Hierarchical porous ZSM-5 (HP-ZSM-5)
was constructed using organosilanes as the growth inhibitors for CO2 capture. The properties of adsorbents were characterized
by X-ray diffraction, N2 adsorption/desorption, scanning
electron microscopy, temperature-programmed desorption of carbon dioxide,
and 27Al magic angle spinning nuclear magnetic resonance.
It was found that HP-ZSM-5 samples synthesized by organosilanes had
a significant effect on the microstructure and morphology. CO2 adsorption capacity of HP-ZSM-5 was up to 58.26 cm3 g–1 at 0 °C and 1 bar, significantly higher
than that of the ZSM-5 sample. The effective improvement of CO2 adsorption performance mainly originated from the micro-/mesoporous
composite structure and complex surface morphology, which can provide
low-resistant pathways for CO2 through the porous network.
Besides, in situ Fourier transform infrared spectroscopy
was carried out to study the adsorption process on adsorbents, and
the results indicated that a faster physical adsorption process was
achieved as a result of the introduction of mesopores.
Ce x Zr 1-x O 2 oxides prepared by a soft reactive grinding (SRG) procedure have been investigated as the catalysts for HCl oxidation. The results show that the catalytic activities and stabilities of Ce x Zr 1-x O 2 oxides are remarkably dependent on the Ce/Zr ratio. A correlation between the physicochemical properties and catalytic performances of these samples reveals that the cubic phase in Ce x Zr 1-x O 2 with higher oxygen storage capacity (OSC) is more activity for HCl oxidation, but the tetragonal phase is crucial to the stability of catalysts. The Ce 0.5 Zr 0.5 O 2 catalyst with mixed phases and the highest OSC (80 µmol O2 ·g cat -1 ) exhibits an excellent activity (1.89 g Cl2 ·g cat -1 ·h -1 at 430 °C) and stability (300 h) in the target reaction. Kinetic studies show that both O 2 and HCl competed for the active sites rendering desorption of surface Cl is the rate-determining step. Accelerating the replacement of surface Cl by O 2 is the essence for the activity improvement of Ce 0.5 Zr 0.5 O 2 .
Alkyltrimethoxysilanes
with different chain lengths (trimethoxypropylsilane,
trimethoxyoctylsilane, and dodecyltrimethoxysilane) were utilized
as mesopore-generating agents to synthesize hierarchical ZSM-5 samples
with different amounts of mesoporous volume. The samples were characterized
by X-ray powder diffraction, nitrogen adsorption–desorption,
scanning electron microscopy, transmission electron microscopy, and
CO2-temperature-programmed desorption. With the growth
of chain length, the alkyltrimethoxysilanes showed low
reactivity and affinity for the surfaces of zeolite precursors due
to the increase of hydrophobic character of the alkyl moiety, which
resulted in the decrease of mesoporous volume. CO2 adsorption
behaviors of the samples including adsorption capacity, adsorption
kinetics, adsorption selectivity, adsorption thermodynamics, and adsorbent
stability were studied. The experimental results indicated that hierarchical
ZSM-5 modified by trimethoxypropylsilane exhibited the
highest mesopores volume (0.12 cm3·g–1), corresponding to the fastest capture rate (about 2.5 times of
conventional ZSM-5) and the highest capture capacity (2.15 mmol·g–1 at 25 °C and 100 kPa). Therefore, hierarchical
ZSM-5 synthesized by the alkyltrimethoxysilanes with short
chain length can generate extra mesopores and active adsorption sites,
which provided a new strategy to regulate the structure of ZSM-5 for
rapid CO2 adsorption.
As appropriate alternatives
to precious metals in volatile organic
compound (VOC) combustion, La-based perovskites have attracted increasing
attention due to their tunable structure and sintering-resistance
capacity. Herein, chemically tailored surface Co-enriched LaCoO3 perovskite oxides (LCO) with abundant surface defects were
successfully constructed via a facile selective acid-etching method,
in which lanthanum located at the A-site was preferentially dissolved
and exsolved cobalt opportunely dispersed on the surface of the perovskite.
The unique LCO catalysts could enhance the electron transfer and facilitate
the activation of oxygen molecules through the interface Co2+/Co3+ redox cycles. Among all as-synthesized LCO catalysts,
the LCO-20 sample (LaCoO3 treated with 1 M HNO3 for 20 min) revealed the optimum catalytic performance (T
50 and T
90 of 184
and 206 °C at a space velocity of 15 000 mL/(g h) with
1000 ppm toluene, respectively), stability, and durability (5 vol
% water). The excellent activity of LCO-20 might be mainly ascribed
to the accelerated activation and circulation of the oxygen species
initiated by the surface defects and Co2+/Co3+ redox cycles.
Mn–Ti amorphous oxides prepared by the combined in situ deposition and freeze-drying strategy exhibited excellent activities and stability in low-temperature NH3-SCR.
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