Structure-catalytic Activity Relationship Research Articles

Low temperature catalytic activity of hydrothermally synthesised ruthenium promoted ceria-zirconia composites for reforming CO2-rich methane

The use of CO2-rich natural gas as feedstock in DRM is an attractive route of carbon dioxide utilisation due to the compositional advantage of these particular resources. The optimal operating conditions would potentially improve the overall thermal efficiency of the DRM process, especially when the temperature is lower than 800 °C. This study reports a catalyst with the demonstrated high performance and high coke-resistance, developed from ruthenium modified ceria-zirconia. Coprecipitation and hydrothermal methods were adopted to prepare the ceria-zirconia supports, and then impregnated with a very small amount of Ru (0.10 wt%). The structure-catalytic activity relationship of the catalyst was further investigated in DRM. High conversions of CH4 and CO2, i.e., 44.0% and 57.4%, respectively, were achieved by using 0.1Ru1CZ5U-180 at low temperature of 600 °C. A significant reduction in the onset reaction temperature was observed from temperature programmed reduction (TPR) and this observation was related to the increased number of exchangeable oxygens in the presence of Ru. Nitrogen adsorption-desorption results suggested that the specific surface area and the total pore volume also improved the exchange of oxygen between adsorbed carbon dioxide molecules and the crystal lattice. It is evident that the presence of ruthenium accelerated the oxygen spillover process on the surface of the catalyst, and facilitated the dynamics of the oxygen exchange between the adsorbed carbon dioxide molecules and the ceria-zirconia, which ultimately contributed to the observed increase in catalytic activity at temperatures below 800 °C. Most importantly, no detectable carbon deposits were formed over the entire experimental period when the ruthenium modified ceria-zirconia catalyst was used.

Propane Oxidative Dehydrogenation on Nanosized Boron Carbide: Effect of Boron Content and Its Oxidation Implicated by DFT Calculations

Metal-free boron-containing materials are growing to be promising choices in oxidative dehydrogenation (ODH) of light alkanes to alkenes, while it remains unclear how the boron content and the second element that constitutes the scaffold to accommodate B in the materials may influence their catalytic activity. Herein, by means of the density functional theory study of nanosized boron carbide, we studied the mechanisms of ODH of propane (ODHP) catalyzed by three types of boron carbides, B13C2, B4C, and h-BC, which differ from each other in their B contents and their chemical topologies. The influence of hydroxyl coverage on the surface was also evaluated to address the structure–catalytic activity relationship in the ODHP reaction. The calculations show that (1) the B element content and the hydroxyl groups could regulate the electronic structure and significantly increase the highest occupied molecular orbital (HOMO) energy to promote chemical reactivity. (2) Boron carbide with higher coverage of hydroxyl groups on the surface (B13C2-H and B4C-H) exhibits higher activity for catalyzing ODHP reaction owing to the enhanced nucleophilicity, which is further confirmed by the noncovalent interaction (NCI) analysis. (3) The reactivity of the catalyst is positively correlated with the B content, and the ODHP catalyzed by B13C2 is kinetically more favorable than that by B4C and h-BC. This study is expected to enrich our understanding of the structure–activity relationship of boron-based catalysts in the ODH system and benefit the optimization of the catalytic systems.

Atom-Precise Heteroatom Core-Tailoring of Nanoclusters for Enhanced Solar Hydrogen Generation.

While core-shell nanomaterials are highly desirable for realizing enhanced optical and catalytic properties, their synthesis with atomic-level control is challenging. Here, the synthesis and crystal structure of [Au12 Ag32 (SePh)30 ]4- , the first example of selenolated Au-Ag core-shell nanoclusters, comprising a gold icosahedron core trapped in a silver dodecahedron, which is protected by an Ag12 (SePh)30 shell, is presented. The gold core strongly modifies the overall electronic structure and induces synergistic effects, resulting in high enhancements in the stability and near-infrared-II photoluminescence. The Au12 Ag32 and its homometal analog Ag44 , show strong interactions with oxygen vacancies of TiO2 , facilitating the interfacial charge transfer for photocatalysis. Indeed, the Au12 Ag32 /TiO2 exhibits remarkable solar H2 production (6810µmolg-1 h-1 ), which is ≈6.2 and ≈37.8 times higher than that of Ag44 /TiO2 and TiO2 , respectively. Good stability and recyclability with minimal catalytic activity loss are additional features of Au12 Ag32 /TiO2 . The experimental and computational results reveal that the Au12 Ag32 acts as an efficient cocatalyst by possessing a favorable electronic structure that aligns well with the TiO2 bands for the enhanced separation of photoinduced charge carriers due to the relatively negatively charged Au12 core. These atomistic insights will motivate uncovering of the structure-catalytic activity relationships of other nanoclusters.

