Function Of Catalyst Loading Research Articles

Probing the local activity of CO2 reduction on gold gas diffusion electrodes: effect of the catalyst loading and CO2 pressure.

Large scale CO2 electrolysis can be achieved using gas diffusion electrodes (GDEs), and is an essential step towards broader implementation of carbon capture and utilization strategies. Different variables are known to affect the performance of GDEs. Especially regarding the catalyst loading, there are diverging trends reported in terms of activity and selectivity, e.g. for CO2 reduction to CO. We have used shear–force based Au nanoelectrode positioning and scanning electrochemical microscopy (SECM) in the surface-generation tip collection mode to evaluate the activity of Au GDEs for CO2 reduction as a function of catalyst loading and CO2 back pressure. Using a Au nanoelectrode, we have locally measured the amount of CO produced along a catalyst loading gradient under operando conditions. We observed that an optimum local loading of catalyst is necessary to achieve high activities. However, this optimum is directly dependent on the CO2 back pressure. Our work does not only present a tool to evaluate the activity of GDEs locally, it also allows drawing a more precise picture regarding the effect of catalyst loading and CO2 back pressure on their performance.

Degradation of phenol using mill scale as a Fenton‐type catalyst

AbstractThe oxidation of phenol using mill scale (waste material produced during the hot rolling of steel) as iron source in a type Fenton process was investigated in this work. The mill scale was characterized by XRF, FT‐IR, XRD and SEM. The oxidation tests were carried at 25°C and atmospheric pressure, controlling the pH to 3.7. The phenol conversion and total organic carbon (TOC) removal as a function of catalyst loading (300–1000 mg/L) and phenol concentration (47 and 100 mg/L) were evaluated. The mill scale achieved high conversion of phenol (between 60.8 ± 2.2 and 94.5 ± 2.5%) and mineralization to CO2 (between 38.9 ± 1.2 and 55.6 ± 2.5%) after 4‐h reaction. The mill scale showed a good catalytic performance, even after three cycles of reaction. Therefore, utilizing mill scale as a catalyst of the Fenton process is an alternative to the use of waste in the steel industry.

Understanding Mechanisms of Membrane Degradation in Membrane Electrode Assemblies with Ultra-Low Platinum Loadings

Further commercialization of fuel cell technology remains to be hindered by the challenges encountered to fulfill the DOE cost, performance, and durability targets for automobile applications. In order to meet performance targets, platinum (Pt) continues to be the catalyst of choice for both electrodes. However, in order to meet the 2020 DOE cost target of $14/kWnet total Pt loadings need to be reduced to less than 0.125 mgPtcm- 2 while maintaining sufficient performance. In this work, we will develop a better understanding about the mechanisms of membrane degradation in membrane electrode assemblies (MEAs) as a function of catalyst loading. Specific emphasis were devoted to ultra-low Pt loadings, i.e., <0.1 mgPt cm-2, with symmetric anode and cathode loadings verified via X-ray fluorescence (XRF). Established accelerated stress tests (ASTs) were utilized to study chemical membrane degradation in MEAs using ion chromatography of effluent water samples collected at various times for the quantification of fluoride emission rates (FER). Membrane thinning was characterized via hydrogen crossover measurements as well as scanning electron microscopy (SEM) and X-ray computed tomography (XCT). Additionally, FER was probed as a function of varying testing conditions, e.g., temperature, relative humidity.

Ultrafast Hole Transfer from CdS Quantum Dots to a Water Oxidation Catalyst

The first step in light-driven multielectron redox catalysis driven by semiconductor nanocrystals is the transfer of a photoexcited carrier to the catalyst. The efficiency of that step defines the upper limit on the efficiency of catalysis. Although progress has been made in transferring electrons from nanocrystals to catalysts for multielectron reduction reactions, there has been little success in moving photoexcited holes to water oxidation catalysts (WOCs). Here, we describe the kinetics of hole transfer from a photoexcited CdS quantum dot to a ruthenium polypyridine molecular WOC. Ultrafast transient absorption and photoluminescence (PL) upconversion experiments reveal that this hole transfer is surprisingly fast, occurring on a picosecond time scale. To determine the rate constant for hole transfer, we develop a model for PL quenching as a function of catalyst loading that takes into account both the catalyst binding equilibrium and the finite quenching efficiency. The rate constant for hole transfer...

