Trends In Catalytic Activity Research Articles

Catalytic Activity, Stability, and Loading Trends of Alcohol Dehydrogenase Enzyme Encapsulated in a Metal-Organic Framework.

Recently, it has been shown that enzyme encapsulation inside metal-organic frameworks (MOFs) can increase enzyme activity and serve as protection from adverse environmental conditions. Little is understood about how the enzymes move into and are held inside the MOFs although it is believed that intermolecular forces between the MOF and the enzyme cause it to be held in place. If this process can be better understood, it can have dramatic implications on the cost-effectiveness and implementation of enzyme-MOF complexes. This is of specific importance in the medical sector for protein therapy and the industrial sector where enzyme use is expected to increase. Herein, we synthesized alcohol dehydrogenase (ADH) and PCN-333 to study encapsulation, stability, and enzyme activity to expand the knowledge of our field and offer a potential improvement to a synthetic route for biofuel synthesis. From this, we found a correlation between the concentration of a buffer and the loading of an enzyme, with surprising loading trends. We conclude that the buffer solution decreases interactions between the enzyme and MOF, supporting conventional theory and allowing it to penetrate deeper into the structure causing higher enzyme loading while allowing for excellent stability over time at various pH values and temperatures and after multiple reactions. We also observe new trends such as a rebounding effect in loading and "out-of-bounds" reactions.

Tuning Single-Atom Catalysts of Nitrogen-Coordinated Transition Metals for Optimizing Oxygen Evolution and Reduction Reactions

Single-atom catalysts based on Earth-abundant elements have recently emerged as one of the most promising alternatives to the precious-metal-based catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Here, we use density functional theory calculations to investigate the OER and ORR catalytic activities of 3d single metal atoms coordinated by nitrogen atoms on carbon substrates. It is found that the adsorption energies of all reaction intermediates increase monotonically with the number of d electrons. By constructing the linear scaling relationships between the adsorption energies of reaction species, a volcano pattern is observed and the optimal conditions for high catalytic activity are obtained. Among the atom/substrate combinations, the Co atom on the pyridine-N4 substrate exhibits the lowest theoretical overpotentials for both reactions. Furthermore, we propose that the trend in catalytic activity is mainly governed by the filling of the antibonding state between the metal atom and the reaction intermediate *O.

Catalyst Engineering for Electrochemical Energy Conversion from Water to Water: Water Electrolysis and the Hydrogen Fuel Cell

Abstract In the context of the current serious problems related to energy demand and climate change, substantial progress has been made in developing a sustainable energy system. Electrochemical hydrogen–water conversion is an ideal energy system that can produce fuels via sustainable, fossil-free pathways. However, the energy conversion efficiency of two functioning technologies in this energy system—namely, water electrolysis and the fuel cell—still has great scope for improvement. This review analyzes the energy dissipation of water electrolysis and the fuel cell in the hydrogen–water energy system and discusses the key barriers in the hydrogen- and oxygen-involving reactions that occur on the catalyst surface. By means of the scaling relations between reactive intermediates and their apparent catalytic performance, this article summarizes the frameworks of the catalytic activity trends, providing insights into the design of highly active electrocatalysts for the involved reactions. A series of structural engineering methodologies (including nanoarchitecture, facet engineering, polymorph engineering, amorphization, defect engineering, element doping, interface engineering, and alloying) and their applications based on catalytic performance are then introduced, with an emphasis on the rational guidance from previous theoretical and experimental studies. The key scientific problems in the electrochemical hydrogen–water conversion system are outlined, and future directions are proposed for developing advanced catalysts for technologies with high energy-conversion efficiency.

