5 research outputs found
Reaction Sensitivity of Ceria Morphology Effect on Ni/CeO<sub>2</sub> Catalysis in Propane Oxidation Reactions
CeO<sub>2</sub> nanocubes
(c-CeO<sub>2</sub>), nanoparticles (p-CeO<sub>2</sub>), and nanorods
calcined at 500 °C (r-CeO<sub>2</sub>-500) and 700 °C (r-CeO<sub>2</sub>-700) were used as supports to synthesize a series of Ni/CeO<sub>2</sub> catalysts for the propane combustion and oxidative dehydrogenation
of propane (ODHP) reactions. The Ni-CeO<sub>2</sub> interaction greatly
promotes the reducibility of CeO<sub>2</sub>, but CeO<sub>2</sub> morphology-dependent
Ni-CeO<sub>2</sub> interaction was observed to form different speciation
of Ni species (Ni<sup>2+</sup> dissolved in CeO<sub>2</sub>, highly
dispersive NiO, NiO aggregate) and oxygen species (strongly activated
oxygen species, medially activated oxygen species, weakly activated
oxygen species) in various Ni/CeO<sub>2</sub> catalysts. Ni-CeO<sub>2</sub> interaction is stronger in Ni/c-CeO<sub>2</sub> catalysts
than in other Ni/CeO<sub>2</sub> catalysts. Different morphology-dependences
of Ni/CeO<sub>2</sub> catalysts in propane combustion and ODHP reactions
were observed. The Ni/r-CeO<sub>2</sub>-500 catalyst with the largest
strongly activated oxygen species is most catalytic active in the
propane combustion reaction while the Ni/c-CeO<sub>2</sub> catalyst
with the largest amount of weakly activated oxygen species exhibits
the best catalytic performance in the ODHP reaction. Thus, the CeO<sub>2</sub> morphology engineering strategy is effective in finely tuning
the metal-CeO<sub>2</sub> interaction and the reactivity of oxygen
species to meet the requirements of different types of catalytic oxidation
reactions
States and Function of Potassium Carbonate Species in the Polytitanate Nanobelt Supported Catalysts Used for Efficient NOx Storage and Reduction
A series of polytitanate nanobelt
supported lean-burn NOx trap
catalysts Pt-<i>x</i>K<sub>2</sub>CO<sub>3</sub>/K<sub>2</sub>Ti<sub>8</sub>O<sub>17</sub> with different weight loading of K<sub>2</sub>CO<sub>3</sub> (<i>x</i> = 0%, 5%, 15%, 20%, 25%,
or 30%) were synthesized by successive impregnation. The nanobelt
support K<sub>2</sub>Ti<sub>8</sub>O<sub>17</sub> displays a specific
surface area as high as 302 m<sup>2</sup>/g, and the corresponding
catalysts Pt-<i>x</i>K<sub>2</sub>CO<sub>3</sub>/K<sub>2</sub>Ti<sub>8</sub>O<sub>17</sub> show excellent NOx storage performance.
As K<sub>2</sub>CO<sub>3</sub> loading increases from 5% to 30%, the
NOx storage capacity (NSC) exhibits a volcano-type altering tendency
with the maximum appearing at 25% (2.68 mmol/g); the highest NOx reduction
efficiency of 99.2% was also achieved over this catalyst in cyclic
alternative lean/rich atmospheres. Further increase of K<sub>2</sub>CO<sub>3</sub> loading induces the formation of more bulk or bulk-like
K<sub>2</sub>CO<sub>3</sub> species, decreasing the performance of
the catalysts for NOx storage and reduction. HR-TEM and FT-IR results
indicate that the K species exist as highly dispersed phases including
K<sub>2</sub>O, K<sub>2</sub>CO<sub>3</sub>, and −OK groups,
which are undetectable by X-ray diffraction (XRD) even at the K<sub>2</sub>CO<sub>3</sub> loading of 30%. Several carbonate species with
different thermal stability and reactivity are identified by FT-IR
and CO<sub>2</sub>-TPD. In situ diffuse reflectance FT-IR (DRIFTS)
reveals that at low K<sub>2</sub>CO<sub>3</sub> loading (<20%)
NOx is mainly stored as monodentate nitrates and monodentate nitrites,
while at higher K<sub>2</sub>CO<sub>3</sub> loading NOx is mainly
stored as bidentate nitrite species, which results from the decrease
of oxidation ability of the catalysts due to the potential covering
of K<sub>2</sub>CO<sub>3</sub> on Pt sites
Activating Edge Sites on Pd Catalysts for Selective Hydrogenation of Acetylene via Selective Ga<sub>2</sub>O<sub>3</sub> Decoration
Pd
catalysts are industrially used in the selective hydrogenation
of acetylene to ethylene. Terrace Pd atoms of the closely packed {111}
facets on supported Pd particles are generally considered to be the
catalytically active sites. We herein report that deposition of an
appropriate amount of Ga<sub>2</sub>O<sub>3</sub> adlayers on Pd particles
supported on alumina by the atomic layer deposition (ALD) technique
substantially enhanced the catalytic activity, selectivity, and stability
in the selective hydrogenation of acetylene to ethylene. Structural
characterization results demonstrate that Ga<sub>2</sub>O<sub>3</sub> is preferentially deposited at the edges and open facets of Pd particles
with the ALD technique. This transforms the poisoning edge sites of
the {111} facets into the catalytically active terrace-like sites,
leading to an increase in the number of active sites and subsequently
the enhancement of the catalytic activity; this also suppresses the
formation of poisoning carbonaceous deposits on the open facets and
blocks the migration of carbonaceous deposits from the open facets
to the neighboring active {111} facets, leading to a significant improvement
in catalytic stability. These results demonstrate a concept of selective
oxide decoration to comprehensively improve the performance of supported
metal catalysts and provide a practical strategy
Ordered Porous Pd Octahedra Covered with Monolayer Ru Atoms
Monolayer
Ru atoms covered highly ordered porous Pd octahedra have
been synthesized via the underpotential deposition and thermodynamic
control. Shape evolution from concave nanocube to octahedron with
six hollow cavities was observed. Using aberration-corrected high-resolution
transmission electron microscopy and X-ray photoelectron spectroscopy,
we provide quantitative evidence to prove that only a monolayer of
Ru atoms was deposited on the surface of porous Pd octahedra. The
as-prepared monolayer Ru atoms covered Pd nanostructures exhibited
excellent catalytic property in terms of semihydrogenation of alkynes
Atomically Dispersed Ru on Ultrathin Pd Nanoribbons
We
report a one-pot synthesis of atomically dispersed Ru on ultrathin
Pd nanoribbons. By using synchrotron radiation photoemission spectroscopy
(SRPES) and extended X-ray absorption fine structure (EXAFS) measurements
in combination with aberration corrected high-resolution transmission
electron microscopy (HRTEM), we show that atomically dispersed Ru
with content up to 5.9% was on the surface of the ultrathin nanoribbon.
Furthermore, the ultrathin Pd/Ru nanoribbons could remarkably prohibit
the hydrogenolysis in chemoselective hydrogenation of Cî—»C bonds,
leading to an excellent catalytic selectivity compared with commercial
Pd/C and Ru/C