Kinetics of heterogeneous catalytic reactions. Laboratory training guidance

2. Determination of the oxygen volume released at full decomposition of the peroxide solution (V∞) by volumetric titration. In three conical flask add 20 mL of the 0.15 M sulfuric acid solution. Pipette 2 mL of the hydrogen peroxide solution. Add 2-3 drops of mixture of the MnSO4 in concentrated H2SO4 (to accelerate the reaction). First mix gently and then titrate each sample by the 0.02 M KMnO4 solution until the pink color not disappearing within 1-2 minutes. Find the arithmetic average of the three values of the potassium permanganate volume. Stoichiometric equation for the reaction is

Thus, it follows that 1 mol of KMnO4 corresponds to 2.5 moles of H2O2. Calculation of the V∞ value obtained by titration method is given in

paragraph 6.

3.Install the equipment (Fig. 5). Place weighed (1 tablet) of activated carbon in offshoot of clean and dry reaction vessel (marked by 1 on the Fig.5). When using manganese dioxide as a catalyst it is necessary to take a small amount of catalyst (about 0.1 g or spatula tip per 1 mL of the perhydrol). Carefully pour 40 mL of prepared hydrogen peroxide solution into the reactor using a special funnel avoiding contact with the catalyst. Close the reaction vessel by the plug with inserted connecting tube.

4.Check the system for leaks. Open the valve 3, lift the vessel 4, and equalize the liquid meniscus in the vessel 4 with the liquid meniscus in the measuring burette 2 at the “zero” level. Close the valve 3 and move down the equalizing vessel 4 to quarter of the burettes height. If there is adequate tightness, the steady level moves down a bit and stop. In the case of leakage system, check tightness of individual parts of the equipment, check the integrity of the rubber tubes, and grease valve 3 by vacuum lubricant.

5.To initiate the reaction, without separating of the equipment units, tilt the reactor so that the coal tablet (catalyst) slipped into solution. The time of contact between catalyst and solution is considered as the beginning of the reaction. After 3-5 minutes make a first measurement of the evolved oxygen volume (at the time of the measurement liquid levels in the burette 2 and in the vessel 4 must be equalized). Measure a liquid level in the burette every 5-10 minutes. More the rate of the gas, more often make the measurements. With further lowering of the liquid level in the burette continue alignment of liquid levels in both legs of the instrument;

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experiment should be completed when the amount of evolved oxygen will be slightly more than a half of the volume that can be released at full decomposition of H2O2. If the capacity of the gas burette is insufficient, it is necessary to pinch the hose connecting the reaction vessel 1 with a gas burette 2, and quickly (lifting vessel 4) displace oxygen through valve 3 into the atmosphere. Then set the level at zero, close the valve and continue measurements summing the results with previous ones. The measured volume values during the reaction correspond to the Vt' values in the eq. (36). With the influence of the water vapor pressure the volume of oxygen is equal to

where Pb and PH2O are the barometric pressure and the water vapor

pressure, mm Hg (see appendix).

Determination of the oxygen volume released at full decomposition of the peroxide solution (V∞) by gasometric technique. At the end of the experiment put the vessel 1 with a reaction mixture in a cup with hot water (70 ºC) without disassembling of the equipment. Higher temperatures accelerate decomposition of hydrogen peroxide. After completion of the reaction (when oxygen stops stand out) remove the vessel from the cup with hot water, let it cool to room temperature. Measure the liquid level in the burette. V∞ must be corrected with the influence of the water vapor pressure (36).

6. To determine the V∞ value by the titration method we calculate the concentration of the solution on the base of equation

separated for the titration.

Number of the H2O2 moles in the solution used for the reaction is given by equation

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where Vs is volume of the solution in the reaction vessel.

On the base of the stoichiometric equation we find the amount of oxygen released during the decomposition of the full amount of the taken H2O2

The oxygen volume released at full decomposition of the peroxide solution (V∞) with volume Vs, can be calculated by the MendeleevClapeyron equation

where nO2 is a number of the oxygen moles;

R = 0.082 L∙atm/deg∙mol; PO2 = 1 atm;

Т is temperature (К).

Equations 37, 38, 39, and 40 can be combined into one

7. Record results of the experiment in the following form. Temperature of the experiment is ______º C;

The volume of solution taken for the reaction Vs = 40 mL; Barometric pressure Pb is ______________ mmHg;

The sample volume (hydrogen peroxide solution) taken for titration is 2 mL;

Potassium permanganate solution concentration is 0.02 M;

Volume of potassium permanganate spent for the titration, is ________ mL;

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Catalyst is _______________________________________.

Volume of oxygen corresponding to complete decomposition of hydrogen peroxide (V∞) is _________mL.

8. Fill the Table 2 on the base of the data obtained. Calculate the rate constant of the decomposition of hydrogen peroxide according to the equation (34) for each report and find the average value of kaver..

9. Calculate the half-life according to the equation for a first order reaction, t1/2 = ln2/kaver..

determine the reaction rate constant kgraph. (Fig. 1). Compare the value obtained with the kaver value.

