Nano-sized Catalysts Research Articles

Magnetic nano-sized solid acid catalyst bearing sulfonic acid groups for biodiesel synthesis and oxidation of sulfides

In this study, the AlFe2O4@n-Pr@Et-SO3H heterogeneous catalyst was successfully synthesized and utilized to produce biodiesel from oleic acid through an esterification process and to oxidize sulfides. To examine the physicochemical characteristics of the AlFe2O4@n-Pr@Et-SO3H nanomaterial, a variety of advanced techniques were employed, including Fourier Transform infrared spectroscopy (FT-IR), Field emission scanning electron microscopy (FE-SEM), Energy dispersive X-ray spectroscopy (EDX), Vibrating sample magnetometer (VSM), Elemental Mapping, Transmission electron microscopy (TEM), Inductively coupled plasma (ICP), and X-ray diffraction (XRD). The AlFe2O4@n-Pr@Et-SO3H materials demonstrated excellent performance in both the esterification of oleic acid and the oxidation of sulfides. Moreover, the catalyst can be easily recovered and reused multiple times without a significant reduction in its effectiveness.

Structure-Reactivity Relationship of Zeolite-Confined Rh Catalysts for Hydroformylation of Linear α-Olefins.

Substituting the molecular metal complexes used in the industrial olefin hydroformylation process is of great significance in fundamental research and practical application. One of the major difficulties in replacing the classic molecular metal catalysts with supported metal catalysts is the low chemoselectivity and regioselectivity of the supported metal catalysts because of the lack of a well-defined coordination environment of the metal active sites. In this work, we have systematically studied the influences of key factors (crystallinity, alkali promoters, etc.) of the Rh-MFI zeolite catalysts on their performances for the hydroformylation of long-chain α-olefins (LAOs). With the help of comprehensive spectroscopy and electron microscopy characterization results, we can correlate the structural features of various Rh-MFI catalysts and their catalytic performances. The resultant structure-reactivity relationship guides us to prepare a nanosized Rh-MFI catalyst, which exhibits about a 3-fold improvement in specific activity compared to the Rh-MFI catalyst with conventional crystallite sizes and maintains very high regioselectivity for hydroformylation of LAOs.

Scale and morphology design of metal-based catalysts for enhanced Li–CO2 battery performance

This review clarifies the significant influence of nano-sized catalysts with various sizes and morphologies on catalytic performance (coordination number, electronic state, adsorption energy, etc.).

Understanding the Mechanism of Evaporation-Induced Islands during the Formation of Catalyst Layers and Their Influence on the Alkaline Oxidation Evolution Reaction

Advancements in anode development substantially reduce the cost and enhance the performance of water electrolysis. The strategic configuration of nano-sized catalyst materials on anode supports is a pivotal factor in the expansion of the production of catalyst layers and has a significant influence on their electrochemical performance [1–3]. Therefore, it is essential to understand the structure formation mechanisms during electrode fabrication. This contribution aims to explore the inherent drying mechanisms in the coating process and their subsequent influence on the morphological evolution of anodes, ultimately establishing a linkage between these morphological changes and electrochemical performance and stability metrics. The initial phase of the study involved a detailed characterization of commercial nickel cobalt oxide nanoparticles via advanced analytical techniques, including transmission electron microscopy and energy-dispersive X-ray spectroscopy [4]. Subsequently, a stable ink was formulated by dispersing the catalyst alongside a binder in a solvent, which was then uniformly applied to a conductive nickel plate utilizing an ultrasonic spray coater. Prior to application, the catalyst inks underwent optimization based on the Hansen solubility parameters of catalyst materials [5, 6] and subsequent visualization of their stability and dispersibility characteristics through transmittogram analysis [7]. The drying process of the coating was conducted at two distinct temperatures, 50 °C and 150 °C, to investigate the effect of temperature on solvent evaporation. Morphological and structural analyses of the anodes were subsequently performed using scanning electron microscopy (SEM), laser scanning microscopy (LSM), and atomic force microscopy (AFM), providing insight into the alterations induced by the drying process. The analyses conducted in this study elucidate significant modifications in the morphology of the layer structures attributable to variations in drying temperatures as illustrated in Figure 1. Specifically, lower temperature resulted in reduced evaporation rates that facilitated the formation of larger, isolated regions/islands on the anode support. These are indicative of a non-uniform coating distribution. In contrast, a higher temperature promoted rapid evaporation, resulting in a quite homogeneous distribution of smaller islands accompanied by the emergence of voids within the anode layer. Electrochemical analysis revealed that these morphological changes are of vital importance: they govern the wetting behaviour and the dynamics of bubble formation which are important for the electrochemical performance and durability of the catalyst layers. Moreover, the insights gleaned from this study are instrumental in identifying optimal configurations of catalyst layer structures, i.e., features that should be maintained during scale-up. In conclusion, this study significantly advances the field by revealing novel principles governing the design and optimization of electrode structures for the oxygen evolution reaction. In particular, the complicated relationship between drying temperatures and morphological evolution, which significantly influences electrochemical performance is explained.