Photocatalytic Activity of Mesoporous Graphitic Carbon Nitride (mpg-C3N4) Towards Organic Chromophores Under UV and VIS Light Illumination

A template-assisted synthetic method including the thermal polycondensation of guanidine hydrochloride (GndCl) was utilized to synthesize highly-organized mesoporous graphitic carbon nitride (mpg-C3N4) photocatalysts. Comprehensive structural analysis of the mpg-C3N4 materials were performed by XPS, XRD, FT-IR, BET and solid-state NMR spectroscopy. Photocatalytic performance of the mpg-C3N4 materials was studied for the photodegradation of several dyes under visible and UV light illumination as a function of catalyst loading and the structure of mpg-C3N4 depending on the polycondensation temperature. Among all of the formerly reported performances in the literature (including the ones for Degussa P25 commercial benchmark), currently synthesized mpg-C3N4 photocatalysts exhibit a significantly superior visible light-induced photocatalytic activity towards rhodamine B (RhB) dye. Enhanced catalytic efficiency could be mainly attributed to the terminated polycondensation process, high specific surface area, and mesoporous structure with a wide pore size distribution.

Study of Stability of Ultrathin Pt Films on Titanium Nitride, Highly Oriented Pyrolytic Graphite and Sigradur G Glassy Carbon Substrates: The Role of Substrate Type and Catalyst Loading on the Degradation Mechanism

We studied degradation mechanism of platinum catalysts films of ultralow loading on titanium nitride, highly oriented pyrolytic graphite and Sigradur G glassy carbon substrates. The films were prepared by magnetron sputtering with platinum amount nominally corresponding to 1, 5 and 10 layers. The catalyst stability was tested by potential cycling in perchloric acid. We find that dependence of catalyst stability on the substrate type is very much function of catalyst loading. This is a result of different catalyst degradation mechanisms. For samples with 1 platinum layer we observe that three dimensional crystallites are formed from two dimensional initial nanoislands and degradation mechanism follows power laws derived for three dimensional nanoparticle growth; for samples with 5 platinum layers we observe formation of interconnected network of two dimensional islands. The electrochemical surface area loss does not depend much on the substrate type and the degradation mechanism follows power law developed for two dimensional particle growth. Catalyst films made by deposition of 10 platinum layers are continuous films on all three studied substrates and after potential cycling, the films stay continuous with small difference of the film stability for studied substrates. For studied platinum loadings carbon substrates performed better than titanium nitride substrate.

Evaluation of kinetic constants on porous, non-noble catalyst layers for oxygen reduction—A comparative study between SECM and hydrodynamic methods

An advanced approach based on scanning electrochemical microscopy (SECM) was used to investigate the kinetics of the oxygen reduction reaction (ORR) on multiwalled carbon nanotubes (MWCNTs) and a composite of MWCNTs and cobalt (IX) protoporphyrin (MWCNTs/CoP). The amount of hydrogen peroxide produced during ORR was studied as a function of catalyst loading in an electrolyte of pH 7. Additionally, a Pt ultra microelectrode (UME) was used to determine changes in interfacial oxygen concentration from which intrinsic rate constants of heterogeneous electron transfer during the ORR were calculated. The amount of hydrogen peroxide produced and the number of electrons exchanged during oxygen reduction, and the heterogeneous electron transfer rate constants determined using SECM were compared with the corresponding values obtained using methods based on forced convection, namely RRDE and RDE. It was found that SECM offers some advantages compared to RDE or RRDE with regard to accuracy in determining the number of electrons transferred during the ORR, particularly in the case of thick and porous catalyst films. However, the heterogeneous electron transfer rate constants were similar for both methods, indicating that the determination of the surface concentration of reactants using RC-SECM suffers from some drawbacks.

