Metal Surface Area Research Articles

Synthesis of single phase LaMn1−XNiXO3 perovskite material

Ni substituted lanthanum manganite of LaMn1−XNiXO3 (x = 0.2, 0.4, 0.5, 0.6, 0.7) of a single phase perovskite structure was synthesised through sol-gel technique. The effect of Ni substitution by varying Ni and Mn amount ratios over LaMn1−XNiXO3 materials were studied. The physio-chemical characteristics like crystallinity were confirmed by XRD, surface area by BET analysis, metallic surface area by CO chemisorption. The optimal level of Ni substitution increases surface area, pores volume and metallic surface area, which leads highly stability. The oxygen vacancies and rapid migration of lattice oxygen from the bulk toward the surface was observed over LaMn0.4Ni0.6O3 compared to other perovskite materials. The LaMn0.4Ni0.6O3 perovskite materials show high surface area, metallic area with absorbed oxygen due to threshold Ni and Mn ratio leads the perfect synergic balance.

Impact of Design and Deployment Technique on the Hydrodynamic Resistance of Flow Diverters

PurposeDespite the high efficacy of flow diverters (FD) in treating sidewall intracranial aneurysms, failures are reported. One of the physical factors determining efficacy is the flow reducing capacity of the FD that is currently unknown to the operator. Our aim was to measure the flow reducing capacity expressed as the hydrodynamic resistance (HR), the metallic surface area (MSA) and pore density (PD) of two different FD designs and quantitatively investigate the impact of sizing and the deployment technique on these parameters.MethodsAltogether 38 Pipeline (Medtronic) and P64 (Phenox) FD‑s were implanted in holder tubes by a neurointerventionist in nominally sized, oversized and longitudinally compressed or elongated manners. The tubes were placed in a flow model with the flow directed across the FD through a side hole on the tube. HR was expressed by the measured pressure drop as the function of the flow rate. Deployed length, MSA and PD were also measured and correlated with the HR.ResultsBoth PD and MSA changed with varying deployment length, which correlates well with the change in HR. Oversizing the device by 1 mm in diameter has reduced the HR on average to one fifth of the original value for both manufacturers.ConclusionThis study demonstrates experimentally that different FD designs have different flow diverting capacities (HR). Parameters are greatly influenced by radial sizing and longitudinal compression or elongation during implantation. Our results might be useful in procedure planning, predicting clinical outcome, and in patient-specific numerical flow simulations.

Effect of Different Chelating Agents on the Physicochemical Properties of Cu/ZnO Catalysts for Low-temperature Methanol Synthesis from Syngas Containing CO<sub>2</sub>

Nanostructured Cu/ZnO catalysts were prepared by a simple solid-state method, using cheap metal nitrates as raw materials. Special attention was paid to the influence of different chelating agents such as citric acid, formic acid and oxalic acid on the physicochemical properties of Cu/ZnO catalysts, which were characterized by detailed investigations. CuO crystallite size, oxygen vacancies and surface compositions were clearly affected by chelating agent types, leading to different CuO–ZnO interactions in the calcined catalysts as well as distinct reducibility. Different chelating agents also had significant effects on specific surface area, metallic Cu0 surface area, and Cu crystallite size, as well as ZnO (002) plane to ZnO (100) plane ratio (I(002)/I(100)) calculated based on the peak intensity of XRD patterns of the reduced samples, so influencing the catalytic activity for low-temperature methanol synthesis from syngas containing CO2. The structure-activity correlations, particularly the relationships between space time yield (STY) of methanol with Cu0 surface area and I(002)/I(100) ratio, were evaluated. Cu/ZnO catalyst prepared with oxalic acid showed the highest STY value, which was 2.3 and 5.3 times higher that of the catalysts obtained with citric acid and formic acid, respectively. The excellent catalytic performance was due to its greater Cu0 surface area, higher specific surface area and smaller Cu crystallite size. Stronger interactions between Cu and ZnO in the reduced samples were also favorable for enhancing catalytic activity for low-temperature methanol synthesis.

