The
synthesis of
a TS-1 zeolite with
high-content framework Ti and small particles has been developed by
adding NH4HCO3 and suspended seeds as an assistant.
With the addition of NH4HCO3, the Hofmann decomposition
of the tetrapropylammonium cation (TPA+) decreased, and
the framework Ti content of the zeolite increased first and then decreased
while the particle became larger. With the assistance of suspended
seeds, the TS-1 synthesized under a low-alkalinity system possesses
small particle size and high-content framework Ti, and it shows the
best catalytic activity among the prepared catalysts. Because the
decomposition of TPA+ decreased, the mother liquid could
be reused in the next run of preparation. Even though the recycled
mother liquid was reused five times, all obtained TS-1 samples exhibited
similar catalytic performances in propylene epoxidation. This work
provides an efficient process for preparing TS-1 with good catalytic
performance and reduces the discharge of the waste liquid.
TS-1 deactivated in industrial cyclohexanone ammoximation can be effectively regenerated by hydrothermal treatment with TPABr and ethanolamine solution.
In the paper, mesopores and macropores are introduced inside the crystals of micrometer microporous titanium silicate-1 (TS-1) to solve the problem of active site coverage and mass transfer during extrusion. Hierarchically porous titanium silicalite-1 (HPTS-1) was acquired by treating micrometer microporous TS-1 with TPABr and ethanolamine. Extruded HPTS-1 maintained greatly superior catalytic performance and possessed high mechanical strength. Characterization results showed that extruded HPTS-1 possessed macroporous, mesoporous structure inside the crystals. These abundant pores are not only beneficial for diffusion reactants, but also make Ti-peroxo species (η2), active oxidation sites in TS-1/H2O2 system become much more reactive. The formula of extruded HPTS-1 was optimized using an orthogonal experiment. The maximum strength of extruded HPTS-1 was up to 200 N/cm, the highest yield of propylene oxide was 92.5% and the specific rate was up to 41.9%. The research provides a scientific basis for producing extruded catalysts with excellent catalytic performance and high mechanical strength in industrial applications.
Ga-doped ZSM-5 zeolites were directly synthesized by
a facile one-step
hydrothermal method without organic templates and calcination and
then investigated in the cyclohexene hydration reaction. The structure,
component, textural properties, and acidity of the as-prepared samples
were examined by X-ray diffraction (XRD), scanning electron microscopy
(SEM), X-ray fluorescence (XRF), Brunauer–Emmett–Teller
(BET), ammonia temperature-programmed desorption (NH
3
-TPD),
pyridine-chemisorbed IR (Py-IR), and
71
Ga,
27
Al,
29
Si, and
1
H magic-angle spinning (MAS)
NMR techniques. The characterization results showed that the introduction
of Ga atoms into the ZSM-5 zeolite framework is much easier than Al
atoms and beneficial to promote the formation of small-sized crystals.
The number of Brønsted acid sites of Ga-doped ZSM-5 samples obviously
increased compared with Ga0-ZSM-5. Additionally, the highest cyclohexanol
yield (10.1%) was achieved over the Ga3-ZSM-5 sample, while the cyclohexanol
yield of the Ga0-ZSM-5 sample was 8.6%. This result indicated that
the improved catalytic performance is related to its larger external
surface area, smaller particle size, and more Brønsted acid sites
derived from Si–OH–Al and Si–OH–Ga of
Ga3-ZSM-5. Notably, the green route reduces harmful gas emission and
provides a basis for doping other heteroatoms to regulate the catalytic
performance of zeolites, especially in industrial production.
The development of green and sustainable techniques for synthesizing a class of significant industrial materials like zeolites has been recognized as an inevitable trend in recent years. Herein, an efficient...
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