The origin of the particle-size-dependent selectivity in 1-butene isomerization and hydrogenation on Pd/Al2O3 catalysts

MIL-53(Al)-derived bimetallic Pd-Co catalysts for the selective hydrogenation of 1,3-butadiene at low temperature

Selective hydrogenation of 1,3-butadiene is a crucial industrial process for the removing of 1,3-butadiene, a byproduct of butene production. Developing catalysts with high catalytic performance for the hydrogenation of 1,3-butadiene at low temperatures has become a research hotspot. In this study, bimetallic Pd-Co catalysts supported on Al2O3 derived from MIL-53(Al) at various calcination temperatures were synthesised via the co-impregnation method. These catalysts were structurally characterised using powder X-ray diffraction, thermogravimetric analysis, N2 adsorption-desorption, X-ray photoelectron spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and inductively coupled plasma optical emission spectroscopy techniques. The characterisations revealed that Pd-Co nanoparticles, averaging 8.5-12.4 nm, were highly dispersed on Al2O3 derived from MIL-53(Al). The effects of reaction temperature, Pd and Co contents, space velocity, and calcination temperature on the catalytic performance for the hydrogenation of 1,3-butadiene were thoroughly investigated. The PdCo/MIL-53(Al)-A700 catalyst exhibited the highest catalytic activity for the hydrogenation of 1,3-butadiene at 40 °C and a space velocity of 900 L/(h·gcat). This catalyst demonstrated a strong synergistic interaction between Pd and Co nanoparticles, resulting in considerably better catalytic performance than the monometallic Pd catalyst under the same conditions. The PdCo/MIL-53(Al)-A700 catalyst achieved superior 1,3-butadiene conversion and total butene selectivity compared to the Pd/MIL-53(Al)-A700 catalyst. In addition, the PdCo/MIL-53(Al)-A700 catalyst maintained its catalytic activity and total butene selectivity after three regenerations in a flow of N2 at 200 °C. This work proposed a new pathway to design efficient and sustainable catalysts for 1,3-butadiene hydrogenation.

Tuning the Selectivity in the Nonoxidative Alkane Dehydrogenation Reaction by Potassium-Promoted Zeolite-Encapsulated Pt Catalysts

The significance of the nonoxidative dehydrogenation of middle-chain alkanes into corresponding alkenes is increasing in the context of the world's declining demands on transportation fuels and the growing demand for chemicals and materials. The middle-chain alkenes derived from the dehydrogenation reaction can be transformed into value-added chemicals in downstream processes. Due to the presence of multiple potential reaction sites, the reaction mechanism of the dehydrogenation of middle-chain alkanes is more complicated than that in the dehydrogenation of light alkanes, and there are few prior studies on elucidating their detailed structure-reactivity relationship. In this work, we have employed Pt catalysts encapsulated in pure-silica MFI zeolite crystallites as model catalysts and studied how the catalytic performances for dehydrogenation of n-pentane can be modulated by the K+ promotor in the Pt-MFI catalyst. A combination of comprehensive structural characterizations by aberration-corrected electron microscopy, X-ray absorption spectroscopy, in situ CO-IR, X-ray photoelectron spectroscopy, and kinetic studies shows that K+ promoter can not only influence the particle size but also modify the electronic properties of Pt species, which further affect the activity and selectivity in the dehydrogenation of n-pentane.

Inherent Behavior of Electrode Materials of Lithium-Ion Batteries

For independency from the fossil fuels and to save environment, we need to move toward the green energies, which requires better energy storage devices, especially for usage in electric vehicles. Li-ion and beyond-lithium insertion batteries are promising to this aim. However, they suffer from some inherent limitations which must be understood to allow their development and pave the way to find suitable energy storage alternatives. It is found that each positive or negative electrode material (cathode or anode) of the intercalation batteries has its own behavioral (charge-discharge) properties. The modification of preparation parameters (composition, loading density, porosity, particle size, etc.) may improve some aspects of the electrode performance, but cannot change the intrinsic property of the electrode itself. Accordingly, these properties are called as the "inherent behavior characteristics" of the active material. It is concluded that the behavior of a specific electrode substance, even following different preparation routes, depends only on diffusion mechanisms. This work shows that the inherent electrode properties can be visualized by representation of current density vs. capacity.

