Metal Catalyst Particles Research Articles

Gas-phase and liquid-phase purification of plastic waste derived carbon nanotubes: Effect of purification agent and operational parameters

The preparation of carbon nanotubes (CNTs) by catalytic pyrolysis of waste plastics is one of the most promising technologies to realize the harmless and high-value recycling of waste plastics. However, there are limited studies on the purification of waste-derived carbons, which is of significance for downstream applications. In this paper, the effects of different gas-phase purification conditions (temperature, gas type), liquid-phase purification (hydrochloric and nitric acid reflux), and combined gas-liquid purification on the properties of CNTs prepared from waste plastics were investigated. The as-obtained and purified CNTs were characterized using SEM, TEM, TPO, XRD, XPS, Raman spectroscopy, and FTIR spectroscopy. Results showed that operational temperatures have distinct impacts on the properties of CNTs during gas-phase purification. An appropriate temperature range for gas-phase purification was determined, with temperatures around 450 °C for air, 650 °C for CO2, and 700 °C for steam respectively, so that the amorphous carbon could be removed and the graphitization of CNTs was retained. Approximately 93 wt% of the metal catalyst particles could be removed with acid treatment for 4 h. In addition, carboxyl and hydroxyl functional groups were introduced to CNTs after acidic treatment. Furthermore, it was found that the approach combining CO2 treatment and nitric acid washing yielded CNTs with relatively higher quantities and lower defect levels. Results showed the properties of CNTs varied from the purification methods, which could meet different needs based on the downstream specific application requirements.

Toward Rational Design of Nickel Catalysts for Thermocatalytic Decomposition of Methane for Carbon Dioxide‐Free Hydrogen and Value‐Added Carbon Co‐Product: A Review

AbstractThermocatalytic decomposition of methane provides opportunities for hydrogen (H2) production with no emission of carbon dioxide. However, high‐value carbon products need to be produced for economic deployment of thermocatalytic decomposition and to achieve a minimum H2 selling price below the U.S, Department of Energy target of $ 1/kg H2. In this review, we re‐evaluate data on catalyst development reported in the literature and propose correlations between catalyst characteristics, catalytic stability, and properties of carbon co‐products. In the first part of the review, growth mechanisms for carbon nanotubes using state‐of‐the‐art chemical vapor deposition are reviewed to catalog the effects of catalyst characteristics, the influence of carbon sources, interactions between metal particles and supports, and metal particle sizes on carbon growth. In the second part, representative developments in mono‐, bi‐, and tri‐metallic nickel catalysts are highlighted. We present kinetic analysis of reactions catalyzed by mono‐metallic nickel catalysts, which generates a correlation between metal particle size and catalyst stability. Rational design of Ni‐based catalysts for TCD of methane requires attention to the size of the metal particle and effective normalization of the reaction rates. Further attention to the distribution of the metal particle sizes may help identify catalyst properties that contribute longevity and selectivity to processes that use them. While it is tempting to focus on the highest valued carbon products (e. g., CNTs and CFs), analysis of the markets for other carbon products suggests that a more flexible approach may generate comparable returns without the risk associated with specialization.

(Invited) Local pH in the (Photo/Electro) Catalytic Environment

(Photo)electrodes designed for improved efficiency and selectivity for CO2 reduction are often nanostructured, for example highly roughened metal films, nanowire arrays, and catalyst particles within a gas diffusion electrode. In all cases, local pockets of water with dissolved CO2 and ions are necessary for the reduction reaction. Although these regions are thought of as having a pH, they are often too small to have a well-defined pH or be at thermodynamic equilibrium until a minimum electrolyte pool size is reached. Computational studies using stochastic chemical kinetics provide a window into this environment, bridging the nanometer scale to the bulk-like scale. The calculations show that the compositions of these regions are characterized by large concentration fluctuations including periods of time when some ions are not present at all. The calculations enable useful trends in electrolyte composition to be identified as a function of electrolyte pool size, providing insights to the complex environments surrounding the catalytic center.