The Pivotal Role of s-, p-, and f-Block Metals in Water Electrolysis: Status Quo and Perspectives.

Transition metals, in particular noble metals, are the most common species in metal-mediated water electrolysis because they serve as highly active catalytic sites. In many cases, the presence of nontransition metals, that is, s-, p-, and f-block metals with high natural abundance in the earth-crust in the catalytic material is indispensable to boost efficiency and durability in water electrolysis. This is why alkali metals, alkaline-earth metals, rare-earth metals, lean metals, and metalloids receive growing interest in this research area. In spite of the pivotal role of these nontransition metals in tuning efficiency of water electrolysis, there is far more room for developments toward a knowledge-based catalyst design. In this review, five classes of nontransition metals species which are successfully utilized in water electrolysis, with special emphasis on electronic structure-catalytic activity relationships and phase stability, are discussed. Moreover, specific fundamental aspects on electrocatalysts for water electrolysis as well as a perspective on this research field are also addressed in this account. It is anticipated that this review can trigger a broader interest in using s-, p-, and f-block metals species toward the discovery of advanced polymetal-containing electrocatalysts for practical water splitting.

Boron: A key functional component for designing high-performance heterogeneous catalysts

Heterogeneous catalysis is a vivid branch of traditional catalysis field, with the advantage of high efficiency and being easily separated from reactants and products after reaction, and have received widespread attentions in large-scale industrial production, especially in the field of energy utilization. Boron has been found to be a key functional component for designing high-performance heterogeneous catalysts. In this review, we cover and categorize the past and recent progress in boron-containing materials and their applications in heterogeneous catalysis particularly in energy‐related fields. The fundamental roles of boron components in the emerging heterogeneous catalysis of construction, regulation and stabilization of active phases/sites are highlighted, with the emphasis on how they regulating structural and electronic properties of host materials. We then categorize boron-containing catalysts into six kinds mainly including intermetallic boride catalysts, metal boride-derived catalysts, boron-doped catalysts, metal boride-decorated catalysts, boron-containing compounds as catalyst supports, and single-boron-site catalysts, as well as try to establish structure-catalytic activity relationship. The catalytic applications of these six boron-containing catalysts are discussed separately, focusing on the energy-related reactions such as hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR) and nitrogen reduction reaction (NRR). Finally, the opportunities and challenges related to boron-containing compounds in the field of catalysis are prospected.

Theoretical investigations into the hydrogen evolution reaction of the carbon schwarzites: From electronics to structure-catalytic activity relationship

Since Earth-abundant materials have received considerable attention for energy applications, interest in developing new carbon-based structures actively continues. One such material, the 3D carbon-based schwarzite structure, has the unusual shape of Triply-Periodic Minimal Surfaces (TPMS) and shows a stable curvature formed of carbon rings with more than six atoms. However, the possibility of application as a catalytic material has not been discussed, even though their geometric and electronic features can improve reactivity with diverse catalytic adsorbents. Herein, we systematically investigated the hydrogen evolution reaction (HER) activity of diverse schwarzites based on thermodynamic, electronic, and geometric viewpoints. Our results reveal that the h8326896 structure has superior HER catalytic activity with binding free energy of hydrogen (ΔGH∗) as −0.02 eV, closer to that of the ideal catalyst (0 eV). Based on this thermodynamic result, we explored the reason for the remarkable activity and found that efficient hydrogen binding clearly originates from the favourable p-orbital tendency with a metallic nature and positively curved geometry. Therefore, we believe that this work will play an important role in uncovering and extending the utility of carbon-based schwarzites as catalytic materials.

On the correlation between structure and catalytic activity of mesoporous ceria nanoparticles

Mesoporous ceria nanoparticles (MCNs) have many superiorities such as higher surface area and more active reaction sites over their solid counterparts. However, the correlation between their structure and catalytic activity is poorly understood due to the lack of methods to synthesize MCNs with variable and well-defined structure parameters. In this study, a MCNs synthesis platform featured with strong structure parameter tuning capacity was established to synthesize plenty of MCNs for exploring their structure-catalytic activity relationship. The platform was composed of Ce(NO3)3·6H2O precursor, trioctylphosphine oxide (TOPO) ligand, and ethanol and octadecene (ODE) solvent. Through altering ligand/precursor ratio, ligand-precursor addition manner and reaction temperature, three groups of MCNs, totally twelve nanoparticles, were synthesized on the platform. The structure parameters of the synthesized MCNs were collected, and their catalytic activities including oxygen storage capacity (OSC), oxidase mimetic activity and photocatalytic activity were evaluated. The MCNs demonstrated wide range of nanoparticle diameter (40–115 nm), pore diameter (2.09–4.17 nm), pore volume (0.20–0.40 cm3 g−1), surface area (119.2–202.8 m2 g−1), and crystallite size (8.8–9.95 nm). These parameters played different roles in controlling different catalytic reactions, where pore size and crystallite size determined the oxygen storage capacity (OSC), pore size regulated the enzyme mimetic activity, and surface area dominated the photocatalytic activity. This study provided important insights into the correlation between structure and catalytic activity of MCNs, which was critical to the fabrication of MCNs based catalytic reactions.

