Rational Design Of Heterogeneous Catalysts Research Articles

Rationally Constructing A Nano MOF-Derived Ni and CQD Embedded N-Doped Carbon Nanosphere for the Hydrogenation of Petroleum Resin at Low Temperature.

A key issue in attaining highly efficient supported catalysts for the hydrogenation of unsaturated polymers arises from the entanglement between the number of exposed active sites and the severe internal mass transfer limitation caused by their large molecular size. Hence, an ultrasmall N-doped carbon nanosphere with Ni NPs and CQDs embedded (Ni-CQDs/NCNs) was reasonably constructed by low-temperature (400 °C) pyrolysis of the precursor CQDs@Nano-Ni-ZIFs. As-prepared Ni-CQDs/NCNs exhibited superior catalytic activity to a commercial 10% Pd/C catalyst in petroleum resin hydrogenation under a low temperature of 150 °C, which is 100 and 60 °C lower than that of previously reported Ni- and Pd-based catalysts, respectively. The excellent catalytic activity of Ni-CQDs/NCNs mainly contributes to the following factors: first, its ultrasmall structure (ca. 50 nm) eliminates the internal mass transfer limitation; second, the CQDs and N-doped carbon matrix stabilize the 53.1 wt % high-loading Ni NPs at a small size of 5.6 nm, providing abundant active sites; and third, the electronic regulation of N-doped carbon enhances the intrinsic activity of Ni, which was revealed by the experiments and DFT calculations. Besides, Ni-CQDs/NCNs exhibits long-term stability and appreciable magnetic separation performance, making it a considerable candidate for industrial application. This work not only offers a facile approach to prepare nano MOF-derived catalysts but also gives helpful instruction to the rational design of heterogeneous catalysts for the reaction involving large molecules.

CATKINAS: A large-scale catalytic microkinetic analysis software for mechanism auto-analysis and catalyst screening.

As an effective method to analyze complex catalytic reaction networks, microkinetic modeling is gaining increasing popularity in the catalytic activity evaluation and rational design of heterogeneous catalysts. An automated simulator with stable and reliable performance is especially useful and in great request. Here we introduce the CATKINAS package developed for large-scale microkinetic modeling and analysis. Featuring with a multilevel solver and a multifunctional analyzer, CATKINAS can provide both accurate solutions and various quantitative and automatic analysis for a wide range of catalytic systems. The structure and the basic workflow are overviewed with the multilevel solver particularly illustrated. Also, we take the CO methanation reaction as an example to illustrate the application and efficiency of the CATKINAS package.

ZrO2-x modified Cu nanocatalysts with synergistic catalysis towards carbon-oxygen bond hydrogenation

Carbon-oxygen bond hydrogenation serves as a versatile fundamental reaction extensively applied in chemicals synthesis, but rational design of heterogeneous catalysts with satisfactory catalytic performance and stability remains a big challenge. Herein, a ZrO2-x modified Cu nanocatalyst with unique interfacial structure Cu-O-Zr3+-Vö (Vö denotes oxygen vacancy), was elaborately designed and prepared via a facile in situ structural transformation from layered double hydroxide precursors, confirmed by a comprehensive study including HADDF-STEM, in situ EXAFS and quasi in situ XPS measurements. The optimized catalyst (Cu/ZrO2-x-S3) exhibits an extremely high catalytic performance toward dimethyl oxalate (DMO) hydrogenation to ethylene glycol (EG), with a yield of 99.5 %. Notably, the turnover frequency (TOF) value and space time yield of EG reach up to 42.4 h−1 and 1.05 gEG⋅gcat−1⋅h−1, respectively. This is, to the best of our knowledge, the highest level compared with previously reported Cu-based catalysts under similar conditions. In addition, the in situ investigations (in situ DMO-FTIR, in situ DMO-EXAFS) and catalytic evaluations substantiate interfacial sites serve as active center: the Zr3+-Vö facilitates adsorption and activation of CO/CO groups; whilst H2 molecule undergoes dissociation at the interfacial Cu species, followed by hydrogen spillover onto Cu-O-Zr for hydrogenation of activated CO/CO bonds. This interfacial synergistic catalysis offers a new reaction pathway with decreased activation energy, accounting for the resulting superior catalytic performance, which can be extended to other carbon-oxygen bonds hydrogenation systems.

