Zhiguo Yan ,SaiTang ,Xumiao Zhou ,LiYang ,*,Xingqing Xiao ,Houyang Chen ,Yuanhang Qin ,WeiSun

1 Key Laboratory of Green Chemical Process of Ministry of Education,Key Laboratory of Novel Reactor and Green Chemical Technology of Hubei Province,School of Chemical Engineering and Pharmacy,Wuhan Institute of Technology,Wuhan 430205,China

2 Department of Chemical and Biomolecular Engineering,North Carolina State University,Raleigh,NC 27695-7905,USA

3 Department of Chemical and Biological Engineering,State University of New York at Buffalo,Buffalo,NY 14260-4200,USA

Keywords:All-silica zeolites Toxic gases Adsorption isotherm GCMC simulation

ABSTRACT The exhaustgases,including SO2,NH3,H2S,NO2,NO,and CO,are principalairpollutants due to their severe harms to the ecologicalenvironment.Zeolites have been considered as good absorbentcandidates to capture the six exhaust gases.In this work,we performed grand canonical ensemble Monte Carlo(GCMC)simulations to examine the capability of 95 kinds of all-silica zeolites in the removal of the six toxic gases,and to predict the adsorption isotherms of the six gases on all the zeolites.The simulation results showed that,H2S,NO,NO2,CO and NH3 are well-captured by zeolite structures with accessible surface area of 1600–1800 m2·g-1 and pore diameter of 0.6–0.7 nm,such as AFY and PAU,while SO2 is well-adsorbed by zeolites containing larger accessible surface area(1700–2700 m2·g-1)and pore diameter(0.7–1.4 nm)at room temperature and an atmospheric pressure.However,at saturated adsorption,zeolites RWY,IRR,JSR,TSC,and ITT are found to exhibit better abilities to capture these gases.Our study provides useful computational insights in choosing and designing zeolite structures with high performance to remove toxic gases for air purification,thereby facilitating the developmentand application of exhaust gas-processing technology in green industry.

1.Introduction

Air pollution has received a widespread attention on account of the uncontrolled combustion and emission of fossil fuel in daily life,chemical industry and military war[1,2].The damages of ecological environment result in many severe respiratory and nervous diseases[3,4].Principal components in exhaust gases are NOx,SOx,and CO,which are hazardous compounds for human health[3,5].To solve the worsening ecological crisis,people have strived to develop novel technologies to capture the toxic gases for a post-processing of air purification[6].Physical adsorption is one of the effective ways to prevent the release of toxic gases in the air due to its low energy consumption,convenient reuse of adsorbentand simple technological design[7].Numerous studies on the physical adsorption of toxic gases,including NH3[8–12],H2S[13–16],SO2[15,17],NO[17],and CO[18],were reported.

Zeolites,which have been used broadly in chemical industry as adsorbents or catalysts,are promising materials for the separation or storage of gas due to their large surface area,abundant pore structure and high thermal stability[2,19–22].Experimentally,the preparations of all zeolite materials and the measurements of adsorption capacity of the zeolites on toxic gases are time-consuming and expensive.Therefore,researchers conducted some non-experimentalmethods for material design,such as molecular simulation[15,17],and classical density functional theory(CDFT)[23,24].To rationally design good zeolite structures to capture toxic gases,we conducted molecular simulations,which have achieved tremendous successes in gas adsorption and separation,to examine the adsorption behaviors of six toxic gases on 95 kinds of all-silica zeolites.