X-ray absorption fine structure studies on nickel phosphide catalysts for the non-oxidative coupling of methane reaction using a theoretical model

SiO2-supported Ni phosphide catalysts are highly active toward the non-oxidative coupling of methane (NOCM) reaction, and their catalytic activity is strongly dependent on their Ni:P ratio. We analyzed Ni phosphide catalysts using X-ray absorption fine structure (XAFS) to elucidate the structure-catalytic activity relationship. Because only Ni2P was available as a reference material, we calculated the theoretical XAFS based on the reference crystal structures using the FEFF program and compared them with the experimental spectra of Ni phosphide catalysts. We demonstrated that catalysts with Ni to P ratios of 1:1, 2:1, and 3:1 consisted mainly of the Ni2P, Ni12P5, and Ni3P, respectively. We found that Ni2P exhibited the highest activity toward NOCM because of its optimum balance of C–H cleavage activity and coke formation. This analysis demonstrated that the theoretical XAFS simulation could be used to identify the structure of supported catalysts based on the crystal structure of reference compounds.

Study of Cu modified Zr and Al mixed oxides in ethanol conversion: The structure-catalytic activity relationship

Here, we study the influence of the Cu modified (Zr + Ce)O2-Al2O3 systems composition and synthesis conditions on their catalytic properties in the ethanol conversion. First, we obtained varios ratios mixed Al-Zr supports at different synthesis temperatures using a sol-gel method. Then we modified the surface of the oxides by Cu, reduced in hydrogen flow. All obtained systems demonstrated а high alcohol conversion and selectivity to acetaldehyde. The surface area (SBET), the pore volume, and the pore distribution were measured by the nitrogen adsorption method. The structure of the samples have been investigated by XRD and XAS-spectroscopy. A correlation between the synthesis temperature and contents of mixed oxide support and textural properties were observed. The results show that Al-Zr mixed oxide support structure plays a crucial role in forming a Cu active site for ethanol dehydrogenation to acetaldehyde.

Theoretical Investigations into the Hydrogen Evolution Reaction of the Carbon Schwarzites: From Electronics to Structure-Catalytic Activity Relationship

Theoretical Investigations into the Hydrogen Evolution Reaction of the Carbon Schwarzites: From Electronics to Structure-Catalytic Activity Relationship

Comparative study of structure-catalytic activity relationship for Ni–Cr–Al–O and Cu–Ni–Cr–Al–O spinel oxide solid solutions

A spinel solid solution expressed by a composition formula of CuxNi1−xAl1.8Cr0.2O4 (0 ≤ x ≤ 0.2) was studied focusing on the role of Cu species in the catalytic activity toward NO reduction under a simulated three-way catalysis condition. X-ray Rietveld analysis revealed that Cu and Cr prefer to occupy the tetrahedral site and the octahedral site, respectively, whereas Ni and Al are distributed across both sites. Although NiAl1.8Cr0.2O4 (x = 0) showed negligible catalytic activity for NO reduction, the partial replacement of Ni by Cu significantly enhanced the activity, achieving the highest activity at x = 0.05 not only for NO reduction but also for CO and C3H6 oxidation. Based on the infrared spectra and pulsed reaction experiments, it was concluded that the monovalent Cu site in the tetrahedral site plays a key role in CO chemisorption, oxygen vacancy formation, and subsequent NO reduction via the Mars–van Krevelen mechanism.

Variation in the In2O3 Crystal Phase Alters Catalytic Performance toward the Reverse Water Gas Shift Reaction

Understanding the structure–catalytic activity relationship is crucial for developing new catalysts with desired performance. In this contribution, we report the performance of In2O3 with different...