Exploring Plasmonic Photocatalysis via Single-Molecule Reaction Imaging

Plasmonic photocatalysis has emerged as a new frontier in heterogeneous catalysis due to its promise in harvesting light to drive reactions. Yet many mechanistic aspects remain to be unambiguously defined. Using single-molecule fluorescence imaging, Li et al studied a fluorogenic and plasmon-enhanced reaction, amplex red oxidation, on single Au nanorods at sub-turnover resolution and under operando conditions. Both the rate-determining step and its activation energy were identified from the multiple elemental reactions. The results provide insights into the mechanism of plasmonic photocatalysis that may help the rationale design of heterogeneous catalysts.

Mechanochemical synthesis of cobalt/copper fluorophosphate generates a multifunctional electrocatalyst.

The utilisation of inductive effects is emerging as a powerful tool to enhance material properties. Within the context of electrocatalysis, such effects may alter an active site's electronic structure and consequently, its catalytic activity. To this end, we introduce catalytically active cobalt species within an electron-withdrawing copper fluorophosphate host via a mechanochemical synthetic method. The resulting mixed-metal material features exceptional performance towards electrochemical water oxidation (η of ∼300 mV for 100 mA cm-2) and biomass valorisation (95% selectivity for 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid conversion), thus opening avenues for the rational design of heterogeneous catalysts.

Statistical learning goes beyond the d-band model providing the thermochemistry of adsorbates on transition metals

The rational design of heterogeneous catalysts relies on the efficient survey of mechanisms by density functional theory (DFT). However, massive reaction networks cannot be sampled effectively as they grow exponentially with the size of reactants. Here we present a statistical principal component analysis and regression applied to the DFT thermochemical data of 71 C{}_{1}–C{}_{2} species on 12 close-packed metal surfaces. Adsorption is controlled by covalent (d-band center) and ionic terms (reduction potential), modulated by conjugation and conformational contributions. All formation energies can be reproduced from only three key intermediates (predictors) calculated with DFT. The results agree with accurate experimental measurements having error bars comparable to those of DFT. The procedure can be extended to single-atom and near-surface alloys reducing the number of explicit DFT calculation needed by a factor of 20, thus paving the way for a rapid and accurate survey of whole reaction networks on multimetallic surfaces.

The Interplay between Structure and Product Selectivity of CO2 Hydrogenation

AbstractIdentification of the active structure under reaction conditions is of great importance for the rational design of heterogeneous catalysts. However, this is often hampered by their structural complexity. The interplay between the surface structure of Co3O4 and the CO2 hydrogenation is described. Co3O4 with morphology‐dependent crystallographic surfaces presents different reducibility and formation energy of oxygen vacancies, thus resulting in distinct steady‐state composition and product selectivity. Co3O4‐0 h rhombic dodecahedra were completely reduced to Co0 and CoO, which presents circa 85 % CH4 selectivity. In contrast, Co3O4‐2 h nanorods were partially reduced to CoO, which exhibits a circa 95 % CO selectivity. The crucial role of the Co3O4 structure in determining the catalytic performance for higher alcohol synthesis over CuCo‐based catalysts is demonstrated. As expected, Cu/Co3O4‐2 h shows nine‐fold higher ethanol yield than Cu/Co3O4‐0 h owing to the inhibition for methanation.

The Interplay between Structure and Product Selectivity of CO2 Hydrogenation.