An Active K‐OMS‐2 Supported Catalyst for Hydrogenolysis of Glycerol

AbstractPropanediols are very important chemical intermediates, which need to be prepared through commercially viable routes. Cryptomelane type octahedral molecular sieve‐2 (K‐OMS‐2), a cheap and environmentally benign microporous oxide was employed to support Ru and used as a catalyst to get 1,2‐propanediol (1,2‐PDO) selectively through hydrogenolysis of glycerol. Three catalysts with different Ru content were prepared and evaluated for glycerol hydrogenolysis. Among these, 1 wt.% Ru‐K‐OMS‐2 showed reasonably good activity towards 1,2‐PDO formation under moderate reaction conditions even at lower Ru loading (0.9 wt.%). When other metals such as Cu and Ni were supported on K‐OMS‐2, their performance was inferior compared to Ru‐supported catalysts. All the catalysts were characterized using various physicochemical techniques like XRD, N2‐sorption, TPD, H2‐TPR, TGA, ICP‐OES, FE‐SEM and TEM. The enhanced catalytic activity with the 1 wt.%Ru‐K‐OMS‐2 catalyst was attributed to the better Ru metal dispersion, higher active metal surface area, basic strength, and porosity of the support. The catalyst was found to be recyclable. Analysis of spent catalyst by TEM showed disintegration of Ru nanoparticles to smaller ones, under high H2 pressure at the reaction temperature. Smaller Ru particles are expected to promote C−C bond cleavage thus suppressing 1,2‐PDO formation. Furthermore, a relationship between the TOF value, Ru nanoparticles size, and the basic strength of the catalysts was established, which provides dipper insight into the different catalytic behavior of the catalysts.

On altering the wetting behaviour and corrosion resistance of a large metallic surface area by wire electrochemical texturing

This paper presents a novel and practically applicable method for a quick fabrication of uniform surface patterns (periodic micro-pillars with rectangular and square cross-section) on a large surface area of any conducting or semi-conducting material using Wire Electrochemical Micromachining (Wire-ECMM). Micro pillars with a rectangular cross-section are generated by machining mutually perpendicular micro channels. The depth, spacing, and cross-sectional area of pillars are controlled by varying the process parameters and tool travel distance. Primary pillars (level-1 texture) are machined with a constant Direct Current (DC) voltage and secondary pillars (level-2 texture) are machined with a pulsed DC voltage using a tungsten wire of diameter 100 μm. An aqueous solution of sodium nitrate (NaNO 3 ) is selected as an electrolyte having a pH of about 7.01. A good repeatability in the geometrical parameters of a pillar profile is observed on analysing 3D profilometer micrographs of the textured surfaces. Wetting behaviour of textured surfaces with different geometrical parameters is observed using drop shape analyser. A surface with two levels of textures offers highest contact angle of 147.3° with deionized water. Corrosion current and resistance of the textured surfaces are obtained using Linear Sweep Voltammetry (LSV) and Electrochemical Impedance Spectroscopy (EIS), respectively. Results suggest that corrosion resistance depends upon the area of texture and is highest for the sample with the largest textured area. Also, a sample with the smallest value of area factor (ratio of total area of the top surface of all the pillars in a region to the total projected area of a region) offers highest resistance to corrosion. • A novel approach for large area texturing on any conducting and semi-conducting surface using Wire Electrochemical Micromachining (Wire-ECMM). • A study of the influence of different process parameters on various geometrical features of a textured surface. • A detailed characterization of different textured surfaces using SEM imaging and surface topography. • In depth analysis of the wetting and corrosion behaviour of the textured surfaces using drop shape analyser and Electrochemical Impedance Spectroscopy (EIS).

