Rate of COS

Fig. XVIII-27. Specific rates of CO oxidation on single crystal and supported catalysts as a function of temperature. (From Ref 308. Reprinted with permission from American Chemical Society, copyright 1988.)...

CO oxidation catalysis is understood in depth because potential surface contaminants such as carbon or sulfur are burned off under reaction conditions and because the rate of CO oxidation is almost independent of pressure over a wide range. Thus ultrahigh vacuum surface science experiments could be done in conjunction with measurements of reaction kinetics (71). The results show that at very low surface coverages, both reactants are adsorbed randomly on the surface CO is adsorbed intact and O2 is dissociated and adsorbed atomically. When the coverage by CO is more than 1/3 of a monolayer, chemisorption of oxygen is blocked. When CO is adsorbed at somewhat less than a monolayer, oxygen is adsorbed, and the two are present in separate domains. The reaction that forms CO2 on the surface then takes place at the domain boundaries. 

Separation of gases and liquids always involves coalescence, but enhancement of the rate of co escence may be required only in difficult separations. 

FIRE SIMULATOR predicts the effects of fire growth in a 1-room, 2-vent compartment with sprinkler and detector. It predicts temperature and smoke properties (Oj/CO/COj concentrations and optical densities), heat transfer through room walls and ceilings, sprinkler/heat and smoke detector activation time, heating history of sprinkler/heat detector links, smoke detector response, sprinkler activation, ceiling jet temperature and velocity history (at specified radius from the flre i, sprinkler suppression rate of fire, time to flashover, post-flashover burning rates and duration, doors and windows which open and close, forced ventilation, post-flashover ventilation-limited combustion, lower flammability limit, smoke emissivity, and generation rates of CO/CO, pro iri i post-flashover. 

The rate of CO transport from the bulk gas into the gas and liquid films is as follows ... 

Fig. 3.11. Rate of CO uptake by R. rubrum with various acetate concentrations at an agitation speed of 200 tpm...

Figures 3.12 and 3.13 show the kinetic parameter evaluation of (3.14.5.2) and (3.14.5.4), i.e. jjbm, qm, Kp, and K p. The inhibition phenomena were examined for the growth rate and the rate of CO uptake, respectively. The experimental data followed the quadratic manner as presented in the (3.14.5.2) and (3.14.5.4), respectively. The Sigma Plot 5 was used to...

Significant differences were observed when S/G was varied from 0.15 to 0.40. At the lower S/G ratios there is no CO shift conversion whereas there is CO shift conversion at the higher S/G ratios. When the data are evaluated and activity constants for CO and C02 methanation and CO shift conversion are determined, the activity for methanation remains the same regardless of the S/G. However, with high S/G, shift conversion occurs at about 25% of the rate of CO methanation. At low S/G, no shift conversion is observed. 

It is expected that the actual rate of CO methanation will always be high, at least under industrial conditions, whereas the C02 methanation rate will vary from about the same as that for CO down to zero, depending on operating pressure, temperature, CO content of the gas, and catalyst particle size. Meanwhile a water-gas shift (or reverse shift) reaction will be occurring at all times at a fairly high rate. 

Figure 2.39. (a) Effect of pcc/Pc>2 on the rate °f CO oxidation (measured as PC02) on Pt(l 11) covered with various Li coverages 0Lj 12 (b) Effect of Li coverage on the rate of CO oxidation at various fixed Pcc/po2 values.112 Reprinted with permission from Elsevier Science. 

Figure 4.16, Effect of catalyst potential, dimensionless catalyst potential n(=FUWR/RT), corresponding linearized51 Na coverage 0ns and pCo on the rate of CO oxidation on Pt/(T-A1203. T=350°C, po2=6 kPa.51 Reprinted with permission from Academic Press.

Figure 4.31. Transition from volcano-type behaviour at low Po2 to electrophobic behaviour at high po2 during CO oxidation on Pt/j3"-A]203.51 Effect of UWr and linearized51 Na coverage 0Na on the rate of CO oxidation on Pt/p"-Al203 at varying po2- Other conditions pco=2 kPa, T=350°C. The top part of the figure shows the corresponding variation of the actual51 Na coverage, 0Na, with UWr- Reprinted with permission from Academic Press.

Figure 5.54. Effect of sodium coverage on the change AUWR of polycrystalline Pt catalyst potential UWr and on the catalytic rates of CO oxidation (solid lines37) and C2H4 oxidation (dashed lines36). Comparison with the theoretical Na coverage required to form the Pt(l 11)-(12xl2)-Na adlayer 0 is based on the number of surface Pt atoms 09a is based on the number of surface O atoms corresponding to the Pt(l 1 l)-(2x2)-0 adlattice. Reprinted from ref. 78 with permission from Elsevier Science,...

Figure 6.11. Effect of Pco Po2 ratio at fixed Li coverage (left) and of Li coverage at fixed PC0/P02 ratio (right) on the rate of CO oxidation on Pt(l 1l).83 Reprinted with permission from Elsevier Science.

