Morphology Of Nanocatalyst Research Articles

Precisely controlled bimetallic nanocatalysts on mesoporous silica nanoparticle supports for highly efficient and selective nitrate reduction

Monodisperse, bimetallic nanocatalysts, homogeneously supported on mesoporous silica nanoparticles, are demonstrated as highly active, reducing catalysts for rapid and selective nitrate transformation. For this, we finely controlled catalyst size and composition based on new synthesis strategies. Specifically, atomic clusters of Mreducing/Cu nanocatalysts (Mreducing = Pd, Pt) were optimized for nitrate reduction via subsequent Mreducing impregnation (Mreducing/Cu/Mreducing combinations). Reaction kinetics were observed to be affected by the ratio of Mreducing to Cu, for which Pd−rich Pd/Cu/Pd nanocatalysts showed better performance than Cu−rich analogs. Product selectivity (ammonium vs. nitrogen) was highly correlated with nanocatalyst morphology, with nitrogen gas (dominant) selectivity observed for relatively larger Pd particles. Lastly, MSN−Pd/Cu/Pd catalyst are highly stable in water, with no catalyst deterioration over multiple reactions (10 cycles), while maintaining consistently high reaction rates and N2 selectivity. Taken together, this study demonstrates the critical importnace of precise catalyst control and stability towards optimizing nitrate reduction processes.

Catalytic merits of Ni0.6Zn0.4Fe2O4/f-MWCNTS–CS–Asp/Ni2+ for tailoring 1H-benzo [4,5] imidazo [1,2-b] [1,2,4]triazepine motifs through green domino strategy

The magnetic nano catalyst mediated synthesis of heterocycles is one of the most fascinating fields of chemistry due to its proven applicability in high-efficiency, eco-friendly and recyclable heterogeneous catalytic system. In order to design a novel Ni0.6Zn0.4Fe2O4/f-MWCNTs–CS–Asp/Ni2+ magnetic heterogeneous catalyst, Ni0.6Zn0.4Fe2O4-decorated multi walled CNTs were modified with crosslinked chitosan with l-aspartic acid entrapped Ni2+ nanoparticles. This nano catalyst showed significant catalytic activity in the synthesis of biologically potent novel seven membered heterocycles embracing fused 1H-benzo [4,5]imidazo [1,21,2-b][1,2,4]triazepine skeleton. Owing to its interesting structure and being an important pharmacophore fragment, it was endeavored to exploit its synthesis. For the first time considering an exquisite and accomplishable access to construct (Kaur et al., 2021; Jiang et al., 2006; Stern, 1980) [1,2,4]triazepine framework. In addition, the structures of synthesized heterocycles and morphology of nano catalyst were corroborated on the basis of various spectroscopical and microscopical techniques. Furthermore, employing ultrasonication as energy source in the synthesis of magnetic nano catalyst employing 3R's (reduce, recycle and reuse), mild reaction conditions with appreciable yield along with no consumption and production of hazardous chemicals put it under the umbrella of green and sustainable approach.

Assessing Pt and Ni dissolution mechanism and kinetics of shape-controlled oxygen reduction nanocatalysts

An electrochemical flow cell combined with inductively coupled plasma mass spectrometry (FC-ICP-MS) is a powerful tool to understand the mechanisms of metal dissolution and to develop mitigation strategies. Herein, we quantified in situ the amount of Pt and Ni atoms dissolved from PtNi/C nanocatalysts employed to electrocatalyze the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cell cathode. The nanocatalysts feature similar crystallite size and Pt:Ni atomic ratio but different morphologies (spheres, octahedra, sponges). The FC-ICP-MS results reveal that the nanocatalyst morphology affects the dissolution rate of Pt and Ni but not the dissolution mechanism. They also provide analytical evidence that dissolution of Pt atoms is consistently accompanied by the dissolution of Ni atoms exceeding the stoichiometric composition. Furthermore, we demonstrate that ex situ acid leaching mitigates, but does not entirely prevent, the electrochemical dissolution of Ni atoms. Stabilized Pt and Ni dissolution rates were achieved after a one hour long accelerated stress test (AST). We provide evidence that the Pt dissolution rate remains constant before and after the AST. In contrast, the dissolution rate of Ni decreases by a factor of 10 following the AST. Among various nanoparticle shapes, spherical PtNi/C nanoparticles offer the best solution regarding the Pt and Ni retention compared to other nanoparticle shapes.

