Catalyst Design Concept Research Articles

A New Dual Site Catalyst Design Concept for Promoting Reaction Kinetics of the Oxygen Reduction Reaction

Introduction Oxygen reduction reaction (ORR) accounts for a substantial portion of the energy loss of the proton exchange membrane fuel cell system used for vehicle application. Current state of art ORR catalysts are typically Pt-alloy nanoparticles supported on carbon, of which surface Pt is solely the active site and their activity improvement is fundamentally limited by a “scaling relationship” [1]. In this study, we report the preparation of a SnOx/Pt−Cu−Ni heterojunctioned nanostructure as one potential strategy to break the scaling relationship in ORR. Experimental results confirm a significant activity enhancement compared with pristine Pt−Cu−Ni. Theoretical study suggests a dual-site cascade mechanism wherein the first two steps occur on SnOx sites, followed by transfer of the intermediate to adjacent Pt sites for the subsequent steps. This new catalyst design offers a plausible new approach to achieve high ORR activity on Pt alloys by introducing a second active site. Materials and Methods Pt−Cu−Ni alloy nanoparticles were synthesized by a solid-state chemistry method involving electrochemical treatment to generate a clean Pt surface prior to use in this study [2]. The as prepared Pt-Cu-Ni catalysts were first de-alloyed and then followed by immersion in SnCl2 solution for various time to coat with SnOx [3]. The resulting heterojunctioned catalysts were characterized by HR-TEM, XPS, XANES, as well as in electrochemical measurement to determine the activity and durability. The density functional theory (DFT) simulations were performed with the Quantum ESPRESSO package to calculate the energy states of reaction intermediates on different surface sites. Results and Discussion The conceptual design of the dual site catalyst, as shown in Figure 1(a). involves a possible migration of reaction intermediates during the steps of ORR. Such a migration should be driven by the difference in free energy of the sites. For proof-of-concept, we synthesized Pt−Cu−Ni nanoparticles and then deposited SnOx on the surface to form a heterojunctioned nanostructure (Figure 1(b)). SEM -EDX and XPS analyses confirmed that the SnOx content increased with deposition time, while the Pt:Cu:Ni ratio remained nearly unchanged before and after the deposition. XANES and high resolution XPS characterization suggest the oxidation state of the SnOx is primarily 4+. A decrease of electrochemical active surface area (ECSA) was observed as the deposition time (td) increases (Figure 1 (c)). The mass activity and specific activity (SA) both exhibit a volcano trend with respect to td with the highest values at td=5 min. The apparent SA increased by 40% as compared to the pristine Pt-Cu-Ni, and if only considering the interfacial sites, the estimated specific activity enhancement may be up to 10 folds (Figure 1(d)). While these results provide unambiguous experimental evidence of SnOx’s promoting effect, DFT simulation of the reaction pathways was performed to obtain insight into the possible mechanism (Figure 1(e)). The results suggest the SnOx and the neighboring Pt sites may have cooperated to find the most kinetically favored pathway (Figure 1(f)), wherein the O2 first protonated on SnOx sites to form *OOH and *O intermediates, and then the *O transfers to Pt sites to complete the remaining steps. Conclusion This study demonstrates a strategy to bypass the energy barrier bottleneck of ORR, providing one more dimension of design flexibility towards developing highly active electrode catalysts for fuel cell applications. References Kulkarni, A. et al., Chem. Rev. 2018, 118 (5), 2302−2312.Zhang, C. et al., J. Am. Chem. Soc. 2014, 136 (22), 7805−7808.Shen, X. et al., J. Am. Chem. Soc. 2019, 141(24), 9463-9467. Figure 1

Front Cover: Asymmetric Synthesis of Multi‐substituted Prolines via a Catalytic 1,3‐Dipolar Cycloaddition Using a Monocationic ZnIIOAc Complex of a Chiral Bisamidine Ligand, Naph‐diPIM‐dioxo‐R (ChemCatChem 22/2020)

