO and 1% O2)., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This work was supported by Ministerio de Ciencia,Innovación y Universidades, (Grant No. PID2019-105542RB-I00), María José Illán Gómez, European Regional Development Fund, Generalitat Valenciana, (Grant No. CIPROM/2021-070 project), María José Illán Gómez, Universidad de Alicante.

Gasoline engines, mainly gasoline direct injection engines (GDI) require, in addition to three-way catalysts (TWC), a new catalytic system to remove the formed soot. Gasoline Particle Filters (GPF) are, among others, a possible solution. BaMnO3 and copper-doped BaMnO3 perovskites seem to be a feasible alternative to current catalysts for GPF. The physical and chemical properties of these two perovskites determining the catalytic performance have been modified using different synthesis routes: (i) sol-gel, (ii) modified sol-gel and iii) hydrothermal. The deep characterization allows concluding that: (i) all samples present a perovskite-like structure (hexagonal), except BMC3 which shows a polytype one (due to the distortion caused by copper insertion in the lattice), and ii) when a low calcination temperature is used during synthesis, the sintering effect decreases and the textural properties, the reducibility and the oxygen mobility are improved. The study of soot oxidation simulating the hardest GDI scenarios reveals that, as for diesel soot removal, the best catalytic performance involves the presence of oxygen vacancies to adsorb and activate oxygen and a labile Mn (IV)/Mn (III) redox pair to dissociate the adsorbed oxygen. The combination of both properties allows the transport of the dissociated oxygen towards the soot., This research was funded by Generalitat Valenciana (CIPROM/2021/70), Spanish Government (PID2019-105542RB-I00) and EU (FEDER Founding).

In this work, it is analyzed the effect of the partial substitution of Fe by Ni in a BaFeO3 perovskite to be used as the catalyst for NOx-assisted diesel soot oxidation. A series of BaFe1−xNixO3 (x = 0, 0.2, 0.4 and 0.8) catalysts have been synthesized by using the sol–gel method. The catalysts have been characterized by ICP-OES, XRD, XPS, O2-TPD, H2-TPR- and TEM. The catalytic activity for NO to NO2 oxidation and NOx-assisted diesel soot oxidation have been determined by Temperature Programmed Reaction experiments (NOx -TPR and Soot-NOx-TPR, respectively) and by isothermal reaction at 450 °C. Ni seems not to be inserted in the BaFeO3 perovskite and, instead of that, BaNiO3 perovskite and NiO are detected on the surface of the perovskite BaFeO3. XPS data reveal the coexistence of Fe(III) and Fe(IV) on the catalyst’s surface (being Fe(III) the main oxidation state) and the presence of oxygen vacancies. All catalysts are active for NO oxidation to NO2, showing BaFeO3 and BaFe0.6Ni0.4O3 the best catalytic performance. BaFe0.6Ni0.4O3 shows the highest proportion of nickel on surface and it combines the highest activity and stability for NOx-assisted diesel soot oxidation. Also, this catalyst presents the highest initial soot oxidation rate which minimizes the accumulation of unreacted soot during reaction., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This study was funded by the Spanish Government (MINCINN: PID2019-105542RB-I00/AEI/10.13039/501100011033 Project), by the European Union (FEDER Funds), by the Regional Government (Generalitat Valenciana CIPROM/2021-070 project) and by the University of Alicante (Final Master’s Project grant of S. Montilla-Verdú).

Carbon-ceramic composites (C/Cer) have been prepared by chemical vapor deposition of coal tar pitch onto clay substrates and characterized by thermogravimetric analyses, powder X-ray diffraction, Raman spectroscopy, and scanning and transmission electron microscopies (SEM and TEM). The study of the dc electrical conductivity, together with the determination of the Hall voltage sign, proves that such C/Cer composites are n-type semiconductors. Our results demonstrate that: 1) the mechanism of electrical conduction of C/Cer semiconductors proceeds through the pathways expected for amorphous solids (ie. variable-range hopping and heat-activated pathways at low and high temperatures, respectively); and 2) their transport properties are strongly dependent on the clay components, as evidenced by microscopy experiments., The authors would like to thank the financial support from Ministerio de Ciencia e Innovación (grant No. PID2019-105542RB-I00/AEI/10.13039/501100011033), the European Union (FEDER Funds), and Generalitat Valenciana (grant No. PROMETEO CIPROM/2021/70).