Nano Photo Catalytic Degradation of the Pharmaceutical Agent Balsalazide Under UV Slurry Photo Reactor

The presence of pharmaceuticals and personal care products (PPCPs) as trace pollutants in natural surface water bodies, ground water and drinking water has recently led to some concern. Advanced oxidation processes (AOPs), which utilize free radical reactions to degrade chemical contaminates, are an alternative to traditional water treatment. Anti-inflammatory drug balsalazide (as model compounds) besides actual wastewater samples were UV photodegraded using suspended titanium silicon oxide (TiSiO4) or UV/H2O2/O2 systems. The photodegradation was favourable in the pH 8–12.8 range. The effect of various parameters such as photocatalyst amount, balsalazide (BSZ) concentration, pH of aqueous solution, irradiation time, addition of H2O2 and temperature on photocatalytic oxidation was investigated. The kinetics of the photocatalytic oxidation of BSZ in aqueous TiSiO4 suspensions was investigated as a function of catalyst loading (2–12 mg/L) and the concentration of BSZ (0.01–0.05 mg/mL) at pH 11.5. The optimum conditions for the degradation of the BSZ have been found as 0.045 mg/mL drug concentration, pH 11.5 and 0.1 g/L catalyst dose. The results indicated that the photocatalytic degradation of BSZ was well described by pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. The effect of temperature on the efficiency of photodegradation of BSZ was also studied in the range 278–298 K. The activation energy was calculated according to Arrhenius plot and was found equal to 24 ± 1 kJ mol−1 for TiSiO4. Decolourization and mineralization of BSZ in the absence of light and/or catalyst were performed to demonstrate that the presence of light and catalyst is essential for the decolourization of this BSZ. This work adds to the global discussion on the role of the advanced oxidation processes in water treatment.

Determination of selectivity and specific area related to oxygen reduction reaction as a function of catalyst loading on non-noble metal based electrocatalyst porous electrodes: an example on nitrogen doped carbon nanotube

In a recent paper, model porous electrodes based on carbon nanotube and platinum organically grafted electrocatalysts were used to establish the determination of a specific surface area related to oxygen reduction reaction (ORR) in HClO4 1M, using cyclic voltammetry as a function of scan speed. Identical behavior was found for the trends of this parameter called S-AO2 and the selectivity of the ORR as a function of catalyst loading, for different model porous electrode structures. In the present paper, we report such a study on porous electrodes based on non-noble metal electrocatalysts built from nitrogen doped carbon nanotubes (N-CNT). The trends observed for S-AO2 and the selectivity of the ORR as a function of N-CNT loading are exactly the same as those observed for model porous electrodes. This suggests the interest of these approaches and in particular the determination of the S-AO2 parameter for the comparison of potentialities of different non-noble electrocatalysts, for example based on nitrogen doped carbon structures towards the ORR. Indeed, although the amount of chemical species supposed to be responsible for the ORR can be estimated using various methods, their accessibility at the level of the nano-object itself and more globally in the porous structure of an active layer is essentially unknown. The S-AO2 parameter value is presumably directly related to the active sites which are accessible to the oxygen reduction in a porous structure.

Degradation of anionic and cationic surfactants in a monolithic swirl-flow photoreactor

The photocatalytic oxidations of anionic, dodecylbenzene sulfonate (DBS), and cationic, cetylpyridinium chloride (CPC) surfactants were studied in a swirl-flow monolithic reactor. The degradation kinetics in aqueous TiO2 suspensions was investigated as a function of catalyst loading, light intensity, initial surfactant concentration, dissolved oxygen concentration, and pH. A systematic analysis of rates at various loadings of TiO2 was carried out to distinguish “kinetic” and “transport” limited regimes for the photocatalytic degradation of DBS and CPC in TiO2 suspensions. The optimal catalyst loading of DBS and CPC in TiO2 suspensions were determined to be 0.75 and 1.5gL−1, respectively, at a neutral pH. A small increase in oxidation rates was observed with an increase in initial concentration of the surfactant and partial pressure of the oxygen in the system. The rates as a function of initial surfactant concentration and partial pressures of oxygen were determined using a Langmuir–Hinshelwood model. The photocatalytic oxidation of DBS and CPC showed an opposite pH dependence. Removal of DBS was efficient in acidic condition while CPC showed efficacy at basic pH. The adsorption of surfactants onto TiO2 surfaces as a function of pH was studied to explain the influence of pH on the oxidation rates. The subsequent decreases in TOC levels of surfactant during oxidation were found to be more efficient at a neutral pH than acidic or basic pH.

The evolution of surface texture in automotive coatings

The curing behavior and texture development of automotive clearcoats was studied by noncontacting profilometry and dynamic viscosity measurements during solvent evaporation and thermal curing. The changing surface texture was shown to be a strong function of temperature and solvent content. Leveling occurred during the initial heating of the clearcoats, while smaller wavelength roughness was observed to appear during cooling after curing. The dynamic viscosity was shown to be a strong function of catalyst loading. Numerical simulations were conducted to calculate the apparent viscosity during the leveling process. Calculated viscosity profiles matched theoretical predictions for the behavior of these clearcoats.