The Front Cover shows a highly efficient catalytic enantioselective 1,3-dipolar cycloaddition of tridentate-type α-imino esters and acrylates. In their Communication, I. N. Chaithanya Kiran et al. explain the catalyst's design concept and its performance for the reaction. The catalyst is a monocationic zinc acetate complex of a chiral bisamidine-type bidentate ligand. An anionic acetate ligand of the Lewis acidic Zn complex acts as a Brønsted base to facilitate a smooth intramolecular deprotonation to generate an imino N,O-cis-Zn enolate. The oxygen atoms of two dioxolanes of the ligand form a C2 chiral scaffold, in which the Zn enolate position is well controlled by a non-bonding n-π* interaction. The catalyst shows high activity, diastero-/enantio-/regio-selectivity, productivity, and broad generality. This reaction provides a path for the synthesis of pyrrolidine-containing chiral bioactive compounds, ligands and organocatalysts. More information can be found in the Communication by I. N. Chaithanya Kiran et al.

Vacancy-enabled N2 activation for ammonia synthesis on an Ni-loaded catalyst

Ammonia (NH3) is pivotal to the fertilizer industry and one of the most commonly produced chemicals1. The direct use of atmospheric nitrogen (N2) had been challenging, owing to its large bond energy (945 kilojoules per mole)2,3, until the development of the Haber-Bosch process. Subsequently, many strategies have been explored to reduce the activation barrier of the N≡N bond and make the process more efficient. These include using alkali and alkaline earth metal oxides as promoters to boost the performance of traditional iron- and ruthenium-based catalysts4-6 via electron transfer from the promoters to the antibonding bonds of N2 through transition metals7,8. An electride support further lowers the activation barrier because its low work function and high electron density enhance electron transfer to transition metals9,10. This strategy has facilitated ammonia synthesis from N2 dissociation11 and enabled catalytic operation under mild conditions; however, it requires the use of ruthenium, which is expensive. Alternatively, it has been shown that nitrides containing surface nitrogen vacancies can activate N2 (refs. 12-15). Here we report that nickel-loaded lanthanum nitride (LaN) enables stable and highly efficient ammonia synthesis, owing to a dual-site mechanism that avoids commonly encountered scaling relations. Kinetic and isotope-labelling experiments, as well as density functional theory calculations, confirm that nitrogen vacancies are generated on LaN with low formation energy, and efficiently bind and activate N2. In addition, the nickel metal loaded onto the nitride dissociates H2. The use of distinct sites for activating the two reactants, and the synergy between them, results in the nickel-loaded LaN catalyst exhibiting an activity that far exceeds that of more conventional cobalt- and nickel-based catalysts, and that is comparable to that of ruthenium-based catalysts. Our results illustrate the potential of using vacancy sites in reaction cycles, and introduce a design concept for catalysts for ammonia synthesis, using naturallyabundant elements.

Catalyst design concept based on a variety of alloy materials: a personal account and relevant studies

An overview of a variety of advanced alloy materials for catalytic use is provided.

Pursuit of C–H Borylation Reactions with Non-Precious Heterobimetallic Catalysts: Hypothesis-Driven Variations on a Design Theme

This article presents a retrospective account of our group’s heterobinuclear (NHC)Cu-[MCO] catalyst design concept (NHC = N-heterocyclic carbene, [MCO] = metal carbonyl anion), the discovery of its application towards UV-light-induced dehydrogenative borylation of unactivated arenes, and the subsequent pursuit of thermal reaction conditions through structural modifications of the catalysts. The account highlights advantages of using a hypothesis-driven catalyst design approach that, while often fruitless with regard to the target transformation in this case, nonetheless vastly expanded the set of heterobinuclear catalysts available for other applications. In other words, curiosity-driven research conducted in a rational manner often provides valuable products with unanticipated applications, even if the primary objective is viewed to have failed.1 Introduction to Heterobinuclear Catalysts for C–H Borylation2 Pursuit of Thermal Borylation Conditions3 Catalysts beyond Copper Carbenes4 Conclusions

Solar-driven efficient methane catalytic oxidation over epitaxial ZnO/La0.8Sr0.2CoO3 heterojunctions