Numerous computational studies regarding adsorption and diffusion of small molecules on zeolites have been reported[16–18,22,25–27].To remove the sulfur from a sulfur-containing mixed gas,Shah etal.[16]performed Gibbs ensemble Monte Carlo(GEMC)simulations to investigate the adsorption behaviors of binary mixtures containing H2S and CH4on seven all-silica zeolites,viz.CHA,DDR,FER,IFR,MFI,MOR,and MWW.Their simulation results revealed that except for MOR,the other zeolites have an increasing selectivity in H2S as the H2S concentration increases due to favorable sorbate-sorbate interactions.Sun et al.[17]computationally studied the adsorption behaviors of SO2,NO2,and NO on four all-silica zeolites,viz.LTA,FAU,DDR and MFI,and found that the loading of the three gases on the four zeolites at 313 K and 100 kPa is ranked as SO2＞NO2＞NO.Many experiments have also been conducted to study the properties of different zeolites and use their excellent properties to apply to industry process[18,21,28,29].Maghsoudi et al.[29]investigated selectivities for H2S over methane on zeolite CHA,and their results show that this zeolite has good performance to remove acid gases,such as H2S,from methane.Therefore,it can be regarded as a promising candidate to be utilized as a zeolite membrane for the removal of acid gases from methane.And they found that all-silica zeolites could perform well to adsorb acid gases even in the presence of water due to their hydrophobic nature.By combining experiments and simulations,Matito-Martos et al.[2]investigated the capture of SO2,CO2and COby differentzeolites as well as the separation processes of these gas mixtures.These studies much more concerned on selectivity of gases in several specific zeolites,however,to the bestofourknowledge,there are rare results aboutscreening large number of zeolites to remove toxic gases.By using both experiments and simulations,Matito-Martos et al.[2]screened zeolites for the removal of SO2.

In this paper,95 all-silica zeolites were selected to remove six toxic gases,including H2S,SO2,NO,NO2,CO and NH3,through computational screening.We aimed to screen zeolites with high adsorptive performance and determined the relationship between the adsorption behavior and the zeolite structure.

2.Simulation Details

Structures of the 95 all-silica zeolites are from International Zeolite Association(IZA)[30]and theirpores'geometry and topology are calculated using Zeo++codes[31].The pore void space,which is crucial for the identification the type of zeolite structures can be determined through a given probe of 0.14 nm to access the surface of zeolites[31].Relevant importantparameters regarding zeolites,such as the diameter of the largest included sphere(Di),the largest free sphere(Df),and the largest included sphere along the free sphere path(Dif),accessible surface area(SASA)which means the surface area of zeolites that adsorbate molecules can access except for the closed pores,and void fraction(VF),is exhibited in Table S1,and the distributionsofpore diametersofthe 95 all-silica zeolites are listed in Table S2.According to the dimensionality of pore,the zeolite structures can be classified into six classes:1D channels,2D channels,3D channels,1D interconnected cages,2D interconnected cages and 3D interconnected cages[2].The distributions of pore diameters of the zeolites are calculated following the methods of reference 31,the value of SASAand VF is obtained in the InternationalZeolite Association(IZA)[30].

Rigid molecular models are adopted for the 95 all-silica zeolites,implying that the silicon and oxygen atoms arefixed on the original crystallographic positions[32–35].The interactions of zeolite and gas are approximated as a sumofpair interactions between allthe atoms.However,since silicon atoms are less polar and surrounded by oxygen atoms,pair interactions between zeolite and gas are calculated effectively by taking the energies within the oxygen atom and gas into account[36].The parameters of zeolites,H2S,SO2,NH3,NO2,NO,and CO are from the work of Gutiérrez-Sevillano[13],Sokoli?[37],Eckl[38],Bourasseau[39],Zhou[40],and Sirjoosingh[41],respectively.These parameters are optimized from experimental data or proven to work well on the gas adsorption.We also listed them on Table S3 of Supporting Information.

Grand canonicalensemble Monte Carlo(GCMC)simulations are carried out at 298 K to predict the adsorption isotherms of six toxic gases on the all-silica zeolites.Chemical potential is computed on a basis of component fugacity of bulk phase according to the equation of state.We considered the six gases as ideal gases,so their fugacity equal to their pressures.The loading L(mmol·g-1)of a gas on a zeolite,which refers to the absolute adsorbed amount,is calculated by the following equation

where Mzeolitesis the relative molecular mass of single unit cell,and Ngas(molecules/unit cell)is the number of adsorbates in single unit cell,Here,L refers to the amount of adsorption of gas in a gram of zeolite.Nzeolitesequals to 1 which represented to a molecule of the specific zeolite.All simulations were implemented in the MuSiC code[42–45].Please see more details of modeling in Supporting Information or our previous work[46].

