Catalyst Particle Size Research Articles

Exploring the Effect of Ball Milling on the Physicochemical Properties and Oxygen Evolution Reaction Activity of Nickel and Cobalt Oxides

Ball milling is commonly used to reduce catalyst particle size. However, little attention is paid to further changes that ball milling can cause to the rest of the catalysts’ physicochemical properties, which can impact their intrinsic catalytic activity. The effect of ball milling on the physicochemical properties of NiCoO2, NiO, CoO, and NiO:CoO mixtures is reported and correlated with their electrochemical oxygen evolution reaction (OER) activity. It is also shown that particle fragmentation is an inherent consequence of ball milling, but some oxides can also experience a phase transformation. In the case of rocksalt‐structured CoO, it is partially or entirely transformed to spinel‐structured Co3O4. Additionally, NiCo2O4 with a spinel structure can be formed by ball milling NiO and CoO simultaneously (both rocksalt structures), but only in the absence of water. The changes impact the electrochemical activity of the initial oxides. Ball milled NiCoO2 exhibits the highest activity with a mean potential of 1.563 V at 10 mA cm−2, demonstrating the advantage of having Ni and Co in the same structure. Although NiCo2O4 is also a binary oxide, the results indicate that its metal coordination environment makes it intrinsically less active than NiCoO2 for the OER in alkaline media.

Experimental investigation on product and temperature distribution in a continuous flow packed-bed reactor for dodecahydro-N-ethylcarbazole dehydrogenation

The dehydrogenation of dodecahydro-N-ethylcarbazole (H12-NEC) generates enormous gas accompanied by intense heat absorption, affecting heat and mass transfer in porous catalysts. A packed-bed reactor equipped with a temperature measurement device was designed to investigate the continuous flow dehydrogenation of H12-NEC. The effects of weight hourly space velocity (WHSV), reaction temperature, catalyst particle size, and pressure were evaluated. The results reveal that the volume flow rate of hydrogen will increase with the increase of WHSV. And the reduction of gas–liquid ratio and catalyst particle size facilitates heat transfer causing a more uniform axial temperature distribution within the reactor. As the temperature rises, the hydrogen yield increases along with more by-products. 456 K and 2 mm of catalyst particle size are determined to be the optimal reaction conditions in the study, achieving the hydrogen production rate of 9.61 molH2·gPd-1·h-1. With pressure increasing, the hydrogen yield gradually decreases, but the decreased evaporation of H12-NEC results in a smaller temperature difference between the reactor and heating wall. A comparison with the thermodynamic equilibrium model reveals that the effect of pressure on chemical equilibrium may be more significant than the temperature.

Pristine and Nature‐Inspired Hematite (α‐Fe2O3) Nanoparticles and Search for their Photocatalytic Application

AbstractThe article describes synthesis of green‐mediated hematite nanoparticles (20–30 nm) using Polianthes tuberosa flower extract. Structural, microscopic, and magnetic studies confirm the synthesis of iron oxide nanoparticles of pure hematite phase. Spectroscopic techniques are employed to identify different electronic transitions and defect levels as well as to estimate the energy bandgap and Urbach energy. A correlation among the particle size, bandgap energy, and Urbach energy is noticed. These hematite nanoparticles act as visible light photocatalyst which degrade dye in aqueous medium without the addition of any additives. The catalyst particle size, catalyst quantity, pH of dye solution, and solution temperature have significant impact on the photodegradation process of dye molecules in aq. solution. All observations advocate that green synthesis of hematite nanoparticles with Polianthes tuberosa flower extract can significantly modulate their optical and photocatalytic properties. These materials may find potential uses in water splitting for hydrogen production and purification of water by removing organic pollutants. The study highlights that using commercially cheap starting materials and extract made from naturally available plant parts, materials having huge application potentials can be synthesized at low cost by the simple green synthesis approach.

