NP Catalyst Research Articles

Efficient one-pot synthesis of 4-hydroxy-2H chromene by heterogeneously catalyzed ZnO NP and mesoporous aluminosilicate catalysts in solvent free condition

4-Hydroxy-2H chromenes are fused benzopyran rings, an important class of biologically active compounds that are widely used as antibacterial, antiviral, antitumor, and anticancer agents. In this paper, we report the synthesis of 4-hydroxy-2H chromenes using two catalysts: (i) ZnO nanoparticles and (ii) mesoporous ZnO/AlSBA-15(7). The ZnO nanoparticle catalyst was prepared using leaf extract, and ZnO/AlSBA-15(7) catalysts were prepared by a wet chemical route. All catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, and N2 sorption techniques. The catalytic activity of the synthesized catalyst was evaluated in a one-pot reaction using aromatic aldehyde and coumarin and was found to have a maximum yield of 81% at 80 °C, with a catalyst dose of 10 mmol %, and in a time limit of 4 h.

Enhancement of the Oxygen Reduction Reaction Activity of Pt by Tuning Its d-Band Center via Transition Metal Oxide Support Interactions

The enhancement of the oxygen reduction reaction (ORR) activity of platinum nanoparticles (Pt NPs) using transition metal oxide (MOx, M = Ti, Nb, Ta, W, Y, and Zr) supports has been examined. To enable the use of transition metal oxides having low electric conductivity as supports, Pt NPs were formed on thin transition metal oxides formed on conducting cup-stacked carbon nanotubes (CSCNTs). Metal oxide composites (M1M2Ox) prepared from two types of transition metal (M1M2: TiNb, NbTa, and TaW) precursors were also used as supports. Pt NPs were photodeposited on MOx/CSCNTs and M1M2Ox/CSCNT supports, resulting in MOx/CSCNT- and M1M2Ox/CSCNT-supported Pt NP catalysts (abbreviated as Pt/MOx/CSCNTs and Pt/M1M2Ox/CSCNTs). Their ORR activities in 0.1 M HClO4 aqueous solution were found to significantly depend on the atomic ratio of M1 and M2 in M1M2Ox and the type of metal oxide support. A “volcano-type” dependence of the ORR activity (represented as the current density, mass activity, and specific activity at 0.9 V vs reversible hydrogen electrode (RHE)) on the Pt d-band center, relative to the Fermi level, was obtained in a series of the Pt/MOx/CSCNTs and Pt/M1M2Ox/CSCNT catalysts. It was found that the d-band center values (ranging from −3.83 to −3.42 eV) of Pt deposited on MOx/CSCNTs and M1M2Ox/CSCNT supports were lower than that (−3.39 eV) of the reference Pt/carbon black (CB) and that the Pt/TiNbOx (Ti/Nb = 1:6.6 in atomic ratio)/CSCNTs with a d-band center of −3.59 eV exhibited the maximum ORR activity, in agreement with the theoretical expectation that an ORR catalyst having a d-band center that is ca. 0.2 eV lower than that of Pt would have maximal ORR activity.

Defective-tin-oxide wrapped gold nanoparticles with strong sunlight harvesting and efficient charge separation for photocatalysis

Strong sunlight harvesting and efficient charge separation are of great significances for solar energy utilization of metal oxides, but it is a challenge to realize these two aspects simultaneously. Here, we strategize oxygen-vacancy-rich (or defective)-SnO2 wrapped gold nanoparticles ([email protected]2 NPs) for this. The designed NPs are fabricated just by adding precursors into boiling pre-prepared Au colloidal solution and then re-dispersing the reacted NPs in water, based on surface alloying and selective oxidation. Typically, the fabricated [email protected]2 NPs (with 12 nm thick shell) exhibit strong absorption in full solar spectrum (200–2000 nm) with an energy absorption efficiency as high as 84%. Meanwhile, the photocurrent response of the typical NPs is 2.3 and 13.6 times as high as that of [email protected]2 NPs (with poor oxygen vacancies) and commercial SnO2 NPs, respectively, showing efficient charge separation. Such excellent performance is attributed to the synergistic effect of surface plasmon resonance (SPR) of the Au core and the band gap narrowing induced by the abundant oxygen vacancies. Further, the excellent photocatalytic performance of the [email protected]2 NP catalyst has been demonstrated via exemplary photocatalytic removal of gaseous ammonia. The catalytic rate is about 4.2 and 25 times as high as that of the [email protected]2 NP and the commercial SnO2 NP catalysts, respectively. It is expected that such excellent photocatalytic performance will also be obtained on other defective oxides wrapped metal structures. This work provides a preparation method for [email protected]2 NPs, which can be used for efficient solar energy utilization.

