Nitrous oxide (N2O) exerts strong effects on global warming and environmental destruction. Various catalytic technologies have been investigated for N2O abatement. We investigated a catalytic system in an electric field, revealing that N2O can be decomposed efficiently, even at low temperatures and in the presence of excess oxygen and water vapour. Reaction mechanisms with and without an electric field have been investigated using kinetics and various operando analyses, which revealed that surface-lattice oxygen on catalyst supports plays a crucially important role in N2O decomposition in an electric field at low temperatures.

Reverse water gas shift (RWGS) can convert CO2 into CO by using renewable hydrogen. However, this important reaction is endothermic and equilibrium constrained, and thus traditionally performed at 900 K or higher temperatures using solid catalysts. In this work, we found that RWGS can be carried out at low temperatures without equilibrium constraints using a redox method called chemical looping (CL), which uses the reduction and oxidation of solid oxide surfaces. When using our developed MGa2Ox (M = Ni, Cu, Co) materials, the reaction can proceed with almost 100% CO2 conversion even at temperatures as low as 673 K. This allows RWGS to proceed without equilibrium constraints at low temperatures and greatly decreases the cost for the separation of unreacted CO2 and produced CO. Our novel gallium-based material is the first material that can achieve high conversion rates at low temperatures in reverse water gas shift using chemical looping (RWGS-CL). Ni outperformed Cu and Co as a dopant, and the redox mechanism of NiGa2Ox is a phase change due to the redox of Ga during the RWGS-CL process. This major finding is a big step forward for the effective utilization of CO2 in the future.

Quantum annealing has been used to predict molecular adsorption on solid surfaces. Evaluation of adsorption, which takes place in all solid surface reactions, is a crucially important subject for study in various fields. However, predicting the most stable coordination by theoretical calculations is challenging for multimolecular adsorption because there are numerous candidates. This report presents a novel method for quick adsorption coordination searches using the quantum annealing principle without combinatorial explosion. This method exhibited much faster search and more stable molecular arrangement findings than conventional methods did, particularly in a high coverage region. We were able to complete a configurational prediction of the adsorption of 16 molecules in 2286 s (including 2154 s for preparation, only required once), whereas previously it has taken 38 601 s. This approach accelerates the tuning of adsorption behavior, especially in composite materials and large-scale modeling, which possess more combinations of molecular configurations.

Methane dry reforming at 373 K in a DC electric field was carried out using Ni/CeO2 and Ni0.8Fe0.2/CeO2 alloy catalysts, and their alloying effects were investigated in detail using XAFS and in-situ surface spectroscopy. For the Ni catalyst, there was a decrease in the adsorption of carbonate species, an increase in the proportion of bidentate carbonate species, and an observed degradation in activity caused by carbon deposition over time. Conversely, the alteration of electronic state occurring as a result of the ligand effect (electronic interaction among atoms by alloying) on the Ni-Fe catalyst contributed to the stabilization of intermediates involved in rate-determining steps specific to electric-field catalysis. Carbon deposition was less likely to occur, resulting in significantly higher activity when compared to the Ni catalyst.

The reverse water–gas shift (RWGS) reaction, a promising carbon-recycling reaction, was investigated by applying an electric field to promote the reaction at a temperature of 473 K or lower. The highly dispersed Ru/ZrTiO4 catalysts with an approximately 2 nm particle size of Ru showed high RWGS activity with a DC electric field below 473 K, whereas CO2 methanation proceeded predominantly over catalysts with larger Ru particles. The RWGS reaction in the electric field maintained high CO selectivity, suppressing CO hydrogenation into CH4 on the Ru surface by virtue of promoted hydrogen migration (surface protonics). The reaction mechanisms of the non-conventional low-temperature reverse water gas shift reaction were investigated and revealed using various characterization methods including in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements. With the DC electric field, the reaction proceeds via a redox reaction where the generated oxygen vacancies are involved in CO2 activation at low temperatures. As a result, the electric field promotes both hydrogen migration and redox reactions using lattice oxygen/ vacancies, resulting in high RWGS activity and selectivity even at low temperatures.