Properties analysis of catalyst particles during stripper distributor fault in industrial fluid catalytic cracking unit

Particle attrition is prevalent in fluid catalytic cracking (FCC) process, and severe particle attrition threatens the steady operation of FCC units. In this study, the processes of attrition and dealing in industrial FCC unit were investigated, and the relationship between particle physical properties and fault source was analyzed. The results showed that the most frequent particle sizes of the attrited equilibrium catalyst and the spent catalyst were 48.85 μm and 55.21 μm, respectively. The replacement of attrited catalyst by equilibrium catalyst with higher mechanical strength could alleviate the catalyst attrition problem, and the most frequent particle size of the catalyst remained at 75.81 μm after experiencing attrition. When the replacement rate reached 66.83 %, catalyst loss was reduced and the stability of FCC unit operation was significantly improved. This study would contribute to a deeper understanding of the particle abrasion and fragmentation behavior in different environments in industrial FCC units.

Fluidized-bed OCM reaction: A promising Mn2O3-Na2WO4/TiO2 catalyst and a numerical study

The fluidized-bed reactor with excellent heat and mass transfer features has great appeal for application in the oxidative coupling of methane (FB-OCM), whereas qualified fluid catalysts represent a grand challenge. Herein, we report a high-performance Mn2O3-Na2WO4/TiO2 fluid catalyst (5.4 wt% Mn2O3 and 2 wt% Na2WO4), which was obtained by the incipient-wetness impregnation method and examined in the OCM reaction in an electric-heating quartz fluidized-bed reactor (i.d., 2 cm). The standard normalization method on the basis of carbon atom was used for calculating the CH4 conversion and C2-C3 selectivity. This catalyst achieves 35.5 % CH4 conversion, 66 % C2-C3 selectivity and particularly 15.1 % single-pass yield of C2H4 for a feed of CH4/O2/H2O=3/1/1 with a catalyst dosage of 20 mL at 700 °C and a total GHSV of 7200 h−1. Such catalyst is stable for at least 50 h without signs of deactivation and agglomeration/defluidization. The catalyst particle size is crucial for the FB-OCM reaction with respect to the reaction light-off and catalyst fluidization. The catalyst with preferable particle size of 450–600 μm can not only trigger the OCM reaction at a relatively low temperature of 630 °C but also warrant active bubbling fluidization. Furthermore, thanks to the low amount of Na2WO4 and interpenetrating structure of TiO2-nanorod, such catalyst achieves good anti-aggregation and robust mechanical strength (with a low attrition index of 1.9 %). The effects of water-adding amount in feedstock and catalyst particle size distribution on the hydrodynamics behaviour were investigated in a laboratory-scale fluidized-bed OCM reactor by using numerical simulation method.

Highly Stable Ni-B/Honeycomb-Structural Al2O3 Catalysts for Dry Reforming of Methane.

Two-component catalysts have garnered significant attention in the field of catalysis due to their ability to inhibit Ni sintering. In the present work, honeycomb-structuralstructured Al2O3-supported Ni and B were prepared to enhance coke tolerance during dry reforming of methane (DRM). Transmission electron microscopy (TEM) results revealed that the average particle sizes on Ni/Al2O3 and Ni-0.16B/Al2O3 were 7.6 nm and 4.2 nm, respectively, indicating that B can effectively inhibit Ni sintering. After a 100-hour reaction, the conversion of CH4 and CO2 on Ni/Al2O3 decreased by approximately 5 %, whereas on Ni-0.16B/Al2O3, there was no significant decrease in CH4 and CO2 conversion, with values of approximately 81.6 % and 87.2 %, respectively. In situ DRIFT spectra demonstrated that Ni-0.16B/Al2O3 enhanced the activation of CO2, thus improving the catalyst's stability. A Langmuir-Hinshelwood-Hougen-Watson (LHHW) model was developed for intrinsic kinetics, and the resulting kinetic expressions were well-fitted fit to the experimental data, with R2 values exceeding 0.9. ActivationThe activation energies were also calculated. The outstanding stability of Ni-0.16B/Al2O3 can be attributed to its stable honeycomb structure and B's ability to significantly inhibit Ni sintering, reduce catalyst particle size, and enhance coke tolerance.