Nanoporous Pd-Cu thin films as highly active and durable catalysts for oxygen reduction in alkaline media

A facile electrochemical etching approach was developed and implemented to enhance the electrocatalytic performance of Pd-Cu films for oxygen reduction reaction (ORR) in alkaline media. The nanoporous (np) Pd-Cu was synthesized through electrochemical de-alloying of pre-deposited Pd-Cu films. Scanning electron microscopy (SEM) with energy dispersive spectroscopy was employed to confirm the residual amount of Cu in the np structure. The accordingly prepared np catalysts showed excellent ORR activity up to 1.11 A/mgPd at a potential of 0.9 V vs. RHE which is around 22-times and 6.2-times higher than that of a plain Pd film and commercial Pd/C catalyst, respectively. The ORR activity enhancement is attributed to the unique porous structure, large Pd surface area, and modified electronic structure of Pd with residual Cu as confirmed by the SEM, hydrogen underpotential deposition, and CO stripping characterizations. The np Pd-Cu catalyst also showed excellent durability which is manifested by a negligible decrease in the half-wave potential (4 mV negative shift) after 10,000 potential cycles in alkaline media. These findings provide insights into the rational design of an electrocatalyst's structure utilizing an electrochemical de-alloying method to achieve high atomic utilization and improved catalytic performance.

A Convenient Method for Synthesis of Fe3O4/FeS2 as High-Performance Electrocatalysts for Oxygen Evolution Reaction and Zinc-Air Batteries

The development of highly efficient and inexpensive electrocatalysts has attracted great attention due to the large demand for renewable energy conversion devices. Magnetite-based electrocatalyst, which is stable in natural environment, has been widely considered as one of the most promising candidates. However, its electrocatalytic performance is still unsatisfactory because it has the characteristics of large resistance and large energy barriers to form intermediate species during water oxidation. In this report, we demonstrate a convenient method to synthesize Fe3O4/FeS2 NP catalyst from MIL-101(Fe) for oxygen evolution reaction and zinc-air batteries. The Fe3O4/FeS2 NP catalyst shows outstanding activity with lower overpotential of 265 mV to reach the current density of 10 mA cm−2, which is better than or comparable to the recently reported Fe-based or Co-based catalysts. Systematic research reveals that thus enhancement can be ascribed to the increase of electrochemically active surface areas and the decrease of bonding energy of intermediates. Based on thus novel Fe3O4/FeS2 NP electrodes, the as-prepared zinc-air batteries can achieve specific capacity of around 560 mAh gZn −1 and impressive cyclic stability. It is believed that these findings would help us to develop high-performance and sustainable electrocatalysts.

Successive degradation of organophosphate nerve agent by integrating the merits of artificial enzyme and metal nanoparticle catalyst

Organophosphate (OP) nerve agents are highly toxic and widely used as pesticides and chemical weapons. In this work, a facile approach for cascade degradation of OP nerve agent simulants is established via a hybrid material, which is prepared by growth of Pd nanoparticles (PdNPs) in metal-organic frameworks (MOFs) (PdNPs@PCN-224) (PCN = porous coordination network). PCN-224 acts not only as the support material but also as an effective enzyme mimic of organophosphorus hydrolysis (OPH), which can completely degrade paraoxon, the model OP compounds, into p-nitrophenol (p-NP). Thereafter, the degraded product (p-NP) with moderate toxicity is further efficiently reduced into p-aminophenol (p-AP) with less toxicity by NaBH4 under the catalyzation of PdNPs. This work displays a great potential to construct highly bifunctional catalysts by integrating the merits of artificial enzymes and metal NP catalysts, which are promising for applications in the successive degradation of OP nerve agents.

Bimetallic nano alloy architecture on a special polymer: Ni or Cu merged with Pd for the promotion of the Mizoroki–Heck reaction and the Suzuki–Miyaura coupling

Novel Ni-Pd and Cu-Pd bimetallic nano alloys was designed and heterogenized on the highly robust ABPBI [poly(2,5-benzimidazole)] polymer in high yields using NaBH4 as reducing agent. These were versatile ligand free catalysts for the Mizoroki–Heck reaction and Suzuki–Miyaura coupling. The bimetallic Ni-Pd-ABPBI catalyst for the Mizoroki–Heck reaction of 4-iodo anisole could be recycled 5 times with high yields. Aryl bromides could also be activated for the Mizoroki–Heck reaction using Cu-Pd-ABPBI NP catalysts, with moderate yields. Synopsis Novel bimetallic Ni-Pd and Cu-Pd nano alloys, heterogenized on the robust ABPBI [poly(2,5-benzimidazole)] polymer using NaBH4 as reducing agent, is described. These were versatile ligand free, noble metal conservative catalysts, for the Mizoroki–Heck reaction and the Suzuki–Miyaura coupling. Aryl bromides were activated for the Mizoroki–Heck reaction using the Cu-Pd-ABPBI catalyst.

