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Novel molten salt synthesis of a highly active intermetallic CaPt2 catalyst supported on titanium oxide for hydrogenation of cyclohexanone to cyclohexanol.

The development of methodologies for CO2 utilization is in high demand worldwide. Here, we propose bifunctional tandem catalysts of ZnZrOx (for CO2-to-methanol hydrogenation) and a series of solid acid catalysts (for subsequent methanol conversion to light olefins). As solid acid catalysts, we used zeolites and silicoaluminophosphates with different topologies, MOR, FER, MFI, ∗BEA, CHA, and ERI, confirmed by X-ray diffraction, electron microscopy, and nitrogen adsorption-desorption. They also showed the corresponding acid properties examined by ammonia adsorption. The tandem catalysts realized a one-pass synthesis of lower olefins, while no hydrocarbons were obtained using ZnZrOx only. According to the reaction test and ammonia adsorption, there seems to be no correlation between product yields and acid strength. The pore sizes and channel dimensionality of zeolites influence the selectivity of products; zeolites with small pores, such as MOR, SAPO-34 and ERI, are promising, while zeolites with larger pores, such as MFI, produce heavier hydrocarbons. The results provide new insight into the design of innovative catalysts for CO2 utilization.

In situ DRIFTS measurements of an Fe/BZY-Ru cathode catalyst in an electrolysis cell using a CsH2PO4/SiP2O7 electrolyte were carried out in a mixed N2–H2 gas flow under polarization.

For efficient methanol synthesis by CO2 hydrogenation, catalysts prepared by mixing sponge copper and amorphous ZrO2 were investigated. The commercial sponge copper itself exhibited catalytic activ...

We examined active sites for CO₂ methanation over Ni/CeO₂ catalysts prepared by a wet impregnation method. Four types of Ni/CeO₂ with Ni loadings of 1, 3, 5, and 10 wt % were used in this study, assuming that the Ni sites are well dispersed in the catalysts when changing the Ni loading. According to powder X-ray diffraction and scanning transmission electron microscopy, the low-loading catalysts (1 and 3 wt %) consist mainly of Ni–Ce mixed oxides. The results of temperature-programmed reduction by H₂ suggested that the Ni–Ce mixed oxides under reducing conditions contain oxygen vacancies (Ni–Vₒₓ–Ce). Note that the CO₂ conversion rate was proportional to the Ni loading, which probably means that Ni–Vₒₓ–Ce sites on the Ni–Ce mixed oxides are active in CO₂ conversion. In contrast, when the Ni loading was high (5 and 10 wt %), the catalysts possessed many metallic Ni nanoparticles supported on CeO₂ and Ni–Ce mixed oxides. Because the turnover frequencies of CO methanation for 5 and 10 wt % Ni/CeO₂ were identical, the presence of a metallic Ni surface could be essential for activation in CO methanation. We focused on the fact that the CO₂ conversion rate was not related to the number of oxygen vacancies on CeO₂ (Ce–Vₒₓ–Ce) but was related to the number of the Ni–Vₒₓ–Ce sites. Hence, the formation of Ni–Vₒₓ–Ce sites (CO production via the reverse water-gas shift reaction) and the exposure of metallic Ni sites (methanation of the thus-formed CO) are essential for CO₂ methanation. Although it has been known that oxygen vacant sites on Ni/CeO₂ catalysts are important for the catalytic activity, this study suggested anew that there are two types of the sites, Ce–Vₒₓ–Ce and Ni–Vₒₓ–Ce. Furthermore, it was clarified that the latter oxygen defect is important for CO₂ methanation.

In this study, we developed an Fe2O3/BZY (yttrium-doped barium zirconate)–RuO2 (Fe/BZY–RuO2) cathode catalyst, which was applied to the electrochemical synthesis of NH3 using a proton-conducting electrolyte, CsH2PO4/SiP2O7, at 220 °C and ambient pressure. The highest faradaic efficiency of 7.1% was achieved at −0.4 V (vs. open-circuit voltage (OCV)) and the highest NH3 yield rate of 4.5 × 10−10 mol (s cm2)−1 was achieved at −1.5 V (vs. OCV). We also successfully detected N2H4 and NH3 at −0.2 V (vs. OCV), which indicated that the N2 reduction proceeded via an associative mechanism. A potentiostatic pulse experiment was conducted under a feed of Ar or N2 in the cathode at different applied voltages to investigate the N2 reduction reaction (NRR) mechanism. A model was developed to fit the current response of the potentiostatic pulse experiment, which comprised the decomposition of adsorbed intermediates on the surface of the cathode catalyst, diffusion of H in the cathode catalyst, and an electrical double layer. The results revealed that the rate constant estimated by the model for the decomposition of intermediates, such as NH or N2H, was lowest at −0.2 V, where N2H4 was detected. The fitting results also indicated that the NRR proceeded via an associative mechanism at lower applied voltages, while a dissociative mechanism dominated at higher applied voltages.