Inhibition of the growth rate of ZnS anode crystal plane: boosting photocatalytic hydrogen production performance

The catalyst's particle size plays a crucial role in enhancing photocatalytic performance. However, it is still unclear to analyse the mechanism by which surfactants affect the particle size of photocatalysts from the perspective of crystal growth. Herein, ZnS nanomaterials with different particle sizes were synthesized using a simple solid-state chemical synthesis method, and the intrinsic influence mechanism between surfactant and catalyst particle size was analyzed from the perspective of crystal growth. It was discovered that the particle size of ZnS kept getting smaller due to changes in polyethylene glycol, cetyltrimethylammonium bromide, and sodium dodecyl sulfate. Analyzing the reasons revealed that the catalyst's particle size was related to the type of surfactant: anionic surfactants could reduce the catalyst size. Correspondingly, the catalyst with a smaller particle size has the optimal performance for photocatalytic hydrogen production. Photocatalysts Z-SDS exhibited outstanding photocatalytic performance, yielding 11.47 mmol/g of hydrogen after a five-hour illumination. Furthermore, the intrinsic influence mechanism between anionic and cationic surfactants, photocatalyst particle size, and catalytic performance was investigated. This investigation provides a new idea for synthesizing small-size and high-performance photocatalysts.

Non-thermal plasma-catalytic ammonia synthesis over alumina-supported iron catalyst: Insights into the effect of alumina calcination temperature

Non-thermal plasma-catalytic ammonia synthesis (NTPCAS) has been regarded as a promising route to store hydrogen by utilizing renewable electricity. Alumina is a suitable support of the catalysts in NTPCAS and its properties can influence the performance of catalysts remarkably. In this study, the influence of the alumina calcination temperatures (Tc) on the catalytic performance of Fe-Al-x (x represents the value of Tc) was analyzed in a dielectric barrier discharge (DBD) reactor for NTPCAS. The results suggested that an increase in Tc transforms the alumina crystalline from γ phase to α phase. The best performance with a synthesized ammonia concentration of 11833 ppm was achieved over Fe-Al-900 with coexisting γ and θ phases of alumina under N2: H2 = 1:1 and SEI = 37.05 kJ/L conditions, which was 37 % higher than that of Fe-Al-800 with only γ phase. In addition, the larger Tc (i.e. 1100 and 1200 °C) decreased the specific surface area, increased the mean catalyst particle size, and led to the non-uniform dispersion of Fe species. The NH3-TPD and XPS studies suggested that an increase in Tc could influence the surface acidity and oxygen vacancy concentration of Fe catalysts, which were crucial to adjusting the catalytic activity for NTPCAS. This study clarifies the value of a suitable design of support of catalysts for improving NTPCAS.

Hydro-co-processing Jatropha oil and crude oil blend with Ni-Mo-supported Al2O3 catalyst to produce hybrid fuels: the effect of catalyst particle size

Hydro-co-processing Jatropha oil and crude oil blend with Ni-Mo-supported Al2O3 catalyst to produce hybrid fuels: the effect of catalyst particle size

Achieving High Performance with High Oxygen Permeability Ionomer (HOPI) in Heavy Duty Fuel Cell MEAs

Heavy-duty PEM fuel cells are expected to last 25,000-30,000 hours in the field. Therefore, materials, components, and interfaces used in these systems must be highly resistant to severe mechanical and chemical stress. Novel, highly active stable Pt and ordered PtCo intermetallic nanoparticles with well-controlled particle size and composition have been synthesized on a highly efficient PGM-free single metal active site rich carbon, to maximize their synergistic effects for enhanced performance and durability. Integrating these catalysts integrated with high O2 permeability ionomer (HOPI) in membrane electrode assemblies (MEAs) improved their fuel cell performance and durability, allowing the MEAs to achieve >1.2 A/cm2 at 0.7 V after 150k square wave accelerated stress test (AST) cycles, with a performance loss < 40 mV after 150K AST cycles.In a PEM fuel cell, the catalyst ink formulation and mixing processes control catalyst layer coating quality, electrode morphology, and the resulting fuel cell performance and durability. Catalyst ink properties are a result of complex solvent-catalyst-ionomer interactions that depend on the mixing method employed. Here, we compare the performance and durability of electrodes made from ball milled inks for Mayer rod coating before and after the catalyst scale up. Ink rheology and catalyst particle size are used to correlate ink properties to electrode morphology and structure and ensure consistency from batch to batch, and from small lab scale to subsequent scale-up. We evaluate and discuss the challenges that arise when coating the more viscous inks on decals, where the HOPI creates many bubbles in the ink. We also present the challenges of hot-pressing inks that contain HOPI, and how employing a Nafion overspray made with different solvents (isopropanol vs. ethanol) can improve hot-pressing. We investigate the how ionomer to carbon ratio affects hot pressing with HOPI and crack formation in the electrode via scanning electron microscopy (SEM).This work provides a comprehensive understanding of interactions between Pt, PtCo, carbon, ionomer, membrane, and GDLs and their impact on electrode structure, fuel cell performance and durability, as well as considerations for scale up to a R2R fabrication process. The attained information will be used to improve fuel cell electrode design, fabrication and scale-up.Acknowledgement: The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-FOA-0002360 (Phase I) and DE-SC0021671 (Phase II). Figure 1