3.Results and Discussion

The adsorbed behaviors of zeolites for six toxic gases were investigated,and the data was summarized in Supporting Information(SI2).In the following sections we chose two typical states to discuss the adsorption capacity of zeolites,i.e.atmospheric pressure adsorption and saturated adsorption.And more data from low pressure(about 0.01 kPa)to high pressure(＞1000 kPa)at 298 K are provided in Supporting Information(SI2 file).So the adsorption capacity of zeolites is still screened by any specific pressure concerned by readers based upon our works.

3.1.Screening of the top-10 zeolites for toxic gases removal

We found that the loading of SO2,H2S and NH3are around 1–12 mmol·g-1while the loading of NO2,NO and CO are 0.1–0.7 mmol·g-1at room temperature and atmospheric pressure.

Firstly,the adsorption capacity was investigated at 100 kPa and 298 K to examine the capture ability ofthe 95 zeolites to each individual gas,viz.SO2,NH3,H2S,NO2,NO and CO.Ranking the simulated results of all the zeolites,we obtained ten zeolite structures with the maximum loading to each individual gas,as listed in Fig.1.Analysis of adsorption amount of the six gases on their respective top-10 zeolites revealed that the SO2has the largest loading amount(6–12 mmol·g-1)on the zeolites at room temperature(298 K)and one atmospheric pressure(100 kPa),then followed by NH3and H2S with a loading of around 4–10 mmol·g-1.The zeolites exhibita relatively-low efficiency in the capture of the gases NO2,NO and CO at 100 kPa and 298 K due to the small loading(＜1.5 mmol·g-1).Through examining the top-10 zeolites ofthe six gases(Fig.1),we identified two kinds of zeolite structures,viz.AFY and PAU,that both exhibit good capability to capture all the toxic gases.

Besides the intrinsic factors of zeolites,such as pore's structures,sizes and distributions,the dependence ofthe adsorption capacity ofzeolites on the kinetic diameters and dipole moments of the six gases was determined and shown in Table S4.The kinetic diameters of H2S,NO2,NO and CO are around 0.35–0.4 nm,while that of NH3is 0.29 nm which is a little smaller than the other gases(Table S4).It indicated that,compared to H2S,NO2,NO and CO,NH3is easier to be adsorbed by zeolites.In addition,dipole moment is another factor to determine the adsorption properties of gas on zeolites.All-silica zeolites with a dipole moment of 2.123 Debye have a strong preference to the gas with high dipole moment.As seen in Table S4,the gas SO2has the highestdipole moment of 1.633 Debye,then followed by NH3(1.472 Debye),H2S(0.978 Debye),NO2(0.316 Debye)and NO(0.158 Debye).The gas CO with the lowest dipole moment of 0.110 Debye,therefore,is difficult to be adsorbed on the zeolites at 298 K and 100 kPa.Furthermore,we calculated the adsorption energies of the six gases SO2,NH3,H2S,NO2,NOand COon the zeolites at298 Kand 100 kPa,and theircorresponding values are-30.21,-31.75,-27.98,-18.22,-13.80 and-10.33 kJ·mol-1,respectively.The same conclusions were found in the computational work by Matito-Martos[2]and Sun[17].Matito-Martos et al.[2]reported that at 298 K,SO2has a larger adsorption heat than CO,which is identical with our calculations for the adsorption energies of SO2and CO.Meanwhile,the zeolite AFY was found to be a good adsorbent to the gas SO2in our simulations(Fig.1a),which was verified in the Matito-Martos'work.Sun[17]examined the adsorption of the gases SO2,NO2and NO on zeolites,and ranked the loading capacity ofthe three gases as SO2＞NO2＞NO.These findings are also in agreement with our simulation results.

