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•Strontium doping enhances NOx storage and reduction performance of bulk LaCoO3.•30% is the optimum strontium doping degree for bulk perovskites, La0.7Sr0.3CoO3.•A more efficient use ...of the perovskite can be achieved by supporting it over Al2O3.•Perovskite loading around 30% over Al2O3 maximizes its utilization.•NSR performance was better for Al2O3 supported perovskites than bulk ones.
Here we report the effects of strontium doping of perovskites (La1-xSrxCoO3) on NOx storage and reduction (NSR) as well as the effects of supporting the perovskite onto an alumina support. The NSR capacity of La0.7Sr0.3CoO3 improved with strontium doping: this material displayed a good balance between NO oxidation capacity and adsorption sites accessibility. Increased accessibility was mainly due to the strontium oxide segregates. In addition, different loadings of La0.7Sr0.3CoO3 perovskite (10, 20, 30, 40 and 50%) were impregnated onto alumina in order to increase the exposed surface area of the perovskite. This had the effect of increasing the NSR capacity of the perovskite. The results of X-Ray diffraction, UV–vis–NIR spectroscopy, N2 adsorption-desorption, electron microscopy, and temperature programmed techniques, demonstrated that the cobalt ions preferably formed cobalt aluminate (CoAl2O4) in the case of low perovskite loadings (<20%). Meanwhile, a well-developed perovskite phase was observed with the higher loadings (>30%). The specific NO oxidation rate per gram of perovskite increased dramatically with the incorporation onto an alumina support. 30% LSCO/Al2O3 sample had an oxidation rate of 138 μmol min-1 (g LSCO)-1 at 350 °C, more than double the rate of the bulk La0.7Sr0.3CoO3 (49 μmol min−1 (g LSCO)−1). Likewise, the 30% LSCO/Al2O3 sample had a higher NOx storage capacity than its bulk counterpart at 400 °C: 306 vs. 115 μmol (g LSCO)−1. The higher oxidation capacity of the alumina-supported samples also facilitated the diffusion of the intermediate compounds from oxidation to adsorption sites. Impregnating alumina with perovskite could be used to improve the efficiency of perovskite mediated NOx removal in automobile applications. Furthermore, adding palladium onto optimum alumina-supported perovskite sample, i.e. 1.5% Pd-30% LSCO/Al2O3, resulted in a clear improvement in NOx storage and reduction capacity. This last sample demonstrated a nitrogen yield as high as 65%, an improvement over the model Pt-based NSR catalyst.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•LaNiO3-derived DFMs for CO2 adsorption and hydrogenation to CH4 are analyzed.•LaNiO3 and 30% LaNiO3/support (support = CeO2, Al2O3 and La-Al2O3) precursors.•CeO2 favours a smaller ...Ni0 particle size and a higher medium-strong basicity.•CeO2-based DFM maintains high CH4 production (80–103 µmol g−1) between 280 and 520 °C.•CeO2-based DFM shows high stability and activity lost recovery in absence of O2.