Phase and orientation effects in X-ray attenuation of carbonaceous epoxy composites

Composites made of carbon nanotubes (CNTs) reinforced in an epoxy matrix have already been successfully used as electromagnetic interference shielding materials. Different weight fractions of randomly distributed and vertically aligned multiwall carbon nanotubes (MWCNTs), graphite, and carbon fiber reinforced in the epoxy matrix were used to make these composites. The comparisons of percentage attenuation of different composite materials were studied under both diagnostic or hard (narrow beam geometry) and soft X-rays (monochromatic X-rays beam). It was found that the concentration of CNTs and graphite in epoxy composites affects attenuation. The results also demonstrate that the percentage attenuation for CNTs (as made) epoxy composite is always higher than graphite epoxy and treated CNTs epoxy composite at any concentration at the same thickness and tube voltage. This study also confirmed that the metal catalyst particles present in CNTs contribute to a considerable attenuation of X-rays along with CNTs and also demonstrated that the increase in metal content inside CNTs increases the attenuation. For hard X-rays, the orientation of CNTs in composites affects attenuation, and this effect gradually weakens at higher tube voltages. Vertically aligned carbon nanotubes (VACNT) array epoxy, and the thin composites are not suitable to attenuate diagnostic X-rays coming from high tube potential. For thin samples, VACNT array epoxy composites always perform better on attenuation of soft X-rays than randomly oriented CNTs in composites with any other composition lower than 15 wt %. This study also showed that there is a difference in the attenuation of soft X-rays amongst CNTs, graphite, and carbon fiber epoxy composites, which confirms that the attenuation depends on the geometry of the carbon structures. There is a clear effect of the orientation of CNTs in VACNTs epoxy composite on soft X-ray attenuation, and it shows that the radial direction of CNTs attenuates more X-ray radiation than the tube axis direction.

Time-Resolved Formation and Operation Maps of Pd Catalysts Suggest a Key Role of Single Atom Centers in Cross-Coupling.

An approach to the spatially localized characterization of supported catalysts over a reaction course is proposed. It consists of a combination of scanning, transmission, and high-resolution scanning transmission electron microscopy to determine metal particles from arrays of surface nanoparticles to individual nanoparticles and individual atoms. The study of the evolution of specific metal catalyst particles at different scale levels over time, particularly before and after the cross-coupling catalytic reaction, made it possible to approach the concept of 4D catalysis-tracking the positions of catalytic centers in space (3D) over time (+1D). The dynamic behavior of individual palladium atoms and nanoparticles in cross-coupling reactions was recorded with nanometer accuracy via the precise localization of catalytic centers. Single atoms of palladium leach out into solution from the support under the action of the catalytic system, where they exhibit extremely high catalytic activity compared to surface metal nanoparticles. Monoatomic centers, which make up only approximately 1% of palladium in the Pd/C system, provide more than 99% of the catalytic activity. The remaining palladium nanoparticles changed their shape and could move over the surface of the support, which was recorded by processing images of the array of nanoparticles with a neural network and aligning them using automatically detected keypoints. The study reveals a novel opportunity for single-atom catalysis─easier detachment (capture) from (on) the carbon support surface is the origin of superior catalytic activity, rather than the operation of single atomic catalytic centers on the surface of the support, as is typically assumed.

Metal supported graphene catalysis: A review on the benefits of nanoparticular supported specialty sp2 carbon catalysts on enhancing the activities of multiple chemical transformations

Transition metal-based heterogeneous catalysts are widely used across many industries. The prevalence of these materials across so many domains has inspired research into many different types of solid supports, the nature of which can affect catalytic performance. One support receiving increased attention because of its many desirable features is graphene. These features include 1) native catalytic properties enabling co-catalysis, 2) enhanced catalytic activity when both metal atoms and nanoparticles are supported, 3) chemical functionalization to tune catalytic properties, 4) tough lattice structure and high electric conductivity, and 5) specific solid-state ligand bond formation augmenting electron transport between graphene and the metal to name a few. Although graphene shows tremendous applicability in heterogeneous catalysis, researchers are still tuning the structure to improve its catalytic performance, such as by incorporating defects or dopants into its morphology. Another important consideration is the interaction between the graphitic support and metal catalyst particle, which in turn is highly dependent upon the nature and quality of the catalyst preparation technique. This work reviews the modification of graphene structure along with the applications of different modified graphene-supported catalysts. It also discusses some of the most used and efficient catalyst preparation techniques for both batch and continuous modes. Various examples of applications that highlight graphene properties and catalytic interactions are discussed. To strengthen our reviews, a set of statistical analysis is included.

