To estimate the positions of Brønsted
acid sites on ITQ-21
containing Al atoms (Al-ITQ-21), the physicochemical and catalytic
properties of Al-ITQ-21 as a solid acid catalyst were investigated.
The 27Al and 1H multinuclear solid-state nuclear
magnetic resonance (MAS NMR) spectra and the NH3 temperature-programmed
desorption spectra of Al-ITQ-21 at several concentrations of Al were
measured. The conversion of n-heptane was examined
over Al-ITQ-21. The positions of the Al atoms in the Al-ITQ-21 lattice
were limited by measuring 27Al MAS NMR spectra. This limitation
made possible the designation of oxygen atoms bonded to acidic protons
by measuring both the NH3 temperature-programmed desorption
and the 1H MAS NMR spectra. Furthermore, the total reaction
rates for the conversion of n-heptane on different
Brønsted acid sites were determined.
Ytterbium was introduced into K+-exchanged Y-zeolite (Yb/K-Y) by impregnation from a liquid ammonia solution of the metal, and the change in the chemical state of the metal with evacuation temperature was investigated by infrared (IR), X-ray absorption fine structure (XAFS) and X-ray photoelectron (XPS) spectroscopies.When ammonia was removed by brief evacuation at room temperature followed by evacuation at 333 K, the IR spectrum showed the presence of Yb amides. The amide species were observed up to 423 K. The Yb L,-edge X-ray absorption near-edge structure (XANES) spectrum showed that the Yb species exist as 16.4% Yb(ii) and 83.6% Yb(iii) after evacuation at 333 K. The fraction of Yb2+ increased with increasing evacuation temperature and reached 44.2% at 573 K by the decomposition of Yb(ii, 111) amides to Yb(ii, 111) imides. The fraction of Yb(iit) species increased at an evacuation temperature >600 K, owing to the decomposition of Yb imides to Yb nitride with concomitant formation of hydrogen. The Yb(ii) imide species catalyses the isomerization of but-1-ene and the Michael reaction of cyclopent-2-enone with dimethylmalonate, while the Yb(iii) nitride species catalyses the hydrogenation of ethene.
Benzene adsorption on a WS 2 (100) surface was studied by ab initio periodic DFT computations. Benzene adsorption is facile on the bridge site of the bare W edge via g 2 or g 3 coordination. Taking into account the stable configuration at the W edge under typical hydrotreating reaction conditions (623 K, H 2 S/H 2 = 0.01), benzene adsorption is found to be difficult, even when defective bridge sites are created.
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