The valorisation of CO2 through its capture and in-situ hydrogenation to methane, using dual function materials (DFMs), emerges as promising alternative to reduce CO2 emissions to atmosphere and the global cost of current CO2 Capture and Utilization (CCU) technology. This work investigates the viability of LaNiO3-derived formulations as precursors of DFMs for CO2 capture and in-situ conversion to CH4. For this purpose, a set of DFMs obtained from 30% LaNiO3/CeO2, 30% LaNiO3/Al2O3, 30% LaNiO3/La-Al2O3 and LaNiO3 precursors were synthesized and systematically characterized before and after a controlled reduction process. Results of XRD analysis, STEM-EDX images, H2-TPR and CO2-TPD experiments reveal that the DFM obtained after reduction of 30% LaNiO3/CeO2 formulation shows the smallest Ni0 particle size (7 nm) and the highest medium-strong basic sites concentration. In fact, this DFM widens operation window with methane production ranging between 80 and 103 µmol g−1 and maintains a selectivity towards methane above 90% in the range of 280–520 °C. The best catalytic behaviour is related to a better contact between the different nature basic sites and the homogenously distributed Ni0 sites, which favours a fast spill-over of dissociated H to near CO2 adsorption sites. The applicability of this formulation is further evidenced by a highly stable CH4 production during long-term experiments and a promoted Ni0/NiO reversibility in the absence/presence of O2 during the CO2 adsorption period, which allows a fast and complete recovery of CH4 production in absence of O2. These aspects favour a versatile application of the 30% LaNiO3/CeO2-based DFM formulation to convert CO2 outlet streams from combustion flue gases of different nature.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A detailed analysis of the DeNO x activity of the novel 0.5% Pd-30% La0.5Ba0.5CoO3/Al2O3 formulation in its application to the single-NSR and combined NSR–SCR systems is carried out using response ...surface methodology (RSM). The complete operational map of the NSR and NSR–SCR configurations has been obtained for any combination of reaction temperature in each catalytic bed (T NSR/T SCR = 150–450 °C) and H2 concentration (C H2 = 1%–4%) in the feed stream during the rich period. In the NSR–SCR configuration, a 4% Cu/SAPO-34 catalyst is placed downstream of the perovskite-based formulation as a SCR formulation. On the basis of the response surface curves of single-NSR system, the operational conditions have been tuned in order to maximize the NO x to N2 conversion of the coupled NSR–SCR system, minimizing the NH3 and N2O productions. The H2 concentration and reaction temperature of the NSR system must be controlled to generate a stoichiometric amount of NH3 to reduce the NO x slipping NSR catalyst in the SCR system placed downstream. The novel NSR–SCR system shows N2 yields above 75% in a wide working window (T NSR/T SCR = 175–425 °C and C H2 = 2%–4%). Specifically, the maximum N2 yield is as high as 92%, when NSR and SCR catalysts were working at 300 °C with a H2 concentration of 3%. Under these conditions NH3 slip and N2O production were nearly zero. In fact, the NO x removal efficiency and hydrothermal stability of NSR and NSR–SCR systems based on 0.5% Pd-30% La0.5Ba0.5CoO3/Al2O3 and model NSR catalysts (1.5% Pt-15% BaO/Al2O3) are comparable. Taking into account the significant decrease of noble metal content, these results demonstrate that the developed catalyst can be considered as a promising alternative for NO x removal by NSR and NSR–SCR technologies.
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IJS, KILJ, NUK, PNG, UL, UM
This work investigates the viability of 10–50% LaNiO3/CeO2 formulations, prepared by combined citric acid and impregnation methods, as precursors of highly active and stable materials for CO2 ...methanation. The prepared materials were widely characterized before and after the controlled reduction process. XRD and STEM-EDS mapping analysis confirmed the ex-solution of Ni NPs during reduction of LaNiO3/CeO2 formulations, leading to Ni–La2O3/CeO2 formation. Low LaNiO3 loading favored the ex-solution of small-sized Ni NPs (<5 nm) highly dispersed over CeO2 and La2O3 surfaces. H2-TPR experiments revealed that the higher reducibility of the samples prepared with low LaNiO3 loading promoted the H2 activation at lower temperatures. XPS experiments suggest that this promotion is due to the higher accessibility of Ni as well as Ni–ceria interaction. The material obtained after the reduction of the 10% LaNiO3/CeO2 formulation shows a higher concentration of weak–medium basic sites due to a higher accessibility of Ni NPs, La2O3 phase and Ni–CeO2 interface. The easier hydrogenation of CO2 adsorbed on these basic sites, together with the promoted H2-activation, maximized the CO2 methanation in the kinetically controlled region for this catalyst up to 71%. The intensification of Ni, La2O3 and CeO2 interactions also enhanced the CO2 methanation efficiency and the stability of the conventional 8.5% Ni/CeO2 catalyst. Thus, the 10% LaNiO3/CeO2 precursor emerges as a novel formulation to obtain highly active, selective and stable catalysts for CO2 methanation.