Identification of the active structure under reaction conditions is of great importance for the rational design of heterogeneous catalysts. However, this is often hampered by their structural complexity. The interplay between the surface structure of Co3 O4 and the CO2 hydrogenation is described. Co3 O4 with morphology-dependent crystallographic surfaces presents different reducibility and formation energy of oxygen vacancies, thus resulting in distinct steady-state composition and product selectivity. Co3 O4 -0 h rhombic dodecahedra were completely reduced to Co0 and CoO, which presents circa 85 % CH4 selectivity. In contrast, Co3 O4 -2 h nanorods were partially reduced to CoO, which exhibits a circa 95 % CO selectivity. The crucial role of the Co3 O4 structure in determining the catalytic performance for higher alcohol synthesis over CuCo-based catalysts is demonstrated. As expected, Cu/Co3 O4 -2 h shows nine-fold higher ethanol yield than Cu/Co3 O4 -0 h owing to the inhibition for methanation.

Self-reconstruction mechanism in NiSe2 nanoparticles/carbon fiber paper bifunctional electrocatalysts for water splitting

Developing efficient bifunctional electrocatalysts and gaining fundamental understanding of reaction mechanisms are crucial for practical water splitting. Herein, a bifunctional NiSe2 nanoparticles/carbon fiber paper (NSN/CFP) electrode is fabricated by the pyrolysis of Ni(NO3)2 on CFP, followed by a selenization step. The as-prepared electrocatalysts exhibit superior overall water splitting behavior in 1 M KOH with low overpotentials of 145 mV and 280 mV at current densities of 10 mA cm−2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) respectively, comparable to the performance of 20% Pt/C and RuO2. Detailed compositional and morphological studies reveal that the NiSe2 gradually transforms into an amorphous Ni(OH)2/NiOOH heterojunction during both HER and OER in alkaline medium. Based on these experimental results, an oxidation-induced self-reconstruction mechanism is proposed. Owing to the highly-oxidized Ni(OH)2/NiOOH active species, the self-reconstructed structure enhances the water splitting under fixed potentials for a prolonged time of 96 h with negligible current degradation. This work not only provides a facile route to fabricate efficient and stable electrocatalysts for large-scale water splitting but also reveals an underlying structural evolution mechanism, which guides the rational design of heterogeneous catalysts.

A Simple and Effective Principle for a Rational Design of Heterogeneous Catalysts for Dehydrogenation of Formic Acid.

Efficient and selective dehydrogenation of formic acid is a key challenge for a fuel-cell-based hydrogen economy. Though the development of heterogeneous catalysts has received much progress, their catalytic activity remains insufficient. Moreover, the design principle of such catalysts are still unclear. Here, experimental and theoretical studies on a series of mono-/bi-metallic nanoparticles supported on a NH2 -N-rGO substrate are combined for formic acid dehydrogenation where the surface energy of a metal is taken as a relevant indicator for the adsorption ability of the catalyst for guiding catalyst design. The AuPd/NH2 -N-rGO catalyst shows record catalytic activity by reducing the energy barrier of rate controlling steps of formate adsorption and hydrogen desorption. The obtained excellent results both in experiments and simulations could be extended to other important systems, providing a general guideline to design more efficient catalysts.

Single-Atom Alloys as a Reductionist Approach to the Rational Design of Heterogeneous Catalysts.

