Novel Covalent Triazine Framework for High ... - ACS Publications

Subscriber access provided by READING UNIV

Functional Nanostructured Materials (including low-D carbon)

Novel Covalent Triazine Framework for High Performance CO2 Capture and Alkyne Carboxylation Reaction Qin-Qin Dang, Chun-Yan Liu, Xiao-Min Wang, and Xian-Ming Zhang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b08964 • Publication Date (Web): 24 Jul 2018 Downloaded from http://pubs.acs.org on July 25, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Novel Covalent Triazine Framework for High Performance CO2 Capture and Alkyne Carboxylation Reaction Qin-Qin Dang,*,† Chun-Yan Liu,† Xiao-Min Wang,†‡ and Xian-Ming Zhang,*,† †School of Chemistry & Material Science, Shanxi Normal University, Linfen, Shanxi 041004, China ‡ The inspection and quarantine technology center of Inner Mongolia Entry-exit inspection and quarantine bureau, Hohhot, 010020 KEYWORDS: Triazine, Framework, CO2 Capture, Silver, Alkyne Carboxylation.

ABSTRACT: Carbon dioxide capture and conversion have attracted extreme enthusiasm from the scientific community owing to global warming and environmental problems. However, conversion of CO2 under atomospheric pressure is of great challenge due to the inertness of CO2.Herein, we present a novel covalent triazine framework (CTF-DCE) prepared via ZnCl2 catalyzed ionothermal trimerization reaction of di(4-cyanophenyl)ethyne, which displays high BET surface area of 1355 m2g-1 and excellent CO2 capture capacity of 191 mg/g at 273K/1 bar. More important, silver species can be successfully fixed on CTF matrix to produce a stable CTF-DCE-Ag heterogenerous catalyst for outstanding catalysis in the terminal alkynes carboxylation reactions under atomospheric pressure. CTF-DCE-Ag exhibited over six-folds higher TONs than Ag@MIL-101. The recyclability test of CTF-DCE-Ag catalyst demonstrated a great potential application in various environmental and energy related applications.

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 20

1. INTRODUCTION Recently, carbon dioxide (CO2) capture and conversion have attracted extreme enthusiasm from the scientific community owing to global warming and a sequence of environmental problems1-4. While CO2 has been frequently utilized as a green and renewable C1 building block in the synthesis of many useful organic compounds due to its low cost, availability and nontoxicity, the transformation of CO2 usually suffer from inefficiency and limited chemical conversions which are attributed to the inherent thermodynamic stability of the inert CO25-7. Thus the exploration of a suitable driving force that can activate the inert CO2 has becoming a key solution to this challenge. To this end, significant progress has been achieved based on organometallic chemistry, and various types of homogeneous or heterogeneous catalysts were employed in CO2 transformation process8-10. In most cases, utilization of expensive phosphine or nitrogen-containing ligands is crucial to homogeneous organometallic catalytic system for controlling the selectivity of CO2 chemical fixation and promoting the transformation efficiently6,11.Although the heterogeneous catalysts represents more superior for industrial applications because of the convenience of product separation and the reuse of catalysts, the concomitant low catalytic activity and poor selectivity were usually observed during the catalytic process, thus limiting its widely application in CO2 transformation. Therefore, the design and synthesis of highly efficient heterogenous catalysts that enable CO2 capture and transformation is still in great demand. Porous organic frameworks (POFs) represent a promising solution to the above mentioned challenge owing to its distinctive properties such as large surface areas and low skeleton density, as well as good physicochemical and thermal stability12-13. The combination of elaborate designed POFs and metal particles in the development of heterogenous catalysts that enable CO2 capture and conversion has becoming an interesting research area14-16. For example, a salen-type microporous polymers with Co/Alcoordination was recently prepared by Deng and co-workers, which displayed outstanding performance for CO2 capture and conversion of cyclopropanes into cyclic carbonates17. The combination of Tröger’sbase-derived POPs with Ru provided good CO2 capture performance and high efficiency in the reaction ACS Paragon Plus Environment

