Herein, the methanol
conversion to aromatic hydrocarbons was studied
over a new family of mesoporous low-silica HZSM-5 (Si/Al = 11) catalysts
in a fixed-bed tubular reactor under ambient pressure at 375 °C,
feeding with weight hourly space velocity of 2 h
–1
. The catalysts were prepared in the absence and presence of Zn and
Fe in both alkaline and neutral aqueous solutions, characterized by
using X-ray diffraction, X-ray fluorescence, temperature programmed
desorption of ammonia, N
2
adsorption/desorption, thermogravimetric
analysis, Fourier-transform infrared, transmission electron microscopy
(TEM), field emission scanning electron microscopy and FE-SEM/energy
dispersive X-ray spectroscopy techniques. The [0.2Fe,0.3Zn]-alk-HZSM-5
catalyst exhibited novel selectivity for aromatics (>86 wt %),
specifically
for
m
and
p
-xylenes (44.7 wt %)
alongside 0.1 wt % for benzene.
A systematic change of HZSM-5 (HZ5)
as a catalyst of the methanol
to aromatics (MTA) reaction was undertaken by employing a fixed-bed
tubular-type reactor under ambient pressure, applying a weight hourly
space velocity (WHSV) of 2 h–1 at 375 °C, as
the first report on the application of low-Si/Al-ratio alkaline-[Mo,Na]-HZSM-5
in the MTA process. To characterize the surface and textural properties
of the catalysts, powder X-ray diffraction (PXRD), nitrogen adsorption/desorption,
temperature-programmed desorption of ammonia (NH3-TPD),
pyridine-infrared spectroscopy (Py-IR), thermogravimetric analysis
(TGA), and energy-dispersive X-ray (EDX) methods were employed. Gas
chromatography (GC) and gas chromatography-mass spectrometry (GC-MS)
measurements demonstrated a selectivity of up to 86 wt % (65.7 wt
% for benzene, toluene, and xylene (BTX)) over 2[Mo]HZ5.
NH3-TPD and Py-IR results indicated a sensible decrease
of strong acid sites on the impregnated samples, while the surface
analyses revealed the highest Lewis acid sites (LAS) together with
the largest mesopore surface area for 2[Mo]alk-HZ5, supporting
the migration of Mo species to the bulk of the catalysts. Mo impregnation
had a minor effect on the observed coke formation in the promoted
catalyst.
An example of zeolite selectivity (MFI MOR) driven by synthesis aging time has been studied. Using N,N,N',N'-tetramethyl-N,N'-dipropyl-ethylenediammonium diiodide (TMDP) as organic structure-directing agent (OSDA), the zeolite phases obtained at...
Two new macrocyclic ligands containing 17- and 19-membered ON-donor aza-crowns anchored to [60]Fullerene were synthesized and characterized by employing HPLC, electrospray ionization mass (ESI-MS), H andC NMR, UV-vis, IR spectroscopies, as well as powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA) in solid state. TGA measurements revealed that upon linking each of these macrocycle rings to [60]Fullerene, the decomposition point measured for [60]Fullerene moiety was increased, indicating on the promoted stability of [60]Fullerene backbone during binding to these macrocyclic ligands. Moreover, the ground state non-covalent interactions of [60]Fullerene derivatives of ON (x=2, and 3) aza-crown macrocyclic ligands namely, L-L with zinc phthalocyanine (ZnPc) were also investigated by UV-vis absorption, steady state and time resolved fluorescence spectrophotometry in N-methyl-2-pyrrolidone (NMP). The calculation of Stern-Volmer constants (K) indicated on existence of an efficient quenching mechanism comprising of the excited singlet state of ZnPc in the presence of L-L. The observation of an appropriate correlation between decrease in fluorescence intensity and lifetime parameters led us to propose the occurrence of a static mechanism for the fluorescence quenching of ZnPc in the presence of L-L. The binding constants (K) of L-L/ZnPc were also determined applying the fluorescence quenching experiments. Meanwhile, the incompatibility of both K and K values found for L was also described in terms of structural features using DFT calculations using the B3LYP functional and 6-31G* basis set.
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