Zeolite@Mesoporous silica-supported-amine hybrids for the capture of CO2 in the presence of water

Accepted Manuscript Zeolite@Mesoporous Silica-Supported-Amine Hybrids for the Capture of CO2 in the Presence of Water Xiaowei Liu, Fei Gao, Jian Xu, Lihui Zhou, Honglai Liu, Jun Hu PII:

S1387-1811(15)00551-X

DOI:

10.1016/j.micromeso.2015.10.006

Reference:

MICMAT 7346

To appear in:

Microporous and Mesoporous Materials

Received Date: 11 June 2015 Revised Date:

29 August 2015

Accepted Date: 6 October 2015

Please cite this article as: X. Liu, F. Gao, J. Xu, L. Zhou, H. Liu, J. Hu, Zeolite@Mesoporous SilicaSupported-Amine Hybrids for the Capture of CO2 in the Presence of Water, Microporous and Mesoporous Materials (2015), doi: 10.1016/j.micromeso.2015.10.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Zeolite@Mesoporous Silica-Supported-Amine Hybrids for

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the Capture of CO2 in the Presence of Water Xiaowei Liua‡, Fei Gaoa ‡, Jian Xub, Lihui Zhoua, Honglai Liua and Jun Hua,* a

Key Laboratory for Advanced Materials, East China University of Science and Technology, 130

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Meilong Road, Shanghai 200237, China. b

Shanghai Institute of Measurement and Testing Technology, 1500 Zhang Heng Road, Shanghai,

*

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201203, China.

Corresponding Author. E-mail: [email protected]; Fax & Tel: 86-21-64252195.

‡Xiaowei Liu and Fei Gao contributed equally to this work.

Abstract: The selective capture of CO2 under humid condition for the commercial adsorbents

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has always been a great challenge. Here, we come up with a simple and effective solution, i.e., fabrication a shell around the commercial zeolite particle which can dynamically hinder the

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diffusion of water molecules into the zeolite core to maintain its good CO2 capacity even in the presence of water. By a sol–gel coating process and a polyethylenimine (PEI) impregnation

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process, a series of 5A zeolite-based hybrids with a shell of mesoporous silica-supported-amine (5A@MSAs) were fabricated. The performance of CO2 separation from the simulated flue gas (with 15:85 v/v CO2/N2 and moisture) was investigated by TG and MS in a flow system. Among the obtained adsorbents, 5A@MSA-30 was demonstrated to be the best candidate for CO2 capture from the simulated humid flue gas, with the CO2 uptake as high as 5.05 mmol/g at 298 K. The results of 10 cyclic adsorption/desorption operation suggested that the PEI molecules can be stably holden in the mesoporous silica shell, resulting in a remained CO2 adsorption capacity.

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The amine modified zeolite not only maintained but also significantly promoted the ability of CO2 capture under humid condition; therefore, it would be a promising solution for the

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commercial adsorbents to capture CO2 in the presence of water. Keywords: amine-modified, zeolites, core–shell structure, CO2 separation, moisture. 1. Introduction

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The significant and continuous rise in atmospheric CO2 concentration has become a worldwide issue leading to the global climate change.1, 2 The reduction of anthropogenic CO2

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emissions is highly demanded. Recently, CO2 capture and storage (CCS) has been proved as an effective strategy to reduce the CO2 emissions from flue gas.3-7 Adsorption based on solid adsorbents, is now being considered as a promising technology because of its low energy consumption and low equipment cost. A great number of potential adsorbents have been investigated for CO2 removal, including zeolites,8-10 activated carbons,11-13 periodic mesoporous

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silica14 and metal organic frameworks (MOFs).15-17 Among them, zeolites, a class of porous crystalline alumino-silicates, such as 5A, 13X, APG-II and WE-G 592, have received

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tremendous industrial attention because of their high CO2 adsorption capacity at low CO2 concentration and normal pressure, as well as the high thermal stability for regeneration. The

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CO2 adsorption mechanism on zeolites has revealed the physical adsorption of CO2 by an ion– dipole interaction or strongly bound carbonate species by bi-coordination. Micropore structure less than 1nm of Zeolite 5A is beneficial to CO2 adsorption. Lower Si/Al ratio leads to more surface oxygen charge and strong polarity which also benefits to the interaction with CO2 and H2O. As a ;result, zeolite 5A has shown promising performance for separating CO2 from gas mixtures over many other zeolite frameworks.18 Most importantly, these zeolites are already commercially available with low price. However, zeolites always lose their adsorption efficiency

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in the presence of water because of their inherently better affinity for polar H2O molecules, as in many real gas separation cases such as flue gases, biogases.19, 20 Therefore, dehumidification is a necessary process before CO2 capture, which would significantly increase the investment cost,

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the total energy consumption, as well as the difficulty of the operation.

