Electron paramagnetic resonance and electron spin echo study of supported and unsupported vanadium oxides

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出版日

DOI 10.1039/A900119K

インパクトファクター 3.676

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要旨

Electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) spectroscopies have been used to characterize paramagnetic centers in crystalline and gel forms of vanadium pentoxide as well as vanadia supported on silica, titania, and magnesia. A number of different paramagnetic centers are observed in the bulk and supported vanadia phases that are characterized by their spin Hamiltonian parameters. ESEEM data for all the bulk vanadium oxide samples show intense modulation at the 51V Larmor frequency. This modulation originates from interlayer VO2+ species in gel samples and from V4+ centers in crystalline oxides. The intensity of the 51V modulation varies considerably from sample to sample depending on the specific nature of the paramagnetic center. For the supported vanadia samples, complex EPR spectra are obtained that show two classes of signals. Signals with narrow linewidths and resolved hyperfine structure are observed suggesting magnetically isolated V4+ in addition to dipolar exchange broadened signals. ESEEM spectroscopy reveals that the spectra observed for vanadia supported on silica are from surface bound vanadyl species that interact with predominantly diamagnetic surface vanadia clusters. In contrast, for vanadia supported on titania, the V4+ signals observed by pulsed EPR show no modulation. The absence of modulation is attributed to well dispersed surface vanadyl species and subsurface V4+6c centers. Vanadium supported on magnesia interacts to form new magnesium vanadate phases containing V4+6c. It is shown that ESEEM is a valuable tool for characterizing vanadia supported on various oxides.

掲載誌

Physical Chemistry Chemical Physics

CiteScore: 5.5

自己引用率: 10.3%

年間論文数: 3036

Physical Chemistry Chemical Physics (PCCP) is an international journal co-owned by 19 physical chemistry and physics societies from around the world. This journal publishes original, cutting-edge research in physical chemistry, chemical physics and biophysical chemistry. To be suitable for publication in PCCP, articles must include significant innovation and/or insight into physical chemistry; this is the most important criterion that reviewers and Editors will judge against when evaluating submissions. The journal has a broad scope and welcomes contributions spanning experiment, theory, computation and data science. Topical coverage includes spectroscopy, dynamics, kinetics, statistical mechanics, thermodynamics, electrochemistry, catalysis, surface science, quantum mechanics, quantum computing and machine learning. Interdisciplinary research areas such as polymers and soft matter, materials, nanoscience, energy, surfaces/interfaces, and biophysical chemistry are welcomed if they demonstrate significant innovation and/or insight into physical chemistry. Joined experimental/theoretical studies are particularly appreciated when complementary and based on up-to-date approaches.