2 research outputs found
Molecular-Level Understanding of CeO<sub>2</sub> as a Catalyst for Partial Alkyne Hydrogenation
The unique catalytic properties of
ceria for the partial hydrogenation
of alkynes are examined for acetylene hydrogenation. Catalytic tests
over polycrystalline CeO<sub>2</sub> at different temperatures and
H<sub>2</sub>/C<sub>2</sub>H<sub>2</sub> ratios reveal ethylene selectivities
in the range of 75ā85% at high degrees of acetylene conversion
and hint at the crucial role of hydrogen dissociation on the overall
process. Density-functional theory is applied to CeO<sub>2</sub>(111)
in order to investigate reaction intermediates and to calculate the
enthalpy and energy barrier for each elementary step, taking into
account different adsorption geometries and the presence of potential
isomers of the intermediates. At a high hydrogen coverage, Ī²-C<sub>2</sub>H<sub>2</sub> radicals adsorbed on-top of surface oxygen atoms
are the initial reactive species forming C<sub>2</sub>H<sub>3</sub> species effectively barrierless. The high alkene selectivity is
owed to the lower activation barrier for subsequent hydrogenation
leading to gas-phase C<sub>2</sub>H<sub>4</sub> compared to that for
the formation of Ī²-C<sub>2</sub>H<sub>4</sub> radical species.
Moreover, hydrogenation of C<sub>2</sub>H<sub>5</sub> species, if
formed, must overcome significantly large barriers. Oligomers are
the most important byproduct of the reaction and they result from
the recombination of chemisorbed C<sub>2</sub>H<sub><i>x</i></sub> species. These findings rationalize for the first time the
applicability of CeO<sub>2</sub> as a catalyst for olefin production
and potentially broaden its use for the hydrogenation of polyunsaturated
and polyfunctionalized substrates containing triple bonds
Merging Single-Atom-Dispersed Silver and Carbon Nitride to a Joint Electronic System <i>via</i> Copolymerization with Silver Tricyanomethanide
Herein,
we present an approach to create a hybrid between single-atom-dispersed
silver and a carbon nitride polymer. Silver tricyanomethanide (AgTCM)
is used as a reactive comonomer during templated carbon nitride synthesis
to introduce both negative charges and silver atoms/ions to the system.
The successful introduction of the extra electron density under the
formation of a delocalized joint electronic system is proven by photoluminescence
measurements, X-ray photoelectron spectroscopy investigations, and
measurements of surface Ī¶-potential. At the same time, the principal
structure of the carbon nitride network is not disturbed, as shown
by solid-state nuclear magnetic resonance spectroscopy and electrochemical
impedance spectroscopy analysis. The synthesis also results in an
improvement of the visible light absorption and the development of
higher surface area in the final products. The atom-dispersed AgTCM-doped
carbon nitride shows an enhanced performance in the selective hydrogenation
of alkynes in comparison with the performance of other conventional
Ag-based materials prepared by spray deposition and impregnationāreduction
methods, here exemplified with 1-hexyne