Dry reforming of methane (DRM) is a promising reaction able to convert greenhouse gases (CO2 and CH4) into syngas: an important chemical feedstock. Several difficulties limit the applicability of DRM in conventional thermal catalytic reactions; it is an endothermic reaction that requires high temperatures, resulting in high carbon deposition and a low H2/CO ratio. Catalysis with the application of an electric field (EF) at low temperatures can resolve these difficulties. Synergistic effects with alloys have also been reported for reactions promoted by the application of EF. Therefore, the synergistic effects of low-temperature DRM and Ni-Fe bimetallic catalysts were investigated using various methods and several characterisations (XRD, XPS, FE-STEM, etc.), which revealed that Ni-Fe binary catalysts show high performance in low-temperature DRM. In particular, the Ni0.8Fe0.2 catalyst supported on CeO2 was found to carry out DRM in EF effectively and selectively by virtue of its bimetallic characteristics.

The effect of OH-groups on the surface of a Ni catalyst for low-temperature (473 K) steam reforming of methane in an electric field (EF) was investigated. Ni-doped YSZ (Zr0.65Y0.05Ni0.3O2) was chosen as a highly active catalyst for this purpose. The effects on catalyst activity of adding hydrogen and steam in the pre-treatment were assessed with and without EF. When an EF was applied, activity increased irrespective of the electronic state of Ni, whereas the metallic Ni state was necessary for activity without EF. Furthermore, the highest activity with EF was observed for the pre-treatment with a mixture of H2 and H2O. Investigation of the superiority using XPS measurements showed an increase in the amount of Ni(OH)2, OH groups and H2O near the surface after the activity test, which are regarded as the reaction sites with EF. This finding suggests that a pre-treatment with steam increases the surface OH groups and Ni(OH)2 on the Ni catalyst, and enhances surface proton conduction, thereby improving the activity.

Catalytic ethane dehydrogenation (EDH) was investigated to improve the efficient production of ethylene, an extremely important chemical feedstock. The perovskite oxide YCrO3 was found to be more suitable than earlier reported catalysts because it exhibits greater activity and C2H4 selectivity (94.3%) in the presence of steam at 973 K. This catalyst shows the highest activity than ever under kinetic conditions, and shows very high ethane conversion under integral reaction conditions. Comparison with EDH performance under conditions without steam revealed that steam plays an important role in stabilizing the high activity. Raman spectra of spent catalysts indicated that steam prevents coke formation, which is responsible for deactivating YCrO3. Transmission IR and XPS measurements also revealed a mechanism by which H2O forms surface oxygen species on YCrO3, consequently removing C2H6-derived coke precursors rapidly and inhibiting coke accumulation.

CO2 conversion to CO by reverse water-gas shift using chemical looping (RWGS-CL) can be conducted at lower temperatures (ca. 723-823 K) than the conventional catalytic RWGS (>973 K), and has been attracting attention as an efficient process for CO production from CO2. In this study, Co-In2O3 was developed as an oxygen storage material (OSM) that can realize an efficient RWGS-CL process. Co-In2O3 showed a high CO2 splitting rate in the mid-temperature range (723-823 K) compared with previously reported materials and had high durability through redox cycles. Importantly, the maximum CO2 conversion in the CO2 splitting step (ca. 80%) was much higher than the equilibrium conversion of catalytic RWGS in the mid-temperature range, indicating that Co-In2O3 is a suitable OSM for the RWGS-CL process.

As automobiles increasingly become electrically driven and as more engines and motors are used together, the exhaust temperatures of internal combustion engines are decreasing. Further improvement of exhaust gas purification catalyst performance is necessary. To purify nitrogen oxides, unburned hydrocarbons, and carbon monoxide simultaneously at low temperatures, electrothermal heating and plasma catalysis have been proposed, but these methods require high power consumption. Results of this study indicate that a direct current electric field applied to a Pd-supported catalyst shows high purification rates even at temperatures lower than 473 K under TWC conditions (NO-CO-C3H6-O2-H2O). For clarifying the reaction mechanism in this process, the adsorption of reactants was evaluated using in situ DRIFTS measurements in an electric field. Factors that improve the activity at low temperatures in the electric field were clarified.

