Abstract
Manganese oxides occur naturally as minerals in at least 30 different crystal structures, providing a rigorous test system to explore the significance of atomic positions on the catalytic efficiency of water oxidation. In this study, we chose to systematically compare eight synthetic oxide structures containing Mn(III) and Mn(IV) only, with particular emphasis on the five known structural polymorphs of MnO2. We have adapted literature synthesis methods to obtain pure polymorphs and validated their homogeneity and crystallinity by powder X-ray diffraction and both transmission and scanning electron microscopies. Measurement of water oxidation rate by oxygen evolution in aqueous solution was conducted with dispersed nanoparticulate manganese oxides and a standard ruthenium dye photo-oxidant system. No Ru was absorbed on the catalyst surface as observed by XPS and EDX. The post reaction atomic structure was completely preserved with no amorphization, as observed by HRTEM. Catalytic activities, normalized to surface area (BET), decrease in the series Mn2O3 > Mn3O4 ≪ λ-MnO2, where the latter is derived from spinel LiMn 2O4 following partial Li+ removal. No catalytic activity is observed from LiMn2O4 and four of the MnO2 polymorphs, in contrast to some literature reports with polydispersed manganese oxides and electro-deposited films. Catalytic activity within the eight examined Mn oxides was found exclusively for (distorted) cubic phases, Mn2O3 (bixbyite), Mn3O4 (hausmannite), and λ-MnO2 (spinel), all containing Mn(III) possessing longer Mn-O bonds between edge-sharing MnO6 octahedra. Electronically degenerate Mn(III) has antibonding electronic configuration eg 1 which imparts lattice distortions due to the Jahn-Teller effect that are hypothesized to contribute to structural flexibility important for catalytic turnover in water oxidation at the surface.
| Original language | English |
|---|---|
| Pages (from-to) | 3494-3501 |
| Number of pages | 8 |
| Journal | Journal of the American Chemical Society |
| Volume | 135 |
| Issue number | 9 |
| DOIs | |
| Publication status | Published - Mar 6 2013 |
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ASJC Scopus subject areas
- Chemistry(all)
- Catalysis
- Biochemistry
- Colloid and Surface Chemistry
Cite this
Photochemical water oxidation by crystalline polymorphs of manganese oxides : Structural requirements for catalysis. / Robinson, David M.; Go, Yong Bok; Mui, Michelle; Gardner, Graeme; Zhang, Zhijuan; Mastrogiovanni, Daniel; Garfunkel, Eric; Li, Jing; Greenblatt, Martha; Dismukes, G Charles.
In: Journal of the American Chemical Society, Vol. 135, No. 9, 06.03.2013, p. 3494-3501.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Photochemical water oxidation by crystalline polymorphs of manganese oxides
T2 - Structural requirements for catalysis
AU - Robinson, David M.
AU - Go, Yong Bok
AU - Mui, Michelle
AU - Gardner, Graeme
AU - Zhang, Zhijuan
AU - Mastrogiovanni, Daniel
AU - Garfunkel, Eric
AU - Li, Jing
AU - Greenblatt, Martha
AU - Dismukes, G Charles
PY - 2013/3/6
Y1 - 2013/3/6
N2 - Manganese oxides occur naturally as minerals in at least 30 different crystal structures, providing a rigorous test system to explore the significance of atomic positions on the catalytic efficiency of water oxidation. In this study, we chose to systematically compare eight synthetic oxide structures containing Mn(III) and Mn(IV) only, with particular emphasis on the five known structural polymorphs of MnO2. We have adapted literature synthesis methods to obtain pure polymorphs and validated their homogeneity and crystallinity by powder X-ray diffraction and both transmission and scanning electron microscopies. Measurement of water oxidation rate by oxygen evolution in aqueous solution was conducted with dispersed nanoparticulate manganese oxides and a standard ruthenium dye photo-oxidant system. No Ru was absorbed on the catalyst surface as observed by XPS and EDX. The post reaction atomic structure was completely preserved with no amorphization, as observed by HRTEM. Catalytic activities, normalized to surface area (BET), decrease in the series Mn2O3 > Mn3O4 ≪ λ-MnO2, where the latter is derived from spinel LiMn 2O4 following partial Li+ removal. No catalytic activity is observed from LiMn2O4 and four of the MnO2 polymorphs, in contrast to some literature reports with polydispersed manganese oxides and electro-deposited films. Catalytic activity within the eight examined Mn oxides was found exclusively for (distorted) cubic phases, Mn2O3 (bixbyite), Mn3O4 (hausmannite), and λ-MnO2 (spinel), all containing Mn(III) possessing longer Mn-O bonds between edge-sharing MnO6 octahedra. Electronically degenerate Mn(III) has antibonding electronic configuration eg 1 which imparts lattice distortions due to the Jahn-Teller effect that are hypothesized to contribute to structural flexibility important for catalytic turnover in water oxidation at the surface.
AB - Manganese oxides occur naturally as minerals in at least 30 different crystal structures, providing a rigorous test system to explore the significance of atomic positions on the catalytic efficiency of water oxidation. In this study, we chose to systematically compare eight synthetic oxide structures containing Mn(III) and Mn(IV) only, with particular emphasis on the five known structural polymorphs of MnO2. We have adapted literature synthesis methods to obtain pure polymorphs and validated their homogeneity and crystallinity by powder X-ray diffraction and both transmission and scanning electron microscopies. Measurement of water oxidation rate by oxygen evolution in aqueous solution was conducted with dispersed nanoparticulate manganese oxides and a standard ruthenium dye photo-oxidant system. No Ru was absorbed on the catalyst surface as observed by XPS and EDX. The post reaction atomic structure was completely preserved with no amorphization, as observed by HRTEM. Catalytic activities, normalized to surface area (BET), decrease in the series Mn2O3 > Mn3O4 ≪ λ-MnO2, where the latter is derived from spinel LiMn 2O4 following partial Li+ removal. No catalytic activity is observed from LiMn2O4 and four of the MnO2 polymorphs, in contrast to some literature reports with polydispersed manganese oxides and electro-deposited films. Catalytic activity within the eight examined Mn oxides was found exclusively for (distorted) cubic phases, Mn2O3 (bixbyite), Mn3O4 (hausmannite), and λ-MnO2 (spinel), all containing Mn(III) possessing longer Mn-O bonds between edge-sharing MnO6 octahedra. Electronically degenerate Mn(III) has antibonding electronic configuration eg 1 which imparts lattice distortions due to the Jahn-Teller effect that are hypothesized to contribute to structural flexibility important for catalytic turnover in water oxidation at the surface.
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U2 - 10.1021/ja310286h
DO - 10.1021/ja310286h
M3 - Article
VL - 135
SP - 3494
EP - 3501
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 9
ER -