Page 3 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of hydrogen gas with CO2 to generate formic acid18. Metalated Azo-MOPs were also employed in methylation of N-methylanilines and transformation of propargyl alcohols to α-alkylidene cyclic carbonates respectively, in which the POFs displayed high CO2 uptake capacity and efficient catalytic performance19. Despite these advances, as an important class of CO2 transformation, metal ligated POFs catalyzed heterogenous reactions of terminal alkynes with CO2, thus providing propiolic acids, has not been reported till now. Propiolic acids are valuable intermediates that give access to various pharmaceuticals and fine-chemicals20, including coumarins21, flavones22 and 3-arylidene-2-oxindole derivatives23. Various heterogeneous catalysts have been developed for the synthesis of propiolic acids through carboxylation of terminal alkynes with CO224. However, owing to their imporosity or low density of grafting functional groups these heterogeneous catalytic systems such as poly(N-heterocyclic carbene) or polystyrene-supported N-heterocyclic carbene can’t effectively capture CO2 and thus limit the access of CO2 to the activated sites25-26. To date there is only one porous materials Ag@MIL-101 that could target CO2 capture and transformation into propiolic acids but demanding high catalyst loading (70mg, 2.7 mol %)27. Therefore the design of efficient metal based POFs materials as heterogenous catalysts to address both high CO2 uptake and subsequently transformation into propiolic acids under mild conditions become exceedingly desirable. Covalent triazine frameworks (CTFs) have been reported to exhibit superior CO2 uptake capacity (up to 245.5 mg/g) due to strong affinity of CO2 with triazine units28-32. Moreover, triazine moieties embedded in CTFs framework can serve as basic sites to anchor active metal species to catalyze several different reactions33-35. CTFs display superior CO2 adsorption capacity associated with strong affinity to active metal species, which make them to be promising candidates for CO2 capture and conversion into industrially useful chemicals. Inspired by the above ideas, herein, we first synthesize a novel porous covalent triazine framework identified as CTF-DCE which displayed excellent CO2 capture capacity of 191 mg/g at 273K/1 bar. The resultant CTF-DCE could anchor Ag species and act as a bifunctional material for both capture of CO2 and high-efficient conversion of CO2 to propiolic acids under ACS Paragon Plus Environment


Page 4 of 20

atmospheric pressure with only 0.4 mol% catalysts loading. Moreover, the CTF-DCE-Ag showed broad substrate scope and good recyclability.

2. EXPERIMENTAL 2.1. Synthesis of Covalent Triazine Framework (CTF-DCE). CTF-DCE was synthesized by heating a mixture of di(4-cyanophenyl)ethyne (0.228 g, 1.0 mmol) and ZnCl2 (1.36g, 10mmol) in a quartz tube (10ml). The tube was evacuated to a high vacuum and then sealed rapidly. Following by a temperature program (250 °C/keep 10 h, 350 °C/keep 10 h, 400 °C/keep 20 h) at the heating rate of 10 o

C/min, the quartz tube was cooled to room temperature, and the reaction mixture was subsequently

ground and then washed thoroughly with water to remove ZnCl2 catalyst. Further stirring in diluted HCl for 15 h was carried out to remove the residual salt. The resulting black powder was filtered and washed successively with water and methyl alcohol, followed by Soxhlet extraction using acetone, methyl alcohol, and hexane as eluting solvent sequentially, and finally dried in vacuum at 150 °C. Yield: 89%. Elemental analysis of guest free samples: Calculated: C, 84.19; H, 3.53; N, 12.27. Found: C, 82.94; H, 5.04; N; 4.78.

3. RESULTS AND DISCUSSION 3.1. Synthesis and Characterization. The dicyano monomer was synthesized by the palladium/copper(I)-cocatalyzed sila-Sonogashira-Hagihara coupling reactions of alkynylsilanes with 4iodobenzonotrile36, which were illustrated in Scheme S1 and characterized by 1HNMR and

13

C NMR

spectrum (Figure S1 and S2). The covalent triazine framework CTF-DCE was prepared under ionothermal strategy37 through a sequence of heat-resistant oligomers formation at moderate temperature and subsequent polymerization at high temperature (Scheme 1).


Page 5 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 1. Idealized structure of CTF-DCE from the polymerization of DCE monomer.