Scale-up studies on electrically driven steam methane reforming

This work is devoted to scale-up parametric studies of a new reactor for the steam reforming of methane driven by electrical current. The main distinguishing feature of this type of reactor is the use of direct electrical current flowing through metal particles to heat the whole reactor volume using Joule heating. The heat and mass transfer model uses six gaseous chemical species in the gas phase and inside the catalyst. Reaction rate expressions are taken from the literature (Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetics). In this work we consider a cylindrical electrically insulated tube with a diameter of 0.5 m and a height of 0.88 m, which is filled with metal particles and catalyst particles with diameters of 10 mm and 4 mm, respectively. Parametric runs have been carried out for different flow rates from 0.04 kg/s to 0.1 kg/s and electrical power from 185 kW to 462 kW. The results of simulations revealed that the cross-sectional temperature profile of a scaled-up reactor is mostly uniform, with small hot spots but a temperature difference that is usually within 100K. It was shown that the gas inflow located on the top gives smoother gradients of the particle temperature and gaseous species in comparison to the case when the gas is supplied from the bottom of the fixed bed.

Steam methane reforming driven by the Joule heating

The main objective of this work is to present a new particle unresolved 3D-1D DEM-CFD-based model enabling predictions of a new steam methane reforming (SMR) driven by the direct electrical current. The main feature of this technology is the use of metal particles heated by the Joule heat resulting from direct electrical current flowing through metal particles in order to heat the gas phase and catalyst particles (Ni/α-Al2O) to sustain endothermic chemical reactions. The model uses six gaseous chemical species (CH4, CO2, CO, H2O, H2, N2) in the gas phase inside the catalyst. The Langmuir–Hinshelwood-Hougen-Watson (LHHW) kinetics is used. The distinguishing feature and the novelty of the model presented in this work consist in the calculation of the 3D distribution of the electric field inside non mono-disperse fixed beds. The electric field distribution is used to calculate the Joule heating term for each electrically conducting particle participating in the electrical current flow. Additionally, the new model predictions are compared with alternative models based on the chemical equilibrium principles. The models have been numerically solved using MATLAB. To illustrate the performance of the models and to check the feasibility of a new electrical steam methane reforming concept, we consider a cylindrical electrically insulated tube with a diameter of 0.1 m and a height of 0.5 m, which is filled with metal particles and catalyst particles with diameters of 5 mm and 2 mm, respectively. Parametric runs for different flow rates from 0.0025 kg/s to 0.01 kg/s and electrical power from 6.9 kW to 39 kW have been carried out. Results of simulations showed that an increase in the flow rate value (ṁ) by keeping constant input electrical power leads to a decrease in the conversion of CH4 proportionally to ṁ-1/2. A linear increase in the flow rate and input power leads to a decrease in methane conversion. When the input electrical power is increased, the difference between catalyst particle temperature and gas temperature decreases.

Overcoming Limitations in the Strong Interaction between Pt and Irreducible SiO2 Enables Efficient and Selective Hydrogenation of Anthracene.

Interactions between metals and oxide supports are crucial in determining catalytic activity, selectivity, and stability. For reducible oxide supported noble metals, a strong metal-support interaction (SMSI) has been widely recognized. Herein we report the intermediate selectivity and stability over an irreducible SiO2 supported Pt catalyst in the hydrogenation of anthracene that are significantly boosted due to the SMSI-induced formation of intermetallic Pt silicide and Pt-SiO2 interface. The limitation in the strong interaction between Pt nanoparticles and irreducible SiO2 has been breached by combining the strong electrostatic adsorption method and following the high temperature reduction strategy. Due to the isolated Pt active sites by Si atoms, the activated H species produced over the Pt2Si/SiO2 catalyst with an initial catalytic activity of 2.49 μmol/(m2/g)/h as well as TOF of 0.95 s-1 preferentially transfer to the outer ring of anthracene to 87% yield of symmetric octahydroanthracene (sym-OHA) by subsequent hydrogenation. In addition, the Pt2Si/SiO2 catalyst presents an excellent stability after five cycles, which can be attributed to the fact that intermetallic Pt2Si nanoparticles are anchored firmly onto the surface of the SiO2 support. The discovery contributes to broaden the horizons on the SMSI effect in the irreducible oxide supported metal particle catalysts and provides guidance to design the metal-SiO2 interface and tune the surface chemical properties in diverse application conditions.

