Support Surface Research Articles

Effects of sample dimensions in compressive strength tests of masonry wall products

Introduction. State standards for testing ceramic masonry wall materials of plastic molding establish grinding as the main method of smoothening supporting (loaded) surfaces. Therefore, studies were conducted on the effect of sample dimensions on the compressive strength of tested masonry products. The effect of a scale factor on the measured strength of brick and stone has so far been only partially reflected in the standard for test methods (GOST 8462 “Wall materials. Methods for determining compressive and bending strength”). According to both Russian and foreign specialists, shape factors values, provided in EN 772-1 European standard “Methods of test for masonry units. Part 1. Determination of compressive strength” need to be adjusted as they do not take into account the void ratio of masonry products and the sample material type.Aim. To assess the effects, caused by the geometric dimensions of masonry product samples, as well as the void ratio and other characteristics, on compressive strength according to the results of laboratory tests. Materials and methods. As a result of conducted control tests of ceramic and silicate single and thickened bricks with a void ratio of up to 27 %, measured values of product compression strength were compared to determine the value of transition coefficients.Results. The performed studies confirmed the shape coefficients, adopted in EN 772-1, to require an adjustment. Based on the results of studies, conducted in Russia and abroad, conclusions and recommendations were made to take into account the dimensions of tested samples during strength tests.Conclusion. Performed studies and analysis of experimental results have demonstrated that in order to increase the accuracy of determining the strength of test samples, taking into account their shape and void ratio, it is necessary to have several tables with shape factors. Currently, until reliable data about the void ratio effect of the masonry material on test results are obtained, it is advisable to take into account only the height of the sample (“longitudinal bending”).

Amino-functionalization of tungsten oxide nanoparticles for stable decoration in the active layer of alumina-supported inorganic-organic hybrid membrane with super-wettable and photocatalytic self-cleaning surfaces for crude oil-in-water emulsion separation

The ceramic membrane was hybridized with an amino-functionalized inorganic metal oxide and organic polymer to achieve the optimal oil and water surface wettability and photo-catalytic self-cleaning capability. The resulting membrane was used for the treatment of crude oil-contaminated wastewater under cross-flow filtration mode. The fundamental functional material, tungsten oxide nanoparticles (NH2-WO3 NPs) modified by aminopropyl triethoxysilane (APTES) was created and coated on the alumina ceramic support surface via interfacial polymerization, in which the material covalently cross-links on the membrane's active layer in the presence of terephthaloyl chloride (TPC) as a cross-linker and piperazine (PIP) as an external amine. Achieving a unique combination of oil and water surface wettability- superhydrophilicity (0° water-in-air contact angle) and underwater super-oleophobicity (160.25° under-water oil contact angle) was the key to creating the water-permeating NH2-WO3/PA@alumina ceramic membrane. The second advantageous feature of the membrane is its capacity for self-cleaning, which results from WO3 NP's innate photocatalytic activity that has been further enhanced by amino functionalization. A water permeate flux of up to 250 L m−2 h−1 and an oil/water separation efficiency of nearly 100 % were attained for an oil concentration of 50 ppm of crude oil-in-water emulsion when NH2-WO3/PA@alumina ceramic membrane was employed as a separation medium in a cross-flow filtration system for the separation of crude oil-in-water emulsion. Furthermore, the permeate flux decreased to ∼25 % of its initial flux after using NH2-WO3/PA@alumina ceramic for approximately 210 min. This was caused by organic pollutants in the oily water clogging the membrane pores. The permeate flux was recovered by exposing the membrane to UV light for photo-catalytic self-cleaning. Due to its water-passing nature, this membrane has high efficiency. Additionally, because the self-cleaning add-on removes the need for chemical cleaning, it is environmentally friendly.

