Transient response curves

Figive 5. Vinyl acetate transient response curve (MW=86) for obtained ftom a typical pump-probe experiment with the palladium-based catalysts and unlabel ethylene. Results were obtained with the Pd-Au w/KOAc catalyst. 

Figure 7. CO transient response curves (MW=12) obtained from a typical pump-probe experiment with the palla um-based catalysts and 1,2 C-ethylene.

The oxidation of carbon monoxide by nitrous oxide and oxygen over a silver catalyst at 20°C was analysed by both the Hougen -Watson procedure and the transient response method. The rival models derived from both procedures were clearly distinguished by the mode of the transient response curves of C02 or N caused by the concentration jump of CO, 02 or N20. 

As has been described in our previous papers > the mode of transient response curves of products caused by the concentration jump of reactants at the inlet... 

Figure 1. Simulated transient response curves at 2(PC of N,0 (including O),...

On the other hand, the N20(inc.,0)-N2 response on the reduced surface indicated a typical overshoot mode with an instantaneous maximum before reaching zero. This characteristic mode strongly suggests that N20 is directly decomposed on active sites, and that the active sites are not regenerated resulting from the irreversible adsorption of the formed oxygen atoms. This is easily presumed from the relation between the mode of transient response curve and reaction mechanism [2]. 

This Set 8 consistently explained all other transient response curves, as typically presented in Figure 2 by a dotted curve. Comparing Sets 6 and 8 in Table 2, the value of k2 in the 02-C0 reaction is a hundred times larger than that in the N20-C0 reaction. This means that adsorbed oxygen is very quickly dissociated into monoatomic oxygen, in contrast to the N20-C0 reaction. This is consistent with Clarkson and Cirillo s estimation [ 1 1 ] in which they evaluated only 0.02% of all adsorbed oxygen to be diatomic oxygen on oxidized silver. 

The validity of parameter-sets 6 and 8 should additionally be confirmed by using the data from non-isothermal experiments to reject a further possibility in the existence of other parameter-sets with a good degree of fitting. The nonisothermal transient experiments, unfortunately, have not been conducted within the period giving a constant activity of the catalyst. The mode of the transient response curve of N2 is significantly affected by the value of kj, rather than... 

Fig. 39. The large graph is a curve of the steady-state rate of CO2 production as a function of Pqo over K25-ZnO at 150°C and P02 = 0.2 bar. The CO2 transient response curves (a)-(e) result from stepwise changes of the CO pressure among the points A-E as shown above the response curves. The response modes are classified as (a) monotonic, (b and c) complex, (d) false start, and (e) overshoot (after 222).

Although this experimentally observed scaling behavior is correctly predicted by the Doi-Ohta theory, the shape of the transient response curve—in particular, the overshoot and undershoot in the shear stress—are not predicted. This implies that the relaxation expressions chosen by Doi and Ohta, Eqs. (9-46) and (9-47), are inaccurate. This is not very surprising, since Eqs. (9-46) and (9-47) were chosen rather arbitrarily from many possible forms that satisfy the scaling relationship. Optical microscopy suggests that the overshoot and undershoot are caused by elongation of droplets followed by their breakup (Takahashi and Noda 1995). Vinckier et al. (1997) have shown that the stress growth after start-up or... 

Figure 1. Transient response curves for a) n-butane, b) CO2, and c) MA obtained by pulsing a 3.5/1 3.5/1 C4Hio/Ar mixture over an oxygen-treated VPO sample at 653 K. The responses labeled Ox were obtained after the sample was first exposed to 1000 pulses n-butane. The unlabeled responses were obtained after exposure to 8000 pulses.

Table 8.2. Typical responses (M. Kobayashi, Characterization of transient response curves in heterogeneous catalysis—I. Classification of the curves. Chemical Engineering Science, 37 (1982) 393).

The transient response curve of the 10263 film to ethanol gas is shown in Figure 9.23. The variation of sensitivity was measured at the optimized temperature of 400°C and ethanol concentration of 900 ppm. Upon injection of ethanol gas, the sensitivity reached saturation in about 4 min, and when dry air was introduced, the sensitivity returned to the initial value after 12 min. The response and recovery times are in several minutes and the obtained value of sensitivity is very low when compared to the Sn02 gas sensors. The sensitivity and transient response of the In203 sensor toward ethanol are poor, which may be improved by incorporating some suitable dopants. In the present... 

