Catalytic Particle Size Research Articles

Modelling and performance analysis for cumene production process in a four-layer packed bed reactor

Abstract A mathematical model is developed and designed for the cumene reactor in cumene production process in Hindustan Organic Chemicals Limited (HOCL), Kochi with improved operating conditions. High purity cumene is produced by the alkylation of benzene with propylene in this catalytic condensation process where solid phosphoric acid (SPA) is used as the catalyst. The mathematical model has been derived from mass and energy balance equations considering the reactor as fixed packed bed reactor and two different numerical methods are presented here to solve the modelling equations. The explicit finite difference method (FDM) involves the approximation of derivatives into finite differences, and in the other one, orthogonal collocation (OC), Ordinary Diffeential Equations (ODEs) are formed at the collocation points and are solved using Runge–Kutta fourth order numerical scheme. Here the analysis shows that the predictions from the model are in good alignment with the plant data. The combined feed has the optimum value of 1:2:8 for propylene, propane and benzene and the profiles of temperature and concentration can be obtained along the reactor. The model has been implemented in COMSOL Multiphysics as a packed bed reactor using the same parameters collected from the plant of study. It has been found that the reaction occurs at a satisfactory level even with a low temperature than the reactor temperature at the plant by changing the catalytic particle size. The reaction performance is also analysed for the physical properties like porosity and catalyst size.

Hexagonal BN- and BNO-supported Au and Pt nanocatalysts in carbon monoxide oxidation and carbon dioxide hydrogenation reactions

Environmental protection requires solving the problem of utilization and reduction of CO and CO2 emissions. Herein, Au/h-BN(O) and Pt/h-BN(O) nanohybrids are thoroughly analyzed in CO oxidation and CO2 hydrogenation reactions. The nanohybrids differ in catalytic particle size and particle distribution. The particles are smaller (1–6 nm) and display a narrower size distribution in the case of Pt-based nanomaterials. The Pt/h-BN(O) nanohybrids exhibit high catalytic activity in CO conversion and carbon dioxide hydrogenation reactions. For both systems, the oxidative state of BN support affects the catalytic activity. The possible catalytic reaction mechanisms are proposed based on DFT calculations. A charge density distribution at the Pt/h-BN interface increases oxygen absorption, thereby accelerating oxygen-associated chemical reactions.

Oxygen Generation Using Catalytic Nano/Micromotors.

Gaseous oxygen plays a vital role in driving the metabolism of living organisms and has multiple agricultural, medical, and technological applications. Different methods have been discovered to produce oxygen, including plants, oxygen concentrators and catalytic reactions. However, many such approaches are relatively expensive, involve challenges, complexities in post-production processes or generate undesired reaction products. Catalytic oxygen generation using hydrogen peroxide is one of the simplest and cleanest methods to produce oxygen in the required quantities. Chemically powered micro/nanomotors, capable of self-propulsion in liquid media, offer convenient and economic platforms for on-the-fly generation of gaseous oxygen on demand. Micromotors have opened up opportunities for controlled oxygen generation and transport under complex conditions, critical medical diagnostics and therapy. Mobile oxygen micro-carriers help better understand the energy transduction efficiencies of micro/nanoscopic active matter by careful selection of catalytic materials, fuel compositions and concentrations, catalyst surface curvatures and catalytic particle size, which opens avenues for controllable oxygen release on the level of a single catalytic microreactor. This review discusses various micro/nanomotor systems capable of functioning as mobile oxygen generators while highlighting their features, efficiencies and application potentials in different fields.

The Denitration and Dedusting Behavior of Catalytic Filter and Its Industrial Application in Glass Kilns

The development of efficient materials and processes is a long-term goal for the integrated flue gas purification in industry. In this study, a large-size V-based catalytic filter (L3000 mm × Φ150 mm) was prepared by loading the catalyst emulsion into a blank filter, which demonstrated excellent performance for simultaneously removing NOx, SOx and dust. The laboratory investigation found that the small catalytic particles, high catalyst loading and low face velocity could improve the DeNOx efficiency, and above 80% NO conversion could be achieved in the temperature range of 250–400 °C on the condition of <300 nm catalytic particle size, >7.41 wt % catalyst loading and <1.00 Nm/min face velocity. The negative effect of SO2/H2O was only observed below 300 °C, and the dust had little negative effects on DeNOx efficiency except for the increase of pressure drop. Moreover, a 90-day industrial test of 2380 catalytic filters over 100,000 Nm3/h of flue gas (0.50 Nm/min) from a glass kiln demonstrated that the removal efficiency of both NOx and SOx could be maintained above 95% with great stability at 320–350 °C, and 99% dust could be removed with a pressure drop of less than 1.40 KPa. The results reported herein indicate the promising application prospect of large-size V-based catalytic filters for integrated flue gas purification in industry.

