Pyridine-Functionalized and Metallized Meso-Macroporous Polymers

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Pyridine-Functionalized and Metallized Mesomacroporous Polymers for Highly Selective Capture and Catalytic Conversion of CO2 into Cyclic Carbonates Qin Wu, Kuan Huang, Fujian Liu, Pengfei Zhang, and Lilong Jiang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b03660 • Publication Date (Web): 30 Nov 2017 Downloaded from http://pubs.acs.org on December 3, 2017

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Industrial & Engineering Chemistry Research

Pyridine-Functionalized and Metallized Meso-macroporous Polymers for Highly Selective Capture and Catalytic Conversion of CO2 into Cyclic Carbonates

Qin Wu ‡, Kuan Huang&, Fujian Liu*†, Pengfei Zhang*§ and Lilong Jiang*†

†

National Engineering Research Center of Chemical Fertilizer Catalyst (NERC-CFC),

School of Chemical Engineering, Fuzhou University, Gongye Road No.523, Fuzhou 350002, Fujian, PR China. E-mail: [email protected], [email protected] ‡

College of Chemistry and Chemical Engineering, Shaoxing University, Shaoxing,

312000, China. §

School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University,

Shanghai 200240, China. E-mail: [email protected] &

Key Laboratory of Poyang Lake Environment and Resource Utilization of Ministry

of Education, School of Resources Environmental and Chemical Engineering, Nanchang University, Nanchang 330031, China. *Correspondence

concerning

this

article

should

be

[email protected] , [email protected], [email protected]

ABSTRACT

-1-

ACS Paragon Plus Environment

addressed

to

Industrial & Engineering Chemistry Research 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

Pyridinic nitrogen functionalized porous organic polymers (PDVB-VP-x, where x represents the volume ratio of VP/DVB) with hierarchical meso-macroporosity were template-free synthesized from solvothermal crosslinking of 4-vinylpyridine with divinylbenzene. PDVB-VP-x can be used as effective supports for metalation with Co2+ and Zn2+, giving metal@PDVB-VP-x composites. CO2 and N2 adsorption tests demonstrate that metal@PDVB-VP-x have competitive capacities for CO2 at low relative pressure of 0.15 bar (0.58–0.89 mmol g-1 and 0.51–0.76 mmol g-1 at 0 and 25 °C) and extraordinary IAST selectivities for CO2/N2 (84.5–96.7 at 0 °C and 130.5–163.5 at 25 °C). The metal@PDVB-VP-x composites also exhibit impressive activities in catalyzing conversion of CO2 from dilute sources (15 % balanced in N2) into cyclic carbonates under ambient condition. Interestingly, the metal@PDVB-VP-x composites have excellent water-tolerant property, endowing them with potentially important applications in selective adsorption and conversion of CO2 from waste gas in the industry. Keywords: Solvothermal synthesis; Meso-macroporous polymers; CO2 capture and catalytic conversion; Cyclic carbonates; Pyridinic nitrogen

1. INTRODUCTION The constant emission of acidic gases such as CO2, H2S in the atmosphere over the past decades is an issue of wide concern because it may cause seriously climatic and environmental problems

1-5

. Emissions of acidic gas of CO2 mainly derive from

industrial activity such as the coal gasification, which was the key step in the areas of -2-


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ammonia synthesis and water-gas shift (WGS) 6. However, traditional fossil fuels will still support the major energy consumption for variously industrial processes in the near future. Eliminating CO2 from variously industrial activity, is thus a direct solution to reducing its emissions 7. Within this regard, aqueous amines have been extensively used for the selective capture of CO2 owing to their reversibly chemical reactivity to CO2 and low cost 8. However, they suffer from considerably volatile loss of solvents, severely corrosive to steel facilities, and intensive energy consumption for regeneration. Therefore, exploring alternatives to aqueous amines as the media for CO2 capture is highly desired. For this purpose, extensive research works were focused on the development of new kinds of porous materials, which could be used as the efficient adsorbents for selective removing of CO2 from flue gas, because of their negligible volatility, reduced corrosion and easy regeneration

3,8-12

. In the family of porous materials,

porous organic polymers (POPs) have received extensive research interest in these years, because they can be constructed with versatile building units via facile and low cost routes, which provide an ideal platform for rational design functional POPs

12-20

.

POPs usually showed enhanced physical and chemical stability due to their unique covalent bonding linkages. Therefore, POPs materials should much improved performances for the selective capture of CO2

12-20

. It is noteworthy that the textural

properties and nitrogen active sites of POPs play important roles for their properties in the CO2 capture. Introducing specific active species, especially nitrogen sites, in targeted POPs could strongly enhance their CO2 capacity and CO2/N2 selectivity. The -3-



incorporated nitrogen sites result in the formation of Lewis acid-base interaction between POPs and CO2