To maintain the outstanding CO2 capture ability of commercial zeolites even in the presence of water, a simple and effective solution is to fabricate a shell around the zeolite particle which

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can hinder the diffusion of water molecules into the zeolite core. In our recent work, we constructed a hydrophobic ZIF-8 shell outside the 5A zeolite core to exhibit a dynamic hindrance

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effect for moisture in the competitive adsorption of CO2,21 Analogously, when we considering the specially excellent CO2 adsorption properties of amine, a novel dynamic reaction-induced hindrance effect for moisture was highlighted.

There are already many amine modify solid adsorbents have been reported,22-26 which are

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generally obtained in two ways: amines covalently bound to the support27,

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and amines

physically impregnated into the pore space of supports.24, 29 For the former, aminosilane is the most used reagent to be grafted on mesoporous silica; moreover, a new type of metal organic

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frameworks (MOFs) with amino groups have been elaborately designed and fabricated as CO2

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adsorbents in humid conditions.30-36 For the later, the most famous work was done by Song’s group37, in which low molecular weight polyethyleneimine (PEI) was impregnated into MCM-41 to create a “molecular basket” adsorbent and applied for CO2 separation from simulated flue gas containing moisture. However, these mesoporous silica and MOFs materials are all relatively expensive and complex, leading to the difficulty in large-scale production and real industrial utilization. The development of a more economical adsorbent is highly desired.

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Compared to the mesoporous adsorbents, zeolites have extremely small pore size and perfect crystalline structure, therefore, neither amine impregnation nor surface amine grafting is practicable. Fortunately, many zeolite-based hierarchical porous structures38-40 have been

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reported because of their improved properties. Zhao et al. fabricated uniform core–shell composites comprising zeolite cores and ordered mesoporous silica shells through a facile sol– gel coating method.41 Inspired by these works, zeolite@mesoporous silica-supported-amine

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hybrids would be an excellent idea for designing zeolite-based CO2 adsorbent even in the

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presence of water.

Herein, a core–shell strategy with amine-impregnation is used to fabricate a series of zeolite@mesoporous silica-supported-amine hybrids which are denoted as 5A@MSA. As illustrated in Scheme 1, under humid conditions, the amino groups in the shell can react with H2O and CO2 to form carbamates initially and then convert to carbonates or bicarbonates,1 which

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would dynamically prevent H2O from diffusing into the inner core of 5A zeolite. With excess CO2 molecules can still transfer through PEI shell into 5A core, 5A micropores can carry its

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good CO2 adsorption capacity forward, and thus to improve the CO2 capacity.

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Scheme 1. Schematic illustration of CO2 and H2O molecules diffusion in the 5A@MSA core– shell hybrids.

2. Experimental 2.1. Materials.

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The 5A zeolite powder was purchased from Shanghai Jiuzhou Chemicals Co., Ltd. Tetraethylorthosilicate (TEOS) was purchased from Shanghai Lingfeng Chemicals Co., Ltd. Cetyltrimethylammonium (CTAB) and ammonia were purchased from Jiangsu Yonghua

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Chemicals Co., Ltd. Polyethylenimine (PEI, Mw=600) were purchased from Alfa Aesar Chemicals Co., Ltd. All chemicals were used without further purification.

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2.2. Synthesis of 5A@MSA hybrids.

The core–shell 5A@mesoporous silica (denoted as 5A@MS) composite was prepared

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according to method reported by Zhao et al.41 Typically, 5A zeolite particles (0.1 g) was dispersed in a mixture containing CTAB (0.07 g), water (20 g), ethanol (12 g), and ammonia (0.25 g) under ultrasonic treatment for 30 min. Next, TEOS (0.112 g) was added dropwise and stirred at room temperature for 4 h. The product was collected by centrifugation and washed with

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water and ethanol. The organic template was removed by calcination at 550 °C for 5 h in air. PEI impregnated sorbents were prepared by the wet impregnation method. Typically, the desired amount of PEI was dissolved in 1.0g of methanol under stirring for 15 min. The core–

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shell 5A@MS (0.1 g) was subsequently added to the amine-methanol solution. The slurry mixture was stirred for 4 h. Finally, the product obtained was dried at 80 °C overnight to remove

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the solvent. The amine modified 5A@MS hybrids were denoted as 5A@MSA-x, where x denoted the weight percentage of PEI impregnated on the sorbent. 2.3. Characterizations.

