The reaction is CO methanation(i.e CO + 3H2 = CH4 + H2O). Since the input gases are CO2 and H2 at the surface of catalyst, the rate of former reaction is zero. As CO2 methanation and Reverse water-gas shift occurs along the radius of catalyst towards the center CO, H2O and CH4 are formed which will initiate the CO methanation reaction which was initially zero at the surface of the catalyst.
Dear Pratheek,
the process of co-methanation of CO and CO2 is described here:
- Habazaki et al. 1998: https://doi.org/10.1016/S0926-860X(98)00121-5
In general, the effectiveness of a heterogeneous catalyst can be calculated as follows:
- measurement of the reaction rate as a function of the partial pressures of the reactants
- determination of the volume-specific phase boundary (e.g. based on the geometry of the catalyst pellets)
- determination of the mass transfer coefficients of the rate-limiting reactants (by considering sorption processes)
- with this dataset, you can calculate the reaction rate constant of the respective heterogeneous reaction
- the Damköhler-Number DaII then provides information on the "effectiveness factor": effectiveness factor = 1/(1+DaII)
Best,
Sascha
Do you mean, division by zero - the overall rate divied by the rate of surface reaction?
First, not one but two reactions - consecutive-competing, and therefore two effectiveness factors. Secondly, what is your purpose, if is it the determination in theoretical way the value of the effectiveness factors - you need to know the kinetic equations and effective diffusion coefficients or experimentally - the type of reactor will be important.
And third, for computations, it is enough to know the value of the overall rates that you will derive from the mass balance of reactants in the catalyst grain.
Also look for work on this topic in Chemical Engineering Science or AIChEJ - there were the sixsties or seventies.
Regards,
Dear Pratheek,
Example –1Turnover Frequency in Fischer–Tropsch Synthesis
CO + 3H = 2 CH 4 + H 2 O
The Fischer–Tropsch synthesis was studied using a commercial 0.5 wt % Ru on -Al 2 O 3 . The catalyst dispersion percentage of atoms exposed, determined fromhydrogen chemisorption, was found to be 49%.At a pressure of 988 kPa and a tem-perature of 475 K, a turnover frequency, , of 0.044 s l was reported for methane.What is the rate of formation of methane, , in mol/s g of catalyst (metal plus sup-port)?
See this file
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