Display omitted
•Nickel catalysts supported on various metal oxides were prepared.•The activity of nickel catalysts for CO2 methanation was evaluated.•The Ni/Y2O3 catalyst exhibited the highest ...activity.•The reaction mainly proceeded via the formation of formate over Ni/Y2O3.
Carbon dioxide methanation is well known to offer some advantages and be catalyzed by Ru, Rh, Pd, and Ni. In this study, Ni catalysts supported on various metal oxides were fabricated and their catalytic activity for CO2 methanation was evaluated. The CO2 conversion for most of catalysts drastically increased at 225–250°C and reached a maximal value at 300–350°C. The order of CH4 yield at 250°C was as follows: Ni/Y2O3>Ni/Sm2O3>Ni/ZrO2>Ni/CeO2>Ni/Al2O3>Ni/La2O3. The catalytic activity could be partly explained by the basic property of the catalysts. Moreover, the chemical species formed on the catalyst surface during CO2 methanation were examined by in situ infrared spectroscopy. From the obtained results, the difference in the activity depending on the support material of Ni catalysts was discussed.
Display omitted
•The Ni/Al2O3 catalysts modified by rare-earth elements were investigated.•The addition of rare-earth elements promoted ammonia decomposition reaction.•La-modified Ni/Al2O3 was most ...active in this study.•The hydrogen inhibition phenomenon was alleviated by the modification.
Ammonia decomposition has attracted much attention as an efficient method for the on-site generation of hydrogen. In this study, alumina-supported nickel catalysts (Ni/Al2O3) modified by rare-earth elements were prepared by the impregnation method and their catalytic activity for the ammonia decomposition was investigated. The addition of rare-earth elements promoted the decomposition reaction over catalysts and the La-modified catalyst achieved the highest ammonia conversion in this work. For the modified catalysts, the adsorbed hydrogen, which is known to be an inhibitive species for the ammonia decomposition, desorbed at lower temperature compared to the unmodified one. Therefore, the effective alleviation of hydrogen inhibition would be responsible for the activity enhancement for the modified catalysts. The reaction kinetics study also supported this proposed mechanism. For the La-modified catalyst, the optimal pretreatment condition was investigated to enhance the catalytic activity. The catalyst calcined at 400°C followed by reduction at 600°C exhibited the highest ammonia conversion of 94% at 550°C.
Ammonia decomposition has attracted increasing attention as a promising process for the on-site generation of hydrogen. In this study, Ni catalysts supported on perovskite-type oxides (ABO
) were ...prepared and the activity for ammonia decomposition was examined. The Ni/ANbO
(A = Na and K) and Ni/AEMnO
(AE = Ca, Sr, and Ba) catalysts were less effective for this reaction. Meanwhile, the Ni/REAlO
(RE = La, Sm, and Gd) catalysts exhibited relatively high activity. For Ni/AETiO
and Ni/AEZrO
, the performance strongly depended on the A-site element of the perovskite-type oxides, and the Sr and Ba elements were more effective than the Ca one in the respective series. The catalytic activity for Ni/AEZrO
was higher than Ni/AETiO
in the case of the same alkaline earth element, and Ni/BaZrO
was the most active among the samples investigated in this work. For these series, the order in the performance corresponded well with that in the basic property. The nitrogen desorption profiles revealed that the evolution of nitrogen atoms, which is one of the kinetically slow steps, effectively proceeded for Ni/SrZrO
and Ni/BaZrO
compared with the conventional Ni catalysts. This promotion effect would be ascribed to the strong basic properties of the SrZrO
and BaZrO
supports, resulting in the high activity of Ni/SrZrO
and Ni/BaZrO
for ammonia decomposition.
Display omitted
► We prepared nickel catalysts supported on various metal oxides. ► We studied the activity of nickel catalysts for ammonia decomposition. ► The Ni/La2O3 catalyst exhibited relatively ...high activity. ► The extent of LaNiO3 formation was a key factor for catalytic activity of Ni/La2O3.