Selective oxidation of styrene to valuable C7 or C8 aromatics via green photocatalysis with TiO2-based catalysts

The selective oxidation of styrene at its side chains to yield value-added C7 or C8 aromatic compounds represents a crucial reaction within the chemical industry. However, achieving precise control over product formation selectivity poses a significant challenge. In this study, we demonstrate the effectiveness of ultra-small nanosized TiO2-based catalysts in facilitating the selective oxidation of styrene through a mild, eco-friendly photocatalytic approach. Following modification with 0.4% NiO, a notable transformation in product selectivity is observed. The primary products shift from C8 with 96% selectivity to C7 with 92% selectivity under UV, and even sunlight-type excitation. Detailed structural and electronic analyses reveal that the incorporation of NiO onto the TiO2 surface induces the formation of a P-N heterojunction and additional active sites, crucial for promoting C-C cleavage, leading to a selectivity shift from C8 to C7 products. This research provides valuable insights into the design of simple TiO2-based catalysts capable of achieving high selectivity in the oxidation of styrene, highlighting the potential of green photocatalysis in industrial applications.

Ni-Fe2O3@SiO2-Pr-DBU: A novel efficient magnetically retrievable catalyst for one-pot synthesis of dihydropyrano [3,2-c] chromene

In the present work, Ni-Fe2O3@SiO2-Pr-DBU was synthesized as a novel magnetically separable nano-catalyst and characterized by various techniques like Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy (SEM), Vibrating-sample magnetometry (VSM), Transmission electron microscopy (TEM) and Elemental analysis by energy dispersive X-ray (EDX). The catalytic efficiency of NiFe2O3@SiO2-Pr-DBU was explored in the synthesis of dihydropyrano[3,2-c] chromenes through a one-pot multicomponent reaction of 4-hydroxycoumarin, malononitrile, and aryl aldehydes in aqueous solution at ambient temperature condition. An external magnet easily removed the nano-sized magnetic core catalyst from the synthesized reaction mixture. It was recycled for five successive runs while maintaining its potential and adhering to our green synthesis approach. We used dihydropyrano chromene, a highly biologically active commercial compound, to prepare some novel derivatives.

Single B-doped palladium electrocatalyst Enabling direct cathodic coupling of carbon dioxide with methanol into dimethyl carbonate

Dimethyl carbonate (DMC) is a green chemical of large market demand with widespread applications. Direct cathodic coupling of carbon dioxide (CO2) with methanol (CH3OH) into DMC represents a green and sustainable electrochemical route yet remains a great challenge. Reported electrochemical syntheses of DMC from CO2 and CH3OH necessitate the use of toxic methyl iodine or carcinogenic propene oxide. Herein, we for the first time employ a nanosized B-doped palladium catalyst (Pd-B) to realize the direct electrosynthesis of DMC through cathodic coupling of CO2 and CH3OH, which no longer requires any hazardous reagent. Under the optimal condition, the DMC Faradaic efficiency reaches to 47.5 % at 30 mA/cm2, and the yield of DMC is up to 257.3 umol.h−1. A thorough mechanistic investigation has proven that the DMC electrochemical synthesis in our work involves three cascade reactions including CO2-to-CO reduction, methanol-to-methoxide (CH3O–) activation and coupling of CO with CH3O–, simultaneously occurring on the surface of Pd-B catalyst assisted by bromine (Br2) generated at the anode. Two key intermediates in the decisive coupling step, CH3OCO* and CH3O*, are detected on the surface of Pd-B catalyst by In situ ATR-SEIRAS. This work provides a first example of direct cathodic coupling of CO2 and CH3OH into DMC, and the mechanistic investigations in this work will benefit the future design of advanced Pd-based catalysts toward DMC electrosynthesis.

