環境触媒化学特論I 10pcat.cat.hokudai.ac.jp/class/pc2020/20200709_BO_Sapporo.pdf2020/07/09 · Advanced Course in Environmental Catalytic Reaction Chemistry I 4 format Please

Advanced Course in Environmental Catalytic Reaction Chemistry I 1

2020/07/09

環境触媒化学特論I

10


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)


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photocatalytic reaction

Photocatalytic reaction is a kind of photoreaction and therefore cannot be a series reaction: a parallel reaction initiated by photoabsorption with short-live species, e.g., photoexcited electrons and positive holes

electron-holepair

recombi-nation

photo-absorption

redox(chemical)reaction

1

2

3


necessary conditions for photocatalytic reactions

reaction initiated by photoabsorption of photocatalyst• (generally accepted) blank test: Copresence of 3 requisites, photoirradiation,

photocatalyst (solid material) and reaction substrate(s) is indispensable.• Photoreaction initiated by photoabsorption of a compound adsorbed by a solid

surface and subsequent electron injection also requires 3 requisites.• action spectrum analyses: possible sole technique to prove what absorbs light to

initiate the photoreaction• checking product(s): adsorption can decrease the amount of substrate(s);

stoichiometry

photoabsorber (= photocatalyst) remaining unchanged• checking turnover frequency: molar ratio of product(s) to photocatalyst to be

more than unity

8killer ?

PClight &solid &

S

notPC

light ||solid ||

S

notPC

light ||solid ||

S

photo-cataly-

sis (PC)

light &solid &subst-rate (S)

&: AND||: OR

__: NOT

notPC

light &solid & S

e.g. dye-sensitizedreaction


methylene blue/titania photoreaction

S-doped TiO2

P-25

S-doped TiO2

MB

Yan, X.; Ohno, T.; Nishijima, K.; Abe, R.; Ohtani, B., Chem. Phys. Lett., 429, 606-610 (2006).


S-doped TiO2

P-25

MB insuspension

methylene blue/titania photoreactionYan, X.; Ohno, T.; Nishijima, K.; Abe, R.; Ohtani, B., Chem. Phys. Lett., 429, 606-610 (2006).


V: visible light-induced photocatalysis

Known: Strategy to prepare visible light-sensitive materials.

Unknown (partly): How to prove a given reaction to be visible light-photocatalytic one.

J. Photochem. Photobiol. C: Photochem. Rev., 11 (2010) 157-178.


S-doped

P-25P-25

S-doped TiO2

acetic acid/titania photoreactionYan, X.; Ohno, T.; Nishijima, K.; Abe, R.; Ohtani, B., Chem. Phys. Lett., 429, 606-610 (2006).

13

PClight &solid &

S

notPC

light ||solid ||

S

notPC

light ||solid ||

S

photo-cataly-

sis (PC)

light &solid &subst-rate (S)

&: AND||: OR

__: NOT

notPC

light &solid & Skiller

e.g. dye-sensitizedreaction


photoreaction/photocatalytic

reaction

wavelength 1

wavelength 2

wavelength 3

wavelength 4

response (product, current...)

・・・

measurement of action spectrum

• plots of apparent quantum efficiency (response normalized by number of incident photons) versus wavelength

wavelength

appa

rent

qua

ntum

effic

ienc

y

1 23

4

5

6


action spectrum

wavelength/nm wavelength/nm

wavelength/nm

photoabsorptionefficiency

appa

rent

qua

ntum

effic

ienc

y

quantumefficiency

action spectrum= apparent quantum

efficiency

example: discrimination of active crystalline phase in anatase-rutile mixtures

T. Torimoto, et al., Phys. Chem. Chem. Phys., 4, 5910-5914 (2002).


anatase-rutile mixture

fanataseanatase content estimated from XRD patterns

0

0.2

0.4

0.6

0.8

1

350 360 370 380 390 400 410 420

abso

rptio

n (n

orm

aliz

ed)

Wavelength / nm

Merck P-25

Wako(A)+CR-EL

CR-ELTIO-5

CR-EL(1473 K)

360

370

380

390

400

0 0.2 0.4 0.6 0.8 1

λ1/

2/ n

mfanatase

Merck

HombikatTIO-2

P-25

Wako(A)Merck+CR-EL

Wako(A)+CR-EL

TIO-5Aldrich(A<R)

Wako(R)CR-EL

CR-EL(1473K)

P-25(1473K)