Electrochemical Imaging of Precisely‐Defined Redox and Reactive Interfaces

AbstractUnderstanding the diverse electrochemical reactions occurring at electrode‐electrolyte interfaces (EEIs) is a critical challenge to developing more efficient energy conversion and storage technologies. Establishing a predictive molecular‐level understanding of solid electrolyte interphases (SEIs) is challenging due to the presence of multiple intertwined chemical and electrochemical processes occurring at battery electrodes. Similarly, chemical conversions in reactive electrochemical systems are often influenced by the heterogeneous distribution of active sites, surface defects, and catalyst particle sizes. In this mini review, we highlight an emerging field of interfacial science that isolates the impact of specific chemical species by preparing precisely‐defined EEIs and visualizing the reactivity of their individual components using single‐entity characterization techniques. We highlight the broad applicability and versatility of these methods, along with current state‐of‐the‐art instrumentation and future opportunities for these approaches to address key scientific challenges related to batteries, chemical separations, and fuel cells. We establish that controlled preparation of well‐defined electrodes combined with single entity characterization will be crucial to filling key knowledge gaps and advancing the theories used to describe and predict chemical and physical processes occurring at EEIs and accelerating new materials discovery for energy applications.

Electrochemical Imaging of Precisely-Defined Redox and Reactive Interfaces.

Understanding the diverse electrochemical reactions occurring at electrode-electrolyte interfaces (EEIs) is a critical challenge to developing more efficient energy conversion and storage technologies. Establishing a predictive molecular-level understanding of solid electrolyte interphases (SEIs) is challenging due to the presence of multiple intertwined chemical and electrochemical processes occurring at battery electrodes. Similarly, chemical conversions in reactive electrochemical systems are often influenced by the heterogeneous distribution of active sites, surface defects, and catalyst particle sizes. In this mini review, we highlight an emerging field of interfacial science that isolates the impact of specific chemical species by preparing precisely-defined EEIs and visualizing the reactivity of their individual components using single-entity characterization techniques. We highlight the broad applicability and versatility of these methods, along with current state-of-the-art instrumentation and future opportunities for these approaches to address key scientific challenges related to batteries, chemical separations, and fuel cells. We establish that controlled preparation of well-defined electrodes combined with single entity characterization will be crucial to filling key knowledge gaps and advancing the theories used to describe and predict chemical and physical processes occurring at EEIs and accelerating new materials discovery for energy applications.

Effect of Catalyst Particle Size on Densification of Carbon Nanotubes

Effect of Catalyst Particle Size on Densification of Carbon Nanotubes

Electrochemical Performance of a Hybrid NiCo2O4@NiFelt Electrode at Different Operating Temperatures and Electrolyte pH

Transition metals such as nickel and cobalt as an alternative to Pt and Pd can be used for oxygen evolution reactions (OERs) and hydrogen production reactions (HERs) in alkaline environments, facilitating green hydrogen production as a sustainable alternative to fossil fuels. In this study, an NiCo2O4 catalyst was produced by a sono-hydrothermal method using urea as a hydrolysis agent. The electrochemical performance of the catalyst-coated NiFelt electrode was evaluated at different KOH concentrations (0.25, 0.5, and 1 M) and four operating temperatures in the interval of 20–80 °C. The electrode characteristics were investigated via electrochemical spectroscopy (cyclic voltammetry, EIS, multistep chronopotentiometry, multistep chronoamperometry) using two different reference electrodes (Ag/AgCl and Hg/HgO), to obtain insight into the anodic and cathodic peaks. XRD, SEM, EDS, and TEM analyses confirmed the purity, structure, and nanoscale particle size (20–45 nm) of the NiCo2O4 catalyst. The electrode showed symmetric CV with Ag/AgCl, making this reference electrode more appropriate for capacitance measurements, while Hg/HgO proved advantageous for EIS in alkaline solutions due to reduced noise. The overpotential of the catalyst-coated NiFelt decreased by 108 mV at 10 mA/cm2 compared to bare NiFelt, showing a good potential for its application in anion exchange membranes and alkaline electrolyzers at an industrial scale.

