Development of Nanocrystalline Zeolite · Zeolites ZSM-5, 0.55 nm Y, 0.75 nm Zeolites are...
Transcript of Development of Nanocrystalline Zeolite · Zeolites ZSM-5, 0.55 nm Y, 0.75 nm Zeolites are...
Development of Nanocrystalline Zeolite Materials as Environmental Catalysts
Vicki Grassian and Sarah LarsenDepartment of Chemistry, University of Iowa
Postdoctoral AssociateDr. Weiguo Song
Graduate StudentsGonghu LiConrad JonesRamasubraman KanthasamyLanell Rupert
UndergraduatesRachelle Justice
R829600
Zeolites
ZSM-5, 0.55 nm
Y, 0.75 nm
Zeolites are aluminosilicates with well-defined openings of molecular dimensions (0.4 - 10 nm).
Currently a large number of applications in:
AdsorptionDrying, purification, separationRemoval of volatile organics from air
streamsCatalysis
Shape selective, acid catalysts, environmental catalysts
Ion exchangeWater-softeners in powdered laundry
detergents
Synthesis of Nanocrystalline Zeolites
Silicalite ZSM-5 Y
20 nm 15 nm 23 nm
173 (576) m2/g198 (492) m2/g174 (506) m2/g
References: Song, Justice, Jones, Grassian and Larsen, a) Langmuir, 2004, 20, 4696-4702, b)Langmuir, 2004, in press
Characterization
0
50
100
150
200
0 50 100 150 200 250 300
Calculated Surface AreaExperimental Data
Ext
erna
l Sur
face
Are
as (m
2 /g)
Crystal Size (nm)
Powder X-ray Diffraction (XRD)Crystallinity and particle size (line width analysis)
Scanning Electron Microscopy(SEM)Particle size and morphology
Spectroscopic CharacterizationSolid State NMR Studies (Al, Si)FTIR Studies (hydroxyl group region to determine more about the acidic properties of the zeolite)Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES)
Physical CharacterizationBET Analysis (external and internal surface area measurements)
xExternal surface area of cubic crystal:
x m2/g3214
Adsorption of VOC’s on Nanocrystalline Zeolites
Helium
Helium
MFC
MFC
MFC
Bubbler Tubular Reactor
TCD Detector
SampleReference
0.20.40.60.8
11.21.41.6
0 100 200 300 400 500 600Surface area (m2/g)
TPD vs. Stotal
Purge vs. Sext
Adsorption vs. S total
Det
ecto
r In
tens
ity
time
Adsorption
RT He PurgeTPD
Silicalite-1-17 (20 nm) Silicalite-1-15 (149 nm) Silicalite-1-22 (1000 nm)
Selective Catalytic Reduction of NO2with Propylene
140016001800200022002400
Aldrich NaYCreaser Y 200 nmCreaser Y 20 nm
Absorbance
Wavenumber (cm-1)
1409
1324
1563
0.2
NaY (20 nm)
NaY (200 nm)
Aldrich NaY (600 nm)
2023
NO2 Adsorption
NO+
NO3-
Propylene(PE) and NO2 on NaY
Gas phase
Surface
species
120013001400150016001700180019002000
1943
1694
16471528
1557
1282
1404
1320
1723
Wavenumber (cm -1)
1387
1354
1598 1483
240030003600
Absorbance
0.2
3563 2985
3747
2451
2317
2187
2272
3649
2239
(a)
(b)
(c)2355
0
5
10
15
20
0 50 100 150 200 250 300 350
NO2
NON2O
Con
cent
ratio
n (1
0-6 m
ol L
-1)
Time (min)
0
5
10
15
20
25
30
0 50 100 150 200 250 300 350
PECO
298 K
373 K
473K
2NO2 --> NO3- + NO+
NO2 is stored on NaY as nitrate and nitrite species. NO2 and propylene on NaY react completely at 473 K to form N2 and O2.
Hierarchical Assemblies of Nanocrystalline Zeolites
A variety of nanoarchitectures can be constructed using nanocrystalline zeolites as building blocks.
Self-assembled films and fibers
Hollow zeolite spheres or tubes
Preparation of Hollow Zeolite Structures
Nanocrystalline zeolites are used as seeds to coat mesoporous silica (MS) with various morphologies.
