HCHO formation rate

Figure 2. Methane Partial Oxidation. Rate of HCHO formation on unpromoted Si02, 5%V205/Si02 and 4%Mo03/Si02 catalysts.

Figure 13.3 Potentiodynamic electrooxidation of (a) formic acid, (b) formaldehyde, and (c) methanol on a Pt/Vulcan thin-film electrode (7 xgpt cm, geometric area 0.28 cm ) in 0.5 M H2SO4 solution containing 0.1 M HCOOH (a), HCHO (b), or CH3OH (c). The potential scan rate was 10 mV s and the electrolyte flow rate was 5 p-L s at room temperature). The top panels show the faradaic current (solid lines), the partial currents for Ci oxidation to CO2 (dashed lines) and for formic acid formation (dash-dotted line), calculated from the respective ion currents, and the difference between the measured faradaic current and the partial current for CO2 oxidation (formic acid oxidation (a), formaldehyde oxidation (b)), or the difference between faradaic current and the sum of the partial currents for CO2 formation and formic acid oxidation (methanol oxidation, (c)) (dotted line). The solid lines in the lower panels in...

Figure 13.6 Potential-step electro-oxidation of formaldehyde on a Pt/Vulcan thin-film electrode (7 p,gpt cm, geometric area 0.28 cm ) in 0.5 M H2SO4 solution containing 0.1 M HCHO upon stepping the potential from 0.16 to 0.6 V (electrolyte flow rate 5 pL at room temperature). (a) Solid line, faradaic current transients dashed line, partial current for HCHO oxidation to CO2 dotted line, difference between the net faradaic current and that for CO2 formation, (b) Solid line, m/z = 44 ion current transients gray line potential-step oxidation of pre-adsorbed CO derived upon HCHO adsorption at 0.16 V, in HCHO-free sulfuric acid solution, (c) Current efficiency transients for CO2 formation (dashed line) and formic acid formation (dotted line).

FIGURE 7.8 Calculated rates of formation of OH radical from photolysis of HONO, 03, and HCHO at Long Beach, California, on December 10, 1987 (adapted from Winer and Biermann, 1994). 

When an excess water is present in a solid acid system, however,it would solvate the —S03H to form -S03 H30+ or dissociate to form a free H30+ ion in an extreme case [13], In such rases, catalytically active species changes from a fixed proton to a fixed or free Il30+. Not only this would reduce the reaction rate [14], but the steric hindrance is also relaxed. Hence, the lowered HCHO conversion and the formation of the N—benzyl compound as shown in Fig. 2 for the reused resin catalyst could be understood. 

The rate constant obtained for G + DMSO in air is slightly more than a factor of 2 slower than the value of (2.0 0.3) xlO 10 cm3 s 1 for the reactiom G + DMS (this laboratory, unpublished results). No effect of the O2 concentration was observed for the reaction of G with DMS. However, this rate constant is already close to the collision frequency and a small O2 effect could remain undetected within the precision of the present experimental method. In air the reaction of G with DMSO leads to the formation of SO , DMSO-), CO, HCHO, and HOOOH with yields of approximately 42% (S), 14% (S), 15% (C), 18% (C), and 2% (C), respectively. As discussed earlier it is not known whether the yield of DMS02 is being over- or underestimated. The total sulfur yield was 56% indicating that probably a major sulfur containing product has not been detected. With the inclusion of the contribution from DMSO the total carbon yield was 63%. The formation of DMSO and SO2 as products indicates that both, addition (13) and abstraction (14) pathways are operative,... 

For NO t > 0-5 ppb (typical of urban and polluted rural sites in the eastern USA and Europe) Equations (3) and (4) represent the dominant reaction pathways for HO2 and RO2 radicals. In this case the rate of ozone formation is controlled largely by the rate of the initial reaction with hydrocarbons or CO (Equations (1) and (2)). Analogous reaction sequences lead to the formation of various other gas-phase components of photochemical smog (e.g., formaldehyde (HCHO) and PAN) and to the formation of organic aerosols. 

Fig. 23. The observed150,151 and calculated156 rate constants for the reaction HCHO + OH. The solid line denotes the calculated rate constant k, whereas the dashed line corresponds to the values of the strong-collision, low-pressure limiting rate constant sckADi,o calculated for the formation of the pre-reaction adduct.

The maximum rate ever observed, during this study, for COj production was 300 pmol kg s while the maxima for formaldehyde and carbon monoxide were 1300 pmol kg s and 3400 pmol kg s respectively. Hence, combination of the rates for HCHO and CO was the important factor in determining the overall shapes of the total product formation curves and CO2 will not be discussed further here. 

CO -HCHO-air 2 NOx offgasing. Insensitive to radical source parameters but O3 formation is very sensitive to NO offgasing rates. Also can be used to obtain formaldehyde photolysis rates... 

Cloud processes have been predicted to have a significant effect on the chemistry of the clean troposphere (Lelieveld and Crutzen, 1990, 1991 Warneck, 1991, 1992). For example, the uptake of HCHO, HOz radicals, and N2Os into cloud droplets can lead to a decrease in the production of ozone. Removal of HCHO reduces the rate of gas-phase production of HOz radicals, and N205 into cloud droplets can lead to a decrease in the production of ozone. Removal of HCHO reduces the rate of gas-phase production of H02 radicals [reactions (33)—(36)1, and consequent conversion of NO to N02. Also, aqueous-phase reactions of H2C(OH)2, the hydrated form of HCHO, lead to the formation of 02, which can react with dissolved 03 to enhance the rate of transfer of 03 to the liquid phase over that based solely on physical solubility. Absorption of N2Os into... 

The reactivity of the system is controlled by the amount of HCHO. Upon photolysis, HCHO provides two HOt radicals on one path and none on the other. Since these paths are roughly comparable in rate, we can say approximately that each HCHO molecule leads to one HO2 molecule. (It leads to exactly one in the OH reaction.) The conversion of NO to NO2 and the formation of O, are therefore driven by HCHO through its production of HOj. Thus the theoretical maximum amount of O3 that could be produced in this system is... 

Fig. 9.—Arrhenius Plot for the Formose Reaction at Intermediate Conversion Levels. [fc = rate of formation of formose/molarity of Ca(OH), E = 16 kcal. mole". Rate of feed (mole.liter" .min" ), of HCHO, 0.52 of Ca(OH), 0.288 —X—, zero-order correlation —O—, experimental data.]...

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