Transient Response Method Research Articles

Catalytic performance of different types of iron zeolites in N2O decomposition

A series of Fe/zeolites (ZSM-35, ZSM-5, beta, and mordenite) samples with Fe/Al molar ratios of 0.33 were prepared using a solid-state ion-exchange method. A combination of ultraviolet-visible diffuse reflectance, in-situ Fourier-transform infrared, and in-situ visible Raman spectroscopic techniques, with a transient response method, was used to investigate the influence of the zeolite framework on the catalytic properties of the Fe/zeolites in N2O decomposition. The results show that the catalytic activity of the Fe/zeolites-HT (HT denotes high-temperature treatment) samples is in the order Fe/ZSM-35-HT > Fe/beta-HT > Fe/ZSM-5-HT > Fe/mordenite-HT. There is a linear relationship between the rate of N2O decomposition and the concentration of binuclear iron sites. This indicates that binuclear iron sites are the active sites for N2O decomposition. A correlation between the formation of binuclear iron sites and Fe ion distribution among the cationic sites is proposed. Two Fe(II) cations located in two adjacent six-membered rings in a 10-membered ring channel (α sites) or in two neighboring six-membered rings in an eight-membered ring channel (β sites) of Fe/ZSM-35 are favorable for the formation of active binuclear iron sites. Similar structure can also be formed in two adjacent six-membered rings in polymorphs A and B of beta zeolite or in the six-membered rings at the intersection of the straight and sinusoidal channels of the ZSM-5 framework. For the Fe/mordenite-HT sample, most of the iron species are present as isolated iron cations, so it has the lowest activity in N2O decomposition.

A Precision and High-Speed Behavioral Simulation Method for Transient Response and Frequency Characteristics of Switching Converters

We propose a fast and precise transient response and frequency characteristics simulation method for switching converters. This method uses a behavioral simulation tool without using a SPICE-like analog simulator. The nonlinear operation of the circuit is considered, and the nonlinear function is realized by defining the nonlinear formula based on the circuit operation and by applying feedback. To assess the accuracy and simulation time of the proposed simulation method, we designed current-mode buck and boost converters and fabricated them using a 0.18-µm high-voltage CMOS process. The comparison in the transient response and frequency characteristics among SPICE, the proposed program on a behavioral simulation tool which we named NSTVR (New Simulation Tool for Voltage Regulators) and experiments of fabricated IC chips showed good agreement, while NSTVR was more than 22 times faster in transient response and 85 times faster in frequency characteristics than SPICE in CPU time in a boost converter simulation.

Analysis of nonlinear transient responses of piezoelectric resonators

The electric transient response method is an effective technique to evaluate material constants of piezoelectric ceramics under high-power driving. In this study, we tried to incorporate nonlinear piezoelectric behaviors in the analysis of transient responses. As a base for handling the nonlinear piezoelectric responses, we proposed an assumption that the electric displacement is proportional to the strain without phase lag, which could be described by a real and constant piezoelectric e-coefficient. Piezoelectric constitutive equations including nonlinear responses were proposed to calculate transient responses of a piezoelectric resonator. The envelopes and waveforms of current and vibration velocity in transient responses observed in some piezoelectric ceramics could be fitted with the calculation including nonlinear responses. The procedure for calculation of mechanical quality factor Q(m) for piezoelectric resonators with nonlinear behaviors was also proposed.

Ranking of Materials’ Erosion Resistance and of Erosion Test Methods’ Intensity by the Transient Response Method

Abstract Modeling of cumulative erosion-time curves by the transient response method is based on the response curve of first-order servo systems to a step input. According to this model, it is possible to accurately model erosion-time curves by means of three parameters: Maximal erosion level, MDEF (MDE denotes mean depth of erosion) (μm), time constant, τ (h), and time lag (h). This method is adequate for ranking of materials by their erosion resistance and ranking of erosion test methods by their intensity. These rankings are performed for five metallic reference materials and seven erosion test methods for 22 erosion tests.

