V2O5 impregnated onto Ce0.6Zr0.4O2‐Al2O3 is a highly active and stable catalyst for the oxidative dehydrogenation of ethylbenzene with CO2. For the first time, highly dispersed vanadium species stabilized with CeO2 and/or CeZrO2 solid solution and deposited carbonaceous materials are revealed to be main factors contributing to its high stability.
The impact of acidity and pore size on the activity and
product
selectivity of the Fischer–Tropsch (FT) synthesis was comparatively
investigated over cobalt supported on a series of alumina-grafted
siliceous SBA-15 (Al-SBA-15) via the post-synthesis method in the
medium of supercritical CO2. X-ray diffraction (XRD) results
indicate that the ordered mesoporous structure of SBA-15 is preserved
after grafting different amounts of alumina. However, both the Brunauer–Emmett–Teller
(BET) surface area and the pore volume of Al-SAB-15 are decreased
with an increasing content of alumina. Ammonia temperature-programmed
desorption (NH3-TPD) results indicate that the acidity
of Al-SBA-15, which is dominantly contributed by weak acidic sites,
increases continuously with an increasing content of alumina. The
20 wt % Co-supported catalysts prepared by the incipient impregnation
method were evaluated for FT synthesis in a fixed-bed reactor under
the conditions of 1.0 MPa, 235 °C, H2/CO = 2, and W/F = 5.02 g h mol–1.
Significantly, Co/SBA-15 shows the highest CO conversion and the lowest
selectivity of long-chain FT hydrocarbons (C21+). Moreover,
both the activity and product selectivity of FT synthesis over Co/Al-SBA-15
are strongly dependent upon the content of alumina. On the basis of
the XRD, transmission electron microscopy (TEM), hydrogen temperature-programmed
reduction (H2-TPR), hydrogen temperature-programmed desorption
(H2-TPD), O2 titration, and N2 adsorption–desorption
results of the catalysts, the reduction behavior and the extent of
reduction of the catalysts are revealed to be main factors for determining
the FT activity. Moreover, the observed product selectivity is reasonably
attributed to the varied diffusion limitations of the small pores
on the desorbed hydrocarbons and the cracking of long-chain FT hydrocarbons
over acidic sites, the extent of which are closely related to the
pore structure, location of Co species, and acidic properties of the
catalysts.
Pillared interlayer clays (PILCs) were synthesized by pillaring montmorillonite with SiO 2 , Al 2 O 3 , and ZrO 2 , and Co-supported PILCs were prepared by the impregnation method. For comparison, Co/SiO 2 and Cosupported montmorillonite treated with dilute HNO 3 (acid-clay) were also prepared. The materials were characterized by XRD, H 2 -TPR, NH 3 -TPD, O 2 titration, and N 2 adsorption-desorption. The Co-supported catalysts were comparatively investigated for Fischer-Tropsch (FT) synthesis in a fixed-bed reactor under the conditions of 1 MPa, 508 K, H 2 /CO ) 2, and W/F ) 5.02 g • h • mol -1 . The results indicate that the activities of the catalysts (i.e., CO conversions) increase in the order of Co/Na-Clay , Co/Si-PILC ≈ Co/ acid-clay ≈ Co/Al-PILC < Co/Zr-PILC ≈ Co/SiO 2 . Moreover, Co/PILCs can effectively narrow the product distribution of FT synthesis showing significantly increased C 5 -C 12 selectivity and much decreased C 21+ selectivity. The results are well explained based on the acidic properties of the PILCs together with the textural properties, pore size distributions, and reduction behaviors of the catalysts.
The hierarchical ZSM-5 zeolites with interconnected meso-/microporosity have been successfully synthesized by using the commercial organosilane surfactant TPOAC as the mesopore structure-directing agent, and the influence of the TPOAC/SiO 2 ratio in the initial synthesis gel on the crystallinity, hierarchical structure, and acidity of the obtained hierarchical ZSM-5 zeolites were systematically investigated through a combination of XRD, FTIR, SEM, TEM, N 2 adsorption, TGA, ICP, and NH 3 -TPD techniques. The catalytic performance was evaluated by the methanol-to-propylene (MTP) reaction, and the obtained results indicated that the hierarchical ZSM-5 catalysts directed by TPOAC exhibited significant enhancement in the catalytic performance reflected at activity, lifetime, product yield, P/E ratio, and coke toleration by virtue of their superior meso-/micropore interconnectivity and appropriately weakened acidity, comparing with the commercial bulky ZSM-5 and the conventional sole micropore ZSM-5.
Composition
analysis of coal tar remains a challenging task because
of its complex components. In this paper, the compositions of low
temperature coal tar (LTCT) and the wash oil fraction of high temperature
coal tar (HTCT) were studied. A thermogravimetric analyzer (TG) combined
with gas chromatography–mass spectrometry (GC/MS) with the
same temperature program was put forward to analyze the quantitative
determination of the GC/MS analyzable part of coal tar, and the composition
and distribution of the GC/MS unanalyzable part (300LTCT and 300HTCT
obtained from TG at the final temperature of 300 °C) was investigated
by a pyrolysis gas chromatography–mass spectrometer (Py-GC/MS).
Results reveal that light compositions can be extracted by petroleum
ether (PE) more effectively than heavy compositions. PE soluble fractions
of LTCT and HTCT cannot be totally gasified by GC/MS, and the remaining
parts at above 300 °C are 6.51 wt % and 4.99 wt %, respectively.
GC/MS combined with TG can accurately analyze the composition of ≤300
°C fractions in coal tar. Four dehydrogenation reactions were
presented in the fast pyrolysis process of coal tar. An intermolecular
association occurs in 300HTCT. 300LTCT is mainly composed of phenols,
aliphatics, and aromatics. The composition analysis of 300LTCT and
300HTCT by Py-GC/MS indicates that there are some bridge bonds in
the macromolecular structure of coal tar, and they have broken down
to produce small molecular weight of phenolic compounds and aromatic
hydrocarbons during pyrolysis.
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