環境触媒化学特論I 6pcat.cat.hokudai.ac.jp › class › pc2020 ›...

Advanced Course in Environmental Catalytic Reaction Chemistry I 1

2020/06/11

環境触媒化学特論I

6


Advanced Course in Environmental Catalytic Chemistry I

understanding chemistry by understanding photocatalysisunderstanding photocatalysis by understanding chemistry

Division of Environmental Material Science, Graduate School of Environmental ScienceThe first semester of Fiscal 202008:45─10:15, Thursday on Zoom

Bunsho Ohtani

Institute for Catalysis, Hokkaido University, Sapporo 001-0021, Japan011-706-9132 (dial-in)/011-706-9133 (facsimile)

[email protected]://pcat.cat.hokudai.ac.jp/pcat

https://pcat.cat.hokudai.ac.jp/cgi-bin/class/db_class_e.cgi?mode=display_pc2020


schedule

(1) May 7 introduction of photocatalysis(2) May 14 interaction between substances and light(3) May 21 electronic structure and photoabsorption(4) May 28 thermodynamics: electron and positive hole(5) June 4 adsorption(6) June 11 kinetic analysis of photocatalysis(7) June 18 steady-state approximation(8) June 25 kinetics and photocatalytic activity(9) July 2 action spectrum analysis (1)(10) July 9 action spectrum analysis (2)(11) July 16 light intensity-dependence analysis(12) July 23 crystal structure (1)(13) July 30 crystal structure (2)(14) August 6 design and development of photocatalysts (1)(15) August 13 design and development of photocatalysts (2)

(questionnaire)


format

Please send email in Japanese or English within 72 hoursto: [email protected]: pc2020MMDD-XXXXXXXX

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photocatalytic reaction

• photoabsorption to yield photoexcited electron (e-) and positive hole (h+)• reaction of SURFACE-ADSORBED compounds with e- and h+.• In other words,

only adsorbed compounds can be reacted.


adsorption isotherm

interaction of compounds with surfaces• van der Waals force: physical adsorption• chemical bond: chemisorption

concentration (pressure) dependenceof adsorbed amount:

isotherm adsorbent

adsorbate

physical adsorption

chemisorption


adsorption isotherms named after proposers

Q Answer the names of these isotherms.

amou

nt o

f ads

orpt

ion

equilibrium pressure/concentration


A B

C D

Henry Langmuir

FreundlichBET


three assumptions for derivation of Langmuir eq.

Q List up the three assumptions for Langmuir adsorption isotherm.

des.

ads.

des.

ads.VVOOO V


three assumptions for derivation of Langmuir eq.

• All the adsorption sites are same in quality, i.e., strength of capturing an adsorbate is constant

• Only one adsorbate is adsorbed by one site.

• There is no interaction between sites, i.e., adsorption not influenced by adsorption of neighboring sites

des.

ads.

des.

ads.VVOOO V


Q: Langmuir isotherm to show amount of ads.

(amount of adsorption) = sKC/(1 + KC )

vacant site: [v], occupied site: [o], concentration at equilibrium: C, rate constants: ka and kd, adsorption equilibrium constant: K = ka/kd, saturation limit of adsorption: s


Q: Langmuir isotherm to show amount of ads.

Same rate of adsorption and desorption at equilibriumrate of adsorption: ra =rate of desorption: rd =

(amount of adsorption) = sKC/(1 + KC )

vacant site: [v], occupied site: [o], concentration at equilibrium: C, rate constants: ka and kd, adsorption equilibrium constant: K = ka/kd, saturation limit of adsorption: s

ka[v]Ckd[o]

ka[v]C = kd[o]KC [v]/([v]+[o]) = [o]/([v]+[o])

KC (1 - θ ) = θ(amount of adsorption) = [o] = sθ


surface phenomenon

Q How does Langmuirian equation show the characteristics of surface phenomenon?

A + B A-BA: surface adsorption site = adsorbentB: adsorbate

• All the adsorption sites are same in quality, i.e., strength of capturing anadsorbate is constant

• Only one adsorbate is adsorbed by one site.• There is no interaction between sites, i.e., adsorption not influenced by

adsorption of neighboring sites


Michaelis–Menten equation

reaction rate of enzymatic reaction assuming

E + S ⇄ ES → E + P

E: enzyme/S: substrate/ ES: complex/P: product

v = vmax [S] / (Km + [S])

k-1

k1 k2


adsorption isotherms named after proposers

amou

nt o

f ads

orpt

ion



Henry Langmuir

FreundlichBET

overlapping ofmultiple curves

linear part ofLangmuir ads.

assumingmultilayer ads.


