Remarkable Enhancement Of Catalytic Activity Research Articles

Hydrogenation of CO2 to formate catalyzed by a Ru catalyst supported on a copolymerized porous organic polymer.

The catalytic hydrogenation of carbon dioxide to formate is of great interest due to its significant role in CO2 utilization. In this study, a novel heterogeneous Ru(III) catalyst was prepared by immobilizing RuCl3 on a porous organic polymer (POP) obtained from 1,4-phthalaldehyde (PTA) and 4,4'-biphenyldicarboxaldehyde (BPDA) with melamine. A copolymerization strategy utilizing monomers of varying lengths was employed to prepare the POP-supported Ru catalyst with adjustable porosity. The optimization of the framework porosity resulted in enhanced CO2 affinity, accelerated mass transfer, and a remarkable enhancement in catalytic activity. A high turnover number (TON) of 2458 was achieved for the CO2 hydrogenation to formate in 2 h with catalyst Cat-3 under 3 MPa (CO2/H2 = 1 : 1) at 120 °C in 1 M Et3N aqueous solution. Moreover, the Cat-3 demonstrated good recyclability and was able to be reused for five consecutive runs, resulting in a high total TON of 9971.

Remarkable Enhancement of Catalytic Activity of Cu-Complexes in the Electrochemical Hydrogen Evolution Reaction by Using Triply Fused Porphyrin.

A bimetallic triply fused copper(II) porphyrin complex (1) was prepared, comprising two monomeric porphyrin units linked through β-β, meso-meso, β'-β' triple covalent linkages and exhibiting remarkable catalytic activity for the electrochemical hydrogen evolution reaction in comparison to the analogous monomeric copper(II) porphyrin complex (2). Electrochemical investigations in the presence of a proton source (trifluoroacetic acid) confirmed that the catalytic activity of the fused metalloporphyrin occurred at a significantly lower overpotential (≈320 mV) compared to the non-fused monomer. Controlled potential electrolysis combined with kinetic analysis of catalysts 1 and 2 confirmed production of hydrogen, with 96 and 71 % faradaic efficiencies and turnover numbers of 102 and 18, respectively, with an observed rate constant of around 107 s-1 for the dicopper complex. The results thus firmly establish triply fused porphyrin ligands as outstanding candidates for generating highly stable and efficient molecular electrocatalysts in combination with earth-abundant 3d transition metals.

Engineering nano-ordered of Ni nanoparticles on KIT-6 for enhanced catalytic hydrogenation of nitrobenzene

Catalytic hydrogenation of nitrobenzene by Ni nanoparticles on supports with high surface area is an economical and green route to produce aniline. To overcome the challenge of Ni nanoparticles blockage in the mesopores of KIT-6, a series of Ni-based KIT-6 catalysts were synthesized by designed engineering approaches. It was found that the engineering approaches were able to tune the nano-ordered of Ni nanoparticles and then remove the blockage on KIT-6, which significantly influence catalytic properties for nitrobenzene hydrogenation. The proposed engineering nano-ordered Ni nanoparticles blockage removal (ENBR) mechanism was systematically characterized. The characterization results confirmed that Ni dispersion, valence and metal surface area were adjusted by the ENBR process. The Ni particles located in the pore were not agglomerated, while the Ni particles located on the surface re-ordered to form larger particles and expose Ni particles blocked in the KIT-6 pores, which is the key factor for the remarkable enhancement of catalytic activity. Among all catalysts, with a specific surface area of 521.4 m2/g and Ni metal surface of 88.2 m2/g, Ni/KIT-6cal+red exhibited the best catalytic activity. This work was promising for the development of supported Ni catalysts to improve catalytic performance by engineering approaches.

Novel peripherally substituted metal-free, zinc (II), and cobalt (II) phthalocyanines with 1,1’-thiobis(2-napthol) and additional tetraphthalonitrile groups: Synthesis, aggregation behavior, electrochemical redox and electrocatalytic oxygen reducing properties

Novel phthalocyanines containing only 1,1′-thiobis(2-napthol) groups or 1,1′-thiobis(2-napthol) and phthalonitrile groups at peripheral positions were prepared by nucleophilic displacement reaction through cyclotetramerization of phthalonitrile derivatives, benzo[b]dinaphtho[1,2-h:2′,1′-e][1,4,7] dioxathionine-5,6-dicarbonitrile and 4,4′-[thiobis(naphthalene-1,2-diyloxy)]diphthalonitrile in penthanol. The aggregation tendencies and electrochemical redox properties of all phthalocyanines were investigated on the basis of central metal, solvent medium and subsituent effects, using UV-Vis spectral and classical electroanalytical techniques. The compounds exhibited metal-and/or phthalocyanine ring-based electron transfer processes which were coupled by distinct spectral changes and thus, net color transformations pointing out the possibility for their usage in electrochromic applications. Furthermore, remarkable enhancement in catalytic activity towards oxygen reduction and high tolerance to methanol during this reaction have been observed when the zinc (II) or 2H center was replaced with cobalt (II).

