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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This report is the first describing a study quantitatively analysing aspects of oxide surface protonics in a dry H2 atmosphere. Elucidating surface protonics is important for electrochemical and catalytic applications. In this study, AC impedance spectroscopy was used to investigate surface conduction properties of porous CeO2 at low temperatures (423–573 K) and in a dry H2 atmosphere. Results demonstrated that the conductivity increased by several orders of magnitude when H2 was supplied. Dissociative adsorption of H2 contributes to conduction by forming proton–electron pairs. Also, H/D isotope exchange studies confirmed protons as the dominant conduction carriers. Furthermore, H2 adsorption equilibrium modelling based on the Langmuir mechanism was applied to explain the H2 partial pressure dependence of conductivity. For the first time, the obtained model explains the experimentally obtained results both qualitatively and quantitatively. These findings represent new insights into surface protonics in H2 atmosphere. [ABSTRACT FROM AUTHOR]

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 CeO2 matrix 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 CeO2 matrix 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 (NH3 synthesis in an electric field). Results confirmed clear correlation between H atom adsorption energy and surface protonics. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The details of the chemoselective methylation of 2-aminoethanol as well as fictionalized amines over solid acid-base catalysts with scCH3OH using a continuous-flow fixed-bed, tubular reactor is presented. The selective methylation was successfully applied to the synthesis of N-methylated amino alcohols and diamines as well as O-methylated ethylene glycol.

This report is the first describing a study quantitatively analysing aspects of oxide surface protonics in a dry H 2 atmosphere. Elucidating surface protonics is important for electrochemical and catalytic applications. In this study, AC impedance spectroscopy was used to investigate surface conduction properties of porous CeO 2 at low temperatures (423-573 K) and in a dry H 2 atmosphere. Results demonstrated that the conductivity increased by several orders of magnitude when H 2 was supplied. Dissociative adsorption of H 2 contributes to conduction by forming proton-electron pairs. Also, H/D isotope exchange studies confirmed protons as the dominant conduction carriers. Furthermore, H 2 adsorption equilibrium modelling based on the Langmuir mechanism was applied to explain the H 2 partial pressure dependence of conductivity. For the first time, the obtained model explains the experimentally obtained results both qualitatively and quantitatively. These findings represent new insights into surface protonics in H 2 atmosphere.

Hydrogen (H) atom adsorption and migration over the CeO 2 -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 CeO 2 -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 CeO 2 (111) surface using density functional theory (DFT) calculations. Results revealed that the electron-deficient lattice oxygen (O lat ) and the flexible CeO 2 matrix played key roles in strong adsorption of H atoms. Heterocations with smaller valence and smaller ionic radius induced the electron-deficient O lat . In addition, smaller cation doping enhanced the CeO 2 matrix 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 (NH 3 synthesis 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 (Sr 1- x Ba x ZrO 3 ; 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 Ba 2+ substitution for Sr 2+ sites provoked local distortion at the Sr 1- x Ba x ZrO 3 oxide surface, which led to a decrement in the H atom adsorption energy. Furthermore, the effect of Sr 2+ /Ba 2+ 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 Sr 2+ sites with a small amount of Ba 2+ ( x = 0.125) contributed to enhancement of ammonia synthesis rate in an electric field, which showed good agreement with predictions made using DFT calculations., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Efficient activation of CO 2 at low temperature was achieved by reverse water-gas shift via chemical 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-In 2 O 3 structured oxide can show a remarkably higher CO 2 splitting rate than ever reported. Various analyses revealed that RWGS-CL on Cu-In 2 O 3 is derived from redox between Cu-In 2 O 3 and Cu-In alloy. Key factors for high CO 2 splitting rate were fast migration of oxide ions in the alloy and the preferential oxidation of the interface of alloy-In 2 O 3 in the bulk of the particles. The findings reported herein can open up new avenues to achieve effective CO 2 conversion at lower temperatures., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Catalytic methane steam reforming was conducted at low temperature using a Pd catalyst supported on Ce 1- x M x O 2 ( x = 0 or 0.1, M = Ca, Ba, La, Y or Al) oxides with or without an electric field (EF). The effects of the catalyst support on catalytic activity and surface proton hopping were investigated. Results show that Pd/Al-CeO 2 (Pd/Ce 0.9 Al 0.1 O 2 ) showed higher activity than Pd/CeO 2 with EF, although their activity was identical without EF. Thermogravimetry revealed a larger amount of H 2 O adsorbed onto Pd/Al-CeO 2 than onto Pd/CeO 2 , so Al doping to CeO 2 contributes to greater H 2 O adsorption. Furthermore, electrochemical conduction measurements of Pd/Al-CeO 2 revealed a larger contribution of surface proton hopping than that for Pd/CeO 2 . This promotes the surface proton conductivity and catalytic activity during EF application., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

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 H 2 O and cerium oxide (ceria, CeO 2 ) surfaces is crucially important for elucidating heterogeneous catalytic reactions of CeO 2 -based oxides. Surfaces of CeO 2 (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 (O vac ), which is backfilled easily by H 2 O. Partially OH-terminated surfaces are formed. Furthermore, dissociative adsorption of H 2 O 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, H 2 O dissociates spontaneously on the small cations. Although a slight change is induced by doping as for the H 2 O adsorption energy at Ce sites, the H 2 O 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.