[Article]
www.whxb.pku.edu
物理化学学报(Wuli Huaxue Xuebao )
Acta Phys.⁃Chim.Sin .2012,28(9),2108-2114
September
Received:April 26,2012;Revid:June 18,2012;Published on Web:June 18,2012.∗
Corresponding author.Email:junwang@njut.edu;Tel:+86-25-83172264;Fax:+86-25-83172261.thq
The project was supported by the National Natural Science Foundation of China (21136005,21101094,20976084).国家自然科学基金(21136005,21101094,20976084)资助项目
ⒸEditorial office of Acta Physico ⁃Chimica Sinica
doi:10.3866/PKU.WHXB 201206181
无有机模板剂水热合成Co 同晶取代的丝光沸石分子筛
王
琦1
吴雅静2
王
军1,*
林晓1
(1南京工业大学化学化工学院，材料化学工程国家重点实验室，南京210009;2
南京工业大学理学院，南京210009)
摘要:
在硅酸钠、硫酸铝、硝酸钴和氢氧化钠的全无机体系条件下，采用无有机模板剂水热法合成了Co 同晶
取代的丝光沸石分子筛.通过粉末X 射线衍射(XRD)、扫描电子显微镜(SEM)、电感耦合等离子体(ICP)光谱、氮气吸附、紫外-可见(UV-Vis)光谱、热重(TG)分析等手段对所得固体产物的织构性质以及钴在分子筛中的存在状态进行了表征.结果表明，该方法成功地将Co 离子引入到丝光沸石分子筛的骨架结构中，未发现骨架外Co 物种.典型的合成条件为n (Co)/n (SiO 2)=0.01-0.04,n (SiO 2)/n (Al 2O 3)=20-50,n (H 2O)/n (SiO 2)=40,n (Na 2O)/n (SiO 2)=0.4，晶化温度170°C，晶化时间3-7d.讨论了Na +离子在无有机模板剂合成中的结构导向作用.全无机体系合成得到的产物无需进行传统的高温煅烧处理，即可获得开放的微孔孔道，实现了低成本、低能耗、环境友好的Co-丝光沸石的合成.关键词:
微孔材料；化学合成；晶体生长;X 射线衍射；杂原子沸石
happy meals中图分类号:
O643.36
Organotemplate-Free Hydrothermal Synthesis of Isomorphously
Co-Substituted Mordenite Molecular Sieve
WANG Qi 1
WU Ya-Jing 2
WANG Jun 1,*
LIN Xiao 1
(1State Key Laboratory of Materials-Oriented Chemical Engineering,College of Chemistry and Chemical Engineering,Nanjing University of Technology,Nanjing 210009,P .R.China ;2College of Sciences,Nanjing University of Technology,
Nanjing 210009,P .R.China )Abstract:An organotemplate-free hydrothermal route was investigated for synthesizing isomorphously Co-substituted mordenite molecular sieve using only the inorganic raw materials such as sodium silicate,aluminum sulfate,cobalt nitrate,and sodium hydroxide.Textural properties and Co ion states for the obtained solid products were characterized by powder X-ray diffraction (XRD),scanning electron microscope (SEM),inductively coupled plasma (ICP),nitrogen adsorption,ultraviolet-visible (UV-Vis)spectra,and thermogravimetric (TG)analysis.The results showed that Co ions were incorporated into the framework structure of the mordenite without the prence of extra-framework Co species.Typical synthesis conditions were n (Co)/n (SiO 2)=0.01-0.04,n (SiO 2)/n (Al 2O 3)=20-50,n (H 2O)/n (SiO 2)=40,n (Na 2O)/n (SiO 2)=0.4,crystallization temperature 170°C,and crystallization time 3-7d.The structure-directing function of Na +ions in the a
bnce of an organic template was discusd.Products obtained by the prent all-inorganic systems posss open micropores and do not require traditional high-temperature calcination.Thus,we demonstrate a low cost,low energy consumption,and environmentally benign synthesis of Co-mordenite.