The structure-catalytic activity relationship for the transient layered zeolite MCM-56 with MWW topology

Abstract Zeolite MCM-56 is a high alumina, monolayered form of the commercially useful framework MWW but it is a transient product during crystallization, so many factors influence its state and quality. This work examines properties of a series of MCM-56 and MCM-49 samples synthesized for different times using Aerosil, Ultrasil and Ludox as silica sources, hexamethyleneimine as the structure directing agent and additionally aniline as structure promoting agent. It was found that the most important parameter, governing the catalytic activity in the test reaction of Friedel-Crafts alkylation of mesitylene with benzyl alcohol, was availability of the Bronsted acid centers located at the external surfaces of the crystals. The key role in correlating physical characteristic with activity was played by infrared spectroscopy as it enabled the study of many properties of the tested materials, starting from the total concentration of acid centers, and their type (Bronsted or Lewis acids) through the concentration of centers available for the reagent molecules, to investigating the correlation of acidity with the degree of zeolite crystallinity.

Higher gold atom efficiency over Au-Pd/TS-1 alloy catalysts for the direct propylene epoxidation with H2 and O2

Bimetallic nanoparticles (NPs) have shown amazing charm for their unique structures and catalytic activity. Herein, AuPd alloy NPs with cuboctahedron structure supported on titanium silicalite-1 (denoted as Au-Pd/TS-1) were prepared by the alcohol reduction method, which exhibited higher gold atom efficiency for the direct propylene epoxidation than the traditional Au/TS-1-DP (prepared by the deposition precipitation method). A combination of experimental characterization with density functional theory (DFT) calculations indicates that the charge transfer from Pd to Au atoms promotes the formation of H2O2 from O2 and H2, and consequently improves the gold atom efficiency of Au-Pd/TS-1 alloy catalysts. The volcano-shaped relationship was established between Pd/Au molar ratio and catalytic activity. Au0.68Pd0.32/TS-1 showed the highest gold atom efficiency of ~1000 gPO h−1 gAu−1 at 200 °C. The insights reported here may pave the way for unraveling the catalyst structure-catalytic activity relationship of supported nano-gold catalysts.

Arylhydrazone ligands as Cu-protectors and -catalysis promoters in the azide-alkyne cycloaddition reaction.

A series of water soluble copper(ii) complexes, [Cu(κO1O2N-H2L1)(H2O)2]·2H2O (2), [Cu(κO-H3L1)2(H2O)4] (3), [Cu(κO-H4L2)2(H2O)4] (5) and [Cu(H2O)6]·2H2L3·2(CH3)2NCHO (7), were prepared by the reaction of Cu(NO3)2·3H2O with sodium (Z)-2-(2-(1-amino-1,3-dioxobutan-2-ylidene)hydrazineyl)benzenesulfonate, [Na(μ4-1:2κO1,2κO2,3κO3,4κO4-H3L1)]n (1; for 2 and 3), sodium (Z)-3-(2-(1-amino-1,3-dioxobutan-2-ylidene)hydrazineyl)-4-hydroxybenzene-sulfonate, [Na(μ-1κO1,2κO2-H4L2)]2 (4; for 5) or sodium (Z)-2-(2-(1,3-dioxo-1-(phenylamino)butan-2-ylidene)hydrazineyl)naphthalene-1-sulfonate, [Na(μ-1κO1O2,2κO3-H2L3)(CH3OH)2]2 (6; for 7). Compounds 1-7 were fully characterized, also by single-crystal X-ray diffraction analysis, and applied as homogeneous catalysts for the azide-alkyne cycloaddition (AAC) reaction to afford 1,4-disubstituted 1,2,3-triazoles. A structure-catalytic activity relationship has been recognized for the first time on the basis of the occurrence of resonance- and charge-assisted hydrogen bond interactions (RAHB and CAHB), in charge and ligand binding modes, enabling the catalytic activity of the compounds to be ordered as follows: Cu(NO3)2≪7 (complex salt with RAHB and CAHB) < 3 (with RAHB and CAHB) < 5 (with RAHB) < 2 (neither RAHB nor CAHB). Complex 2, without such non-covalent interactions, was found to be the most efficient catalyst for the AAC reaction, affording up to 98% product yield after being placed for 15 min, at 125 °C, in a water/acetonitrile mixture under low power (10 W) MW irradiation.

