To valorize lignin as a renewable source of aromatics, it is necessary to develop selective heter... more To valorize lignin as a renewable source of aromatics, it is necessary to develop selective heterogeneous catalysts for the hydrodeoxygenation reaction of aromatic oxygenates such as anisole. Most of the metal supported catalysts tested so far exhibit a high conversion but a low selectivity towards valuable aromatic hydrocarbons, yielding mainly phenolic compounds. To gain insights into that catalytic system, we performed surface science experiments (X-ray Photoelectron Spectroscopy and Temperature Programmed Desorption) under Ultra-High Vacuum conditions (UHV). Dosing anisole on Pt(111) surprisingly gave benzene, carbon monoxide and hydrogen as the main desorbing products of decomposition. With the help of Density Functional Theory (DFT) we successfully explain the unexpected selectivity. In the present work we show in particular that phenoxy PhO stands as a key intermediate. Although the UHV conditions do not allow the hydrogenation of phenoxy into phenol, i.e. the catalytic produ...
Hydrogen Rydberg-atom time-of-flight spectroscopy was used to study the photolysis of HX (X=Cl, B... more Hydrogen Rydberg-atom time-of-flight spectroscopy was used to study the photolysis of HX (X=Cl, Br, I) adsorbed on LiF(001). Adsorption characteristics were investigated by temperature programmed desorption. While HCl and HBr appeared to form stable but perforated monolayers on LiF(001), HI did not wet the surface under equilibrium conditions. This behavior of HI was ascribed to the mismatch of its van
Trimetallic perovskite oxides, Sm(1 − x)CexFeO3 ± λ (x = 0–0.05), were prepared by thermal decomp... more Trimetallic perovskite oxides, Sm(1 − x)CexFeO3 ± λ (x = 0–0.05), were prepared by thermal decomposition of amorphous citrate precursors followed by calcinations. The material properties of the substituted perovskites were characterized by X-ray diffraction (XRD), X-ray florescence spectroscopy (XRF), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The doped materials exhibited a single perovskite phase in air up to 1350 °C and have specific surface areas in the range of 2.696–8.665 m2/g. In reducing atmosphere (5%v/vH2/N2), the unsubstituted perovskite (x = 0) decomposed into two phases while the ceria stabilized materials (x = 0.01, x = 0.03, x = 0.05) remained in a single phase as revealed by XRD analysis. Their conductivities were measured by the four point probe method in air and in dilute hydrogen (5%v/vH2/N2) separately. The ceria substituted materials show increased stability versus reduction and phase separation for a wide temperature range (up to 1000 °C). Although undoped SmFeO3 has higher conductivity under oxidizing conditions than ceria doped SmFeO3 due its p-type nature, the situation is reversed under reducing conditions. The ceria substituted perovskites (Sm(1 − x)CexFeO3 ± λ, x = 0–0.05) showed higher conductivity in reducing than in oxidizing conditions, suggesting that ceria doping at the A-site has changed the SmFeO3 from p-type to n-type semi-conducting behavior.
A new series of perovskite materials with formula Sm0.95Ce0.05Fe1 − xNixO3 − δ (0 ≤ x ≤ 0.10) has... more A new series of perovskite materials with formula Sm0.95Ce0.05Fe1 − xNixO3 − δ (0 ≤ x ≤ 0.10) has been prepared by sol–gel combustion via a citrate precursor route. X-ray diffraction data showed that materials prepared by this method had a single orthorhombic phase belonging to the Pnma (62) space group. The study of powders sintered in air and in reducing atmospheres reveals that these materials do not show phase separation in air (up to 1350 °C) nor under 5% v/v H2/N2 (up to 700 °C), but a phase separation of Sm2O3 does occur at and above 800 °C under 5% v/v H2/N2 without deterioration of the perovskite phase. The surfaces of all the powders (fresh, in-situ reduced and ex-situ reduced) were Sm rich, and multiple oxidation states for Fe were observed. XP analysis of in-situ reduced samples (800 °C and above) shows that metallic Fe forms in all nickel doped materials except x = 0.07. The surface oxygen vacancies and percentages of lattice and adsorbed oxygen for this series of Ni doped materials were determined and the oxygen recapturing ability is explained in terms of the multiple oxidation states of Fe.► Stable Sm0.95Ce0.05Fe1 − xNixO3 − δ perovskites in oxidizing and reducing atmospheres. ► Ni induces vacancy formation. ► Redox processes enable oxygen loss and recapture.