Transmission electron microscopy (TEM) images were obtained using a JEM-1400 electron microscope. Field-emission scanning electron microscope (FESEM) images were conducted by using a Nova NanoSEM 450. Powder X-ray diffraction (PXRD) patterns were obtained on a

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D/Max2550 VB/PC spectrometer using Cu Kα radiation (40 kV and 200 mA). Fourier transform infrared (FTIR) spectra of the samples were conducted at room temperature on a Thermo Scientific Nicolet iS10. Nitrogen adsorption measurements were conducted at 77 K on a

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Micrometrics ASAP 3020 sorptionmeter. The total surface area was determined by the BET (Brunauer-Emmett-Teller) model. The size distribution of the mesopores was determined by the Non-local Density Functional Theory (NLDFT) model.42 Thermogravimetric analysis (TGA)

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measurements were conducted on a NETZSCH STA 449 F3 Jupiter. Mass Spectrometry (MS) measurements were conducted on a NETZSCH QMS 403 D Aёolos. The moisture was

2.4. Gases sorption measurements.

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introduced by a NETZSCH Modular Humidity Generator MHG-32.

The CO2 adsorption performance of the obtained 5A@MSA hybrids in the presence of water was examined through the joint of TG-MS. The samples were first degassed in pure N2 stream

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with a flow rate of 20 ml/min at 100 °C for 1 h. When they cooled down to the desired temperature, the samples were exposed to a gas mixture of 15CO2:85N2 (vol/vol) in which a certain amount of moisture was introduced. The flow rate of the whole feed stream was fixed as

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20 ml/min. Then, a thermal desorption process up to 100 °C with a heating rate of 10 °C/min was

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carried out under the purge of pure N2. The signals of the mass losses of the samples as well as the mass spectrometry of H2O (mass/charge ratio = 18) were recorded simultaneously during the desorption process.

3. Results and discussion

Confirmed by both small-angle and wide-angle XRD patterns (Fig. 1), all 5A@MSA hybrids show characteristic diffraction peaks assigned to the typical zeolite structure of 5A. While for their small-angle XRD patterns, a diffraction peak at a 2θ value of approximately 2.4°, indexed

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as the mesoporous structure, can be observed in 5A@MS composite. With PEI loading increasing from 0 to 40%, the intensity of the diffraction peak at small angle reduced but shows no significant changes in large angles, suggesting PEI molecules occupied the space in the

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mesoporous channels in the shell.

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5A@MSA hybrids with different PEI loadings.

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Fig. 1. (a) Small-angle XRD patterns and (b) wide-angle XRD patterns of the core–shell

The SEM and TEM images (Fig. 2) of 5A@MS and 5A@MSA clearly reveal their morphology keep the cubic shape of the pristine 5A zeolite (Fig. 2a and 2d). Compared to the pristine 5A zeolite (Fig. S1), 5A@MS composite (Fig. 2b) exhibits a relatively coarse surface

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and the TEM image (Fig. 2c) reveals that the coarse surface is caused by the successful formation of thin mesoporous silica shells, which is in good agreement with the results of XRD analysis. The thickness of the thin mesoporous silica shells is about 40 nm. After the

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impregnation of PEI, the soft polymer coating can be significantly observed at the surface of 5A@MSA-30 particles in the SEM image (Fig. 2 e). A well-defined core–shell micro-

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mesoporous structure still clearly presents in the TEM image (Fig. 2f).Because of the relatively uniform core@shell structure of 5A@MS, most of the micropores of 5A are accessible through the mesopore layer. However, the SEM image (Fig. 2b) shows some defects in the shell, which are inevitable because of the unevenly adsorbed CTAB at the surface of 5A. Fortunately, there are very few defects after PEI coating for the 5A@MSA hybrids. Therefore, as illustrated in Scheme 1, the gas molecules can penetrate into the 5A core through PEI shell.