Low-Temperature Composite CO2 Sorbents Based on Amine-Containing Compounds

The use of technologies based on combustion of carbon-containing fossil fuel leads to emission of large amounts of CO2, one of the main greenhouse gases, into the atmosphere. To reduce the CO2 level in the atmosphere, systems for CO2 sorption from various gas sources are being developed. The systems allowing the CO2 sorption and desorption at low temperatures (25–200°С) are of most interest. Most frequently, such systems are composite materials consisting of a porous support and a CO2 chemisorbent dispersed on it. Low-volatile amine-containing compounds are the most promising among organic chemisorbents. Classification of the amine-containing sorbents with respect to the preparation procedure is discussed. The procedures include impregnation, covalent grafting, and in situ polymerization on the support surface. The impregnation procedure is simple and cheap in implementation. The sorption characteristics of materials prepared by impregnation depend on the efficiency of the dispersion of the active component, which is determined by the characteristics of the support pore structure, in particular, by the ability of the pore surface for chemical or electrostatic interaction with the supported amine-containing compound. The covalent grafting is based on immobilization of alkoxyaminosilanes on the surface of porous silica materials. The supports for implementing this approach should contain a large amount of silanol groups on the surface and should have the pore size sufficient for the efficient transport of CO2 molecules to amino groups. The main drawback of the grafting method is low thickness of the amine-containing component layers obtained. In situ polymerization is used for preparing materials with high content of grafted functional groups. Provided that the blocking of support pores is excluded in the course of in situ polymerization, materials of this type exhibit the highest sorption capacity for CO2.

Noncovalent Grafting of Molecular Complexes to Solid Supports by Counterion Confinement.

Grafting molecular complexes on solid supports is a facile strategy to synthesize advanced materials. Here, we present a general and simple method for noncovalent grafting on charge-neutral surfaces. Our method is based on the generic principle of counterion confinement in surface micropores. We demonstrate the power of this approach using a set of three platinum complexes: Pt1 (Pt1L4(BF4)2, L = p-picoline), Pt2 (Pt2L4(BF4)4, L = 2,6-bis(pyridine-3-ylethynyl)pyridine), and Pt12 (Pt12L24(BF4)24, L = 4,4'-(5-methoxy-1,3-phenylene)dipyridine). These complexes share the same counterion (BF4-) but differ vastly in their size, charge, and structure. Imaging of the grafted materials by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) and energy-dispersive X-ray (EDX) showed that our method results in a homogeneous distribution of both complexes and counterions. Nitrogen sorption studies indicated a decrease in the available surface area and micropore volume, providing evidence for counterion confinement in the surface micropores. Following the adsorption of the complexes over time showed that this is a two-step process: fast surface adsorption by van der Waals forces was followed by migration over the surface and surface binding by counterion confinement. Regarding the binding of the complexes to the support, we found that the surface-adsorbate binding constant (KS) increases quadratically with the number of anions per complex up to KS = 1.6 × 106 M-1 equaling ΔG°ads = -35 kJ mol-1 for the surface binding of Pt12. Overall, our method has two important advantages: first, it is general, as you can anchor different complexes (with different charges, counterions, and/or sizes); second, it promotes the distribution of the complexes on the support surface, creating well-distributed sites that can be used in various applications across several areas of chemistry.

The static balance ability on soft and hard support surfaces in older adults with mild cognitive impairment

Objective This study aimed to assess the static balance ability of the older adults with mild cognitive impairment (MCI) while standing on soft and hard support surfaces. Methods Forty older adults participated in this study (21 in the MCI group and 19 in the control group). Participants were required to perform balance tests under four conditions of standing: standing on a hard support surface with eyes open, standing on a soft support surface with eyes open, standing on a hard support surface with eyes closed, and standing on a soft support surface with eyes closed. Each test was measured in three trials and each trial lasted 30 seconds. Participants were asked to take off their shoes and place their feet in a parallel position with a 20-centimeter distance for bipedal support. The trajectories of the center of pressure (COP) were measured using a Kistler force platform with a frequency of 1000 Hz to assess balance while standing in both groups, with larger COP trajectories indicating poorer static balance in older adults. Results With eyes open, the displacement of COP in the anterior-posterior direction(D-ap) (hard support surface: P = 0.003) and the 95% confidence ellipse area(95%AREA-CE) (soft support surface: P = 0.001, hard support surface: P < 0.001) of the COP in the MCI group standing on hard and soft support surfaces were significantly larger than the control group. The 95%AREA-CE (P < 0.001) of the COP in the MCI group on the soft support surface was significantly larger than on the hard support surface. With eyes closed, the root mean square distance(RDIST), root mean square distance-ML(RDISTml), and 95%AREA-CE of the COP were no significant between-group differences when standing on hard support surfaces. However, the RDIST (P = 0.014), RDISTml (P = 0.014), and 95%AREA-CE (P = 0.001) of the COP in the MCI group on the soft support surfaces were significantly larger than the control group. The 95%AREA-CE (P < 0.001), RDIST (P < 0.001), and RDISTml (P < 0.001) of the COP in the MCI group on the soft support surface were significantly larger than the hard support surface. Conclusion With eyes open, the older adults with MCI showed poorer static balance ability compared to the older adults with normal cognition on soft and hard support surfaces. With eyes closed, the older adults with MCI showed poorer static balance on soft support surfaces, but no differences on hard support surfaces compared with the older adults with normal cognition. With eyes open and closed, the older adults with MCI showed poorer static balance on soft support surfaces as compared to hard support surfaces.