Ligand-free synthesis of PtPdCu ternary nanostructures with controllable morphologies for efficient methanol oxidation

Nanocatalysts prepared by the ligand-free synthesis method generally exhibit superior catalytic activity due to the absence of ligand interference. Nevertheless, the morphologies of nanocatalysts and the components, particularly for ternary nanoalloys, in ligand-free synthesis are challenging to regulate. In this work, we successfully fabricated a range of ligand-free PtPdCu ternary nanocatalysts with controlled morphologies and sizes employing the Cu2O template sacrificial method while precisely adjusting the components of Pt, Pd, and Cu. The synthesized PtPdCu ternary nanocatalysts have two types: PtPdCu ternary nanodendrites with varied sizes, and PtPdCu ternary nanoboxes with different arm thicknesses. In all the synthesized PtPdCu nanocatalysts, the molar ratio of Pt/Pd is maintained at 1/3, and the proportion of Cu in the ultimate nanocatalysts is positively correlated with the proportion of the initial Cu2O. Due to the synergistic ternary composition, distinct morphology, and unique surface electronic configuration of PtPdCu ternary nanocatalysts, they show significantly enhanced activity and stability for the methanol oxidation reaction. This paper provides novel insights into the ligand-free synthesis of morphology-regulated and multi-component-controlled nanocatalysts, which can be used for high-performance catalysis.

Facet‐Dependent Intrinsic Activity of Single Co3O4 Nanoparticles for Oxygen Evolution Reaction

AbstractDeciphering the influence of nanocatalyst morphology on their catalytic activity in the oxygen evolution reaction (OER), the limiting reaction in water splitting process, is essential to develop highly active precious metal‐free catalysts, yet poorly understood. The intrinsic OER activity of Co3O4 nanocubes and spheroids is probed at the single particle level to unravel the correlation between exposed facets, (001) vs. (111), and activity. Single cubes with predominant (001) facets show higher activity than multi‐faceted spheroids. Density functional theory calculations of different terminations and reaction sites at (001) and (111) surfaces confirm the higher activity of the former, expressed in lower overpotentials. This is rationalized by a change in the active site from octahedral to tetrahedral Co and the potential‐determining step from *OH to *O for the cases with lowest overpotentials at the (001) and (111) surfaces, respectively. This approach enables the identification of highly active facets to guide shape‐selective syntheses of improved metal oxide nanocatalysts for water oxidation.

Photoelectrochemical Hydrocarbon Oxidation Augmented By Plasmonic Nanostructures

Solar energy can be absorbed via surface plasmon resonance (SPR) to promote excitation of energetic, or “hot”, charge carriers that can be locally transferred or thermally dissipated to augment photocatalytic processes. The “hot” carriers can selectively drive energy-intensive photoelectrochemical reactions at low temperatures by activating adsorbed reactants and accelerating surface kinetics. Plasmonically-sensitized nanocatalysts were investigated for their photocatalytic and photoelectrochemical oxidation of ethanol, with an emphasis on carbon-carbon bond cleavage, under solar simulated-light irradiation. Material approaches included the (i) SPR-functionalization of a traditional metal oxide semiconductor (TiO2) and (ii) bimetallic nanocatalysts composed of epitaxially photodeposited catalytic Pd at targeted locations on plasmonic Au nanorods. Results are correlated with nanocatalyst morphology, composition, and homogeneity to maintain SPR-induced charge separation and mitigate carbon monoxide poisoning. Ensemble photoelectrochemical measurements were complimented with single-particle dark-field scattering and photoluminescence spectroscopies to understand the extraction and utilization of SPR-excited “hot” carriers. Ethanol oxidation was achieved, yielding a solar-driven method for low temperature, complete photo-oxidation of complex hydrocarbons via plasmonic photocatalysis.

Crystal structure engineering in multimetallic high-index facet nanocatalysts.

In the context of metal particle catalysts, composition, shape, exposed facets, crystal structure, and atom distribution dictate activity. While techniques have been developed to control each of these parameters, there is no general method that allows one to optimize all parameters in the context of polyelemental systems. Herein, by combining a solid-state, Bi-influenced, high-index facet shape regulation strategy with thermal annealing, we achieve control over crystal structure and atom distribution on the exposed high-index facets, resulting in an unprecedentedly diverse library of chemically disordered and ordered multimetallic (Pt, Co, Ni, Cu, Fe, and Mn) tetrahexahedral (THH) nanoparticles. Density functional theory calculations show that surface Bi modification stabilizes the {210} high-index facets of the nanoparticles, regardless of their internal atomic ordering. Moreover, we find that the ordering transition temperatures for the nanoparticles are dependent on their composition, and, in the case of Pt3Fe1 THH nanoparticles, increasing Ni substitution leads to an order-to-disorder transition at 900 °C. Finally, we have discovered that ordered intermetallic THH Pt1Co1 nanocatalysts exhibit a catalytic performance superior to disordered THH Pt1Co1 nanoparticles and commercial Pt/C catalysts toward methanol electrooxidation, highlighting the importance of crystal structure and atom distribution control on high-index facets in nanoscale catalysts.