Fig.1.Top-10 zeolites with the maximum loading to the six gases(a)SO2(b)NH3(c)H2S(d)NO2(e)NO and(f)CO at 100 kPa and 298 K.

Next,we studied the adsorption behaviors of the six gases on the 95 zeolites at room temperature(298 K)and saturated pressure.It should be noted that different gases have different saturated pressures.The saturated adsorption of SO2,NH3and H2S is closed to 200,400 and 400 kPa at 298 K,respectively,while the pressures for the saturated adsorption of NO2,NO and CO are increased up to 10000,20000 and 30000 kPa,respectively,at same condition.Fig.2 shows the top-10 zeolites with the maximum saturated adsorption to the gases SO2,NH3,H2S,NO2,NO and CO.Examination of these top-10 zeolites yields five promising zeolites,viz.RWY,IRR,JSR,TSC and ITT,which were found in the simulations to have the maximum loading to the six gases.

Fig.2.Top-10 zeolites with the maximum loading to the six gases(a)SO2(b)NH3(c)H2S(d)NO2(e)NO and(f)CO at 298 K and saturated adsorption.

Structuralanalysis of the five promising zeolites revealed that atsaturated adsorption,SASAand VF of pore of the zeolites are two primary factors in controlling the loading of the gases.As seen in Table S1,a large SASA(1300–2700 m2·g-1)and a high VF(0.25–0.46)are observed for the zeolites RWY,IRR,JSR,TSC and ITT,especially for RWY with the largest SASAof 2656.48 m2·g-1and the highest VF of 0.4553.Moreover,the structures of all the top 10 zeolites belong to the 3D channel or 3D interconnected cage(Table S1).However,the absolute adsorption of each gas performed differentresults in the same adsorbent.The average interaction energies of adsorbate–adsorbate of top 10 adsorbents for SO2,NH3and H2S are about-8.66,-2.65 and-1.94 kJ·mol-1at saturation adsorption,respectively.But interactions of adsorbate–adsorbate for NO2,NO and CO are weak and the values are-0.15,-0.056 and-0.017 kJ·mol-1,respectively.This is the reason why CO is dif ficultly adsorbed into zeolites compared to other gases,so the saturated adsorption of CO has a higher pressure(higher than 30000 kPa at 298 K).

In general,among the 95 zeolites,AFY and PAU are the best candidates for the removal of these gases at room temperature and atmospheric pressure.For saturation adsorption,RWY,IRR,JSR,TSC and ITT are the best candidates for storage of these gases at room temperature and high pressure.In addition,we found that AFY,PAU and RHO are best candidates for the removal of acid gases(H2S,SO2and NO2)at room temperature and atmospheric pressure.NPT is a good candidate for the alkaline gas(NH3)removal,whereas DDR is a good candidate for the neutral gases(NO and CO)removal.

3.2.Adsorption isotherms of toxic gases on top-10 zeolites

Fig.3.The adsorption isotherm of(a)SO2,(b)NH3,(c)H2S,(d)NO2,(e)NO,and(f)CO on the top-10 zeolites with the maximum gas loading at 100 kPa and 298 K.