In-situ synthesis of carbon nanotubes-graphite hybrid materials

This contribution deals with a commercially scalable catalyst preparation method for the synthesis of a new generation of hybrid materials based on carbon-nanotubes-graphite. Commercial natural graphite in spherical or flake shapes, with varying particle sizes and textural properties, were used as catalyst support. They were impregnated with aqueous solutions containing cobalt nitrate in the presence of a non-ionic surfactant agent and then dried and calcined under controlled experimental conditions. Catalytic activity properties were evaluated in a rotary tube reactor using ethylene as a carbon source at a temperature of 650 °C and a residence time of 5 min. It was observed that the use of a surfactant agent in the impregnation step significantly improved the adsorption and dispersion of the active metal on the hydrophobic catalyst support surface, enabling the formation of a dense coating of carbon nanotubes on the graphite particles after the synthesis. The multi-walled carbon nanotubes (MWCNTs) showed diameters ranging from 10 to 20 nm and lengths between 5 and 10 µm, with most of them growing via the base-mode growth mechanism. The morphology properties of the graphite particles play a key role in influencing the active metal surface deposition, the MWCNT yield, and their aspect ratio properties

Assessment of influence of considering the flexibility of the front loader frame on the emerging loads in the multibody system

BACKGROUND: Dynamic models are widely used for vehicle dynamics simulation. Increase of simulation accuracy is achieved with adding flexible bodies in a model, making problem solving more complicated. Therefore, assessment of influence of considering the flexibility of the front loader frame on the emerging loads in the multibody system becomes necessary.
 AIM: Assessment of considering the flexibility of the front loader frame on the emerging loads in the multibody system becomes necessary.
 METHODS: The solution of the problem is presented with the example of a multibody model of a 14.5-ton front loader (FL) with a frame coupled with wheel movers rigidly fixed to the front half-frame and a swinging axle at the rear half-frame. This method of coupling makes it possible to assess the effect of the flexibility of the elements of the FL by comparing the vertical forces that occur in the contact patch of the wheels with the support surface. The multibody models are built in the NX Motion application of the NX 2206 software package.
 RESULTS: The comparison of vertical wheel forces in given load conditions (symmetrical and skew-symmetric) using absolutely rigid and flexible models of the frame is carried out. It is found that the forces for skew-symmetric loading modes can differ by up to 20% depending on the frame stiffness.
 CONCLUSION: As a result of the conducted research, it can be stated that taking into account the suppleness of the load-bearing system of the vehicle significantly affects the results obtained in the process of modeling.

Kinetic and thermodynamic studies on the thermal inactivation of lipase immobilized on glutaraldehyde-activated rice husk silica.