One-pot synthesis of highly branched Pt@Ag core-shell nanoparticles as a recyclable catalyst with dramatically boosting the catalytic performance for 4-nitrophenol reduction

Herein, highly branched Pt@Ag core-shell nanoparticles (Pt@Ag NPs) were fabricated by a facile one-pot wet-chemical approach, where poly(ethyleneimine) (PEI) served as structure-directing and capping agents. Their structure, morphology and composition were mainly characterized by a set of techniques. And their growth mechanism was discussed in some detail. The prepared catalyst exhibited remarkable enhancement in catalytic activity of 4-nitrophenol (4-NP) reduction as a proof-of-concept application, surpassing commercial Pt black and home-made Ag NPs catalysts. Also, the as-obtained catalyst showed superior stability without sacrificing the catalytic activity. These observations endow the catalyst possibility for practical applications in nitrophenols environmental remediation.

Elucidating the binding efficacy of β‐galactosidase on polyaniline–chitosan nanocomposite and polyaniline–chitosan–silver nanocomposite: activity and molecular docking insights

AbstractBACKGROUNDAspergillus oryzae β‐galactosidase (β‐gal; EC 3.2.1.23) was physically adsorbed on polyaniline–chitosan nanocomposite (PANI‐CS‐NC) and polyaniline–chitosan–silver nanocomposite (PANI‐CS‐Ag‐NC). Stability and kinetic studies were assessed, along with reusability and molecular docking interactions.RESULTSAccording to transmission electron microscopy images, the sizes of the respective NCs were found to be in the range of 23–39 and 6–18 nm. The η (effectiveness factor) values for PANI‐CS‐NC‐ and PANI‐CS‐Ag‐NC‐bound β‐gal were calculated to be 0.89 and 1.23, respectively, suggesting an enhancement in the activity of the enzyme in the presence of silver ions. Significant broadening was observed in pH and temperature profiles. Kinetic properties of PANI‐CS‐NC‐ and PANI‐CS‐Ag‐NC‐bound β‐gal showed lower Km, and two‐ and fourfold higher Vmax, respectively, compared to free enzyme. PANI‐CS‐Ag‐NC‐bound β‐gal was able to retain 94% of its initial activity after 10 repeated uses. Circular dichroism analysis revealed conformational changes in the secondary structure of protein upon immobilization. The genotoxic assessment revealed non‐toxic behaviour of both free and enzyme‐bound NC. The rate of lactose hydrolysis at 50 °C exhibited by PANI‐CS‐‐Ag‐NC bound β‐gal was 7% higher than that for the native enzyme. In‐silico analysis showed efficient binding of β‐gal on PANI‐CS‐ NCs due to interaction with residues that were exclusive of the active site of the enzyme.CONCLUSIONPANI‐CS‐Ag‐NC‐bound β‐gal preparation proved to be a robust nano‐biocatalyst due to remarkable enhancement in catalytic activity along with excellent stability and reusability characteristics, which could be further utilized for efficient construction of nano‐biosensors for producing lactose‐free dairy products to feed lactose‐intolerant patients. © 2018 Society of Chemical Industry

Cu-ZSM-5 zeolite supported on SiC monolith with enhanced catalytic activity for NH3-SCR

Here, we developed a new kind of hetero-structural catalyst through the homogeneous growth of Cu-ZSM-5 zeolite onto silicon carbide (SiC) monolith by using a one-pot hydrothermal method combined with an ion-exchange process in a rotary oven. The new catalyst formulation was tested towards NH3-SCR, where the catalytic activity and stability of Cu-ZSM-5/SiC at T > 350 °C appear significantly higher than those obtained with Cu-ZSM-5 alone. In particular, the NO consumption rate of the former is 7.5 times larger on the average than that of the latter. This remarkable enhancement of catalytic activity is ascribed to the very good thermal conductivity of the SiC monolithic support. This research work could provide the means for the future design of more active and stable monolithic Cu-ZSM5-based catalytic systems with even lower Cu loading than the ones used in present de-NOx applications.