Clean protocol for deoxygenation of epoxides to alkenes via catalytic hydrogenation using gold

Au NP catalyst combined with triethylphosphite, P(OEt)3, is remarkably more reactive than solely Au NPs for the selective deoxygenation of epoxides to alkenes.

Recyclable nanocellulose-confined palladium nanoparticles with enhanced room-temperature catalytic activity and chemoselectivity

We describe the synthesis of even-dispersed palladium nanoparticles (Pd NPs) confined within a cellulose nanofiber (CNF) matrix for developing a high-performance and recyclable catalyst. The CNF matrix was composed of CNF-assembled mesoporous nanosheets and appeared as soft and hydrophilic foam. Ultrafine Pd NPs (∼6 nm) with high-loading (9.6 wt%) were in situ grown on these mesoporous nanosheets, and their dense spatial distributions were likely to generate nano-confinement catalytic effects on the reactants. Consequently, the CNF-confined Pd NPs (CNF-Pd) exhibited an enhanced room-temperature catalytic activity on the model reaction of 4-nitrophenol hydrogenation with a highest rate constant of 8.8×10−3 s−1 and turnover frequency of 2640 h The CNF Pd catalyst possessed good chemical stability and recyclability in aqueous media which could be reused for at least six cycles without losing activity. Moreover, chemoselective reduction of 3 nitrostyrene was achieved with high yield (80%–98%) of 3-aminostyrene in alcohol/water cosolvent. Overall, this work demonstrates a positive nanoconfinement effect of CNFs for developing stable and recyclable metal NP catalysts.

Pt Deposits on Bi/Pt NP Catalyst for Formic Acid Oxidation: Catalytic Enhancement and Longer Lifetime.

This work presents an improvement in the activity and catalytic lifetime of Pt deposits on Bi-modified Pt nanoparticles (Bi/Pt NP) toward formic acid oxidation (FAO). Using an irreversible adsorption method, Bi was deposited on Pt NP to form Bi/Pt NP and sequentially Pt was deposited on Bi/Pt NP to form Pt/Bi/Pt NP. Voltammetric studies of Pt NP, Bi/Pt NP, and Pt/Bi/Pt NPs supported that Pt deposits of Pt/Bi/Pt NPs provided quite a unique behavior: simultaneous surface oxidation of deposited Pt and Bi and significant resistance to the oxidative removal of Bi. Furthermore, combined spectroscopic investigations revealed that the concentration of the employed Pt precursor ion solution determined the amount of deposited Pt from ∼0.2 to ∼0.4 in coverage. The best Pt/Bi/Pt NP catalyst with a Pt coverage of ∼0.25 enhanced the dehydrogenation processes below ∼0.4 V by a factor of more than 2 and increased the FAO current at ∼0.8 V roughly by 15 times, referring to those of Bi/Pt NP. The lifetime measurement works revealed that after the 1000th voltammetric cycle to 0.4 V, the FAO currents of Pt/Bi/Pt NPs were 2 and 4 times higher than those of Bi/Pt NP and Pt NP, respectively. The Pt deposits on Bi/Pt NP were concluded to play two roles in FAO: the promotion of FAO processes to increase the activity and the retardation of Bi oxidative removal to maintain the activity much longer.

Compressive Strain in Core-Shell Au-Pd Nanoparticles Introduced by Lateral Confinement of Deformation Twinnings to Enhance the Oxidation Reduction Reaction Performance.

In this work, quasi-spherical, uniform gold nanoparticles with rich deformation twinning (Audt NPs) were first synthesized with the assistance of copper(II) ions. Then, these Audt NPs were used as the cores for the fabrication of core-shell (CS) Audt-Pd NPs with ultrathin Pd layers, which also can bear compressive strain because of the formation of corrugated structured Pd shells led by the lateral confinement imposed by deformation twinning in the Au cores. The presence of compressive strain in the CS Audt-Pd NPs can result in the widening of the d-band width of the Pd shell and further the downshift of their d-band center, which can then improve the desorption ability of intermediates and still maintain the adsorption ability of the reactants because of the broad adsorption potential range. Taking the oxidation reduction reaction and the ethanol oxidation reaction as examples, the as-prepared Audt-Pd NPs indeed exhibited superior catalytic performances because of the synergism of compressive strain and the electronic effect. Thus, our work opens a new way to introduce compressive strain in the Pd-based CS NP catalysts, which can achieve the enhancement in the electrocatalytic performance by combining the merit of compressive strain and the electronic effect.

