Transient Response Technique Research Articles

Optimizing photocatalytic and supercapacitive performance by β-Bi2O3@BiFeO3 modification with PVDF polymer based nanocomposites

The PVDF (Poly-Vinyl-difloride) membrane modified with Bismuth oxide (β-Bi2O3)/Bismuth Ferrite (BiFeO3) p-n heterojunction synthesized via hydrothermal process to explore its energy storage and conversion applications. The PVDF-Bi2O3/BiFeO3 nanocomposites (NCs) prepared in this study were subjected to analysis using PXRD, FTIR, UV-Vis DRS, FE-SEM with EDX, TEM, and transient photocurrent response techniques, individually. The as-prepared materials were evaluated for their photocatalytic performance in the visible light-induced degradation of Methylene Blue (MB) and Rhodamine-B (RhB) dyes. The photocatalytic performance demonstrates degradation efficiencies of 95% for MB dye and 83% for RhB dye when utilizing the PVDF-β-Bi2O3@BiFeO3 nanocatalyst. The enhancement in the photocatalytic performance of the PVDF-Bi2O3/BiFeO3 heterojunction was a result of improved visible light absorption, suppression of photogenerated electron-hole pair recombination, accelerated separation and migration of photogenerated charges. The capacitance behavior of PVDF-β-Bi2O3@BiFeO3 is significantly higher than β-Bi2O3@BiFeO3 in 3 M KOH solution which has specific capacitance of 300 F g−1at 1 A g−1 of current density and fabricated a symmetric device has10.08 Wh kg−1 and 999.39 W kg−1 specific energy and specific power at 0.5 A g−1 of current density with the 88.7% of capacitance retention and 94.12% of coulombic efficiency up to 10000 cycles.

Molecular Structure Effect on the Epoxidation of 1-Butene and Isobutene on the Titanium Silicate Catalyst under Transient Conditions in a Trickle Bed Reactor.

Epoxidation of two butane isomers (1-butene and isobutene) on the commercial titanium silicate (TS-1) catalyst was studied in a laboratory-scale trickle bed reactor. The transient step response technique was used as the main tool in the investigation. The transient responses revealed different dynamics of product formation in continuous operation. The study of isomers showed the impact of the molecular structure on the transient and stationary states of the system. The four-carbon chain present in 1-butene displayed a dynamic behavior with a prominent maximum of the conversion as a function of time-on-stream. On the contrary, the behavior of isobutene was displayed to be closer to ethene and propene under similar conditions reaching a steady state after ca. 2 h. The structure of the epoxide was an important factor in order to achieve a high epoxide selectivity. In isobutene epoxidation, the primary product 1,2-epoxy-2-methylpropane was highly reactive, giving a spectrum of parallelly formed byproducts. Therefore, the selectivity of the epoxide from isobutene was limited to ca. 70%. In the epoxidation of 1-butene, 1,2-epoxybutane was displayed to be a highly stable product with a selectivity close to 99%. Based on the transient and stationary data, a reaction mechanism was proposed for the epoxidation and ring-opening reactions present in the system.

Effect of Al doping on the photocatalytic activity of ZnO nanoparticles decorated on CNTs and graphene: Solvothermal synthesis and study of experimental parameters

With the motive of the improvement of the photocatalytic activity in the visible region and high inhibition of electron-hole pairs recombination rate, we presented a facile single step solvothermal route synthesized pure ZnO, Al doped ZnO, Al doped ZnO/CNTs and Al doped ZnO/graphene composite using ethylene glycol as solvent and reducing agent. The as-synthesized photocatalysts were characterized by XRD, SEM, TEM, EDX, BET, UV–Vis DRS, PL, transient photocurrent response and EIS techniques. The experimental results for the photocatalytic Congo red degradation confirmed the successful incorporation of Al, CNTs and graphene into the lattice of ZnO and showed that Al doped ZnO/graphenecomposite revealed the highest photocatalytic activity of 100% within 60 min of simulated sunlight irradiation compared with pure ZnO, Al doped ZnO and Al doped ZnO/CNTs. The effect of operational parameters such as graphene loading, catalyst dose, initial pH, initial dye concentration, light intensity, oxidants, cations and anions on the photocatalytic activity of the optimum photocatalyst (Al doped ZnO/graphene) was also studied. The results of the operational parameters verified that 50 mg/L of Congo red could be completely degraded at graphene loading: 7 wt%, initial pH: 9, light intensity: 300 W/m2, catalyst dose: 0.7 g/L over 50 min sunlight irradiation. Under the effect of optimum operational conditions, five times recycle experiments revealed negligible decline in the degradation efficiency of Al doped ZnO/graphene catalyst and confirmed its efficient reusability and stability.