Iron catalyzed CO2 hydrogenation to formate enhanced by Lewis acid co-catalysts.

A family of iron(ii) carbonyl hydride complexes supported by either a bifunctional PNP ligand containing a secondary amine, or a PNP ligand with a tertiary amine that prevents metal-ligand cooperativity, were found to promote the catalytic hydrogenation of CO2 to formate in the presence of Brønsted base. In both cases a remarkable enhancement in catalytic activity was observed upon the addition of Lewis acid (LA) co-catalysts. For the secondary amine supported system, turnover numbers of approximately 9000 for formate production were achieved, while for catalysts supported by the tertiary amine ligand, nearly 60 000 turnovers were observed; the highest activity reported for an earth abundant catalyst to date. The LA co-catalysts raise the turnover number by more than an order of magnitude in each case. In the secondary amine system, mechanistic investigations implicated the LA in disrupting an intramolecular hydrogen bond between the PNP ligand N-H moiety and the carbonyl oxygen of a formate ligand in the catalytic resting state. This destabilization of the iron-bound formate accelerates product extrusion, the rate-limiting step in catalysis. In systems supported by ligands with the tertiary amine, it was demonstrated that the LA enhancement originates from cation assisted substitution of formate for dihydrogen during the slow step in catalysis.

Remarkable enhancement of catalytic activity and selectivity of MSE-type zeolite by post-synthetic modification

Besides conventional MCM-68, Al-rich MSE-type zeolites with a 12-10-10-ring micropore system were successfully synthesized in a remarkably short crystallization period by some different synthetic methods: (1) hydrothermal conversion of an FAU-type zeolite with the aid of the dipyrrolidinium-type organic structure-directing agent (OSDA) and (2) hydrothermal synthesis without using any OSDA with the aid of seed crystals. The dealumination behaviors during post-synthetic acid treatments as well as the properties of the products differed depending on the synthetic method. The dealuminated version of each Al-rich MSE-type zeolite showed a high level of coking resistance in addition to a significant yield of propylene in the hexane-cracking reaction, and the MSE synthesized under OSDA-free conditions showed the best catalytic performance among three different MSE-type zeolites after post-synthetic modification. The Al-rich MSE products obtained in this work are promising parent materials for industrial applications as highly selective and long-lived catalysts.

Unique Properties of Ceria Nanoparticles Supported on Metals: Novel Inverse Ceria/Copper Catalysts for CO Oxidation and the Water-Gas Shift Reaction

Oxides play a central role in important industrial processes, including applications such as the production of renewable energy, remediation of environmental pollutants, and the synthesis of fine chemicals. They were originally used as catalyst supports and were thought to be chemically inert, but now they are used to build catalysts tailored toward improved selectivity and activity in chemical reactions. Many studies have compared the morphological, electronic, and chemical properties of oxide materials with those of unoxidized metals. Researchers know much less about the properties of oxides at the nanoscale, which display distinct behavior from their bulk counterparts. More is known about metal nanoparticles. Inverse-model catalysts, composed of oxide nanoparticles supported on metal or oxide substrates instead of the reverse (oxides supporting metal nanoparticles), are excellent tools for systematically testing the properties of novel catalytic oxide materials. Inverse models are prepared in situ and can be studied with a variety of surface science tools (e.g. scanning tunneling microscopy, X-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, low-energy electron microscopy) and theoretical tools (e.g. density functional theory). Meanwhile, their catalytic activity can be tested simultaneously in a reactor. This approach makes it possible to identify specific functions or structures that affect catalyst performance or reaction selectivity. Insights gained from these tests help to tailor powder systems, with the primary objective of rational design (experimental and theoretical) of catalysts for specific chemical reactions. This Account describes the properties of inverse catalysts composed of CeOx nanoparticles supported on Cu(111) or CuOx/Cu(111) as determined through the methods described above. Ceria is an important material for redox chemistry because of its interchangeable oxidation states (Ce⁴⁺ and Ce³⁺). Cu(111), meanwhile, is a standard catalyst for reactions such as CO oxidation and the water-gas shift (WGS). This metal serves as an ideal replacement for other noble metals that are neither abundant nor cost effective. To prepare the inverse system we deposited nanoparticles (2-20 nm) of cerium oxide onto the Cu(111) surface. During this process, the Cu(111) surface grows an oxide layer that is characteristic of Cu₂O (Cu¹⁺). This oxide can influence the growth of ceria nanoparticles. Evidence suggests triangular-shaped CeO₂(111) grows on Cu₂O(111) surfaces while rectangular CeO₂(100) grows on Cu₄O₃(111) surfaces. We used the CeOx/Cu₂O/Cu(111) inverse system to study two catalytic processes: the WGS (CO + H₂O → CO₂ + H₂) and CO oxidation (2CO + O₂ → 2CO₂). We discovered that the addition of small amounts of ceria nanoparticles can activate the Cu(111) surface and achieve remarkable enhancement of catalytic activity in the investigated reactions. In the case of the WGS, the CeOx nanoparticle facilitated this process by acting at the interface with Cu to dissociate water. In the CO oxidation case, an enhancement in the dissociation of O₂ by the nanoparticles was a key factor. The strong interaction between CeOx nanoparticles and Cu(111) when preoxidized and reduced in CO resulted in a massive surface reconstruction of the copper substrate with the introduction of microterraces that covered 25-35% of the surface. This constitutes a new mechanism for surface reconstruction not observed before. These microterraces helped to facilitate a further enhancement of activity towards the WGS by opening an additional channel for the dissociation of water. In summary, inverse catalysts of CeOx/Cu(111) and CeO₂/Cu₂O/Cu(111) demonstrate the versatility of a model system to obtain insightful knowledge of catalytic processes. These systems will continue to offer a unique opportunity to probe key catalytic components and elucidate the relationship between structure and reactivity of novel materials and reactions in the future.

