A high performance Pt-free cathode catalyst for polymer electrolyte fuel cells has been synthesized by the multi-step pyrolysis of polyimide fine particles with a diameter of about 100 nm.
Although the structure and properties
of water under conditions
of extreme confinement are fundamentally important for a variety of
applications, they remain poorly understood, especially for dimensions
less than 2 nm. This problem is confounded by the difficulty in controlling
surface roughness and dimensionality in fabricated nanochannels, contributing
to a dearth of experimental platforms capable of carrying out the
necessary precision measurements. In this work, we utilize an experimental
platform based on the interior of lithographically segmented, isolated
single-walled carbon nanotubes to study water under extreme nanoscale
confinement. This platform generates multiple copies of nanotubes
with identical chirality, of diameters from 0.8 to 2.5 nm and lengths
spanning 6 to 160 μm, that can be studied individually in real
time before and after opening, exposure to water, and subsequent water
filling. We demonstrate that, under controlled conditions, the diameter-dependent
blue shift of the Raman radial breathing mode (RBM) between 1 and
8 cm–1 measures an increase in the interior mechanical
modulus associated with liquid water filling, with no response from
exterior water exposure. The observed RBM shift with filling demonstrates
a non-monotonic trend with diameter, supporting the assignment of
a minimum of 1.81 ± 0.09 cm–1 at 0.93 ±
0.08 nm with a nearly linear increase at larger diameters. We find
that a simple hard-sphere model of water in the confined nanotube
interior describes key features of the diameter-dependent modulus
change of the carbon nanotube and supports previous observations in
the literature. Longer segments of 160 μm show partial filling
from their ends, consistent with pore clogging. These devices provide
an opportunity to study fluid behavior under extreme confinement with
high precision and repeatability.
A dual catalyst system has been developed for tandem hydroformylation/hydrogenation to produce n‐undecanol from 1‐decene in one pot. A combination of xantphos/[Rh(acac)(CO)2] and Shvo's catalyst (1) afforded the best results (see scheme; acac=acetylacetonate, DMA=N,N‐dimethylacetamide). Polar solvents effectively suppressed the formation of undecyl formate.
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