Understanding electrocatalytic mechanisms and ultra-trace uranyl detection with Pd nanoparticles electrodeposited in deep eutectic solvents

This research paper investigates the electrocatalytic mechanisms and ultra-trace detection abilities of uranyl ions (UO22+) using palladium nanoparticles (PdNPs) electrodeposited in deep eutectic solvents (DESs). The unique properties of DESs, such as their adjustable viscosity and ionic conductivity, offer an advantageous and environmentally friendly medium for Pd nanoparticle electrodeposition, resulting in highly active and stable electrocatalysts. Various characterization techniques, including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), were used to examine the morphology, size distribution, and crystallographic structure of the Pd nanoparticles. Electrochemical tests revealed that the Pd-modified electrodes show exceptional electrocatalytic activity and current sensitivity towards uranyl ions, with detection limits as low as 3.4 nM. Density functional theory (DFT) calculations were conducted to elucidate the mechanism of the electrocatalytic reduction of UO22+ by the PdNPs, providing a plausible explanation for the high sensitivity of PdNPs in detecting uranyl ions based on the calculated structural parameters and reaction energetics. This study underscores the potential of Pd nanoparticles electrodeposited in DESs as a promising method for sensitive uranyl ion detection, contributing to advancements in environmental monitoring and nuclear safety.

Defect-Rich CuZn Nanoparticles for Model Catalysis Produced by Femtosecond Laser Ablation

Femtosecond laser ablation of Cu0.70Zn0.30 targets in ethanol led to the formation of periodic surface nanostructures and crystalline CuZn alloy nanoparticles with defects, low-coordinated surface sites, and, controlled by the applied laser fluence, different sizes and elemental composition. The Cu/Zn ratio of the nanoparticles was determined by energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and selected area electron diffraction. The CuZn nanoparticles were about 2-3 nm in size, and Cu-rich, varying between 70 and 95%. Increasing the laser fluence from 1.6 to 3.2 J cm-2 yielded larger particles, more stacking fault defects, and repeated nanotwinning, as evident from high-resolution transmission electron microscopy, aided by (inverse) fast Fourier transform analysis. This is due to the higher plasma temperature, leading to increased random collisions/diffusion of primary nanoparticles and their incomplete ordering due to immediate solidification typical of ultrashort pulses. The femtosecond laser-synthesized often nanotwinned CuZn nanoparticles were supported on highly oriented pyrolytic graphite and applied for ethylene hydrogenation, demonstrating their promising potential as model catalysts. Nanoparticles produced at 3.2 J cm-2 exhibited lower catalytic activity than those made at 2.7 J cm-2. Presumably, agglomeration/aggregation of especially 2-3 nm sized nanoparticles, as observed by postreaction analysis, resulted in a decrease in the surface area to volume ratio and thus in the number of low-coordinated active sites.

Bimetallic Metal Sites in Metal-Organic Frameworks Facilitate the Production of 1-Butene from Electrosynthesized Ethylene

Converting CO2 to synthetic hydrocarbon fuels is of increasing interest. In light of progress in electrified CO2 to ethylene, we explored routes to dimerize to 1-butene, an olefin that can serve as a building block to ethylene longer-chain alkanes. With goal of selective and active dimerization, we investigate a series of metal-organic frameworks having bimetallic catalytic sites. We find that the tunable pore structure enables optimization of selectivity and that periodic pore channels enhance activity. In a tandem system for the conversion of CO2 to 1-C4H8, wherein the outlet cathodic gas from a CO2-to-C2H4 electrolyzer is fed directly (via a dehumidification stage) into the C2H4 dimerizer, we study the highest-performing MOF found herein: M' = Ru and M″ = Ni in the bimetallic two-dimensional M'2(OAc)4M″(CN)4 MOF. We report a 1-C4H8 production rate of 1.3 mol gcat-1 h-1 and a C2H4 conversion of 97%. From these experimental data, we project an estimated cradle-to-gate carbon intensity of -2.1 kg-CO2e/kg-1-C4H8 when CO2 is supplied from direct air capture and when the required energy is supplied by electricity having the carbon intensity of wind.