Key Words:Microporous material;Chemical synthesis;
Crystal growth;X-ray diffraction;
Heteroatomic zeolite
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1Introduction
Zeolite materials have been widely ud as catalysts,ion-ex-changers,and adsorbents due to their uniform micropores,high surface areas,adjustable acidities,and stable structures.Incor-poration of tra
培森
nsition metals like Fe,Ti,Ni,Co,or V into zeo-lites may cau new applications.1-5Particularly,Co-containing zeolites have attracted attention becau they are efficient cata-lysts for reduction of NO x,6,7Fischer-Tropsch reaction,8,9and -lective oxidation of alkanes.10,11However,in most of previous efforts,Co atoms were introduced into zeolites by impregna-tion and ion-exchange.In order to obtain single and highly dis-perd Co sites without blocking the intrinsic micropores of ze-olites,isomorphous substitution of Co ions into zeolite frame-work via a direct hydrothermal synthesis becomes an interest-ing topic.Nowadays,some framework-substituted Co-alumino-phosphate(CoAPO)molecular sieves have been synthe-sized,12-14nevertheless,only a few Co-substituted aluminosili-cate zeolites have been reported,such as MFI(mobil fifth), BEA(beta),ANA(analcime),and PHI(phillipsite)zeolites.15-17 Mordenite(MOR)has been widely applied in petroleum in-dustry for isomerization,dewaxing,and alkylation,18,19but Co-mordenite has been scarcely reported.Kato et al.20success-fully synthesized a Co-mordenite by a dynamic hydrothermal treatment with a cobalt-ethylenediamine-N-monoacetic acid complex as the cobalt source.On the other hand,synthesizing heteroatomic zeolites always employs organic templates as the structural directing agencies.21-26For catalytic utilizations,the organic templates have to be removed by a high-temperature calcination so as to obtain the prerequisite open micropores. Conquently,the high-temperature treatment results in envi-ronmental pollution,large energy consu
mption,and high cost.27,28 In earlier studies,Fe-and Zn-containing mordenites were ob-tained by a conventional static hydrothermal synthesis using so-dium silicate as the silica source in the prence of organic tem-plates.29,30Moreover,an organotemplate-free synthesis could cau the produce of Fe-mordenite,still needing the dynamic hydrothermal condition.31Although Kato et al.20did not u an organic template in the synthesis of Co-mordenite,as men-tioned above,the rearch on the organotemplate-free synthe-sis is insufficient due to the demand of dynamic operation and the u of the organic-containing cobalt source.
Herein,we report a direct static hydrothermal route for the incorporation of Co ions into the framework of mordenite with sodium silicate,aluminum sulfate,and cobalt nitrate as raw ma-terials,and sodium hydroxide as the pH-adjusting agency,in the abnce of any organic compounds,eds,and pretreat-ments.The obtained products are complementarily character-ized.
2Experimental
2.1Synthesis
The hydrothermal synthesis of framework-substituted Co-mordenite in the abnce of organic templates and eds was carried out with the following procedures.Under vigorous stirring,10.51g of
sodium silicate(w(SiO2)=56%,w(Na2O)= 20%,AR,Wako,Japan)was added and dissolved into the aque-ous solution containing0.44g of sodium hydroxide (w(NaOH)=96.0%,AR,Wuxi Yasheng Chem.Ind.Com.Ltd.) and40g of deionized water to obtain solution A.Solution B was made by adding1.65g of aluminum sulfate(w(Al2(SO4)3·18H2O)=99%,AR,Shantou Xilong Chem.Ind.Com.Ltd.)into 10g of deionized water,and solution C was gotten by adding 0.29g of cobaltous nitrate(w(Co(NO3)2·6H2O)=99%,AR, Shantou Xilong Chem.Ind.Com.Ltd.)into10g of deionized water.Then,solutions B and C were added successively into solution A under stirring to give the gel mixture with a molar composition n(Na2O):n(SiO2):n(Al2O3):n(Co(NO3)2):n(H2O)=0.4: 1:0.025:0.01:40,which was stirred further at ambient tempera-ture for2h.Finally,the slurry was transferred to a Teflon-lined stainless steel autoclave and left to crystallize statically at170°C for3d.The resultant solid from the synthesis was parated by centrifugation,followed by washing with deionized water and air-drying at70°C for12h.
