50 Search Results

Activation of surface lattice oxygen and chemisorbed oxygen on catalyst surfaces constitutes a pivotal step in heterogeneous oxidative catalysis. Herein, we report a strategy for enhancing oxygen activation by rational design of catalysts with single-atom promoters. Single-site Zr species in CeO₂ (Zr₁-CeO₂) are synthesized using the atom-trapping method. The Zr₁-CeO₂-supported Pt catalyst exhibits enhanced catalytic performance over the CeO₂-supported Pt catalyst in the oxidation of CO, C₃H₈, and C₃H₆, achieving significantly lower T₅₀ values (temperature required to reach 50% conversion). This enhanced catalytic activity is attributed to the formation of an asymmetric Zr₁-O-Pt₁ structure, which favors the activation of themore » adjacent surface lattice oxygen and chemisorbed molecular oxygen. This work exemplifies that incorporating single-site atoms into oxide support facilitates oxygen activation, providing new insights into the role of atomically dispersed promoters in heterogeneous catalysis.« less

NO_x abatement from H₂ internal combustion engines (H₂-ICEs) is challenging due to high H₂O content and unburned H₂ in the exhaust. This study examines Cu-SSZ-13 SCR catalysts, focusing on the effects of high H₂O and H₂ levels on its activity and stability. High H₂O content typical of H₂-ICE exhaust hinders low-temperature SCR activity by impeding Cu migration and oxidation half cycle efficacy. H₂ slip decreases high-temperature SCR activity by reducing active Cu sites to the inactive CuI state. Combined, high H₂O and H₂ slip reduce SCR performance across all temperatures, making it less effective than in diesel applications. Additionally, agingmore » under high H₂O and H₂ contents induce a severe deterioration of Cu-SSZ-13 via CuO_x formation and dealumination, further degrading catalyst performance. This suggests Cu-SSZ-13 may not be suitable for H₂-ICE aftertreatment, especially given the ongoing development of H₂-ICE itself. Parallel efforts in H₂-ICE and catalyst development are essential to accelerate H₂-ICE deployment.« less

Adsorbate–adsorbate lateral interactions at relevant surface coverages have a significant effect on chemical kinetics, thereby influencing the activity of a heterogeneous catalyst. Coverage-dependent kinetic and thermodynamic parameters therefore must be included in studies of such complex systems to properly predict the turnover frequencies and kinetic trends. Thus, it becomes extremely important to accurately capture the strength of lateral interactions between neighboring species under realistic reaction conditions. In this Perspective, we discuss the various existing computational and experimental methods for determining adspecies coverage and configurational effects. The choice of the tools and methods employed in such studies depends on factors suchmore » as time, length scales, computational cost, the presence of solvents, and reaction conditions. The applications of each method and the respective challenges are also discussed here. As a result, we discuss the recent developments and future of the state-of-the-art for inclusion of surface coverage and configuration into a holistic picture for accurate predictions of catalytic behavior.« less

Yttrium-modified dealuminated Betazeolite (Y-BEA) represents a type of Lewis acid zeolite that has gained attention for its potential to efficiently catalyze the conversion of biomass-derived oxygenates. The structure of the Y active sites and their dynamics during biomass conversion reactions, which normally involve substantial amounts of water, necessitate thorough investigation for the rational design of more active and stable catalysts. Here, we conducted a study where a series of Y-BEA catalysts with different yttrium loadings (1–7 wt.%) were subjected to hydrothermal treatment (450 °C, 20% water) and investigated for their structural and catalytic activity changes through a combination of multiplemore » characterizations and kinetic measurements. The number of acid sites of Y-BEA decreased without a change in acid strength following the hydrothermal treatment, which was confirmed by the results of acid site titration, infrared spectroscopy of probe molecules, and kinetic measurements for probe reactions (acetone aldol condensation). Structural analysis using X-ray diffraction (XRD), specific surface area measurement, X-ray absorption spectroscopy (XAS), and X-ray photoelectron spectroscopy (XPS) demonstrated that both the zeolite structure and the isolation status of the Y site remain intact after hydrothermal treatment. Further, the Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) spectra, thermogravimetric analysis (TGA), and operando ¹H and ²⁹Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) revealed the dehydroxylation of Y-BEA induced by hydration-rearrangement-condensation restructuring during the high-temperature steam treatment. Dehydroxylation affects the structure of Y sites by reducing their vicinal silanol sites. In conclusion, this conversion of Lewis acidic Y sites into nonacidic sites is the primary factor behind the change in acid site quantity and catalytic activity on Y-BEA.« less

Dual Lewis acidic centers, CeO _x and framework Sn, confined in Beta zeolite, catalyze the acetone C–C coupling followed by deoxygenation to isobutene, achieving a desirable product distribution and stability in the absence of water.

Ultra small Pd₄ clusters form in the micropores of FER zeolite during low temperature treatment (100 °C) in the presence of humid CO gas. They effectively catalyze CO oxidation below 100°C, whereas Pd nanoparticles are not active as they are poisoned by CO. Using catalytic measurements, infrared (IR) spectroscopy, X-ray absorption spectroscopy (EXAFS), microscopy, and density functional theory calculations we provide the molecular level insight into this previously unreported phenomenon. Pd nanoparticles get covered with CO at low temperatures which effectively blocks O₂ activation until CO desorption occurs. Small Pd clusters in zeolites, in contrast, demonstrate fluxional behavior in themore » presence of CO, which significantly increases their affinity for binding O₂. In conclusion, our study shows a pathway for achieving low temperature CO oxidation activity on the basis of well-defined Pd/zeolite system.« less

To capture the dominant interactions (surface-mediated and through-space steric) in catalytic hydrodeoxygenation systems, coverage-dependent mean-field models of aromatic adsorption are developed on Pt(111) and Ru(0001). We derive three key insights from this work: (1) we can universally apply mean-field models to capture the coverage-dependent behavior of oxygenated aromatics on transition metal surfaces, (2) we can deconvolute surface-mediated and throughspace steric interactions from the mean-field model, and (3) we can develop relatively accurate models that predict the adsorption energy of aromatics on transition metal surfaces for the full coverage range using the work function at lowest modeled coverage. In conclusion, ourmore » approach enables the rapid prediction of coverage-dependent behavior of oxygenated aromatics on transition metal surfaces, reducing the computational cost associated with these studies by an order of magnitude.« less

Proton transfer is critically important to many electrocatalytic reactions, and directed proton delivery could open new avenues for the design of electrocatalysts. However, although this approach has been successful in molecular electrocatalysis, proton transfer has not received the same attention in heterogeneous electrocatalyst design. Here, in this work, we report that a metal oxide proton relay can be built within heterogeneous electrocatalyst architectures and improves the kinetics of electrochemical hydrogen evolution and oxidation reactions. The volcano-type relationship between activity enhancement and pK_a of amine additives confirms this improvement; we observe maximum rate enhancement when the pK_a of a proton relaymore » matches the pH of the electrolyte solution. Density-functional-theory-based reactivity studies reveal a decreased proton transfer energy barrier with a metal oxide proton relay. These findings demonstrate the possibility of controlling the proton delivery and enhancing the reaction kinetics by tuning the chemical properties and structures at heterogeneous interfaces.« less