Fourier transform infrared (FT-IR) analysis confirmed the successful formation of the covalent triazine framework. The disappearance of intense characteristic carbonitrile stretching band around 2178 cm-1 and weak peaks around 1497 cm-1, and 1352 cm-1 revealed that a triazine ring was generated (Figure S3a), the weak peaks is likely attributed to the occurrence of carbonization or fragmentation during ionothermal process. We also performed

13

C CP/MAS NMR to characterize CTF-DCE at

molecular level (Figure S4). A broad peak at approximately 125 ppm corresponded to the aromatic carbons, while a small shoulder in the signal at 170 ppm was from the sp2 carbon of triazine unit. XPS study further confirmed the formation of triazine ring moieties. The C1s peak (Figure S5) of CTF-DCE can be deconvoluted into two peaks at 284.2 and 286.4 eV which were ascribed to the aromatic and triazine sp2 carbons, respectively38. The N1s XPS spectra (Figure S6) contained three contributions with binding energies at 398.5, 400.3 ev and 402.0 ev, which belonged to the triazine rings, pyrrolic nitrogen and “oxygenated (N−O)” due to decomposition of the framework39. In addition, Elemental Analysis (EA) also revealed a significant diminution of nitrogen content during the polymerization reaction. PXRD pattern of CTF-DCE showed broad diffraction peak at 4.5° and 25.1°(Figure S7), which indicated dominantly amorphous structure with weak crystalline nature as observed in most reported CTFs. ACS Paragon Plus Environment


Scanning electron microscopy (SEM) images showed that CTF-DCE was composed of irregular shape and size particles (Figure S8). Transmission electron microscopy (TEM) showed that CTF-DCE exhibited a stacking or layer structure (Figure S9). Thermogravimetric analysis (Figure S10) under air atmosphere indicated the good thermal stability of CTF-DCE which decomposed above 450 oC. Also, the resulting material was insoluble in many organic solvents, including DMSO, NMP, THF, chloroform and various aqueous conditions including HCl and NaOH, implying its good chemical stability. FT-IR spectra also confirmed the chemical stability of CTF-DCE when immersing in different solvents (Figure S3b). 3.2 Porosity Measurements and CO2 Storage Properties. Porosity parameters and surface areas of CTF-DCE were investigated by nitrogen sorption at 77 K. As shown in Figure 1a, the isotherms exhibited a sharp nitrogen uptake at low pressure (P/Po) less than 0.01, which is typical of microporosity. The hysteresis and continuous adsorption of N2 in the medium and high pressure indicated additional presence of mesoporosity and macroporosity. CTF-DCE provided a remarkable BET surface areas of 1355 m2g-1 within the pressure range of P/Po= 0.05-0.2. The total pore volumes estimated at P/Po=0.99 is 0.93 cm3g-1. The ratio of micropore volume to total pore volume was 0.8 according to t-plot method, suggesting a very high fraction of micropores in the framework. The pore size distributions evaluated by the nonlocal density functional theory (NLDFT) exhibited a dominant micropores centered at 0.6 and 1.2 nm and mesopores spreading over 2-4 nm (Figure 1b).

700 0.4

N2-77k- Adsorption N2-77k- desorption

600 500

3 dV(r) (cm /Å/g)

3 Adsorption (cm /g, STP)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 20

400 300 200

0.3 0.2 0.1

100 0.0

0 0.0

0.2

0.4

0.6

0.8

1.0

0

10

Relative Pressure P/Po

(a)

20

30

40

(b)


50

Pore Width (Å)

60

70

Page 7 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. (a) N2 adsorption/desorption isotherm for CTF-DCE at 77K. (b) Pore-size distribution of analyzed by NLDFT. The dominant micropores together with the nitrogen-rich triazine units within the CTF-DCE framework inspired us to investigate its affinity toward CO2. As shown in Figure 2a, CTF-DCE showed high CO2 capture capacities of 191 mg/g and 158 mg/g at 273 K and 298 K under 1 bar respectively. The adsorption amount ranked in the upper level among most reported CTFs materials. The uptakes of CTF-DCE at 273 K/1 bar were slightly inferior to CTF-MM2 (207 mg/g)40, FCTF-1 (205.5 mg/g)28, lutCTF400 (200.2 mg/g)41 but notably exceed most CTFs, such as CTF-0 (103 mg/g)42, PCTF-1-7 (81.0143.1 mg/g)43-44, and NOP-19-21 (106-123 mg/g)45. The high CO2 uptakes of CTF-DCE framework were related to the dominance of microporosity and the nitrogen rich triazine units. The isosteric enthalpy Qst of CTF-DCE approximated to 24.9 kJ mol-1 at low coverage (Figure 2b). The Qst value of CTF-DCE is relatively low compare to phthalazinone-based covalent triazine frameworks (PHCTFs, near or higher than 30 kJ mol-1 at low coverage)29, nitrogen rich covalent triazine frameworks (CTFs) based on lutidine, pyrimidine, bipyridine, and phenyl units (31.6-40.5 kJ mol-1)41, CTF-ph and CTF-py (33.2 and 35.4 kJ mol-1)46, but is similar to CTFs prepared based on novel N-heteroaromatic building blocks (22-28 kJ mol-1)30, PCTF-3-7 (25-28 kJ mol-1)43 and HAT-CTF (27.1 mol-1)32. A single gas (CO2 and N2) adsorption isotherm was performed at 273K to calculate the selectivity of CO2 over N2 by the Henry equation and the ideal adsorbed solution theory (IAST). The Henry’s and IAST selectivity of CO2 over N2 for CTF-DCE reaches up to 56 and 54 respectively at 273K (Figure 2c and 2d), which demonstrated its excellent selectivity for capturing CO2 over N2. The superior CO2/N2 selectivity can be attributed to the triazine group and high fraction of the ultramicropores (6 Å) in CTF-DCE framework. 3.3. Preparation of CTF-DCE-Ag and Its Catalytic Performance. The N-rich triazine units embedded in the CTF-DCE framework could provide strong nitrogen-metal interaction to anchor metal species into the CTF-DCE matrix. Silver anchored CTF-DCE (CTF-DCE-Ag) was prepared by treating the CTF-DCE framework with AgNO3 in hot DMSO at 80oC. The Ag loading in CTF-DCE-Ag was 4.3 wt % as determined by inductively coupled plasma (ICP) spectrometry. FT-IR spectra (Figure S3) ACS Paragon Plus Environment