A series of cobalt doped Sm0.95Ce0.05FeO3−δ perovskites with formula Sm0.95Ce0.05Fe1−xCoxO3−δ (x=... more A series of cobalt doped Sm0.95Ce0.05FeO3−δ perovskites with formula Sm0.95Ce0.05Fe1−xCoxO3−δ (x=0–0.10) were prepared by thermal decomposition of amorphous citrate precursors followed by calcination at 850°C in air for 24h. These materials are stable in air even at 1350°C and under reducing conditions (5% v/v H2/N2) up to ∼800°C, when phase separation ensues. Their conductivities were measured both in air and
ABSTRACT Trimetallic perovskite oxides, Sm(1−x)CexFeO3±λ (x=0–0.05), were prepared by thermal dec... more ABSTRACT Trimetallic perovskite oxides, Sm(1−x)CexFeO3±λ (x=0–0.05), were prepared by thermal decomposition of amorphous citrate precursors followed by calcinations. The material properties of the substituted perovskites were characterized by X-ray diffraction (XRD), X-ray florescence spectroscopy (XRF), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The doped materials exhibited a single perovskite phase in air up to 1350 °C and have specific surface areas in the range of 2.696–8.665 m2/g. In reducing atmosphere (5%v/vH2/N2), the unsubstituted perovskite (x=0) decomposed into two phases while the ceria stabilized materials (x=0.01, x=0.03, x=0.05) remained in a single phase as revealed by XRD analysis. Their conductivities were measured by the four point probe method in air and in dilute hydrogen (5%v/vH2/N2) separately. The ceria substituted materials show increased stability versus reduction and phase separation for a wide temperature range (up to 1000 °C). Although undoped SmFeO3 has higher conductivity under oxidizing conditions than ceria doped SmFeO3 due its p-type nature, the situation is reversed under reducing conditions. The ceria substituted perovskites (Sm(1−x)CexFeO3±λ, x=0–0.05) showed higher conductivity in reducing than in oxidizing conditions, suggesting that ceria doping at the A-site has changed the SmFeO3 from p-type to n-type semi-conducting behavior.
To valorize lignin as a renewable source of aromatics, it is necessary to develop selective heter... more To valorize lignin as a renewable source of aromatics, it is necessary to develop selective heterogeneous catalysts for the hydrodeoxygenation reaction of aromatic oxygenates such as anisole. Most of the metal supported catalysts tested so far exhibit a high conversion but a low selectivity towards valuable aromatic hydrocarbons, yielding mainly phenolic compounds. To gain insights into that catalytic system, we performed surface science experiments (X-ray Photoelectron Spectroscopy and Temperature Programmed Desorption) under Ultra-High Vacuum conditions (UHV). Dosing anisole on Pt(111) surprisingly gave benzene, carbon monoxide and hydrogen as the main desorbing products of decomposition. With the help of Density Functional Theory (DFT) we successfully explain the unexpected selectivity. In the present work we show in particular that phenoxy PhO stands as a key intermediate. Although the UHV conditions do not allow the hydrogenation of phenoxy into phenol, i.e. the catalytic produ...
Hydrogen Rydberg-atom time-of-flight spectroscopy was used to study the photolysis of HX (X=Cl, B... more Hydrogen Rydberg-atom time-of-flight spectroscopy was used to study the photolysis of HX (X=Cl, Br, I) adsorbed on LiF(001). Adsorption characteristics were investigated by temperature programmed desorption. While HCl and HBr appeared to form stable but perforated monolayers on LiF(001), HI did not wet the surface under equilibrium conditions. This behavior of HI was ascribed to the mismatch of its van
Trimetallic perovskite oxides, Sm(1 − x)CexFeO3 ± λ (x = 0–0.05), were prepared by thermal decomp... more Trimetallic perovskite oxides, Sm(1 − x)CexFeO3 ± λ (x = 0–0.05), were prepared by thermal decomposition of amorphous citrate precursors followed by calcinations. The material properties of the substituted perovskites were characterized by X-ray diffraction (XRD), X-ray florescence spectroscopy (XRF), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The doped materials exhibited a single perovskite phase in air up to 1350 °C and have specific surface areas in the range of 2.696–8.665 m2/g. In reducing atmosphere (5%v/vH2/N2), the unsubstituted perovskite (x = 0) decomposed into two phases while the ceria stabilized materials (x = 0.01, x = 0.03, x = 0.05) remained in a single phase as revealed by XRD analysis. Their conductivities were measured by the four point probe method in air and in dilute hydrogen (5%v/vH2/N2) separately. The ceria substituted materials show increased stability versus reduction and phase separation for a wide temperature range (up to 1000 °C). Although undoped SmFeO3 has higher conductivity under oxidizing conditions than ceria doped SmFeO3 due its p-type nature, the situation is reversed under reducing conditions. The ceria substituted perovskites (Sm(1 − x)CexFeO3 ± λ, x = 0–0.05) showed higher conductivity in reducing than in oxidizing conditions, suggesting that ceria doping at the A-site has changed the SmFeO3 from p-type to n-type semi-conducting behavior.