Figure 6.12. Example of rules Gl, G2 and G3 Effect of pCo (=Pd) and of Na coverage and corresponding UWr and AO values on the rate of CO oxidation on Pt films deposited on P"-A1203 at fixed Po2=6 kPa71 Note that dr/dO(= dr/edUWR) always traces dr/dpco for negative, positive and zero (volcano peak) values. In the right figure the raw data (left) have been fitted to a polynomial expression.71 Reprinted with permission from Academic Press.

Figure 6.25, Experimental71 (left) and modelled simulated" (right) dependence of the rate of CO oxidation on Pt deposited on J3"-A1203 as a function of pco, catalyst potential UWR and dimensionless catalyst work function Il(=A

Figure 8.28. Steady-state effect of catalyst potential and work function on the rate of CO oxidation on Pt. Open symbols correspond to open-circuit conditions , T=485°C> ro=0.5xl0 7 mol/s , T=505°C, r0=f. 0xl0 7mol/s, , T=535°C, ro=1.5xl0 7 mol/s. pco=0.25xl0"2bar, Po2-l 1.3x1 O 2 bar.34 Reprinted with permission from Trans Tech Publications.

Figure 8.30. Effect of gaseous composition on the rate of CO oxidation on Pt/YSZ. T= 535°C O, open-circuit >UWr=500 mV A.Uwr—SOO mV.34 Reprinted with permission from Trans Tech Publications.

As already shown in Figure 6.3b the system exhibits remarkable electrophilic promotional behaviour with p values up to 20.64 This is also shown in Fig. 8.60 which depicts a galvanostatic transient. Application of a negative current between the Pt catalyst-working electrode and the Au counter electrode causes a sharp increase in all reaction rates. In the new steady state of the catalyst (achieved within lhr of current application) the catalytic rate increase of C02 and N2 production is about 700%, while lesser enhancement (250-400%) is observed in the rates of CO and N20 production. The appearance of rate maxima immediately after current application can be attributed to the reaction of NO with previously deposited carbon.64... 

Wei-Ping won the bet. A series of rapid kinetic experiments provided strong support for the concept of two independent active sites. CODH/ACS was reacted with CO and the rate of development of each of the enzyme s characteristic EPR signals was compared with the rates of CO oxidation and acetyl-CoA synthesis. On the basis of these... 

Rather limited information is available on how the nature of R affects the rate of CO insertion, all other factors being constant. A generalization that ethylmetal complexes react faster than the corresponding methyl carbonyls derives from investigations on four systems RIr(CO)2(AsPh3)Cl2 (92), RMn(CO)5 (51), CpFe(CO)2R (98), and CpMo(CO)jR (80). When R = Et the reactions with CO or P and As donor ligands proceed at least 6 times faster than when R = Me. 

Kinetic 37, 50-52, 97, 168) and stereochemical 54, 191, 192) investigations on the carbonylation of manganese alkyls and the decarbonylation of manganese acyls were already discussed in Sections III-V. The original finding (50) that the rate of CO insertion follows second-order kinetics has now been qualified 192). At higher pressures of CO (>15 atm) the first-order rate law [Eq. (23)] is obeyed. 

In this expression, Xi and Xi are the fractions of terrace versus step-edge sites, ri is net rate of conversion of adsorbed CO to methanol on a terrace site, and t2 is the rate of CO dissociation at a step-edge-type site. Increased CO pressure will also enhance the selectivity, because it will block dissociation of CO. 

Fig. 1. Rate of CO oxidation of ( 4 ) 02-treated Au/Nano-Ti02, (A) 03/02-treated Au/Nano-Ti02 and (O) 03/02-treated Au/P25 from 298 to 473 K.

Our preliminary experiment using a PBR showed that the order of foe rate of foe CO oxidation over Pt/Al203 was positive with respect to O2 concentration and was negative with respect to CO concentration. This result indicated that the reaction occurs via L-H mechanism with strong adsorption of CO. For this type of reaction, foe surfece coverage of O is suppressed hy CO adsorption, and therefore the rate of CO oxidation is slow in a PBR. On the other hand, adsorption of O onto the surface occurs in foe O2 zone. In other words, in foe countercuirent flow of COad and O2 there exists a reaction fi ont where foe net concentration... 

In the case of the hexacarbonyls, the rate-expression contains not only the same type of first-order term but in addition one second-order overall. For good entering groups (but not CO, for example) the rate expression contains a term strictly first-order in both the complex and the entering nucleophile. The first-order rates of CO exchange are practically identical with the rates of substitution in hydrocarbon solvents, but there is nevertheless some acceleration in ether (THF, dioxan) solutions. This solvent-dependence is not so well-marked ° as in the case of nickel tetracarbonyl. The second-order rate of substitution very strongly depends upon the basicity of the entering nucleophile... 

Figure 9. Relative rate of CO hydrogenation as a function of copper coverage on a Ru(OOOl) catalyst Reaction temperature 575K. Results for sulfur poisoning from Figure 7 have been replotted for comparison.

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