Deep eutectic solvent-assisted synthesis of highly efficient PtCu alloy nanoclusters on carbon nanotubes for methanol oxidation reaction

Deep eutectic solvents are promising in the green synthesis of advanced functional materials owing to their several distinct advantages including good solubility, wide electrochemical window, high conductivity, low cost, nontoxicity and tolerance to humidity. Herein, we report a novel green protocol to design the hybrid PtCu nanoclusters on multi-walled carbon nanotubes in deep eutectic solvents medium without adding any surface controlling agent. Subsequently, the structure, elemental composition and electrocatalytic aspects of the as-synthesized nanohybrids are characterized by transmission electron microscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopic features and electrochemical investigations. Typically, the synthesis medium plays a key role to control the dispersion of Pt-based nanoparticles and to enhance the electronic transfer interaction among the catalytic nanoparticles and support material. On other hand, the addition of alloyed Cu not only further decreases the crystallite size of catalytic particles but also results in the formation of cluster nanostructure with the coarse surface. Moreover, the methanol oxidation electrocatalytic activity of the as-fabricated material is clearly composition dependent, their maximum mass activity (Pt/Cu mass ratio 1:0.25) is about 2.5 times that of the carbon nanotubes-supported monometallic Pt catalyst. And it also presents the good CO-tolerance ability and evident long-term electrochemical durability. This study suggests that the synthesis strategy in deep eutectic solvents is of great importance to design and fabricate the high-performance electrocatalysts for fuel cells applications.

High-purity helical carbon nanotubes by trace-water-assisted chemical vapor deposition: Large-scale synthesis and growth mechanism

Helical carbon nanotubes (HCNTs) are highly desirable due to their unique geometrical elegance and inherent physical properties; however, high-efficiency synthesis of high-purity HCNTs with high yield and full elucidation of their growth mechanism remains challenging. Traditional methods to achieve the high-yield growth of HCNTs mainly focus on controlling the size of catalytic particles. Herein, we found that addition of trace water greatly benefits large-scale synthesis of HCNTs. Uniform HCNTs with ∼ 100% purity can be obtained, and the yield of HCNTs can reach ∼ 8,078% in a run of 6 h, much higher than that obtained without trace water and any of the reported yields. Experiments and theoretical simulations are performed to reveal that the trace water can react with the dangling bond on carbon, thus inhibiting the generation of amorphous species. Furthermore, the trace water can enhance the anisotropy of the catalyst surface. This results in different segregation rates of carbon atoms coming out of different crystal planes and further periodic mismatch of the graphite layers, thus leading to the formation of HCNTs. Therefore, this new and efficient method is promising for practical, large-scale production of HCNTs.

Plant lignocellulose‐based feedstocks hydrogenolysis into polyols over a new efficient nickel–tungsten catalyst

AbstractHere, we developed a new strategy for preparation of series of in‐situ reduction bimetallic catalysts Ni‐W/SiO2 by introducing of reducing agent in the preparation process. And these catalysts were applied into the catalytic hydrogenolysis of microcrystalline cellulose and pretreated lignocellulose. The results show that the in situ reduction 15%Ni–20%W/SiO2 shows the prominent activity for microcrystalline cellulose conversion into ethylene glycol (EG), 1,2‐propylene glycol, and glycerol with the highest yield of EG at 61.30% under the experimental condition. And the relative high of EG yield (30.23%) was obtained when a combinative pretreatment technology of steam explosion (0.45 MPa) coupled with hot alkali (70 °C) was introduced to enhance the hydrogenolysis of plant lignocellulose‐based feedstocks over the in situ reduction catalyst 15%Ni–20%W/SiO2. The SEM and thermogravimetry analysis revealed that segmental lignin and hemicellulose were removed partly by hot alkali pretreatment. Meanwhile, the existence of Ni–W alloys and metal Ni particles were evidenced by X‐ray diffraction spectra. In addition, by the detailed analysis via transmission electron microscopy and X‐ray photoelectron spectroscopy, the catalytic particle size was distributed in the range of 9.3 ± 1.3 nm.