Cu/KIT-5 catalysts for hydrogenation of fatty acids: a comprehensive study of the chemical species and their performance

Cu as an active phase represents a great alternative in heterogeneous catalysis for biomass feedstocks. New Cu/KIT-5 catalysts were synthesized by varying the metal precursor in aqueous solution. Copper chloride, nitrate or sulfate were impregnated to three-dimensional mesoporous KIT-5 material and the catalysts were characterized. The catalysts were tested in hydrogenation of palmitic acid. We found that the catalytic activity trend as a function of the salt precursor is: NO3− > Cl− = SO42−. The catalyst prepared with CuSO4 resulted in high quantities of linear alkanes and alkenes, while the other two materials prefer the hydrogenation reaction to the alcohol. The hydrocarbon molecules produced over these Cu/KIT-5 materials point out the possibility of tuning their selectivity to desired products. Those features might be exploited for cleaner catalysts applied to biomass transformation.

Electronic Structural Origin of the Catalytic Activity Trend of Transition Metals for Electrochemical Nitrogen Reduction

As an alternative to the conventional Haber–Bosch process for NH3 synthesis that operates under harsh conditions, an electrochemical process has recently been pursued. Here, using a joint experimen...

A Brønsted Acidic Ionic Liquid as an Efficient and Selective Catalyst System for Bioderived High Molecular Weight Poly(ethylene 2,5-furandicarboxylate).

Green synthesis of bioderived high-molecular-weight poly(ethylene 2,5-furandicarboxylate) (PEF) over metal-free catalysts is a significant challenge. This study focuses on PEF prepared from ethylene glycol and 2,5-furandicarboxylic acid (FDCA) through a direct esterification method with ecofriendly metal-free ionic liquids (ILs) as catalysts. The catalytic activities of a series of imidazolium cations in the presence of various anions are systematically investigated and found to be mainly governed by the anions. Among the ILs studied, 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2 MIM]BF4 ) is identified as the best catalyst, showing excellent catalytic activity, selectivity, and stability, even at low catalyst loadings (0.1 mol % w.r.t. FDCA). Optimization of the polymerization parameters enables [C2 MIM]BF4 -catalyzed production of PEF with a high number-average molecular weight (Mn =5.25×104 g mol-1 ). The relationship between Brønsted acidity and catalytic activity is also investigated and the results show that the trend in catalytic activity is in good agreement with that in Brønsted acidity, as determined by the Hammett method. Additionally, on the basis of experimental results and density functional theory calculations, an electrophilic activation mechanism induced by hydrogen bonds is proposed. This strategy of adjustable acidity and anion structure in ILs provides an opportunity to develop other ILs for bio-based polyesters through green synthesis pathways.

Catalytic activity trends from pure Pd nanoclusters to M@PdPt (M = Co, Ni, and Cu) core-shell nanoclusters for the oxygen reduction reaction: A first-principles analysis

The trends of the catalytic activity toward the oxygen reaction reduction (ORR) from Pd44 nanoclusters to M6@Pd30Pt8 (M = Co, Ni, and Cu) core-shell nanoclusters was investigated using auxiliary density functional theory. The adsorption energies of O and OH were computed as predictors of the catalytic activity toward the ORR and the following tendency of the electrocatalytic activity was computed: Pt44 ≈ M6@Pd30Pt8 > M6@Pd38 > Pd44. In addition, the adsorption of O2 on the Ni6@Pd30Pt8 and Pt44 nanoclusters were investigated, finding an elongation of the O–O bond length when O2 is adsorbed on the Ni6@Pd30Pt8 and Pt44 nanoclusters, suggesting that the O2 is activated. Finally, the stabilities of the M6@Pd38 and M6@Pd30Pt8 core-shell nanoclusters were analyzed both in vacuum and in oxidative environment. From the calculated segregation energies for the bimetallic and trimetallic nanoclusters in vacuum, it can be clearly observed that the M atoms prefer to be in the center of the M6@Pd38 and M6@Pd30Pt8 nanoclusters. Nevertheless, it is observed that the segregation energies of M atoms for the M6@Pd38 nanoclusters with an oxidizing environment tend to decrease compared with their M6@Pd38 nanoclusters counterparts in vacuum, which suggests that in an oxidative environment, M atoms may tend to segregate to the surface of the M6@Pd38 nanoclusters.