Alkaline modified A-site deficient perovskite catalyst surface with exsolved nanoparticles and functionality in biomass valorisation

Environmental problems associated with the use of fossil fuels and increase in energy demands due to rise in population and rapid industrialisation, are the driving forces for energy. Catalytic conversion of biomass to renewable energies is among the promising approaches to materialize the above. This requires development of robust catalysts to suppress deactivation due to carbon deposition and agglomeration. In this work, surface properties and chemistry such as exsolution of B-site metal catalyst nanoparticles, particle size and distribution, as well as catalyst-support interactions were tailored through the use of alkaline dopants to enhance catalytic behaviour in valorisation of glycerol. The incorporation of alkaline metals into the lattice of an A-site deficient perovskite modified the surface basic properties and morphology with a consequent robust catalyst-support interaction. This resulted in promising catalytic behaviour of the materials where hydrogen selectivity of over 30% and CO selectivity of over 60% were observed. The catalyst ability to reduce fouling of the catalyst surface as a result of carbon deposition during operation was also profound due to the robust catalyst-support interaction occurring at the exsolved nanoparticles due to their socketing and the synergy between the dopant metals in the alloy in perovskite catalyst systems. In particular, one of the designed systems, La0.4Sr0.2Ca0.3Ni0.1Ti0.9O3±δ, displayed almost 100% resistance to carbon deposition. Therefore, lattice rearrangement using exsolution and choice of suitable dopant could be tailored to improve catalytic performance.

Statistical Product Selectivity Modeling and Optimization for γ-Al2O3-Supported Cobalt Catalysts-Based Fischer–Tropsch Synthesis

The statistical selectivity models were developed for four different Fischer–Tropsch synthesis product range, including methane (CH4), light olefins (C2=C4), light paraffins (C2–C4), and long-chain hydrocarbons (C5+), based on the experimental data obtained over thirteen γ-Al2O3 supported cobalt-based catalysts with different cobalt particle and pore sizes. The input variables consist of cobalt metal particle size and catalyst pore size. The cubic and quadratic polynomial equations were fitted to the experimental data, however, the mathematical models were subjected to model reduction for the enhancement of model adequacy, which was investigated through ANOVA. The multi-objective optimization revealed that the maximum C5+ selectivity (84.150%) could be achieved at the cobalt particle size and pore sizes of 14.764 and 23.129 nm, respectively, while keeping the selectivity to other hydrocarbon products minimum.

Analysis of Single-Walled Carbon Nanotubes in Estuarine Sediments by Density Gradient Ultracentrifugation Coupled to Near-Infrared Fluorescence Spectroscopy Reveals Disassociation of Residual Metal Catalyst Nanoparticles.