Mesoporous Silica from Parangtritis Beach Sand Templated by CTAB as a Support of Mo Metal as a Catalyst for Hydrocracking of Waste Palm Cooking Oil into Biofuel

In this study, natural source Parangtritis beach sand was extracted into mesoporous silica (MS). Synthesis of mesoporous silica (MS) was carried out at sodium silicate: CTAB ratio of 1:0.5 (w/w). Monometallic catalyst was used to improve the performance of the catalyst. The monometallic used was Mo metal, which was synthesized using the wet impregnation method. Catalysts were characterized using FTIR, XRD, Surface Area Analyzer (SAA), SEM–EDX, and TEM. MS has pore diameters and surface area of 2.62 nm and 897.3 m2/g, respectively. Mo/MS has pore diameters, surface area, and Mo metal concentration of 2.46 nm, 593 m2/g, and 4.75%, respectively. Catalytic activity and selectivity were evaluated in hydrocracking of waste palm cooking oil at 500, 550, and 600 °C, and catalyst: waste palm cooking oil ratio of 1:100, 1:200, and 1:300. The best catalyst will be tested for reusability 3 times through the hydrocracking process. Mo/MS produces better liquid products and hydrocarbon compounds than MS. The results of the conversion of liquid products analyzed using GCMS. The yield of liquid products obtained in the hydrocracking of waste palm cooking oil using Mo/MS with the optimum temperature and the weight ratio of catalyst: feed at 550 °C and 1: 300 was 66.99 wt.% with consists of hydrocarbon compound as 62.79 wt.%. The yield of liquid products obtained in the hydrocracking waste palm cooking oil using the used Mo/MS catalyst in the last run was 80.26 wt.% with consist of hydrocarbon compound as 74.13 wt.%.Graphic Abstract

Hydrogenation of dimethyl oxalate to ethylene glycol on Cu/SiO2 catalysts prepared by a deposition-decomposition method: Optimization of the operating conditions and pre-reduction procedure

Cu/SiO2 catalysts prepared by a deposition-decomposition (DD) method using ammonium hydroxide are currently among the most promising catalysts for oxalates hydrogenation to ethylene glycol (EG). Here, a Cu/SiO2 catalyst prepared by the DD method was pre-reduced at a) 200–350 °C in 100% H2, and 2) 200 °C in a 50% H2/N2 mixture. Then, it was tested at 200 °C, and 25 barg, while EG yields were optimized, with H2-GHSV and H2/DMO ratios in the ranges 1000–4000 h−1 and 30–200 mol/mol. The calcined catalyst presents an XRD amorphous Cu phyllosilicate phase. After pre-reduction in pure H2 at 200–250 °C (Tred), the Cu metallic surface area increased from 6 to 12 m2/gcat and slightly decreased at 350 °C. Simultaneously, the silanol's band, measured by DRIFT experiments, increased with Tred. The highest ethylene glycol yield (91%) was achieved after pre-reduction at 200 °C in pure hydrogen, working with an H2-GHSV and H2/DMO of 1050 h−1 and 68 mol/mol, respectively. The catalyst was stable for more than 36 h after a 20 h induction period. Catalyst characterization results as a function of Tred confirm that mixed-valence copper nanoparticles favor the EG selective formation, while side reactions leading to ethanol and 1,2-butanediol are related to exposed acidic and basic sites due to decreased Cu/support interactions.

Highly N2-Selective Activated Carbon-Supported Pt-In Catalysts for the Reduction of Nitrites in Water

The catalytic reduction of nitrites over Pt-In catalysts supported on activated carbon has been studied in a semi-batch reactor, at room temperature and atmospheric pressure, and using hydrogen as the reducing agent. The influence of the indium content on the activity and selectivity was evaluated. Monometallic Pt catalysts are very active for nitrite reduction, but the addition of up to 1 wt% of indium significantly increases the nitrogen selectivity from 0 to 96%. The decrease in the accessible noble metal surface area reduces the amount of hydrogen available at the catalyst surface, this favoring the combination of nitrogen-containing intermediate molecules to promote the formation of N2 instead of being deeply hydrogenated into NH4+. Several activated carbon-supported Pt-In catalysts, activated under different calcination and reduction temperatures, have been also evaluated in nitrite reduction. The catalyst calcined and reduced at 400°C showed the best performance considering both the activity and the selectivity to nitrogen. This enhanced selectivity is ascribed to the formation of Pt-In alloy. The electronic properties of Pt change upon alloy formation, as it is demonstrated by XPS.