Structural elucidation of N^O (ethylimino-methyl)phenol Fe(II) and Co(II) complexes and their applications in ethylene oligomerization catalysis

Reactions of 2-[(2-hydroxyethyl)imino]methyl]phenol (L1H), 2-[1-[(2-hydroxyethyl)imino]ethyl]phenol (L2H) and 2-[{[(2-diethylamino)ethyl]imino}methyl]phenol (L3H) with CoCl2 and FeCl2 salts produced the metal complexes [Co(L1)2] (Co1), [Fe(L1)2] (Fe1), [Co(L2)2] (Co2), [Fe(L)2] (Fe2), [Co2(L3H)2Cl4)] (Co3) and [Fe2(L3H)2Cl4] (Fe3), respectively. Molecular structureof Fe1 confirmed the formation of mononuclear complex containing two tridentate bound anionic ligand L1. On the other hand, the solid state structure of Co3 established the formation of a dinuclear complex bearing a bidentate zwitterionic ligand L3H. Activation of the Fe(II) and Co(II) complexes with EtAlCl2 or MAO co-catalysts, gave active catalysts in oligomerization of ethylene to give C4 and C6 oligomers. Generally, the Co(II) complexes exhibited higher catalytic activities than their Fe(II) analogues. While activation with MAO produced mainly C4 oligomers (96%), EtAlCl2 gave predominantly C6 oligomers. Density functional theory data provided insights on the catalytic activity trends and effect of complex/ligand structure on the ethylene oligomerization reactions.

Degradation and Stabilization of Porphyrin-Based Metal Organic Framework Electrocatalysts for the Oxygen Reduction Reaction

One limiting factor in the efficiency of hydrogen fuel cells is poor stability and activity of non-platinum group catalysts for the oxygen reduction reaction (ORR). Porphyrin metal organic frameworks (PMOFs) are an interesting class of materials that have seen a large increase in interest as electrocatalysts for the ORR due to the potential for confinement-based activity enhancement.1 Characterizing the fundamental or intrinsic activity of these catalysts is convoluted due to the high activity of the porphyrin precursor, their low electrical conductivity, and the unclear active site accessibility within the 3D structure. We have characterized the stabilization and degradation of Co-based PMOFs (CoPMOFs) compared to their metal porphyrin precursor as a function of pH and electrolyte composition. CoPMOFs were synthesized via a clean, non-pyrolysis technique, in which the cobalt-tetrakis(4-carboxyphenyl)porphyrin (CoTCPP) precursor was coordinated in a face-to-face orientation with aluminum-based nodes.2,3 As deposited structures were characterized using x-ray diffraction. Using coupled transmission electron microscopy and quantitative elemental analysis (using an inductively coupled plasma) we show that the framework structure can degrade while the catalyst retains activity. This framework degradation was monitored by measuring the relative Al and Co dissolution (see attached figure). Degradation of the framework, as seen by loss of ~ 80 % of the Al, but only ~ 15% of the Co at pH 1, indicates that the Co-N4 porphyrin rings are more important in activity than the framework-structure. This suggests that the electrochemical evaluation of CoPMOFs in pH 1 electrolyte is largely a measurement of the precursor performance. We further demonstrate the stabilization of the 3D structure of CoPMOF nanoparticles in near-neutral, phosphate buffered conditions, however, there are no clear activity enhancements due to the framework. We hypothesize the leaching of the metal-porphyrin site and not the destruction of the 3D framework is responsible for loss of activity in these types of catalysts. While no structure-based enhancement was evident, it is important that we were able to find the optimal electrochemical testing conditions to evaluate these structure-activity relationships. This work highlights the importance of rigorous post-test or operando structural-electrochemical analyses for the validation of complicated activity mechanisms and provides simple engineering controls to facilitate the improvement of these analyses. References (1) Kulkarni, A.; Siahrostami, S.; Patel, A.; Nørskov, J. K. Understanding Catalytic Activity Trends in the Oxygen Reduction Reaction. 2018, 118, 2302–2312. (2) Fateeva, A.; Chater, P. A.; Ireland, C. P.; Tahir, A. A.; Khimyak, Y. Z.; Wiper, P. V.; Darwent, J. R.; Rosseinsky, M. J. A Water-Stable Porphyrin-Based Metal-Organic Framework Active for Visible-Light Photocatalysis. Angew. Chemie - Int. Ed. 2012, 51, 7440–7444. (3) Lions, M.; Tommasino, J.-B.; Chattot, R.; Abeykoon, B.; Guillou, N.; Devic, T.; Demessence, A.; Cardenas, L.; Maillard, F.; Fateeva, A. Insights into the Mechanism of Electrocatalysis of the Oxygen Reduction Reaction by a Porphyrinic Metal Organic Framework. Chem. Commun. 2017, 53, 6496–6499. Figure 1