This research work focuses on a preliminary study of the behaviour of several ceria-praseodymia mixed oxides along with three model catalysts under isotopic oxygen pulses at different temperatures in an attempt to investigate their ability to interact with 18O2 (uptaking/releasing/exchanging) with their own lattice oxygen, under conditions which could simulate those existing in GDI exhaust gases. Furthermore, these ceria-praseodymia mixed oxides were studied to explore their responses towards soot combustion under two consecutive 18O2 pulses at 500 oC. It was observed that the capacity of oxygen activation and uptake is very dependent on the nature of the catalyst. Ce1-xPrxO2-δ catalysts present different responses in the O2 activation and uptake processes, as a function of temperature, praseodymium content and method of preparation. Moreover, some of these ceria-praseodymia formulations exhibited high soot combustion activity with a marked intervention of unlabelled active oxygen species during the inert period after the 18O2 pulse., The authors gratefully acknowledge the financial support of Generalitat Valenciana (CIPROM/2021/070 project) and the Spanish Ministry of Science and Innovation/Research Spanish Agency (PID2019-105542RB-I00 /AEI/10.13039/501100011033 project) and the UE-FEDER funding. JCMM acknowledges Spanish Ministry of Science and Innovation for the financial support through a FPU grant (FPU17/00603). MCR also wants to thank the University of Alicante for the financial support for the internship (INV19-07).

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., This research was funded by the Spanish Government (MINCINN: PID2019-105542RB-I00/AEI/10.13039/501100011033 Project), the European Union (FEDER Funds), and Generalitat Valenciana (CIPROM/2021-070 Project).

The present work aims to assess the impact of morphology and reducibility on lanthanum-doped ceria nanocatalysts with controlled morphology on the NO oxidation reaction. Specifically, samples were prepared using a hydrothermal method incorporating lanthanum at varying molar concentrations (0, 5, 10, and 15 mol.%) into ceria with a controlled morphology (nanocubes and nanorods). The structural, compositional, and redox characterization of these catalysts has been performed via scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (X-EDS), inductively coupled plasma (ICP), hydrogen temperature-programmed reduction (H2-TPR), and oxygen storage capacity (OSC). NO oxidation catalytic tests were conducted, and the results were compared with estimated curves (obtained by considering the proportions of the corresponding components), which revealed the presence of a synergistic effect between lanthanum and ceria. The degree of enhancement was found to depend on both the morphology and the amount of lanthanum incorporated into CeO2. These findings may facilitate the optimization of features concerning ceria-based nanocatalysts for the removal of NOx emissions from exhaust gases., This research was funded by Generalitat Valenciana (CIPROM/2021/070 project), the Spanish Ministry of Science and Innovation/Research Spanish Agency (PID2019-105542RB-I00/AEI/10.13039/501100011033, PID2020-113006RB-I00/AEI/10.13039/501100011033 and PID2020-113809RB-C33 projects), and UE-FEDER funding.

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)., This research was funded by Ministerio de Ciencia e Innovacion (MINCINN: PID2019-105542RB-I00/AEI/10.13039/501100011033 project), the European Union (FEDER Funds), and the Generalitat Valenciana (CIPROM/2021-070).

In this work, several ceria-zirconia based catalysts with very low (and equimolar) metal contents were prepared, characterised and tested for the CO oxidation reaction (under lean and stoichiometric conditions), trying to emulate those conditions found in a diesel oxidation catalyst (DOC) system from a diesel engine and those encountered under gasoline exhaust (λ = 1). The metals chosen are Cu, Co, Ag and Pt (as a reliable benchmark). The results reveal enormous differences among reducibility and catalytic activity despite quite similar structural and textural properties of the catalysts, showing differences among dispersion (Ag-catalyst seems to present a low level of dispersion). This catalyst seems to be characterised, as well, by a strong electronic interaction between Ce and Ag centres which is suggested to yield an improved reducibility under H2-TPR conditions. Nevertheless, the order in catalytic activity (Cu > Ag > Co ≈ Pt >> support) seems not to follow the order found in reducibility and the Cu-catalyst seems to be the most active independently on the reaction conditions, yielding nearly overlapped CO oxidation catalytic curves. Interestingly, a strong correlation between the catalytic activity under the two conditions tested and the OSC values of the Ce0.8Zr0.2O2-supported metal catalysts is found. Therefore, OSC parameter measured at 150 °C can be used as a relevant descriptor to evaluate the CO oxidation activity at low and medium conversions for the investigated catalysts, much better than the H2-TPR measurements., The authors gratefully acknowledge the financial support of the Spanish Ministry of Science and Innovation/Research Spanish Agency (PID2019-105542RB-I00/AEI/10.13039/501100011033 project), UE-FEDER funding and Generalitat Valenciana (CIPROM/2021/070 project). JCMM acknowledges Spanish Ministry of Science and Innovation for the financial support through a FPU grant (FPU17/00603).