Growth and morphology control of β-Ga2O3 nanostructures by atmospheric-pressure CVD

Growth experiments of monoclinic gallium oxide (β-Ga2O3) nanostructures were performed by the atmospheric-pressure CVD using metal gallium (Ga) beads and water (H2O) as source materials and a Au film as a catalyst in terms of substrate materials, Au film thickness, growth temperature and growth time. Local structure analysis based on transmission electron microscope (TEM) observations and selective area electron diffraction (SAED) measurements revealed the successful growth of single crystalline β-Ga2O3 nanowires (NWs) through vapor-liquid-solid (VLS) growth mechanism. The average diameter of the NWs was changed in the range from ~60 to ~1500nm under the growth conditions picked up in this paper. The critical temperature for the VLS growth using the 30nm-thick Au catalytic film was experimentally estimated to be ~789°C. The diversity of shapes of nanostructures was probably due to the temperature evolution of Au catalytic particle size, the film growth on the NW sides by vapor-solid (VS) growth mechanism, and the epitaxial relation between the substrate and the individual NW. The photoluminescence intensity of the blue band emission at ~490nm relative to that of the ultraviolet band emission at ~360nm became larger with increasing average diameter, suggesting the increase in the native defects formed near the surface region.

Catalytic Particle Size Effects in the Catalytic CO2 Electroreduction on Cu

A combined experimental and computational study of catalytic particle size effects during CO2 electroreduction on size-controlled Cu nanoparticles is presented. Cu nanoparticle catalysts in the 2 – 15 nm mean size range were prepared, and their catalytic activity and selectivity during CO2 electroreduction were analyzed and compared to bulk Cu electrode. An increase in the catalytic activity as well as the H2 and CO selectivity was observed with decreasing Cu particle size, in particular for particles below around 2 nm. Hydrocarbon (methane and ethylene) selectivity was increasingly suppressed with smaller particle size. A spherical Cu particle model was used to analyze the size dependence of the surface atomic coordination, which was correlated to experimental results.

ChemInform Abstract: Overcoming Limitation in the Design of Selective Solid Catalysts by Manipulating Shape and Size of Catalytic Particles: Epoxidation Reactions on Silver

AbstractReview: 10 refs.

Overcoming Limitation in the Design of Selective Solid Catalysts by Manipulating Shape and Size of Catalytic Particles: Epoxidation Reactions on Silver

Overcoming Limitation in the Design of Selective Solid Catalysts by Manipulating Shape and Size of Catalytic Particles: Epoxidation Reactions on Silver

Influence of catalytic particle size on the performance of fluidized-bed chemical vapor deposition synthesis of carbon nanotubes

In this paper, the impacts of catalytic particle size on the overall reactor performance for carbon nanotubes (CNTs) production using a fluidized-bed chemical vapor deposition (FBCVD) process have been studied. Six different particle size fractions (10–20 μm, 20–53 μm, 53–75 μm, 75–100 μm, 100–200 μm, and 200–300 μm) were selected. It was observed that the smaller the catalytic particle diameter, the greater the carbon deposition efficiency and the greater CNT synthesis selectivity. The 10–20 μm catalytic particles exhibited 30% higher carbon deposition efficiency than the 200–300 μm catalytic particles. The selectivity toward CNTs formation was also approximately 100%. These observations could be explained by the fact that when the diameter of the catalytic particle gets smaller, the breakthrough capacities during frontal diffusion will be bigger due to a shorter diffusion path length within the particle. Moreover, the fine particles ensured high interstitial velocity which subsequently enhances the heat and mass transfer, and consequently improves the CVD reaction.

Calculation of the sizes of individual few-walled carbon nanotubes and their bundles

The temperature dependences of the number of nucleating single-walled and few-walled nanotubes and their diameter have been determined over a wide range of model parameters in the framework of the problem regarding the nucleation of carbon nanotubes from catalytic particles supersaturated with carbon. It has been demonstrated that, initially, individual nanotubes nucleate and grow and, then, they can be joined together into bundles. The mechanism of the formation of bundles in the proposed model follows from the quantum-chemical analysis of the steady-state growth of nanotubes at the level of release of individual carbon atoms. During the growth, the axis of the nanotube rotates about the normal to the surface of the catalytic particle. This leads to the cross-linking of nanotubes into bundles. The characteristic diagram of the regions of the existence of individual single-walled, few-walled, and multiwalled nanotubes and their bundles has been constructed as a function of the temperature and the size of catalytic particles.

Helical Carbon Nanotubes: Catalytic Particle Size-Dependent Growth and Magnetic Properties

The exact knowledge of helical carbon nanotube (HCNT) growth mechanism has not yet been completely clarified, and effective synthesis of high-purity helical carbon nanotubes in high yield still remains a tremendous challenge. In this study, HCNTs were synthesized via a catalytic chemical vapor deposition method using Fe nanoparticles as catalysts. We performed systematic experiments to investigate the specific effect of catalytic particle size (CPS) on the selective growth of HCNTs, such as on the morphology, yield, mobility of carbon atoms, and HCNT purity of carbon products. Our study showed that the CPS plays a key role in the selectivity to HCNTs, yield, and morphology of the carbon products, and a small catalytic particle is favorable to HCNT formation. We hope that this result may give a beneficial suggestion to obtain highly pure HCNTs. A CPS-dependent growth mechanism for HCNTs was finally proposed. Magnetic measurements demonstrated that the HCNTs are ferromagnetic properties and show high magnetization at room temperature.

