Enhancing Activity and Stability of Pd-on-TiO Single-Atom Catalyst for Low-Temperature CO Oxidation through Local Environment Tailoring.

The development of efficient Pd single-atom catalysts for CO oxidation, crucial for environmental protection and fundamental studies, has been hindered by their limited reactivity and thermal stability. Here, we report a thermally stable TiO-supported Pd single-atom catalyst that exhibits enhanced intrinsic CO oxidation activity by tunning the local coordination of Pd atoms via H treatment. Our comprehensive characterization reveals that H-treated Pd single atoms have reduced nearest Pd-O coordination and form short-distanced Pd-Ti coordination, effectively stabilizing Pd as isolated atoms even at high temperatures.

Size-Dependent Dispersion of Rhodium Clusters into Isolated Single Atoms at Low Temperature and the Consequences for CO Oxidation Activity.

Understanding the dynamic structural evolution of supported metal clusters under reaction conditions is crucial to develop structure reactivity relations. Here, we followed the structure of different size Rh clusters supported on Al O using in situ/operando spectroscopy and ex situ aberration-corrected electron microscopy. We report a dynamic evolution of rhodium clusters into thermally stable isolated single atoms upon exposure to oxygen and during CO oxidation.

Elucidating the Effect of Ion Exchange Protocol on the Copper Exchange Efficacy, Copper Siting, and SCR Activity in Cu-SSZ-13.

The front cover artwork is provided by Professor Jean-Sabin McEwen at Washington State University. The image shows how ion exchanges prepared with different copper precursors influence how the copper ultimately sites relative to the zeolite framework, which ultimately impacts its catalytic reactivity for the selective catalytic reduction (SCR) of NO in Cu-SSZ-13. Read the full text of the Research Article at 10.

Elucidating the Effect of Ion Exchange Protocol on the Copper Exchange Efficacy, Copper Siting, and SCR activity in Cu-SSZ-13.

The influence of the copper ion exchange protocol on SCR activity of SSZ-13 is quantified. Using the same parent SSZ-13 zeolite, four exchange protocols are used to assess how exchange protocol impacts metal uptake and SCR activity. Large differences in the SCR activity, nearly 30 percentage points at 160 °C at constant copper content, are observed for different exchange protocols implying that different exchange protocols lead to different copper species.

Aqueous-Phase Destruction of Nerve-Agent Simulants at Copper Single Atoms in UiO-66.

Metal-organic frameworks (MOFs) have shown great success in aqueous-phase hydrolysis of nerve agents, with some even showing promise in the gas phase. However, both aqueous-phase reactivity and gas-phase reactivity are hindered because of the binding of the hydrolyzed products to the MOF nodes in a stable, bridging configuration, which limits turnover. Single transition-metal atoms in MOFs have been a growing field of interest for catalytic applications, and single atoms have been proposed to prevent the unwanted bridged conformation and increase catalytic turnover.

Effect of Pd Coordination and Isolation on the Catalytic Reduction of O to HO over PdAu Bimetallic Nanoparticles.

The direct synthesis of hydrogen peroxide (H + O → HO) may enable low-cost HO production and reduce environmental impacts of chemical oxidations. Here, we synthesize a series of PdAu nanoparticles (where 0 ≤ ≤ 220, ∼10 nm) and show that, in pure water solvent, HO selectivity increases with the Au to Pd ratio and approaches 100% for PdAu. Analysis of XAS and FTIR of adsorbed CO and CO show that materials with Au to Pd ratios of ∼40 and greater expose only monomeric Pd species during catalysis and that the average distance between Pd monomers increases with further dilution.

Solvent molecules form surface redox mediators in situ and cocatalyze O reduction on Pd.

Solvent molecules influence the reactions of molecular hydrogen and oxygen on palladium nanoparticles. Organic solvents activate to form reactive surface intermediates that mediate oxygen reduction through pathways distinct from reactions in pure water. Kinetic measurements and ab initio quantum chemical calculations indicate that methanol and water cocatalyze oxygen reduction by facilitating proton-electron transfer reactions.

Solvent manipulation of the pre-reduction metal-ligand complex and particle-ligand binding for controlled synthesis of Pd nanoparticles.

Understanding how to control the nucleation and growth rates is crucial for designing nanoparticles with specific sizes and shapes. In this study, we show that the nucleation and growth rates are correlated with the thermodynamics of metal-ligand/solvent binding for the pre-reduction complex and the surface of the nanoparticle, respectively. To obtain these correlations, we measured the nucleation and growth rates by in situ small angle X-ray scattering during the synthesis of colloidal Pd nanoparticles in the presence of trioctylphosphine in solvents of varying coordinating ability.

The role of nanoparticle size and ligand coverage in size focusing of colloidal metal nanoparticles.