Synthesis of In2O3 nanocubes, nanocube clusters, and nanocubes-embedded Au nanoparticles for conductometric CO sensors

Cubic indium oxide (In2O3) of different sizes, In2O3 nanocube clusters, and In2O3 nanocube clusters embedded Au nanoparticles were obtained using solvothermal method. Compared with the large size or monodispersed In2O3 nanocubes, In2O3 nanocube clusters shows a higher response to carbon monoxide (CO), due to increased surface area and pore structures. Moreover, In2O3 nanocube clusters with an Au nanoparticle core (Au@In2O3) leads to a further increase of response to CO. Our results also show that 1 at% Au@In2O3 system presents the best sensing properties with response of 42.1–100 ppm CO, response/recovery speed of 2/2 s and ultra-low limit detection. The CO concentration dependence of the sensor response implies that ∼0.5 ppb and ∼28 ppb could be detected with a response value of 1.4 under 20 % and 93 % relative humidity, respectively. This increase in sensing response is due to the fact that Au nanoparticles can enhance the receptor function of the semiconductor gas sensor. Remarkably, Au@In2O3 system unifies three key factors of a semiconductor gas sensor, i.e., high specific surface area, high porosity, and noble metal loading.

Heavy metals in the “plastisphere” of marine microplastics: adsorption mechanisms and composite risk

Heavy metals that are adhered to the surfaces of microplastics in the natural marine environment pose potential threats to marine life. However, little is known about their adsorption mechanisms and composite risks. This study collected seawater, suspended particulate matter (SPM), plankton, and microplastic samples from the waters surrounding Hong Kong, established a method for analyzing 13 heavy metals in the plastisphere, and explored the extrinsic and intrinsic sources of the heavy metals by analyzing natural matrices (seawater, SPM, and plankton) and anthropogenic plastics. We found that heavy metals in the plastisphere were significantly affected by the surrounding matrices, as indicated by its positive correlations with the heavy metals in SPM and plankton at most of the sampling sites. Heavy metals in plankton usually occurred as traces of oxides such as As2O3 and ZnO. The partition coefficients of the studied heavy metals between seawater and the plastisphere were identical to those between the SPM and the plastisphere. No correlations were found between the concentrations of heavy metals in the plastisphere and the heavy metal concentrations, masses, quantities, or surface areas of the microplastics, although some polymer types contained extremely high Cd (676 mg/kg), Pb (1,742 mg/kg), and Zn (1,712 mg/kg) concentrations. Only the Cr, Cu, and Ni concentrations were positively correlated with the specific surface area of the microplastics. A cluster analysis showed that Cr, Cu, and Ni were derived from anthropogenic sources, indicating that adventive heavy metals could be adsorbed by plastics with large specific surface areas. We also established a new composite risk assessment method for heavy metals and microplastics that leverages the specific surface areas of microplastics. The assessment results showed that Cd from Tolo Harbor had a strong ecological risk, while As and Cd from the eastern waters off Hong Kong had moderate composite ecological risks.

Photo-Fenton Process Using Fe(III) Ions from Modified Sugarcane Bagasse for Reactive Black 5 Dye (RB5) Removal

Brazil is one of the largest generators the sugarcane bagasse, this kind of biomass has already shown efficiency related to its in natura adsorption potential (when physically or chemically activated), it can also be used to remove contaminants from water in methods such as advanced oxidative processes. In this study, chemical modifications were carried out in sugarcane bagasse to enable its application in photo-Fenton processes for the degradation of reactive black 5 dye. The materials were chemically activated through immersion in Fe(III) solution for different periods of time: 3, 6, 9, 12, 24, 48 and 96 h; and were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), zeta potential analysis, internal surface area and leached metal quantification. The results showed the cellulose structure, which is predominant in the sugarcane bagasse it was not considerably modified after activation with FeCl3 and evidence of the presence of Fe(III) ions on the surface of the studied material. The degradation efficiency (after 5 min and using 11.5 mg L-1 hydrogen peroxide) for the activated materials was respectively: 55.85%, 49.44%, 71.22%, 92.87%, 88.16% and 98.02%, considering the decrease of the band related to the chromophore group (598 nm). DOI: http://dx.doi.org/10.17807/orbital.v13i2.1482