0.5

diffuse reflectance spectra in the unit of absorption normalized at 350 nm

λ1/2: wavelength giving half value to that at 350 nm


λ1/2 versus fanatase

360

370

380

390

400

410

0 0.2 0.4 0.6 0.8 1

λ 1/2

/ nm

fanatase

Merck

CR-EL

Merck+CR-ELP25TIO-5

Aldrich(A<R)

Wako(A)+CR-EL

Wako(R)

Hombikat

CR-EL(1473 K)

P25 (1473 K)

TIO-2Wako(A)

370

380

390

400

410

0 0.2 0.4 0.6 0.8 1

λ 1/2

/ nm

fanatase

MerckP25

Wako(A)

Merck+CR-EL

Aldrich(A<R)TIO-5

CR-EL

Wako(R)Wako(A)+CR-EL

CR-EL(1473 K)P25 (1473 K)

TIO-2

360

370

380

390

400

410

0 0.2 0.4 0.6 0.8 1

λ 1/2

/ nm

fanatase

Wako(R)CR-EL

Hombikat

Merck

Wako(A)

Merck+CR-EL(1:1)Aldrich(A<R)

TIO-5

TIO-2

CR-EL(1473 K)P25 (1473 K)

P25

dehyderogenation of methanol

absorption edge wavelengthanatase: ca. 370 nmrutile: ca. 410 nm

R >> A

R ≈ A

A >> R

oxygen evolution & silver metal deposition

decomposition of acetic acid

inner-filter effectby rutileWhy?


activity decrease by high-temperature calcination

possible reasons:(1) higher activity of anatase

compared with that of rutile(2) decrease in specific surface

area

dehydrogenation of 2-propanol（↑）S.-i. Nishimoto, B. Ohtani, H. Kajiwara, T. Kagiya, J.

Chem. Soc., Faraday Trans. 1 1985, 81, 61. （←）S.-i. Nishimoto, B. Ohtani, A. Sakamoto, T. Kagiya,

Nippon Kagaku Kaishi 1984, 246 (in Japanese).

fromtitanium(IV) sulfate

from titanium(IV) tetra-2-propoxide

How are these distinguished?


Chem. Lett., 38(3), 238-239 (2009)

Correlation between structural and physical properties and photocatalytic activities for five kinds of reactions of 35 titaniasamples was obtained through multivariable analyses: photocatalytic activities were empirically reproduced by a linear combination of six properties with fair reliability. While a portion of results could be interpreted using a conventional mechanism, significant activity dependences on properties, not disclosed yet, were suggested.

Ohtani, B.; Prieto-Mahaney, O. O.; Amano, F.; Murakami, N.; Abe, R., J. Adv. Oxidat. Tech., 13, 247-261 (2010).

skip


statistical multivariable analyses

to find out WHAT is/are the DECISIVE factor(s) for each reaction

by solving the matrix equation below to determine coefficients of each physical and structural properties

[rate]35×1 = [property]35×6 × [coefficient]6×1

rates and properties, were standardized using mean of data and standard deviation in order to make the calculated coefficients have the same weight being independent of properties, i.e., enabling direct comparison of partial regression coefficients (k).


physical properties used for analysis

BET specific surface area by BET method

PPS primary particle size by Scherrer equation

SPS secondary particle size by particle analyzer

DEF density of defective sites by Ti(III) formation

ANA its presence/absence (OR anatase ratio)

RUT its presence/absence (OR rutile ratio)

Phys. Chem. Chem. Phys., 2003, 5, 778–783


anatase and rutile

anatase: relatively large for all the reactions except for (a)rutile: a little large only for (b)

(a) 4Ag+ + 2H2O = 4Ag + O2 + 4H+

(b) CH3OH = HCHO + H2(c) CH3COOH + 2O2 = 2CO2 + 2H2O(d) CH3CHO + 5/2O2 = 2CO2 + 2H2O(e) L-lysine = PCA + NH3


Degussa (Evonik) P25 (Nippon Aerosil)

AEROXIDE TiO2 P 25Titanium Dioxide P25 (AEROSIL Technical Report 5)Titanium Dioxide P 25 (AEROSIL Technical Report 21) Japan Reference Catalyst TIO-4(2) (Catalysis Society of Japan)

One of the most popular photocatalystsOne of the most active commercial photocatalystsA de-facto standard for photocatalysts

What we know... as bulk propertiesspecific surface area of ca. 50 m2 g-1 = ca. 30 nm particlescontains both anatase and rutile (and amorphous) with the ratio of 70:30 or 80:20


synergetic effect of anatase and rutile

Ohno et al., Appl. Catal. A: Gen. 244, 383-391 (2003).