showed that the characteristic peaks of CTF-DCE are similar to CTF-DCE-Ag, which confirms the maintenance of the framework after Ag embedding. XPS spectra of CTF-DCE-Ag (Figure. S14) demonstrated two binding energy peaks at 367.9 (Ag 3d5/2) and 373.7 ev (Ag 3d3/2), respectively, indicative of the presence of metallic Ag0 species27. This suggested that Ag+ ions were reduced in situ to metallic Ag0 and deposited on the CTF-DCE framework in the preparation of the CTF-DCE-Ag catalyst. There are several reports that porous polymers could in situ reduce Ag+ to metallic Ag0.19,47-48 PXRD patterns of CTF-DCE-Ag (Figure S7) showed the characteristic peaks of Ag nanoparticles at 2θ = 38°, and 44°, attributed to the (111) (200) crystal planes of metallic Ag0, further confirming the successful deposition of Ag nanoparticles on the CTF-DCE framework. TEM images showed that Ag nanoparticles were uniformly distributed throughout the CTF-DCE support and the particle size were 15-20 nm (Figure. S15). Compared to pure CTF-DCE, both the BET surface area and total pore volume of CTFDCE-Ag decreased from 1355 m2g-1 and 0.9 cm3g-1 to 409 m2g-1 and 0.3 cm3g-1 respectively (Figure. S16a). This was probably due to the incorporation of the Ag species leading to weight increase and slight blockage of the cavities. The pore size distributions of CTF-DEC-Ag exhibited a dominant micropores centered at 0.7 nm, 1.2 nm and 1.49 nm (Figure. S16b). CTF-DCE-Ag exhibited high CO2 adsorption capacities of 92.3 mg/g and 64.8 mg/g at 273K and 298K, respectively (Figure. S17). The high CO2 capture capacities and high density of embedded Ag sites inspired us to explore the catalytic activities of CTF-DCE-Ag for CO2 conversion.

Heat of adsorption (kJ/mol)

200

CO2 Uptake(mg/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 20

150

100

50

0 0.0

0.2

0.4

0.6

0.8

1.0

1.2

40

30

20

10

0 0

Relative Pressure (P/Po)

(a)

10

20

30

(b)


40

50

CO2 adsorbsd (mL/g)

60

70

Page 9 of 20

ACS Applied Materials & Interfaces 200

IAST Selectivity CO2 vs N2

200 N2-273K-adsorption) CO2-273K-adsorption

160

Uptake(mg/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

120 80 Selectivity CO2/N2 56 40 0 0.0

0.2

0.4

0.6

0.8

1.0

Relative Pressure P/PO

160 120 80 40 0 0

(c)

20

40

60

Pressure (kPa)

80

100

(d)