Self-healing and high reusability of Au nanoparticles catalyst based on supramolecular hydrogel

In this work, supramolecular hydrogels were utilised as soft reactor for gold nanoparticles (Au NPs) to prepare cucurbit[8]uril (CB[8]) based supramolecular hydrogel loaded with Au NP(Au/CB[8] hydrogel) catalysts. The morphology and structure of the catalysts were characterized via UV–vis spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray powderdiffraction and thermo gravimetric analyzer analysis. The Au/CB[8] hydrogels were utilised as catalysts and reaction media for the reduction reactions of 4-nitrophenol (4-NP) with NaBH4 aqueous. The reduction rate constants at four temperatures (16 °C, 25 °C, 34 °C and 43 °C) and the activation parameters were calculated. The activation energy of 4-NP was 65.83 kJ mol−1. These types of hydrogel-composite catalyst systems exhibit self-healing and can be used repetitively up to seven times with 100% conversion and only 20% reduction in the initial reduction rate. This process provides a novel method for the production of highe fficiency and self-healing nanomaterals with various applications.

Formation of PdO on Au–Pd bimetallic catalysts and the effect on benzyl alcohol oxidation

A series of catalysts consisting of gold–palladium bimetallic nanoparticles (Au–Pd NPs in the range of 1–6 nm) anchored on foamlike mesoporous silica were used for the aerobic oxidation of benzyl alcohol. A remarkable synergistic effect was observed on these Au–Pd NP catalysts prepared by a one-pot method. Both experimental and theoretical study revealed a close relationship between the surface PdO species on the catalysts and their catalytic performance; that is, higher surface PdO content leads to lower catalytic activity. The surface content of PdO species on the catalysts could be tuned by controlling the Au/Pd ratios, because the formation of Au–Pd alloy NPs and electron transfer between surface Au and Pd atoms prevented the oxidation of surface Pd and retarded the formation of PdO species. An optimal Au/Pd ratio of 1/4.5 on the foamlike mesoporous silica support was obtained, with nearly no surface PdO species formed, and resulted in the highest benzyl alcohol conversion of 96%. The bimetallic Au–Pd catalysts exhibited much higher catalytic activity for benzyl alcohol oxidation (TOF = 50,000–60,000 h−1) than the monometallic Pd catalyst (TOF = 12,500 h−1), on which surface Pd is easily oxidized to PdO. These results provide direct evidence for the synergistic effect of Au–Pd bimetallic catalysts in benzyl alcohol oxidation.

Regioselective Hydrogenation of Itaconic Acid to γ-Isovalerolactone by Transition-Metal Nanoparticle Catalysts.

Current methods for hydrogenation of bio-derived itaconic acid (IA) lead to a mixture of isomeric lactone products. Transition-metal nanoparticles (TM-NPs), in situ-generated through thermolysis of TM(0) (Ru, Fe, W, Cr) carbonyls, in particular Ru-NPs, were found to catalyze regioselective hydrogenation of IA by syngas (2 H2 /CO) into γ-isovalerolactone (GiVL) in approximately 70 % isolated yield. Key sustainability features of this new route include: a one-pot direct transformation of bio-renewable IA into value-added GiVL selectively, use of inexpensive and renewable syngas in aqueous solution, and development of a supported recyclable NP catalyst system, Al2 O3 -Ru-NPs.

Selective synthesis of 1,3-propanediol from glycidol over a carbon film encapsulated Co catalyst

A carbon film encapsulated Co NP catalyst (Co@NC) was highly active, selective and stable for the hydrogenation of glycidol to 1,3-PDO.

Heterogeneous Rh and Rh/Ag bimetallic nanoparticle catalysts immobilized on chiral polymers.

The development of heterogeneous chiral catalysts has lagged far behind that of homogeneous chiral catalysts in spite of their advantages, such as environmental friendliness for a sustainable society. We describe herein novel heterogeneous chiral Rh and Rh/Ag bimetallic nanoparticle catalysts consisting of polystyrene-based polymers with chiral diene moieties. The catalysts enable high-to-excellent yields and enantioselectivities to be obtained in asymmetric 1,4-addition reactions of arylboronic acids with α,β-unsaturated carbonyl compounds such as ketones, esters, and amides, and in other asymmetric reactions. The catalysts could be readily recovered by simple filtration and reused; they could also be applied to continuous-flow synthesis. We also discuss the nature of possible reaction species based on XPS analysis.