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Fig. 2. SEM and TEM images of the core–shell 5A@MS composite (a, b and c) and 5A@MSA-

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30 hybrid (d, e and f)

The PEI loading was further illustrated by the FT-IR spectra (Fig. S2). Compared with the

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spectra of 5A@MS composite, after PEI loading, some additional bands, such as the bands at 2950 cm-1 and 2840 cm-1, assigned to the CH2 asymmetric and symmetric stretching of the PEI

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chain, and the bands at 1571 cm-1 and 1479 cm-1, attributed to the NH2 asymmetric and symmetric bending,30 could be observed, respectively. With increasing PEI loading, the intensity of peaks of amino groups exhibits a significant increase. This thin PEI layer is expected to effectively hinder the water molecules from entering the 5A core. Consequently, the 5A@MSA

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hybrids could exhibit the good CO2 adsorption capacity of 5A, meanwhile, the PEI component would provide an additional contribution for CO2 uptake through chemical adsorption. Nitrogen adsorption isotherms and the corresponding pore size distributions (Fig. 3) show that

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5A@MS composite exhibits a sharp uptake when the relative pressure is below 0.01 (type I isotherm) and a capillary condensation occurring over a relatively wide pressure range of 0.4–0.6

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(type IV isotherm), indicating the bimodal micro-mesopores structure. The H2-type hysteresis loop is attributed to the random worm-like mesoporous or aggregations of the particles. After PEI loading, the characteristic hysteresis of the isotherm disappears gradually with increasing PEI loading, which is attributed to the occupancy of the PEI chains in the mesoporous channels. The calculated porosity properties of each sample are summarized in Table 1. 5A@MS composite possesses a BET surface area of 485 m2/g, higher than that of pristine 5A, which is due to the contribution of mesopores of mesoporous silica. The BET surface area and pore

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volume of 5A@MSA hybrids decrease with increasing PEI loading, confirming that PEI was successfully introduced into 5A@MS. The pore size distribution curves (Fig. 3b) reveal that the mesopores diameter of 5A@MS is about 2.3 nm. With increasing PEI loading, the intensity of

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the peak decreases and the peak shifts to the smaller size, suggesting the porosity is gradually filled by PEI. Therefore, PEI molecules are mostly located in the mesoporous layer, meanwhile, SEM image (Fig. 2e) shows that existence of PEI on the external surface of the 5A@MSA-30

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particles is also very likely. However, because of the small micropores of 5A, PEI molecules can hardly penetrate into 5A. It is noted that 5A@MSA-40 fully lost porosity because the

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overloading of PEI resulted in a serious blockage of the mesoporous channel and it was very difficult for N2 gas molecules to permeate through the PEI shell.

Fig. 3. (a) Nitrogen adsorption-desorption isotherms and (b) pore size distributions of the

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5A@MS composite and 5A@MSA hybrids with different PEI loadings

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To evaluate the real CO2 adsorption performance of 5A@MSA hybrids, the dynamic adsorption properties was studied by the joint of TG-MS quantitative method from the simulated

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flue gases containing 15 % (v/v) of CO2 in N2 with a relative humidity range from 0 to 90%. Here, we only take the sample 5A@MSA-30 as an example, when it was exposed to the simulated flue gas with 70% relative humidity, the typical dynamic adsorption and desorption curves (Fig. 4a) was quantitatively determined by TG analysis. During the thermal desorption under the purge of pure N2, MS was used to monitor the amount of H2O desorbed in the effluent during the desorption process (Fig. 4b). Since the adsorption selectivity of CO2 or H2O towards N2 of all 5A@MSA hybrids is so high that the amount of N2 adsorbed could be neglected,

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therefore, the weight increase (or loss) during the adsorption (or desorption) process is only

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attributed to that of CO2 and H2O.

Fig. 4. (a) Dynamic adsorption and desorption curve of 5A@MSA-30 from the simulated flue gas with 70% relative humidity, the adsorption temperature is 298 K. (b) MS signal curves of

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5A@MSA-30 at the thermal desorption stage. (c) Dynamic adsorption and desorption TG curves of all the samples from the simulated flue gas with 70% relative humidity. (d) Dynamic uptakes

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of H2O and CO2 of 5A@MSA-30 during the adsorption process

Consequently, the CO2 uptakes can be estimated by subtracting the calculated amount of H2O from the total mass increase in the TG curve during the adsorption process. 21 The H2O and CO2

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uptakes of all samples after exposed to the simulated flue gases with different relative humidities for 2 h can be calculated. The measurement at 298 K and calculation details are listed in Table S1, and the results of CO2 and H2O uptakes under the dry condition and 70% relative humidity at

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298 K are summarized in Table 1.