Ecotoxicological effects of micronized car tire wear particles and their heavy metals on the earthworm (Eisenia fetida) in soil

As one of the most common and persistent emerging human-made pollutants, microplastics (MPs) have become a global environmental problem. Although many studies have demonstrated the impact of MPs on aquatic organisms, the potential effects on terrestrial fauna are relatively unknown, even though soil is a major sink for plastic pollution. In this study, earthworms (Eisenia fetida) were exposed to MPs from tires (TMPs) in artificial soil at different TMP concentrations (0, 1, 5, 10, and 20%, w/w), at different TMP size fractions (2 mm–350 μm; 350 μm–50 μm; 50 μm–25 μm; and <25 μm), and time periods (14 and 28 days). The purpose was to evaluate the impact of TMPs on the bioaccumulation of heavy metals (Zn, Cd, and Pb) and levels of oxidative stress in the earthworms. Fluorescence imaging of TMPs stained with Nile red dye clearly showed that the worms had ingested the TMPs, with smaller particles preferentially consumed. The ingested TMPs had altered the surface morphology, degradation that increased surface area and uptake of heavy metals into the organisms. Earthworms exposed to TMPs at the higher concentrations showed clear signs of oxidative stress, with significantly (p < 0.05) increased catalase and peroxidase activity and lipid peroxidation levels, and reduced activity of superoxide dismutase and glutathione S-transferase. SOD, POD, and CAT are important cell protection enzymes that prevent excessive levels of reactive oxygen species in cells. MDA represents the total scavenging ability of free radicals in the tissue. SOD decreases and MDA accumulates rapidly. GST has a detoxification effect. Overall, this study adds to the growing body of evidence that TMPs are harmful to certain terrestrial organisms.

Plasma assisted preparation of highly active NiAl2O4 catalysts for propane steam reforming

In this study, Ni–Al spinel catalyst prepared with glycine-nitrate combustion method and treated by DBD plasma in different atmospheres have been investigated for propane steam reforming (PSR). It is revealed by H2-TPR that compared with traditional calcination method, NiO/Ni particles have much stronger interaction with the supports on the plasma-treated Ni–Al spinel catalysts. Therefore, catalysts with smaller NiO/Ni grains sizes, higher metallic Ni active surface areas can be achieved, as evidenced by XRD and H2 adsorption-desorption measurements. NH3-TPD results demonstrate that the plasma treatment led to a decrease of the acidity of the Ni–Al spinel catalyst. Furthermore, larger quantities of surface active oxygen sites are also formed after plasma treatment, as testified by the O2-TPD and XPS results. As a consequence, the plasma-treated catalysts show significantly improved catalytic activities and coke resistance. Plasma treatment in H2/Ar atmosphere after calcination process is considered to be the best route to prepare NiAl2O4 catalysts, which could be employed to obtain PSR catalysts with the highest catalytic activity and best anti-coking performance. It is believed that the higher metallic Ni active surface area and much more surface active oxygen sites induced by plasma treatment are the inherent reasons accounting for the enhanced catalytic performance of the Ni–Al spinel catalysts.

Triazine-based N-rich porous covalent organic polymer for the effective detection and removal of Hg (II) from an aqueous solution