Considering the expansion of the use of renewable energy in the future, the technology to store and transport hydrogen will be important. Hydrogen is gaseous at an ambient condition, diffuses easily, and its energy density is low. So liquid organic hydrogen carriers (LOHCs) have been proposed as a way to store hydrogen in high density. LOHC can store, transport, and use hydrogen at high density by hydrogenation and dehydrogenation cycles. In this review, we will focus on typical LOHCs, methylcyclohexane (MCH), 18H-dibenzyltoluene (DBT), and 12H-N-ethylcarbazole (NECZ), and summarize recent developments in dehydrogenation catalytic processes, which are key in this cycle.

A Pd catalyst (Pd/Ce0.7Zr0.3O2) in an electric field exhibits extremely high three-way catalytic activity (TWC: NO-C3H6-CO-O2-H2O). By applying an electric field to the semiconductor catalyst, low-temperature operation of TWC can be achieved even at 473 K by virtue of the activated surface-lattice oxygen.

It has over the last few years been reported that the application of a DC electric field and resulting current over a bed of certain catalyst-support systems enhances catalytic activity for several reactions involving hydrogen-containing reactants, and the effect has been attributed to surface protonic conductivity on the porous ceramic support (typically ZrO2, CeO2, SrZrO3). Models for the nature of the interaction between the protonic current, the catalyst particle (typically Ru, Ni, Co, Fe), and adsorbed reactants such as NH3 and CH4 have developed as experimental evidence has emerged. Here, we summarize the electrical enhancement and how it enhances yield and lowers reaction temperatures of industrially important chemical processes. We also review the nature of the relevant catalysts, support materials, as well as essentials and recent progress in surface protonics. It is easily suspected that the effect is merely an increase in local vs. nominal set temperature due to the ohmic heating of the electrical field and current. We address this and add data from recent studies of ours that indicate that the heating effect is minor, and that the novel catalytic effect of a surface protonic current must have additional causes.

Introducing a catalyst for dehydrogenation of ethane (EDH) for steam cracking represents a promising solution with high feasibility to realize efficient ethylene production. We investigated EDH over transition-metal-doped CeO2 catalysts at 873 K in the presence of steam. Ce0.8Co0.2O2 exhibited high EDH activity and selectivity to ethylene (ca. 95%). In the absence of H2O, the catalytic activity dropped rapidly, indicating the promotive effect of H2O on ethylene formation. Catalytic experiments with water isotopes (D2O and H218O) demonstrated that EDH over Ce0.8Co0.2O2 proceeds through the Mars-van Krevelen (MvK) mechanism in which the reactive lattice oxygen in Ce0.8Co0.2O2 contributes to EDH. The consumed lattice oxygen was subsequently regenerated with H2O. X-ray diffraction and in situ X-ray absorption fine structure spectroscopy revealed that cobalt species were mainly present as CoO under EDH conditions and that redox between Co2+ and Co0 proceeded concomitantly with EDH. In contrast with Ce0.8Co0.2O2, no contribution of the lattice oxygen of CoO to EDH was verified in the case of CoO supported on α-Al2O3, which exhibited lower activity than Ce0.8Co0.2O2. Therefore, Co-CeO2 interactions are expected to play a crucially important role in controlling the characteristics of the reactive lattice oxygen suitable for EDH via the MvK mechanism.

Hydrogen (H) atom adsorption and migration over the CeO2-based materials surface are of great importance because of its wide applications to catalytic reactions and electrochemical devices. Therefore, comprehensive knowledge for controlling the H atom adsorption and migration over CeO2-based materials is crucially important. For controlling H atom adsorption and migration, we investigated irreducible divalent, trivalent, and quadrivalent heterocation-doping effects on H atom adsorption and migration over the CeO2(111) surface using density functional theory (DFT) calculations. Results revealed that the electron-deficient lattice oxygen (Olat) and the flexible CeO2matrix played key roles in strong adsorption of H atoms. Heterocations with smaller valence and smaller ionic radius induced the electron-deficient Olat. In addition, smaller cation doping enhanced the CeO2matrix flexibility. Moreover, we confirmed the influence of H atom adsorption controlled by doping on surface proton migration (i.e.surface protonics) and catalytic reaction involving surface protonics (NH3synthesis in an electric field). Results confirmed clear correlation between H atom adsorption energy and surface protonics.

