Supporting Information. Experimental and Theoretical Investigation of Mesoporous MnO 2

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1 Supporting Information Experimental and Theoretical Investigation of Mesoporous MnO 2 Nanosheets with Oxygen Vacancy for High-Efficiency Catalytic DeNO x Jia Liu,, Yajuan Wei,,, Pei-Zhou Li,, Peipei Zhang, Wei Su, Yan Sun, Ruqiang Zou, * Yanli Zhao * Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore High Pressure Adsorption Laboratory, Department of Chemistry, School of Science, Tianjin University, Tianjin , PR China. School of Chemical Engineering and Technology, Tianjin Key Laboratory of Membrane and Desalination Technology, Tianjin University, Tianjin , People's Republic of China Beijing Key Lab of Theory and Technology for Advanced Battery Materials, Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing , China. These authors contributed equally to this work. zhaoyanli@ntu.edu.sg, rzou@pku.edu.cn Equipment: N 2 adsorption/desorption isotherms at 77 K were measured by surface area analyzer Micromeritics (ASAP 2020) for calculations of BET surface area and DFT pore size distribution. Pore volume was calculated from the adsorbed amounts at P/P o = Transmission electron microscopy (TEM) images and energy dispersive X-ray spectrometer (EDS) patterns were recorded on JEM 2100F (JEOL Ltd. Japan) for porous structure and component analysis. Powder X-ray diffraction (PXRD) patterns were recorded on a Rigaku D/max 2250VB/PC diffraction with CuKα radiation (λ = Å). X-Ray photoelectron spectroscopy (XPS) analysis was performed on ESCALAB 250 multi-technique X-ray photoelectron spectrometer (UK) using a monochromatic Al Kα X-ray source (hν = ev). UV-visible absorption spectra were measured in a transmission mode using a Shimadzu UV-VIS-NIR spectrophotometer. Raman scattering spectra were collected at room temperature with 20 s recording time. The samples were illuminated by a 532 nm He Ne laser on an Olympus BX 40 confocal microscope with a 20 objective. A laser power of 2 mw was S1

2 used. NH 3 -TPD was carried out on Micromeritics ChemiSorb Calculations. The DFT having the Perdew Burke Ernzerhof (PBE) functional was employed for the calculations. A Hubbard U term was added to the PBE functional (DFT+U), where only the difference (U eff = U-J) between the Coulomb U and exchange J parameters enters. The projector augmented wave method (PAW) was employed to describe the interaction between electrons and ions with the frozen-core approximation. The kinetic energy cut off was set to 400 ev. For Mn, a value of U eff = 4.5 ev was employed on its d orbital. The model was a periodic slab with a (2 2 3) surface unit cell. The vacuum gap was set to be 15 Å. The Mn atom and top atomic layers of the slab were allowed to relax, while other bottom layers were fixed to their bulk positions. The location and energy of transition states were calculated with the linear synchronous transit method. Component Analyzer Scheme S1. Schematic illustration for the denitrification system of SCR. MFC = mass flow controller. S2

3 (a) (b) (c) (d) Figure S1. (a) N 2 isotherms at 77 K. (b-d) Pore size distributions of MnO x synthesized from Mn(AC) 2 with different molar ratios of KMnO 4 to Mn(Ac) 2 The MnO 2 synthesized from Mn(Ac) 2 and KMnO 4 via the SIR method presents type IV isotherm curve (Figure S1) defined by IUPAC, indicating mesoporous structures. When the molar ratio of M 2+ /MnO 4 - is 1.5 that agrees with stoichiometric ratio of the reaction, the obtained sample (Mn-S-Ac-1.5) possesses the largest surface area about 339 m 2 /g. While the samples obtained under other conditions have relatively lower surface areas. When molar ratio of M 2+ /MnO - 4 is 1.8, the pore size of the obtained sample is obviously larger than that of others due to blocking effect of negative ions. When using MnCl 2 as raw material, the obtained samples also present type IV isotherm curve. The pore sizes of three samples under different molar ratios (M 2+ /MnO - 4 ) calculated from isotherm curves (Figure S2) center at 5 nm. Among these three samples, the largest surface area (334 m 3 /g) was observed on Mn-S-Cl-1.5. Compared with Mn(Ac) 2, the surface area of samples obtained from MnCl 2 is slightly lower due to different size of negative ions and different polarity. S3

4 When using MnNO 3 as a raw material, the obtained samples display obviously different isotherm curves (Figure S3). During the SIR process, MnNO 3 presents liquid state due to its low melt point (25 o C), which is hard to keep the SIR feature. The Mn 2+ ion surrounded by NO 3 - ions could migrate on the surface easily to form large crystals and recover surface defects. The large pore size observed on Mn-S-NO 3 is attributed to the stacking of particles. Figure S2. (a) N 2 isotherms at 77 K. (b-d) Pore size distributions of MnO x synthesized from MnCl 2 with different molar ratios of KMnO 4 to MnCl 2. S4

5 (a) (b) (c) (d) Figure S3. (a) N 2 isotherms at 77 K. (b-d) Pore size distributions of MnO x synthesized from Mn(NO 3 ) 2 with different molar ratios of KMnO 4 to Mn(NO 3 ) 2. Figure S4. Powder XRD patterns of pure KMnO 4 and Mn(Ac) 2 as well as their mixture after exposed in air for 24 h. S5