Heterogeneous catalysts are workhorses in the industrial production of most commodity and specialty chemicals, and have widespread energy and environmental applications, with the annual market value of the catalysts themselves reaching almost $20 billion in 2018. These catalysts are complex, comprising multicomponent materials and multiple structures, making their rational design challenging, if not impossible. Furthermore, typical active metals like Pt, Pd, and Rh are expensive and can be susceptible to poisoning by CO, coking, and they are not always 100% selective. Efforts to use these elements sparingly and improve their selectivity has led to recent identification of single-atom heterogeneous catalysts in which individual transition metal atoms anchored on oxide or carbon-based supports are excellent catalysts for reactions like the CO oxidation, water-gas shift, alcohol dehydrogenation, and steam reforming. In this Account, we describe a new class of single-atom heterogeneous catalysts, namely, Single-Atom Alloys (SAAs) that comprise catalytically active elements like Pt, Pd, and Ni alloyed in more inert host metals at the single-atom limit. These materials evolved by complementary surface science and scanning probe studies using single crystals, and catalytic evaluation of the corresponding alloy nanoparticles with compositions informed by the surface science findings. The well-defined nature of the active sites in SAAs makes accurate modeling with theory relatively easy, enabling the rational design of SAA catalysts via a complementary three-prong approach, encompassing surface science model catalysts, theory, and real catalyst synthesis and testing under industrially relevant conditions. SAAs constitute one of just a few examples of when heterogeneous catalyst design has been guided by an understanding of fundamental surface processes. The Account starts by describing scanning tunneling microscopy studies of highly dilute alloys formed by doping small amounts of a catalytically active element into a more inert host metal. We first discuss hydrogenation reactions in which dissociation of H2 is often rate limiting. Results indicate how the SAA geometry allows the transition state and the binding site of the reaction intermediates to be decoupled, which enables both facile dissociation of reactants and weak binding of intermediates, two key factors for efficient and selective catalysis. These results were exploited to design the first PtCu SAA hydrogenation catalysts which showed high selectivity, stability and resistance to poisoning in industrially relevant hydrogenation reactions, such as the selective conversion of butadiene to butenes. Model studies also revealed spillover of hydrogen atoms from the Pt site where dissociation of H2 occurs to Cu sites where selective hydrogenation is facilitated in a bifunctional manner. We then discuss selective dehydrogenations on SAAs demonstrating that they enable efficient C-H activation, while being resistant to coking that plagues typical Pt catalysts. SAA PtCu nanoparticle catalysts showed excellent stability in butane dehydrogenation for days-on-stream at 400 °C. Another advantage of SAA catalysts is that on many alloy combinations CO, a common catalyst poison, binds more weakly to the alloy than the pure metal. We conclude by discussing recent theory results that predict the energetics of many key reaction steps on a wide range of SAAs and the exciting possibilities this reductionist approach to heterogeneous catalysis offers for the rational design of new catalysts.

An electronic structure descriptor for oxygen reactivity at metal and metal-oxide surfaces

Identifying and understanding relationships between the electronic and atomic structure of surfaces and their catalytic activity is an essential step towards the rational design of heterogeneous catalysts for both thermal and electrochemical applications. Herein, we identify a relationship between the atom-projected density of states of surface oxygen and its ability to make and break bonds with the surrounding metal atoms and hydrogen. This structure-property relationship is shown to hold across different classes of materials (metals, rutile metal-oxides, and perovskite metal-oxides) and for different oxygen binding sites (i.e. different oxygen coordination numbers). We utilize understanding from the d-band model and the simple two-level quantum coupling problem to shed light on the physical origin of this relationship for transition metal surfaces and we hypothesize similar principles extend to the other materials considered. Finally, we demonstrate the utility of the identified descriptor to serve as a tool for high throughput screening of oxygen active sites for large systems where many unique oxygen sites exist and can be computationally expensive to probe individually. As an example, we predict the reactivity of 36 unique oxygen atoms at a kinked RuO2 extended surface from a single self-consistent DFT calculation.

The Molecular Surface Property Approach: A Guide to Chemical Interactions in Chemistry, Medicine, and Material Science

AbstractThe current status of the molecular surface property approach (MSPA) and its application for analysis and prediction of intermolecular interactions, including chemical reactivity, are reviewed. The MSPA allows for identification and characterization of all potential interaction sites of a molecule or nanoparticle by the computation of one or more molecular properties on an electronic isodensity surface. A wide range of interactions can be analyzed by three properties, which are well‐defined within Kohn–Sham density functional theory. These are the electrostatic potential, the average local ionization energy, and the local electron attachment energy. The latter two do not only reflect the electrostatic contribution to a chemical interaction, but also the contributions from polarization and charge transfer. It is demonstrated that the MSPA has a high predictive capacity for non‐covalent interactions, for example, hydrogen and halogen bonding, as well as organic substitution and addition reactions. The latter results open up applications within drug design and medicinal chemistry. The application of MSPA has recently been extended to nanoparticles and extended surfaces of metals and metal oxides. In particular, nanostructural effects on the catalytic properties of noble metals are rationalized. The potential for using MSPA in rational design of heterogeneous catalysts is discussed.