Hydrogen (H) atomic migration over a metal oxide is an important surface process in various catalytic reactions. Control of the interaction between H atoms and the oxide surfaces is therefore important for better catalytic performance. For this investigation, we evaluated the adsorption energies of the H atoms over perovskite-type oxides (Sr1−xBaxZrO3; 0.00 ≤x≤ 0.50) using DFT (Density Functional Theory) calculations, then clarified the effects of cation-substitution in the A-site of perovskite oxides on H atom adsorption, migration, and reaction. Results indicated local distortion at the oxide surface as a key factor governing H atom adsorption. Subtle Ba2+substitution for Sr2+sites provoked local distortion at the Sr1−xBaxZrO3oxide surface, which led to a decrement in the H atom adsorption energy. Furthermore, the effect of Sr2+/Ba2+ratio on the H atoms' reactivities was examined experimentally using a catalytic reaction, which was promoted by activated surface H atoms. Results show that the surface H atoms activated by the substitution of Sr2+sites with a small amount of Ba2+(x= 0.125) contributed to enhancement of ammonia synthesis rate in an electric field, which showed good agreement with predictions made using DFT calculations.

Efficient activation of CO2at low temperature was achieved by reverse water-gas shiftviachemical looping (RWGS-CL) by virtue of fast oxygen ion migration in a Cu-In structured oxide, even at lower temperatures. Results show that a novel Cu-In2O3structured oxide can show a remarkably higher CO2splitting rate than ever reported. Various analyses revealed that RWGS-CL on Cu-In2O3is derived from redox between Cu-In2O3and Cu-In alloy. Key factors for high CO2splitting rate were fast migration of oxide ions in the alloy and the preferential oxidation of the interface of alloy-In2O3in the bulk of the particles. The findings reported herein can open up new avenues to achieve effective CO2conversion at lower temperatures.

To prevent global warming, further reductions in carbon dioxide are required. It is therefore important to promote the spread of electric vehicles powered by internal combustion engines and electric vehicles without internal combustion engines. As a result, emissions from hybrid electric vehicles equipped with internal combustion engines should be further reduced. Interest in catalytic reactions in an electric field with a higher catalytic activity compared to conventional catalysts has increased because this technology consumes less energy than other electrical heating devices. This study was therefore undertaken to apply a catalytic reaction in an electric field to an exhaust emission control. First, the original experimental equipment was built with a high voltage system used to conduct catalytic activity tests. Second, experiments with palladium cerium-zirconium oxide support catalysts showed that a three-way catalytic activity in an electric field could be found. at lower exhaust temperatures than conventional catalysts. Then it became clear that catalytic compositions that include semiconductor properties are a key for researching and developing this technology. In addition, applied electrical current control has been shown to be another focus of research and development. Finally, experimental results with several reducing species demonstrate that the electron-promoted surface proton and lattice oxygen greatly contributed to catalytic activity in an electric field.

For future removal of NOx by catalysts, low-temperature NO reduction is desired. Results confirmed that a drastic improvement of catalytic activity by H2O on NO–CO–O2 reaction over Pd/La0.9Ba0.1AlO3-δ catalyst at the low temperature of 473 K or below. In a humidified condition, NO reaction with CO on Pd/La0.9Ba0.1AlO3-δ proceeded without being affected by competitive adsorption of NO and CO, whereas that on Pd/Al2O3 was inhibited by strong adsorption of CO on a Pd surface. From in-situ DRIFTS measurements, results showed that nitrite species on the support react with CO adsorbed onto Pd at the periphery of Pd particles and that carbonate species accumulated on Pd/La0.9Ba0.1AlO3-δ are removed rapidly in a humidified condition. Although NO reduction proceeds dominantly on the Pd surface in a dry condition, supplied steam promotes desorption of the surface carbonate to advance the reaction of nitrite with CO for de-NOx in a humidified condition. This mechanism occurs specifically on Pd/La0.9Ba0.1AlO3-δ by virtue of the lattice oxygen and oxygen vacancy on La0.9Ba0.1AlO3-δ.

Low-temperature heterogeneous catalytic reaction in an electric field is anticipated as a novel approach for on-demand and small-scale catalytic processes. This report quantitatively reveals the important role of proton coverage on the catalyst support for catalytic ammonia synthesis in an electric field, which shows an anti-Arrhenius behaviour.