Engineering the Coordination Environment of Single‐Atom Platinum Anchored on Graphdiyne for Optimizing Electrocatalytic Hydrogen Evolution

AbstractTwo Pt single‐atom catalysts (SACs) of Pt‐GDY1 and Pt‐GDY2 were prepared on graphdiyne (GDY)supports. The isolated Pt atoms are dispersed on GDY through the coordination interactions between Pt atoms and alkynyl C atoms in GDY, with the formation of five‐coordinated C1‐Pt‐Cl4 species in Pt‐GDY1 and four‐coordinated C2‐Pt‐Cl2 species in Pt‐GDY2. Pt‐GDY2 shows exceptionally high catalytic activity for the hydrogen evolution reaction (HER), with a mass activity up to 3.3 and 26.9 times more active than Pt‐GDY1 and the state‐of‐the‐art commercial Pt/C catalysts, respectively. Pt‐GDY2 possesses higher total unoccupied density of states of Pt 5d orbital and close to zero value of Gibbs free energy of the hydrogen adsorption (|Δ |) at the Pt active sites, which are responsible for its excellent catalytic performance. This work can help better understand the structure–catalytic activity relationship in Pt SACs.

Engineering the Coordination Environment of Single-Atom Platinum Anchored on Graphdiyne for Optimizing Electrocatalytic Hydrogen Evolution.

Two Pt single-atom catalysts (SACs) of Pt-GDY1 and Pt-GDY2 were prepared on graphdiyne (GDY)supports. The isolated Pt atoms are dispersed on GDY through the coordination interactions between Pt atoms and alkynyl C atoms in GDY, with the formation of five-coordinated C1 -Pt-Cl4 species in Pt-GDY1 and four-coordinated C2 -Pt-Cl2 species in Pt-GDY2. Pt-GDY2 shows exceptionally high catalytic activity for the hydrogen evolution reaction (HER), with a mass activity up to 3.3 and 26.9 times more active than Pt-GDY1 and the state-of-the-art commercial Pt/C catalysts, respectively. Pt-GDY2 possesses higher total unoccupied density of states of Pt 5d orbital and close to zero value of Gibbs free energy of the hydrogen adsorption (|ΔGPtH* |) at the Pt active sites, which are responsible for its excellent catalytic performance. This work can help better understand the structure-catalytic activity relationship in Pt SACs.

Metal-Free Oxygen Evolution and Oxygen Reduction Reaction Bifunctional Electrocatalyst in Alkaline Media: From Mechanisms to Structure–Catalytic Activity Relationship

We have systematically investigated a metal-free bifunctional electrocatalyst of heteroatom-doped carbon nitride (XY-C3N4, where X and Y indicate the dopant and doping site on C3N4, respectively) for oxygen evolution and oxygen reduction reactions (OER and ORR), considering the possible reaction pathways based on the Eley–Rideal (ER) mechanism as well as the doping effects on electrocatalytic activity. In this work, the relative stability of O* and OOH* intermediates was a key factor in determining the ORR pathway; accordingly, ORR follows a two-step reaction pathway governed by O* rather than a four-step reaction pathway governed by OOH*. In addition, we found that P and S codoped C3N4 shows superior OER/ORR activity with synergistic geometric and electronic effects, which coordinatively increase unsaturated sp3-C via structural deformation and improve electrical conductance by modulating the electronic structure with extra electrons from dopants. In particular, PCSC-C3N4 (C3N4 with P and S codoped at th...

Atomically Thin Two-Dimensional Solids: An Emerging Platform for CO2 Electroreduction

Benefiting from the high specific surface area and the ensuing novel electronic structures, atomically thin two-dimensional (2D) solids have drawn intense interest in the field of carbon dioxide (CO2) catalysis. Here we review the major advantages of atomically thin 2D solids for electrochemical CO2 reduction, and special emphasis will be paid to the recent advances in fine characterization and controllable tailoring of the local atomic and electronic structure. Because surface atoms in atomically thin 2D solids are comparable to the overall atoms, we highlight surface modifications, such as molecular functionalization, heteroatom incorporation, and defect engineering, as effective ways to manipulate the reactivity. Finally, the major challenges and opportunities for future development of this field are discussed. As a well-defined model system, atomically thin 2D solids offer practical possibilities to study the structure–catalytic activity relationship at the atomic level.

Continuous-Flow Monolithic Silica Microreactors with Arenesulphonic Acid Groups: Structure–Catalytic Activity Relationships

The performance of monolithic silica microreactors activated with sulphonic acid groups and a packed bed reactor with Amberlyst 15 resin were compared in the esterification of acetic acid with n-butanol. The monolithic microreactors were made of single silica rods with complex pore architecture, differing in the size of mesopores, and in particular, flow-through macropores which significantly affected the flow characteristic of the continuous system. The highest ester productivity of 105.2 mol·molH+−1·h−1 was achieved in microreactor M1 with the largest porosity, characterized by a total pore volume of 4 cm3·g−1, mesopores with 20 nm diameter, and large flow-through macropores 30–50 μm in size. The strong impact of the permeability of the monoliths on a reaction kinetics was shown.