Fig.3 shows the adsorption isotherm of six toxic gases in top 10 zeolites at 100 kPa and 298 K.The adsorption isotherms of H2S,NO2,NO,CO and most adsorption isotherms of SO2and NH3are type I isotherms,i.e.Langmuir adsorption isotherm,because these gases are easily adsorbed on the surface of pore on these candidate zeolites.The initial partofthe type Iisotherm represents porefilling due to the strong interaction between the adsorbed gases and adsorbent.Note that there are three types of adsorption isotherms for the adsorption of SO2in zeolites(Fig.3a).The adsorption isotherms ofSO2in RWY,JSR and IRRbelong to type V isotherm because of the weak adsorbate–adsorbent interaction.In the six selected gases,SO2has strongest interaction with zeolites,so it can be adsorbed in RWY and IRR whose primary pore diameters of 1.4 nm and 1.39 nm are larger than the other zeolites'pore diameter.The adsorption isotherms of SO2in TSC and ITT belong to type IV isotherm,and the characteristic of this isotherm is that there are two peaks in the isotherm as shown in Fig.3a.Two primary pore diameters of TSC and ITT are 1.01 nm and 1.58 nm,and 1.21 nm and 1.27 nm,respectively.So SO2can be slightly adsorbed in the smaller pore at low pressure and be further adsorbed in the bigger pore at relatively high pressure.The adsorption isotherms of SO2in AFY,LTA,and KFI belong to type I isotherm,and the primary diameters are smaller than the zeolites mentioned above,which are 0.74 nm,1.02 nm and 1.01 nm,respectively.In particular,SO2is much more adsorbed in AFY at about 10 kPa which is lower than others,because the primary diameter of AFY is the smallest and the interaction between SO2and AFY is the strongest.Regarding the NH3,the adsorption isotherm of NH3in NPT belongs to type V,while other isotherms are type I isotherms.That is due to the strongest interaction between SO2and zeolites just for the size of SO2who has the largest kinetic diameter(0.411–0.429 nm)and dipole moment(1.63 Debye).

As shown in Fig.4a–c,the screening zeolites are most the same materials for SO2,NH3and H2S at saturated pressure,but the adsorption isotherms have differentbehaviors.There are severalisotherms thatobviously belong to type V isotherm,such as the adsorption isotherm of SO2,NH3,and H2S in RWY,TSC and ITT because these three gases are rapidly adsorbed into small size pore due to stronger interacions with pore surface of zeolite,and then the molcules are pushed into large size pore with increasing of pressure.There are still type I adsorption isotherms for NO2,NO and CO(Fig.4d–f)because their interactions with zeolites are much weaker than other three gases,hence,higher pressure is needed to approach the saturation adsorption,especially for CO.

3.3.The effect of geometry of zeolites on capture ability to toxic gases

Fig.4.The adsorption isotherm of(a)SO2,(b)NH3,(c)H2S,(d)NO2,(e)NO and(f)CO on top-10 zeolites with the maximum saturated adsorption at 298 K and saturated pressures.

Fig.5.Loading of the gases(a)SO2,(b)NH3,(c)H2S,(d)NO2,(e)NO and(f)CO vs.Accessible Surface Area(S ASA)and Void Fraction(VF)ofthe 95 zeolites at298 K and 100 kPa.The size of bubble re flects the loading amount of gas on a zeolite.In other word,a large bubble size at a certain S ASA and VF indicates that the zeolite corresponding to the S ASA and VF has a high adsorption capacity to gas.The zeolite structures with best performance in capturing each individual gas at 298 K and 100 kPa are present on the right.Important geometric parameters and pore information regarding the best zeolite are shown as well at the bottom.

Fig.5 and Fig.S1 present a comprehensive overview of the six gases SO2,NH3,H2S,NO2,NO and CO captured by the 95 all-silica zeolites at room temperature and an atmospheric pressure,and at saturated adsorption.We analyzed the relationship of adsorption behavior with the zeolite structures for the 6 toxic gases in the following discussions.In addition,it is screened that the zeolites with good adsorption performance fortoxic gases atroom temperature and atmospheric pressure or saturated adsorption.In Figs.5 and S1,the size of the bubble represents the loading of toxic gases in zeolites,the bigger the bubble,the greater the loading capacity.In Figs.6 and S2,the color of plot represents the storage value of each toxic gas in zeolites,with blue representing the lowest value and red representing the highest value.In order to design new zeolites to remove toxic gases,these 2D color filled contourplots of SO2,NH3,H2S,NO2,NO,and CO based upon simulation results at 298 K and 100 kPa,and at 298 K and saturated adsorption,respectively.The adsorption performance of new zeolites would be predicted from these plots through the value of SASAand VF which are the primary factors to impact the adsorption behavior of toxic gases.And the detail information of zeolites including primary pore diameter,SASAand VF are also listed in the Tables S1–S2.