Understanding heteroatom doping effects on the interaction between H2O and cerium oxide (ceria, CeO2) surfaces is crucially important for elucidating heterogeneous catalytic reactions of CeO2-based oxides. Surfaces of CeO2 (111) doped with quadrivalent (Ti, Zr), trivalent (Al, Ga, Sc, Y, La), or divalent (Ca, Sr, Ba) cations are investigated using density functional theory (DFT) calculations modified for onsite Coulomb interactions (DFT + U). Trivalent (except for Al) and divalent cation doping induces the formation of intrinsic oxygen vacancy (Ovac), which is backfilled easily by H2O. Partially OH-terminated surfaces are formed. Furthermore, dissociative adsorption of H2O is simulated on the OH terminated surfaces (for trivalent or divalent cation doped models) and pure surfaces (for Al and quadrivalent cation doped surfaces). The ionic radius is crucially important. In fact, H2O dissociates spontaneously on the small cations. Although a slight change is induced by doping as for the H2O adsorption energy at Ce sites, the H2O dissociative adsorption at Ce sites is well-assisted by dopants with a smaller ionic radius. In terms of the amount of promoted Ce sites, the arrangement of dopant sites is also fundamentally important.

For a liquid organic hydride system used for a hydrogen carrier, methylcyclohexane (MCH)–toluene cycle is promising. In this cycle, dehydrogenation of MCH is an endothermic reaction and a key step. We have conducted dehydrogenation of MCH over Pt/anatase-TiO2 catalyst in an electric field to promote MCH dehydrogenation at a temperature as low as 448 K. The electric field application brought high activity of 37% conversion even at 448 K, exceeding the thermodynamic equilibrium of 12%. This Pt/anatase-TiO2 catalyst showed only a small amount of methane and carbon by-production and showed high activity for 360 min because of surface protonics.

CO2 methanation was conducted at low temperatures with an electric field. Results show that 5 wt %Ru/CeO2 catalyst exhibited high and stable catalytic activity for CO2 methanation with the electric field. The kinetic investigations and in-situ DRIFTS measurements revealed that Ru/CeO2 catalyst promoted CO2 methanation and Ru at the RuCeO2 interface (low-coordinated Ru sites) contributes to the reverse water gas shift reaction at low temperatures in the electric field.

Dehydrogenation of ethane over perovskite oxide catalysts was investigated using the redox of perovskites and H2O as an oxidizing agent. The La0.8Ba0.2MnO3-δ (LBMO) perovskite showed a high catalytic activity for dehydrogenation of ethane. Periodic dry (without H2O)-wet (with H2O) operation tests revealed that dehydrogenation of ethane in the presence of H2O over LBMO proceeded via the Mars-van Krevelen (MvK) mechanism. Under the wet condition with D2O instead of H2O, D2 formation was verified, demonstrating that reactive lattice oxygens in LBMO contributed to the dehydrogenation reaction and that they were regenerated by water. Isotopic transient tests with H218O and in situ X-ray absorption fine structure measurements revealed that the reduction and oxidation of Mn in LaMnO3 and LBMO occurred under the reaction atmosphere and that the partial replacement of the La sites with Ba improved the redox ability of Mn, resulting in its high activity. Furthermore, temperature-programmed reduction under H2 elucidated that the reduction of Mn3+ to Mn2+ was promoted by Ba doping. The LBMO perovskite showed the very high activity for dehydrogenation of ethane in the presence of H2O via the MvK mechanism by virtue of the high redox properties of Mn.

Efficient ammonia synthesis at low temperatures is anticipated for establishing a hydrogen carrier system. We reported earlier that application of an electric field on the Cs/Ru/SrZrO3 catalyst enhanced catalytic ammonia synthesis activity. It is now clear that N2 dissociation is activated by hopping protons in the electric field. Efficient ammonia synthesis proceeds by an "associative mechanism" in which N2 dissociates via an N2H intermediate, even at low temperatures. The governing factor of ammonia synthesis activity in an electric field for active metals differed from that in the conventional mechanism. Also, N2H formation energy played an important role. The effects of dopants (Al, Y, Ba, and Ca) on this mechanism were investigated using activity tests and density functional theory calculations to gain insights into the support role in the electric field. Ba and Ca addition showed positive effects on N2H formation energy, leading to high ammonia synthesis activity. The coexistence of proton-donating and electron-donating abilities is necessary for efficient N2H formation at the Ru-support interface.

