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 ¹³C and ²⁹Si NMR Enhanced by Dynamic Nuclear Polarization

We show that dynamic nuclear polarization (DNP) can be used to enhance NMR signals of ¹³C and ²⁹Si 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 ¹H–¹H spin diffusion and transferred to rare spins by cross-polarization, yielding signal enhancements ε_on/off of around 8. When the CTAB molecules are extracted, so that the radicals can enter the mesopores, the enhancements increase to ε_on/off ≈ 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