FIGURE 9.23 Transient response curve of lUjOj gas sensor toward ethanol (900 ppm) at 400°C. 

The response and recovery times are important parameters for tailoring sensors for desired applications. The response time is defined as the time required for the sensitivity to reach 90% of the equilibrium value after the test gas in injected. The recovery time is the time necessary for the sensor to attain sensitivity 10% above the original value in air. The transient response curve of the Mgln204 sensors before and after and Li+ implantation are shown in Figure 9.26. The variations... 

Fig. 14 Transient response curve of the SAW sensor for determining reproducibility...

It is clear that the 12 parameters corresponding to the proposed reaction scheme cannot be statistically significant by modeling only two transient response curves. No real physical meaning should be attributed to these parameter estimates. However, the modeling... 

Figure 10.8(a) displays pump-probe data sets obtained at 140, 170, and 350°C. Figure 10.8(c) shows the plots of the amount of CO2 produced during each pulse and the total amount for each pump-probe cycle at a series of temperatures. The amount of CO2 produced is determined by measuring the area (zeroth moment) under the transient response curve (91). The zeroth moment is normalized relative to the amount of CO per pulse to determine the CO2 yield. The absolute amounts of O2, CO, and CO2 are determined by comparing the response obtained in a reaction with one obtained using a standard blend. At 170°C the yield for the individual O2 and CO pulses reaches a... 

Oberoi, A.S. Fuller, O.M., and Kelly, J.F.. Methods of interpreting transient response curves from dynamic sorption experiments, Ind. Eng. Chem. Fund., 19(1), 17-21 (1980). 

Fig. 20.3 (a) Typical transient response curves of OTFT upon exposure to different concentrations of NO, NO, ... 

To gather information for the role of O2 in the H2-SCR mechanism, similar SSITKA experiments with the use of 02 were conducted at 140 °C. Figure 26.8 presents the transient response curves of N2 0, N2 0, and Ar obtained on Pt/Lao.sCeo.sMnOs (Figure 26.8a) and Pt/Si02 (Figure 26.8b) catalysts after the switch N0/H2/ 02/Ar/He N0/H2/ 02/He was made at 140 °C. As seen in Figure 26.8, the concentration of N2 0 produced by both catalysts is reduced after the isotopic switch, whereas the continuous evolution of N2 0 is noticed. The sum of the steady-state concentrations of N2 0 and N2 0 formed under H2-SCR in the isotopic gas mixture is the same as the steady-state concentration... 

Figure 26.8 Dimensionless transient response curves of N2 0, N2 0, and Ar obtained following the isotopic switch NO/H2/ 02/Ar/He N0/H2/ 02/Ar/He at 140 °C over...

Rh nor rhodium oxide, but probably Rh+. Mallens et al. studied the response of pulsing methane, oxygen or a mixture of the two over Rh sponge and reported that CO and H2 were the primary products, from transient response curves where these products appeared before CO2 and H20. Similar studies and results are reported for several noble metal catalysts on various supports (see, for example. Ref. 57 and the references therein). However, even for noble metal catalysts, steep temperature gradients, indicating a combustion-reforming reaction scheme, are observed for reactants under atmospheric pressure. ... 

Figure 3.4 Transient response curves of CO, COj, and Ar during the CO step of the gas delivery sequence 1.5% 02/He (30 s) He (30 s) —> 3% CO/3% Ar/He (t) at 400 °C over a commercial Pd-Rh TWC. Adapted with permission from...

Figure 3.7 Transient response curves of and gaseous species...

F nre 3.12 Transient response curves for (a) Oj and (b) 0 0 gaseous oxygen isotopic species obtained during TPIE over fresh Ceo.5Zro.5O2 solids and Ceo,5Zro 5O2 solids contaminated with P, P-Zn, or P-Ca. Adapted with permission from Christou et alP Copyright 2011 Elsevier. 

Figure 3.12 shows the transient response curves of 02(g) and i8oi6o(g), obtained during a TPIE experiment over uncontaminated... 

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