Modified Ga-α-Al2O3 catalyst with Ba showed high catalytic activity, selectivity and low carbon formation on catalytic ethane dehydrogenation to ethylene even in the presence of steam. The resultant Ba-Ga-α-Al2O3 (Ba/Ga molar ratio = 0.10) catalyst showed high ethylene selectivity (98%), high activity, and stability. Temperature-programmed oxidation measurements revealed that Ba addition suppressed coke formation at Ga sites. XRD, XAFS and TEM results showed the existence of highly dispersed β-Ga2O3 on the α-Al2O3 support, irrespective of Ba addition. Observation of hydrogen adsorption using FT-IR spectroscopy revealed a decrease in the surface tetrahedrally coordinated Ga (designated as Ga(T)) sites by Ba modification, indicating that the surface Ga(T) sites are covered with Ba. Density functional theory calculation revealed that coke formation through ethylene decomposition is likely to occur at surface Ga(T) sites, and revealed that the addition of an optimal amount of Ba to Ga-α-Al2O3 inhibits coke formation at the surface Ga(T) sites, leading to high ethylene selectivity.

The role of the electric field and surface protonics on low temperature catalytic dry reforming of methane was investigated over 1 wt %Ni/10 mol %La-ZrO2 catalyst, which shows very high catalytic activity even at temperatures as low as 473 K. We investigated kinetic analyses using isotope and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and kinetic analyses revealed synergetic effects between the catalytic reaction and the electric field with less than one-fifth the apparent activation energy at low reaction temperatures. Results of kinetic investigations using isotopes such as CD4 and 18O2, in situ DRIFTS in the electric field, and density functional theory calculation indicate that methane dry reforming proceeds well by virtue of surface protonics. CH4 and CO2 were activated by proton collision at the Ni-La-ZrO2 interface based on the "inverse" kinetic isotope effect.

Methane activation on diluted metal ensembles is a challenging task in the field of alloy chemistry. This report describes that synergy between an electric field and Pd-Zn alloy allows improved catalytic activities in the steam reforming of methane. Because of surface protonics, Pd-Pd ensembles are no longer needed. Ligand effects facilitate methane conversion.

A Pd catalyst supported on Ba-substituted LaAlO3 perovskite (Pd/La0.9Ba0.1AlO3-δ) was investigated for NO reduction at low temperature by propylene, which revealed that Pd/La0.9Ba0.1AlO3-δ has remarkably higher activity than other Pd catalysts at low temperatures (≤573 K) for NO reduction by propylene. To elucidate the surface reaction pathway, transient response tests were conducted using 18O2. Also, X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements were conducted. Comparison with a Ba-impregnated catalyst (Pd/Ba/LaAlO3) demonstrated that Pd/La0.9Ba0.1AlO3-δ shows higher activity for the formation of oxygenated species (CxHyOz) as an intermediate for NO reduction because the surface lattice oxygen has improved mobility via Ba2+ substitution in LaAlO3. Therefore, Pd/La0.9Ba0.1AlO3-δ have high activity for NO reduction, even at low temperatures in a humid condition.

10wt%Ni-10wt%Mg-La0.1Zr0.9O2-x (LZO) catalyst shows high reforming activity of methane while suppressing methane combustion on tri-reforming of methane at low temperatures of 473 K in an electric field. On the basis of results of light-on and light-off tests for methane oxidation and temperature dependencies for catalytic methane steam reforming activity with or without the electric field, we found that Mg addition to 10wt%Ni-LZO catalyst suppresses methane combustion, while the methane steam reforming proceeds well by virtue of surface protonics in the electric field. Ni2+ on 10wt%Ni-10wt%Mg-LZO catalyst was more cationic than that on 10wt%Ni-LZO catalyst, and NiO-MgO solid solution formed on LZO support played an important role in combustion suppression.

Organic chemical hydrides are one of the most potential methods for hydrogen storage, however, aromatic compound remains unreacted after the hydrogenation process due to equilibrium limitations. To address this, a solid-state adsorbent which could selectively adsorb toluene from methylcyclohexane - toluene mixture was developed. Several La-based oxides were tested and La0.8Ba0.2CoO3-d (LBCO) exhibited high adsorption and selectivity for toluene. Analyses of the electronic state and adsorption state of toluene found part of the Co ions in the LBCO lattice were Co4+. The high oxidation state of Co4+ in the LBCO lattice and surface lattice oxygen mediates the selective adsorption of toluene.

