SUPPORTING INFORMATION High-Temperature CO 2 Sorption on Hydrotalcite Having a High Mg/Al Molar Ratio Suji Kim, Sang Goo Jeon, and Ki Bong Lee*, Department of Chemical and Biological Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 136-713, Republic of Korea Climate Change Research Division, Korea Institute of Energy Research, 152 Gajeong-ro, Yuseong-gu, Daejeon 305-343, Republic of Korea *Corresponding author email address: kibonglee@korea.ac.kr S-1
EXPERIMENTAL SECTION Preparation of hydrotalcite In this study, magnesium nitrate hexahydrate (Mg(NO 3 ) 2 6H 2 O, 99%), aluminum nitrate nonahydrate (Al(NO 3 ) 2 9H 2 O, 98%), sodium carbonate (Na 2 CO 3, 99.5%), and sodium hydroxide (NaOH, 97%) were purchased from Sigma-Aldrich (USA) to synthesize hydrotalcites with high Mg/Al ratios using a co-precipitation method. 200 ml of a salt solution containing 0.005 x mol Mg(NO 3 ) 2 6H 2 O and 0.005 mol Al(NO 3 ) 3 9H 2 O (molar ratio of Mg:Al = x:1), and 50 ml of basic solution containing 0.0025 mol Na 2 CO 3 were added drop-wise to an empty beaker. The ph value of this mixture was maintained at 10 by addition of 1.5 M NaOH solution. The resulting mixture was aged at 60 C for 24 h with continuous stirring. The mixture was then filtered and washed with 100 ml distilled water using a vacuum filter, and dried at 110 C for 24 h. Finally, the resulting white powder was calcined at 500 C for 3 h under N 2 flow. Characterization of hydrotalcite The structure of the synthesized hydrotalcites was analyzed by X-ray diffraction (XRD). XRD patterns at room temperature were measured using a Rigaku X-ray diffractometer (Rigaku D/ Max-2500 V) with Cu Kα radiation (40 kv/40 ma). The scan range was from 5 to 70 (2θ) at a scanning rate of 4 min -1. Also, in-situ XRD spectra were recorded using a Rigaku X-ray diffractometer (Rigaku D/ Max-Ⅲ C) over the temperature range of 25 C to 500 C in a flow of N 2 or CO 2 gas. The Brunauer-Emmett-Teller (BET) surface area was estimated from the N 2 adsorption-desorption isotherm at 77 K measured using a volumetric sorption analyzer S-2
(ASAP2020, Micromeritics). Prior to N 2 adsorption, each sample was degassed under vacuum at 350 C for 12 h. Pore size and volume were calculated by the Barrett-Joyner-Halenda (BJH) method. CO 2 sorption measurement Thermogravimetric analysis (TGA, TA instruments, Q50) was used to measure CO 2 sorption on hydrotalcite. Before CO 2 sorption, a sample was pre-heated at 500 C for 3 h under a flow of N 2 to remove moisture and sorbed CO 2. Then, the weight change of the sample was recorded under a flow of pure CO 2 at a pressure of 1 atm and a temperature between 200 C and 330 C. S-3
Figure S1. Weight change of NaNO 3 with increasing temperature under a flow of (a) N 2 and (b) CO 2. NaNO 3 (sodium nitrate, 99.0 %) was purchased from Sigma-Aldrich (USA). S-4
Volume adsorbed (cm 3 g -1, STP) 500 400 300 200 (a) (b) (c) (d) (e) (f) 100 0 0.0 0.2 0.4 0.6 0.8 1.0 Relative pressure (P/P 0 ) Figure S2. N 2 adsorption (closed symbols) and desorption (open symbols) isotherms of hydrotalcite with a Mg/Al molar ratio in the feed of (a) 3, (b) 9, (c) 12, (d) 20, (e) 25, and (f) 30. S-5
dv/dlog(d) pore volume (cm 3 g -1 ) 2.0 1.6 1.2 0.8 0.4 (a) (b) (c) (d) (e) (f) 0.0 0 20 40 60 80 100 120 Pore diameter (nm) Figure S3. Pore size distribution of hydrotalcite with a Mg/Al molar ratio in the feed of (a) 3, (b) 9, (c) 12, (d) 20, (e) 25, and (f) 30. S-6
Figure S4. SEM images of hydrotalcite with a Mg/Al ratio in the feed of (a) 9, (b) 12, (c) 20, and (d) 30. S-7
Figure S5. XRD patterns of hydrotalcite with a Mg/Al molar ratio of 12, which was prepared (a) without additional washing, (b) with washing using 100 ml distilled water, and (c) with washing using 250 ml distilled water. : hydrotalcite, : Mg(OH) 2, : NaNO 3, : Na 2 CO 3. S-8
Figure S6. CO 2 sorption behavior at 240 C and 1 atm CO 2 for hydrotalcite with a Mg/Al molar ratio of 12, which was prepared (a) without additional washing, (b) with washing using 100 ml distilled water, and (c) with washing using 250 ml distilled water. S-9
Figure S7. Relation between the relative amount of NaNO 3 in hydrotalcite and CO 2 sorption uptake for 300 min at 240 C and 1 atm CO 2. (The relative amount of NaNO 3 was represented by the ratio of the NaNO 3 and hydrotalcite peak intensities at their characteristic XRD peak angles 2θ 29 and 11, respectively) S-10
Figure S8. Cyclic CO 2 sorption/desorption test for hydrotalcite having a Mg/Al molar ratio of 20. Sorption at 240 C for 4 h under a flow of CO 2 (1 atm) and desorption at 400 C for 1 h under a flow of N 2 (1 atm). S-11
Figure S9. CO 2 sorption equilibrium isotherm data for hydrotalcite having a Mg/Al molar ratio of 20. Sorption for 300 min at 240 C and 1 atm. S-12