Interface Engineering of Graphene-Supported Cu Nanoparticles Encapsulated by Mesoporous Silica for Size-Dependent Catalytic Oxidative Coupling of Aromatic Amines.

In this study, graphene nanosheet-supported ultrafine Cu nanoparticles (NPs) encapsulated with thin mesoporous silica (Cu-GO@m-SiO2) materials are fabricated with particle sizes ranging from 60 to 7.8 nm and are systematically investigated for the oxidative coupling of amines to produce biologically and pharmaceutically important imine derivatives. Catalytic activity remarkably increased from 76.5% conversion of benzyl amine for 60 nm NPs to 99.3% conversion and exclusive selectivity of N-benzylidene-1-phenylmethanamine for 7.8 nm NPs. The superior catalytic performance along with the outstanding catalyst stability of newly designed catalysts are attributed to the easy diffusion of organic molecules through the porous channel of mesoporous SiO2 layers, which not only restricts the restacking of the graphene nanosheets but also prevents the sintering and leaching of metal NPs to an extreme extent through the nanoconfinement effect. Density functional theory calculations were performed to shed light on the reaction mechanism and to give insight into the trend of catalytic activity observed. The computed activation barriers of all elementary steps are very high on terrace Cu(111) sites, which dominate the large-sized Cu NPs, but are significantly lower on step sites, which are presented in higher density on smaller-sized Cu NPs and could explain the higher activity of smaller Cu-GO@m-SiO2 samples. In particular, the activation barrier for the elementary coupling reaction is reduced from 139 kJ/mol on flat terrace Cu(111) sites to the feasible value of 94 kJ/mol at step sites, demonstrating the crucial role of the step site in facilitating the formation of secondary imine products.

MoS2 nanosheets grown on nickel chalcogenides: controllable synthesis and electrocatalytic origins for the hydrogen evolution reaction in alkaline solution

Catalytic mechanisms and activity trend of Ni-based heterostructures were revealed by combining experimental data and theoretical calculation results.

Controlling Reversible Expansion of Li2O2 Formation and Decomposition by Modifying Electrolyte in Li-O2 Batteries

Summary The aprotic lithium-oxygen (Li-O2) battery has attracted worldwide attention because of its ultrahigh theoretical energy density. However, its practical application is critically hindered by cathode passivation, large polarization, and severe parasitic reactions. Here, we demonstrate an originally designed Ru(II) polypyridyl complex (RuPC) though which the reversible expansion of Li2O2 formation and decomposition can be achieved in Li-O2 batteries. Experimental and theoretical results revealed that the RuPC can not only expand the formation of Li2O2 in electrolyte but also suppress the reactivity of LiO2 intermediate during discharge, thus alleviating the cathode passivation and parasitic reactions significantly. In addition, an initial delithiation pathway can be achieved when charging in turn; thus, the Li2O2 products can be decomposed reversibly with a low overpotential. Consequently, the RuPC-catalyzed Li-O2 batteries exhibited a high discharge capacity, a low charge overpotential, and an ultralong cycle life. This work provides an alternative way of designing the soluble organic catalysts for metal-O2 batteries.