The objective of this study was to obtain sufficient information on the thermal stabilization of a food-grade lipase from Thermomyces lanuginosus (TLL) using the immobilization technique. To do this, a new non-porous support was prepared via the sequential extraction of SiO2 from rice husks, followed by functionalization with (3-aminopropyl) triethoxysilane - 3-APTES (Amino-SiO2), and activation with glutaraldehyde - GA (GA-Amino-SiO2). We evaluated the influence of GA concentration, which varied from 0.25% v v-1 to 4% v v-1, on the immobilization parameters and enzyme thermal stabilization. The thermal inactivation parameters for both biocatalyst forms (soluble or immobilized TLL) were calculated by fitting a non-first-order enzyme inactivation kinetic model to the experimental data. According to the results, TLL was fully immobilized on the external support surface activated with different GA concentrations using an initial protein load of 5mgg-1. A sharp decrease of hydrolytic activity was observed from 216.6 ± 12.4 U g-1 to 28.6 ± 0.9 U g-1 of after increasing the GA concentration from 0.25% v v-1 to 4.0% v v-1. The support that was prepared using a GA concentration at 0.5% v v-1 provided the highest stabilization of TLL - 31.6-times more stable than its soluble form at 60°C. The estimations of the thermodynamic parameters, e.g., inactivation energy (Ed), enthalpy (ΔH#), entropy (ΔS#), and the Gibbs energy (ΔG#) values, confirmed the enzyme stabilization on the external support surface at temperatures ranging from 50 to 65°C. These results show promising applications for this new heterogeneous biocatalyst in industrial processes given the high catalytic activity and thermal stability.

Immobilization of Cyclodextrin glycosyltransferase onto three dimensional- hydrophobic and two dimensional- hydrophilic supports: A comparative study.

Cyclodextrin glycosyltransferase (CGTase) degrades starch into cyclodextrin via enzymatic activity. In this study, we immobilize CGTase from Thermoanaerobacter sp. on two supports, namely graphene nanoplatelets (GNP) consisting of short stacks of graphene nanoparticles and a calcium-based two-dimensional metal organic framework (Ca-TMA). The uptakes of CGTase on GNP and Ca-TMA reached 40 and 21mg g-1 respectively, but immobilized CGTase on Ca-TMA showed a higher specific activity (38 U mg-1 ) than that on GNP (28 U mg-1 ). Analysis of secondary structures of CGTase, shows that immobilization reduces the proportion of β-sheets in CGTase from 56% in the free to 49% and 51.3% for GNP and Ca-TMA respectively, α-helix from 38.5% to 18.1 and 37.5%, but led to increased β-turns from 5.5 to 40% and 11.2% for GNP and Ca-TMA, respectively. Lower levels of conformational changes were observed over the more hydrophilic Ca-TMA compared to hydrophobic GNP, resulting in its better activity. Increased β-turns were found to correlate with lower β-CD production, while more β-sheets and α-helix favored more β-CD. Reusability studies revealed that GNP retains up to 74% of initial CGTase activity, while Ca-TMA dropped to 33% after eight consecutive uses. The results obtained in this work provide insight on the effect of support's surface properties on CGTase performance and can assist in developing robust CGTase-based biocatalysts for industrial application.

Accelerated stress tests for Pt/C electrocatalysts: An approach to understanding the degradation mechanisms

The degradation of the nanostructured platinum-based electrocatalysts during their operation poses a major problem for the performance and durability of PEMFCs and devices based on them. Therefore, the methodological aspects of research related to the quantitative assessment of the materials’ degradation as well as the mechanism of the processes causing it are gaining increasing attention. The degradation processes of the same Pt/C catalyst containing the nanoparticles of similar size uniformly distributed over the surface of the carbon support were studied using eight relevant protocols of the accelerated stress testing. Special attention was paid to electron microscopy examination of the catalyst’s microstructure before and after stress tests as well as to determination of the electrochemically active surface area and the activity of the catalyst in the ORR after the stress testing. We also studied the influence of the atmosphere, in which testing was performed, as well as the effect of the electrode rotation on the degradation rate. The results of the study carried out demonstrate the features of the catalyst’s degradation in different modes and facilitate the choice of optimal protocols and stress testing conditions.

Quantitative Description of Metal Center Organization and Interactions in Single-Atom Catalysts.