Catalytic combustion of dimethyl ether over α-MnO2 nanostructures with different morphologies

Herein, α-MnO2 catalysts with three well-defined morphologies (nanorod, ultra-long nanowire and microsphere) were rational designed and prepared by the hydrothermal route, and their catalytic activities were evaluated for the dimethyl ether (DME) combustion. These nanostructured α-MnO2 catalysts were characterized in detail by various analytical techniques: XRD, FESEM, TEM, BET, XPS and H2-TPR. As a result, the α-MnO2 nanorod exhibited the higher catalytic activity (T10=170°C and T90=238°C at WHSV=30,000mLg−1h−1) than the other two α-MnO2 samples due to its larger specific surface area, higher average oxidation state of Mn, more abundant surface lattice oxygen (Olatt) species and higher reducibility, and there was no obvious decrease after the α-MnO2 nanorod was run for 50h. Moreover, the transient response technique revealed that the Olatt species of the α-MnO2 nanorod should be the crucial role in the deep oxidation of DME.

Carbon gasification from Fe–Ni catalysts after methane dry reforming

Carbon species removal was studied from a Fe–Ni catalyst supported on MgAl2O4 after methane dry reforming at 1023K, atmospheric pressure and a CH4/CO2 molar ratio of 1:1. The deactivated and regenerated catalysts were characterized using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and energy-dispersive X-ray spectroscopy (EDX)-STEM mapping. The catalyst regeneration was studied by CO2 and O2 temperature programmed oxidation (TPO) and by operando time-resolved X-ray diffraction (XRD). A transient response technique, Temporal analysis of products (TAP), was applied to investigate the isothermal carbon species gasification.Two different types of carbon species, graphitic and amorphous, were present after reaction. CO2 oxidation could remove part of the carbon species, although EDX-STEM mapping showed the presence of carbon species located far from active metals phase even after CO2–TPO at 1123K. Carbon species removal by CO2 involves two contributions: (1) the dissociation of CO2 over Ni followed by the oxidation of carbon species by surface oxygen; (2) Fe oxidation by CO2 and subsequent carbon species oxidation by Fe oxide lattice oxygen. The oxidation of carbon species by O2 was identified from temperature programmed and isothermal experiments as a process including two processes: (1) oxidation of surface carbon by lattice oxygen and (2) particles migration to carbon species deposited far from active metals and subsequent oxidation through lattice oxygen of the iron and/or nickel oxides. The contribution of oxygen spillover in carbon gasification was considered to be negligible.

Experimental and Theoretical Investigation of SO2 Adsorption over the 1,3-Phenylenediamine/SiO2 System

The reversible adsorption of SO2 on 1,3-phenylenediamine was investigated using the step transient response technique coupled with operando infrared spectroscopy, mass spectrometry, UV–vis spectrometry, and density functional theory (DFT). At 50 °C, the reaction of SO2 at the amine site resulted in fixation of sulfur as hydrogen-bonded SO32– (sulfite) and SO42– (sulfate) species. Simulated infrared and UV–vis spectra at the DFT B3LYP/6-31G(d,p) level were compared to the experimental results to help characterize the infrared spectra, molecular interactions, and bonding of the adsorbing species. The theoretically calculated binding energies revealed the sulfite and sulfate species bind stronger at the ammonium sites as compared to the amine site, which agrees with the infrared spectroscopic observations. Temperature-programmed desorption showed a capacity of 1.39 mol SO2/mol sorbent for pure 1,3-phenylenediamine and 2.8 mol SO2/mol sorbent for the SiO2 supported sorbent. The presence of sulfite and sulfate...