Gas flaring in oil/gas drilling and gas leakage in natural gas power plant lead to significant energy loss and environmental burden. Here, solar-driven efficient methane oxidation was demonstrated under high velocity continuous flow over the ZnO/La0.8Sr0.2CoO3 (ZnO/LSCO) heterojunctions. The ZnO/LSCO heterojunctions enable a unique epitaxial hetero-interface, which effectively regulates the electron transfer between Zn 3d-O 2p hybrid orbital in ZnO and Co eg orbital in LSCO and promotes the rapid generation and refill of oxygen vacancy with unpaired electron (Vo), thus enhancing the activity and mobility of surface lattice oxygen in ZnO/LSCO. Under solar illumination, the synergy of photothermal and photocatalytic effect boosts the reversible electron transfer in the interface, which further activates surface lattice oxygen, resulting in a ∼2 times higher methane oxidation activity. Such a solar-driven system not only enables a promising pathway for emitted methane utilization, but also provides an advanced catalyst design concept of epitaxial interface construction.

Selective conversion of syngas to propane over ZnCrO -SSZ-39 OX-ZEO catalysts

Abstract Oxide-Zeolite (OX-ZEO) bifunctional catalyst design concept has been exemplified in several processes to direct conversion syngas to value-added chemicals and fuels such as mixed light olefins, ethylene, aromatics and gasoline. Herein we demonstrate that the product can be steered toward liquefied petroleum gas (LPG) with a selectivity up to 89% in hydrocarbons especially propane selectivity reaching 80% at CO conversion of 63% using ZnCrOx-H-SSZ-39 catalyst. Interestingly, the quantity of the acid sites of SSZ-39 does not influence obviously the hydrocarbon distribution but the strength is crucial for selective formation of propane. This finding provides an alternative route of LPG synthesis from a variety of carbon resources via syngas.

Size Effects of ZnO Nanoparticles in Bifunctional Catalysts for Selective Syngas Conversion

The oxide–zeolite (OX–ZEO) bifunctional catalyst design concept has shown promising potential for selectivity control in syngas conversion by separating CO activation and C–C coupling onto oxides a...

Development of Highly Chemoselective Oxidative Transformations by Designing Organoradicals.

To conduct organic synthesis in the field of pharmaceutical science, methodologies that can easily and quickly supply compounds with high drug-likeness are highly desirable. Based on the original catalyst design concept "Radical-Conjugated Redox Catalysis (RCRC)" established during my research, various C(sp3)-H functionalizations and protein modifications have been developed, taking advantage of the high reactivity and chemoselectivity of the single-electron transfer process. This review focuses on the eight-year research efforts by my collaborators and me, from conception to results.

The Catalytic Reduction of Carboxylic Acid Derivatives and CO2 by Metal Nanoparticles on Lewis-Acidic Supports.

The development of heterogeneous catalysts for green chemical synthesis is currently a growing area in catalysis and sustainable chemistry. Especially the use of renewable carbon resources such as carbon dioxide (CO2 ) and biomass-derived compounds (e. g. carboxylic acids, esters, and amides) represent highly attractive research targets. As these substances reside in a high oxidation state, efficient reduction processes are required in order to convert these substrates into useful and value-added chemicals. Moreover, in the interest of mass production, these substrates should be reduced by molecular H2 and a heterogeneous catalyst. In this context, our group has developed advanced catalysts and established design guidelines for catalysts that promote the reductive transformations of carboxylic acid derivatives and CO2 . Our studies show that cooperative catalysis between Lewis-acidic sites on the catalyst support and supported metal nanoparticles are crucial for the success of these challenging hydrogenations. In this review, we summarize the results of our recent studies on the direct synthesis of value-added chemicals from CO2 and carboxylic acid derivatives using supported transition-metal catalysts, and we propose a design concept for heterogeneous catalysts that promote these processes.

Development of Proton-Responsive Catalysts.