The zeolite with best performance to remove SO2is RWY which is the biggest bubble in Fig.5a representing the large loading of 11.78 mmol·g-1and its structure is shown at the right side of Fig.5a.The channel system of RWY is 3D interconnected supercage 1.4 nm as shown at the right side of Fig.5a.SO2is easily captured in these supercages at atmospheric pressure.Fig.S1a has similar performance as Fig.5a,because the pressure of SO2atsaturation adsorption is nearby 200 kPa.And then RWY is still the highest SO2storage capacity of 16.24 mmol·g-1as the biggest bubble as shown in Fig.S1a.As Fig.6a shown for the SO2removal,the best zeolites contain VF up to 0.25 and SASAof 1700–2700 m2·g-1at atmospheric pressure.And geometric effects of adsorptions for the zeolites have the similar features to remove SO2with larger pore diameter,higher SASAand bigger VF such as RWY,IRR and TSC at saturated adsorption shown in Fig.S2a.

The bubble plotof Fig.5b is performance for the removalofNH3.The highest loading zeolite is NPT about 7.5 mmol·g-1as the biggest bubble.The structure of NPT is a 3D interconnected cage whose primary pore diameter,SASA,and VF of NPT are 0.55 nm,2051.51 m2·g-1and 0.1905,respectively.Because the size of NH3is the smallest(0.29 nm)in six toxic gases,so the pore diameter of adsorbent in demand is smaller than other gases.And then it can be well adsorbed in NPT containing smaller cage.However,the best candidate is RWY because it contains the biggest SASAand VF in all zeolites at saturation adsorption as shown in Fig.S1b.The RWY has the highest NH3storage capacity of 27.9 mmol·g-1,whereas other 9 best candidates are 10–14 mmol·g-1.Fig.6b shows that the good adsorption performance of zeolites to remove NH3contains SASA1700–2300 m2·g-1and VF 0.15–0.25 at 100 kPa and 298 K.But geometric effects of saturation adsorption have different performances compared with the condition of atmospheric pressure as shown in Fig.S2b.The SASAand VF of zeolites with the good adsorption performance are up to 2000 m2·g-1and 0.3,respectively.

The bubbles in Fig.5c represent the loading of all zeolites to remove H2S.The top 3 zeolites of H2S adsorption are AFY,PAU,and MER with loading 7.8,5.5 and 5.4 mmol·g-1,respectively.The AFY performs best to remove H2S at atmospheric pressure whose primary pore diameter,SASAand VF are 0.74 nm,1773.41 m2·g-1and 0.2188,respectively.AFY has 3D channel as shown in Fig.5c,so H2S can be inserted in AFY from three sides.PAU has different pore sizes,and the primary pore diameter is 0.62 nm which accounts for 49.1%in pore size distribution.Its SASAand VF are 1477.60 m2·g-1and 0.1239,respectively.The remaining 7 zeolites adsorbed H2S with loading of 4–4.8 mmol·g-1.The trend ofbubble plots of H2S as shown in Fig.S1c is similar to the adsorption performance of NH3as described in Fig.S1b.Fig.6c shows that SASAspanning 1500 m2·g-1to 2000 m2·g-1and VF ranging from 0.2 to 0.27 have better performance than others to remove H2S at 298 K and 100 kPa.The geometric effects of all zeolites to remove H2S at saturated adsorption are shown in Fig.S2c,which shows that zeolites with SASAand VF up to 1700m2·g-1and 0.3 are good candidates to remove H2S.In top 10 zeolites at saturation adsorption,RWY exhibits the highest H2S storage capacity with 17.74 mmol·g-1,and other 9 zeolites have 8–10 mmol·g-1for H2S adsorption.AFY performs well with adsorption at low and high pressure because it not only contains relatively smaller pore diameter of 0.74 nm,butalso has high SASAof 1773.41 m2·g-1and VF of 0.2188.