In the synthesis gels,the contents of Al2(SO4)3and Co(NO3)2 were changed(n(SiO2)/n(Al2O3)=20-100,n(Co)/n(SiO2)=0-0.05)to investigate the applicability of the prent new synthe-sis route,with otherwi conditions unaltered.The pure morde-nite sample,ud as the reference material in this study with a suppod100%crystallinity,was prepared according to the above procedures from a Co-
free gel mixture with molar com-position n(Na2O):n(SiO2):n(Al2O3):n(H2O)=0.4:1:0.025:40.The relative crystallinities of Co-mordenite samples were calculat-ed by comparing the summed intensity of the X-ray diffraction (XRD)peaks featured for MOR at2θvalues of6.5°,8.7°,9.7°, 13.5°,15.3°,19.6°,22.3°,25.7°,26.4°,and27.6°with that of the reference material.For comparison,colloidal silica(HS-40, Aldrich)was also ud as the silica source in the organotem-plate-free synthesis.
2.2Characterization
Powder X-ray diffraction(XRD)patterns were collected on the powder diffractometer(Bruker D8Advance,Germany)us-ing Ni-filtered Cu Kαradiation source(λ=0.1542nm)at40kV and40mA with a scanning speed of0.02(°)·s-1.The unit cell parameters of the synthesized zeolites were calculated by XRD curves.32Co,Al,and Si contents were determined by an induc-tively coupled plasma(ICP)spectrometer(PerkinElmer Jar-rell-Ash1100,America).BET surface areas were evaluated with nitrogen sorption isotherms using an automatism isother-mal adsorption instrument(Micromeritics ASAP2010,Ameri-ca)at77K.Scanning electron microscopy(SEM)images were characterized on an instrument(ThermoNicolet Quanta200 FEI,America).The UV-Vis spectra were obtained using a spec-trophotometer(PerkinElmer PE Lambda950,America) equipped with a di
ffu reflectance attachment.Thermogravi-metric(TG)analysis was carried out on an instrument
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(NETZSCH STA 409PC,Germany)using a Pt pan,with the heating temperature from 35to 800°C at a heating rate of 10°C ·
min -1
.
3Results and discussion
3.1Influence of n (Co)/n (SiO 2)ratios
Fig.1shows the XRD patterns for the Co-mordenite samples synthesized with various n (Co)/n (SiO 2)ratios in starting gels,with otherwi similar conditions.The Co-free sample exhibit-ed a t of diffra
ction peaks well assignable to the MOR struc-ture,19without detecting other crystalline phas.Moreover,all the Co-containing samples gave the same peaks as tho of the pure mordenite,while peak intensities decread with the in-crea of n (Co)/n (SiO 2)ratios.
Table 1lists unit cell parameters,crystallinities,and BET surface areas for the samples synthesized with various n (Co)/n (SiO 2)ratios in starting gels.The Co loadings in final solid products were lower than the concentrations in starting gels,in-dicating that not all the cobalt species could be incorporated in-to the solid products.Meanwhile,the Co loadings in the solids incread gradually with the ri of n (Co)/n (SiO 2)ratios in starting gels up to 0.04(entries 1-5).More importantly,the unit cell volumes incread monotonically with the increa of n (Co)/n (SiO 2)up to 0.04,which is indicative of the inrtion of
Co ions into the TO 4(T denotes tetrahedrally bonded cation)framework sites of MOR structure.This consists with the much larger radii of Co ions (0.0745nm)than that of Si 4+(0.040nm).The increa of Co contents caus a gradual de-crea in crystallinities,which is probably caud by the distor-tion of TO 4tetrahedron due to the inrtion of Co ions.At a very high n (Co)/n (SiO 2)ratio of 0.05,the unit cell volume de-cread obviously (entry 6),still corresponding to the drop of the n (Co)/n (SiO 2)ratio in solid product.It is thus drawn that the molar ratio 0.04for n (Co)/n (SiO 2)in the starting gel i
s an upper limit to produce Co-mordenite.