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 Ba0.9Ce0.1Mn0.7Cu0.3O3 (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., This research was funded by the Spanish Government (MINCINN: PID2019-105542RB-I00/AEI/10.13039/501100011033 Project), the European Union (FEDER Funds), and Generalitat Valenciana (CIPROM/2021-070 Project). N. Ghezali thanks Argelian Government for her thesis grant and Á. Díaz-Verde of the University of Alicante for his predoctoral contract.

In this study, we analyzed the role of a series of BaMn1−xNixO3 (x = 0, 0.2, and 0.4) mixed oxide catalysts, synthesized using the sol–gel method, in NOx-assisted diesel soot oxidation. ICP-OES, XRD, XPS, and H2-TPR techniques were used for characterization and Temperature-Programmed Reaction experiments (NOx-TPR and Soot-NOx-TPR), and isothermal reactions at 450 °C (for the most active sample) were carried out to determine the catalytic activity. All samples catalyzed NO and soot oxidation at temperatures below 400 °C, presenting nickel-containing catalysts with the highest soot conversion and selectivity to CO2. However, the nickel content did not significantly modify the catalytic performance, and in order to improve it, two catalysts (5 wt % in Ni) were synthesized via the hydrothermal method (BMN2H) and the impregnation of nickel on a BaMnO3 perovskite as support (M5). The two samples presented higher activity for NO and soot oxidation than BMN2E (obtained via the sol–gel method) as they presented more nickel on the surface (as determined via XPS). BMN2H was more active than M5 as it presented (i) more surface oxygen vacancies, which are active sites for oxidation reactions; (ii) improved redox properties; and (iii) a lower average crystal size for nickel (as NiO). As a consequence of these properties, BMN2H featured a high soot oxidation rate at 450 °C, which hindered the accumulation of soot during the reaction and, thus, the deactivation of the catalyst., This research was funded by the Spanish Government (MINCINN: PID2019-105542RB-I00/AEI/10.13039/501100011033 Project), the European Union (FEDER Funds), and Generalitat Valenciana (CIPROM/2021-070 Project). A. Díaz-Verde thanks the University of Alicante for his predoctoral contract.

BaMnO3 (BM) and Ba0.9A0.1MnO3 (BM-A) (A = Ce, La or Mg) perovskite-type mixed oxides were synthesized by the aqueous sol–gel method; thoroughly characterized by ICP-OES, XRD, H2-TPR, BET, and O2-TPD; and tested as catalysts for CO oxidation under simulated automobile exhaust conditions. The characterization results indicate that the main effects of the partial substitution of Ba with A-metal in BM perovskite are the maintenance of the hexagonal structure of the perovskite and the increase in reducibility and oxygen mobility. All samples catalyze the CO to CO2 oxidation reaction in the different reactant mixtures employed, showing the best performance for the mixture with the lowest CO/O2 ratio and in the presence of a dopant in the BM perovskite formulation. BM-La is the most active catalyst for improving CO oxidation, as it is the most reducible, and because is able to evolve oxygen at intermediate temperatures., This research was funded by the Spanish Government (MINCINN: PID2019-105542RB-I00/AEI/10.13039/501100011033 Project), the European Union (FEDER Funds), and Generalitat Valenciana (CIPROM/2021-070 Project). N. Ghezali thanks Argelian Government for her thesis grant and Á. Díaz-Verde of the University of Alicante for his predoctoral contract.

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., This research was funded by the Spanish Government (MINCINN: PID2019-105542RB-I00/AEI/10.13039/501100011033 Project), the European Union (FEDER Funds), and Generalitat Valenciana (CIPROM/2021-070 Project). N. Ghezali thanks Argelian Government for her thesis grant and Á. Díaz-Verde thanks the University of Alicante for his predoctoral contract.

Soot combustion experiments with 5%O2/He were conducted using model soot, and four distinct compositions of CexPr1-xO2-δ oxides of varying nominal cerium compositions (x = 0, 0.2, 0.3, and 1) were prepared. The catalyst samples were comprehensively characterized using techniques such as XRD, Raman spectroscopy, HR-TEM, N2 adsorption at −196 °C, XPS, O2-TPD, H2-TPR, and work function measurements. The Pr-rich compositions, ranging from Ce0.3Pr0.7O2-δ to PrO2-δ, resulted in a significant increase in the total evolved O2 amounts and enhanced catalyst reducibility. However, a decrease in the textural properties of the catalysts was noted, which was particularly important for the pure praseodymia under the synthesis route conducted. The catalytic activity was investigated under the two following contact modes of mixing between soot and catalyst: loose and tight. The results revealed that the catalytic performance is associated with the surface contact in tight contact mode and with the combination of surface/subsurface/bulk oxygen mobility and the BET surface area in loose contact mode. Notably, the temperatures estimated at 10% and 50% of the conversion (T10 and T50) parameters were achieved at much lower temperatures than the uncatalyzed soot combustion, even under loose contact conditions. Specifically, the 50% conversion was achieved at 511 °C and 538 °C for Ce0.3Pr0.7O2 and Ce0.2Pr0.8O2, respectively. While no direct correlation between catalytic activity and work function was observed, a significant relationship emerges between work function values and the formation of oxygen vacancies, whatever the conditions used for these measurements. On the other hand, the ability to generate a high population of oxygen vacancies at low temperatures, rather than the direct activation of gas-phase O2, influences the catalytic performance of Pr-doped ceria catalysts, highlighting the importance of surface/subsurface oxygen vacancy generation, which was the parameter that showed a better correlation with the catalytic activity, whatever the soot conversion value or the mode of contact considered., This research was funded by the financial support of the Spanish Ministry of Science and Innovation/Research Spanish Agency (PID2019-105542RB-I00/AEI/10.13039/501100011033 project), UE-FEDER funding, and Generalitat Valenciana (CIPROM/2021/070 project). I.M. also acknowledges the Algerian Ministry of Higher Education and Scientific Research for the financial support provided through the national grant.