Table 1 Porosity of 5A and 5A@MSA hybrids and their CO2 and H2O uptakes at 298 K

As illustrated in Table 1, under dry condition, the CO2 uptake of 5A@MS composite (2.45 mmol/g) is lower than that of pristine 5A (3.28 mmol/g), since the mesopore has a relatively smaller contribution to the CO2 uptake but increases a lot for the total weight of the adsorbent.

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The impregnation of PEI shows two contrast effects on the dynamic CO2 uptakes of 5A@MSA hybrids. The positive one is that it can promote chemical adsorption of CO2 through its abundant amino groups; whereas the negative one is that it can block the channels for CO2 molecules

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transport into the core of 5A, thus decreases the CO2 capacity. When PEI loading is low, in the range of 10~20%, the negative effect is dominated, resulted in a low CO2 capacity (smaller than 1.5 mmol/g) due to the decreased surface area. Increasing PEI loading to 30%, the CO2 capacity

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is significantly enhanced (1.63 mmol/g) due to the positive effect of PEI, although the surface area decreased significantly. However, PEI overloading (~40%) shows no enhancement for the

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CO2 adsorption performance anymore. As we can see the amino groups of the PEI component could promote the chemical adsorption of CO2, but the overall CO2 uptakes of all 5A@MSA hybrids still show a lower performance than that of pristine 5A under dry condition. Whereas under 70 % relative humidity, the dynamic CO2 adsorption behavior were totally

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different. As the dynamic adsorption-desorption curves shown in Fig. 4c and the calculated results summarized in Table 1, the pristine 5A, as expected, almost loses its CO2 adsorption capacity (0.73 mmol/g) due to the predominated adsorption of H2O molecules in the micropores

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(7.91 mmol/g). For the same reason, 5A@MS also shows a poor CO2 uptake. After PEI loading, all 5A@MSA hybrids show significantly improved CO2 uptakes and demonstrate an increase

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trend with increasing PEI loading. Compared with pristine 5A, with only 10% PEI loading, 5A@MSA-10 shows a much better CO2 uptake (1.67 mmol/g) with a reduction of H2O uptake (7.79 mmol/g). Increasing PEI loading to 30%, 5A@MSA-30 exhibits the highest CO2 uptake of 5.05 mmol/g, almost 10 times larger than pristine 5A. Again, increasing PEI loading up to 40%, it shows no further enhancement with a similar CO2 uptake of 4.35 mmol/g. As a proof, it

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provides a strong evidence for the reality of our designing and fabricating strategy of amine modified zeolite-based adsorbents for CO2 capture in the presence of water.

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To better understand the respective contributions of PEI shell and 5A core for the CO2 adsorption, the corresponding data of mesoporous silica MS and amine modified mesoporous silica with different PEI loading but without 5A core, MSA-x hybrids, were prepared and their CO2 separation performance were determined at the same conditions. As listed in Table S2,

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similar as the 5A@MSA, the CO2 uptake of all samples after PEI loading are much better in the

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humidity condition than that in the dry condition. Compared with the same loading of PEI such as 30%, 5A@MSA-30 shows better CO2 uptakes than MSA-30, suggesting that the micropores of 5A core would play an important role for the CO2 capture. Based on the synthesis yield that 1 g 5A powder can produce 1.69 g 5A@MSA-30 powder，the mass ratio of mesoporous layer with PEI loading would be 40%. Since the mesoporous layer is very thin, and all the mesopores

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are full filled by PEI, we approximately used the CO2 uptake of MS-60 sample (7.16 mmol/g) to represent the adsorption performance of PEI shell. Therefore, the CO2 adsorption contribution of the PEI shell is cursorily estimated as 40%×7.16 = 2.86 mmol/g and that of 5A core will be 5.05

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- 2.86 = 2.19 mmol/g, which confirms the success of designing approach that 5A core can still

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maintain its good adsorption capacity with the chemical adsorption of PEI and its hindrance effect for the H2O molecules. More importantly, for the dynamic adsorption operation, the adsorption rate should be carefully taken into account. In this regard, we make an enlargement of the dynamic adsorption segment of the TG curves (Fig. 4c insert). To our surprise, the adsorption segments of 5A, 5A@MS and 5A@MSA are almost in parallel with each other, the slopes of the adsorption

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segments, which can represent the adsorption rate, show no significant different, revealing PEI loading had very little effects on the diffusion of CO2 and H2O molecules through PEI shell.