Photocatalytic oxidation of cyanide in aqueous titanium dioxide suspensions: Effect of ethylenediaminetetraacetate

The kinetics of the photocatalytic oxidation of cyanide in aqueous TiO 2 suspensions was investigated as a function of catalyst loading (0.1–5.0 g l −1), air-flow rate (0.2–1.1 l min −1), and the concentration of ethylenediaminetetraacetate, EDTA (0.4–40 mM) at pH 13.0. The cyanide oxidation rate did not vary with the TiO 2 loading while a slight increase in the degradation rate with an increase in the air-flow rate was found. Cyanate (NCO −) was the only product of the cyanide decomposition. The effect of EDTA on the photocatalytic oxidation of cyanide was examined at different molar ratios of EDTA to cyanide (0.1–10.5) by keeping the initial cyanide concentration at 3.85 mM. EDTA retarded the photocatalytic oxidation of cyanide and the decrease in the oxidation rate was not proportional to the molar ratio of EDTA to cyanide. The first-order rate constant, k (min −1) for the oxidation of cyanide in the presence of EDTA may be expressed as k = 3.38 × 10 −3 × ([EDTA]/[CN −]) −0.23. A mechanism of the oxidation of cyanide by a photocatalytic process in absence and presence of EDTA is presented.

Impact of Loading in RRDE Experiments on Fe–N–C Catalysts: Two- or Four-Electron Oxygen Reduction?

We have investigated the impact of electrocatalyst loading on rotating ring-disk electrode (RRDE) experiments for the oxygen reduction reaction on Fe-N-C catalysts (ORR) in acid medium. In particular, the fraction of H 2 O 2 produced as a function of catalyst loading was studied. A dramatic increase in H 2 O 2 release was observed as the catalyst loading was decreased. For the same non-noble metal catalyst (NNMC), the fraction of produced H 2 O 2 varied between less than 5% and greater than 95%, depending on the catalyst loading. These observations suggest that oxygen reduction occurs stepwise, via H 2 O 2 , and if the catalyst is sparsely loaded, the produced H 2 O 2 cannot be efficiently reduced to H 2 O before it escapes. These studies have important implications for fundamental studies of ORR on NNMCs.

Ru xCr ySe z electrocatalyst loading and stability effects on the electrochemical performance in a PEMFC

The present paper presents a study of the Ru x Cr y Se z chalcogenide electrocatalyst based on physical–chemical characterization through scanning electron (SEM), atomic force (AFM) microscopy and energy dispersion elemental analysis (EDS), thermal stability using differential scanning calorimeter (DSC), electrochemical kinetics towards the oxygen reduction reaction (ORR) in acid media by rotating ring-disk electrode (RRDE) and single and three-stack membrane-electrode assembly (MEA) performance as a function of catalyst loading (10%, 20% and 40% W from 0.2 to 2 mg cm −2). Results indicate an electrocatalyst with chemical composition of Ru 6Cr 4Se 5. AFM images showed 80–160 nm nanoparticle agglomerates. Good thermal stability of the cathode Ru 6Cr 4Se 5 was established after 100 h of continuous operation. The electrochemical kinetics study (RRDE) resulted in a electrocatalyst with high activity towards the ORR, preferentially proceeding via 4e − charge transfer pathway towards water formation ( i.e., O 2+4H ++4e −→2H 2O), with a maximum of 2.8% H 2O 2 formation at 25 °C. Finally, MEA tests revealed a maximum power density of 220 mW cm −2 with a catalyst loading of 20 wt% at 1.6 mg cm −2.