12-31

. Among various nitrogen species, pyridinic nitrogen

shows enhanced interaction with CO2 molecule in comparison with most others, and pyridinic nitrogen is thought to be a kind of effective site in porous materials favoring complexation with CO2 32. On the other hand, the chemical fixation of CO2 has also received extensive attention, which is an inexpensive and abundant C1 building unit 31. Among various routes for CO2 conversion, the catalytic cycloaddition of CO2 to produce cyclic carbonates shows potentially important applications, because cyclic carbonates are important chemical intermediates, which have been widely used in industry. In addition, this type of reaction is quite promising from the point of views of green chemistry and atomic economy, as the transformation of CO2 into cyclic carbonates does not produce any side products

33-35

. Therefore, the integration of selective

capture and chemical fixation of CO2 is a most attractive solution to CO2 emissions in these years 33-40, through which the waste CO2 is transformed into high-value products. The key is to develop materials that can not only enrich CO2 from diluted sources (as low as 10~15 % in flue gas) 9, but also exhibit enhanced catalytic activities for transforming CO2 into fine chemicals. More importantly, the materials should be resistant to other components in flue gas, especially for water. In terms of catalysis, the efficient transformation of CO2 into useful chemicals under mild conditions is also important for their widely practical applications.

-4-


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To achieve the above-mentioned goals, we rational design and synthesis of pyridine-functionalized and metallized POPs composites (metal@PDVB-VP-x) with hierarchical meso-macroporosity and tunable nitrogen contents via template-free solvothermal crosslinking of 4-vinylpyridine with divinylbenzene, followed by further metalation with metals through the coordination of pyridine with metal ions (i.e., Co2+ and Zn2+) 31, which exhibit very good catalytic activity for conversion of CO2 into useful chemicals such as cyclic carbonates. Many recent works have disclosed the importance of mesopores and/or macropores in the selective adsorption of CO2 from N2

18,41,42

. More importantly, abundant mesopores and/or macropores provide

enhanced pathways for the fast diffusion of reactants during CO2 conversion

18,41,42

.

Therefore, the metal@PDVB-VP-x composites prepared in this work are expected to have high performance for the selective capture and conversion of CO2 from dilute sources. Up to now, there are still few research works on the usage of nitrogen-functionalized and metallized meso-macroporous polymers for selective capture and conversion of CO2.

2. EXPERIMENTAL SECTION

2.1 Chemicals The chemicals in this work were purchased and used directly. Divinylbenzene (DVB),

4-vinylpyridine

(VP),

azobisisobutyronitrile

(AIBN),

ethyl

acetate,

CoCl2·6H2O and Zn(OAc)2·2H2O were supplied by Sinopharm Chemical Reagent -5-



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Co.,Ltd, China. Mixed gas of CO2 (15 v%) and N2 (85 v%) were supplied by APK Gas Co. Ltd., Shanghai. 2.2 Synthesis of POPs To synthesize pyridine-functionalized POPs, 0.065 g of AIBN initiator, 2mL of DVB cross-linker, and 1 mL of VP functional monomer were mixed together, then 25 mL of ethyl acetate solvent was introduced, after stirring of the mixture for 3 h at room temperature. The reaction solution was solvothermally treated at 120 °C for 24 h in an autoclave, the pristine POPs was obtained with white color. The ethyl acetate solvent confined in the pristine POPs could be removed from drying of samples at 80 °

C under vacuum condition for 12-24 h. The resultant POPs are named as

PDVB-VP-x, the x is the volume ratio of VP/DVB. By changing the ratio of reactants, a variety of pyridine-functionalized POPs (PDVB-VP-0.25, PDVB-VP-0.5, and PDVB-VP-1.0) supports were synthesized in this work. To synthesize metal@PDVB-VP-x composites, PDVB-VP-0.5 (0.80 g) and CoCl2·6H2O (0.81 g, ~20 wt. % of Co2+) were added to degassed DMF (ca. 150 mL), then the mixture was treated at 120 °C for 12 h under vigorous stirring protected with flowing nitrogen. The solid could be obtained from filtration, and washed with abundant hot DMF to remove adsorbed Co2+, which was then dried at 60 °C for 48 h under vacuum condition. [email protected] was obtained in 84.3 % yield. [email protected]

was

synthesized

from

PDVB-VP-0.5

(0.80

g)

and

Zn(OAc)2·2H2O (0.67 g, ~20 wt.% Zn2+) through a similar procedure with that of [email protected], where ethanol was used as the solvent, and [email protected] -6-


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was obtained in 86.5 % yield. Notably, the large amounts of metal ions located in PDVB-VP-x have negative effect on their properties for the capture of CO2, which will largely decrease the BET surface areas and consume the basic site of PDVB-VP-x. In addition, the increasing of pyridine content in PDVB-VP-x will also decrease their BET surface areas. To select optimal synthetic condition, we should consider suitable contents of pyridinic nitrogen and metal sites. Moreover, the high metal contents in PDVB-VP-0.5 result in the sintering phenomenon and limited degree of exposure of active sites in the samples, which was not favorable for the enhancement of their catalytic performances. Therefore, the metal content in metal@PDVB-VP-x was chosen at around 20 wt%.35

2.3 Characterizations Prior the characterizations, the samples were treated at 150 °C under low pressure (

Pyridine-Functionalized and Metallized Meso-Macroporous Polymers

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