2 research outputs found
Hierarchically Ordered Nanoporous Pd/SBA-15 Catalyst for the Aerobic Selective Oxidation of Sterically Challenging Allylic Alcohols
The
utility of a hierarchically ordered nanoporous SBA-15 architecture,
comprising 270 nm macropores and 5 nm mesopores (MM-SBA-15), for the
catalytic aerobic selective oxidation of sterically challenging allylic
alcohols is shown. Detailed bulk and surface characterization reveals
that incorporation of complementary macropores into mesoporous SBA-15
enhances the dispersion of sub 2 nm Pd nanoparticles and thus their
degree of surface oxidation. Kinetic profiling reveals a relationship
between nanoparticle dispersion and oxidation rate, identifying surface
PdO as the catalytically active phase. Hierarchical nanoporous Pd/MM-SBA-15
outperforms mesoporous analogues in allylic alcohol selective oxidation
by (i) stabilizing PdO nanoparticles and (ii) dramatically improving
in-pore diffusion and access to active sites by sesquiterpenoid substrates
such as farnesol and phytol
Reactive-Atom Scattering from Liquid Crystals at the LiquidâVacuum Interface: [C<sub>12</sub>mim][BF<sub>4</sub>] and 4âCyano-4â˛-Octylbiphenyl (8CB)
Two complementary
approaches were used to study the liquidâvacuum
interface of the liquid-crystalline ionic liquid 1-dodecyl-3-methylÂimidazolium
tetrafluoroborate ([C<sub>12</sub>mim]Â[BF<sub>4</sub>]) in the smectic
A (SmA) and isotropic phases. O atoms with two distinct incident translational
energies were scattered from the surface of [C<sub>12</sub>mim]Â[BF<sub>4</sub>]. Angle-dependent time-of-flight distributions and OH yields,
respectively, were recorded from high- and low-energy O atoms. There
were no significant changes in the measurements using either approach,
nor the properties derived from them, accompanying the transition
from the SmA to the isotropic phase. This indicates that the surface
structure of [C<sub>12</sub>mim]Â[BF<sub>4</sub>] remains essentially
unchanged across the phase boundary, implying that the bulk order
and surface structure are not strongly correlated for this material.
This effect is ascribed to the strong propensity for the outer surfaces
of ionic liquids to be dominated by alkyl chains, over an underlying
layer rich in anions and cation head groups, whether or not the bulk
material is a liquid crystal. In a comparative study, the OH yield
from the surface of the liquid crystal, 8CB, was found to be affected
by the bulk order, showing a surprising step increase at the SmAânematic
transition temperature, whose origin is the subject of speculation