Nature of the active sites for the total oxidation of toluene by CuO[sbnd]CeO2/Al2O3

The binary metal oxide, CuOCeO2/γ-Al2O3, has been compared with the single oxide components CuO/γ-Al2O3 and CeO2/γ-Al2O3 for toluene total oxidation. The nature of the active sites was determined by means of several spectroscopic techniques, while the transient response technique TAP (Temporal Analysis of Products) was used to investigate the catalytic performance.The improved performance of the CuOCeO2/γ-Al2O3 catalyst compared to CuO/γ-Al2O3 is attributed to the formation of a Ce1−xCuxO2−x solid solution with a crystallite size of 6nm. Within this phase, oxidation of toluene occurs at Cu2+ sites and reduction of oxygen at Ce3+ sites. Similar to Wacker chemistry, two redox couples, Ce4+/Ce3+ and Cu2+/Cu1+, are operational. Apart from the solid solution, a copper oxide phase with a crystallite size of 100nm shows significantly lower catalytic activity.X-ray absorption near-edge structure (XANES) experiments at the copper and cerium edge indicate that Ce4+ is reduced at lower temperature than Cu2+. Upon re-oxidation with CO2 or H2O, Ce3+ is partly re-oxidized, while Cu0 is not. This explains an activity increase in the CuOCeO2/γ-Al2O3 in the presence of H2O or CO2. CuO/γ-Al2O3 shows loss of activity in the presence of H2O as site blocking is not compensated by an increase in the re-oxidation rate.

Studies on regeneration mechanism of sulfur transfer additives of FCC flue gas by H2 reduction

Transient response technique in combination with online quadruple mass spectrometry was used to study the reduction mechanism of different gaseous reducing agents on sulfate compounds formed on a sulfur transfer catalyst at atmospheric pressure and different temperatures. The results indicated that the SO2 and H2S released almost at the same time and after several cycles of pulse reaction, the formation of SO2 ceased and only H2S was detected as reduction product.

Role of metal components in Pd–Cu bimetallic catalysts supported on CeO2 for the oxygen-enhanced water gas shift

Catalytic hydrogen production and CO removal in a post-reforming process are critical for low-temperature fuel cell applications. The present study aims at clarifying the role of metal components in bimetallic catalysts for oxygen-enhanced water gas shift (OWGS), wherein a small amount of O2 is added to H2-rich reformate gas to enhance CO shift. Among CeO2-supported bimetallic catalysts, Pd–Cu and Pt–Cu combinations were found to show strong synergetic promoting effect in OWGS, which leads to much higher CO conversion and higher H2 yield than WGS at low temperature around 250°C. Temperature programmed reduction (TPR) showed strong interaction between Pd and Cu in Pd–Cu/CeO2 by a single reduction peak in contrast to multiple peaks on monometallic Cu/CeO2. Extended X-ray absorption fine structure (EXAFS) analysis revealed that such bimetallic Pd–Cu and Pt–Cu form alloy nanoparticles, where noble metal is mainly surrounded by Cu atoms. Oxygen storage capacity (OSC) measurements point to higher resistance of Pd–Cu to oxidation indicating that Pd keeps Cu in reduced state in air pulse condition. From kinetic study, Pd in Pd–Cu was found to promote CO shift, rather than CO oxidation by increasing the number of active sites and by suppressing H2 activation (that is inherent to monometallic Pd), which minimizes both the inhibition effect of H2 and the loss of H2 by oxidation in OWGS. Transient response technique revealed that Cu in Pd–Cu enhances desorption of strongly chemisorbed CO2 on catalyst surface in contrast to very slow CO2 desorption from surface of monometallic Pd. Thus, the excellent OWGS activity of Pd–Cu catalyst has been attributed to the complementary roles of the two metals for enhancing CO shift, which is realized by its alloy structure and the accompanying strong interaction between metal components.