The characteristic size of carbon nanotube bundles

The dependence of the size of a carbon nanotube bundle on the size of catalytic particles and separate nanotubes was calculated. The size of bundles was shown to be determined by the distortions of van der Waals bonds between nanotubes in the vicinity of a catalytic particle and nanotube bending in the bundle. Both effects increased as the thickness of the bundle grew. The calculated bundle sizes were compared with the experimental data on growing nanotubes obtained by the chemical vapor deposition, arc, and laser methods.

Using the Box-Benkhen technique to statistically model phenol photocatalytic degradation by titanium dioxide nanoparticles

Abstract A four factor three level Box-Benkhen design (BBD) was developed to describe the photocatalytic degradation of phenol in an aqueous media. The four process variables under consideration in BBD model included titanium dioxide (TiO2) catalyst size, TiO2 concentration, dissolved oxygen (DO) concentration and phenol concentration. The model predicted a maximum degradation rate (0.083 min−1) with conditions set at 9.091 nm TiO2 particle size, 1.0 g/l TiO2, 31.0 mg/l DO and 40 mg/l phenol. A response outcome computed using experimental data for the 10 nm nanoparticle size catalyst was 13% less than the maximum value. The data suggest that small catalytic particle size augmented the quantum yield in the photocatalytic degradation process with the maximum located at an approximate catalyst size of 10 nm. The photocatalytic degradation rate constant followed an Arrhenius dependency with activation energy of 13.55 kJ/mol K for the 10 nm TiO2 particles.

Reduction of Pd catalytic particle size by a double activation process

We have used a double activation method to reduce the size of Pd catalytic particles commonly used as an activation layer for electroless Cu deposition. The method produces Pd particles with sizes reduced by a factor of 4 and density increased by a factor of 10 compared to the single activation method. The first activation and the Pd etching process in the double activation removes the native Ti oxide on TiN surface and largely increase the nucleation sites for Pd. With more nucleation sites, nucleation events outrun ripening events throughout the deposition time range. However, excessive etching of Pd and the underlying TiN layer could lead to rougher electroless Cu films. Secondary ion mass spectrometry data show that the double activation step does not increase the net amount of Pd deposited on TiN surface; it only changes its particle size and density. Electroless Cu deposited on a doubly Pd activated surface has a larger grain size and appears to have a lower resistivity.

Synthesis of carbon nanostructures on the Fe-Mo catalysts supported on modified SiO2

Carbon nanostructures were synthesized by the pyrolysis of an CH4-H2 mixture. The synthesis was carried out on the Fe-Mo catalysts supported on the SiO2 surface by high-frequency diode sputtering or chemical deposition from a solution of a heterometallic carbonylchalcogenide complex. Structure features of the formed carbon nanostructures affected by the size of catalytic particles, temperature of the process, and composition of the gas mixture were revealed. The presence of sulfur in the catalyst composition results in the formation of nanofibers with the bamboo-like structure.

H2-assisted control growth of Si nanowires

Large-scale desired silicon nanowires without amorphous silicon oxide sheath have been synthesized by thermal chemical vapor deposition using SiH4 gas at 650°C in a flow mixture of H2 and N2, compared with the short and thick Si nanowires with amorphous SiOx coating obtained in N2. Scanning electron microscopy (SEM), Energy dispersive X-ray spectrometry (EDX) analysis, and high-resolution transmission electron microscopy (HRTEM) have been employed to characterize the Si nanowires. The effects of H2 gas on the catalytic particle size and on the formation of Si nanowires are discussed in detail. Photoluminescence (PL) characteristics further demonstrate the large differences between the H2-assisted grown Si nanowires and the Si nanowires grown in N2.

Particle size dependence and model for iron-catalyzed growth of carbon nanotubes by thermal chemical vapor deposition

The catalytic particle size dependence of chemical vapor deposition growth of multiwall carbon nanotubes was systematically investigated using two different molecules, C2H2 and C60, as carbon feedstock gases. In the particle size range between 25 and 500 nm, the use of C2H2 leads exclusively to growth of carbon nanotubes. The nanotube diameters increase with increasing catalytic particle sizes but do not scale 1:1. In contrast, nanotube formation from C60 is observed only if the particle sizes are sufficiently small with an optimum between 20 and 30 nm. For catalyst samples with considerably larger diameters, C60 is transformed into a nontubular deposit. A growth model is given that explains the different behavior.