In Situ Measurement of Steady-State Hydrogen Concentrations during a Hydrogenation Reaction in a Gas-Inducing Stirred Slurry Reactor

A new instrument, the Fugatron, is presented that was developed to make in situ measurements of dissolved hydrogen concentrations in laboratory reactors. The principle of measurement is based on a probe with a tip that consists of a small porous metal substrate coated with a dense layer of fluoropolymer. The probe is exposed to the liquid phase and is internally purged by a constant flow of carrier gas. Driven by the hydrogen concentration gradient between the external and internal side of the composite layer, the hydrogen molecules permeate into the carrier gas stream. The concentration of the permeate in the carrier gas stream is measured by a gas analyzer. The analyzer signal is proportional to the partial pressure of dissolved gas. The steady-state concentration of dissolved hydrogen in the liquid is calculated from the analyzer signal by using solubility data. Calibration methods are described for immersion probes used for in situ measurements in reactors which are operated in batch or continuous mode as well as for flow-through probes used for liquid stream analysis. The sensitivity of the instrument and the reliability of the measurements were tested in different solutions as a function of temperature and pressure. The hydrogenation of an alkyne with a suspended palladium catalyst was chosen as a model reaction for in situ measurements. The hydrogenation experiments were carried out in a 0.5-L stirred-tank reactor with a turbine stirrer in a semibatch mode. Initial hydrogen uptake rates and dissolved hydrogen concentrations during this model reaction were measured as a function of the amount of catalyst in the liquid. The solubility of hydrogen in the pure liquid was determined by a gas absorption measurement at reaction conditions. From these measurements, the volumetric liquid-side mass transfer coefficient kLa at the gas−liquid interface was calculated as a function of catalyst loading. In addition, the kLa value was also determined in the absence of solid particles by the dynamic pressure drop method. Discrepancies that may result from calculating steady-state dissolved hydrogen concentrations using kLa values obtained from measurements conducted either in pure liquids or in liquids that contain suspended catalyst particles are discussed and illustrated by these measurements. The new method allows direct measurement of the concentrations of dissolved gases during a reaction, which can be a decisive factor for the rate as well as for the selectivity of a process. Estimations of the gas concentrations via reaction rate data and cumbersome determinations of kLa values are, therefore, no longer necessary.

Intrinsic kinetics of photocatalytic oxidation of formic and oxalic acid on immobilised TiO 2 films

Titanium dioxide (TiO 2) photocatalysis is a possible alternative/complementary technology to conventional water treatment methods. The TiO 2 catalyst may be used as slurry or it may be immobilised onto a supporting substrate. With immobilised TiO 2 films mass transfer problems occur in most photocatalytic reactors, which results in a reduction of reactor efficiency and in the accuracy of measured catalyst efficiency and kinetics. In order to determine the real intrinsic kinetics of photocatalytic reactions on immobilised TiO 2 films a stirred tank reactor (STR) was used. The reactor incorporated a propeller and a baffle, thus providing good mixing and efficient mass transfer to the TiO 2 film. Degussa P25 was immobilised onto borosilicate glass by a dip coating method and the kinetics of the photocatalytic degradation of the model pollutants, formic acid and oxalic acid were investigated as a function of catalyst loading, initial pollutant concentration and propeller rotation speed. The rate of degradation, of either acid, was not mass transfer limited at propeller speeds greater than 1000 rpm. The rate of formic acid degradation was dependent upon catalyst loading up to a maximum loading above which a decrease in the degradation rate was observed. The apparent quantum yield for the photocatalytic degradation was 5% for oxalic acid and 10% for formic acid. This compares very well with usual reported apparent quantum efficiencies for photocatalysis which are ∼1%. The photocatalytic oxidation of both acids could be described using a Langmuir–Hinshelwood kinetic model.

Oxidation of glucose on immobilized glucose oxidase in a trickle-bed reactor: Effect of liquid-solid contacting efficiency on the global rate of reaction.

Oxidation of glucose to gluconic acid using a catalyst consisting of glucose oxidase and catalase both immobilized on activated carbon was employed to study the liquid-solid contacting efficiency (f) in a trickle-bed reactor. The global rates of reaction were measured at 25°C and at atmospheric pressure, as a function of catalyst loading (1.0 to 9.0 g), catalyst partiole size (0.055 and 0.110 cm), superficial liquid velocity (0.044 to 0.337 cm/s), and superficial gas velocity (1.63 to 7.35 cm/s). The measured rate was considered to be the sum of the rates at the liquid-covered and gas-covered outer surfaces of catalyst particles. The value of f was determined by integrating numerically the mass balance equations for oxygen and the equation for the intrinsic rate of reaction simultaneously. The estimated value of f did not vary with catalyst loading. While f was independent of gas flow rates, it was influenced by both liquid flow rates and particle sizes. The effects of these operating parameters on f are discussed on the basis of the static and/or dynamic holdup.