Study on Co-Effect of K<sub>2</sub>SO<sub>4</sub> Deposition and Low Concentration SO<sub>2</sub> on Performances of V<sub>2</sub>O<sub>5</sub>/AC Catalysts for Low Temperature SCR

Simulated compounds were prepared by loading K2SO4 onto V2O5/AC catalysts. Study the effect of K2SO4 on V1/AC catalysts in the presence of low concentration SO2. Transient response techniques, TPD was carried out. The results indicated that the DeNO activity of V1/AC catalysts was decreased seriously in the early period of operation, but the deactivation was gradually diminished with SO2 adsorption and then, it was completely eliminated. For the sulphated catalysts (saturated catalysts by sulphate), their SCR activity were free from existence of gaseous SO2. the loss of activity about 10% caused by K2SO4 was found on them. The deactivation of K2SO4 deposited catalysts was due to the decrease of adsorbed and activated NH3, or some acid sites.

Thermal Annealing Effect on P3HT:PCBM Free Polarons Lifetime and Charge Transport

ABSTRACTA transient response technique has been employed to investigate the lifetime of free polarons in bulk heterojunction blends of regioregular poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methylester (PCBM) at different annealing temperatures. Device efficiency and charge mobility were also measured. The longest lifetime, ∼ 1.5 microseceonds, was achieved for an annealing temperature of 140˚C; this represents a 2.5 x increase in lifetime relative to unannealed samples. The 140˚C annealing temperature also yields the highest efficiency. These measurements provide an estimate of the mobility-lifetime product, a figure of merit for charge transport in organic bulk heterojunctions.

Determination of free polaron lifetime in organic bulk heterojunction solar cells by transient time analysis

A transient response technique that is widely used to measure the minority carrier lifetime in inorganic semiconductors is proposed to measure the lifetime of free polarons in a polymer:fullerene bulk heterojunction (BHJ) solar cell. A numerical model that can be used to describe the transient behavior of BHJ devices has been developed. Using the proposed method, the lifetime of free polarons in poly (3-hexylthiophene) and [6, 6]-phenyl C61-butyric acid methyl ester blend film is estimated to be in the range of 300–400 ns.

Dynamic Methods in Catalytic Reaction Engineering: Applications to the Investigation of the NH3 Selective Catalytic Reduction Reactions for Diesel Emission Control

For the case of the NH3 selective catalytic reduction (NH3-SCR) reactions over V-based and metal-exchanged zeolite catalysts, we have used step response and temperature-programmed experiments in a fixed-bed flow microreactor in order to accomplish the following. (i) Identify the adspecies and evaluate their storage capacities: it was found that, in addition to ammonia, NO2 as well is adsorbed in comparable amounts onto SCR catalysts in the form of nitrites and nitrates. (ii) Investigate the individual steps of mechanistic schemes: the key role of surface nitrates in the NO2-related SCR chemistry was demonstrated by dedicated transient experiments. (iii) Discriminate rival mechanistic hypotheses: the differences in the temporal evolutions of NO and NO2 during transient runs unambiguously indicated that they participate in different steps of the fast SCR mechanism. (iv) Analyze the red-ox features of the catalytic mechanism: specifically designed transient tests highlighted the superior efficiency of surface nitrates in reoxidizing the V-related redox sites. (v) Evaluate surface kinetics: chemically consistent transient kinetic models were developed from systematic sets of transient runs and applied to design and optimization of commercial SCR converters for vehicles. The results of the overall SCR investigation prove that transient response techniques can yield a superior level of mechanistic and kinetic information under process relevant conditions with a limited experimental effort.

Pulse Transient Responses of NO Decomposition and Reduction with H2on Ag−Pd/Al2O3

Catalytic decomposition of nitric oxide (NO) over Pd/Al2O3 and Ag−Pd/Al2O3 has been studied using the pulse transient response technique coupled with in situ infrared (IR) and mass spectrometry (MS) at 723−823 K. In the absence of H2, pulsing NO over the Pd/Al2O3 catalyst produces adsorbed NO species (i.e., Pd+−NO, Pd0−NO, and Pd−NO−) as well as gaseous N2, O2, and N2O products. Transient responses of the N2 and O2 profiles show that the addition of Ag onto Pd/Al2O3 catalyst shifts the O2 profile forward, increases oxygen formation and the oxidation resistance of Pd, but did not decrease the amount of retained oxygen (Oret) and did not improve the catalytic cycle for NO decomposition. Oret on the Pd surface is not able to desorb in the temperature range of this study; however, Oret on Ag−Pd/Al2O3 can be desorbed at higher temperatures than its formation and adsorption temperature. The presence of H2 during the NO pulse allowed NO reduction to occur, producing N2, N2O, O2, NH3, and H2O. Pd/Al2O3 is a more ...