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., This research was funded by the Spanish Government (MINCINN: PID2019-105542RBI00/AEI/10.13039/501100011033 Project), the European Union (FEDER Funds), and Generalitat Valenciana (CIPROM/2021-070 Project). N.G. thanks Argelian Government for her thesis grant, and Á.D.V. thanks the University of Alicante for his predoctoral contract.

In the present work, a series of supports with varying compositions (ranging from pure CeO2 to pure PrO2-y) was designed to investigate their ability to release oxygen (with the concomitant formation of oxygen vacancies) under diverse reducing atmospheres: hydrogen (H2), helium (He), and in the presence of a carbonaceous substance that mimics eventual carbon deposits formed under practical reaction conditions (DRM). Oxygen vacancies were generated effectively in all three atmospheres (following the order He < H2 < carbon material). With regard to the influence of the composition, the capability to generate oxygen vacancies clearly increased with the Pr content, for whatever the conditions tested. Notably, the non-stoichiometry obtained with the support of pure praseodymia in both inert and reducing atmospheres is very remarkable, as it approaches the maximum non-stoichiometry value of the well-established theoretical Bevan cluster. This leads to consider this formulation as a very promising support for applications in catalysis and other fields where oxygen vacancies play a crucial role. Dry Reforming of Methane requires catalytic supports that possess highly mobile oxygen, enabling it to actively participate in the reactions step involved or potentially gasify undesirable carbon deposits generated during parallel reactions. Consequently, designing and elucidating the behavior of ceria-praseodymium-based supports with high reducibility and generation of oxygen vacancies (oxygen storage and release capacity) holds particular relevance in this context. Actually, the very preliminary results comparing two counterpart formulations (5%Ni/PrO2-y versus 5%Ni/Al2O3) already confirm the suitability of the choice of pure praseodymia in terms of activity, stability and very high selectivity towards H2 and CO, reaching a very close value to the ideal H2/CO ratio of 1., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. L.H.S. and A.G.G gratefully acknowledge the financial support of Generalitat Valenciana through a PROMETEO project (CIPROM/2021/070 project) and through the co-financing Organism PRTR—NextGeneration EU (INVEST/2022/253). The financial support from the Ministry of Science and Innovation is also acknowledged (PID2019-105542RB-I00/AEI/https://doi.org/10.13039/501100011033 project). Finally, the authors acknowledge ELECMI-ICTS (code of proposal: ELC181-2023) for the hours allocated allowing the use of the node: TEM/DME Cádiz/TALOS F200X.

Mixed oxides featuring perovskite-type structures (ABO3) offer promising catalytic properties for applications focused on the control of atmospheric pollution. In this work, a series of BaxMnO3 (x = 1, 0.9, 0.8 and 0.7) samples have been synthesized, characterized and tested as catalysts for CO oxidation reaction in conditions close to that found in the exhausts of last-generation automotive internal combustion engines. All samples were observed to be active as catalysts for CO oxidation during CO-TPRe tests, with Ba0.7MnO3 (B0.7M) being the most active one, as it presents the highest amount of oxygen vacancies (which act as active sites for CO oxidation) and Mn (IV), which features the highest levels of reducibility and the best redox properties. B0.7M has also showcased a high stability during reactions at 300 °C, even though a slightly lower CO conversion is achieved during the second consecutive reaction cycle. This performance appears to be related to the decrease in the Mn (IV)/Mn (III) ratio., This research was funded by the Spanish Government (MINCINN: PID2019-105542RB-I00 Project), the European Union (FEDER Funds) and the Generalitat Valenciana (Prometeo II 2018/076 Project). Á. Díaz-Verde thanks the University of Alicante for his predoctoral contract.