Reaction Sensitivity of Ceria Morphology Effect on Ni/CeO₂ Catalysis in Propane Oxidation Reactions

CeO₂ nanocubes (c-CeO₂), nanoparticles (p-CeO₂), and nanorods calcined at 500 °C (r-CeO₂-500) and 700 °C (r-CeO₂-700) were used as supports to synthesize a series of Ni/CeO₂ catalysts for the propane combustion and oxidative dehydrogenation of propane (ODHP) reactions. The Ni-CeO₂ interaction greatly promotes the reducibility of CeO₂, but CeO₂ morphology-dependent Ni-CeO₂ interaction was observed to form different speciation of Ni species (Ni²⁺ dissolved in CeO₂, highly dispersive NiO, NiO aggregate) and oxygen species (strongly activated oxygen species, medially activated oxygen species, weakly activated oxygen species) in various Ni/CeO₂ catalysts. Ni-CeO₂ interaction is stronger in Ni/c-CeO₂ catalysts than in other Ni/CeO₂ catalysts. Different morphology-dependences of Ni/CeO₂ catalysts in propane combustion and ODHP reactions were observed. The Ni/r-CeO₂-500 catalyst with the largest strongly activated oxygen species is most catalytic active in the propane combustion reaction while the Ni/c-CeO₂ catalyst with the largest amount of weakly activated oxygen species exhibits the best catalytic performance in the ODHP reaction. Thus, the CeO₂ morphology engineering strategy is effective in finely tuning the metal-CeO₂ 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>K₂CO₃/K₂Ti₈O₁₇ with different weight loading of K₂CO₃ (<i>x</i> = 0%, 5%, 15%, 20%, 25%, or 30%) were synthesized by successive impregnation. The nanobelt support K₂Ti₈O₁₇ displays a specific surface area as high as 302 m²/g, and the corresponding catalysts Pt-<i>x</i>K₂CO₃/K₂Ti₈O₁₇ show excellent NOx storage performance. As K₂CO₃ 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 K₂CO₃ loading induces the formation of more bulk or bulk-like K₂CO₃ 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 K₂O, K₂CO₃, and −OK groups, which are undetectable by X-ray diffraction (XRD) even at the K₂CO₃ loading of 30%. Several carbonate species with different thermal stability and reactivity are identified by FT-IR and CO₂-TPD. In situ diffuse reflectance FT-IR (DRIFTS) reveals that at low K₂CO₃ loading (<20%) NOx is mainly stored as monodentate nitrates and monodentate nitrites, while at higher K₂CO₃ 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 K₂CO₃ on Pt sites

Activating Edge Sites on Pd Catalysts for Selective Hydrogenation of Acetylene via Selective Ga₂O₃ 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 Ga₂O₃ 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 Ga₂O₃ 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 CC bonds, leading to an excellent catalytic selectivity compared with commercial Pd/C and Ru/C