Analyzing the active sites of carbocatalyst for peroxydisulfate activation: Specific surface area or electrochemical surface area?

Persulfates activation by various nanomaterials has been intensively reported for advanced oxidation processes (AOPs), and substantial progress has been made in understanding the mechanism. However, most of the published articles only present the unnormalized catalytic properties, which generated confusion to compare different catalysts and identify the active sites. Herein, we presented electrochemical surface area (ECSA) as a practical normalized method and confirmed the primary active sites in N-doped graphene. By controlling the aggregation state of graphene sheets to adjust the activity of doped graphite-N species, the active sites for peroxydisulfate (PDS) activation were accurately estimated. In further experiments, specific surface area (SSA, by N2-physisorption and methylene blue adsorption) and ECSA were adopted to conclude the normalized oxidation rate constant and graphitic-N was confirmed as the primary site in nitrogen-doped graphene for the carbocatalyst/PDS system. The normalized results revealed that SSA derived from inert gas on materials could not reflect the true active sites at solid-liquid interface, while ECSA considering the operated solid-liquid situation can be used for accurate estimation of the active sites. Therefore, this study suggests that ECSA integrates the properties of both kinetics and thermodynamics, which can be adopted as a useful methodology for analyzing nano-sized environmental catalysts performance.

One-step combustion synthesis of high-performance nanosized Co3O4 and Ag-Co3O4 catalysts for propane total oxidation

Devising an effective strategy to refine the physicochemical properties of Co3O4 and tune the Ag-Co interaction is pivotal for developing superior Ag-Co3O4 catalysts targeting VOCs abatement. In this study, nanosized Co3O4 and Ag-Co3O4 (Ag content of 0.5–5.0 wt%) catalysts were prepared via a facile one-pot urea combustion method. The as-prepared catalysts were characterized using various techniques and their performance in propane total oxidation was evaluated. Compared to its counterpart obtained through the direct decomposition of cobalt nitrate, the nanosized Co3O4 exhibited a larger surface area, more oxygen vacancies, better reducibility, and thus superior propane oxidation activity. The addition of Ag can further enhance the catalytic performance by significantly improving the redox properties of Co3O4. The best performance was achieved with the catalyst 3.5 wt% Ag-Co3O4, which mineralized 90 % of propane into CO2 at 200 °C and exhibited excellent cycling stability and long-term durability. In addition, 3.5 wt% Ag-Co3O4 demonstrated high activity under various conditions, including high propane concentration (6000 ppm), high space velocity (160,000 mL g−1h−1), and high water content (10 vol%), making it a promising candidate for practical VOCs removal.

Palladium nanoparticles anchored on NiO particles-modified micro-size chitosan spheres: A promising, active, and retrievable catalyst system for treatment of environmental pollutants

Efficient treatment of toxic organic pollutants in water/wastewater by using innovative, cost efficient, and simple technologies has recently become an important issue worldwide. Remediation of these pollutants with chemical reduction in the presence of a nano-sized catalyst and a reducing agent is one of the most useful methodologies. In the present study, we have designed a promising heterogeneous catalyst system (Pd@CS-NiO) by easy and efficient stabilization of palladium nanoparticles on the surface of microspheres composed of chitosan (CS)-NiO particles (CS-NiO) for the reduction of organic pollutants. The nano-structure of the developed Pd@CS-NiO was successfully validated using FE-SEM, XRD, EDS, TEM, and FTIR/ATR and its particles size was determined as 10 nm. The catalytic power of Pd@CS-NiO was then assessed in the reduction of 4-nitro-o-phenylenediamine (4-NPDA), 4-nitrophenol (4-NP), 4-nitroaniline (4-NA), 2-nitroaniline (2-NA), and some organic dyes, namely methylene blue (MB), methyl orange (MO), and rhodamine B (RhB) in aqueous medium at room temperature. The reductions were thoroughly studied spectro-photometrically. The tests displayed that the synthesized Pd@CS-NiO was a highly active and useful catalyst that reduced these pollutants in 0–145 s. Moreover, the rate constants for 2-NA, 4-NP, 4-NA, 4-NPDA, MO, and RhB were found to be 0.017 s−1, 0.011 s−1, 0.006 s−1, 0.013 s−1, 0.023 s−1, and 0.03 s−1, respectively. Moreover, the recycling test indicated that Pd@CS-NiO may be recovered easily thanks to its micro size nature and could be used up to seven steps, confirming its practical application potential.

