3 research outputs found
Bifunctional Adsorbent-Catalytic Nanoparticles for the Refining of Renewable Feedstocks
A hybrid
adsorbent-catalytic nanostructured material consisting
of aminopropyl groups and nickel nanoparticles immobilized in mesoporous
silica nanoparticles (AP-Ni-MSN) was employed to selectively capture
free fatty acids (FFAs) and convert them into saturated hydrocarbons.
The working principle of these sorbent-catalytic particles was initially
tested in the hydrogenation of oleic acid. Besides providing selectivity
for the capture of FFAs, the adsorbent groups also affected the selectivity
of the hydrogenation reaction, shifting the chemistry from hydrocracking-based
(Ni) to hydrotreating-based and improving the carbon economy of the
process. This approach was ultimately evaluated by the selective sequestration
of FFAs from crude microalgal oil and their subsequent conversion
into liquid hydrocarbons, demonstrating the suitability of this design
for the refinery of renewable feedstocks
Solvent-Induced Reversal of Activities between Two Closely Related Heterogeneous Catalysts in the Aldol Reaction
The relative rates of the aldol reaction catalyzed by
supported
primary and secondary amines can be inverted by 2 orders of magnitude,
depending on the use of hexane or water as a solvent. Our analyses
suggest that this dramatic shift in the catalytic behavior of the
supported amines does not involve differences in reaction mechanism,
but is caused by activation of imine to enamine equilibria and stabilization
of iminium species. The effects of solvent polarity and acidity were
found to be important to the performance of the catalytic reaction.
This study highlights the critical role of solvent in multicomponent
heterogeneous catalytic processes
Mesoporous Silica Nanoparticles Loaded with Surfactant: Low Temperature Magic Angle Spinning <sup>13</sup>C and <sup>29</sup>Si NMR Enhanced by Dynamic Nuclear Polarization
We show that dynamic nuclear polarization (DNP) can be
used to
enhance NMR signals of <sup>13</sup>C and <sup>29</sup>Si nuclei located
in mesoporous organic/inorganic hybrid materials, at several hundreds
of nanometers from stable radicals (TOTAPOL) trapped in the surrounding
frozen disordered water. The approach is demonstrated using mesoporous
silica nanoparticles (MSN), functionalized with 3-(<i>N</i>-phenylureido)propyl (PUP) groups, filled with the surfactant cetyltrimethylammonium
bromide (CTAB). The DNP-enhanced proton magnetization is transported
into the mesopores via <sup>1</sup>H–<sup>1</sup>H spin diffusion
and transferred to rare spins by cross-polarization, yielding signal
enhancements ε<sub>on/off</sub> of around 8. When the CTAB molecules
are extracted, so that the radicals can enter the mesopores, the enhancements
increase to ε<sub>on/off</sub> ≈ 30 for both nuclei.
A quantitative analysis of the signal enhancements in MSN with and
without surfactant is based on a one-dimensional proton spin diffusion
model. The effect of solvent deuteration is also investigated