A study using a semi-analytical approach to the reaction kinetics that describes the behavior of heterogeneous reaction–diffusion process with a glyoxyl-agarose immobilized enzyme (penicillin G acylase) in a batch reactor

This research article examines the reaction–diffusion process in a batch reactor by means of immobilized penicillin G acylase (PGA) with a glyoxyl-agarose matrix support. This study employs the Akbari-Ganji’s Method (AGM) when the system is under the internal (intra-particle) diffusional restrictions, and the external (film) diffusional restrictions is negligible. The semi-analytical approximations by the AGM technique are employed for computing the dimensionless steady-state solutions for a system of nonlinear differential equations to examine the impact of internal diffusional restrictions (IDR) as a function of catalyst enzyme loading and particle size. The model entails highly nonlinear components that adhere to the standard Michaelis-Menten kinetics. In addition to the proposed model, the dynamics for the mean integrated effectiveness factor (MIEF) of the dimensionless substrate concentration phenylglycine methyl ester (PGME) is presented. In light of this, there is a satisfactory level of agreement on the comparison of the semi-analytical result with the simulated numerical results across the whole concentration range where the dimensionless initial substrate and product concentrations are S1b=30,S2b=15, and P1b=60,P2b=100. The behavior of concentration profiles under the steady/unsteady state conditions for the effect of IDR on the overall reaction rates by immobilized biocatalyst PGA were examined. A sensitivity analysis is carried out to identify the effective parameter which can influence the diffusional restrictions on MIEF. An error analysis is performed on the dimensionless concentration equations to assess the amount of accuracy and the convergence of a solution.

The liquid-phase hydrogenation of TMCB for preparation of CBDO by fluorine-modified Ruthenium-Stannum bimetallic catalysts

A series of Ruthenium-Stannum bimetallic catalysts were prepared using the isovolumetric impregnation method and investigated for the liquid-phase hydrogenation of 2,2,4,4-tetramethyl-1,3-cyclobutanedione to its corresponding 2,2,4,4-tetramethyl-1,3-cyclobutanediol. The effects of the reaction temperature and pressure, fluorine-modified alumina, reaction solvent, and catalyst particle size on the catalytic performance were discussed. The optimum reaction conditions were obtained with a temperature of 80 ℃, a hydrogen pressure of 4.0 MPa, and a reaction solvent of tetrahydrofuran. In addition, characterization techniques, such as BET, XRD, TEM, NH3-TPD, and Py-IR, showed that the active component nanoparticles were effectively introduced into the alumina carriers, and the alumina was modified by a low concentration of NH4F solution (0.05 mol/L), which ensured that the complete conversion of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was obtained while maintaining a selectivity of over 95 % for the 2,2,4,4-tetramethyl-1,3-cyclobutanediol.

Efficient synthesis of 1,6-Hexanediol via the hydrogenation of dimethyl adipate on CuZn nanoparticles with balanced Cu+-Cu0 sites

In this paper, Cu-based catalyst was prepared by co-precipitation method with DMA hydrogenation as a probe reaction. Compared to the binary Cu-ZnO catalyst, the Cu-ZnO-MxOy (M=Ce, Ti, Zr and Al) catalyst modified with the addition of a third component showed a significant increase in 1,6-Hexanediol (HDO) selectivity. Especially, the dimethyl adipate (DMA) conversion, HDO selectivity and yield of the CZZ catalyst were up to 75.7 %, 53.6 % and 40.6 %, respectively, higher than others. Combining the results of XPS and N2O titration, HDO selectivity was adjusted by varying the Cu+/(Cu0+Cu+) ratio via the third component. The addition of ZrO2 prevented further reduction of Cu+ due to the formation of Cu/ZrO2 or Cu/ZnO species, thus maintaining a constant Cu+/(Cu0+Cu+) ratio and realizing the efficient selectivity of HDO. Furthermore, higher alkaline site density on the CZZ catalyst facilitated CO bond activation further favored the formation of 1,6-hexanediol. In addition, CZZ catalyst had better hydrogen dissociation capacity and smaller catalyst particle size, which will further promote the hydrogen dissociation and thus the hydrogenation process of DMA.