no synergy

synergyfor oxidation of naphthalene to

dialdehyde


isolation of anatase and rutile from P25

anatasesuspended in a mixture of 30% hydrogen peroxide aq. and 25%ammonia aq. for 12 h at ambient temperatureOhtani, B.; Azuma, Y.; Li, D.; Ihara, T.; Abe, R. Trans. Mater. Res. Soc. Jpn. 32, 401-40 (2007).

rutilesuspended in 10% hydrofluoric acid for 24 h at ambient temperatureT. Ohno, K. Sarukawa, M. Matsumura, J. Phys. Chem. B, 105, 2417-2420 (2001).

amorphousno available methods for isolation


reconstruction of P25anatase:rutile:amorphous = 74:18:8

P-25

rutile

anatase

(Wako Pure Chemical)amorphous

fluffy/white

bulky/slightly yellow

fluffy/white


reconstructed sample

anatase:rutile:amorphous = 78:14:8Prepared only by shaking in a bottle, but not brayed

reconstructed sampleshows almost the same

specific surface areaXRD patterns

diffuse reflection spectra

with original P25


test reactions

A：oxidative decomposition of acetic acid (liquid phase/ aerated)

CH3COOH + 2O2 = 2CO2 + 2H2O

B： oxidative decomposition of acetaldehyde (gas phase/ aerated)

CH3CHO + 5/2O2 = 2CO2 + 2H2O

C：dehydrogenation of aqueous methanol (liquid phase/deaerated/platinized)

CH3OH = HCHO + H2

D：oxygen liberation and metal deposition from silver salt solution (liquid phase/deaerated)

4Ag+ + 2H2O = 4Ag + O2 + 4H+


photocatalytic activities of samplesA 78:14:8 mixture of particles shows the activity similar to that of P25.pure crystallites show better activities

= no synergy effect

normalizedto 100%

0

50

100

150

P25pure anatase pure rutilereconstructed mixture

CH3COOH(CO2)

CH3CHO(CO2)

CH3OH(H2) <Pt>

Ag+

(Ag/O2)

amorphous

91100

120 56

?!


hydrogen evolution from methanol

isolated anatase: Aisolated rutile: Rplatinization:

photodeposition (0.2 or 2wt% loading)

• negligible activity of all bare samples

• 0.2wt%-Pt loaded P25 ~ A + Pt/R (85:15)

• 2wt%-Pt loaded P25 ~ Pt/A + Pt/R (85:15)

comparable activity of Rwith A when platinized

photodeposition occurs preferentially on rutile particles

0

0.2

0.4

0.6

0.8

1

360 390 420

appa

rent

qua

ntum

effi

cien

cy

wavelength/nm

2wt%Pt/R

0.2wt%Pt/P25

2wt%Pt/P25

A + Pt/R(85:15)

A/Pt + Pt/R(85:15)

2wt%Pt/A

0

0.2

0.4

0.6

0.8

1

360 390 420

2wt%Pt/R

0.2wt%Pt/P25

2wt%Pt/P25

A + Pt/R(85:15)

A/Pt + Pt/R(85:15)

2wt%Pt/A

0

0.2

0.4

0.6

0.8

1

360 390 420

2wt%Pt/R

0.2wt%Pt/P25

2wt%Pt/P25

A + Pt/R(85:15)

A/Pt + Pt/R(85:15)

2wt%Pt/A


wavelength dependence100% anatase titania powders

dehydrogenation of methanol<platinum-loaded/under argon>

mineralization of acetic acid<under air>

CH3COOH + 2O2

→ 2CO2 + 2H2OCH3OH →

HCHO + H2

Why shifted?


action spectrum: case 2

wavelength/nm wavelength/nm

wavelength/nm

photoabsorptionefficiency

action spectrum

appa

rent

qua

ntum

effic

ienc

y

quantumefficiency

Change of (intrinsic) quantum efficiency, i.e., efficiency of electron-hole utilization depending on the irradiation wavelength

may induce

shift of action spectrum

skip

light-intensity dependence


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・・

pc20200709-57388301

pc20200709-57388301

pc20200709-57388301

Documents

環境触媒化学特論I 10pcat.cat.hokudai.ac.jp/class/pc2020/20200709_BO_Sapporo.pdf2020/07/09 · Advanced Course in Environmental Catalytic Reaction Chemistry I 4 format Please