Investigation of NO dissociation and reduction by H 2 on nanosized W 2N surface with transient-response techniques

Nanosized W 2N was prepared by NH 3-temperature-programmed reaction and characterized by XRD, transmission electron microscopy (TEM), BET, X-ray photoelectron spectroscopic (XPS) and temperature-programmed desorption (TPD) techniques. Transient-response experiments were applied in order to improve understanding of the mechanism of NO reduction with H 2 on W 2N surface. Switches of He into 1% NO/0–7% H 2/He gas streams on W 2N surface were performed at 500 °C. The 1% NO/He step-response experiment showed that NO dissociation in the absence of H 2 was not effective on W 2N surface because the surface oxygen from dissociated NO was strongly bond to the catalyst surface, poisoning the NO dissociation sites and inhibiting further NO dissociation. In the 1% NO/1–7% H 2/He step-response experiments, N 2, NH 3, H 2O and N 2O (little or none) were detected as reaction products. The formation of H 2O on the catalyst surface was the most crucial step for NO dissociation to proceed and that it depended on the NO:H 2 ratio in the reaction mixture. Reasonable NO:H 2 ratio of 1:5 in feed gas was determined to keep the catalyst surface sites active for the catalytic dissociation of NO. Reaction pathways explaining the reduction of NO with H 2 were proposed.

Development of a transient response technique for heterogeneous catalysis in liquid phase, Part 2: Applying membrane inlet mass spectrometry (MIMS) for detection of dissolved gasses

A home-made analyzer for dissolved gasses in water, based on membrane inlet mass spectrometry (MIMS), was successfully applied for the first time as an in-line method for detection of gases dissolved in an aqueous stream, at the exit of a catalytic reactor in a transient experiment. The technique was applied for measuring the metal dispersion of three different catalysts (EuroPt-1, Pt/SiO 2 and Pt/CNF) in liquid phase via H 2 O 2 titration. The titration stoicheometry obtained (i.e. ratio of H 2 and O 2 consumption) is in agreement with the stoicheometry obtained in gas phase titration experiments in literature. The platinum dispersions obtained in liquid phase are in excellent agreement with dispersions based on hydrogen chemisorption in gas phase for all three catalysts. Clearly, water does not influence the accessibility of the Pt atoms, disagreeing with recent suggestions in literature. In addition, the detector is universal and allows calibration of H 2, O 2, N 2 and Ar dissolved in water with insignificant cross contamination. Despite the relatively slow dynamic response of the detector (between 4 min for hydrogen up to more than 40 min for oxygen), it was proven possible to perform quantitative experiments in pulse mode, with a detection limit in the order of 0.5 m 2 Pt. The capability of this method is further demonstrated by the surprising observation that dissolved hydrogen physisorbs significantly on a reduced Pt catalyst whereas dissolved oxygen does not interact with an oxidized catalyst.

Development of a transient response technique for heterogeneous catalysis in the liquid phase, Part 1: Applying an electrospray ionization mass spectrometry (ESI-MS) detector

We have developed a novel, transient response technique for liquid-phase heterogeneous catalytic studies, equipped with an electrospray ionization mass spectrometry (ESI-MS) detector. The technique was successfully applied as an online method for real-time detection of species dissolved in aqueous product streams at the exit of a catalytic reactor. Two test reactions, nitrite reduction with Pt/SiO 2 and glucose oxidation with Pt/CNF/Ni, were used to demonstrate semi-quantitative monitoring of reactants, intermediates, and products. The capability of the novel technique is demonstrated by the fact that the ESI-MS detector is sufficiently sensitive to determine quantitatively extreme small amounts of physisorbing nitrite, down to 0.5% of a monolayer on the Pt surface. Nitrite also reacts with preadsorbed hydrogen, and the quantitative experimental results agree with the formation of both nitrogen and ammonia. The ESI-MS detector is able to distinguish between different components simultaneously, as in the case of glucose oxidation; this is its most significant advantage over existing transient techniques. A limitation of ESI-MS is its inability to detect gases dissolved in liquids, due to the relatively mild ionization process through electrospray. The second part of this article discusses an alternative detector to satisfy this deficiency.