Hydrogenation of alkenes and alkynes catalysed by NˆO (imino)phenol palladium(II) complexes: Structural, kinetics and chemoselectivity studies

Reactions of 2-(2-methoxyethylimino)ethyl)phenol (HL1), 2-(2-hydroxyethylimino)ethyl)phenol (HL2), 2-(2-aminoethylimino)ethyl)phenol (HL3) and 2-(2-hydroxyethylimino)methyl)phenol (HL4) with [PdCl2(COD)] afforded the neutral palladium complexes [PdCl2(HL1)] (1), [PdCl2(HL2)] (2), [PdCl2(HL3)] (3), [PdCl2(HL4)] (4) respectively. Treatment of complex 1 with PPh3 gave the cationic complex [Pd(HL1)ClPPh3]+ (5), while reactions of 4 with Pd(OAc)2, in the presence of PPh3 and p-TsOH produced the corresponding palladium complex, [Pd(L1) (OTs) (PPh3)] (6). The molecular structure of 4a (derivative of 4) contained two bidentate anionic ligands (L4). Complexes 1–6 formed active catalysts in hydrogenation of alkenes and alkynes, in which the catalytic activities were largely dependent on the pendant donor atom of the ligand motif. Isomerization reactions were dominant in terminal alkenes hydrogenation reactions, while hydrogenation of alkynes to alkanes occurred in two steps via alkene intermediates. Kinetics data were consistent with homogeneous active species. Density functional theory studies supported the hemi-labile nature of the ligands, and offered insights into the catalytic activity trends observed.

Phase Exploration and Identification of Multinary Transition-Metal Selenides as High-Efficiency Oxygen Evolution Electrocatalysts through Combinatorial Electrodeposition

Designing high-efficiency electrocatalysts for water oxidation has become an increasingly important concept in the catalysis community due to its implications in clean energy generation and storage. In this respect transition-metal-doped mixed-metal selenides incorporating earth-abundant elements such as Ni and Fe have attracted attention due to their unexpectedly high electrocatalytic activity toward the oxygen evolution reaction (OER) with low overpotential in alkaline medium. In this article, quaternary mixed-metal selenide compositions incorporating Ni-Fe-Co were investigated through combinatorial electrodeposition by exploring the ternary phase diagram of Ni-Fe-Co systems. The OER electrocatalytic activity of the resultant quaternary and ternary mixed-metal selenide compositions was measured in order to systematically investigate the trend of catalytic activity as a function of catalyst composition. Accordingly, the composition(s) exhibiting the best catalytic efficiency for the quaternary Fe-Co-Ni m...

Understanding Catalytic Activity Trends in the Oxygen Reduction Reaction.

Despite the dedicated search for novel catalysts for fuel cell applications, the intrinsic oxygen reduction reaction (ORR) activity of materials has not improved significantly over the past decade. Here, we review the role of theory in understanding the ORR mechanism and highlight the descriptor-based approaches that have been used to identify catalysts with increased activity. Specifically, by showing that the performance of the commonly studied materials (e.g., metals, alloys, carbons, etc.) is limited by unfavorable scaling relationships (for binding energies of reaction intermediates), we present a number of alternative strategies that may lead to the design and discovery of more promising materials for ORR.

Role of non-metallic atoms in enhancing the catalytic activity of nickel-based compounds for hydrogen evolution reaction.