Core-Shell Design of Metastable Phase Catalyst Enables Highly-Performance Selective Hydrogenation

Highly selective semihydrogenation of alkynes to alkenes is a highly important reaction for catalytic industry. Developing non-noble metal based catalysts with platinum group metal-like activity and selectivity is extremely crucial yet challenging. Metastable phase catalysts provide a potential candidate to realize high activity, yet the control of selectivity remains an open question. Here, this work first reports a metastable phase core-shell: face-centered cubic (fcc) phase Ag (10 at%) core-metastable hexagonal closest packed (hcp) phase Ni (90 at%) shell catalyst, which represents high conversion rate, high selectivity, and remarkable universality for the semihydrogenation of phenylacetylene and its derivatives. More impressively, a turnover frequency (TOF) value of 8241.8 h-1 is achieved, much higher than those of stable phase catalysts and reported platinum group metal based catalysts. Mechanistic investigation reveals that the surface of hcp Ni becomes more oxidized due to electron transfer from hcp Ni shell to fcc Ag core, which decreases the adsorption capacity of styrene on the metastable phase Ni surface, thus preventing full hydrogenation. This work has gained crucial research significance for the design of high performance metastable phase catalysts.

Iterative multiscale and multi-physics computations for operando catalyst nanostructure elucidation and kinetic modeling

Modern heterogeneous catalysis has benefitted immensely from computational predictions of catalyst structure and its evolution under reaction conditions, first-principles mechanistic investigations, and detailed kinetic modeling, which are rungs on a multiscale workflow. Establishing connections across these rungs and integration with experiments have been challenging. Here, operando catalyst structure prediction techniques using density functional theory simulations and ab initio thermodynamics calculations, molecular dynamics, and machine learning techniques are presented. Surface structure characterization by computational spectroscopic and machine learning techniques is then discussed. Hierarchical approaches in kinetic parameter estimation involving semi-empirical, data-driven, and first-principles calculations and detailed kinetic modeling via mean-field microkinetic modeling and kinetic Monte Carlo simulations are discussed along with methods and the need for uncertainty quantification. With these as the background, this article proposes a bottom-up hierarchical and closed loop modeling framework incorporating consistency checks and iterative refinements at each level and across levels.

Bimetallic Sites for Catalysis: From Binuclear Metal Sites to Bimetallic Nanoclusters and Nanoparticles

Heterogeneous bimetallic catalysts have broad applications in industrial processes, but achieving a fundamental understanding on the nature of the active sites in bimetallic catalysts at the atomic and molecular level is very challenging due to the structural complexity of the bimetallic catalysts. Comparing the structural features and the catalytic performances of different bimetallic entities will favor the formation of a unified understanding of the structure-reactivity relationships in heterogeneous bimetallic catalysts and thereby facilitate the upgrading of the current bimetallic catalysts. In this review, we will discuss the geometric and electronic structures of three representative types of bimetallic catalysts (bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles) and then summarize the synthesis methodologies and characterization techniques for different bimetallic entities, with emphasis on the recent progress made in the past decade. The catalytic applications of supported bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles for a series of important reactions are discussed. Finally, we will discuss the future research directions of catalysis based on supported bimetallic catalysts and, more generally, the prospective developments of heterogeneous catalysis in both fundamental research and practical applications.

Promoting Effect of Nitride as Support for Pd Hydrodechlorination Catalyst

Pd-catalyzed reductive decontamination is considerably promising in the safe handling of various pollutants, and previous studies on heterogeneous Pd catalysts have demonstrated the key role of support in determining their catalysis performance. In this work, metal nitrides were studied as supports for Pd as a hydrodechlorination (HDC) catalyst. Density functional theory study showed that a transition metal nitride (TMN) support could effectively modulate the valence-band state of Pd. The upward shift of the d-band center reduced the energy barrier for water desorption from the Pd site to accommodate H₂/4-chlorophenol and increased the total energy released during HDC. The theoretical results were experimentally verified by synthesizing Pd catalysts onto different metal oxides and the corresponding nitrides. All studied TMNs, including TiN, Mo₂N, and CoN, showed satisfactorily stabilized Pd and render Pd with high dispersity. In line with theoretical prediction, TiN most effectively modulated the electronic states of the Pd sites and enhanced their HDC performance, with mass activity much higher than those of counterpart catalysts on other supports. The combined theoretical and experimental results shows that TMNs, especially TiN, are new and potentially important support for the highly efficient Pd HDC catalysts.