12.From the Vt = f(t) dependence determine the approximate half-life (t1/2graph.) of hydrogen peroxide (Fig. 2) and compare the value obtained with the previously calculated half-life t1/2.

13.Draw conclusions based on the data obtained.

Questions

1.What is the kinetic equation for the reaction?

2.What kind of factors affect on the rate of reaction?

3.What is the physical meaning of the rate constant?

4.What methods of the reaction order determination do you know?

5.How temperature affects the reaction rate (Van't Hoff rule)?

6.What kind of parameters can be calculated using the Arrhenius equation?

7.Define the concept of activation energy and the energy barrier.

8.What is the activated complex in catalytic reactions?

9.From what stages consist of heterogeneous catalytic reactions?

10.Features of diffusion processes.

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11.Features of catalytic reactions?

12.Mechanisms of catalytic reactions.

13.What is adsorption?

14.The main types of adsorption, give a brief description of them.

15.Explain the role of adsorption in heterogeneous catalytic reactions.

16.The basic of Langmuir`s theory.

17.Why use Langmuir equation?

18.What is the degree of surface filling by the adsorbate? What data is needed to calculate it?

19.What determines the activity of the solid catalyst?

20.Name the basic theories of heterogeneous catalysis. What is the difference between them?

References

1.Peter Atkins, Julio de Paula, Atkins’ Physical Chemistry 9th ed., [English] OUP Oxford, 2009, 1008 p.

2.R.J. Silbey, R.A. Alberty, M.G. Bawendi. Physical Chemistry. 4th ed., [English] John Wiley and Sons, 2004, 960 p.

3.Thomas Engel, Philip Reid, Physical Chemistry. 2nd ed., [English] Prentice Hall, 2009, 1088 p.

4.K.S. Krasnov et al., Physical chemistry. V.2. Electrochemistry. Chemical kinetics and catalysis. Textbook for universities in 2 volums. Ed. K.S. Krasnov. 3rd ed., [Russian] Moscow: Vysshaya Shkola, 2001, 319 p.

5.G.A. Golikov, Guide to Physical Chemistry. Tutorial for chemicaltechnological special universities. [Russian] Moscow: Vysshaya Shkola, 1988, 383 p.

6.S.M. Kochergin et al., Brief course of physical chemistry. A textbook for high schools. Ed. S.N. Kondratieff. 2nd ed., [Russian] Moscow: Vysshaya Shkola, 1978, 312 p.

7.N.N. Mushkambarov, Physical and Colloid Chemistry. A Textbook for medical schools. 3rd ed., [Russian] Moscow: Medical Information Agency Ltd., 2008, 295 p.

8.S.V. El'tsov, N.A. Vodolazkaya, Physical and Colloid Chemistry. Textbook. [Russian] Kharkov, 2005, 239 p.

9.L.V. Senicheva, V.A. Yargaeva, Physical chemistry: chemical equilibrium. A tutorial. [Russian] Khabarovsk: Pacific. Reg. University Press, 2008, 83 p.

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10.I.A. Semiohin, Physical chemistry. Textbook. [Russian] Moscow State University Press, 2001, 272 p.

11.B.P. Nikolsky et al., Physical chemistry. Theoretical and practical guide. A textbook for high schools. Ed. B.P. Nikolsky, 2nd ed., [Russian] Leningrad: Khimiya, 1987, 880 p.

12.A.N. Alexandrov et al., Practical works on Physical Chemistry. Ed. V.V. Budanov, N.K. Vorobyov. 5th ed., [Russian] Moscow: Khimiya, 1986, 352 p.

13.E.A. Vaitulevich et al., Laboratory practical works in physical chemistry. Ed. I.A. Kurzina, [Russian] Tomsk State Arhit.-builds. University Press, 2008, 72 p.

14.S.I. Levchenkov, Physical and Colloid Chemistry. Summary of lectures. Part 2. Khim. kinetics and catalysis. Rostov-on-Don, 2004, 27 p.

15.T.V. Lapova et al., Physical chemistry. Chemical kinetics and equilibrium. Electrochemistry. Tutorial. Ed. T.V. Lapova. Tomsk State Arhit.-builds. University Press, 2009, 104 p.

16.E.I. Mingulina et al., The general chemistry course. The textbook for the students of the Energy Special Universities. Ed. N.V. Korovin. 2nd ed., [Russian] Moscow: Vysshaya Shkola, 1990, 446 p.

17.A.G. Stromberg, D.P. Semchenko, Physical chemistry. A textbook for Chem. Specials. Universities, Ed. A.G. Stromberg. 4th ed., [Russian] Moscow: Vysshaya Shkola, 2001, 527 p.

Appendix

Saturated vapor pressure of water (PH2O ) at various temperatures.

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KINETICS OF HETEROGENEOUS CATALYTIC

REACTIONS

Contributors:

Radik R. Shamilov, Docent

Azat V. Bilalov, Professor

Ramzya I. Yusupova, Docent

Yuriy G. Galyametdinov, Professor

Responsible for publishing A. A. Konopleva

Kazan National Research Technological University Publishing house

Offset laboratory of Kazan National Research Technological University

420015, Kazan, Karl Marx street, 68

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