Effect of Water on Active Iron Sites for N2O Decomposition over Fe/ZSM-5 Catalyst

The effect of H2O on N2O decomposition in Fe/ZSM-5 catalyst was investigated by steady-state kinetics, transient response methods, in situ Raman, and IR spectroscopies. Fe/ZSM-5 catalysts show very high activity in N2O decomposition but are deactivated rapidly when trace amounts of water are present. In situ Raman spectra results indicate that the peroxide bridge on the binuclear Fe sites are converted to the hydroxylated binuclear Fe sites when exposed to water. It was found that the Raman band at 743 cm−1 and the IR bands at 3628 and 3672 cm−1 are associated with the deactivation of the catalyst during N2O decomposition. The catalyst was regenerated after calcination at a temperature over 773 K. The inhibiting effect of H2O on N2O decomposition indicates that the presence of water leads to the structural transformation from the dehydroxylated binuclear Fe sites to the hydroxylated binuclear Fe sites on Fe/ZSM-5.

The NOx Reduction by CO on a Pt−K/Al2O3 Lean NOx Trap Catalyst

The reduction by CO under dry conditions of NOx species stored at 350 °C onto a Pt−K/Al2O3 lean NOx trap catalyst is investigated by means of transient response methods (CO-TPSR and CO-ISC experiments) and complementary FT-IR spectroscopy. The results show that the pathway for the reduction of stored NOx by CO under dry and near isothermal conditions (and in the absence of CO2) is the same as that proposed by some of us in a previous work for a Pt−Ba/Al2O3 catalyst. In particular, (i) the reduction of stored NOx by CO occurs according to a Pt-catalyzed surface pathway that does not involve, as a first step, the release of NOx in the gas phase, is effective already at low temperature, and leads to nitrogen; (ii) the reaction scheme implies the formation of surface isocyanate species, followed by the reaction of these species with residual NOx to give nitrogen; and (iii) the reaction of NCO species with nitrates to give nitrogen is slightly slower than the reduction of nitrates to give NCO species; but on the Pt−K/Al2O3 catalyst, this last step is faster than on the Pt−Ba/Al2O3 system. As a consequence, the amount of isocyanate species present on the surface at the end of the reduction is lower for Pt−K/Al2O3 than for the Pt−Ba/Al2O3 catalyst.

Component Synthesis Method for Transient Response of Nonproportionally Damped Structures

A component synthesis technique for calculating the transient response of nonproportionally damped structures is presented in this paper. The structure can be composed of nonproportionally damped components or proportionally damped components with different damping factors, and the components are joined by connecting elements at their boundaries. In the synthesis technique, the transient responses of the nonproportionally damped components are defined by a newly developed direct integration method, which keeps the analytical solution of the mode displacement superposition method for the proportionally damped structure with the interpolation of excitation forces as the input. The structural responses are obtained based on the geometric compatibility and the force equilibrium conditions of the connecting elements. The proposed method is most suitable for the recalculation of structural responses induced by modification of the connecting elements. Numerical examples are given to validate the correctness and to show the effectiveness of the proposed method.

Reaction pathway of the reduction by CO under dry conditions of NO x species stored onto Pt [sbnd]Ba/Al 2O 3 Lean NO x Trap catalysts

The reduction by CO under dry condition of NO x species stored at 350 °C onto a Pt Ba/Al 2O 3 Lean NO x Trap catalyst is investigated by means of transient response methods (CO-TPSR and CO-ISC experiments) and complementary FTIR spectroscopy. It is shown that the reduction by CO under nearly isothermal conditions of nitrates stored onto Pt Ba/Al 2O 3 occurs through a Pt-catalyzed pathway which leads mainly to nitrogen and does not proceeds via the thermal decomposition of stored nitrates with release of NO x in the gas phase. The CO-TPSR and CO-ISC experiments and the combined FTIR study show that (i) the reduction of nitrates by CO occurs via a consecutive reaction scheme with formation of nitrites and then of surface isocyanate/cyanate species followed by the reaction of these species with residual nitrites to give nitrogen; (ii) the reaction of NCO species with nitrites to give nitrogen is slower than the reduction of nitrates to give nitrites and then NCO species; (iii) upon contact with oxygen at increasing temperature, NCO species can be re-oxidized to surface nitrites at first and then to surface nitrates; (iv) the formation of nitrogen is observed during the reduction of stored NO x by CO, and during the oxidation of surface NCO species upon oxygen addition and upon admission of NO in the presence of excess O 2. In all cases, the formation of nitrogen can be explained by the reaction between surface NCO species and nitrites. The mechanism for the reduction of stored NO x by CO under dry and near isothermal conditions is discussed.