Surface and length effects for aqueous electrochemical reduction of CO2 as studied over copper nanowire arrays

Knowing efficient strategies for improving activity and selectivity of catalysts is critical for the development of nanocatalysts. Herein, we demonstrate that surface effect and length effect both play an important role in the catalytic activity and selectivity of copper nanowire arrays for aqueous electrochemical reduction of CO2. To be specific, the faradaic efficiency and reaction rate of hydrogen evolution decreased with the CO2 reduction activity increased when the grain-boundary density and nanowire length became higher at applied potentials. The effect of length alone was able to slightly promote the electrochemical reduction of CO2. Thus, future efforts can be applied to the synergetic effects of surface and morphology of nanocatalysts, especially copper catalysts, for aqueous electrochemical CO2 reduction.

Insight into the effect of facet-dependent surface and oxygen vacancies of CeO2 for Hg removal: From theoretical and experimental studies

The reaction mechanisms of Hg oxidation on CeO2(111) and (110) surface are clarified by a group of designed experiments and density functional theory (DFT) calculations. CeO2 nanorods and nanoparticles with exposure (110) and (111) faces were prepared by hydrothermal methods, and their morphological properties were investigated using XRD, XPS and HRTEM. Combined experimental and DFT results, the nanorods show better activity than nanoparticles. The total oxidation of Hg can be partially prohibited by the high barriers for the incorporated chlorine activation at reduced surfaces, due to the strong electronic repulsion of heavily accumulated charges. The energy barrier profiles suggest Hg oxidation is much more favorable on CeO2(110) surface than that on CeO2(111) surface. In the Hg oxidation via HCl and O2, the role of O2 is not only replenishment of lattice oxygen, but also could generate surface oxygen as active center for HCl active. The complete catalytic cycle can be identified as four parts: (i) HCl activated by lattice oxygen, (ii) Hg oxidation on defect surface, (iii) HCl activated by adsorbed oxygen and (iv) Hg oxidation on stoichiometric surface. The results of this study provide deep insights into the effects of CeO2 nanocatalyst morphology on the Hg oxidation.

The shape effect of La2O2CO3 in Pd/La2O2CO3 catalyst for selective hydrogenation of cinnamaldehyde

Controllably adjusting the morphology of nanocatalysts is known as an effective way to improve catalytic performance. Pd/La2O2CO3 catalysts with different morphologies (nanorods and nanoparticles) were successfully synthesized via simple hydrothermal method and evaluated for selective hydrogenation of cinnamaldehyde. The highly catalytic activity (86% HCAL selectivity at 100% CAL conversion at 3h) occurred over Pd/La2O2CO3-NRs with La2O2CO3 nanorods as support. Remarkably, Pd/La2O2CO3-NRs catalyst not only showed better catalytic performance, nearly 10 times higher than Pd/La2O2CO3-NPs catalyst, but also exhibited excellent cycling stability. CO2-TPD showed that the intense desorption peaks at about 560K represented the medium-strength basic sites (La3+–O2− pairs) with a total amount of 0.13mmolg−1 on the La2O2CO3-NPs and 0.21mmolg−1 on the La2O2CO3-NRs. These results indicated that support morphology has a significant effect on catalytic activity and can modify surface basicity, which resulting in enhanced hydrogenation activity.

Molecular dynamics simulations of ternary PtxPdyAuz fuel cell nanocatalyst growth

Molecular dynamics simulation of PEMFC cathodes based on ternary Pt70Pd15Au15 and Pt50Pd25Au25 nanocatalysts dispersed on carbon indicate systematic Au segregation from the particle bulk to the surface, leading to an Au layer coating the cluster surface and to the spontaneous formation of a Pt@Pd@Au core–shell structure. For Au content below 25 at%, surface PtxPdy active sites are available for efficient oxygen reduction reaction, in agreement with DFT calculations and experimental data. Simulations of direct core@shell system prepared in conditions mimicking those of plasma sputtering deposition pointed out an increase of the number of accessible PtxPdy surface active sites. Core-shell nanocatalyst morphology changes occur due to impinging Pt kinetic energy confinement and dissipation.