Supported nano-sized precious metal catalysts for oxidation of catalytic volatile organic compounds.

Volatile organic compounds (VOCs) are common contaminants found as indoor as well as outdoor pollutants, which can induce acute or chronic health hazards to the human physiological system. The catalytic oxidation method is widely considered as one of the effective methods for removing VOCs, and the development of highly effective catalysts is highly urgent for booming this interesting field. This review focuses on the recent progress of VOC oxidation catalyzed by supported nano-sized precious metal catalysts, and discusses the effects of metal composition, supports, size, and morphology on the catalytic activity. In addition, the roles played by both nano-sized precious metals and supports in enhancing the performance of catalytic VOCs are also systematically discussed, which will guide the further development of more advanced VOC catalysts.

Mechanochemical and Sonochemical Obtaining of Nanosized Oxides Materials and Catalysts: A Review

Mechanochemical and Sonochemical Obtaining of Nanosized Oxides Materials and Catalysts: A Review

Nanosized curing catalyst via nano-templated plasma PVD for attaining superior low-cure powder coating films

The addition of curing catalysts into powder coating is a key method to fabricate low-temperature curing powder coating for reducing energy consumption and expanding its applications to heat-sensitive substrates. However, the heterogeneous dispersion of the unmodified catalysts in powder coatings results in inconsistent catalysis of resin crosslinking, thus leading to compromised surface smoothness and gloss. Utilizing nanosized catalysts is an efficient solution to such problems. In this paper, we propose a nano-templated dielectric barrier discharge (DBD) plasma-assisted physical vapor deposition (PVD) strategy to fabricate the nanosized catalysts. The curing catalyst, 2-ethylimidazole (2-elm), is successfully vaporized and deposited on nano-carrier SiO2 (SiO2-NPs) in the DBD plasma reactor at atmospheric pressure, producing 2-elm@SiO2-NPs. The mechanical strength and chemical resistance of finishes of powder coating incorporated with the 2-elm@SiO2-NPs remained at low curing temperature (170 °C for 15 min) and fast curing condition (190 °C for 8 min). In addition, their surface qualities are comparable to that of the original powder coating, with up to 100 % gloss retention, successfully eliminating the issue of more than 25 % gloss attenuation of the powder coating with unmodified 2-elm. This study provides an effective, solvent-free strategy for fabricating nanosized curing catalysts and achieving high-quality film finishes.

Surface exsolved NiFeOx nanocatalyst for enhanced alkaline oxygen evolution catalysis

A synergistically improved alkaline oxygen evolution catalyst of the NiFeOx nanoalloy oxide structure is introduced using an in-situ exsolution method. The separately doped Ni and Fe ions are exsolved on the surface of the perovskite as homogeneously distributed NiFeOx oxide alloy catalysts via following reduction and oxidation processes. The incorporation of additional Fe into the surface embedded NiFeOx catalyst improved the inherent oxygen evolution reaction (OER) property with fast reaction kinetics. Density functional theory (DFT) result indicates the lowest OER overpotential of NiFeOx catalyst is originated from the reduced energy barrier of surface *O formation from *OH group. The NiFeOx exsolved catalyst shows the smallest overpotential of 0.49 V (j = 10 mA∙cm−2) and Tafel slope (93 mV∙dec-1), compared with that of single NiO (0.54 V, 132 mV∙dec-1) and Fe3O4 catalyst. This study provides an effective method for developing nanosized OER catalysts for various energy conversion and storage electrode materials.