Mechanistic insights into phosphatase triggered self-assembly including enhancement of biocatalytic conversion rate

We report on the mechanistic investigation of alkaline phosphatase (AP) triggered self-assembly and hydrogelation of Fmoc-tyrosine (Fmoc-Y). We studied separately the biocatalytic conversion using HPLC, changes in supramolecular interactions and chirality using CD and fluorescence spectroscopy, nanostructure formation by AFM and gelation by oscillatory rheometry. Three consecutive stages could be distinguished (which may overlap, depending on the enzyme concentration). Typically, the phosphorylated Fmoc-Y (Fmoc-pY) undergoes rapid and complete dephosphorylation, followed by formation of aggregates which reorganise into nanofibres and consequently give rise to gelation. We observed a remarkable enhancement of catalytic activity during the early stages of the self-assembly process, providing evidence for enhancement of enzymatic activation by the supramolecular structures formed. Overall, this study provides a further step in understanding biocatalytic self-assembly.

Remarkable enhancement of catalytic activity of a 2 : 1 complex between a non-planar Mo(v)–porphyrin and a ruthenium-substituted Keggin-type heteropolyoxometalate in catalytic oxidation of benzyl alcohols

A 2 : 1 complex composed between a non-planar Mo(v)-porphyrin complex ([Mo(DPP)(O)](+), DPP(2-) = dodecaphenylporphyrin) and a ruthenium-substituted Keggin-type heteropolyoxometalate (Ru-POM), [SiW(11)O(39)Ru(III)(DMSO)](5-), acts as an efficient catalyst for oxidation of benzyl alcohols with iodosobenzene as an oxidant in CDCl(3) at room temperature. The catalytic oxidation afforded the corresponding benzaldehydes, whereas neither the ammonium salt of Ru-POM nor [Mo(DPP)(O)](+) alone exhibited catalytic reactivity under the same experimental conditions. This enhancement can be attributed to a large anodic shift of the redox potential of the ruthenium centre due to the complexation of the Ru-POM with two cationic {Mo(DPP)(O)}(+) units. The kinetic analysis demonstrated that the catalytic oxidation proceeded via formation of a catalyst-substrate complex, and electron-withdrawing substituents at the para position of benzyl alcohol accelerated the reaction. The rate constants of the oxidation reactions correlate to the bond dissociation energies of the C-H bonds of the substrate. A linear correlation was observed for logarithm of the rate constants of oxidation reactions of benzyl alcohols with that of hydrogen abstraction by cumyl peroxyl radical, indicating the reaction proceeds via hydrogen abstraction. The observed kinetic isotope effect (KIE) indicates that the hydrogen abstraction occurs from the benzyl group rather than the hydroxy group.

ZnO–CuO core–branch nanocatalysts for ultrasound-assisted azide–alkyne cycloaddition reactions

ZnO-CuO core-branch hybrid nanoparticles, synthesized by copper oxide growth and controlled oxidation on ZnO nanospheres, exhibited remarkable enhancement of catalytic activity and stability for ultrasound-assisted [3+2] azide-alkyne cycloaddition reactions, due to their high surface area and active facets of the CuO branches.

