SUPPORTING INFORMATION Mechanism and Kinetics of CO 2 Adsorption on Surface Bonded Amines Maximilian W. Hahn, Matthias Steib, Andreas Jentys*, Johannes A. Lercher* Department of Chemistry, Catalysis Research Center Technische Universität München Lichtenbergstraße 4, 85747 Garching, Germany Experimental Elemental Analysis. The C, H and N content of SBA-15 impregnated with MEA, DEA, DETA, TEPA and PEI were determined by a EURO EA elemental analyzer. Approximately 2 mg of each sample were weight in a tin beaker for each sample. The samples are burned at 1000 C in a stream of He. After the reduction of NO x compounds the gas stream was separated with a GC column. The products (CO 2, NO 2, H 2 O) were analyzed with a thermal conductivity detector. Synthesis of SBA-15. 6 g of hydrochloric acid (Sigma Aldrich, 37 wt.%) were added to 188.5 g of DI water and 10.25 g of the surfactant P123 (BASF, M w of 5750 ) under rigid stirring. The solution was stirred for 1 day at 35 C until a homogenous phase was obtained. Tetraethylorthosilicate (TEOS, Sigma Aldrich, purity 99 %) was added to the solution and the mixture was kept stirring at 35 C for additional 24 h. The polymerized solution was aged in autoclaves at 80 C for 24 h. The solution was filtered with deionized (DI) water for 3 times and the precipitate was dried at 60 C for 5 h prior to calcination in synthetic air (8 h at 600 C, heating rate: 2.5 C/min, total flow rate: 100 ml min -1 ). S1
Physicochemical Properties Figure S1. N 2 physisorption isotherms and pore size distribution (BJH method) of (a,b) SBA-15, (c,d) DETA 9, (e,f) DETA 23, (g,h) TEPA 9, (i,j) TEPA 23, (k,l) PEI 5, (m,n) PEI 18. Filled and empty symbols represent the adsorption and desorption branch, respectively. S2
Activation of the sorbents. The changes in the chemical composition of DETA 23 before and after activation at 100 C and 10-2 mbar for 2 h are shown in Table S1. DETA impregnated SBA-15 with an amine loading of 23 wt.% was used, because the amine exhibits a boiling point of 200 C and the highest vapor pressure (50 Pa) of all employed amines. The vapor pressure of TEPA and PEI are both significantly lower and therefore these molecules are less likely to desorb during the thermal activation in vacuum. The concentration of C and H decreased significantly, (15 % for C and 11 % for H) because chemisorbed CO 2 and physisorbed H 2 O were removed during activation. In contrast, the concentration of N was not affected (within the limits of accuracy ± 5 %) confirming that the loss of amines in the activation step prior to N 2 physisorption can be neglected. Table S1. C, H, N analysis before and after activation of DETA 23 at 100 C for 2 h at 10-2 mbar. C H N [mmol g -1 ] [mmol g -1 ] [mmol g -1 ] DETA 23 no activation 9.7 41.3 6.5 DETA 23 activated 8.6 35.1 6.3 S3