Fabrication of silver nanoparticles decorated on sodium alginate microbeads enriched with keratin and investigation of its catalytic and antioxidant activity

In this study, an environmentally friendly, effective, easily synthesizable and recoverable nano-sized catalyst system (Ag@NaAlg-keratin) was designed by decorating Ag nanoparticles on microbeads containing sodium alginate (NaAlg) and keratin obtained from goose feathers. The structure, morphology and crystallinity of the Ag@NaAlg-keratin nanocatalyst were evaluated by XRD, FT-IR, FE-SEM, EDS/EDS mapping and TEM analyses. Catalytic ability of designed Ag@NaAlg-keratin nanocatalyst was then investigated against 4-nitrophenol (4-NP) and methyl orange (MO) reductions. Ag@NaAlg-keratin nanocatalyst effectively reduced 4-NP in 6 min and MO in 5 min, with rate constants of 0.17 min−1 and 0.16 min−1, respectively. Additionally, activation energies (Ea) were found as 39.8 kJ/mol for 4-NP and 37.9 kJ/mol for MO. Performed recyclability tests showed that the Ag@NaAlg-keratin nanocatalyst was easily recovered due to its microbead form and successfully reused five times, maintaining both its activity and structure. Furthermore, antioxidant activity of Ag@NaAlg-keratin nanocatalyst was the highest (73.16 %).

Dual-catalytic activation of Pt and MoSxOy on carbon nanofibers for NO2 sensors

To achieve highly sensitive chemiresistive gas sensors, facile and effective synthesis for catalytic decoration is essential on an electrically conductive scaffold containing a large surface area and high porosity. Herein, we report a new synthetic strategy for the functionalization of one-dimensional carbon nanofibers (CNFs) using dual-catalytic nanoparticles (NPs) of both oxygen-incorporated MoS2 (MoSxOy) and Pt. The functionalized CNFs were synthesized through an electrospinning process followed by heat treatment in a reducing ambient to ensure the decoration of ultra-small MoSxOy and Pt NPs along the CNFs (Pt-MoSxOy@CNFs). As a result, Pt-MoSxOy@CNFs exhibited an improved sensing response of 39.6% toward 5 ppm of NO2 as compared to the responses of pristine CNFs (7.3%) and MoSxOy@CNFs (13.7%) at room temperature. At the optimized operating temperature of 150 °C, the Pt-MoSxOy@CNFs exhibited a 5.8-fold higher response than that of the pristine CNFs and also presented fully reversible and selective sensing properties. The enhanced NO2 sensing properties were primarily attributed to the chemical sensitization of Pt NPs toward NO2 and a p-n heterojunction between the CNFs and MoSxOy NPs. This study demonstrates the uniform distribution of multiple nano-sized catalysts on CNFs, paving the way for establishing multiplexed sensor arrays and application in electronic nose systems.

A sulfur-modified pore-blocking method to enhance the electrocatalytic stability of carbon-supported platinum nanoparticles.

Currently, the durability of electrode materials remains a big obstacle to the widespread adoption of proton exchange membrane fuel cells (PEMFCs). Herein thiourea and sodium dodecyl benzene sulfonate (SDS) were employed as sulfur source and carbon source to modify the pristine carbon black (Ketjen black EC300 J). A highly durable carbon supported Pt nanosized catalyst with higher platinum utilization for oxygen reduction reaction (ORR) in PEMFCs was produced by doping elemental sulfur into carbon supports and decreasing the carbon pore sizes and volume through a successive impregnation technique. The catalyst exhibits an initial activity of 0.167 A mgPt -1 at 0.90 V and demonstrates minimal activity loss after acceleration stress test (30,000 cycles of AST). The half-wave potential loss for representative sample (Pt/S-C-3) is only 14 mV with only 21.8 % ECSA decrease, 27.5 % MA loss and 5.9 % SA loss. A sintering test at various temperature shows a minor average size increase for sulfur-doped carbon (S-C) supported one (from 2.09 to 2.52 nm). In single-cell test, the MEA sample employing the platinum catalyst on modified carbon as cathode exhibited almost negligible performance loss after 30,000 cycles of AST.