The typical sample of entry 4was ion exchanged with aque-ous solution of NH 4Cl (2mol ·L -1)at 90°C for 3h and then calcined at 550°C for 3h.This procedure was repeated three times,and the resultant sample was analyzed by ICP.The treat-ed sample gave n (SiO 2)/n (Al 2O 3)=24.1and n (Co)/n (SiO 2)=0.021,very clo to tho for the untreated one,strongly indi-cating that the Co ions in MOR framework are rather stable.Ratios of n (SiO 2)/n (Al 2O 3)are also listed in Table 1.Much lower n (SiO 2)/n (Al 2O 3)ratios of around 20were obrved for the final solid products compared with the constant value of 40in starting ,the increa of Co loadings did not signifi-cantly influence the amount of Al ions incorporated in MOR framework.This result may be relative to the condition of n (Na 2O)/n (SiO 2)=0.4,a high alkalinity ud for the hydrother-mal synthesis.
BET surface areas and micropore volumes in Table 1show that the pure mordenite had a high surface area of 434m 2·g -1,and the Co-mordenites also possd considerably high sur-face areas of around 350m 2·g -1.This strongly demonstrates the existing of open micropores for the organotemplate-free synthesized samples.The micropore volumes for Co-morde-nite samples were only slightly lower than that of the pure mor-denite,which may ari from the lower crystallinities of Co-mordenites due to the isomorphous substitution of the large Co ions in the MOR framework.
The thermal properties for the pure mordenite and the lect-ed Co-mordenite sample (n (Co)/n (SiO 2)=0.03)were tested by the TG analysis,as shown in Fig.2.The gradual mass loss up to 350°C for the two samples due to water desorption is
very
1XRD patterns for the Co-mordenites synthesized with various n (Co)/n (SiO 2)ratios in starting gels
conditions:n (SiO 2)/n (Al 2O 3)=40,n (H 2O)/n (SiO 2)=40,T =170°C,t =3d;n (Co)/n (SiO 2):(a)0,(b)0.01,(c)0.02,(d)0.03,(e)0.04,(f)0.05
Table 1Textural properties for the Co-mordenites synthesized with various n (Co)/n (SiO 2)ratios in starting gels
a molar ratios analyzed by ICP,
英语演讲下载b relative crystallinities,
c micropore volume calculate
d according to thon and on
e difference between the total and mesopore volumes using BJH method,d silica sol instead o
f sodium silicate was ud as the silica source while 0.1%(w )mordenite crystalline ed was added in the startin
g gel.
conditions:n (SiO 2)/n (Al 2O 3)=40,n (H 2O)/n (SiO 2)=40,T =170°C,t =3d
Entry 1234567
d
n (SiO 2)/n (Al 2O 3)gel 20404040404040
solid
a
17.524.018.524.819.724.523.9
n (Co)/n (SiO 2)gel 00.010.020.030.040.050.01
roughsolid a
-0.0060.0150.0200.0250.0150.004
Unit cell parameters
a /nm 1.74101.74811.75241.75611.79591.73361.7852
b /nm 1.98431.98351.98951.99162.03521.94322.0282
c /nm 0.73770.73770.73770.73780.74420.74010.7453
V /nm 32.54842.55792.57192.58032.72002.49312.6985
Crystallinity/%b
10010078666961100
S BET /(m 2
·g -1)434311422399350408319
V mic /(cm 3
·g -1)c
0.16780.15970.14860.14200.13090.13690.1344
2110
WANG Qi et al .:Organotemplate-Free Hydrothermal Synthesis of Isomorphously Co-Substituted Mordenite
pasrby的中文是什么
No.9
distinguished from the drastic decea at 420-520°C due to the decomposition of the involved organic templates for the template-synthesized mordenite.33This confirms that the sam-ples prepared herein do not bear any organic species,needless to be subjected to a high-temperature calcination.