Figure 2. (a) CO2 sorption isotherms of CTF-DCE at 273K (square) and 298K (circle). (b) Qst of CO2 for CTF-DCE. (c) CO2/N2 selectivity from Henry’s law. (d) CO2/N2 selectivity obtained from IAST calculation (CO2/N2=15:85). Propiolic acids are important intermediates for applications in pharmaceutical and fine chemicals including flavones, coumarins, aminoalkynes and arylidene oxindoles21,24,49. Thus, the catalytic activities of CTF-DCE-Ag materials were examined by CO2 with terminal alkynes to afford propiolic acid under atmospheric pressure. Initially, phenylacetylene was used as model substrate to screen the optimal reaction conditions for CO2 transformation. As described in Table S1, we can see that the reaction was greatly influenced by catalyst loading (entries 1-3). The yield of propiolic acid was increased from 52.4% to 68.5% when the catalyst dosage was increased from 5 mg to 10 mg. However, further increase of catalyst (15 mg) led to an unexpected lower yield (34.2%), presumably because of the decarboxylative activity of excess Ag species50-51. Thus the catalyst loading of 10 mg proved to be optimal. The absence of CTF-DCE-Ag or the CTF-DCE material alone resulted in poor yield of propiolic acid (Table S1, entries 4 and 5). Note that the yield can be increased up to 90.2% when 2.0 equivalents of Cs2CO3 were used (Table S1, entry 6). This is significantly higher than the pure AgNO3 systems under the same reaction conditions (Table S1, entry 7, 8.6%). Furthermore, reaction temperature effects were also surveyed (Table S1, entry 6-9). The reaction performed at 50 oC was found to be optimal. Low temperature (room temperature) was also possible but a decreased yield (58.5%) was observed possibly because of the lack of sufficient reactivity at low temperature. On the ACS Paragon Plus Environment


Page 10 of 20

other hand, the reaction conducted at evaluated temperature (65 oC) also led to a decreased yield (79.3%) probably due to the decarboxylation of propynoate intermediate at high temperature11,25,52. We next explored the generality of terminal alkynes substrates for the carboxylation reaction after established the optimum conditions (10 mg CTF-DCE-Ag catalyst, 2.0 equiv Cs2CO3, 1 atm CO2, 50 oC, DMF). As listed in Table 1, moderate to excellent yields (80.8-99.0%) were obtained when either electron-donating (-CH3, -OCH3) or electron-withdrawing (-Cl) substituted phenylacetylenes were employed. Heteroaromatic (thiophene) acetylenes were also found to achieve high yield (98.9%). The catalytic activity of CTF-DCE-Ag was superior to previously reported homogeneous catalyst which required high pressure of CO211,50,52-53, addition of ligands25 and high catalyst loadings (1-10 mol%)53-55. Moreover, compared to the only material Ag@MIL-10127 for CO2 capture and conversion into propiolic acids, CTF-DCE-Ag exhibited over six-folds higher TONs under the similar conditions. The good catalytic performance of CTF-DCE-Ag material should be mainly ascribed to the synergistic effects 1) the high CO2 capture capability which intensified the local concentration of CO2 around Ag centers; 2) the nanosized pores and good dispersion of Ag nanoparticles that were accessible to the reactant substrate and resulting high catalytic performance. The catalytic mechanism for CO2 conversion into propiolic acids by CTF-DCE-Ag catalyst has been illustrated in Scheme 2. First the terminal alkynes entered into the porosity of the CTF-DCE framework and were activated by silver nanoparticles with Cs2CO3 forming a silver acetylide intermediate (Step A). Subsequently the nucleohilic attack of enriched and activated CO2 by the silver acetylide (Step B and C) would afford a CTF-DCE-Ag based propiolate II, which can undergo salt metathesis with terminal alkyne to provide corresponding propiolic acid and restore the silver catalyst (Step D). Meanwhile released the carboxylic acid product as previously reported24. Table 1. Direct carboxylation of terminal alkynes with CO2.

Entry

Alkyne

Product

Yield[a] [%]


TON

Page 11 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

90.2

226

2

99.0

248

3

80.8

202

4

84.1

210

5

98.9

247

Furthermore, to verify the practicality and utility of CTF-DCE-Ag catalyst in CO2 conversion, a recyclability test was examined by using p-tolyacetylene as substrate. The recovered CTF-DCE-Ag after using for five times gave almost equally yield as the pristine one (Figure S18), thus indicating the stability and recyclability of the catalyst. TEM images showed that Ag species were still highly dispersed throughout the framework although the catalyst was reused five times (Figure. S15b). In addition, no detectable Ag species were monitored in the filtrate (

Novel Covalent Triazine Framework for High ... - ACS Publications

Recommend Documents