Supporting Information MgFeCe ternary layered double hydroxide as highly efficient and recyclable heterogeneous base catalyst for synthesis of dimethyl carbonate by transesterification Nayana T. Nivangune a, Vivek V. Ranade b*, Ashutosh A. Kelkar a* a Chemical Engineering and Process Development (CEPD) Division, National Chemical Laboratory, Pune 411008, India. b School of Chemistry and Chemical Engineering, Queen's University Belfast, Belfast BT9 5AG, Northern Ireland, UK. Corresponding Author: a* E-mail: aa.kelkar@ncl.res.in b* E-mail:V.Ranade@qub.ac.uk S1
Materials: Ethylene carbonate (99%), benzoic acid (99.5%), Ce(NO 3 ) 3.6H 2 O (99%) were purchased from Sigma-Aldrich Co. Chemical reagents including Ethylene glycol (99%), DMC (99.5%), Mg(NO 3 ) 2.6H 2 O (99.5%), NaOH (99.5%), Na 2 CO 3 (99.5%), phenolphthalein, bromothymol blue, were obtained from Loba Chemical Co., India. KBR IR grade (99.8%), IPA (99.5%), methanol (99.8%), Fe (NO 3 ) 3.9H 2 O (98%), toluene (99.8%) were purchased from Merck Co. Table S1. Composition of Ce incorporated LDHs prepared based on ICP analysis. Sample ICP analysis Theoretical Measured LDH-1 Mg 3 Fe 1 2.98:1 LDH-2 Mg 3 Fe 0.95 Ce 0.05 3:0.92:0.04 LDH-3 Mg 3 Fe 0.85 Ce 0.15 2.97:0.83:0.13 LDH-4 Mg 3 Fe 0.75 Ce 0.25 2.9:0.73:0.23 LDH-5 Mg 3 Fe 0.55 Ce 0.45 3:0.53:0.44 LDH-6 Mg 3 Ce 1 3:0.97 From ICP analysis; metal composition of all LDH samples prepared (Measured) was found to be in good agreement with the values expected based on compositions used for the preparation (Theoretical). S2
Synthesis of ternary Mg 3 :Fe 0.85 +M 0.15 LDH : (where M III = La, Sm, Y and Cr) In typical procedure solution A was prepared by dissolving desired amount of Mg(NO3) 2.6H 2 O, Fe(NO 3 ) 3.9H 2 O and M(NO 3 ) 3.xH 2 O in deionized water and solution B was prepared by dissolving NaOH and Na 2 CO 3 (2 M) in deionized water. Solutions A and B were added simultaneously while ph of the resultant solution was maintained at 10-11 with constant stirring at room temperature. The gel obtained was hydrothermally treated at 90 0 C for 15 h. Then the precipitate was filtered, washed several times with deionized water till filtrate became neutral. Finally, the synthesized ternary LDHs were dried at 100 0 C for 12 h in air. LDHs prepared with different M III (M III = La, Sm, Y and Cr) were named as Mg 3 Fe 0.85 La 0.15, Mg 3 Fe 0.85 Sm 0.15, Mg 3 Fe 0.85 Y 0.15 and Mg 3 Fe 0.85 Cr 0.15 respectively. Figure S1: XRD patterns of Mg 3 :Fe 0.85 +M 0.15 ternary LDHs with different M III cations. All synthesized LDHs showed typical X-ray diffractions pattern of LDHs materials. S3
Experimental procedure for transesterification of ethylene carbonate and methanol using synthesized Mg 3 :Fe 0.85 +M 0.15 LDHs as catalysts: The transesterification of ethylene carbonate and methanol over the LDHs prepared was performed in a 50 ml jacketed glass reactor equipped with magnetic stirrer and reflux condenser. Typically, the reactor was charged with 2 gm (23 mmol) of ethylene carbonate, 7.3 gm (230 mmol) of methanol and 0.05gm of LDH catalyst (2.5 wt% relative to EC). The reaction was carried out at 70 o C for 3 h reaction time under vigorous stirring. After 3 h of the reaction, the glass reactor was cooled to room temperature; and sample was analyzed by gas chromatography to monitor the progress of the reaction. Experimental procedure for recycle of the catalyst Mg 3 Fe 0.85 Ce 0.15 (LDH-3): Transesterification of EC and DMC was carried out as per the procedure described earlier. The catalyst from the reaction mixture was recovered by centrifugation, washed with methanol, and then dried overnight at 373 K for 12 h in air. The recovered catalyst was used to perform a new reaction of transesterification