UV-Vis spectra provide convincing evidences for the isomor-phous substitution of metal ions for Si 4+in zeolite crystal lat-tice.34Fig.3shows the UV-Vis spectra for the Co-mordenite samples synthesized with various n (Co)/n (SiO 2)ratios in start-ing gels.All the Co-mordenites prented well-resolved triplet bands in the wavelength range of 500-650nm,attributable to 4
A 2→4T 1(4P ),4A 2→4T 1(4F ),and 4A 2→4T 2transitions of high-spin
Co 2+in tetrahedral coordination sites.17,35-41In contrast,the trip-let band could not be found for the pure mordenite.Further-more,except for the sample with a very high n (Co)/n (SiO 2)ra-tio of 0.05,the relative intensities of the triplet bands incread with Co contents in initial gels,which again suggests that the more Co 2+introduced into initial gels,the more Co 2+incorporat-ed in MOR frameworks.12,15The abnce of the band at ca 300nm featured for cobalt oxides excludes the possible existence of extra-framework Co species.42-44
The SEM images for the samples with various n (Co)/n (SiO 2)ratios are illustrated in Fig.4.Ellipsoidal crystal particles
were
Fig.2TG curves for the organotemplate-free synthesized pure
mordenite and the Co-mordenite with a n (Co)/n (SiO 2)
ratio of 0.03in the starting
of cour是什么意思
gel
3UV-Vis spectra for the Co-mordenites synthesized with various n (Co)/n (SiO 2)ratios in starting gels
conditions:n (SiO 2)/n (Al 2O 3)=40,n (H 2O)/n (SiO 2)=40,T =170°C,t =3d;n (Co)/n (SiO 2):(a)0,(b)0.01,(c)0.02,(d)0.03,(e)0.04,(f)
0.05
Fig.4SEM images for the Co-mordenites synthesized with various n (Co)/n (SiO 2)ratios in starting gels
conditions:n (SiO 2)/n (Al 2O 3)=40,n (H 2O)/n (SiO 2)=40,T =170°C,t =3d;n (Co)/n (SiO 2):(a)0,(b)0.01,(c)0.02,(d)0.03,(e)0.04,(f)0.05布鲁塞尔自由大学
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obrved for Co-mordenites,similar to the pure mordenite and the previously reported result.19Also,the particle sizes for Co-mordenites generally incread with the Co contents in syn-thesis gels.Obviously,amorphous phas occurred for Co-mor-denites at high Co content,which is responsible for the low-ered crystallinities,as already shown in Fig.1and Table 1.The color of the obtained Co-mordenite was violescent,suggesting that the Co ions do not exist in the pore of the MOR structure.203.2Influence of crystallization time
The crystallization process for Co-mordenite was investigat-ed by changing the crystallization time from 0to 7d on the sample with n (Co)/n (SiO 2)=0.03in the starting gel.The crystal-lization curve is plotted in Fig.5.The relative crystallinities in-cread quickly at the early stage of the hydrothermal tr
eat-ment without obrving an induction period.The increasing rate became slow at the time beyond 3d.A long hydrothermal period of 7d was needed to obtain a quite high crystallinity of 81%.In comparison,a short time of 3d could result in a con-siderably high crystallinity 78%with a n (Co)/n (SiO 2)ratio of 0.02(entry 3,Table 1).The results indicate that the obtained well crystallized Co-mordenite with a higher Co content re-quires longer crystallization time.