In this study, ternary intermetallic nickel silicide, Ti6Si7Ni16, nanoparticles with a high surface area of 37.5 m2 g−1 were chemically prepared from SiO2-impregnated oxide precursors, which were reduced at as low as 600 °C by a CaH2 reducing agent in molten LiCl, resulting in the formation of single-phase Ti6Si7Ni16 with a nanosized morphology. The intermetallic Ti6Si7Ni16 phase in the nanoparticles was stabilized in air by surface passive oxide layers of TiOx–SiOy, which facilitated the handling of the nanoparticles. Considering our previous successful work of preparing single-phase LaNi2Si2 (39.3 m2 g−1) and YNi2Si2 (27.0 m2 g−1) nanoparticles in a similar manner, the proposed chemical method showed to be a versatile approach in preparing ternary silicide nanoparticles. In this study, we applied the obtained Ti6Si7Ni16 nanoparticles as catalyst supports in CO methanation. The supported nickel catalyst showed an activation energy of 56 kJ mol−1, which is half as low as that of common TiO2-supported nickel catalysts. Also, Ni/Ti6Si7Ni16 provided the lower activation energy more than any previous Ni-based catalyst. Since the measured work function of Ti6Si7Ni16 (4.5 eV) was lower than that of nickel (5.15 eV), it was suggested that the Ti6Si7Ni16 support can accelerate the rate-determining step of C–O bond dissociation in CO methanation due to its good electron donation capacity.

Porous intermetallic Ni2XAl (X = Ti or Zr) nanoparticles with small crystallite sizes (24–34 nm) and high Brunauer–Emmett–Teller (BET) surface areas (10–71 m2 g−1) were prepared from oxide precursors by a chemical route. CaH2 acted as a template to form the porous morphologies and assisted the reduction.

Dispersion of metallic Cu nanoparticles on a metal oxide support increases the number of exposed metallic Cu sites and/or Cu-support interfacial sites, resulting in good catalytic performance for C...

To open up the possibility of synthesizing useful substances from CO2, we have developed new catalysts that hydrogenate CO2 to methanol with high yield at 300 °C and higher. In this study, methanol...

Electrolysis at intermediate temperatures (100-600 degrees C) is promising because high reaction rates and high product selectivity can be achieved simultaneously during CO2 reduction. However, intermediate temperature electrolysis has rarely been reported owing to electrolyte limntions. Here, solid acid electrolysis cells (SA:Cs) were adopted for electrochemically reducing CO2. Carbon monoxide, methane, methanol, ethane, ethylene, ethanol, acetaldehyde and propylene were produced from CO2 and steam, using Cu-containing composite cathodes at 220 degrees C and atmospheric pressure. The results demonstrate the potential of SAECs for producing valuable chemical feedstocks. At the SAEC cathode, CO2 was electrochemically reduced by protons and electrons. The product selectivity and reaction rate were considerably different from those of thermochemical reactions with gaseous hydrogen. Based on the differences, plausible reaction pathways were proposed.

In this study, ternary intermetallic nickel silicide, Ti

A novel mesoporous intermetallic NiAl nanocompound was successfully prepared at 600 °C in a molten LiCl with an assistance of CaH2. The obtained powder had a fine crystal structure assigned to a si...

Ethane was converted directly to acetaldehyde and ethanol by partial oxidation at 220 degrees C and ambient pressure using an electrolysis cell with a proton-conducting electrolyte, CsH2PO4/SiP2O7, and Pt/C electrodes. The ethane conversion and the selectivity to the products increased with the voltage applied to the cell. It was found that O species generated by water electrolysis functioned as a favorable oxidant for partial oxidation of ethane on the Pt/C anode at intermediate temperatures. The production rates of acetaldehyde and ethanol recorded in this study were significantly higher than those in preceding reports.

Intermetallic Pt2Y bulk nanopowder (2.9 m2 g−1, 28 nm) was chemically obtained from H2PtCl6·6H2O and Y2O3 that were finally reduced and alloyed in molten LiCl–CaH2 under Ar at 600 °C. It is a novel simple approach to obtain nanopowders with no gloveboxes, vacuum systems, or even organic solvents.