Q: Who are BET?

vm： saturation amount offirst layer of adsorption

c： a constantx： relative pressure

(0-1)


Brunauer–Emmett–Teller isotherm



(0-1)

a kind of "agglomeration"

得られた1層めの飽和吸着量に窒素の吸着断面積（0.162 nm2）をかけて表面積（m2）をもとめ，さらにつかった固体量でわって比表面積（m2 g-1）とする．

Dewar bottle with liquid nitrogen

cell

joint

vacuumpressure gauge

gas

thermo-meter


Q: How is relative pressure, x, measured?



(0-1)

x : pressure of nitrogen measured under the same CONDITIONS = saturated vapor pressure of nitrogen

The condition: boiling point of nitrogen at the temperature of liquid nitrogen in a Dewar bottle, and the vapor pressure is the same at atmospheric pressure around an instrument. Therefore, atmospheric pressure has to be measured.

Dewar bottle with liquid nitrogen

cell

joint

vacuumpressure gauge

gas

thermo-meter


kinetics

Q If a compound adsorbed on a photocatalyst surface in Langmuirian fashion is oxidized (or reduced) by the positive hole (or photoexcited electron) in the photoirradiated photocatalyst, what is a rate expression for the reaction?


general reaction kinetics

rate (r) of reaction for

A → Bis expressed using k (rate constant) and concentrations of A ([A]), as

r = k [A]


Why the rate is proportional to concentration?

Q Interpret the reason why the rate is proportional to concentration?


kinetic energy = temperature (heat)

Translational motion: Average velocity is defined as "temperature" The higher the temperature, the more the number of particles (molecules) of higher kinetic energy.


activation energy

• Arrhenius equation shows the relation between a rate constant (k) and activation energy (Ea) and temperature (T), as well as a constant A.

Q Show Arrhenius equation.


activation energy

• Arrhenius equation shows the relation between a rate constant (k) and activationenergy (Ea[J mol-1]) and temperature (T/K), using gas constant R and a constantA.

• Arrhenius equation is

k = A exp(-Ea/RT).

• This equation tells that the rate constant is proportional to the proportion ofmolecules having energy greater than Ea, since the rate is proportional to thenumber of those molecules. The absolute number (concentration) of thosemolecules should be a product of exp(-Ea/RT) and [A]. Therefore, for a reactionfrom A to B, the rate r is

r = [A]·A exp(-Ea/RT).


What is "Boltzmann distribution"?

Energy distribution: occupied statesBoltzmann distribution: occupied/unoccupied balance depending on the

energy gap between them

(probability of excited state) =

∆E energy measured from a standardk Boltzmann constant = 1.38×10-23 J K-1

T absolute temperature = 298 K (ambient temperature)kT [ 4.11×10-21 J ] at ambient temperatureA 1 (assumption)


What is "Boltzmann distribution"?

Energy distribution: occupied statesBoltzmann distribution: occupied/unoccupied balance depending on the

energy gap between them

(probability of excited state) = A exp( –∆E / kT）

∆E energy measured from a standardk Boltzmann constant = 1.38×10-23 J K-1

T absolute temperature = 298 K (ambient temperature)kT [ 4.11×10-21 J ] at ambient temperatureA 1 (assumption)

if ∆E = 10-19 J (visible region), the probability is almost 0.if ∆E = 10-20 J (infrared region), the probability is ca. 4.5 × 10-5

if ∆E = 10-24 J (microwave region), the probability is ca. 0.999


time course of a reaction

• Assuming a first-order kinetics, derive the equation of substrate concentration ([A]t) as a function of time, using a rate constant k, time tand initial concentration [A]0.


format

Please send email in Japanese or English within 72 hoursto: [email protected]: pc2020MMDD-XXXXXXXX

[email protected](full name)(nickname)(what is learnt from today's lecture) + (questions if any)[blank line](answer for question 1)(answer for question 2)(answer for question 3)・・


email example

to

subject

(same as subject)email addressfull namenicknamecomment(s) +

question(blank line)answer 1answer 2answer 3・・

pc20200611-57388301

pc20200611-57388301

pc20200611-57388301

環境触媒化学特論I 6pcat.cat.hokudai.ac.jp › class › pc2020 ›...

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