An analysis of transient thermal properties for high power GaN‐based laser diodes

AbstractThermal properties of 405 nm GaN‐based laser diodes were investigated by employing a transient heating response method based on the temperature dependence of diode forward voltage. Thermal resistances of materials consisting of packaged laser diodes were differentiated in transient thermal response curves at a current below threshold current. With a current above threshold current, no significant change in thermal resistances and difference between junction‐up and junction‐down laser diodes was observed at pulses shorter than 3 sec. From an analysis with long current injections, thermal resistance of a packaged laser diode with a junction‐up bonding was ∼45 °C/W which was higher than that of a junction‐down bonded laser diode by ∼10 °C/W. Further analyses based on parameters obtained from voltage recovery curves indicated that the time constant for cooling is directly related to the thermal resistance and thermal capacitance of a laser diode package. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The promotional effect of NO on N 2O decomposition over the bi-nuclear Fe sites in Fe/ZSM-5

Combining transient response method, steady-state kinetics, in situ IR, and in situ Raman spectroscopic techniques, the effect of NO on N 2O decomposition over Fe/ZSM-5 catalyst was investigated in detail, which reveals that the active sites are bi-nuclear Fe sites. The presence of NO increases the desorption rate of O 2 and lowers the apparent activation energy of N 2O decomposition. Trace amount of water vapor can lead to the deactivation of the Fe/ZSM-5 catalyst due to the oxidation of the active Fe 2+ sites during N 2O decomposition. On the other hand, NO treatment causes the regeneration of the inactive Fe sites by releasing O 2 at relatively low temperature. For the first time, it was found that a Raman band at 743 cm −1, assigned to the bi-nuclear Fe sites, changes accordingly with the deactivation and regeneration of the Fe/ZSM-5 catalyst. The in situ IR spectroscopic study reveals that NO treatment of the deactivated catalyst can remove the hydroxyl groups bound to the inactive Fe 3+ species. These results demonstrate that H 2O and NO play important roles in the structural transformation between the hydroxylated bi-nuclear Fe 3+ sites and the dehydroxylated bi-nuclear Fe 2+ sites in Fe/ZSM-5. Our conclusion is that the positive effect of NO on N 2O decomposition is due to the dehydroxylation of the hydroxylated bi-nuclear Fe sites facilitated by NO, as well as the enhancement of the O 2 desorption rate regulated by NO.

Calculation Method for Transient Concentration Response on the Steady State Flow Field : Part 3-Identification Technique for Environmental Impact Material based on Response Factor Method Using Sensing Information

Calculation Method for Transient Concentration Response on the Steady State Flow Field : Part 3-Identification Technique for Environmental Impact Material based on Response Factor Method Using Sensing Information

101 デジタルフィルタに基づく過渡応答周波数分析(騒音・振動の能動制御(1))

We are studying a new analysis method for transient responses by using the digital filter. This paper demonstrates some time-frequency analysis results of responses based on typical differential equations. First, we present the results for the linear free and forced vibration responses of one degree-of-freedom system. Then we consider the responses based on Duffing's equation and it is shown that the dominant frequency change of the responses can be visualized in the time-frequency analysis results. And the responses based on Van del Pol equation are analyzed to understand the several dominant frequencies. Finally, we apply the time-frequency analysis to the data of car bumping and it is shown that the phenomena may be described by the Duffing's equation.

