CO2 formation rate

Figure 10.7. CO2 formation rate from CO and O2 over Rh(l 11) and Rh(l 10) surfaces [Adapted from M. Bowker, Q. Guo, and R.W. Joyner, Catal. Lett. 18 (1993) 119]. Note the similarity to the simple model used to describe the rate in Fig. 2.12.

O showed a profound difference in CO2 formation rate [M.J.P. Hopstaken and J.W. Niemantsverdriet, J. Chem. Phys. 113 (2000) 5457]. Hence, care should be taken to interpret apparent structure sensitivity found under normal operating conditions of high pressure and coverage in terms of the intrinsic reactivity of sites. From the theory of chemisorption and reaction discussed in Chapter 6 it is hard to imagine how the concept of structure insensitivity can be maintained on the level of individual sites on surfaces, as atoms in different geometries always possess different bonding characteristics. 

In the case of PBT the conversion of oxygen into CO and CO2 is independent of the weathering time. For PA6, after an oxygen uptake of about 600 mmol/kg, which corresponds to a weathering time of 100-150 hours, an increase in the CO2 formation rate was observed. The conversion of oxygen into CO is about 5% and into CO2 about 10%. For both polymers CO can be formed by photolysis, but in the case of PA6, CO2 can only be formed by oxidation. 

Cox et al (82) used low-energy electron diffraction (LEED) to probe the surface structure of the Pt(lOO) crystal during the oscillations of the CO oxidation at 500 K. Figure 4 shows the CO2 formation rate, the LEED... 

Catalytic Turn-Over-Frequency. From the kinetic fit, it is possible to simulate the CO2 formation rate and thus to obtain the turn-over-frequency (TOF) of the catalytic reaction. The simulated C02-yield under the reaction conditions of Fig. 1.64a is displayed in Fig. 1.68. The corresponding TOF amounts to 0.4 CO2 molecules per gold cluster per second. For the conditions of Fig. 1.64c, a TOF of 0.3 CO2 molecules per gold cluster per second was estimated. These values are in the same order of magnitude as the catalytic activity of oxide supported gold cluster particles with a size of a few nanometers, which ranges between 0.2 s per Au atom ( 2 nm diameter particles at 273 K) and 4s per Au atom (3.5 nm particles at 350 K) [238,366,367]. 

Figure 7.5a shows molecular beam results on the temperature dependence of the steady-state rate of CO oxidation over a Pd(l 1 0) surface. At 300 K the reaction is Umited by oxygen adsorption because the surface is covered with COads In the temperature interval between 370 and 650 K, however, the rate for CO2 production increases rapidly, presumably because of desorption of some of the CO, which reduce the COads coverage on the surface. A bistability is seen in this temperature region, as indicated by the hysteresis in CO2 formation rate seen between experiments with increase and decrease of temperature (Figure 7.5a). As the temperature is increased, the transfer from the CO layer to the Oads layer is delayed, while when the temperature is decreased, the reverse is true. Local single oscillations are also seen for the CO2 rate at 372 and 382 K in the...

Our interest is focused on a real intermediate in the CO2 production path. To respond this request, the amount of In (qin ) can be related to the CO2 formation rate. 

The most frequent use of DBMS is for studies of possible fuels in fuel cells. Figure 5 shows the faradaic and ion currents for CO2 and methylformate during methanol oxidation at carbon-supported Pt nanoparticles. Note that the formation of methylformate starts at a slightly lower potential than that of CO2. The ratio of the CO2 formation rate to the faradaic current yields a current efficiency of 90 % in this case. Under flow and at smooth Pt electrodes, the current efficiency for CO2 remains at 30 % for all flow rates [4]. This proves the parallel reaction mechanism suggested by Bagotsky [30]. One path leads to formaldehyde and formic acid. Under flow, these molecules diffuse away fi om the electrode, while under stagnant conditions as in the pores of a porous electrode, they are further oxidized to CO2. The other path leads to CO2 via adsorbed CO and is independent of flow rate. 

Fig. 9.20 CO oxidation reaction on Pd(lll) at 300 °C. (a) Partial pressures of Oj, CO, and CO2 monitored by mass spectroscopy, and (b) O li/Pd 3p>3,2 and (c) Pd 3dsn AP-XP spectra of a Pd(l 11) surface taken at region a in (a) where the CO2 formation rate is maximized under exposure to 2 X10" Torr O2 and 2x 10" Torr CO gases. Reproduced from ref. [56] with modification...

As a result of this exercise, we find the steady-state coverages on Pt of 9co = 0-215 ML, 002 = 8.4xlO , and 0o = 5.6xlO and a steady-state CO2 formation rate of 6.16x10 s ... 

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