Mitigation of CO2 emissions by integrated CO2 capture and utilization (ICCU) is challenging. This work focuses on widening operation temperature window of the hydrogenation of adsorbed CO2 to CH4. ...For this, a set of dual function materials (DFMs) 4%Ru-x%Na2CO3-y%CaO/γ-Al2O3 are prepared. DFMs are deeply characterized by N2 adsorption-desorption, XRD, H2 chemisorption, TEM, H2-TPR and CO2-TPD. The catalytic behavior, in cycles of CO2 adsorption and hydrogenation to CH4, is evaluated and the temporal evolution of the concentration of reactants and products is analyzed. The presence of both adsorbents in the DFMs improves ruthenium dispersion and the basicity is modulated with the Na2CO3/CaO ratio. Ru-8Na/8Ca improves methane production over the whole temperature window compared to DFMs based only on a unique adsorbent. The best results are assigned to the promotion of contact between the carbonates of medium strength with the metallic sites, which boost the CO2 adsorption and hydrogenation to CH4.
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•Ru-Na2CO3-CaO/Al2O3 DFMs for CO2 adsorption and hydrogenation to CH4 are reported.•The joint presence of Na and Ca in the DFM boost the Ru dispersion.•By varying the Na2CO3/CaO ratio it is possible to modulate the basicity.•The presence of Na and Ca boost the contact between the carbonates and metal sites.•Ru-8Na/8Ca produces 364 μmol g−1 of CH4 at 370 °C with a selectivity of 99%.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Ru-Na2CO3-CaO/Al2O3 DFMs for CO2 adsorption and hydrogenation to CH4 are synthesized.•DFMs are subjected to different calcination protocols in static or dynamic streams.•The calcination atmosphere ...influences the DFM physicochemical properties.•Calcination under N2 stream accommodates better the adsorbent and Ru phases.•RuNaCa-N2 is most efficient for CH4 production (449 µmol g−1 at 370°C) with high selectivity.
Integrated CO2 capture and utilization (ICCU) technology requires dual functional materials (DFMs) to carry out the process in a single reaction system. The influence of the calcination atmosphere on efficiency of 4% Ru-8% Na2CO3-8% CaO/γ-Al2O3 DFM is studied. The adsorbent precursors are first co-impregnated onto alumina and calcined in air. Then, Ru precursor is impregnated and four aliquotes are subjected to different calcination protocols: static air in muffle or under different mixtures (10% H2/N2, 50% H2/N2 and N2) streams. Samples are characterized by XRD, N2 adsorption-desorption, H2 chemisorption, TEM, XPS, H2-TPD, H2-TPR, CO2-TPD and TPSR. The catalytic behavior is evaluated, in cycles of CO2 adsorption and hydrogenation to CH4, and temporal evolution of reactants and products concentrations is analyzed. The calcination atmosphere influences the physicochemical properties and, ultimately, activity of DFMs. Characterization data and catalytic performance discover the acccomodation of Ru nanoparticles disposition and basic sites is mostly influencing the catalytic activity. DFM calcined under N2 flow (RuNaCa-N2) shows the highest CH4 production (449 µmol/g at 370°C), because a well-controlled decomposition of precursors which favors the better accomodation of adsorbent and Ru phases, maximizing the specific surface area, the Ru-basic sites interface and the participation of different basic sites in the CO2 methanation reaction. Thus, the calcination in a N2 flow is revealed as the optimal calcination protocol to achieve highly efficient DFM for integrated CO2 adsorption and hydrogenation applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The influence of the adsorbent nature on the CO2 capture and in situ methanation efficiency of novel Dual Function Materials (DFMs) is studied. Several 20% La0.7A0.3NiO3/CeO2–type precursors, with ...La3+ partially substituted by basic metal oxides (Na, K, Ca and Ba) are prepared. Samples are deeply characterized before and after catalytic tests by XRD, N2 adsorption-desorption, H2-TPR, H2-TPD, STEM-EDS, XPS, CO2-TPD and H2-TPSR. Characterization results show that Ca2+ and Ba2+ cations accommodate better inside the perovskite structure, due to their similarity in oxidation state and ionic radius to La3+. Corresponding DFMs result in enhanced textural properties, more homogenous phase distribution and promoted surface basic sites accessibility and concentration. Finally, the