Heterogeneous Nanocatalysis Research Articles

Activating colloidal synthesized Au catalyst by the electrochemical strategy: Gas atmosphere, electrolyte and electrochemical technique

Organic ligands are necessarily used to stabilize nanoparticles (NPs) in colloid synthesis, and the presence of these ligands in most cases can have adverse effects on heterogeneous nanocatalysis. Therefore, it is crucial to develop efficient methods to remove ligands and study the removal mechanism. In this article, we developed a combined electrochemical method (chronoamperometry (CA) + cyclic voltammetry (CV)), which can completely and efficiently remove thiol ligand from Au NPs to produce cleaned Au/C catalyst. Using the oxygen reduction reaction (ORR) activity as the evaluation criterion for ligand removal, we found that gas atmosphere (O2) plays an important role in the removal process, while the acidity and alkalinity of electrolyte have no effect on the removal efficiency. A proposed thiol ligand removal mechanism along with Au degradation is presented. The results of CA activation at an oxidation constant potential (1.7 V) indicate that oxidation of thiol alone cannot remove thiol ligand. Only if a reduction constant potential of 0.2 V is further applied, the ORR activity of Au/C catalyst will increase, indicating that both the oxidation and reduction processes of Au NPs are crucial for ligand removal. Although the CA method (with an upper potential of 1.7 V and a lower potential of 0.2 V) can efficiently remove the majority of thiol ligand, complete removal of thiol ligand requires further CV activation. Based on the relevant results, a combined electrochemical method (CA + CV) is established. Developing standardized methods for removing ligands on the surface of catalysts is important for obtaining efficient catalysts and is also important for the reproducibility of catalytic results.

Kinetics of enantioselective heterogeneous nanocatalysis with limited cluster occupancy: Beyond the coverage concept

Theoretical analysis is presented for kinetics of enantioselective reactions on nanocatalysts, when the cross-section of the reacting molecules and the non-reacting modifiers is similar to the size of nanoclusters and only two or three molecules can be adsorbed on a cluster. The rate expressions have been derived, considering the exact configurations of the reactants and a non-reactive modifier, rather than utilizing the classical Langmuirian methodology of the surface coverage. The developed approach was used to explain rate acceleration, enantioselectivity and enantiomeric excess as a function of the modifier concentration, as well as the nonlinear behavior showing even maxima of enantiomeric excess for mixtures of modifiers.

Polystyrene Resins: Versatile and Economical Support for Heterogeneous Nanocatalysts in Sustainable Organic Reactions**

AbstractRecent developments in heterogeneous nanocatalysis have illustrated the great strides metal nanoparticles (NPs) have made due to their several significant features. However, the major lingering challenge has been their deactivation in organic reactions by migration‐coalescence largely due to their high surface energy. In this context, various supports materials have been designed to overcome the stability issues for metal NPs. Furthermore, the activity and selectivity could be simultaneously enhanced by taking advantage of the synergy between the metal NPs and the support material, like abundantly available inexpensive polystyrene resins (PSR). Herein, the recent developments on PSR‐supported catalysts are deliberated for assorted organic reactions conducted under sustainable conditions. The salient advantageous attributes of nanocatalyst‐adorned PSR are discussed in terms of their activity, recyclability, stability and selectivity for various organic transformations. Further, the enduring challenges associated with the PSR‐supported nanocatalysts and future perspectives for further developments are explicated.

Toward Totally Defined Nanocatalysis: Deep Learning Reveals the Extraordinary Activity of Single Pd/C Particles.

Homogeneous catalysis is typically considered "well-defined" from the standpoint of catalyst structure unambiguity. In contrast, heterogeneous nanocatalysis often falls into the realm of "poorly defined" systems. Supported catalysts are difficult to characterize due to their heterogeneity, variety of morphologies, and large size at the nanoscale. Furthermore, an assortment of active metal nanoparticles examined on the support are negligible compared to those in the bulk catalyst used. To solve these challenges, we studied individual particles of the supported catalyst. We made a significant step forward to fully characterize individual catalyst particles. Combining a nanomanipulation technique inside a field-emission scanning electron microscope with neural network analysis of selected individual particles unexpectedly revealed important aspects of activity for widespread and commercially important Pd/C catalysts. The proposed approach unleashed an unprecedented turnover number of 109 attributed to individual palladium on a nanoglobular carbon particle. Offered in the present study is the Totally Defined Catalysis concept that has tremendous potential for the mechanistic research and development of high-performance catalysts.

Ionic Liquid-Assisted Fabrication of Bioactive Heterogeneous Magnetic Nanocatalyst with Antioxidant and Antibacterial Activities for the Synthesis of Polyhydroquinoline Derivatives.