The continued growth of the nanotechnology industry and the incorporation of nanomaterials into consumer applications will inevitably lead to their release into environmental systems. Single-walled carbon nanotubes (SWCNTs) in particular have exhibited many attractive optical, mechanical, and electrical properties that lend themselves to new and exciting applications. Assessing their environmental impact upon release into the environment is contingent upon quantifying and characterizing SWCNTs in environmental matrixes. In this study, SWCNTs were isolated from estuarine sediments using density gradient ultracentrifugation (DGU), followed by online flow-through analysis of the density fractions via near-infrared spectroscopy. This approach yielded significant improvements in the quantitative detection limit, from 62 to 1.5 μg g-1. In addition, fractions of the density gradient were also obtained for further analysis by bulk inductively coupled plasma mass spectrometry (ICP-MS) and single-particle ICP-MS. Using fluorescent, semiconductive SWCNTs, the primary fluorescent nanotube fraction was found to be separated from the sediment matrix during DGU; however, the residual metal catalyst particles that had been assumed to be physically bound to the SWCNTs were found to form a separate band in the density gradient apart from the fluorescent SWCNTs. This result was repeated for a number of SWCNT types regardless of the metal catalyst and synthesis method, with a 0.1 g cm-3 density difference between most fractions. The apparent disconnect between the fluorescent fraction of SWCNTs and their metal-containing constituents potentially complicates CNT risk assessment as analysis techniques focusing solely on either CNT fluorescence or metal fingerprints may misrepresent exposure concentrations and their toxicological implications.

Interactions between atmospheric pressure plasmas and metallic catalyst particles in packed bed reactors

Atmospheric-pressure plasmas sustained in packed bed reactors (PBRs) are being investigated for chemical conversion of gases and pollution control. Metallic catalysts added to the surfaces of the dielectric beads of PBRs can increase the energy efficiency and selectivity of chemical processes by reducing operating temperature and providing additional reaction pathways. In this paper, results from a computational investigation of plasma surface interactions between micron-scale metallic catalysts and humid-air plasmas in PBRs are discussed. We found that high plasma density regions form in the proximity of the metallic catalysts. These higher-density plasma regions were confirmed experimentally using ICCD imaging. The intense plasmas result from geometrical electric field enhancement and redistribution of charges within the conductive particles, leading to further enhancement. The high electric field at the triple points of the catalysts can produce electric field emission of electrons, which provides a pre-ionization source or additional source of electrons. These regions of high electric field and sources of electrons guide discharges towards the catalysts and increases fluxes of excited species, ions, electrons and photons to their surfaces. These fluxes are focused primarily at the triple points between the metal, dielectric and gas. As a result, the catalyst is locally heated, which could lead to further increased rates of thermocatalytic reactions on the surface. Surface roughness of the metal inclusions can lead to additional electric field enhancement, which changes the character of the discharges in the vicinity of the catalysts while reducing breakdown voltage.

Metal Exsolution to Enhance the Catalytic Activity of Electrodes in Solid Oxide Fuel Cells.

Exsolution is a novel technology for attaching metal catalyst particles onto ceramic anodes in the solid oxide fuel cells (SOFCs). The exsolved metal particles in the anode exhibit unique properties for reaction and have demonstrated remarkable stabilities under conditions that normally lead to coking. Despite extensive investigations, the underlying principles behind exsolution are still under investigation. In this review, the present status of exsolution materials for SOFC applications is reported, including a description of the fundamental concepts behind metal incorporation in oxide lattices, a listing of proposed mechanisms and thermodynamics of the exsolution process and a discussion on the catalytic properties of the resulting materials. Prospects and opportunities to use materials produced by exsolution for SOFC are discussed.

Effect of catalyst size on flameless combustion's hysteresis characteristics of air-gas mixtures with combustible gas's impurities

Analytical models of heat and mass transfer's hysteresis and combustion kinetics of combustible gas impurities on a metal catalyst particle (wire) in the presence of only one onesided reaction are proposed. The analysis is carried out taking into account thermal diffusion and depending on the catalyst's size and the gas-air mixture's temperature. The dependences of platinum wire's temperature on hydrogen-air mixture's temperature at various wire diameters are presented. Decrease in the wire's diameter under unchanged other conditions leads to a decrease in the hysteresis region and its further degradation. The method used for analytical determination of hysteretic regions and degradation points, which lies in representing the desired dependences of operating parameters in a parametric form (parameter is catalyst's temperature). Analytical dependence (spinodal) gas-air mixture's temperature on catalyst's diameter was found that describes all critical points, including degradation points.The value of the diameter's and temperature's wire catalyst, the mixture's temperature, which correspond to critical condition’s degradation, were obtained in explicit form.

Surface passivation dictated site-selective growth of aligned carbon nanotubes.

