A series of substituted acetylenes has been polymerized with WOC14/Ph4Sn metathesis catalyst and [Rh(cod)OMe]2 insertion catalyst, and the thermal degradation of the polyacetylenes prepared has been studied using pyrolysis capillary gas chromatography (Py-GC) with flame ionization and mass spectrometric detection to obtain information on the effect of the catalyst on the head-tail (H-T) isomerism of polyacetylenes (poly(phenylacetylene), poly[(4-methylphenyl)acetylene], poly(benzylacetylene), poly((2-fluorophenyl)acetylene], poly[(3-fluorophenyl)acetylene], and poly[(4-fluoro-phenyl)acetylenel). Cyclotrimers have been found to be the main pyrolysis products in all cases. Direct Py-MS connection was used to determine the temperature profiles of the released pyrolysis products. 1,3,5-Trisubstituted benzenes were found to be the predominant pyrolysis products of the polymers prepared with the insertion catalyst, which proves the presence of long head-to-tail sequences of monomeric units in these polyacetylenes. On the other hand, both 1,2,4- and 1,3,5-trisubstituted benzenes are present in significant amounts in the pyrolysis products of polymers prepared with the metathesis catalyst, which proves the presence of a significant content of the head-to-head (HH) and tail-to-tail (TT) linkages in these isomers of polyacetylenes. Contents of the regular (HT) and inverse (HH-TT) monomer linkages (RML and IML, respectively) in polymer chains were determined from the relative amounts of di-, tri-, and tetrasubstituted benzenes found in the Py-GC products.
In
this work, we prepared and investigated in ultra-high vacuum
(UHV) two stoichiometric CeO2(111) surfaces containing
low and high amounts of step edges decorated with 0.05 ML of gold
using synchrotron-radiation photoelectron spectroscopy (SRPES) and
scanning tunneling microscopy (STM). The UHV study helped to solve
the still unresolved puzzle on how the one-monolayer-high ceria step
edges affect the metal–substrate interaction between Au and
the CeO2(111) surface. It was found that the concentration
of ionic Au+ species on the ceria surface increases with
increasing number of ceria step edges and is not correlated with the
concentration of Ce3+ ions that are supposed to form on
the surface after its interaction with gold nanoparticles. We associated
this with an additional channel of Au+ formation on the
surface of CeO2(111) related to the interaction of Au atoms
with various peroxo oxygen species formed at the ceria step edges
during the film growth. The study of CO oxidation on the highly stepped
Au/CeO2(111) model sample was performed by combining near-ambient-pressure
X-ray photoelectron spectroscopy (NAP-XPS), UHV-STM, and near-ambient-pressure
STM (NAP-STM). This powerful combination provided comprehensive information
on the processes occurring on the Au/CeO2(111) surface
during the interaction with CO, O2, and CO + O2 (1:1) mixture at conditions close to the real working conditions
of CO oxidation. It was found that the system demonstrates high stability
in CO. However, the surface undergoes substantial chemical and morphological
changes as the O2 is added to the reaction cell. Already
at 300 K, gold nanoparticles begin to grow using a mechanism that
involves the disintegration of small gold nanoparticles in favor of
the large ones. With increasing temperature, the model catalyst quickly
transforms into a system of primarily large Au particles that contains
no ionic gold species.
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