Antibacterial materials have obtained much attention in recent years due to the presence of hazardous agents causing oxidative stress and observation of pathogens. However, materials with antioxidant and antibacterial activities can cause toxicity due to their low biocompatibility and safety profile, urging scientists to follow new ways in the synthesis of such materials. Ionic liquids have been employed as a green and environmentally solvent for the fabrication of electrically conductive polymers. In the present study, an antibacterial poly(p-phenylenediamine)@Fe3O4 (PpPDA@Fe3O4) nanocomposite was fabricated using [HPy][HSO4] ionic liquid. The chemical preparation of PpPDA@Fe3O4 nanocomposite was initiated through the oxidative polymerization of p-phenylenediamine by ammonium persulfate in the presence of [HPy][HSO4]. The PpPDA@Fe3O4 nanocomposite exhibited antibacterial properties against Gram-negative (Escherichia coli) and Gram-positive (Bacillus subtilis) bacteria. The PpPDA@Fe3O4 nanocomposite was employed as a heterogeneous nanocatalysis for one-pot synthesis of polyhydroquinoline derivatives using aromatic aldehyde, dimedone, benzyl acetoacetate, and ammonium acetate. Polyhydroquinoline derivatives were synthesized in significant yields (90–97%) without a difficult work-up procedure in short reaction times. Additionally, PpPDA@Fe3O4 nanocatalyst was recycled for at least five consecutive catalytic runs with a minor decrease in the catalytic activity. In this case, 11 derivatives of polyhydroquinoline showed in vitro antioxidant activity between 70–98%.

The Critical Impacts of Ligands on Heterogeneous Nanocatalysis: A Review

Ligand utilization is a necessary and powerful technique for the colloidal synthesis of nanoparticles (NPs) with controllable sizes and regulated morphologies. For catalysis applications, it is com...

β-Cyclodextrin polymer networks stabilized gold nanoparticle with superior catalytic activities

Support materials play a significant role in heterogeneous nanocatalysis. In this work, β-cyclodextrin (β-CD) was used directly as a monomer to construct polymer networks for gold nanoparticles (Au NPs) immobilization. Using the simple nucleophilic substitution reaction, β-CD based polymer networks (β-CDP-N and β-CDP-C) were successfully prepared. Compared to β-CDP-C, the hydroxyl groups and N atoms in β-CDP-N played a synergistic role in immobilizing smaller Au NPs, thus leading to high catalytic activities. Notably, the apparent rate constant (Kapp) value for Au@ β-CDP-N in the reduction of 4-nitrophenol to 4-aminophenol is 14.15 × 10−2 s−1, which shows a significant improvement over all previously reported Au NPs with solid supports under similar conditions. Considering the negligible porosity of the β-CDP-N support, we purposed a “capture-catalysis-release” model to explain the high catalytic activity of Au@ β-CDP-N. This explanation is supported by the guest-responsive properties of β-CDP-N. Moreover, the Au@ β-CDP-N is easily recycled and maintained its high catalytic efficiency after seven successful cycles.

10×-Enhanced Heterogeneous Nanocatalysis on a Nanoporous Gold Disk Array with High-Density Hot Spots.

Certain noble metal nanostructures as heterogeneous photocatalysts have drawn significant attention in the recent past because of their unique optical properties which lead to the excitation of localized surface plasmon resonance (LSPR). The LSPR concentrates electromagnetic fields to the surfaces and its relaxation processes can convert photon energy to energetic charge carriers or heat, which can be subsequently harvested to enhance surface catalysis. Here, we report the catalytic performance of a novel plasmonic nanostructure, disk-shaped nanoporous gold (NPG) nanoparticles or simply NPG disks, using a well-tested reduction pathway of resazurin to resorufin. We show that the catalytic reaction rate of NPG disks is enhanced by 10-fold upon external light illumination because of the excitation of LSPR. The plasmon-enhanced catalytic reaction follows a linear-to-superlinear transition in the rate dependence on the input light power. In addition, the light input results in a room temperature reaction rate equivalent to that of an ambient temperature of 70 °C. Together, the results support that hot charge carriers play the dominant role in the enhancement.

A Magnetic-Field Guided Interface Coassembly Approach to Magnetic Mesoporous Silica Nanochains for Osteoclast-Targeted Inhibition and Heterogeneous Nanocatalysis.