Ammonia decomposition is a promising process for on-site generation of hydrogen. In this study, various nickel catalysts supported on metal oxides were prepared and their catalytic activity for ammonia decomposition was investigated. Ni/Al2O3 catalyst achieved the highest ammonia conversion among catalysts investigated due to the high surface area of Al2O3 support (200m2g−1). Despite the low surface area of support material (4.7m2g−1), the catalytic activity of Ni/La2O3 was comparable to that of Ni/Al2O3. The basicity of support materials was not specifically related with the catalytic activity. For Ni/La2O3 catalyst, the small nickel particles were deposited over La2O3 from LaNiO3 during the reduction treatment. When the Ni loading amount was changed in the range of 10–70wt% for Ni/La2O3 catalyst, the sample with 40wt% Ni exhibited the highest conversion of 78.9% at 550°C. The catalytic performance of Ni/La2O3 was also affected by the preparation method and calcination temperature. The LaNiO3 formation was responsible for the high activity of Ni/La2O3 catalyst for the ammonia decomposition.
Ammonia decomposition has attracted the interest of many researchers as a promising process for the on‐site generation of H2. In this study, Ni catalysts supported on various rare‐earth oxides were ...prepared by the impregnation method and employed for ammonia decomposition. The Ni/Y2O3 catalyst exhibited the best performance among the samples investigated. The reaction kinetics study indicated that most of rare‐earth oxide supports were effective for the alleviation of the hydrogen inhibition phenomenon in the decomposition reaction. The desorption behavior of hydrogen has revealed that the amount of hydrogen atoms adsorbed strongly on the Ni surface up to high temperatures was relatively small in the case of Ni/Y2O3. Furthermore, for Ni/Y2O3 the optimal Ni loading was 40 wt % in terms of the catalytic activity because of the appropriate Ni dispersion.
Y2O3 support effect: In catalytic ammonia decomposition, hydrogen atoms adsorbed on the active metal inhibit the reaction. For Ni/Y2O3, the desorption of hydrogen from the Ni surface terminates at a low temperature. The Y2O3 support is effective for the alleviation of hydrogen inhibition.
Display omitted
•A novel composite cathode BCZY is developed via a one-step sol-gel method.•The strongly interacting interface is introduced by replacing Ce with Zr.•The strongly interacting ...interface enhances ORR activity and stability.•BCZY exhibits a low polarization resistance of 0.25 Ω cm2 at 600 °C.
Here, a novel triple-conducting composite cathode for protonic ceramic fuel cells, with superior oxygen reduction reaction (ORR) activity and stability, is developed by replacing cerium with zirconium in BaCo0.7(Ce0.8Y0.2)0.3O3−δ (BCCY) to construct strongly interacting interfaces. The one-step synthesized BaCo0.7(Zr0.8Y0.2)0.3O3−δ (BCZY) is composed of multiple phases with different functionalities, reaching a polarization resistance of 0.25 Ω cm2 at 600 °C while maintaining excellent performance stably for 206 h. The excellent ORR activity is attributed to the high concentration of active sites and the strong hydration capability at strongly interacting interfaces of Co-rich and Zr-rich phases which is introduced by the interdiffusion of Co and Zr. The low thermal expansion coefficient is also achieved through this interface, contributing to the excellent stability of BCZY. This study highlights the role of strongly interacting interfaces in enhancing the ORR activity and stability of materials and provides a new strategy for developing triple-conducting composite cathodes.