A new series of perovskite materials with formula Sm0.95Ce0.05Fe1 − xNixO3 − δ (0 ≤ x ≤ 0.10) has... more A new series of perovskite materials with formula Sm0.95Ce0.05Fe1 − xNixO3 − δ (0 ≤ x ≤ 0.10) has been prepared by sol–gel combustion via a citrate precursor route. X-ray diffraction data showed that materials prepared by this method had a single orthorhombic phase belonging to the Pnma (62) space group. The study of powders sintered in air and in reducing atmospheres reveals that these materials do not show phase separation in air (up to 1350 °C) nor under 5% v/v H2/N2 (up to 700 °C), but a phase separation of Sm2O3 does occur at and above 800 °C under 5% v/v H2/N2 without deterioration of the perovskite phase. The surfaces of all the powders (fresh, in-situ reduced and ex-situ reduced) were Sm rich, and multiple oxidation states for Fe were observed. XP analysis of in-situ reduced samples (800 °C and above) shows that metallic Fe forms in all nickel doped materials except x = 0.07. The surface oxygen vacancies and percentages of lattice and adsorbed oxygen for this series of Ni doped materials were determined and the oxygen recapturing ability is explained in terms of the multiple oxidation states of Fe.► Stable Sm0.95Ce0.05Fe1 − xNixO3 − δ perovskites in oxidizing and reducing atmospheres. ► Ni induces vacancy formation. ► Redox processes enable oxygen loss and recapture.
A series of cobalt doped Sm0.95Ce0.05FeO3−δ perovskites with formula Sm0.95Ce0.05Fe1−xCoxO3−δ (x=... more A series of cobalt doped Sm0.95Ce0.05FeO3−δ perovskites with formula Sm0.95Ce0.05Fe1−xCoxO3−δ (x=0–0.10) were prepared by thermal decomposition of amorphous citrate precursors followed by calcination at 850°C in air for 24h. These materials are stable in air even at 1350°C and under reducing conditions (5% v/v H2/N2) up to ∼800°C, when phase separation ensues. Their conductivities were measured both in air and
ABSTRACT Trimetallic perovskite oxides, Sm(1−x)CexFeO3±λ (x=0–0.05), were prepared by thermal dec... more ABSTRACT Trimetallic perovskite oxides, Sm(1−x)CexFeO3±λ (x=0–0.05), were prepared by thermal decomposition of amorphous citrate precursors followed by calcinations. The material properties of the substituted perovskites were characterized by X-ray diffraction (XRD), X-ray florescence spectroscopy (XRF), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The doped materials exhibited a single perovskite phase in air up to 1350 °C and have specific surface areas in the range of 2.696–8.665 m2/g. In reducing atmosphere (5%v/vH2/N2), the unsubstituted perovskite (x=0) decomposed into two phases while the ceria stabilized materials (x=0.01, x=0.03, x=0.05) remained in a single phase as revealed by XRD analysis. Their conductivities were measured by the four point probe method in air and in dilute hydrogen (5%v/vH2/N2) separately. The ceria substituted materials show increased stability versus reduction and phase separation for a wide temperature range (up to 1000 °C). Although undoped SmFeO3 has higher conductivity under oxidizing conditions than ceria doped SmFeO3 due its p-type nature, the situation is reversed under reducing conditions. The ceria substituted perovskites (Sm(1−x)CexFeO3±λ, x=0–0.05) showed higher conductivity in reducing than in oxidizing conditions, suggesting that ceria doping at the A-site has changed the SmFeO3 from p-type to n-type semi-conducting behavior.
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Papers by Javier Giorgi