Infrared Spectroscopy Table S1 Overview of relevant IR bands of amine functionalized SiO 2 supports. Wavenumber [cm -1 ] Assignment References >3750 OH stretching vibration of free silanol groups (support) 3700-3000 OH stretching of hydrogen bonded OH groups (H 2 O) 3650-3630 OH stretching of hydrogen bonded OH groups (support) 3370-3360 Asymmetric NH 2 -stretching vibration of primary amines 3330-3300 Symmetric NH 2 stretching vibration of primary amines NH stretching vibration of secondary amines 3090-3010 CH stretching vibration in aromatics 2930-2850 CH 2 stretching vibration 2820-2760 NCH 3 stretching vibration 1680-1600 Deformation of primary (NH 2 ) and secondary amines (NH) (primary amines show broad band, sharp band for secondary) 1470-1440 CH 2 bending 1440-1410 CN stretching 1-3 1, 4 1, 5-6 5, 7-8 5-7, 9 10-11 5-6, 9 12 1, 5-8 1, 6, 9, 13 6, 9, 13-14 Table S2. Overview of relevant IR bands for the adsorption of CO 2 on amine functionalized SiO 2 supports. Wavenumber [cm -1 ] Assignment References 3615, 3715 Combination bands of gas phase CO 2 3440-3420 NH stretching vibration (carbamates, carbamic acid) 3000 Stretching vibration of COOH (carbamic acid, broad peak) 2345 Gas phase CO 2 Asymmetric stretching of linearly physisorbed CO 2 1720-1670 CO stretching vibration (carbamic acid) 1660-1620 Asymmetric NH 3 + / NH 2 + deformation 1565-1550 Asymmetric COO - stretching vibration (carbamate) 1490-1480 Symmetric NH 3 + / NH 2 + deformation 1430-1400 Symmetric COO - stretching (carbamate) 1380 OH deformation (carbamic acid) 1330-1300 NCOO skeletal vibration 6, 15 1, 8, 16 10, 17 8, 18 1, 5, 19-20 2, 6, 10 1, 3, 8, 16 6, 8, 10 6, 8, 10 1, 19-20 3, 5, 16 S4
Figure S2. Absolute IR spectra of (I) DETA 9 and (II) DETA 23, (III) TEPA 9 and (IV) TEPA 23, (V) PEI 5 and (VI) PEI 18 at 50 C and CO 2 partial pressure of (a) 0 mbar and (b) 10 mbar. Figure S3. Integrated equilibrium IR peak areas (1750 1350 cm -1 ) of (a) DETA 9, (b) DETA 23, (c) TEPA 9, (d) TEPA 23, (e) PEI 5, (f) PEI 18 at CO 2 partial pressures between 0.05 mbar and 10 mbar. Resonances at ( ) 1670 cm - 1, ( ) 1630 cm -1, ( ) 1563 cm -1, ( ) 1490 cm -1, (x) 1430 cm -1 and (+) 1415 cm -1. S5
Figure S4. Difference IR spectra (3500 2950 cm -1 ) taken every 120 sec in a pressure range of 0.05 mbar 10 mbar: 0.05 mbar (orange line), 0.5 mbar (blue line), 1.0 mbar (green line) and 10 mbar (red line). (a) DETA 9 (I) and DETA 23 (II), (b) TEPA 9 (III) and TEPA 23 (IV), (c) PEI 5 (V) and PEI 18 (VI). Figure S5. Integrated equilibrium IR peak areas (3440 3300 cm -1 ) of (a) DETA 9, (b) DETA 23, (c) TEPA 9, (d) TEPA 23, (e) PEI 5, (f) PEI 18 at CO 2 partial pressures between 0.05 mbar and 10 mbar. Resonances at ( ) 3440 cm -1, ( ) 3365 cm -1 and ( ) 3300 cm -1. S6
Figure S6 Desorption species monitored by mass spectrometry during activation (30-100 C) at 10-6 mbar for (a) DETA 23 and (b) TEPA 23. Figure S7. Time resolved IR peak areas of (a) DETA 9, (b) DETA 23, (c) TEPA 9, (d) TEPA 23, (e) PEI 5, (f) PEI 18. CO 2 partial pressures of (I) 0.05 mbar, (II) 0.5 mbar, (III) 1 mbar and (IV) 10 mbar. Resonances at 1670 cm -1 ( ), 1630 cm -1 ( ), 1563 cm -1 ( ), 1490 cm -1 ( ), 1430 cm -1 (x) and 1415 cm -1 (+). S7