Recent Advancements in Graphene-Based Supports of Metal Complexes/Oxides for Epoxidation of Alkenes.

In the past decade, there has been great progress in the preparation and catalytic applications of graphene-supported metal complexes/oxide catalysts. Graphene-based materials have attracted tremendous research interest owing to special physicochemical properties, for example, unique two-dimensional structure, high theoretical specific surface area, high electrical conductivity, and outstanding acid-base resistance properties. Graphene-supported metal complexes/oxides have been extensively investigated, and exhibit good catalytic activity and stability in water splitting (H2 generation or oxygen evolution), oxidation/epoxidation of alkenes, C-C bond formation, and so forth. Herein, recent developments in graphene-supported metal complexes/oxides for the catalytic epoxidation of different alkenes are summarized. Site isolation and synergistic interactions between metal complexes/oxides and graphene are the two key roles for enhancing the catalytic activity, whereas the hydrophobicity of the support can efficiently improve epoxide selectivity. In addition, the possible mechanisms of catalytic epoxidation are summarized. This review provides a feasible scheme for the potential application of graphene-based materials and guidance for the rational design of heterogeneous catalysts for catalytic applications.

Intermetallic structures with atomic precision for selective hydrogenation of nitroarenes

Bridging the structure-properties relationship of bimetallic catalysts is essential for the rational design of heterogeneous catalysts. Different from random alloys, intermetallic compounds (IMCs) present atomically-ordered structures, which is advantageous for catalytic mechanism studies. We used Pt-based intermetallic nanoparticles (iNPs), individually encapsulated in mesoporous silica shells, as catalysts for the hydrogenation of nitroarenes to functionalized anilines. With the capping-free nature and ordered atomic structure, PtSn iNPs show >99% selectivity to hydrogenate the nitro group of 3-nitrostyrene albeit with a lower activity, in contrast to Pt3Sn iNPs and Pt NPs. The geometric structure of PtSn iNPs in eliminating Pt threefold sites hampers the adsorption/dissociation of molecular H2 and leads to a non-Horiuti-Polanyi hydrogenation pathway, while Pt3Sn and Pt surfaces are saturated by atomic H. Calculations using density functional theory (DFT) suggest a preferential adsorption of the nitro group on the intermetallic PtSn surface contributing to its high selectivity.

Direct instrumental identification of catalytically active surface sites.

The activity of heterogeneous catalysts-which are involved in some 80 per cent of processes in the chemical and energy industries-is determined by the electronic structure of specific surface sites that offer optimal binding of reaction intermediates. Directly identifying and monitoring these sites during a reaction should therefore provide insight that might aid the targeted development of heterogeneous catalysts and electrocatalysts (those that participate in electrochemical reactions) for practical applications. The invention of the scanning tunnelling microscope (STM) and the electrochemical STM promised to deliver such imaging capabilities, and both have indeed contributed greatly to our atomistic understanding of heterogeneous catalysis. But although the STM has been used to probe and initiate surface reactions, and has even enabled local measurements of reactivity in some systems, it is not generally thought to be suited to the direct identification of catalytically active surface sites under reaction conditions. Here we demonstrate, however, that common STMs can readily map the catalytic activity of surfaces with high spatial resolution: we show that by monitoring relative changes in the tunnelling current noise, active sites can be distinguished in an almost quantitative fashion according to their ability to catalyse the hydrogen-evolution reaction or the oxygen-reduction reaction. These data allow us to evaluate directly the importance and relative contribution to overall catalyst activity of different defects and sites at the boundaries between two materials. With its ability to deliver such information and its ready applicability to different systems, we anticipate that our method will aid the rational design of heterogeneous catalysts.

