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