The structure of Pt-Mn/Al2O3 catalyst which shows high performance for dehydrogenation of methylcyclohexane, a prospective hydrogen carrier, was investigated by XAFS and DFT calculations. Mn addition on Pt/Al2O3 brings higher activity, selectivity, and stability for dehydrogenation of MCH than with Pt/Al2O3 alone. Results of XAFS and DFT calculations revealed that MnOx selectively covered the unsaturated coordination of Pt. On the unsaturated step facets such as Pt (1 1 0) and Pt (3 1 1), demethylation proceeds easily. Addition of Mn on Pt/Al2O3 catalyst brought selective dehydrogenation of MCH by coverage of such step sites with MnOx.

© 2018 Elsevier B.V. Development of a highly efficient ammonia synthesis process is desirable for achieving a sustainable society. Regarding conventional heterogeneous catalysts, Ru-supported catalyst exhibits higher turn-over frequency (TOF) than Fe-supported or Ni-supported catalysts. However, we found that Fe-supported and Ni-supported catalysts show higher TOF than Ru-supported catalyst in an electric field at the low temperature of 373 K. Density functional theory (DFT) calculations revealed that N2 dissociation through the “associative mechanism” plays a key role in the electric field. The ammonia synthesis activity in the electric field is determined by the N2H formation energy at the metal-support interface.

Ba addition to supported Ni catalysts was investigated on steam reforming of toluene, as a model compound of biomass tar. Ba addition showed drastic promotive effects on catalytic activity and tolerance against oxidation. Various catalytic tests and characterization were conducted, including pressure dependence, Arrhenius plots, STEM and XAFS observations, dispersion of supported Ni, and temperature programmed reduction. Results revealed that the electron donation from Ba to Ni enabled high catalytic performance of Ba/Ni/LaAlO3 perovskite catalyst.

To elucidate specific functions of supports, we investigated steam reforming of toluene as a model compound of biomass tar over Co catalyst supported on perovskite-type oxide. Co-supported La0.7Sr0.3AlO3-δ catalyst showed the highest activity among various Co-supported catalysts. STEM measurements and XPS measurements revealed the coexistence of La cation and lattice oxygen defect produces an anchoring effect to Co particles. The lattice oxygen release rate on each catalyst was measured with H218O steady-state isotopic transient kinetic analysis (SSITKA). The anchoring effect, higher dispersion of Co and redox property, are important for the high catalytic performance of Co/La0.7Sr0.3AlO3-δ catalyst on toluene steam reforming.

Methylcyclohexane (MCH) is a prospective hydrogen carrier candidate. Although Pt/Al2O3 catalyst shows high conversion for dehydrogenation of MCH at 623 K, methane formation and deactivation caused by coke deposition are issues over the catalyst. Results of this study demonstrate that Mn addition to Pt/Al2O3 brought higher selectivity and stability for dehydrogenation of MCH than with Pt/Al2O3 alone. Although Pt and Mn do not form an alloy structure, Pt and Mn form an adjacent structure, and the unsaturated coordination of Pt which promotes methane formation and deactivation decreased. Pt-Mn/Al2O3 shows high catalytic performance by virtue of the coverage of such sites by MnOx.

Dehydrogenation of methylcyclohexane (MCH) was conducted over Pt/TiO2-Al2O3 catalysts, showing high activity, selectivity, stability, and high mechanical strength. XPS measurements revealed that the binding energy of Pt 4d5/2 shifted to a lower energy by adding TiO2 due to electron donation from TiO2. Formed toluene released immediately on electron-rich Pt before further decomposition to form methane and coke thanks to π-coordination. This phenomenon improved the catalytic performance, ensuring high selectivity, and durability for methylcyclohexane dehydrogenation.