Supporting References (1.) Knöfel, C.; Martin, C.; Hornebecq, V.; Llewellyn, P. L., Study of Carbon Dioxide Adsorption on Mesoporous Aminopropylsilane-Functionalized Silica and Titania Combining Microcalorimetry and in Situ Infrared Spectroscopy. J Phys Chem C 2009, 113, 21726-21734. (2.) Hiyoshi, N.; Yogo, K.; Yashima, T., Adsorption Characteristics of Carbon Dioxide on Organically Functionalized SBA-15. Micropor Mesopor Mat 2005, 84, 357-365. (3.) Huang, H. Y.; Yang, R. T.; Chinn, D.; Munson, C. L., Amine-Grafted MCM-48 and Silica Xerogel as Superior Sorbents for Acidic Gas Removal From Natural Gas. Ind Eng Chem Res 2003, 42, 2427-2433. (4.) Tanaka, K.; White, J. M., Characterization of Species Adsorbed on Oxidized and Reduced Anatase. J Phys Chem-Us 1982, 86, 4708-4714. (5.) Tanthana, J.; Chuang, S. S. C., In Situ Infrared Study of the Role of PEG in Stabilizing Silica-Supported Amines for CO 2 Capture. Chemsuschem 2010, 3, 957-964. (6.) Danon, A.; Stair, P. C.; Weitz, E., FTIR Study of CO 2 Adsorption on Amine-Grafted SBA-15: Elucidation of Adsorbed Species. J Phys Chem C 2011, 115, 11540-11549. (7.) Sayari, A.; Heydari-Gorji, A.; Yang, Y., CO 2 -Induced Degradation of Amine-Containing Adsorbents: Reaction Products and Pathways. J Am Chem Soc 2012, 134, 13834-13842. (8.) Bacsik, Z.; Ahlsten, N.; Ziadi, A.; Zhao, G. Y.; Garcia-Bennett, A. E.; Martin-Matute, B.; Hedin, N., Mechanisms and Kinetics for Sorption of CO 2 on Bicontinuous Mesoporous Silica Modified with n-propylamine. Langmuir 2011, 27, 11118-11128. (9.) Srikanth, C. S.; Chuang, S. S. C., Spectroscopic Investigation into Oxidative Degradation of Silica- Supported Amine Sorbents for CO 2 Capture. Chemsuschem 2012, 5, 1435-1442. (10.) Colthup, N. B.; Daly, L. H.; Wiberly, S. E., Introduction to Infrared and Raman Spectroscopy; Academic press: San Diego, 1990; Vol. Third Edition. (11.) Akalin, E.; Akyüz, S., Force Field and IR Intensity Calculations of Aniline and Transition Metal (II) Aniline Complexes. J Mol Struct 1999, 482, 175-181. (12.) Schwetlick, K., Organikum; Wiley VCH: Weinheim, 2009; Vol. 23. (13.) Socrates, G., Infrared and Raman Characteristic Group Frequencies: Tables and Charts; Wiley: Chichester, New York, 2001; Vol. 3rd Edition. (14.) Langer, J.; Schrader, B.; Bastian, V.; Jacob, E., Infrared-Spectra and Force-Constants of Urea in the Gaseous-Phase. Fresen J Anal Chem 1995, 352, 489-495. (15.) Herzberg, G., Infrared and Raman spectra; Van Nostrand: New York, 1945. (16.) Wang, X. X.; Schwartz, V.; Clark, J. C.; Ma, X. L.; Overbury, S. H.; Xu, X. C.; Song, C. S., Infrared Study of CO 2 Sorption over "Molecular Basket" Sorbent Consisting of Polyethylenimine-Modified Mesoporous Molecular Sieve. J Phys Chem C 2009, 113, 7260-7268. (17.) Khanna, R.; Moore, M., Carbamic Acid: Molecular Structure and IR Spectra. Spectrochim Acta Mol Biomol Spectros 1999, 55, 961-967. (18.) Cheng, Z. H.; Yasukawa, A.; Kandori, K.; Ishikawa, T., FTIR Study of Adsorption of CO 2 on Nonstoichiometric Calcium Hydroxyapatite. Langmuir 1998, 14, 6681-6686. (19.) Bossa, J. B.; Theule, P.; Duvernay, F.; Borget, F.; Chiavassa, T., Carbamic Acid and Carbamate Formation in NH 3 :CO 2 ices-uv Irradiation Versus Thermal Processes. Astron Astrophys 2008, 492, 719-724. (20.) Bossa, J. B.; Borget, F.; Duvernay, F.; Theule, P.; Chiavassa, T., Formation of Neutral Methylcarbamic Acid (CH 3 NHCOOH) and Methylammonium Methylcarbamate [CH 3 NH 3 + ][CH 3 NHCO 2 - ] at Low Temperature. J Phys Chem A 2008, 112, 5113-5120. S8