Effects of Co3O4 nanocatalyst morphology on CO oxidation: Synthesis process map and catalytic activity

This study focuses on drawing a hydrothermal synthesis process map for Co3O4 nanoparticles with various morphologies and investigating the effects of Co3O4 nanocatalyst morphology on CO oxidation. A series of cobalt-hydroxide-carbonate nanoparticles with various morphologies (i.e., nanorods, nanosheets, and nanocubes) were successfully synthesized, and Co3O4 nanoparticles were obtained by thermal decomposition of the cobalt-hydroxide-carbonate precursors. The results suggest that the cobalt source is a key factor for controlling the morphology of cobalt-hydroxide-carbonate at relatively low hydrothermal temperatures (≤ 140 °C). Nanorods can be synthesized in CoCl2 solution, while Co(NO3)2 solution promotes the formation of nanosheets. Further increasing the synthesis temperature (higher than 140 °C) results in the formation of nanocubes in either Co(NO3)2 or CoCl2 solution. The reaction time only affects the size of the obtained nanoparticles. The presence of CTAB could improve the uniformity and dispersion of particles. Co3O4 nanosheets showed much higher catalytic activity for CO oxidation than nanorods and nanocubes because it has more abundant Co3+ on the surface, much higher reducibility, and better oxygen desorption capacity.

Nano-cellulose-OSO3H as a new, green, and effective nano-catalyst for one-pot synthesis of pyrano [4,3-b] pyrans

A facile, green, and efficient method has been developed for the synthesis of biologically important pyrano [4,3-b] pyrans in the presence of nano-cellulose-OSO3H as a new solid acid catalyst. The reaction involves the use of 4-hydroxy-6-methyl-2H-pyran-2-one, malononitrile, and aldehydes. A wide range of aldehydes is compatible in this reaction, producing excellent yields in short time. The morphology of nano-catalyst (nano-cellulose-OSO3H) was observed using a scanning electron microscopy (SEM). The cellulose-OSO3H surface was studied by the energy dispersive X-ray spectroscopy (EDX) method to find out the chemical composition. The decomposition steps and thermal stability of the catalyst were investigated by thermal analysis techniques (TGA/DTG). In addition, the vibrational spectrum analysis (FT-IR) and X-ray diffractogram (XRD) of the catalyst have been performed.

Nano-sawdust–BF3 as a new, cheap, and effective nano catalyst for one-pot synthesis of 2-amino benzo[h]chromene derivatives

An atom-efficient, three-component synthetic methodology has been developed for the preparation of biologically important 2-amino benzo[h]chromene using nano-sawdust–BF3 as a new catalyst. The reaction involves the use of 2-naphthol, malononitrile, and various aldehydes. A wide range of aldehydes is compatible in this reaction, producing excellent yields in short time. The morphology of nanocatalyst (nano-sawdust–BF3) was observed using a scanning electron microscopy. Also, the sawdust–BF3 surface was studied by energy dispersive X-ray spectroscopic method to find out the chemical composition.

Nano-sawdust-OSO3H as a new, cheap and effective nanocatalyst for one-pot synthesis of pyrano[2,3-d]pyrimidines

An atom-efficient, three-component synthetic methodology has been developed for the preparation of biologically important pyrano[2,3-d]pyrimidines using nano-sawdust-OSO3H as a new catalyst. The reaction involves the use of barbituric acid or thiobarbituric acid, malononitrile and aldehydes. A wide range of aldehydes is compatible in this reaction, producing excellent yields in short time. The morphology of nanocatalyst (nano-sawdust-OSO3H) was observed using a scanning electron microscopy (SEM). The decomposition steps and thermal stability of the catalyst were investigated by thermal analysis techniques (TGA/DTG). The sawdust-OSO3H surface was studied by energy dispersive X-ray spectroscopy (EDX) method to find out the chemical composition. Also, the vibrational spectrum analysis (FT-IR) of the catalyst has been performed.