Triazine-based N-rich covalent organic polymer (TBN-1) was prepared for effective removal and selective detection of Hg2+ from model solutions. The π-π conjugated structure formed by alternating electron-deficient triazine group and electron-rich benzene group promotes the electron transfer and strong fluorescence. The ultra-high specific surface area and abundant metal complex groups provide excellent adsorption sites for heavy metals. The TBN-1 suspension has obvious fluorescence quenching effect when encountering Hg2+ even when the solutions are treated with co-ions and humic acid. The merits of TBN-1 are unreservedly manifested when further testing the adsorption kinetics of TBN-1 for Hg2+ removal. With the maximum adsorption capacity of 1630 mg g−1, 99.99% of Hg2+ can be removed within 20 min from a 10 ppm solution using TBN-1. The covalent organic polymer (COP) also exhibits a high stability in a wide range of pH and a significant selectivity for Hg2+. About 99.9% Hg2+ can be adsorbed in acidic, co-ions competitive and humic acid contaminated solutions. The TBN-1 can be also reused for at least 5 cycles with acceptable Hg2+ adsorption capacity retention. The mechanism for the excellent Hg2+ adsorption performance of TBN-1 is revealed by coupling physico-chemical model fitting, chemical computation, and experimental characterization, which indicates the coordination and cation-π effects and high electron density of the material to facilitate its complexation with Hg2+. This work offers new prospects for the application of triazine-based COPs for environmental remediation.

Electron Beam Irradiation-Induced Formation of Defect-Rich Zeolites under Ambient Condition within Minutes.

Zeolites are a well-known family of microporous aluminosilicate crystals with a wide range of applications. Their industrial synthetic method under hydrothermal condition requires elevated temperature and long crystallization time and is therefore quite energy-consuming. Herein, we utilize high-energy electron beam irradiation generated by an industrial accelerator as a distinct type of energy source to activate the formation reaction of Na-A zeolite. The initial efforts afford an attractive reaction process that can be achieved under ambient conditions and completed within minutes with almost quantitative yield, leading to notable energy saving of one order of magnitude compared to the hydrothermal reaction. More importantly, electron beam irradiation simultaneously exhibits an etching effect during the formation of zeolite generating a series of crystal defects and additional pore windows that can be controlled by irradiation dose. These observations give rise to significantly enhanced surface area and heavy metal removal capabilities in comparison with Na-A zeolite synthesized hydrothermally. Finally, we show that this method can be applied to many other types of zeolites.

Synthesis of La0.8Zn0.2MnO3 nanocatalysts for decomposition of VOCs in a DBD plasma reactor; Influence of sol-gel parameters

In this study, La0.8Zn0.2MnO3 nanocatalysts were synthesized using sol-gel method at different citric acid to metal nitrate (C/N) ratios and different calcination temperatures. The synthesized catalysts were used for oxidation of benzene, toluene, and xylene (BTX) in a catalytic-plasma hybrid reactor at different input voltages of 5, 7.5, 10, 12.5, and 15 kV. The synthesized catalysts were analyzed by XRD, FESEM, EDX, FTIR, BET, and TEM. XRD analysis confirmed the effect of calcination temperature on crystalline degree of LnMnO3 phase in perovskite La0.8Zn0.2MnO3 catalyst. TEM analysis also confirmed production of particles in nanometer range. Moreover, FTIR and BET analyses indicated that C/N ratio has a direct effect on the amount of metal oxide functional groups and surface area of the resultant catalyst, respectively. The reactor tests showed that the use of C/N= 0.5 and calcination temperature of 700°C in catalyst preparation resulted in the best performance in BTX oxidation. Increasing the voltage up to 15 kV had a good effect on the oxidation ability of the catalyst as well. In these conditions, the highest oxidation percentages of benzene, toluene and xylene were equal to 90.00, 89.86, and 88.64 %, respectively.

Electron Beam Irradiation‐Induced Formation of Defect‐Rich Zeolites under Ambient Condition within Minutes

AbstractZeolites are a well‐known family of microporous aluminosilicate crystals with a wide range of applications. Their industrial synthetic method under hydrothermal condition requires elevated temperature and long crystallization time and is therefore quite energy‐consuming. Herein, we utilize high‐energy electron beam irradiation generated by an industrial accelerator as a distinct type of energy source to activate the formation reaction of Na‐A zeolite. The initial efforts afford an attractive reaction process that can be achieved under ambient conditions and completed within minutes with almost quantitative yield, leading to notable energy saving of one order of magnitude compared to the hydrothermal reaction. More importantly, electron beam irradiation simultaneously exhibits an etching effect during the formation of zeolite generating a series of crystal defects and additional pore windows that can be controlled by irradiation dose. These observations give rise to significantly enhanced surface area and heavy metal removal capabilities in comparison with Na‐A zeolite synthesized hydrothermally. Finally, we show that this method can be applied to many other types of zeolites.