Fig.6.Panels show that the variations of the S ASA and VF lead to the changes on the gas loading of(a)SO2,(b)NH3,(c)H2S,(d)NO2,(e)NO and(f)CO at 298 K and 100 kPa.

The bubbles of Fig.5d–f described the loading of NO2,NO and CO in all zeolites.As shown in Fig.5d–e,the biggest bubble is DDR whose structure is also described in the same figure.The structure of DDR is 2D channel that toxic gases can only access to it from two sides.In fact the SASAand VF of DDR are smaller than other zeolites screened for SO2,NH3and H2S at room temperature and atmospheric pressure.The reason is that the loading of NO2and NO at room temperature and atmospheric pressure is small and DDR can perform well to remove them although its SASAand VF are not large.And the adsorption of NO2and NO in top 10 zeolites at 100 kPa and 298 K is in range of 0.7–1.2 mmol·g-1and 0.3–0.7 mmol·g-1,which DDR has highest loading about 1.23 mmol·g-1and 0.68 mmol·g-1,respectively.Fig.5f showed that AFY performed best to remove CO which is the biggest bubble.And the adsorption ofCOin top 10 zeolites at100 kPa and 298 Kis in range of 0.14–0.19 mmol·g-1.The trend of bubble plots of NO2,NO and CO as shown in Fig.S1d–f is similar to the adsorption performance of NH3as described in Fig.S1b.Fig.6d–e shows that zeolites containing VF 0.1–0.15 and SASA1200–1800 m2·g-1have good adsorption performance to remove NO2and NO at atmospheric pressure.Zeolites containing VF 0.2–0.25 and SASA1500–2000 m2·g-1have good adsorption performance to remove CO atatmospheric pressure as shown in Fig.6f.Atsaturation adsorption,zeolites with SASAup to 1700m2·g-1and VF up to 0.3 perform well to remove NO2,NO and CO as shown in Fig.S2d-f.

Therefore,RWY exhibits the highest storage capacity and is the biggest bubble due to its largest loading each gas at saturated adsorption.One can conclude that whatever the adsorbed gas is,zeolites containing SASAand VF up to 1500 m2·g-1and 0.3 have good adsorption performance at saturated adsorption.From the above discussion SASAand VF are important factors to in fluence the adsorption performance of zeolites for new zeolite design.

4.Conclusions

We used molecular simulations to investigate the adsorption of H2S,SO2,CO,NO,NO2and NH3in 95 zeolites and screened top 10 zeolites for the removalofeach gas at298 K with 100 kPa orsaturated pressure.Our calculations showed that AFY and PAU performed well for the removal of all selected gases at ambient temperature and pressure.Zeolites with good performance to remove all selected gases according to saturation adsorption are RWY,IRR,JSR,TSC and ITT.At ambient temperature and pressure,the interaction between SO2and zeolites are the strongest in all selected gases due to its biggest kinetic diameter and largest dipole moment,and zeolites with small primary pore diameter and large SASAperformed well to remove all selected gases except for SO2.Moreover,zeolites with 3-dimensional structure,large SASAand VF worked wellforthe removalofallselected gases when gases reached to saturation adsorption.

Supplementary Material

The information of zeolites structures are provided in the word file(SI).The detail parameters of force field of zeolites are summarized.And the properties of zeolites structures are still found in SI,such as pore diameters,accessible surface area,pore volume ratio and the type of pore channel.All these simulation results of the adsorptions are in excel file(SI2).Supplementary data to this article can be found online at https://doi.org/10.1016/j.cjche.2018.02.025.