The influence of support materials and preparation methods on CO2 methanation activity was investigated using Ru nanoparticles supported on amorphous ZrO2 (am-ZrO2), crystalline ZrO2 (cr-ZrO2), and SiO2. Among them, Ru/am-ZrO2 showed high CO2 methanation activity. Of note, Ru/am-ZrO2 prepared by a selective deposition method was superior to that prepared by a wet impregnation method. This is because the Ru nanoparticles were highly dispersed when prepared by the selective deposition method, as evidenced by XPS. Interestingly, when NaOH solution was used as a pH adjuster for the selective deposition method, Ru/am-ZrO2 catalysts activated the formate species (one of the important reaction intermediates of CO2 methanation), leading to high CO2 conversion (73%, 250 °C).

Power-to-gas is an emerging technology to convert electrical energy into chemical energy, and usually consists of two steps. First, hydrogen or syngas is produced in electrolysis cells, and then the hydrogen is used to methanate COx in catalytic reactors. Solid oxide electrolysis cells (SOECs) have the potential to integrate these two steps because methane can be directly synthesized in the SOEC cathodes. However, the advantages and drawbacks of such a direct process have not been discussed quantitatively. In the present work, we established a model using Aspen Plus to simulate the direct process. By analyzing the energy conversion processes in detail, it was clarified that the suppression of SOEC overpotentials at low temperatures is crucial. If the SOEC overpotentials are decreased at 400 °C, the energy conversion efficiency of the direct process will become higher than that of the conventional two-step process especially at small methane production rates. The superior performance can be ascribed to the recuperative heat utilization between the exothermic methanation reaction and the endothermic electrolysis reactions.

Optimization of Pt-based electrode structure is a key to enhance power generation performance of fuel cells and to reduce the Pt loading. This paper presents a new methodology for anode fabrication for solid acid fuel cells (SAFCs) operating at ca. 200 °C. Our membrane electrode assembly for SAFCs consisted of a CsH2PO4/SiP2O7 composite electrolyte and Pt-based electrodes. To obtain the anode, a commercial Pt/C catalyst and carbon substance, such as carbon black and carbon nanofiber, were mixed. The composite anode with Pt loading = 0.5 mg cm−2 demonstrated superior current-voltage characteristics to a benchmark Pt/C anode with Pt loading = 1 mg cm−2. We consider that the mixing of Pt/C catalyst and carbon substrate facilitated H2 mass transfer and increased the number of active sites.

This paper presents the influence of different types of copper precursors on CO2-to-methanol hydrogenation over copper nanoparticles on amorphous ZrO2. Here, we chose copper nitrate hydrate, copper...

In this study, four pyrochlore oxides such as (Gd0.9Ca0.1)2Ti2O7-δ, Gd2(Ti0.8Ru0.2)2O7-δ, (Sm0.9Ca0.1)2Ti2O7-δ, and (Y0.9Ca0.1)2Ti2O7-δ were investigated as new mixed ionic and electronic conductors for SOFC anodes. Cermets of nickel and the pyrochlores were fabricated as an anode, and current-voltage (I-V) characteristics were evaluated using yttria-stabilized zirconia and lanthanum manganite as an electrolyte and cathode, respectively. It was found that ohmic resistance and polarization resistance for the anodic reaction over some of the Ni-pyrochlore cermet anodes were smaller than those of Ni-YSZ, whereas the polarization resistance stemming from gas diffusion in the anode was significantly large over the pyrochlore anodes, leading to inferior I-V characteristics to Ni-YSZ. To improve the anode structure for better gas diffusion, pyrochlore oxides were prepared by solid-state synthesis method. The anode using these pyrochlore oxides exhibited smaller gas diffusion resistance and comparable I-V characteristics with Ni-YSZ anode.

Metal oxide addition is one of the major techniques to improve the performance of SOFC cermet anodes. However, the effects of the metal oxide addition on hydrogen oxidation activity of the anodes have not been clarified so far. In this study, Ni-CaO/YSZ anodes were prepared to examine the interaction between YSZ and Ca species. The hydrogen oxidation activities of the prepared anodes were investigated by introducing electrochemical impedance spectroscopy. The anodic resistance of the electrochemical hydrogen oxidation was determined by impedance fitting, and its temperature dependency was analyzed by means of Arrhenius plots. It was found that activation energy of the reaction was decreased with the CaO addition, suggesting the possibility of the SOFC operation at lower temperatures.

Oxidative coupling of methane (OCM) is one of the most promising technologies for the effective use of methane. In this study, La0.3Sr0.7TiO3 was examined as an anode material for solid oxide electrolysis cell with OCM reaction. X-ray diffraction measurement was conducted for the material characterization, and alternating current impedance and current-voltage measurement were conducted for the cell characterization. The activity test was conducted at different current densities, and the anode gas compositions were analyzed. The electrochemical production rates of CO, CO2, C2H6, and C2H4 were increased linearly as the applied current voltages were increased, while the selectivities of all products were almost constant.