6 (a) (b) Figure S5. (a) N 2 isotherm curves at 77 K and (b) pore size distribution of MnO 2 synthesized via the precipitation method from Mn(Ac) 2. (a) (b) 1µm 1µm Figure S6 Global morphology (SEM images) of (a) layered MnO 2 Mn-S-AC-1.5 and (b) amorphous MnO 2 Mn-P-Ac. S6

7 Figure S7. EDS spectrum of Mn-S-Ac-1.5. Figure S8. Powder XRD patterns of Mn-P-Ac. S7

8 Figure S9. Full scan XPS pattern of Mn-S-Ac-1.5. Figure S10. NH 3 TPD profile of Mn-S-Ac-1.5. S8

9 Figure S11. Configuration of NH 3 adsorption on (a) Lewis acid site and (b) Brønsted acid site of α-mno 2 (001) surface. Table S1 Comparison of catalytic activity with literature reports. S BET m 2 g -1 NO Conversion % GHSV Mn-S-AC , This work Mn(0.25)/TNT-H , MnCe(0.3)O x , MnCe/TiO , MnCe/Al 2 O , α-mno 2 nanorode , β-mno 2 nanoparticle , β-mn 4 Ce 6 (ST) , MnO x /CeO 2 (DP) , MnO x (RP-350) , Ce(0.2)MnTi , Mn-Ce/Ti-CNT , MnFe(0.15) , Co Mn O , nf-mnox@cnts , FeMnTiOx , h -1 T o C Refs S9

10 References (1) Pappas, D. K.; Boningari, T.; Boolchand, P.; Smirniotis, P. G. Novel Manganese Oxide Confined Interweaved Titania Nanotubes for the Low-Temperature Selective Catalytic Reduction (SCR) of NO x by NH 3. J. Catal. 2016, 334, (2) Wei, Y.; Liu, J.; Su, W.; Sun, Y.; Zhao, Y. Controllable Synthesis of Ce-Doped α-mno 2 for Low-Temperature Selective Catalytic Reduction of NO. Catal. Sci. Technol. 2017, 7, (3) Jin, R.; Liu, Y.; Wu, Z.; Wang, H.; Gu, T. Low-Temperature Selective Catalytic Reduction of NO with NH 3 over Mn-Ce Oxides Supported on TiO 2 and Al 2 O 3 : A Comparative Study. Chemosphere 2010, 78, (4) Tian, W.; Yang, H.; Fan, X.; Zhang, X. Catalytic Reduction of NO x with NH 3 over Different-Shaped MnO 2 at Low Temperature. J. Hazard. Mater. 2011, 188, (5) Liu, Z.; Yi, Y.; Zhang, S.; Zhu, T.; Zhu, J.; Wang, J. Selective Catalytic Reduction of NO x with NH 3 over Mn-Ce Mixed Oxide Catalyst at Low Temperatures. Catal. Today 2013, 216, (6) Xu, L.; Li, X.-S.; Crocker, M.; Zhang, Z.-S.; Zhu, A.-M.; Shi, C. A Study of the Mechanism of Low-Temperature SCR of NO with NH 3 on MnOx/CeO 2. J. Mol. Catal. A 2013, 378, (7) Tang, X.; Hao, J.; Xu, W.; Li, J. Low Temperature Selective Catalytic Reduction of NO x with NH 3 over Amorphous MnO x Catalysts Prepared by Three Methods. Catal. Commun. 2007, 8, (8) Wu, Z.; Jin, R.; Liu, Y.; Wang, H. Ceria Modified MnO x /TiO 2 as a Superior Catalyst for NO Reduction with NH 3 at Low-Temperature. Catal. Commun. 2008, 9, (9) Fan, X.; Qiu, F.; Yang, H.; Tian, W.; Hou, T.; Zhang, X. Selective Catalytic Reduction of NO X with Ammonia over Mn Ce O X /TiO 2 -Carbon Nanotube Composites. Catal. Commun. 2011, 12, (10) Zhan, S.; Qiu, M.; Yang, S.; Zhu, D.; Yu, H.; Li, Y. Facile Preparation of MnO 2 Doped Fe 2 O 3 Hollow Nanofibers for Low Temperature SCR of NO with NH 3. J. Mater. Chem. A 2014, 2, (11) Meng, B.; Zhao, Z.; Chen, Y.; Wang, X.; Li, Y.; Qiu, J. Low-Temperature Synthesis of Mn-Based Mixed Metal Oxides with Novel Fluffy Structures as Efficient Catalysts for Selective Reduction of Nitrogen Oxides by Ammonia. Chem. Commun. 2014, 50, (12) Fang, C.; Zhang, D.; Cai, S.; Zhang, L.; Huang, L.; Li, H.; Maitarad, P.; Shi, L.; Gao, R.; Zhang, J. Low-Temperature Selective Catalytic Reduction of NO with NH 3 over Nanoflaky MnO x on Carbon Nanotubes in Situ Prepared via a Chemical Bath Deposition Route. Nanoscale 2013, 5, (13) Liu, F.; He, H.; Ding, Y.; Zhang, C. Effect of Manganese Substitution on the Structure and Activity of Iron Titanate Catalyst for the Selective Catalytic Reduction of NO with NH 3. Appl. Catal. B 2009, 93, S10