A changeable ligand, which involves in activation of a catalyst or assists a reaction, draws an increasing attention, in contrast to a classical ligand as spectator. Proton-responsive catalysts, which are capable of undergoing changes of properties on gaining/losing one or more protons, provides interesting features as follows: (i) catalyst activation by electronic effect, (ii) pH-tuning of water-solubility, and (iii) second-coordination-sphere interaction. On the basis of this catalyst design concept, we developed several highly efficient proton-responsive catalysts for CO2 hydrogenation as H2 storage, formic acid (FA) dehydrogenation as H2 production, and transfer hydrogenation. The transformable ligands of proton-responsive catalysts in promoting effective catalysis have aroused our interest. In this account, we summarize our efforts for the development and application of proton-responsive catalysts. Specifically, the important role of pH-dependent proton-responsive complexes will be discussed.

Preferential Horizontal Growth of WS2 Nanoplate on Porous Carbon: A Highly Efficient Electrocatalyst for the Hydrogen Evolution Reaction

Two-dimensional layered transition metal dichalcogenides (2D TMDs) have been of tremendous recent interests. Understanding their growth behavior on specific substrate or support can provide critical insights for designing the TMDs with desirable structure and functionality for targeted applications. Particularly for the electrocatalytic hydrogen evolution reaction (HER), where porous carbons are predominantly used as conductive supports, revealing the growth behavior of TMDs on porous carbon materials can suggest rational design concept for the TMD-based HER catalysts. With an aim to investigate the growth orientation on porous carbon support, we synthesized MS2 (M = W or Mo) nanoplates embedded on porous carbon nanorod arrays by limiting their growth space at the nanoscale. We found that the horizontal growth is preferred in WS2 giving rise to monolayer nanoplates, which is contrast to the growth of MoS2 that favors vertical stacking to generate multilayer structure. Density functional theory calculations of adhesion energy of TMDs on porous carbons and their stacking energies revealed that WS2 favor the basal plane bonding with carbon support and horizontal growth, wheareas the edge bonding and vertical growth is favored for MoS2, supporting experimental results. The orientation-controlled WS2 monolayer NPs embedded in mesoporous carbon exhibited highly efficient electrocatalytic activity for the HER with a low overpotential of 179 mV (vs RHE) at ‒10 mA cm-2 and low Tafel slope of 63 mV sec-1.

Enhancing Sulfur Tolerance of Pd Catalysts by Hydrogen Spillover with Two Different Zeolite Supports for Low-Temperature Hydrogenation of Aromatics

Pd catalysts supported on zeolite Y and zeolite A (Pd/Y and Pd/A) were prepared separately and combined for improving sulfur tolerance based on our proposed catalyst design concept for low-temperat...

Sandwich-like graphene nanocomposites armed with nanoneedles

A novel strategy for preventing aggregation, increasing surface area, and maintaining catalytic activity of water-soluble graphene nanosheet (GNS) catalysts is introduced, and use of the synthesized nanocatalyst [GNS (matrix)/metal (catalyst)/metal oxide (spacer)/ceramic (protector)] as recyclable nanocatalysts without loss of performance is demonstrated. Our graphene nanocomposite (GNC) armed with nanoneedles is fabricated by the synthesis of Au on GNS, followed by stepwise synthesis of needle-like IO and SiO2, in order. The distinctive structures of the needle-like layers prevent aggregation and contamination of the GNS catalysts, and allow recycling, both of which enhanced catalytic ability. The research demonstrates the possibility of a safe coating for water-soluble GNS catalysts, which are reactive to ionic species, and their application as nanocatalysts for the chemo-selective transformation of toxic substances. Our sandwich-like GNCs for recyclable nanocatalysts provide a new design concept for reusable GNS catalysts.