Surface defects play a significant role in the nucleation and growth of metal particles. Site-selective nucleation of metal catalyst particles, and the subsequent growth of nanostructures, could thus be accomplished by defect engineering. This paper demonstrates the switching of growth sites of vertically aligned multiwall carbon nanotubes (MW-CNTs) by manipulation of surface passivation of the substrate and discusses the possible mechanism behind this selectivity. A complementary growth pattern of CNTs is observed for pre-treatment of identically patterned SiO2/Si substrates under a reducing and non-reducing atmosphere. Variation in the number density of oxygen vacancies on the silicon dioxide surface and the presence of native oxide on the silicon face are believed to dictate the observed selectivity. The CNT architectures mimic the substrate pattern meticulously, exhibiting sharp edges, illustrating a high degree of site selectivity. The chemical state of the substrate surface and catalyst particles has been studied using Auger electron spectroscopy. Electron microscopy and Raman spectroscopy were employed to characterize the synthesized CNTs. The Hermans orientation factor was calculated to quantify the degree of alignment of the MWCNTs. Such facile control over the growth site of aligned carbon nanotubes on a substrate is a desirable aspect of synthesis for easy integration with existing silicon fabrication technology.

Direct growth of multiwall carbon nanotube on metal catalyst by chemical vapor deposition: In situ nucleation

Carbon nanotubes (CNTs) are among the most promising materials for applications in future nanotechnology. The combination of excellent physical and mechanical properties beside chemical resistance seems very interesting for different industrial applications. However, the commercialization of nanotube-based nanocomposites has been hampered by their high cost and minuscule production. In the present study, we have tried to understand the fundamental aspects of multiwall carbon nanotubes (MWCNTs) direct growth on metal catalyst particles via thermal chemical vapor deposition (T.CVD) in the presence of zirconium hydride (ZrH2) and aluminum nanoparticles. The effects of different parameters such as gas flow rates, metal catalyst systems, and temperature on the quality and quantity of the obtained MWCNTs were investigated and some interesting results were obtained. It was found that at moderate temperatures, MWCNTs growth rate on iron-based (Fe) catalyst was much more than that on nickel (Ni) and cobalt (Co) particles. Transmission electron microscopy (TEM) results and TGA analysis revealed that metal nanoparticles as the nucleation sites come from the fragmentation of catalyst surfaces and the application of relatively small amounts of ZrH2 significantly enhances this mechanism. Besides, crystalline structure of MWCNTs was performed by Raman spectroscopy, X-ray diffraction (XRD) and selected area electron diffraction (SAED) technique. This method shows great promise for achieving the goal of mass-production due to its high quality and yield; simplicity, and ease of scale-up.

Восстановление каталитической активности поверхности и стабилизация активирующего раствора на основе меди(I) перед химическим меднением

Methods of chemical activation of the dielectric surface, in which metal-catalyst particles are formed on it as a result of chemical transformations, are more universal, since they allow to vary the compositions of solutions of chemical deposition of metal and to precipitate metals on substrates of different chemical nature with different morphology and surface structure. Noble metal compounds and colloidal solutions characterized by limited storage stability due to the coagulation process are mainly used for surface activation. Palladium-free activation is used for metallization of the surface of unfolded dielectrics and metallization of through holes of printed circuit boards. As a dielectric material used inorganic materials (ceramics, polycore, various types of ceramics) and organic fiberglass with epoxiconazole adhesive layer. The aim of this work is to improve the technology of activation of non-conductive surfaces by true solutions based on copper(I) by optimizing the composition of the activator. It is shown that the drying temperature affects the composition of the activator layer. Activates the layer obtained by drying at 323-373 K, is composed of CuCl2∙2H2O and Cu2O. The optimum mode of drying an activating solution based on copper(I) (T = 353-373 K, τ = 15-20 minutes). The compounds formed during the drying of the activating solution based on copper monochloride do not have catalytic activity sufficient to initiate chemical and electrochemical metallization reactions. Therefore, it is necessary to carry out an additional operation-acceleration in solutions of reducing agents. Solutions of hydrazine chloride (N2H4∙HCl), sodium hypophosphite (NaH2PO4∙H2O), hydroxylammonium chloride (NH2OH∙HCl), the concentration of which varied in the range (0.1-0.5) mol∙l‒1, as well as a solution of alkaline formaldehyde were taken as these solutions. The technology of activator acceleration in a solution of the following composition: hydroxylammonium chloride (NH2OH∙HCl)  0.5 mol∙l-1; pH = 8-10; T = 298 K, which allows to significantly increase the surface concentration of catalytically active centers on the dielectric surface. In order to determine the durability and performance of the activating solution, the stability of the copper (I)  based solution was studied. The durability and performance of the activating solution is ensured by the presence of copper monochloride in it. This is possible if the solution will constantly undergo a reaction of reduction of divalent copper to a monovalent state. For this purpose, sodium hypophosphite in an amount of 0.5 mol∙l‒1 and metallic copper with a concentration of 30 g∙l‒1 were introduced into the activating solution as a reducing agent. The optimal composition of the activating solution containing (mol∙l‒1): copper chloride(I) ‒ 3.10; hydrochloric acid ‒ 3.10; surfactant OP-10  0.01; metallic copper 0.47 was established. Methods of regeneration of copper(I) concentration in activation solutions have been developed, which can significantly extend their service life.