Influence of oxide buffer layers on the growth of carbon nanotube arrays on carbon substrates

Controllable growth of carbon nanotube (CNT) arrays on carbon substrates requires an oxide buffer layer material such as Al2O3 and SiO2. This research analyzes the influence of these buffer layers on a model carbon substrate composed of pyrolyzed carbon film on flat silicon. Electron microscopy was used to analyze nanocatalyst morphology, particle density, CNT nucleation rate, and CNT morphology for selected growth conditions. It was observed that nanotubes grown on Al2O3 buffer layers had the fastest CNT nucleation rates and more uniform tube diameters, with residual nanocatalyst particles having elongated shapes. In contrast, CNTs formed on SiO2 buffer layers nucleated slower and had more variation in tube diameters, while the nanocatalyst particles remained spherical. Comparisons among SiO2 buffer layers deposited using three different techniques—atomic layer deposition, microwave plasma enhanced chemical vapor deposition and thermal oxidation—indicated that surface roughness plays an important role. Silica layers with the highest roughness had the highest catalytic particle density and tallest carpet height for identical growth conditions. These results provide new insight into the importance of buffer layer chemistry and morphology on growth and controllability of CNT arrays.

Morphology Effect of Ir/La2O2CO3 Nanorods with Selectively Exposed {110} Facets in Catalytic Steam Reforming of Glycerol

Tuning the morphology of nanocatalysts has been regarded as a powerful approach to high-performance heterogeneous catalysts, since the highly active facets might be selectively exposed to reactants. Herein, we report how the shape effect significantly improves the performance of Ir/La2O2CO3 catalyst in the steam reforming of glycerol at high temperatures up to 650 °C toward a sustainable hydrogen production. La2O2CO3 nanorods (NRs) with different sizes and aspect ratios were synthesized for supporting Ir nanoparticles. Compared with conventional Ir/La2O2CO3, the NR catalysts considerably improved the activity, selectivity, and stability, allowing for a stable hydrogen production for 100 h without obvious deactivation. The role of the NRs was rationalized by XRD, XPS, TPR, TPD, and HRTEM analysis. The high performance of the NR catalyst is elucidated by the formation of hexagonal La2O2CO3 NRs with selectively exposed {110} facets under reaction conditions, which strongly interact with Ir catalysts, thereby...

Preparation and characterization of Fe-V/TiO2-SiO2 nanocatalyst modified by zinc

The Fe-V/TiO2-SiO2 nanocatalyst promoted with zinc is prepared by combination of sol-gel and wetness impregnation methods. The effects of different weight percentages of iron, vanadium and zinc, titania to silica mole ratio, synthesis temperature and heating rate of calcination on the structure and morphology of nanocatalyst are investigated. Results showed that the modified nanocatalyst containing 40 wt% of Fe, 12 wt% of V and 2 wt% of zinc (all on weight percent) supported on TiO2-SiO2 with synthesis temperature of 45 °C has highest surface area, pore volume and pore diameter. Characterizations of catalysts were carried out using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectrometry, scanning electron microscopy (SEM), vibrating sample magnetometry (VSM) and N2 physisorption measurements. It was found that the nanocatalyst has a particle size about 56 nm and its saturation magnetization factor is equal to 10.173 emu/g. The catalyst can easily be separated from medium by a magnet.

Preparation and characterization of V/TiO2 nanocatalyst with magnetic nucleus of iron

A magnetic composite containing V/TiO2 was prepared by combination of sol–gel and wetness impregnation methods. The effects of synthesis temperature, different weight percents of Fe supported on TiO2, vanadium loading and the heating rate of calcination on the structure and morphology of nanocatalyst were investigated. The optimum conditions for synthesized catalyst were 40wt.% of Fe, 15wt.% of V and synthesis temperature equal to 30°C. Characterization of catalyst is carried out using XRD, TGA, DSC, SEM, FTIR and N2 physisorption measurements. The magnetic character of nanocatalyst was measured using VSM, which showed the typical paramagnetic behavior of sample at room temperature with a saturation magnetization value equal to 8.283emu/g. The nanocatalyst has a particle size about 56nm and can easily be separated from medium by a magnet.

Electrochemical Behavior and Morphology of Nano Catalyst for Fuel Cell: The effect of Ultrasonic and Microwave Techniques

In this work, we succeed to prepare the Pt/C and PtRu/C composite electrodes by thermal, sonochemical and microwave methods. The synthesized catalysts are nano uniform particles of 1-6 nm diameters, deposited on pretreated Vulcan carbon 30-50 nm sized aggregates. The pH has important effect on reduction efficiency, the structure and particle-size distribution of synthesized catalyst. The ultrasonification gives smaller and more uniform nano particles than others. The electrochemical measurements of composite electrode in methanol showed that oxidation is irreversible and incompleted, the current density increase with pH and the ultrasonic irradiation gives the best catalytic performance.