Transient study of the dry reforming of methane over Pt supported on different γ-Al 2O 3

CO 2 reforming of methane has been studied over Pt/Al 2O 3 model catalysts in a temperature range of 600–800 °C using steady-state and transient methods (Transient Response Method (TRM) and DRIFT-MS). Pt-supported catalysts were prepared using two different alumina (γ-Al 2O 3(S) Sasol-Puralox and a synthesized γ-Al 2O 3(N) with nanofibrous structure). Catalysts and supports were characterized by conventional methods (XRD, TEM, A BET, XPS) before and after reaction. Pt 0 species are present in the catalysts, with a higher relative contribution for the catalyst that has a nanostructured support. Pt/γ-Al 2O 3(N) catalyst presented the best performance in reactivity and showed a low rate of carbon formation and a minimal water production. From TRM and DRIFT-MS results it can be concluded that, when CO 2 and CH 4 are fed separately into the reaction system, they are activated over the catalytic surface. Besides, when both reactants are fed contemporaneously the presence of CH X species promotes the CO 2 activation that is responsible for the reforming reaction.

Role of Lattice Oxygen of Metal Oxides in the Dehydrogenation of Ethylbenzene under a Carbon Dioxide Atmosphere

The mechanism for the dehydrogenation of ethylbenzene over V, Cr, and Fe oxides loaded on activated carbon, powdered diamond, Al(2)O(3), and MgO was studied in the presence of CO(2). Vanadium oxide-loaded catalysts provided higher styrene yields under CO(2) than Ar flow. The transient response method was carried out to understand the reaction behaviors of lattice oxygen of various metal oxides on the support. The results showed that lattice oxygen of vanadium oxide (V=O) was consumed in the dehydrogenation reaction and that reduced vanadium oxide was reoxidized with CO(2). A similar redox cycle was observed on iron oxide-loaded activated carbon catalyst. Spectroscopic characterization revealed that vanadium oxide and iron oxide on the support were reduced to a low valence state during the dehydrogenation reaction, and that CO(2) could oxidize the reduced metal oxides. In contrast, chromium(III) oxide was not reduced during dehydrogenation. From these findings, the redox cycle over vanadium oxide- and iron oxide-loaded catalysts was concluded to be an important factor in promoting the catalytic activity with CO(2).

N2O Decomposition over Fe‐ZSM‐5 Studied by Transient Techniques

AbstractN2O decomposition to gaseous N2 and O2 catalyzed by a commercial Fe‐ZSM‐5 has been studied by different transient techniques: (i) via the transient response methods at ambient pressure, (ii) via the temporal analysis of products (TAP) reactor under vacuum, and (iii) by temperature‐programmed desorption (TPD) under vacuum. The catalyst was activated in He at 1323 K. Two main steps can be distinguished within the transient period of N2O decomposition under constant N2O feed at 603 K: the first step consists of molecular N2 formation and surface atomic oxygen (O)Fe. It follows a period of stoichiometric N2O decomposition to gaseous N2 and O2 with increasing conversion until steady state is reached. The observed rate increase is assigned to a slow accumulation on the surface of NOx,ads species formed from N2O and participating as co‐catalyst in the N2O decomposition. The NOx,ads species accelerates the atomic oxygen recombination/desorption, which is the rate‐determining step of N2O decomposition. The formation and accumulation of NOx,ads species during N2O interaction with the catalyst was confirmed by TAP studies. The amount of NOx,ads was found to depend on the number of N2O pulses injected into the TAP reactor. In the presence of adsorbed NOx on the catalyst surface (NOx,ads) the desorption of dioxygen is facilitated. This results in a shift of the oxygen desorption temperature from 744 K to considerably lower temperatures of 580 K in TPD experiments. Pulses of gaseous NO had a similar effect leading to the formation NOx,ads, thus facilitating the oxygen recombination/desorption.

Analytical modeling for transient probe response in pulsed eddy current testing

An improved analytical model by the Fourier method for transient eddy current response is presented. In this work, an alternative approach is considered to solve the harmonic eddy current problem by the reflection and transmission theory of electromagnetic waves, thus a more concise closed-form expression is expected to be obtained. To reduce the inherent Gibbs phenomenon, a harmonic order-dependent decreasing factor is employed to weight the Fourier series (FS) representation. It is shown that the developed model is promising to be used as a fast and accurate analytical solver for the transient probe response and is helpful to gain a deep insight into pulsed eddy current (PEC) testing.