We investigated steam reforming of toluene as a model compound of aromatic hydrocarbons included in biomass tar over Co supported La0.7Sr0.3AlO3-δ (LSAO), perovskite oxide. Ni-supported LSAO catalyst has shown high activity and coke resistance from the redox property of lattice oxygen in/on the LSAO support. Co is known as an active metal for this reaction, so Co/LSAO catalyst was investigated in this work. Co/LSAO catalyst, which showed high steady-state activity and stability, was characterized using H218O isotopic transient response tests, STEM, FT-IR, Arrhenius plot and partial pressure dependence to elucidate high and stable catalytic activity. In situ FT-IR measurements revealed that reaction intermediates on Co/LSAO desorbed at 873 K or lower temperatures. Although redox property of lattice oxygen did not change at around 848 K based on isotopic transient tests, the Arrhenius plots indicate that the rate-determining step changed at around 848 K because of reaction intermediate decomposition desorption. Fast reaction and desorption of absorbed intermediates on Co/LSAO enable catalytic stability during toluene steam reforming.

Methylcyclohexane (MCH) is expected as a hydrogen carrier. Dehydrogenation of MCH was conducted over supported Pt catalysts at 623 K. Pt/TiO2 showed high stability for dehydrogenation and good resistance for coke formation. The partial pressure dependence of MCH, toluene, and H2 was investigated for Pt/TiO2 and Pt/Al2O3 catalysts, which showed different tendencies for toluene partial pressure. The reaction order of toluene partial pressure for Pt/TiO2 was almost zero, but that for Pt/Al2O3 was a negative value. Toluene inhibited the Pt/Al2O3 catalytic activity, but that of Pt/TiO2 was unaffected. The SMSI effect was confirmed on Pt/TiO2 by CO chemisorption measurement. Pt on TiO2 became an electron-rich state compared to Pt0 because of the electron donation from TiOx, and the toluene adsorption to Pt on TiO2 was weakened.

Ni/perovskite-type oxide catalyst (Ni/La<inf>0.7</inf>Sr<inf>0.3</inf>AlO<inf>2.85</inf>: LSAO) shows high catalytic activity and low carbon formation during the steam reforming of aromatic hydrocarbons because of the high mobility of lattice oxygen in the support. The reaction mechanisms of the catalyst were investigated by characterizations and catalytic activity tests for steam reforming of various hydrocarbons including toluene, methylcyclohexane, and n-heptane. The catalytic performance was affected by the reactant structure, as revealed by Arrhenius plots and FT-IR analyses. Adsorption state and stability of reaction intermediates were very important factors in the catalytic activity for steam reforming.

Pt/Ni/La0.7Sr0.3AlO3-δ (Pt/Ni/LSAO) catalyst showed high catalytic activity and low coke formation for hydrogen production by steam reforming of toluene, even without pre-reduction. STEM-EDX and XAFS analyses revealed that Pt and Ni formed adjacent or alloy structure. Electron donation from supported Pt to Ni was observed by XPS observation, and the improvement of reducibility of Ni by Pt addition was observed by H 2-TPR. Catalytic activity of the reduced Ni was brought by the PtNi interaction. The impregnation order of Pt and Ni affected the catalytic activity and the amount of coke formation due to the difference of the structure of supported metals. Dilution effects of Pt on Ni metal and the contact between Ni and LSAO support apparently affect the suppression of coke formation. © 2013 Elsevier B.V.

Steam reforming of toluene as a model compound of biomass tar was conducted on supported Ni catalysts. The Ni catalyst supported on perovskite oxide (La0.7Sr0.3AlO3-δ: LSAO) showed the highest toluene conversion (58%) and lowest coke formation (57 mg g-cat -1) at 873 K thanks to the smaller Ni particle size and larger perimeter between Ni and perovskite support, confirmed by XRD, BET, STEM and XAFS. In this paper, adsorption of toluene on Ni/LSAO catalyst was investigated using FT-IR method to estimate the reaction mechanism. IR spectra during temperature programmed desorption revealed that strong adsorption of toluene was observed only on LSAO and Ni/LSAO. The decomposition of adsorbate to CO or CO2 was promoted by supported Ni metal. Lattice oxygen of perovskite support contributed to the oxidation of the intermediate at the interface of Ni and perovskite. In addition, the oxidation of intermediate was promoted by introducing steam. Investigating adsorptions of various probe molecules (benzene, n-heptane, ethylene and benzaldeyde) revealed that decomposition of aromatic ring proceeded on Ni/LSAO. © 2013 Elsevier B.V. All rights reserved.