higher proximity and interactions between CO2 adsorption and active sites enhances CH4 formation in a wider temperature window. The order of reactivity has been observed in terms of CH4 production: Ca-doped ≥ Ba-doped > non-doped ≫ Na-doped > K-doped. The 20% La0.7Ca0.3NiO3/CeO2-derived DFM improves methane production of the conventional 15% Ni-15% CaO/Al2O3 DFM (128.0 vs. 118.0 μmol CH4 g−1 at 400 ºC) in the presence of CO2 during the adsorption period, whereas the incorporation of O2 and/or NOx during the adsorption period shows similar detrimental effect in both cases. However, the partial confinement of Ni nanoparticles (NPs) on Ni-La2O3, Ni-CaO or La-Ce-O interfaces prevents synthesized DFM from deactivation and promotes its regenerability related to the conventional formulation. Thus, Ca doping emerges as the more effective way of tailoring CO2 adsorption and in-situ hydrogenation to CH4 efficiency of 20% LaNiO3/CeO2-derived DFMs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Diesel engines operate under net oxidizing environment favoring lower fuel consumption and CO2 emissions than stoichiometric gasoline engines. However, NOx reduction and soot removal is still a ...technological challenge under such oxygen-rich conditions. Currently, NOx storage and reduction (NSR), also known as lean NOx trap (LNT), selective catalytic reduction (SCR), and hybrid NSR–SCR technologies are considered the most efficient control after treatment systems to remove NOx emission in diesel engines. However, NSR formulation requires high platinum group metals (PGMs) loads to achieve high NOx removal efficiency. This requisite increases the cost and reduces the hydrothermal stability of the catalyst. Recently, perovskites-type oxides (ABO3) have gained special attention as an efficient, economical, and thermally more stable alternative to PGM-based formulations in heterogeneous catalysis. Herein, this paper overviews the potential of perovskite-based formulations to reduce NOx from diesel engine exhaust gases throughout single-NSR and combined NSR–SCR technologies. In detail, the effect of the synthesis method and chemical composition over NO-to-NO2 conversion, NOx storage capacity, and NOx reduction efficiency is addressed. Furthermore, the NOx removal efficiency of optimal developed formulations is compared with respect to the current NSR model catalyst (1–1.5 wt % Pt–10–15 wt % BaO/Al2O3) in the absence and presence of SO2 and H2O in the feed stream, as occurs in the real automotive application. Main conclusions are finally summarized and future challenges highlighted.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The CO2 methanation mechanism over the highly active (TOF=75.1 h−1), selective (>92%) and stable 10% LaNiO3/CeO2-derived catalyst is still unresolved. The surface of the catalyst is monitored under ...hydrogenation (H2), oxidizing (CO2) and CO2 methanation (H2 +CO2) conditions by near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) using synchrotron radiation. Meanwhile, the main reaction intermediates are identified by in situ FTIR analysis. NAP-XPS experiments confirm that LaNiO3 perovskite reduction leads to the ex-solution of Ni0 nanoparticles and Ni2+CeO2−x and Ni2+La2O3 interfaces conformation, favouring the CO2 adsorption and the H2 dissociation/transfer. In situ FTIR experiments combined with the C1s spectra (NAP-XPS) suggest that the CO2 activation occurs on CeO2−x (oxygen vacancies and OH–) at low temperatures, in the form of bicarbonates; whereas, mono-/bidentate carbonates are formed on different strength La2O3 sites at increasing temperatures. These species are consecutively reduced to formates, as the main reaction intermediate, and methane by the H spilled from Ni0 nanoparticles near to NiOCeO2−x and NiOLa2O3 interfaces.
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•Novel 10% LaNiO3/CeO2-derived catalyst with high CO2 to CH4 conversion and stability.•The role and the nature of different active sites is explored by NAP-XPS experiments.•Key reaction intermediates are identified by in situ FTIR analysis.•Ni0 nanoparticles as well as Ni2+CeO2−x/Ni2+La2O3 are conformed after reduction.•Formate acts as main reaction intermediate based on FTIR and NAP-XPS results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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