For
the effect of structural features on the catalytic performance
of the conversion of ethanol and acetaldehyde to butadiene to be investigated,
a series of MgO–SiO2 catalysts with different structural
properties were synthesized by tuning the calcination temperature,
investigated, and characterized. The best butadiene selectivity of
80.7% appears for the MgO–SiO2 catalyst calcined
at 500 °C using a mixture
of acetaldehyde/ethanol/water (22.5:67.5:10 wt %) as feed. Addition
of the appropriate amount of water (10 wt %) improved butadiene selectivity
by inhibiting the formation of 1-butanol and C6 compounds.
Results from XRD, FT-IR, and 29Si MAS NMR indicate the
generation of a significant amount of amorphous magnesium silicates
along with few crystalline magnesium silicates for the catalyst calcined
at 500 °C. XPS results indicate that it contains the lowest binding
energies of both Si–O and Mg–O from Si–O–Mg
bonds. For the catalysts calcined at low temperature (350 and 400
°C), more 1-butanol and C6 compounds formed, which
are considered to be related to residual Mg(NO3)2. Additionally, more ethylene, diethyl ether, and butylene isomers
were produced over the MgO–SiO2 catalyst calcined
at 700 °C with the formation of forsterite Mg2SiO4. Further results from Fourier transform infrared spectroscopy
after pyridine adsorption and CO2 temperature-programmed
desorption show that the high catalytic performance is related to
the presence of Lewis acidic sites and an intermediate number of basic
sites.
Hydrophobic interaction has been considered to be responsible for adsorption of perfluorooctanesulfonate (PFOS) on the surface of hydrophobic adsorbents, but the long C-F chain in PFOS is not only hydrophobic but also oleophobic. In this study, for the first time we propose that air bubbles on the surface of hydrophobic carbonaceous adsorbents play an important role in the adsorption of PFOS. The level of adsorption of PFOS on carbon nanotubes (CNTs), graphite (GI), graphene (GE), and powdered activated carbon (PAC) decreases after vacuum degassing. Vacuum degassing time and pressure significantly affect the removal of PFOS by these adsorbents. After vacuum degassing at 0.01 atm for 36 h, the extent of removal of PFOS by the pristine CNTs and GI decreases 79% and 74%, respectively, indicating the main contribution of air bubbles to PFOS adsorption. When the degassed solution is recontacted with air during the adsorption process, the removal of PFOS recovers to the value obtained without vacuum degassing, further verifying the key role of air bubbles in PFOS adsorption. By theoretical calculation, the distribution of PFOS in air bubbles on the adsorbent surfaces is discussed, and a new schematic sorption model of PFOS on carbonaceous adsorbents in the presence of air bubbles is proposed. The accumulation of PFOS at the interface of air bubbles on the adsorbents is primarily responsible for its adsorption, providing a new mechanistic insight into the transport, fate, and removal of PFOS.
A novel magnetic fluorinated adsorbent with selective and fast adsorption of perfluorooctanesulfonate (PFOS) was synthesized via a simple ball milling of FeO and vermiculite loaded with a cationic fluorinated surfactant. The loaded FeO nanoparticles increased the dispersibility of fluorinated vermiculite (F-VT) in water and allowed the magnetic separability. The nanosized FeO was homogeneously embedded into the adsorbent surfaces, improving the hydrophilicity of F-VT external surface, and this hybrid adsorbent still kept the hydrophobic fluorinated interlayer structure. With this unique property, FeO-loaded F-VT has very fast and selective adsorption for PFOS in the presence of other compounds, due to the fluorophilicity of C-F chains intercalated in the adsorbent interlayers. This novel adsorbent has a high sorption capacity for PFOS, exhibiting PFOS removal from fire-fighting foam wastewater that is much higher than that of powdered activated carbon and resin due to its high selectivity for PFOS. The used FeO-loaded F-VT was successfully regenerated by methanol and reused five times without reduction in PFOS removal and magnetic performance. The FeO-loaded F-VT demonstrates promising application for PFOS removal from real wastewater.
The multiproduct
upgrade of ethanol and acetaldehyde to butadiene
as a high-value chemical and butanol as a biofuel was investigated
over the Y–SiO2 heterogeneous catalysts. The sum
selectivity of butanol and butadiene is over 90% for the Y–SiO2 catalysts with Y/Si ratios from 0.05 to 0.35, while the distribution
changes with the Y/Si ratio. The highest butadiene selectivity of
81.2% with a butanol selectivity of 10.3% was obtained over the Y–SiO2 catalyst with a Y/Si ratio of 0.05. To study the effect of
the catalyst structure and acid–base property on catalytic
performance, the Y–SiO2 catalysts with different
Y/Si ratios were further comprehensively characterized by techniques
including nitrogen adsorption–desorption, X-ray diffraction,
X-ray photoelectron spectroscopy (XPS), 29Si cross–polarization/magic-angle
spinning nuclear magnetic resonance (29Si CP MAS NMR),
Fourier transform infrared resonance (FTIR), UV–Vis diffuse
reflectance spectra (UV–Vis DRS), temperature-programmed desorption
of NH3 and CO2 and NH3 (NH3-TPD and CO2-TPD), and FTIR spectroscopy of adsorbed pyridine
(Pyridine-IR). Results from XPS, 29Si CP MAS NMR, FTIR,
and UV–Vis DRS reveal the electron transfer and the formation
of chemical linkages between Y2O3 and SiO2 rather than the simple deposition of Y2O3 on the surface of the fumed silica. What is more, the amounts and
coordination of Y–O–Si linkages on the surface of the
fumed silica vary with the Y/Si ratio varying, thus resulting in variation
of the acid–base property. Combining with the catalytic activity,
NH3-TPD, CO2-TPD, and Pyridine-IR results indicate
that the strength of acid and base sites has a significant role on
the catalytic performance. The base sites with stronger strength contribute
to the formation of butanol. To obtain a high butadiene selectivity,
a balance of the acid–base property is necessary. A combination
of Y3+ Lewis acid sites with a higher density ratio of
stronger acid sites to the total acid sites and base sites with an
intermediate strength is inclined toward a high butadiene selectivity.
It means that a proper distribution between butadiene and butanol
could be achieved by tuning the acid–base property of theY–SiO2 catalysts on the premise of a high C4 selectivity
of over 90%.
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