Ultra-high-density single-atom catalysts (UHD-SACs) present unique opportunities for harnessing cooperative effects between neighboring metal centers. However, the lack of tools to establish correlations between the density, types, and arrangements of isolated metal atoms andthe support surface properties hinders efforts to engineer advanced material architectures. Here, this work precisely describes the metal center organization in various mono- and multimetallic UHD-SACs based on nitrogen-doped carbon (NC) supports by coupling transmission electron microscopy with tailored machine-learning methods (released as a user-friendly web app) and density functional theory simulations. This approach quantifies the non-negligible presence of multimers with increasing atom density, characterizes the size and shape of these low-nuclearity clusters, and identifies surface atom density criteria to ensure isolation. Further, it provides previously inaccessible experimental insights into coordination site arrangements in the NC host, uncovering a repulsive interaction that influences the disordered distribution of metal centers in UHD-SACs. This observation holds in multimetallic systems, where chemically-specific analysis quantifies the degree of intermixing. These fundamental insights into the materials chemistry of single-atom catalysts are crucial for designing catalytic systems with superior reactivity.

Development of asymmetric ceramic membranes for dairy wastewater treatment – A comparison between co-sintering and conventional firing process

Ceramic membranes have high potential for wastewater recovery. However, the high cost of raw materials and the high energy consumption for manufacturing, limit their use. This study aimed to prepare ceramic membranes using kaolin and alumina, emphasizing firing in a single step. On the support, corn starch was used as a porogenic agent and to evaluate the performance of the membrane, a simulation was used for the dairy industry effluent. The supports were manufactured by the extrusion process, which were sintered (1100, 1200 and 1300 °C), for the analysis of their properties. A suspension was applied to the inner surface of the green supports, and the cosintering process was employed. The supports containing 15 % corn starch sintered at 1100 °C showed high porosity (48 %), pure water permeate flux of 1385 L/h.m2 at 2 bar and mechanical strength of 8 MPa. The active layer exhibited pore sizes that indicate that the membrane can be used in the microfiltration process, with a permeate flux of 897 L/h.m2. The membrane showed adequate microfiltration performance for the removal of components present in the milk solution and responsible for the turbidity of the permeate, with a permeate flux stabilized at 30 L/h.m2.

Electrospun Polysulfone Hybrid Nanocomposite Fibers as Membrane for Separating Oil/Water Emulsion

Commercial polymer membranes are largely utilized to separate oil/water mixtures; however, membrane fouling, flux decline, and short lifetime often inhibit their high performance. In order to resolve these drawbacks of the commercial membranes, we introduce a surface modification strategy following the electrospinning method. Electrospun fibers of polysulfone (PSf)/iron oxide (FeO)/halloysite nanotubes (HNT) nanocomposite are applied to modify the polyether sulfone (PES) standard membrane support surface for developing highly efficient oil/water emulsion separating membranes. This facile and simple spinning process for shorter periods ensures nanocomposite coatings on the standard PES membranes and allows a better oil/water separation. We analyze the structural and morphological characteristics of the modified membrane surface using scanning electron microscopy, Fourier transformation infrared spectroscopy, and X-ray diffraction studies and hydrophilicity from contact angle studies. FeO nanoparticles of 2–5 nm and HNTs of < 50 nm size mixed in PSf produce fibers of 531 ± 162 nm average diameter at a relatively lower applied electrical voltage of 14.5 kV, compared to PSf. Underwater and under-oil contact angle values are used to prove the surface characteristics of the membranes and total organic content (TOC) values for the emulsion separation performance. From PES support to PSf and PSf/HNT-FeO, the TOC values respectively change from 67 to 75 and 79%. We find moderately hydrophilic membranes (PSf/HNT-FeO) resulting in a higher permeate flux (28,447 Lm−2·h−1) and quicker separation performance. We believe this study provides a notable solution to modify the surface of commercial membranes for better emulsion separation performance.

Generalized Abel equations and applications to translation invariant Radon transforms

Abstract Generalized Abel equations have been employed in the recent literature to invert Radon transforms which arise in a number of important imaging applications, including Compton Scatter Tomography (CST), Ultrasound Reflection Tomography (URT), and X-ray CT. In this paper, we present novel injectivity results and inversion methods for generalized Abel operators. We apply our theory to a new Radon transform, R j \mathcal{R}_{j} , of interest in URT, which integrates a square integrable function of compact support, 𝑓, over ellipsoid and hyperboloid surfaces with centers on a plane. Using our newly established theory on generalized Abel equations, we show that R j \mathcal{R}_{j} is injective and provide an inversion method based on Neumann series. In addition, using algebraic methods, we present image phantom reconstructions from R j ⁢ f \mathcal{R}_{j}f data with added pseudo-random noise.