Nanoscale coupling of acidic sites and metal sites on Cu/Al2O3 catalysts boosting dimethyl ether steam reforming

Dimethyl ether steam reforming (DME SR) is a tandem reaction involving DME hydrolysis over acidic sites and then methanol steam reforming (MSR) over metal sites. However, developing bifunctional catalysts with highly efficient relay effect of the two-step reaction remains a great challenge. Herein, we facilely synthesize a Cu/Al2O3 catalyst (CuAl-AC) with nanoscale-coupled acidic sites and metal sites, which increases DME SR reaction rate 3-fold compared with the catalyst with micron-scale coupled acidic sites and metal sites. Compared with the traditional Cu/Al2O3 catalyst typically prepared by alkaline carbonate coprecipitation, the CuAl-AC catalyst eliminates the toxic effect of alkali metal cations on acidic sites, improves DME hydrolysis activity, and thus increases DME SR activity 5-fold. Additionally, compared with the CuAl-IM catalyst prepared by impregnation, the CuAl-AC catalyst exhibits strengthened metal-support interactions, significantly improving the stability. Furthermore, the efficient relay effect, high Cu+ content and small Cu particle sizes of the CuAl-AC catalyst result in ultrahigh H2 space-time yield of 0.95 mol gcat−1 h−1 compared with catalysts reported in literatures, and low CO selectivity of ∼4% when the DME conversion reaches 95%. In-situ infrared spectroscopy results suggest that MSR over the CuAl-AC catalyst follows the HCOOCH3* pathway over Cu sites.

Antimony tin oxide supported iridium oxide nanocatalyst with bi-directional strains for oxygen evolution reaction in PEM electrolyzers

The use of proton exchange membrane (PEM) electrolyzers in H2 production encounters notable challenges related to the activity and stability of the oxygen evolution reaction (OER). To address these issues, we introduce antimony tin oxide as carriers to support a core–shell structured Sb0.3Ir0.7Ox@TB-IrOx, featuring twin boundaries (TB) with bi-directional (shear and axial) strains. This catalyst exhibits a remarkably low overpotential of 198 mV at 10 mA cm−2 for OER in 0.5 M H2SO4 and impressively maintains stability for 200 h. Moreover, Sb0.3Ir0.7Ox@TB-IrOx/Sb0.2Sn0.8O2 demonstrates an exceptionally high mass activity of 4.06 A mg Ir-1 (η = 270 mV). The improved catalytic activity and stability are attributed to the introduction of antimony, which brings the Ir 5d band center (εd) closer to the Fermi level and results in a smaller catalyst particle size, exposing more active sites. Furthermore, a PEM electrolyzer employing the Sb0.3Ir0.7Ox@TB-IrOx/Sb0.2Sn0.8O2 nanocatalyst maintains a cell voltage of 2 V at 2 A cm−2 and exhibits a stability more than 200 h.

Investigating the catalytic effect of rock minerals during the aquathermolysis process of heavy oil in the presence of oil-soluble catalyst precursors

In this investigation, we explored the impact of thermal steam treatment (TST) on Yarega bituminous rock samples, with and without catalyst precursor compounds based on transition metals. After subjecting the materials to TST at 300°C in the presence of iron thallate, there was a notable 21% increase in the proportion of saturated hydrocarbons compared to the control experiment, and a substantial 27% increase compared to the original bituminoid composition. Simultaneously, the resin fraction witnessed a reduction of 25% against the control and a significant 50% decrease compared to the original oil. Scanning electron microscopy (SEM) analysis revealed that post-TST at 250 °C, the catalyst was composed of nanodispersed particles approximately sized between ≈20–50 nm. However, following TST at 300 °C, the catalyst particle size expanded to an estimated range of ≈60–90 nm. Furthermore, this study introduced a technology utilizing a commercial form of the catalyst precursor for application at the Yarega deposit.