Probing the chemical state of tin oxide NP catalysts during CO2 electroreduction: A complementary operando approach

In this paper we combine two operando methods, Raman spectroscopy and X-ray absorption spectroscopy (XAS), in order to probe reduced graphene-oxide supported tinIV oxide nanoparticles (SnO2NPs@rGO) as they are being used to catalyse CO2 electroreduction. To achieve high reaction rates it is necessary to apply sufficiently cathodic electrode potentials. Under such conditions, however, not only CO2 is reduced electrochemically, but also the catalyst particles may be transformed from the initial SnIV state to SnII or, in an extreme case, to metallic Sn. While SnII species still favour CO2 electroreduction, yielding formate as a primary product, on metallic Sn CO2 reduction is disfavoured with respect to the competing hydrogen evolution reaction (HER). We show that operando XAS, a robust technique yielding information averaged over a large surface area and a relatively large thickness of the catalyst layer, is a very expedient method able to detect the reduction of SnO2NPs@rGO to metallic Sn. XAS can thus be used to establish an optimum potential for the electroreduction in practical electrolysing cells. It takes, however, a complementary method offered by operando Raman spectroscopy, having greater sensitivity at the catalyst/electrolyte solution interface, to probe reduction intermediates such as the SnII state, which remain undetectable for ex situ methods. As it is shown in the paper, Raman spectroscopy may also find further use when investigating the recovery of catalyst particles following exposure to extreme reducing conditions.

Tuning Gold Nanoparticles with Chelating Ligands for Highly Efficient Electrocatalytic CO2 Reduction

AbstractCapped chelating organic molecules are presented as a design principle for tuning heterogeneous nanoparticles for electrochemical catalysis. Gold nanoparticles (AuNPs) functionalized with a chelating tetradentate porphyrin ligand show a 110‐fold enhancement compared to the oleylamine‐coated AuNP in current density for electrochemical reduction of CO2 to CO in water at an overpotential of 340 mV with Faradaic efficiencies (FEs) of 93 %. These catalysts also show excellent stability without deactivation (<5 % productivity loss) within 72 hours of electrolysis. DFT calculation results further confirm the chelation effect in stabilizing molecule/NP interface and tailoring catalytic activity. This general approach is thus anticipated to be complementary to current NP catalyst design approaches.

Tuning Gold Nanoparticles with Chelating Ligands for Highly Efficient Electrocatalytic CO2 Reduction

Capped chelating organic molecules are presented as a design principle for tuning heterogeneous nanoparticles for electrochemical catalysis. Gold nanoparticles (AuNPs) functionalized with a chelating tetradentate porphyrin ligand show a 110-fold enhancement compared to the oleylamine-coated AuNP in current density for electrochemical reduction of CO2 to CO in water at an overpotential of 340 mV with Faradaic efficiencies (FEs) of 93 %. These catalysts also show excellent stability without deactivation (<5 % productivity loss) within 72 hours of electrolysis. DFT calculation results further confirm the chelation effect in stabilizing molecule/NP interface and tailoring catalytic activity. This general approach is thus anticipated to be complementary to current NP catalyst design approaches.

Self-Assembly Template Driven 3D Inverse Opal Microspheres Functionalized with Catalyst Nanoparticles Enabling a Highly Efficient Chemical Sensing Platform.

The design of semiconductor metal oxides (SMOs) with well-ordered porous structure has attracted tremendous attention owing to their larger specific surface area. Herein, three-dimensional inverse opal In2O3 microspheres (3D-IO In2O3 MSs) were fabricated through one-step ultrasonic spray pyrolysis (USP) which employed self-assembly sulfonated polystyrene (S-PS) spheres as a sacrificial template. The spherical pores observed in the 3D-IO In2O3 MSs had diameters of about 4 and 80 nm. Subsequently, the catalytic palladium oxide nanoparticles (PdO NPs) were loaded on 3D-IO In2O3 MSs via a simple impregnation method, and their gas sensing properties were investigated. In a comparison with pristine 3D-IO In2O3 MSs, the 3D-IO PdO@In2O3 MSs exhibited a 3.9 times higher response (Rair/Rgas = 50.9) to 100 ppm acetone at 250 °C and a good acetone selectivity. The detection limit for acetone could extend down to ppb level. Furthermore, the 3D-IO PdO@In2O3 MSs-based sensor also possess good long-term stability. The extraordinary sensing performance can be attributed to the novel 3D periodic porous structure, highly three-dimensional interconnection, larger specific surface area, size-tunable (meso- and macroscale) bimodal pores, and PdO NP catalysts.