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To explicate the variation rules of competitive adsorptions between CO2 and H2O during the adsorption process. The dynamic uptakes of CO2 and H2O during the adsorption process was further investigated by exposing each 5A@MSA-30 to the simulated flue gas for a series of periods. As shown in Fig. 4d, during the initial adsorption process before 10 min, the CO2 and

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H2O uptakes are similar with each other, since CO2 and H2O molecules firstly reach to the PEI

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layer, and amino groups of PEI react with CO2 and H2O simultaneously, with the stoichiometric ratio of CO2 to H2O of 1:1. After that, the CO2 uptake surpasses that of H2O, indicating some CO2 molecules penetrated through the PEI shell and were adsorbed by 5A core, which is consisted with our designing mechanism. However, when the adsorption time is more than 50 min, the H2O uptake surpasses that of CO2, and increase almost linearly, whereas CO2 uptake

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gradually approaches saturated at about 90 min. These phenomena indicate that the PEI shell can effectively hinder the entrance of water molecules by the chemical adsorption, but allow the free diffusion of CO2 molecules into the inner 5A core, maintaining the overall good affinity to CO2

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in the initial adsorption stage. However, H2O molecules can still gradually penetrate into the sample with the adsorption time prolonged, resulting in a continuous increase of H2O uptake,

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which we definite as “dynamic reaction-induced hindrance effect for moisture” It should be noted that the adsorption temperature and humidity are two important parameters for CO2 chemical adsorption on amines, therefore, their simultaneous influences on the CO2 adsorption performance of 5A@MSA-30 were carefully investigated. As shown in Fig. 5, in the temperature range of 25 to 50 °C, the CO2 uptake decreases with increasing temperature at any humidity, which is opposite to the most reported phenomena that CO2 adsorption capacity

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increases with the temperature for amine modified mesoporous materials25,

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. For our

designed amine modified zeolite-based hybrid 5A@MSA adsorbents, there are two factors which determine the CO2 adsorption capacity: one is the exothermic physical adsorption caused by 5A

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core, favouring for lower adsorption temperature; the other is the diffusion of the adsorbed CO2 from the exposed surface of PEI into the bulk PEI, benefiting from relatively higher temperature. For 5A@MSA-30, decreasing the adsorption temperature will be advantageous in CO2 capture,

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indicating that the physical adsorption by 5A core is the dominant contribution for CO2 uptakes, whereas the PEI shell can effectively prevent H2O from diffusing into the inner core of 5A

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zeolite, because the very small amount of H2O molecules can react with the amino groups of PEI and are fixed on the mesoporous shell. In addition, at any adsorption temperature, the great effect of the humidity of the flue gas on the adsorption performance shows similar trends. At lower humidity, the CO2 uptake of the hybrid sample increases with the humidity and achieves a

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maximum at 70% relative humidity. When the relative humidity reaches 90%, the CO2 uptake decreases a little, suggesting the reaction-induced hindrance effect for humidity really is a dynamic effect. When the humidity is high enough, H2O molecules would ultimately diffuse into

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the 5A core, and accordingly depress the CO2 adsorption performance. Considering the effects as a whole, 5A@MSA-30 shows the best CO2 adsorption performance at 25 °C from the simulated

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flue gas with the relative humidity of 70%.

Fig. 5. Influences of adsorption temperature and humidity on the CO2 adsorption performance of the 5A@MSA-30 hybrids

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Long-term stability and regeneration ability are also very important parameters for the real practical applications. The good stabilization can be attributed to the feed or purge gases containing water vapor which could avoid the CO2-induced deactivation. 44, 45 Fig. 6 shows the

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regeneration performance of 5A@MSA-30 measured in 10 consecutive adsorption-desorption runs by TG. After 10 cycles, the adsorption capacity shows almost no change, therefore, the sample demonstrates a very stable cyclic adsorption-desorption performance. In a word,

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5A@MSA-30 would be a prospective adsorbent for the dynamic removal of CO2 from the humid

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flue gas.