1D core-shell magnetic materials with mesopores in shell are highly desired for biocatalysis, magnetic bioseparation, and bioenrichment and biosensing because of their unique microstructure and morphology. In this study, 1D magnetic mesoporous silica nanochains (Fe3 O4 @nSiO2 @mSiO2 nanochain, Magn-MSNCs named as FDUcs-17C) are facilely synthesized via a novel magnetic-field-guided interface coassembly approach in two steps. Fe3 O4 particles are coated with nonporous silica in a magnetic field to form 1D Fe3 O4 @nSiO2 nanochains. A further interface coassembly of cetyltrimethylammonium bromide and silica source in water/n-hexane biliquid system leads to 1D Magn-MSNCs with core-shell-shell structure, uniform diameter (≈310 nm), large and perpendicular mesopores (7.3 nm), high surface area (317 m2 g-1 ), and high magnetization (34.9 emu g-1 ). Under a rotating magnetic field, the nanochains with loaded zoledronate (a medication for treating bone diseases) in the mesopores, show an interesting suppression effect of osteoclasts differentiation, due to their 1D nanostructure that provides a shearing force in dynamic magnetic field to induce sufficient and effective reactions in cells. Moreover, by loading Au nanoparticles in the mesopores, the 1D Fe3 O4 @nSiO2 @mSiO2 -Au nanochains can service as a catalytically active magnetic nanostirrer for hydrogenation of 4-nitrophenol with high catalytic performance and good magnetic recyclability.

Supported Single Atom and Pseudo‐Single Atom of Metals as Sustainable Heterogeneous Nanocatalysts

AbstractThe field of heterogeneous nanocatalysis has developed catalysts with excellent activities, superior selectivities and high stabilities. Their properties can be easily tuned by tailoring the size, shape and morphology of the nanomaterial. Thus, nanocatalysis is no longer just a field of academic curiosity, but an evolving field for industries to develop green and sustainable processes with very high turnover numbers, rates, and stabilities. The key to increase the efficiencies of these catalysts is to maximize the number of active centers on the surfaces, which can be achieved by reducing the size of metal NPs to single atom and pseudo‐single atom sizes. This field is growing exponentially, and several reports have described the syntheses, characterizations, and applications of these catalysts for a variety of reactions. This Review discusses the recent advances in the synthesis and catalytic performance of single and pseudo‐single atoms/sub‐nanometer (<1 nm) catalysts. We have reviewed experimental and theoretical studies performed for different reactions and, in the last section a brief outlook on the future prospects.

Integrative Approach to Biological Networks for Emerging Roles of Proteomics, Genomics and Transcriptomics in the Discovery and Validation of Human Colorectal Cancer Biomarkers from DNA/RNA Sequencing Data under Synchrotron Radiation

Nano catalytic hydrogenation is the useful and widely applicable method for the reduction of chemical substances and belongs to the basic processes of modern medicinal and pharmaceutical chemistry. It has found numerous applications in biological networks for emerging roles of proteomics, genomics and transcriptomics in the discovery and validation of human colorectal cancer biomarkers from DNA/RNA sequencing data under synchrotron radiation. Majority of medicinal and pharmaceutical nano catalytic hydrogenations is still carried out using heterogeneous nano catalysts due to the process advantages such as ability, easy separation, and wide range of applicable reaction conditions. The homogenous nano catalysts, which have been further developed during the past years, have extended the scope of nano catalytic hydrogenation especially in the field of highly stereo selective transformations in biological networks for emerging roles of proteomics, genomics and transcriptomics in the discovery and validation of human colorectal cancer biomarkers from DNA/ RNA sequencing data under synchrotron radiation. However, new developments continue to appear also in the field of heterogeneous nano catalysis, particularly in cases where a high chemo-, region-, or stereo selectivity must be achieved.

Efficient FeCl3/SiO2 as heterogeneous nanocatalysis for the synthesis of benzimidazoles under mild conditions

Iron(III) supported on nano silica as a new catalyst has been synthesized. Structural properties of this complex have been studied by TEM, SEM and EDX. The average crystalline size of Iron(III) supported on nano silica is 30–50 nm. Catalytic activity of this catalyst has been investigated by synthesis of benzimidazoles from 1, 2-diaminobenzene and aromatic aldehydes, and also the other variables investigated such as the amount of catalyst, reaction temperature and the effect of various solvents are also studied. The present procedure offers several advantages such as short reaction time, simple workup, recovery and reusability of the catalyst.

ChemInform Abstract: Metallic Nanocatalysis: An Accelerating Seamless Integration with Nanotechnology

AbstractReview: 188 refs.

Metallic nanocatalysis: an accelerating seamless integration with nanotechnology.