The transition-metal compounds (MX) have gained wide attention as hydrogen evolution reaction (HER) electrocatalysts; however, the interaction between the non-metallic atom (X) and the metal atom (M) in MX, and the role of X in the enhanced catalytic activity of MX, are still ambiguous. In this work, we constructed a simple model [X/Ni(100)] to decipher the contribution of X towards enhancing the catalytic activity of NiX, which allows us to accurately predict the trend in HER catalytic activity of NiX based on the easily accessible physico-chemical characteristics of X. Theoretical calculations showed that the electronegativity (χX) and the principle quantum number (nX) of X are two important descriptors for evaluating and predicting the HER catalytic activity of NiX catalysts effectively. X atoms in the VIA group can enhance the HER activity of X/Ni(100) more significantly than those in the second period due to the large χX or nX. At a relatively low X coverage, the S/Ni(100) possesses the best HER activity among all of the discussed X/Ni(100) models, and the optimum surface S : Ni atomic ratio is about 22-33%. Further experiments demonstrated that the Ni-Ni3S2 catalyst with a surface S : Ni atomic ratio of 28.9% exhibits the best catalytic activity and lowest charge transfer resistance. The trend in catalytic activity of NiX with differing X offers a new possible strategy to exploit MX materials and design new active catalysts rationally.

Design of bimetallic Rh-M catalysts for N2O decomposition: From DFT calculation to experimental study

To understand the second doped metal influence on catalytic activity for N2O decomposition, the mechanisms of N2O decomposition over Rh-M(M = Co, Ni and Cu) bimetallic catalysts were investigated by density functional theory (DFT). Co doped into Rh catalyst can increase the activity for N2O decomposition due to the decrease of the activation energy of rate-determining step while Ni and Cu present contrary performance. A series of corresponding RhM catalysts supported on SBA-15 was prepared and applied in N2O catalytic decomposition. The catalytic activity trend of Rh-M catalysts for N2O decomposition is determined as Rh7Co1/SBA-15 > Rh/SBA-15 > Rh7Ni1/SBA-15 > Rh7Cu1/SBA-15, which is in consistency with the corresponding DFT calculation results.

Cationic Co–Salphen Complexes Bisligated by DMAP as Catalysts for the Copolymerization of Cyclohexene Oxide with Phthalic Anhydride or Carbon Dioxide

For the copolymerization of cyclohexene oxide (CHO) with phthalic anhydride (PA), cationic complex [Co(III)(dmap)2–Salphen][BF4] (3) showed higher activity than a combination of Co–Salphen–Cl (2) with 1 equiv of DMAP. The catalytic activity was further improved by using a bimetallic complex 5 in which the Co(III)(dmap)2–Salphen moiety was bridged by a 1,2,5,6-substituted naphthalene linker. A similar trend of catalytic activity was detected for the copolymerization of CHO with CO2.

Effects of base strength on the copper-catalyzed cycloisomerization of propargylic acetates to form indolizines: A DFT study

Our calculations find that the base strength is the primary factor that controls the catalytic capability of cocatalysts CH3CN, Propargylic acetates (1a) and Et3N. In the proton-transfer process, the trend of catalytic activity increases in the order: Et3N > 1a > CH3CN, which matches well with the enhanced trend of base strength (Et3N > 1a > CH3CN). Et3N is the most appropriate for the present Cu-catalyzed cycloisomerization of propargylic acetates, which is in agreement with the experimental phenomena. Besides, our calculations give a reasonable explanation for the effects of terminal substituents (H- vs. Ph-) of alkyne on the catalytic reaction.

Catalytic Activity and Product Selectivity Trends for Carbon Dioxide Electroreduction on Transition Metal-Coated Tungsten Carbides

Electrochemical reduction of CO2 is a promising technology to produce hydrocarbon and alcohol fuels in a carbon neutral cycle. To utilize the technology on a commercial scale, inexpensive and earth-abundant catalysts are needed. Here, we employ density functional theory calculations to investigate activity and product selectivity trends for CO2 electroreduction reaction on transition metal monolayer coated tungsten carbides, M/WC (M = Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Ir, Pt, and Au). Such core–shell systems have the potential to reduce the loading of precious metals, such as Ag and Au, while the catalytic properties for CO2-to-CO reduction of metal surfaces remain. We find that at low potentials (<0.5 V) Cu/WC and Pd/WC core–shell particles catalyze CO2 reduction to CO as the main product due to low COOH formation and CO desorption free energies. Furthermore, we show that the binding energies of the carbo- and oxo-intermediates on the M/WC catalyst surface obey scaling relations with the binding en...