Controlling the size distribution of nanoparticles is important for many applications and typically involves the use of ligands during synthesis. In this study, we show that the mechanism of size focusing involves a dependence of the growth rate on the size of the nanoparticles and the ligand coverage on the surface of the nanoparticles. To demonstrate these effects, we used small angle X-ray scattering (SAXS) and population balance kinetic modeling (PBM) to investigate the evolution of size distribution during the synthesis of colloidal Pd metal nanoparticles.

Ligand-Mediated Nucleation and Growth of Palladium Metal Nanoparticles.

The size, size distribution and stability of colloidal nanoparticles are greatly affected by the presence of capping ligands. Despite the key contribution of capping ligands during the synthesis reaction, their role in regulating the nucleation and growth rates of colloidal nanoparticles is not well understood. In this work, we demonstrate a mechanistic investigation of the role of trioctylphosphine (TOP) in Pd nanoparticles in different solvents (toluene and pyridine) using in situ SAXS and ligand-based kinetic modeling.

Colloidal nanoparticle size control: experimental and kinetic modeling investigation of the ligand-metal binding role in controlling the nucleation and growth kinetics.

Despite the major advancements in colloidal metal nanoparticles synthesis, a quantitative mechanistic treatment of the ligand's role in controlling their size remains elusive. We report a methodology that combines in situ small angle X-ray scattering (SAXS) and kinetic modeling to quantitatively capture the role of ligand-metal binding (with the metal precursor and the nanoparticle surface) in controlling the synthesis kinetics. We demonstrate that accurate extraction of the kinetic rate constants requires using both, the size and number of particles obtained from in situ SAXS to decouple the contributions of particle nucleation and growth to the total metal reduction.

Gaining Control over Radiolytic Synthesis of Uniform Sub-3-nanometer Palladium Nanoparticles: Use of Aromatic Liquids in the Electron Microscope.

Synthesizing nanomaterials of uniform shape and size is of critical importance to access and manipulate the novel structure-property relationships arising at the nanoscale, such as catalytic activity. In this work, we synthesize Pd nanoparticles with well-controlled size in the sub-3 nm range using scanning transmission electron microscopy (STEM) in combination with an in situ liquid stage. We use an aromatic hydrocarbon (toluene) as a solvent that is very resistant to high-energy electron irradiation, which creates a net reducing environment without the need for additives to scavenge oxidizing radicals.

Hierarchically structured catalysts for cascade and selective steam reforming/hydrodeoxygenation reactions.

We report a hierarchically structured catalyst with steam reforming and hydrodeoxygenation functionalities being deposited in the micropores and macropores, respectively. The catalyst is highly efficient to upgrade the pyrolysis vapors of pine forest product residual, resulting in a dramatically decreased acid content and increased hydrocarbon yield without external H2 supply.

Catalytic fast pyrolysis of lignocellulosic biomass.

Increasing energy demand, especially in the transportation sector, and soaring CO2 emissions necessitate the exploitation of renewable sources of energy. Despite the large variety of new energy carriers, liquid hydrocarbon still appears to be the most attractive and feasible form of transportation fuel taking into account the energy density, stability and existing infrastructure. Biomass is an abundant, renewable source of energy; however, utilizing it in a cost-effective way is still a substantial challenge.

The effect of zinc addition on the oxidation state of cobalt in Co/ZrO2 catalysts.

The effect of zinc promotion on the oxidation state of cobalt in Co/ZrO(2) catalysts was investigated and correlated with the activity and selectivity for ethanol steam reforming (ESR). Catalysts were synthesized by applying incipient wetness impregnation and characterized by using Brunauer-Emmett-Teller (BET), temperature-programmed reduction (TPR) measurements, X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Higher ethanol conversion and lower CH(4) selectivity are observed for the Co/ZrO(2) catalyst promoted with Zn as compared to the Co/ZrO(2) catalyst alone.

Correlating particle size and shape of supported Ru/gamma-Al2O3 catalysts with NH3 decomposition activity.

While ammonia synthesis and decomposition on Ru are known to be structure-sensitive reactions, the effect of particle shape on controlling the particle size giving maximum turnover frequency (TOF) is not understood. By controlling the catalyst pretreatment conditions, we have varied the particle size and shape of supported Ru/gamma-Al(2)O(3) catalysts. The Ru particle shape was reconstructed by combining microscopy, chemisorption, and extended X-ray absorption fine structure (EXAFS) techniques.

Controlling ZnO morphology for improved methanol steam reforming reactivity.

The selectivity towards CO2 during steam reforming of methanol on Pd increases in the order Al2O3 < ZrO2 < ZnO. However, conventional catalyst preparation can damage the ZnO surface, even causing complete dissolution. The faceted, prismatic ZnO crystals in the support (Aldrich) get easily destroyed during catalyst preparation.