The electrochemical oxidation of ammonia over Pt electrode in alkaline aqueous solutions was studied by in situ attenuated total reflection infrared (ATR-IR) spectroscopy. In 0.1 M NH3–1 M KOH, the ...band ascribable to the HNH bending mode of adsorbed NH3 was confirmed at 1662–1674 cm–1 in the potential range of 0.1–1.1 V. The intensity of this band decreased continuously with a rise in potential, indicating the oxidative consumption of adsorbed ammonia. In response to this behavior, the band at 1269 cm–1 appeared alternatively above 0.2 V, and its intensity reached the local maximal value at ca. 0.4 V. Note that this potential of ca. 0.4 V agreed well with the onset potential of ammonia oxidation, ca. 0.45 V, in the linear sweep voltammogram. This 1269 cm–1 band was assigned to the NH2 wagging mode of N2H4, which was one of the active intermediates, N2H x+y,ad (x = 1 or 2, y = 1 or 2), according to the mechanism proposed by Gerischer and Mauere. To the best of our knowledge, this is the first report for the detection of N2H4 as a reaction intermediate over Pt electrode. Furthermore, the formation of bridged NO was also observed above the onset potential of ammonia oxidation, ca. 0.5 V. Such adsorbed NO species probably inhibit the electrochemical reaction due to the occupation of reaction sites at higher potential.
The recent development of anion exchange membranes (AEMs) has increased the potential of anion exchange membrane fuel cells (AEMFCs). Although highly active electrocatalysts for specific reactions ...have been successfully developed by placing the most importance on the fuel species, only a few studies have focused on OHad (hydroxyl adsorbed species), which is known to be a common reactive species in alkaline environments. In this study, highly oxophilic CeO2 was selected as a surface modifier for a Pt electrode. We first applied in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy to ionomer-coated Pt and CeO2-modified Pt surfaces for clarifying the adsorption behavior of OHad. As a result, a distinct change in adsorption behavior of OHad was confirmed in blank KOH solution. These peculiar characteristics were applicable to various electrochemical oxidation reactions. During the ammonia oxidation reaction, the acceleration of the formation of NOad species was observed in CeO2-modified Pt, suggesting the enhancement of OH adsorption. Furthermore, the degree of activity enhancement by CeO2 addition was investigated for the CO oxidation reaction, methanol oxidation reaction, and ethanol oxidation reaction. Under basic conditions, each of these reactions exhibited distinct activity enhancement. In contrast, under acidic conditions, the promoting effect on these reactions was not observed. These results strongly indicate the potential of our catalyst design strategy and the importance of OHad species as reactive species in alkaline environments.
The electrochemical performance of Ni–gadolinia-doped ceria (GDC) cathode was studied for CO2 reduction on solid oxide electrolysis cell (SOEC) at 1000 °C and compared with that of Ni–yttria ...stabilized zirconia (Ni–YSZ) cathode. Ni–GDC cathode demonstrated higher performance for CO2 reduction. Furthermore, lanthanum strontium cobalt ferrite (LSCF) anode exhibited lower overpotential than lanthanum strontium manganite–yttria stabilized zirconia (LSM–YSZ) anode. Ni–GDC cathode and LSCF anode were found to be stable under a constant current density of −0.90 A cm−2 at 900 °C. Moreover, no substantial performance degradation was observed for the cell having Ni–GDC cathode and LSCF anode even after 9 h of electrolysis operation under a constant current density of −1.2 A cm−2 at 1000 °C.
•Galvanostatic experiments were conducted for high-temperature CO2 reduction.•No delamination was observed for LSCF anode operated at extreme conditions.•Contrary to Ni–YSZ, microstructure of Ni–GDC was unchanged after current loading.
The Ni-based spinel-type oxides, NiB
2O
4 (
B = Al, Fe, Mn), were investigated for their catalysis of the ethanol steam reforming reaction. Ethanol conversion over spinel-type oxides without ...reduction treatment was comparable to that over γ-alumina-supported Ni catalyst with reduction. The spinel oxide of NiAl
2O
4 showed extremely stable performance for 48 h, while the activity of NiFe
2O
4 and NiMn
2O
4 catalysts was reduced by carbon deposition. Catalyst stability for reforming reaction was closely related to the stability of the nickel metal dispersed on the catalyst surface and the spinel structure. Differences in crystallinity and surface area among the catalysts were not crucial factors for determining ethanol conversion for NiAl
2O
4 calcined between 800 °C and 1100 °C. The catalyst calcined at 900 °C exhibited the highest activity for the reforming reaction.
PDF