Rational creation of mutant enzyme showing remarkable enhancement of catalytic activity and enantioselectivity toward poor substrates

Catalytic activity and enantioselectivity of lipase toward poor substrates bearing bulky substituents on both sides have been dramatically improved by rational design; the E value for a poor substrate was increased from 5 (wild-type enzyme) to >200 (I287F/I290A double mutant) with an acceleration of the reaction rate.

A remarkable enhancement of catalytic activity for KBH4 treating the carbothermal reduced Ni/AC catalyst in glycerol hydrogenolysis

It reported a novel procedure for preparing Ni/AC catalyst for the glycerol hydrogenolysis, which involved carbothermal reduction of supported nickel nitrate and further treatment with KBH4. The activity of the as-prepared catalyst was remarkably enhanced compared with KBH4, H-2 or carbothermal reduced Ni/AC catalyst. The Ni particles and the variation of oxygen-containing surface groups (OSGs) were studied by XRD, TEM, FT-IR, He-TPD and NH3-TPD techniques. The high dispersed Ni and the acidity generated by the OSGs have the synergy effect on the activity of glycerol hydrogenolysis. (C) 2009 Elsevier B.V. All rights reserved.

Selective Isopropylation of Isobutylbenzene over H-Mordenite in Supercritical CO2 Medium: Remarkable Enhancement in Catalytic Activity and Selectivity for 4-Isobutylcumene

Remarkable enhancement in the catalytic activity and selectivity for the formation of 4-isobutylcumene (4-IBC) was observed in the isopropylation of isobutylbenzene (IBB) over highly dealuminated H-mordenite in supercritical CO2 (sc-CO2) medium. Thermogravimetric analyses confirm that reduced coking of the catalysts in sc-CO2 medium and stronger acid sites in dealuminated H-mordenite (MOR) are the key factors for superior activity and selectivity for 4-IBC.

New Design in Homogeneous Palladium Catalysis: Study of Transformation of Group 14 Element Compounds and Development of Nanosize Palladium Catalysts

This account reports an overview of our findings in homogeneous Pd-catalyzed reactions. Herein we describe the new design in reactions of Group 14 element compounds and in homogeneous nanosize Pd catalysts. In the early stages of our study, we developed Pd-catalyzed transformations of allylic esters with disilanes, silylcyanides and acylsilanes to the corresponding silylation, cyanation and acylation products, respectively. We also developed a Pd-catalyzed three component coupling reaction of Group 14 element compounds involving 1,3-diene and acid chlorides to form β,γ-unsaturated ketone as a single product. Recently, we focus our attention on modifying the catalytic environment by nanosize Pd in order to improve the performance of Pd catalysts. These nanosystems realize efficient catalytic environment with remarkable enhancement in catalytic activity and unprecedented selectivity.

Recent Development of Homogeneous Transition Metal Catalysts with Nanosize Ligands

Abstract Expanding catalytic environment to a nanosize is one of the most promising ways to improve performance of homogeneous catalysts. In this highlight review, recent development in homogeneous transition metal catalysts with well-defined nanosize ligands is overviewed. These systems realize efficient catalysts with remarkable enhancement of catalytic activity, suppression of metal aggregation, and unprecedented selectivity.

Remarkable Enhancement of Catalytic Activity of FSM-16 by Modification with Ammonium Sulfate for Acid-Catalyzed Reactions

Abstract Impregnation of FSM-16 with ammonium sulfate followed by optimized thermal pretreatments, especially by evacuation, leads to a remarkable enhancement in the catalytic activity of FSM-16 for acid-catalyzed reactions.

Enhancement of the Catalytic Activity of a Macrocyclic Cobalt(II) Complex for the Electroreduction of O(2) by Adsorption on Graphite.

In solution, the [(tim)Co](2+) complex (tim = 2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) reacts only slowly with O(2), but upon adsorption on graphite electrodes, it becomes an active catalyst for the reduction of O(2) to H(2)O(2). The electroreduction of O(2) proceeds in a single voltammetric step at close to the diffusion-controlled rate at a relatively positive potential (0.25 V vs SCE). The remarkable enhancement in catalytic activity is attributed to a higher affinity for O(2) of the adsorbed complex as a result of its interactions with functional groups on the surface of roughened or oxidized graphite. A possible mechanism for the catalytic reduction of O(2) is proposed. It differs from the one employed by the analogous [(hmc)Co](2+) complex (hmc = C-meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) which operates at less positive potentials and exhibits two separated voltammetric steps in the reduction of O(2), via [(hmc)CoOOH](2+), to H(2)O(2).