Mechanistic Insights into Molecular Crystalline Organometallic Heterogeneous Catalysis through Parahydrogen-Based Nuclear Magnetic Resonance Studies

The heterogeneous solid-gas reactions of crystals of [Rh(L₂)(propene)][BAr^F₄] (1, L₂ = ^tBu₂PCH₂CH₂P^tBu₂) with H₂ and propene, 1-butene, propyne, or 1-butyne are explored by gas-phase nuclear magnetic resonance (NMR) spectroscopy under batch conditions at 25 °C. The temporal evolution of the resulting parahydrogen-induced polarization (PHIP) effects measures catalytic flux and thus interrogates the efficiency of catalytic pairwise para-H₂ transfer, speciation changes in the crystalline catalyst at the molecular level, and allows for high-quality single-scan ¹H, ¹³C NMR gas-phase spectra for the products to be obtained, as well as 2D-measurements. Complex 1 reacts with H₂ to form dimeric [Rh(L₂)(H)(μ-H)]₂[BAr^F₄]₂ (4), as probed using EXAFS; meanwhile, a single-crystal of 1 equilibrates NMR silent para-H₂ with its NMR active ortho isomer, contemporaneously converting into 4, and 1 and 4 each convert para-H₂ into ortho-H₂ at different rates. Hydrogenation of propene using 1 and para-H₂ results in very high initial polarization levels in propane (>85%). Strong PHIP was also detected in the hydrogenation products of 1-butene, propyne, and 1-butyne. With propyne, a competing cyclotrimerization deactivation process occurs to afford [Rh(^tBu₂PCH₂CH₂P^tBu₂)(1,3,4-Me₃C₆H₃)][BAr^F₄], while with 1-butyne, rapid isomerization of 1-butyne occurs to give a butadiene complex, which then reacts with H₂ more slowly to form catalytically active 4. Surprisingly, the high PHIP hydrogenation efficiencies allow hyperpolarization effects to be seen when H₂ is taken directly from a regular cylinder at 25 °C. Finally, changing the chelating phosphine to Cy₂PCH₂CH₂PCy₂ results in initial high polarization efficiencies for propene hydrogenation, but rapid quenching of the catalyst competes to form the zwitterion [Rh(Cy₂PCH₂CH₂PCy₂){η⁶-(CF₃)₂(C₆H₃)}BAr^F₃].

Model Catalysis with HOPG-Supported Pd Nanoparticles and Pd Foil: XPS, STM and C2H4 Hydrogenation

A surface science based approach was applied to model carbon supported Pd nanoparticle catalysts. Employing physical vapour deposition of Pd on sputtered surfaces of highly oriented pyrolytic graphite (HOPG), model catalysts were prepared that are well-suited for characterization by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Analysis of the HOPG substrate before and after ion-bombardment, and of Pd/HOPG before and after annealing, revealed the number of “nominal” HOPG defects (~ 10¹⁴ cm⁻²) as well as the nucleation density (~ 10¹² cm⁻²) and structural characteristics of the Pd nanoparticles (mean size/height/distribution). Two model systems were stabilized by UHV annealing to 300 °C, with mean Pd particles sizes of 4.3 and 6.8 nm and size/height aspect ratio up to ~ 10. A UHV-compatible flow microreactor and gas chromatography were used to determine the catalytic performance of Pd/HOPG in ethylene (C₂H₄) hydrogenation up to 150 °C under atmospheric pressure, yielding temperature-dependent conversion values, turnover frequencies (TOFs) and activation energies. The performance of Pd nanocatalysts is compared to that of polycrystalline Pd foil and contrasted to Pt/HOPG and Pt foil, pointing to a beneficial effect of the metal/carbon phase boundary, reflected by up to 10 kJ mol⁻¹ lower activation energies for supported nanoparticles.