Inorganic Fe-O and Fe-S oxidoreductases: paradigms for prebiotic chemistry and the evolution of enzymatic activity in biology.

Oxidoreductases play crucial roles in electron transfer during biological redox reactions. These reactions are not exclusive to protein-based biocatalysts; nano-size (<100nm), fine-grained inorganic colloids, such as iron oxides and sulfides, also participate. These nanocolloids exhibit intrinsic redox activity and possess direct electron transfer capacities comparable to their biological counterparts. The unique metal ion architecture of these nanocolloids, including electron configurations, coordination environment, electron conductivity, and the ability to promote spontaneous electron hopping, contributes to their transfer capabilities. Nano-size inorganic colloids are believed to be among the earliest 'oxidoreductases' to have 'evolved' on early Earth, playing critical roles in biological systems. Representing a distinct type of biocatalysts alongside metalloproteins, these nanoparticles offer an early alternative to protein-based oxidoreductase activity. While the roles of inorganic nano-sized catalysts in current Earth ecosystems are intuitively significant, they remain poorly understood and underestimated. Their contribution to chemical reactions and biogeochemical cycles likely helped shape and maintain the balance of our planet's ecosystems. However, their potential applications in biomedical, agricultural, and environmental protection sectors have not been fully explored or exploited. This review examines the structure, properties, and mechanisms of such catalysts from a material's evolutionary standpoint, aiming to raise awareness of their potential to provide innovative solutions to some of Earth's sustainability challenges.

Fe-doped TiO2/PVDF-HFP electrospun membranes for tetracycline photocatalytic degradation under visible light

Heterogeneous photocatalysis operated under visible light is considered an efficient and ecofriendly method to remove pharmaceuticals from water streams. However, the recovery of the nano-sized catalyst particles limits this technology to small-scale applications. In this study, we prepared Fe-doped P25 TiO2 photocatalysts and immobilized them over PVDF-HFP electrospun membranes for the photocatalytic degradation of Tetracycline antibiotic under visible light. To ensure uniform distribution of the nanoparticles on the fibers, the electrospinning voltage and the weight percentage of TiO2 were varied, and two preparation methods were applied to disperse the catalyst in the polymeric solution. In order to maximize the visible light exposure of the membranes, 3D printed membrane holders with square and circular shapes were designed to immerse the membrane in Tetracycline solution. The results showed that immobilizing P25 catalysts on the fibers of the membranes limited their visible light absorption when the light source was assembled on the top of the aqueous reaction medium. This occurred due to the membrane's opacity limited light penetration, resulting in uneven irradiation throughout its depth. Based on this, a new photocatalytic reactor design was proposed with immersed light illumination source to reduce the distance between the membrane and the light source for improved activation of the P25 particles. In this design, a 3D-printed vertical membrane holder was also included to accommodate a larger membrane surface area and therefore minimize the required spatial area for large industrial applications.

Raspberry-like hydroxyl-rich carbon layer coated solid catalyst to promote the hydrolysis of cellulose to sugar through local strong absorption

Raspberry-like carbon layer coated silica nanoparticles (MSN-x-NH2 @C) with controllable hydroxyl-rich rough surface is designed and synthesized by use of alkaline etching strategy and hydrothermal carbonization (HTC) method, which is utilized as catalyst to provide particular interaction with cellulose between the solid-solid interfaces. Through the control of surface roughness of the raspberry-like catalyst, it induces the formation of local area with strong absorption on the surface and thus enhance the capability to disrupt the aggregated structure of cellulose. Accordingly, in low acidic aqueous system with MSN-x-NH2 @C, the cellulose conversion rate is up to 91.99% with the total reducing sugar yield at 81.46% and glucose yield of ∼70% after the second hydrolysis in aqueous system. Furthermore, the obtained MSN-x-NH2 @C exhibits good thermal stability and reusability. This research provides a new perspective for the design and preparation of nano-sized solid catalyst with controlled surface topological structure to enable the surface adsorption capability towards cellulose more efficiently in aqueous system.