3.3Influence of n (SiO 2)/n (Al 2O 3)ratios
n (SiO 2)/n (Al 2O 3)ratios in starting gels are known to affect significantly the synthes of heteroatomic zeolites.25The afore-said synthes focud on a certain n (SiO 2)/n (Al 2O 3)of 40;fur-
thermore,Table 2prents the results for the Co-mordenites at n (SiO 2)/n (Al 2O 3)ratios of 20and 50.It can be en that whatev-er the n (SiO 2)/n (Al 2O 3)ratios,the Co contents in solid products raid with the increa of n (Co)/n (SiO 2)ratios in starting gels except for the high n (Co)/n (SiO 2)ratio of 0.05.The unit cell volumes also incread with the Co loadings in the final prod-ucts with simultaneously decread crystallinities.The obr-vations,together with the tendency of n (SiO 2)/n (Al 2O 3)ratios for final products,are consistent with tho in Table 1at n (SiO 2)/n (Al 2O 3)=40.I
t therefore ems that the prent organo-template-free method is applicable to a broad range of n (SiO 2)/n (Al 2O 3)ratios in starting gels;nevertheless,n (SiO 2)/n (Al 2O 3)ratios for final products have not been significantly enhanced by a higher n (SiO 2)/n (Al 2O 3)ratio in the starting gel.
Comparing the samples at n (Co)/n (SiO 2)=0.03with different n (SiO 2)/n (Al 2O 3)ratios of 20,40,and 50(entries 3and 6in Ta-ble 2,and entry 4in Table 1),it is found that both the crystal-linities and Co loadings in final products are enhanced with the rai of n (SiO 2)/n (Al 2O 3)ratios in starting gels.Thus,a high n (SiO 2)/n (Al 2O 3)ratio in gel mixture ems favorable to the in-rtion of Co ions into MOR framework.However,synthesiz-ing an extremely high silica mordenite is still known as a chal-lenging topic.Therefore,when a parate experiment for the very high n (SiO 2)/n (Al 2O 3)ratio of 100in the starting gel was conducted,it is not surprising that only a very low crystallinity of 38%for the resultant solid product was obtained.
3.4Preliminary understanding of the organotemplate-free synthesis
The prent organotemplate-free synthesis us sodium sili-cate as the Si source and NaOH as the alkalinity-adjusting agency.It is known that Na +may play a role as an inorganic template instead of organic ones that leads to nucleation for the growth of zeolite crystals.45-47It is thus propod that in the prent approach,the Na +ion in starting gels acts as a central body in its positive tetrahedral model,around which the dis-perd silicate ions and Co ions would have condend to form the Si-O-Co linkages,the primary building blocks of nuclei for mordenite crystals.
To understand this proposal,veral control tests were fur-ther carried out.If silica sol,rather than sodium silicate,was ud as the silica source under the same synthesis conditions
asdovetail
5Crystallization curve for Co-mordenite synthesized at n (Co)/n (SiO 2)=0.03,n (SiO 2)/n (Al 2O 3)=40,n (H 2O)/n (SiO 2)=40,and T =170°C
Table 2Textural properties for Co-mordenites synthesized with various n (Co)/n (SiO 2)ratios in starting gels
conditions:n (H 2O)/n (SiO 2)=40,T =170°C,t =3d.a
molar ratios analyzed by ICP,b
relative crystallinities
Entry 12345678
n (SiO 2)/n (Al 2O 3)gel 2020205050505050
solid a 16.118.815.426.118.817.024.032.6
n (Co)/n (SiO 2)gel 0.010.020.030.010.020.030.040.05
solid a 0.0040.0090.0160.0060.0120.0240.0240.011
Unit cell parameters a /nm 1.74901.75311.80311.80311.80461.81051.81821.7506
b /nm 1.98111.98872.03552.03392.04022.04902.04081.9736
c /nm 7.37207.38067.46517.46877.49237.47797.49727.3669
V /nm 32.55442.57312.73992.73912.75852.77422.78192.5454
Crystallinity/%b
91935610098716560
2112