by charging EC and methanol to the glass reactor. Catalyst was recycled seven times using the same procedure and the results are presented in Figure 9. Stability of the LDH-3 catalyst (leaching test): Leaching of the LDH-3 into the reaction mixture was studied during the course of the reaction. Reaction was carried out under selected reaction conditions (EC: MeOH 1:10, 70 o C for 30 min). After 30 min reaction was stopped and catalyst was separated by filtration of hot reaction mixture (~70 o C). The filtered reaction mixture was charged to the glass reactor and reaction was continued for next 1-3h under same reaction conditions. The results are shown in the Figure S7. S4
XPS analysis of Ce 3d and O 1s of all synthesized Mg 3 Fe x Ce 1-x LDHs: XPS spectra of the Ce 3d core level can be resolved into 10 groups. The five main 3d5/2 features are denoted as components v o (881.7 ev), v (882.9 ev), v (885.7 ev), v (889.0 ev), and v''' (897.6 ev), and the five 3d3/2 features are assigned as u o (899.1 ev), u (901.2 ev), u (903.0 ev), u (907.7 ev), and u''' (916.8 ev), respectively [1]. The % amount of surface Ce 4+ and Ce 3+ ion can be determined by using the following equation. Ce (III) = v o + v' + u o + u' Ce (IV) = v + v''+ v''' + u + u''+ u'' Where, the notations Ce (III) and Ce (IV) represent the corresponding sums of the integrated peak areas related to the Ce 3+ and Ce 4+ XPS signals respectively. Figure S2: XPS Ce 3d spectra of synthesized Mg 3 Fe x Ce 1-x LDHs where Ce 3+ and Ce 4+ contributions are dominant are highlighted with dotted line. S5
Figure S3: XPS O1s spectra of all synthesized Mg 3 Fe x Ce 1-x LDHs, peaks correspond to oxygen bonded carbon species (O β ) is 530.6 ev and oxygen in hydroxide form is 532.3 ev (O α ). S6
Table S3. Surface composition and relative atomic ratio for the synthesized LDHs determined from XPS measurements. Sample % Ce 3+ Ce 4+ O α O β Ce 3+ : Ce 4+ O α : O β LDH-1 nd nd 78.3 21.6 nd 3.6 LDH-2 49.5 50.4 86.9 13 0.98 6.6 LDH-3 47.2 52.7 87.2 12.7 0. 9 6.8 LDH-4 39.7 60.2 85.2 14.3 0.7 5.9 LDH-5 33.2 66.7 84.7 15.3 0.5 5.5 LDH-6 30.9 69.1 81.6 18.4 0.4 4.4 nd : not detected S7
The effect of EC:MeOH molar ratio, reaction temperature and catalyst loading was investigated in detail for transesterification of EC and methanol. All the experiments in this study were carried out with sampling in a time range of 1-5 h. conversion/selectivity Vs time profiles obtained under various reaction conditions are presented below. Effect of EC: MeOH molar ratio : Figure S4: Effect of molar ratio on EC conversion (A) and DMC selectivity (B) Reaction conditions: EC: MeOH: 1:5-1:20, catalyst: 2.5 wt % relative to EC, reaction time: 1-5 h, temperature: 70 C. S8
Effect of reaction temperature: Figure S5: Effect of reaction temperature on EC conversion (A) and DMC selectivity (B) Reaction conditions: EC: MeOH molar ratio: 1:10, catalyst: 2.5 wt % relative to EC, reaction time: 1-5 h, temperature: 30-70 C. S9
Effect of catalyst loading: Figure S6: EC conversion and DMC selectivity profile at catalyst loading of 0.6-5 wt%. Reaction conditions: EC: MeOH molar ratio: 1:10, reaction time: 1-5 h, temperature: 70 C. S10
Stability of the LDH-3 catalyst (leaching test): Figure 7: Catalyst leaching test by hot filtration of reaction mixture for the transesterification of ethylene carbonate with methanol. Reaction conditions: EC: MeOH molar ratio: 1:10, catalyst: 2.5 wt % relative to EC, reaction time: 30-180 min, temperature: 70 C. S11
XRD pattern of fresh and used LDH-3 (after 7 th recycle experiments): Figure 8: XRD patterns of fresh and used Mg 3 :Fe 0.85 Ce 0.15 (LDH-3). References: 1. Hu Z, Liu X, Meng D, Guo Y, Guo Y, Lu G (2016) ACS Catalysis 6:2265 S12