Dynamic analysis of space frames: The method of reverberation-ray matrix and the orthogonality of normal modes

The formulation of reverberation-ray matrix analysis has been proposed to study wave propagation in planar frames. It is applied here to modal analysis of complex three-dimensional framed structures, optionally with lumped masses and/or elastic supports. Furthermore, by means of Betti's reciprocity theorem, orthogonal conditions are established for different natural modes, and hence transient response analysis based on mode superposition is developed. Both the reverberation-ray matrix analysis for free vibration and the mode superposition method for transient response are illustrated by numerical examples.

Characterization and catalytic performance of CeO 2-Co/SiO 2 catalyst for Fischer-Tropsch synthesis using nitrogen-diluted synthesis gas over a laboratory scale fixed-bed reactor

The surface species of CO hydrogenation on CeO 2-Co/SiO 2 catalyst were investigated using the techniques of temperature programmed reaction and transient response method. The results indicated that the formation of H 2O and CO 2 was the competitive reaction for the surface oxygen species, CH 4 was produced via the hydrogenation of carbon species step by step, and C 2 products were formed by the polymerization of surface-active carbon species (-CH 2-). Hydrogen assisted the dissociation of CO. The hydrogenation of surface carbon species was the rate-limiting step in the hydrogenation of CO over CeO 2-Co/SiO 2 catalyst. The investigation of total pressure, gas hourly space velocity (GHSV), and product distribution using nitrogen-rich synthesis gas as feedstock over a laboratory scale fixed-bed reactor indicated that total pressure and GHSV had a significant effect on the catalytic performance of CeO 2-Co/SiO 2 catalyst. The removal of heat and control of the reaction temperature were extremely critical steps, which required lower GHSV and appropriate CO conversion to avoid the deactivation of the catalyst. The feedstock of nitrogen-rich synthesis gas was favorable to increase the conversion of CO, but there was a shift of product distribution toward the light hydrocarbon. The nitrogen-rich synthesis gas was feasible for F-T synthesis for the utilization of remote natural gas.

Calculation Method for Transient Concentration Response on the Steady Flow Field : Part 2-Analysis in Multi-rooms Building Using Macro-Micro Multiplicative Model

Calculation Method for Transient Concentration Response on the Steady Flow Field : Part 2-Analysis in Multi-rooms Building Using Macro-Micro Multiplicative Model

NMR microimaging of fluid flow in model string-type reactors

Magnetic resonance microimaging (MRM) was employed to obtain quantitative velocity maps of water flowing in the channels possessing unconventional cross-section shapes formed by a bundle of parallel fibers within a tubular string-type reactor. The maps obtained demonstrate the presence of large amounts of an almost stagnant liquid in the stretched corners of the cross-sections representing distorted triangles or squares. This fact together with the irregularity of the filaments packing in the model string-type reactor was demonstrated to lead to a broad residence time distributions (RTDs) for liquid flow. Next, the pulsed field gradient NMR (PFG NMR) technique was employed to compare transport of water with that of butane gas in the same model string-type reactor. The experimentally measured average propagators (travel distance probability density functions) have demonstrated that Taylor dispersion can lead to much better RTDs for gas as compared to liquid in channels with sub-millimeter equivalent diameters. The PFG NMR data were compared with the RTD obtained using the conventional tracer time-of-flight transient response method. It is concluded that due to the differences in the quantities actually measured by the two techniques, and the significant differences in the measurement length scales (microns to 1–2 cm for NMR/MRM, tens of centimeters for transient response methods), there is no reliable way of directly comparing these results. The information obtained by NMR/MRM and more conventional techniques such as time-of-flight should be considered as complementary. In particular, NMR/MRM can reveal the reasons for the observed overall reactor performance by providing access to the transport processes on short length scales inside the reactor and by revealing structure–transport interrelations. 2007 Elsevier Ltd. All rights reserved.