Rapidly growing research interests surround heterogeneous nanocatalysis, in which metal nanoparticles (NPs) play a pivotal role as structure-sensitive active centers. With advances in nanotechnology, the morphology of metal NPs can be precisely controlled, which can provide well-defined models of nanocatalysts for understanding and optimizing the structure-reactivity correlations and the catalytic mechanisms. Benefiting from this, further credible evidence can be acquired on well-defined nanocatalysts rather than common multiphase systems, which is of great significance for the design and practical application of active metal nanocatalysts. Numerous studies demonstrate that enhanced structure-sensitive catalytic activity and selectivity are dependent not only on an increased surface-to-volume ratio and special surface atom arrangements, but also on tailored metal-metal and metal-organic-ligand interfaces, which is ascribed to the size, shape, composition, and ligand effects. Size-reactivity relationships and underlying size-dependent metal-oxide interactions are observed in many reactions. For bimetallic nanocatalysts, the composition and nanostructure play critical roles in regulating reactivities. Crystal facets favor individual catalytic selectivity and rates via distinct reaction pathways occurring on diverse atomic arrangements, both to low-index and high-index facets. High-index facets exhibit superior reactivities owing to their high-energy active sites, which facilitate rapid bond-breaking and new bond generation. Additionally, organic ligands may enhance the catalytic activity and selectivity of metal nanocatalysts via changing the adsorption energies of reactants and/or reaction energy barriers. Furthermore, atomically dispersed metals, especially single-atom metallic catalysts, have emerged recently, which can achieve better specific catalytic activity compared to conventional nanostructured metallic catalysts due to the low-coordination environment, stronger interaction with supports, and maximum service efficiency. Here, recent progress in shaped metallic nanocatalysts is examined and several parameters are discussed, as well as finally highlighting single-atom metallic catalysts and some perspectives on nanocatalysis. The integration of nanotechnology and nanocatalysis has been shaping up and, no doubt, the combination of sensitive characterization techniques and quantum calculations will play more important roles in such processes.

In Situ Generated Iron Oxide Nanocrystals as Efficient and Selective Catalysts for the Reduction of Nitroarenes using a Continuous Flow Method

The best of both worlds: The benefits of homogeneous and heterogeneous nanocatalysis are combined, whereby highly reactive colloidal Fe3O4 nanocrystals are generated in situ that remain in solution long enough to allow the efficient and selective reduction of nitroarenes to anilines in continuous-flow mode (see scheme). After completion of the reaction, the nanoparticles aggregate and can be recovered by a magnet.

A first-principles theoretical approach to heterogeneous nanocatalysis

A theoretical approach to heterogeneous catalysis by sub-nanometre supported metal clusters and alloys is presented and discussed. Its goal is to perform a computational sampling of the reaction paths in nanocatalysis via a global search in the phase space of structures and stoichiometry combined with filtering which takes into account the given experimental conditions (catalytically relevant temperature and reactant pressure), and corresponds to an incremental exploration of the disconnectivity diagram of the system. The approach is implemented and applied to the study of propylene partial oxidation by Ag(3) supported on MgO(100). First-principles density-functional theory calculations coupled with a Reactive Global Optimization algorithm are performed, finding that: (1) the presence of an oxide support drastically changes the potential energy landscape of the system with respect to the gas phase, favoring configurations which interact positively with the electrostatic field generated by the surface; (2) the reaction energy barriers for the various mechanisms are crucial in the competition between thermodynamically and kinetically favored reaction products; (3) a topological database of structures and saddle points is produced which has general validity and can serve for future studies or for deriving general trends; (4) the MgO(100) surface captures some major features of the effect of an oxide support and appears to be a good model of a simple oxide substrate; (5) strong cooperative effects are found in the co-adsorption of O(2) and other ligands on small metal clusters. The proposed approach appears as a viable route to advance the role of predictive computational science in the field of heterogeneous nanocatalysis.

Conjugate addition of arylboronic acids to α,β-unsaturated carbonyl compounds in aqueous medium using Pd(ii) complexes with dihydroxy-2,2′-bipyridine ligands: homogeneous or heterogeneous nano-catalysis?

The conjugate addition of arylboronic acids to α,β-unsaturated carbonyl compounds in water under air has been studied using a series of palladium(II) derivatives containing symmetrically disubstituted-2,2′-bipyridine ligands. Among them, best results were obtained with complex [PdCl2{3,3′-(OH)2-2,2′-bipy}] (2a), which selectively provides the desired addition products in good to high yields under mild conditions. Catalytically active palladium nanoparticles are formed in the course of the reactions. In the presence of sodium dodecyl sulfate (SDS) these nanoparticles can be stabilized and recycled.