Interrelation Between External Pressure, SEI Structure, and Electrodeposit Morphology in an Anode‐Free Lithium Metal Battery

AbstractThe interrelation is explored between external pressure (0.1, 1, and 10 MPa), solid electrolyte interphase (SEI) structure/morphology, and lithium metal plating/stripping behavior. To simulate anode‐free lithium metal batteries (AF‐LMBs) analysis is performed on “empty” Cu current collectors in standard carbonate electrolyte. Lower pressure promotes organic‐rich SEI and macroscopically heterogeneous, filament‐like Li electrodeposits interspersed with pores. Higher pressure promotes inorganic F‐rich SEI with more uniform and denser Li film. A “seeding layer” of lithiated pristine graphene (pG@Cu) favors an anion‐derived F‐rich SEI and promotes uniform metal electrodeposition, enabling extended electrochemical stability at a lower pressure. State‐of‐the‐art electrochemical performance is achieved at 1MPa: pG‐enabled half‐cell is stable after 300 h (50 cycles) at 1 mA cm−2 rate −3 mAh cm−2 capacity (17.5 µm plated/stripped), with cycling Coulombic efficiency (CE) of 99.8%. AF‐LMB cells with high mass loading NMC622 cathode (21 mg cm−2) undergo 200 cycles with a CE of 99.4% at C/5‐charge and C/2‐discharge (1C = 178 mAh g−1). Density functional theory (DFT) highlights the differences in the adsorption energy of solvated‐Li+ onto various crystal planes of Cu (100), (110), and (111), versus lithiated/delithiated (0001) graphene, giving insight regarding the role of support surface energetics in promoting SEI heterogeneity.

Use of a novel pressure distribution system for severely ill neonates: a clinical pilot study carried out by the PREPICare consortium

BackgroundPressure Injuries are not exclusively an adult phenomenon; various risk factors contribute to a high prevalence rate of 43% in the neonatal and pediatric intensive care population. Effective preventive measures in this population are limited.MethodsWe performed a pilot study to analyze the distribution and localization of support surface interface pressures in neonates in a pediatric intensive care unit (PICU). The hypothesis was that pressure redistribution by a novel air mattress would reduce pressure peaks in critical neonates. The measurements were conducted in a 27-bed level III PICU between November and December 2020. This included measuring pressure distribution and pressure peaks for five neonates positioned on either a state-of-the-art foam mattress or a new prototype air mattress.ResultsWe confirmed that the pressure peaks were significantly reduced using the prototype air mattress, compared with the state-of-the-art foam mattress. The reduction of mean pressure values was 9–29%, while the reduction of the highest 10% of pressure values was 23–41%.ConclusionsThe journey to an effective, optimal, and approved product for severely ill neonates to reduce Pressure Injuries is challenging. However, a crucial step was completed by this pilot study with the first pressure measurements in a real-world setting and the successful realization of a decrease in pressure peaks obtained using a prototype air mattress.

Proton Transport Functionality-Enabled Carbon Support for Improved Fuel Cell Performance and Durability.

A novel Monarch carbon material with proton conduction capability due to the presence of sulfone/sulfoxide/sulfonic groups on the surface was evaluated as a potential cathode catalyst support to enable an electrode design with low ionomer content in proton exchange membrane (PEM) fuel cells. X-ray photoelectron spectroscopy of the carbon support confirmed the sulfonic acid functionality, while dynamic vapor sorption measurements proved higher water uptake. Electrochemical impedance spectroscopy of the PtCo/Monarch electrodes showed higher proton conductivity than state-of-the-art PtCo/C with decreasing ionomer to carbon (I/C) content due to the presence of sulfonic acid functional groups on the carbon support surface. Fuel cell performance and durability measurements showed better high-current density performance for PtCo/Monarch with a 75% lower ionomer content in the electrode compared to that of PtCo/C. Our studies indicate that Monarch carbon could be a viable alternative support for PEM fuel cell catalyst applications.