Fig. 6. 10-cycle stability of adsorption and desorption on 5A@MSA-30 from the simulated flue

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gas

When we compared our results with some available work,30-36 as summarized in Table S3, various amine modified adsorbents, no matter through the physical impregnation or the chemical

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modification, all of them showed good CO2 uptake in the presence of water. Among these essential adsorbents, the hybrids prepared in this work presented a better CO2 uptake than most

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adsorbents. Therefore, the adsorbents prepared in this work would be much more practical. 4. Conclusion

In summary, we have synthesized core–shell micro-mesoporous 5A@MSA hybrids. Under humid conditions, the amino groups of PEI in the shell can react with H2O and CO2 to form carbonates or bicarbonates, which effectively fixed the H2O molecules and prevented H2O from diffusing into the inner core of 5A zeolite, and thus to maintain its excellent CO2 adsorption

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capacity. Based on this, we proposed the dynamic reaction-induced hindrance effect of moisture for CO2 capture. Increasing the amount of PEI loading would increases this effect and also make a great contribution for improving CO2 uptake, but also would block the channels for CO2

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transfer. Among a series of hybrids, 5A@MSA-30 was demonstrated to be the most potential candidate for CO2 capture in the presence of water, with the CO2 uptake as high as 5.05 mmol/g from the simulated humid flue gas (with 15% CO2 and 70% relative humidity at 298 K). In

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addition, the adsorbent also exhibited good stability and regeneration ability over 10 adsorptiondesorption cycles. Therefore, the novel strategy of utilizing the dynamic reaction-induced

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hindrance effect through a core–shell structure with amine-impregnated would be a good solution for improving the CO2 separation performance in practical applications. Appendice A. Supplementary data

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Supplementary data related to this article can be found at the supplementary material. Acknowledgment

Financial supports for this study were provided by the National Basic Research Program of

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China (2013CB733501), the National Natural Science Foundation of China (Nos. 91334203, 21176066, 21376074), the 111 Project of China (No. B08021), the project of FP7-PEOPLE-

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2013-IRSES (PIRSES-GA-2013-612230), and the Fundamental Research Funds for the Central Universities of China

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ACCEPTED MANUSCRIPT Table 1 Porosity of 5A and 5A@MSA hybrids and their CO2 and H2O uptakes at 298 K

Dry Vtot

(m2/g)

(cm3/g)

70% Relative Humidity

CO2 uptake

CO2 uptake

(mmol/g)

(mmol/g)

(mmol/g)

7.91

334

0.18

3.28

0.73

5A@MS

485

0.29

2.45

0.82

5A@MSA-10

356

0.19

1.34

1.67

5A@MSA-20

190

0.11

0.65

5A@MSA-30

16

0.01

5A@MSA-40

0.8

0

7.93

7.10

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7.79

2.41

1.63

5.05

7.07

1.06

4.35

7.00

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H2O uptake

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Fig. 1. (a) Small-angle XRD patterns and (b) wide-angle XRD patterns of the core–

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shell 5A@MSA hybrids with different PEI loadings.

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Fig. 2. SEM and TEM images of the core–shell 5A@MS composite (a, b and c) and

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5A@MSA-30 hybrid (d, e and f)

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Fig. 3. (a) Nitrogen adsorption-desorption isotherms and (b) pore size distributions of

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the 5A@MS composite and 5A@MSA hybrids with different PEI loadings

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Fig. 4. (a) Dynamic adsorption and desorption curve of 5A@MSA-30 from the simulated flue gas with 70% relative humidity, the adsorption temperature is 298 K. (b) MS signal curves of 5A@MSA-30 at the thermal desorption stage. (c) Dynamic

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adsorption and desorption TG curves of all the samples from the simulated flue gas

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with 70% relative humidity. (d) Dynamic uptakes of H2O and CO2 of 5A@MSA-30 during the adsorption process

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Fig. 5. Influences of adsorption temperature and humidity on the CO2 adsorption

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performance of the 5A@MSA-30 hybrids

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Fig. 6. 10-cycle stability of adsorption and desorption on 5A@MSA-30 from the

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simulated flue gas

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Scheme 1. Schematic illustration of CO2 and H2O molecules diffusion in the

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5A@MSA core–shell hybrids.

ACCEPTED MANUSCRIPT Highlights Core-shell zeolite@mesoporous silica-supported-amine hybrids (5A@MSAs) were synthesized. 5A@MSAs exhibited excellent CO2 adsorption capacity (5.05 mmol/g) even in the presence of water. PEI shell dynamically hindered H2O molecules diffusion into 5A core through the chemical adsorption.

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5A core maintained its good CO2 adsorption performance with the designed core@shell structure.

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5A@MSA-30 demonstrates a very stable cyclic adsorption-desorption performance.