Hollow zeolite sphere(purely silicon forms)
It is also possible to incorporate guest species in the interior.
Hydrothermalsynthesis
Electrostaticassembly
MS coated withnanocrystalline zeolite seeds
Mesoporous silica(spheres, tubes)
Reference: Dong, et al. Microp. Mesopor. Mat. 64 (2003), 69-81; Schulz-Ekloff, Rathousky, Zukl, Int. J. Inorg. Mater. 1 (1999), 97.
Incorporation of Aluminum intoZeolite Shells
Mesoporous silica(hexagonal tubes)
MS coated withnanocrystalline zeolite seeds
Hollow hexagonal zeolite tube
Al(NO3)3
27Al MAS NMR
-100-50050100150200ppm
Before HT
After HT
After Calcination
-2
50
Reference: Song, Grassian and Larsen, Chem. Comm., 2004, in press (Chem Comm Hot Article) 27Al MAS NMR confirms the
presence of aluminum in thezeolite framework
Synthesis Mechanism and Applications
SEM images of MS seeded with nanocrystalline silicalite after hydrothermal treatment 0, 1, 4, and 16 h.
• The next step is to incorporate active species into the interior of the hollowzeolite structures (metal nanoparticles, catalysts)• Potential applications
Cr(VI) reduction on iron-loaded zeolite tubesEncapsulate magnetic materials into interior space so that hollow zeolite
structures can be recovered from the environment after use as adsorbents
Functionalization ofZeolite Surfaces
Functionalize external and internal surfaces with different functional groupsVary “solubility”, acid base properties
Expand environments in which zeolites may be useful for applications in remediation and environmental catalysis
Si-O-H Si-O-Si-Cx(SiCl3)C8H16
+HCl
References: a) Usher, Michel, Stec and Grassian, Atmos. Env. 37 (2003) 5337-5347 b) Zhan, White, Lumsden, Langmuir 2003, 19, 4205-4210.
Nanocrystalline ZSM-5 Functionalized by Octyltrichlorosilane
Toluene/Pyridine R1R1Si Cl
R2Si OH + Si O Si
95 ºC, 3 hours R2
-110 ppm (framework Si)
-60 ppm (Si-C)
29Si MAS NMR
-200-150-100-50050100ppm
NanoZSM-5 treated with octyltrichlorosilane
Untreated nano-ZSM-5
Water Hexane
Functionalization of Zeolites with Different Sizes
29 Si NMR Spectra of ZSM-5 Functionalizedby Octylmethyldichlorosilane
ZSM-5 ( 15 nm)
ZSM-5 (60 nm)
ZSM-5 ( 200 nm)
-21 -110
X10
X10
X10
• Functionalization of silanol groups on the externalsurface
• Relative amount of silane grafted on zeolites is proportional to external surface areas.
• Similar results observed on Y zeolites
5.4%
1.7%
0%
-200-150-100-50050100150200
Applications for FunctionalizedZeolites
Adsorption of VOC’s, such as toluene, from humid or aqueous environmentsBifunctional Catalysts
Design catalyst for specific applications by incorporating acid/base, hydrophobic/hydrophilic propertiesExterior surface is functionalized with acid sites- can break a reactant molecule up on external surface- into smaller pieces that can diffuse into the zeolite pores for further reaction.
H+
H+H+
H+
H+
H+
H+H+
H+ BBBB
Development of Nanocrystalline Zeolite Materials - Summary
Zeolite particle size can be systematically tuned in the nanometer range by varying reaction conditions.
The nanocrystalline zeolites can be used as building blocks for hierarchical zeolite structures (fibers, films, hollow zeolite structures)
20 nm 39 nm 149 nm
Environmental applications for nanocrytalline zeolites and hierarchical structures:Adsorption of volatile organic compounds (VOCs)
Toluene on silicalite, ZSM-5 and Y Adsorption of VOCs from aqueous solutions or humid environments on functionalized zeolitesSelective Catalytic Reduction(SCR) of NO2 with hydrocarbons on nanocrystalline Y zeolitesCr(VI) Reduction on iron-loaded hollow zeolite structuresDemonstration of a bifunctional nanocrystalline zeolite catalyst
Different functionality on external and internal surfaces