Measurement of Reinforcement Corrosion Rate Using Transient Galvanostatic Pulse Method

Corrosion rate evaluation of concrete structure steel reinforcement was performed through investigation of a galvanostatic pulse transient response technique. A number of short sections of concrete embedded steel bar were used to conduct measurement of galvanostatic pulse transient measurements. There was a 30 to 180 second variation in applied galvanostatic pulse duration. A typical 1 kHz sampling rate was used to investigate the resulting transient potential response. To obtain separate equivalent electronic components, comprising a capacitance and resistance series, with reinforcing steel corrosion condition dependent values, there was analysis of the electrochemical potential transient response. Separate resistive components summation allowed evaluation of corrosion rate, which was then compared with a conventional linear polarization resistance (LPR) measurement corrosion rate on the same specimens. That the galvanostatic pulse transient technique enables resolution of the separate polarization resistance components, which provides a more conservative ongoing corrosion rate evaluation and offers significant advantages over either the galvanostatic or potentiostatic LPR method, is shown by obtained results.

정전류 펄스법을 이용한 콘크리트 내 보강철근의 부식 연구

An electrochemical transient response technique was used to study the corrosion of reinforcing steel bar in the concrete. Analysis of the transient electrochemical potential response in a corrosion interface to an applied current has enabled the separate components that make up the measured transient response to be isolated. These components display a range of resistances and capacitances, dependent on the corrosion conditions of the reinforcing steel, which may be attributed to the corrosion process, to effects within the concrete cover or to film effects on the surface of the concrete. In this technique, the corrosion rate was evaluated by summing all of the resistances in the separate components to obtain an aggregated corrosion resistance. However, it is possible that not all resistances identified are associated with the corrosion process. The results obtained show that the corrosion rates are significant dependent on the assignment of the separate components to either corrosion or to other processes. The assignment of resistive components associated with the corrosion rate can be clearly identified by taking a series of the transient measurement at different lateral distances from the corroding reinforcing steel. An inappropriate selection of measurement time however may result in an additional resistance, which is not associated with corrosion, being included or part of the resistance associated with corrosion being left out.

Assessment of Corrosion Rate of Reinforcing Steel in Concrete Using Galvanostatic Pulse Transient Technique

This paper discusses a method of measuring transient potential response of a corrosion interface to a small galvanostatic pulse perturbation for a rapid assessment of the corrosion rate of reinforcing steel in concrete structures. Measurements were taken on 100 mm sections of steel bars which were subjected to a wide range of corrosion conditions, from passive steel to actively corroding steel. The duration of the applied galvanostatic pulse was varied between 5s and 180s, and the lateral distance of the point of measurement on the steel bar varied from zero to 400 mm. The result of the electrochemical transient response was investigated using a typical sampling rate of 1 kHz. Analysis of the transient potential response to the applied galvanostatic pulse has enabled the separation of equivalent electronic components so that the components of a series of capacitances and resistances, whose values are dependent on the corrosion condition of the reinforcing steel, could be isolated. The corrosion rate was calculated from a summation of the separate resistive components, which were associated with the corrosion interface, and was compared with the corrosion rate obtained from linear polarization resistance (LPR) method. The results show that the galvanostatic pulse transient technique enables the components of the polarization resistance to be evaluated separately so as to give more reliable corrosion rate values than those obtained from the LPR method. Additionally, this paper shows how the galvanostatic pulse transient response technique can be implemented. An appropriate measurement time for passive and actively corroding reinforcing steel is suggested for the galvanostatic pulse transient response measurements in the field site.