A rational catalyst design of CO oxidation using the bonding contribution equation

A rational design of heterogeneous catalysts is an important yet challenging task. We show how the bonding contribution equation, a quantitative relation between the surface structure and adsorption energy, can be utilized for a rational catalyst design. Dozens of catalysts were efficiently designed, and full DFT calculations demonstrate that they possess excellent activities.

Catalyst design for biorefining.

The quest for sustainable resources to meet the demands of a rapidly rising global population while mitigating the risks of rising CO2 emissions and associated climate change, represents a grand challenge for humanity. Biomass offers the most readily implemented and low-cost solution for sustainable transportation fuels, and the only non-petroleum route to organic molecules for the manufacture of bulk, fine and speciality chemicals and polymers. To be considered truly sustainable, biomass must be derived from resources which do not compete with agricultural land use for food production, or compromise the environment (e.g. via deforestation). Potential feedstocks include waste lignocellulosic or oil-based materials derived from plant or aquatic sources, with the so-called biorefinery concept offering the co-production of biofuels, platform chemicals and energy; analogous to today's petroleum refineries which deliver both high-volume/low-value (e.g. fuels and commodity chemicals) and low-volume/high-value (e.g. fine/speciality chemicals) products, thereby maximizing biomass valorization. This article addresses the challenges to catalytic biomass processing and highlights recent successes in the rational design of heterogeneous catalysts facilitated by advances in nanotechnology and the synthesis of templated porous materials, as well as the use of tailored catalyst surfaces to generate bifunctional solid acid/base materials or tune hydrophobicity.

ChemInform Abstract: Model Approach in Heterogeneous Catalysis: Kinetics and Thermodynamics of Surface Reactions

AbstractReview: 37 refs.

Model Approach in Heterogeneous Catalysis: Kinetics and Thermodynamics of Surface Reactions.

Heterogeneous catalysts are widely employed in technological applications, such as chemical manufacturing, energy harvesting, conversion and storage, and environmental technology. Often they consist of disperse metal nanoparticles anchored onto a morphologically complex oxide support. The compositional and structural complexity of such nanosized systems offers many degrees of freedom for tuning their catalytic performance. However, a rational design of heterogeneous catalysts based on an atomistic-level understanding of underlying surface processes has not been fully achieved so far and remains one of the primary goals for catalysis research. In our group, we developed concepts for replacing highly complex real supported catalysts by simplified model systems, which complexity can be gradually increased in order to mimic certain structural aspects of practically relevant catalysts in a controlled way. Well-defined model systems consisting of metal-nanoparticle ensembles supported on planar oxide substrates have proven to provide a successful approach to achieve fundamental insights into heterogeneous catalysis. In this Account, two mechanistic case studies focusing on an atomistic-level understanding of surface chemistry are presented in which we investigate how the nanoscopic nature of metal clusters affects their interaction with the adsorbates and the reactive processes. Particularly, we investigate the effects of the particle size and the flexibility of the atoms constituting metal clusters on the binding energy of gas-phase adsorbates, such as CO and oxygen. We identified two major structural factors determining the binding energy of gas phase adsorbates on metal nanoparticles: the local configuration of the adsorption site and the particle size. While the effect of the local configuration of the adsorption site was found to be adsorbate specific, the reduction of the cluster size results in a pronounced decrease of binding energy for both adsorbates and appears to be a general trend. In the second case study, we address the role of the surface modifiers, such as carbon, on the process of hydrogen diffusion into volume of Pd nanoparticles that was previously identified is an important step in hydrogenation chemistry. We provide for the first time direct experimental evidence that, inline with the recent theoretical predictions, the atomically flexible low-coordinated surface sites on Pd particles play a crucial role in the diffusion process and that their selective modification with carbon results in marked facilitation of subsurface hydrogen diffusion. By virtue of these examples, we demonstrate how model studies on complex nanostructured materials may provide an atomistic view of processes at the gas-solid interface related to heterogeneous catalysis.