Pillared
clay-supported NiMo catalysts were synthesized in their
reduced and sulfided forms and applied to the hydrodeoxygenation of
guaiacol (2-methoxyphenol) as a bio-oil model compound. The sulfided
catalyst displayed better activity and selectivity as compared to
the reduced catalyst, yielding phenol as the major product. Quasielastic
neutron scattering demonstrated that jump diffusion of guaiacol was
seen after adsorption on both the sulfide catalyst and pillared clay.
Inelastic neutron scattering was carried out in conjunction with an
infrared study and reveal that there were two types of interaction
of guaiacol with the catalyst. The first is guaiacol adsorbed via
various types of H-bonding interaction, as observed in the sulfided
catalyst. The second type of interaction is guaiacol adsorbed on the
surface, presumably at a Mo vacant site, by chemisorption through
formation of a methoxyphenate species as seen in the reduced catalyst.
The interactions were greater in the sulfided catalyst by which guaiacol
was selectively adsorbed in coordination with the Ni–Mo–S
site.
Density-functional calculations were performed to study Pt-O bonding interaction on core-shell Ni@Pt and pure Pt clusters composed of 55 atoms each. Based on oxygen adsorption energy and ν(Pt-O) stretching frequency, the global trend of Pt-O bonding strength in the clusters accommodates the successive order of bridge (and/or hcp-like) > fcc-like > vertex site. Further analysis on oxygen-induced reconstruction effect using first nearest neighbor (1NN) analysis shows that 1NN Pt-Pt distribution pattern of surface atoms changes abruptly after oxygen adsorbed. The profiles of distorted 1NN distribution pattern are greatly determined by the position and the number of adsorbed oxygen on the clusters including whether the cluster type is core-shell or not. The broadening distribution pattern clearly indicates deviation of Pt-Pt bond length due to Pt-O bonds formation and the general trend is similar with the one observed in platinum-related spectroscopy studies.
The nitrogen monoxide (NO) adsorption on platinum tetramer (Pt4) clusters supported on gamma alumina (gamma-Al2O3) with surface index (111) was investigated by using ab-initio calculation based on density functional theory. The Pt4 geometries used in this study are tetrahedron and planar rhombus. The adsorption of Pt4 on gamma-Al2O3 (111) surface in tetrahedron configuration is energetically more favorable as compared to that of the planar rhombus. However, it was found that NO molecule adheres strongly to Pt4 with planar configuration on gamma-Al2O3(111) surface. In addition, the NO adsorption calculation on the isolated Pt4 clusters also shows similar preference to planar configuration. The local density of states (LDOS) reveals that the difference in reactivity comes from the different hybridization strengths between the electronic states of nitrogen atom and those of platinum tetramers. The results are in good agreement with the experiments which show similar tendency for CO and N2O reactivity to gas-phase platinum clusters.
We present the results of density functional theory calculation in oxygen dissociative adsorption process on two types of isolated platinum (Pt) clusters: Pt4 and Pt10, by taking into account the effect of cluster reconstruction. The strength of Pt–Pt bonds in the clusters is mainly defined by d–d hybridization and interstitial bonding orbitals (IBO). Oxygen that adsorbed on the clusters is weakening the IBO and thus inducing geometry reconstruction as occurred in Pt10 cluster. However, cluster that could undergo structural deformation is found to promote oxygen dissociation with no energy barrier. The details show that maintaining well-balanced of attractive and repulsive (Hellmann–Feynman) forces between atoms is considered to be the main key to avoid any considerable rise of energy barrier. Furthermore, a modest energy barrier that gained in Pt4 cluster is presumed to be originate from inequality of intramolecular forces between atoms.
The vibrational spectroscopy of CS2 has been investigated many times in all three phases. However, there is still some ambiguity about the location of two of the modes in the solid state. The aim of this work was to locate all of the modes by inelastic neutron scattering (INS) spectroscopy, (which has no selection rules), and to use periodic density functional theory to provide a complete and unambiguous assignment of all the modes in the solid state. A comparison of the observed and calculated INS spectra shows generally good agreement. All four of the ν2 bending mode components are calculated to fall within 14 cm−1. Inspection of the spectrum shows that there are no bands close to the intense feature at 390 cm−1 (assigned to ν2); this very strongly indicates that the Au mode is within the envelope of the 390 cm−1 band. Based on a simulation of the band shape of the 390 cm−1 feature, the most likely position of the optically forbidden component of the ν2 bending mode is 393 ± 2 cm−1. The calculations show that the optically inactive Au translational mode is strongly dispersed, so it does not result in a single feature in the INS spectrum.
Biochar (BCR) was obtained from the pyrolysis of a palm-oil-empty fruit bunch at 773 K for 2 h and used as a catalyst for the hydrodeoxygenation (HDO) of guaiacol (GUA) as a bio-oil model compound. Brunauer–Emmet–Teller surface area analysis, NH3 and CO2-temperature-programmed desorption, scanning electron microscope–dispersive X-ray spectroscopy, CHN analysis and X-ray fluorescence spectroscopy suggested that macroporous and mesoporous structures were formed in BCR with a co-presence of hydrophilic and hydrophobic sites and acid–base behavior. A combination of infrared, Raman and inelastic neutron scattering (INS) was carried out to achieve a complete vibrational assignment of BCR. The CH–OH ratio in BCR is ~5, showing that the hydroxyl functional groups are a minority species. There was no evidence for any aromatic C–H stretch modes in the infrared, but they are clearly seen in the INS and are the majority species, with a ratio of sp3–CH:sp2–CH of 1:1.3. The hydrogen bound to sp2–C is largely present as isolated C–H bonds, rather than adjacent C–H bonds. The Raman spectrum shows the characteristic G band (ideal graphitic lattice) and three D bands (disordered graphitic lattice, amorphous carbon, and defective graphitic lattice) of sp2 carbons. Adsorbed water in BCR is present as disordered layers on the surface rather than trapped in voids in the material and could be removed easily by drying prior to catalysis. Catalytic testing demonstrated that BCR was able to catalyze the HDO of GUA, yielding phenol and cresols as the major products. Phenol was produced both from the direct demethoxylation of GUA, as well as through the demethylation pathway via the formation of catechol as the intermediate followed by deoxygenation.
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