Porous intermetallic Ni

Nanosizing of TiFe hydrogen storage alloy is conducted to facilitate its activation. Here, pure intermetallic TiFe nanoparticles (45 nm) were prepared using chemical reduction of oxide precursors at 600 °C, which is the lowest temperature ever used in chemical synthesis. This was achieved using a strong reducing agent (CaH2) in a molten LiCl. When used for hydrogen absorption, the obtained nanoparticles surprisingly exhibited almost no hydrogen absorption. The results demonstrated that TiFe nanoparticles are more difficult to activate than the bulk powder because the oxidized surface layers of the nanoparticles become stabilized, which prevents the morphological change necessary for their activation.

Copper nanoparticles supported on zirconia (Cu/ZrO2) or related supported oxides (Cu/ZrO2/SiO2) show promising activity and selectivity for the hydrogenation of CO2 to CH3OH. However, the role of the support remains controversial because most spectroscopic techniques provide information dominated by the bulk, making interpretation and formulation of structure–activity relationships challenging. In order to understand the role of the support and in particular of the Zr surface species at a molecular level, a surface organometallic chemistry approach has been used to tailor a silica support containing isolated Zr(IV) surface sites, on which copper nanoparticles (∼3 nm) are generated. These supported Cu nanoparticles exhibit increased CH3OH activity and selectivity compared to those supported on SiO2, reaching catalytic performances comparable to those of the corresponding Cu/ZrO2. Ex situ and in situ X-ray absorption spectroscopy reveals that the Zr sites on silica remain isolated and in their +4 oxidation ...

We examined the formation mechanism of active sites on Cu/ZrO2 specific toward CO2-to-methanol hydrogenation. The active sites on Cu/a-ZrO2 (a-: amorphous) were more suitable for CO2-to-methanol hydrogenation than those on Cu/t-ZrO2 (t-: tetragonal) and Cu/m-ZrO2 (m-: monoclinic). When a-ZrO2 was impregnated with a Cu(NO3)2·3H2O solution and then calcined under air, most of the Cu species entered a-ZrO2, leading to the formation of a Cu–Zr mixed oxide (CuaZr1-aOb). The H2 reduction of the thus-formed CuaZr1-aOb led to the formation of Cu nanoparticles on a-ZrO2, which can be dedicated to CO2-to-methanol hydrogenation. We concluded that the selective synthesis of CuaZr1-aOb, especially amorphous CuaZr1-aOb, is a key feature of the catalyst preparation. The preparation conditions of the amorphous CuaZr1-aOb specific toward CO2-to-methanol hydrogenation is as follows: (i) Cu(NO3)2·3H2O/a-ZrO2 is calcined at low temperature (350 °C in this study) and (ii) the Cu loading is low (6 and 8 wt % in this study). Vi...

The effect of Ag loading (wt%) of Ag/CuO/ZrO2 catalysts for the CO2 hydrogenation to methanol was investigated. The addition of a small amount of Ag (≤1 wt%) to CuO/ZrO2 did not change the turnover frequency of methanol production per exposed Cu sites (TOFmethanol) but increased the selectivity towards methanol due to a synergy developed between Cu and Ag, which was supported by H2-TPR studies.

We prepared Cu/a-ZrO2 (a-ZrO2: amorphous ZrO2), Cu/m-ZrO2 (m-ZrO2: monoclinic ZrO2), Cu/a-ZrO2/KIT-6, and Cu/t-ZrO2/KIT-6 (t-ZrO2: tetragonal ZrO2) by a simple impregnation method and examined the effect of the ZrO2 phase on CO2-to-methanol hydrogenation. We discovered a-ZrO2-containing catalysts with high activity and selectivity in CO2-to-methanol hydrogenation. Next, we focused on Cu species formation on the above-described catalysts. While pure CuO was observed on Cu/m-ZrO2 and Cu/t-ZrO2/KIT-6, copper-zirconium mixed oxide (CuxZryOz), not pure CuO, was formed on Cu/a-ZrO2 and Cu/a-ZrO2/KIT-6, as evidenced by X-ray absorption spectroscopy (XAS) and the powder color. After reducing a-ZrO2-containing catalysts with H2 at 300 °C, we observed highly dispersed Cu nanoparticles in close contact with a-ZrO2 (or CuxZryOz). In addition, methanol vapor sorption revealed that methanol adsorbed more weakly on a-ZrO2 than on m-ZrO2. Therefore, the high dispersion of Cu species and weak adsorption of methanol led to...

Flame made CuO–ZrO2 catalysts for CO2 hydrogenation to methanol were prepared such that only the Cu size was varied. Smaller CuO clusters in CuO–ZrO2 showed a higher activity for methanol synthesis via CO2 hydrogenation. Thus, the two-nozzle flame spray pyrolysis technique is a promising one-step preparation process for CO2 hydrogenation catalysts.