Sulfur stabilizing metal nanoclusters on carbon at high temperatures

Supported metal nanoclusters consisting of several dozen atoms are highly attractive for heterogeneous catalysis with unique catalytic properties. However, the metal nanocluster catalysts face the challenges of thermal sintering and consequent deactivation owing to the loss of metal surface areas particularly in the applications of high-temperature reactions. Here, we report that sulfur—a documented poison reagent for metal catalysts—when doped in a carbon matrix can stabilize ~1 nanometer metal nanoclusters (Pt, Ru, Rh, Os, and Ir) at high temperatures up to 700 °C. We find that the enhanced adhesion strength between metal nanoclusters and the sulfur-doped carbon support, which arises from the interfacial metal-sulfur bonding, greatly retards both metal atom diffusion and nanocluster migration. In catalyzing propane dehydrogenation at 550 °C, the sulfur-doped carbon supported Pt nanocluster catalyst with interfacial electronic effects exhibits higher selectivity to propene as well as more stable durability than sulfur-free carbon supported catalysts.

Demonstrating Concepts in Catalysis, Renewable Energy, and Chemical Safety with the Catalytic Oxidation of Hydrogen

A versatile and portable apparatus was developed to demonstrate exciting visual displays of catalytic phenomena that introduce basic concepts in catalysis, renewable energy, and chemical safety, in order to pique scientific curiosity in a variety of audiences including middle and high school students, undergraduate and graduate students, and the general public. The demonstration uses the platinum-catalyzed oxidation of hydrogen by oxygen as a model reaction to illustrate concepts in thermodynamics, reaction kinetics, and electrochemistry. The apparatus was designed to contain inherent safety features and the versatility to adopt several configurations to perform a wide range of experiments in classroom settings, informal science education activities, and public outreach events. Soap bubbles are used to confine small, controlled volumes (<35 cm3) of hydrogen/oxygen gas mixtures and probe the reactivity of bulk and nanoparticle forms of platinum to illustrate how high metal surface areas increase catalytic reaction rates. In parallel, a hydrogen/oxygen proton-exchange fuel cell is used to demonstrate how chemical energy released from the exergonic hydrogen oxidation reaction can be converted into electricity by using a platinum-containing electrocatalyst. With adjustments of the operating configuration and the experimental conditions of the apparatus, the demonstrations can be tailored toward target demographics of varying scientific proficiency to emphasize specific learning objectives for topics in reaction chemistry and engineering. Potential hazards and important safety precautions are addressed.

Ex-LDH-Based Catalysts for CO2 Conversion to Methanol and Dimethyl Ether

CO2-derived methanol and dimethyl ether can play a very important role as fuels, energy carriers, and bulk chemicals. Methanol production from CO2 and renewable hydrogen is considered to be one of the most promising pathways to alleviate global warming. In turn, methanol could be subsequently dehydrated into DME; alternatively, one-step CO2 conversion to DME can be obtained by hydrogenation on bifunctional catalysts. In this light, four oxide catalysts with the same Cu and Zn content (Cu/Zn molar ratio = 2) were synthesized by calcining the corresponding CuZnAl LDH systems modified with Zr and/or Ce. The fresh ex-LDH catalysts were characterized in terms of composition, texture, structure, surface acidity and basicity, and reducibility. Structural and acid–base properties were also studied on H2-treated samples, on which specific metal surface area and dispersion of metallic Cu were determined as well. After in situ H2 treatment, the ex-LDH systems were tested as catalysts for the hydrogenation of CO2 to methanol at 250 °C and 3.0 MPa. In the same experimental conditions, CO2 conversion into dimethyl ether was studied on bifunctional catalysts obtained by physically mixing the ex-LDH hydrogenation catalysts with acid ferrierite or ZSM-5 zeolites. For both processes, the effect of the Al/Zr/Ce ratio on the products distribution was investigated.