Carbon Nanotube-Quicklime Nanocomposites Prepared Using a Nickel Catalyst Supported on Calcium Oxide Derived from Carbonate Stones.

Carbon nanotube-quicklime nanocomposites (CQNs) have been synthesized via the chemical vapor deposition (CVD) of n-hexane using a nickel metal catalyst supported on calcined carbonate stones at temperatures of 600–900 °C. The use of a Ni/CaO(10 wt%) catalyst required temperatures of at least 700 °C to obtain XRD peaks attributable to carbon nanotubes (CNTs). The CQNs prepared using a Ni/CaO catalyst of various Ni contents showed varying diameters and the remaining catalyst metal particles could still be observed in the samples. Thermogravimetric analysis of the CQNs showed that there were two major weight losses due to the amorphous carbon decomposition (300–400 °C) and oxidation of CNTs (400–600 °C). Raman spectroscopy results showed that the CQNs with the highest graphitization were synthesized using Ni/CaO (10 wt%) at 800 °C with an IG/ID ratio of 1.30. The cyclic voltammetry (CV) of screen-printed carbon electrodes (SPCEs) modified with the CQNs showed that the performance of nanocomposite-modified SPCEs were better than bare SPCEs. When compared to carboxylated multi-walled carbon nanotubes or MWNT–COOH-modified SPCEs, the CQNs synthesized using Ni/CaO (10 wt%) at 800 °C gave higher CV peak currents and comparable electron transfer, making it a good alternative for screen-printed electrode modification.

Catalytically sustainable, palladium-decorated graphene oxide monoliths for synthesis in flow

Continuous flow synthesis is an essential route towards high throughput manufacturing of fine chemical and pharmaceutical products. The mentioned chemistries are often catalyzed by solid-supported catalysts via packed beds which are characterized by multiple issues such as high pressure-drops, micro channeling through the bed, and leaching of the metallic catalyst into the product stream. These issues lower the overall process efficiency. Three dimensional (3D) structures, known as monoliths, with high porosity and mechanical robustness, offer the ideal properties to be used macroscopic supports for metallic catalyst particles. This approach has shown to alleviate several known issues with catalyst packed beds effectively.Herein centimeter-scale monolithic catalysts of palladium (Pd)-decorated, covalently-bonded graphene oxide (GO) layers have been prepared via a completely aqueous, one-pot system. These monolithic composite structures were designed for Suzuki cross-coupling reactions in flow. As highly engineered materials, monoliths’ properties such as oxygen content and Pd catalyst ionic species were tuned via microwave irradiation and ethanol vapor reduction treatments. The optimal monolithic catalysts showed over 5 h of operational longevity in flow, which was 300% higher than the conventional Pd on GO catalyst packed beds. As a proof of concept, the monolithic catalyst was successfully used as a model structure for nondestructive X-ray CT-scan elemental and porosity mapping in the centimeter scale.