Reduced valence state of iridium supported on antimony doped tin oxide as a highly active and robust oxygen evolution reaction electrocatalyst for proton exchange membrane-based electrolysis

We use facile microwaves (MWs)-assisted polyol method to synthesize metallic Ir-nanoparticles (Ir-NPs) supported on antimony-doped tin oxide (ATO). Parameters such as Ir loading, reaction temperature and reaction time were optimized to achieve high electrocatalytic performance of oxygen evolution reaction (OER) activity and durability under the corrosive OER environment of acidic electrolyzers. Electrocatalysts with varying Ir loading between 10 and 40 wt% were synthesized at two different temperatures (140 °C and 160 °C) to compare morphology, Ir valence state, OER activity and stability. This analysis has revealed efficient electrocatalyst synthesis with a narrow size distribution and homogeneous dispersion over the support surface. An electron rich state of Ir, contributing to the electrocatalyst activity and stability, was achieved at the synthesis temperature of 160 °C. Among the as-synthesized electrocatalysts, one, named Ir/ATO.AT-40-160, has demonstrated high activity (449 ± 2.7 A gIr−1) and high AST stability (75.1% retained current), reaching respectively 1.5 and 2 times those of a state-of-the-art commercial electrocatalyst. The high catalytic activity and excellent stability can both be attributed to the depressed overoxidation of the active Ir due to the low valence state, appropriate composition, and highly dispersed Ir NPs over the support surface.

Influence of Ag particle size and Ag : Al2O3 surface ratio in catalysts for the chloride-promoted ethylene epoxidation

Ethylene epoxidation is catalyzed by α-alumina supported silver catalysts. The influence of silver particle size has been a topic of debate, and was typically investigated without the industrially essential chloride promoter. We studied the catalyst behavior in the presence of chloride. Transient behavior was observed in the first tens of hours on stream, not as a result of particle growth, but due to the gradual change in the nature of the active silver site in the presence of chloride. Different strategies were used to tune the particle size: either varying the silver loading or varying the decomposition atmosphere. Increasing the particle size from 13 to 50 nm by changing the Ag loading from 2 to 15 wt% increased the selectivity from 35 to 80%. However, increasing the 15 wt% Ag particle size from 48 to 184 nm by varying the heat treatment led to a decrease in selectivity from 80 to 50%. Changing the Ag particle size with both strategies also changes the Ag : Al2O3 surface ratio. The ethylene oxide selectivity is actually correlated to the Ag : Al2O3 surface ratio, rather than to the particle size in this size range. This can be explained by its influence on the probability of a formed ethylene oxide molecule to subsequently further react over support surface groups.

Effect of Support on Oxidative Esterification of 2,5-Furandiformaldehyde to Dimethyl Furan-2,5-dicarboxylate

One-step oxidative esterification of 2,5-furandiformaldehyde (DFF) derived from biomass to prepare Dimethyl Furan-2,5-dicarboxylate (FDMC) not only simplifies the catalytic process and increases the purity of the product, but also avoids the polymerization of 5-hydroxymethylfurfural (HMF) at high-temperature conditions. Gold supported on a series of acidic oxide, alkaline oxide, and hydrotalcite was prepared using colloidal deposition to explore the effect of support on the catalytic activities. The Au/Mg3Al-HT exhibited the best catalytic activity, with 97.8% selectivity of FDMC at 99.9% conversion of DFF. This catalyst is also suitable for oxidative esterification of benzaldehyde and furfural. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and CO2 temperature programmed desorption (CO2-TPD) were performed to characterize the catalysts. The results indicated that the medium and strong basic sites in the catalysts benefited for the absorption of intermediate agents and facilitated the oxidative esterification of aldehyde groups, while neutral or acidic supports tended to produce an acetal reaction. It is worth noting that basicity on the support surface reduced the electronic state of the Au nanoparticle (Auδ−) and, thus, enhanced the catalytic selectivity of oxidative esterification. This finding demonstrated that the support plays a crucial role in oxidative esterification.