Size- and support-dependent selective amine cross-coupling with platinum nanocluster catalysts

γ-Alumina-supported Pt nanoclusters with an average particle size of 0.8 nm, Pt/Al2O3-0.8, act as an effective heterogeneous catalyst for mono-N-alkylation of amines with different amines. To establish a catalyst design concept, systematic studies on the structure–activity relationship are carried out, combined with characterization by Pt L3-edge XAFS (X-ray absorption fine structure), X-ray photoelectron spectroscopy (XPS), and infrared (IR) study of CO adsorption. By changing the particle size of Pt over the size range of 0.8–24 nm, it is demonstrated that the present reaction is a structure-sensitive reaction, demanding coordinatively unsaturated Pt atoms on metallic nanoclusters. The support also affects the activity and electronic state of Pt. The electron density of Pt increases with basicity of the support oxide, and the support with moderate basicity (Al2O3) gives the highest activity probably due to a moderate electron density of Pt. Kinetic studies suggest that the present reaction proceeds through a “hydrogen-borrowing” mechanism.

Silver Cluster Catalysts for Green Organic Synthesis

Development of platinum-group-metal (PGM)-free catalysts for green chemical synthesis is an important topic in synthetic catalysis, because PGM will soon be in short supply in the near future. Our group has paid attention to the catalytic functions of Ag clusters. Here, we summarize our recent work on size- and support-specific catalysis of Ag clusters for green organic synthesis. Ag clusters supported on Al2O3 act as effective heterogeneous catalysts for (1) oxidant-free dehydrogenation of alcohols to carbonyl compounds, (2) coupling of alcohols with amines to form amides and H2, (3) N-alkylation of anilines with alcohols, (4) C–C cross-coupling reaction of alcohols, (5) selective hydrogenation of nitroaromatics, and (6) direct synthesis of N-substituted anilines from nitroaromatics and alcohols. To establish a catalyst design concept, effects of Ag particle size and acid-base character of support oxides are investigated. The structure-activity relationships for all reactions show similar tendencies; metallic Ag clusters with smaller size and acid-base bifunctional nature of the support oxide are preferable. We propose that cooperation between coordinatively unsaturated Ag sites of Ag clusters and acid-base pair sites at the metal-support interface is a key concept for the design of Ag cluster catalysts for the above reactions.

Cover Picture: Expanding the Scope of Metal-Free Catalytic Hydrogenation through Frustrated Lewis Pair Design (Angew. Chem. Int. Ed. 37/2010)

The evolution of deep and shallow flowers is a response to a “race” with pollinating organisms that determines the length and form of the bill of hummingbirds. Likewise, the selection of the Lewis basic component for a frustrated Lewis pair is dictated by the steric congestion around the boron center of the Lewis acid. In their Communication on page 6559 ff., T. Soós and co-workers show that this “selection phenomenon” can be exploited as a design concept for metal-free hydrogenation catalysts.

Selective Bifunctional Catalytic Conversion of Cellulose over Reshaped Ni Particles at the Tip of Carbon Nanofibers

Access to cellulose: Carbon nanofibers grown over Ni supported on γ-Al2O3 act as efficient catalysts for the one-pot conversion of cellulose to sugar alcohols, owing to the enhanced accessibility of the water-insoluble substrate towards the active catalytic sites. The new catalyst design concept yields unprecedented results for selective cellulose conversion using inexpensive Ni catalysts.

熱可塑性エラストマーの今そして未来 オレフィン重合新触媒の開発とポリオレフィン新材料への展開

This contribution reports on the development and applications of a new family of next generation olefin polymerization catalysts for the creation of value-added olefin-based materials. Our own research based on a ligand oriented catalyst design concept has resulted in the discovery of new high-performance olefin polymerization catalysts named FI catalysts. FI catalysts in association with appropriate cocatalysts can exhibit a number of unique features, including exceptionally high ethylene insertion ability, high functional group tolerance, MAO- and borate-free polymerization catalysis and precise control over chain transfers. Due to these features, FI catalysts have created a wide variety of value-added olefin-based materials which include ethylene/polar monomer copolymers, ultrafine and noncoherent polyethylene (PE) particles, polyolefinic block copolymers and selective vinyl-terminated PEs. The vinyl-terminated PEs can readily be converted to well-defined terminally-functionalized PEs and PE/polyethylene glycol hybrid materials.

ChemInform Abstract: High‐Performance Olefin Polymerization Catalysts Discovered on the Basis of a New Catalyst Design Concept

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.