ACS Present a Ion in Dever

8/4/2019 ACS Present a Ion in Dever

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Molecular Sieves SAPO-34 with Chabazite (CHA)

Structure:Theoretical Study of Silicon Incorporation and

Structural Properties

Hong Wang1, Yingxu Wei2, Cecil ODell1, Zhongmin Liu2 and James P. Lewis11Department of Physics, West Virginia University, Morgantown, WV2Dalian Institute of Chemical Physics, Dalian, P. R. China


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Introduction

Zeolite is a broad term used to describe a family ofmicroporous aluminosilicate minerals.

Contain small pores and large surface area Constructed of AlO4-5 and SiO4-4 groups bound by oxygen Zeolites are synthesized by manipulating:

Structure Silica-Aluminum Ratio Pore Size Density

"Green Chemistry with Zeolite Catalysts." Chemical Engineering, The Chemical Engineers'ResourcePage, Distillation, HeatTranser, Design, Spreadsheet Solutions, Departments, Chemistry. Web. 22 Apr. 2010..


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Application of Zeolite Materials Adsorption

Drying, purification, and separation Carbon dioxide separation

Catalysis Shape-selective catalyst- on the basis

of molecular diameter Acid catalysts used in thepetrochemical industry

Ion Exchange Detergent formulas- replace

phosphates as water softening agents

Exchange Na in zeolite for Ca or Mgin water

http://s3.amazonaws.com/memebox/uploads/3562/kanatzidis-gasNorthwester.jpg


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Zeolite Catalysis in Methanol to Olefins Conversion (MTO)

CoalNatural

Gas

Synthesis Gas

Methanol

Olefins

MTO

https://mailhost-2.tamu.edu/service/home/~/Zeolite_seminar.pdf?auth=co&loc=en_US&id=46940&part=5

Z-H +n(CH3OH) Z +H2O+olefin(C2, C3, C4)

Z-H: ZSM-5 catalytic zeolite1977, Chang, Lang and Silvestri, US patent 4062905


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SAPO-34:Microporous Silico-Aluminophosphate Molecular Sieve

ZSM-5 SAPO-34

Al P

Al Si P

Al

Al

P

Al

Al

Al (Al-O)3-Si

HO

Al-(O-P)3

Pore size around Strong acid sites Low selectivity in

light olefins High selectivity

ZSM-5


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SAPO-34

SAPO-34:Microporous Silicon Aluminumphospate Molecule Sieve

Al P

Al Si P

Al

Al

P

Al

Al

Al (Al-O)3-Si

HO

Al-(O-P)3

Small size pores Suitable acid sites Strong stability High selectivity

0.43n

m

C2H4 0.39nm

C3H6 0.43nm

C6H6 0.58nm


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SAPO-34: Crystallization Mechanism

J. Tan, Z. M. Liu, X. H. Bao, X. C. Liu, X.W. Han, C. Q. He, R. Z. Zhai,Microporous andMesoporousMateirals 53 (2002), 97 (108)

SM1: Al Si (not yield)

SM2: P Si, H SM3: Al,P Si,SiAcidity: Si(4Al)


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Current Challenge of Silicon Incorporationin SAPO-34 Framework

Substantial computational timeinvolved

Extensive possibilities of silicon

incorporation into a largerframework Identify optimal acid sites with a

variety of silicon-incorporatingenvironments

Unravel the puzzle of silicon

incorporation trends during theSAPO-34 crystallization processand accompany the experimentaldesign with a full-knowledgeframework.

[AlPO4]+(n+m)Si4++(m-n)H+ [(n+m)Si,(m-n)H]nAl,mP+mP5++nAl3+


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SAPO-34 Computational Model and Goal

Rhombohedral unit cell

12 tetrahedral (T) sites- 6 Al & 6 PSpace Group:

2x2x2 supercell (288 atoms total)

96 tetrahedral (T) sites- 48 Al & 48 PSpace Group: P1 (after silicon substitution)

[AlPO4]+(n+m)Si4++(m-n)H+ [(n+m)Si,(m-n)H]nAl,mP+mP5++nAl3+

3R


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We investigate the properties of a non-uniformly distributed Si in a2x2x2 AlPO-34 supercell.

6 Sis in 288 atoms supercell - 1010 possible arrangements(C48/5*C48.)

Randomly distribute Si throughout the supercell and see what trends wecan learn.

Clustering Factor root mean square from perfect Si-Si distance (3.15 )in Si-O-Si configuration.

For each Si in the supercell, sum over all Si neighbors of Si (choosing

smallest Si cluster in supercell). Each 288 atom supercell optimization is approximately 10-12 hours. Generate high-throughput scenario from 100s of supercell calculations (a

few 1000s are also feasible).

High Throughput Calculations Clustering


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Pseudopotentials, density-functional theorymulti-center approximations

Local excited" orbitals (fireball orSankey-Niklewski orbitals)Atom in the box Fermi compressionfinite wavefunction

Linear-scaling, massively-parallelmolecular-dynamics capabilitiessimulate 1000s of atoms

J.P. Lewis et al., Phys. Rev. B. 64, 195103 (2001)S.D. Shellman et al.,J. Comp. Phys. 188, 1-15 (2003)P. Jelineket al.,Phys. Rev. B. 64, 235101 (2005)

J.P. Lewis et al., Phys. Stat. Sol. B. 248, 1989-2007 (2011)

Fast Computational Approach to Evaluation of MaterialProperties and Chemical Reactivity:Ab initio DFT (FIREBALL)


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167

49 213

361

364

108

Clustering/Energy Correlation of 720 individual Structures


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structure No. 49 structure No. 167

Low clustering factor, but different energies.

2 (Al,P Si,Si)pair substitution Al,5P Si(4P), 4Si(4Al)all isolated


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167

49 213

361

364

108

Clustering/Energy Correlation


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structure No. 49 structure No. 364structure No. 213

2 (Al,P Si,Si)two pairs close

2 (Al,P Si,Si)

two pairs far away

Lower energy structure compared to smallerclustering factor

(2Al, P) Si Si Si

triplet


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167

49 213

361

364

108

Clustering/Energy Correlation


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structure No. 108structure No. 364

4 (P Si) Si(4Al)(2Al, P) Si Si Sitriplet

Lower energy structure compared to larger

clustering factor


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What we see ..

Higher clustering factors mean thatthe silicon incorporation in theframework is spread throughoutthe entire supercell.

Silicon substitution of Al, P pair is acommon trend for our random

silicon incorporation calculationsand these pairs lower the bindingenergy.

In our low concentrationincorporation (6 out of 96 possiblesites), silicon prefers to form short

range clusters.

structure No. 364


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Future Steps and Outline

Calculate the electrostatic potentialsfor our random networks todetermine the affects introduced bysilicon incorporation into the SAPO-34 framework.

Design a computational route to alsonon-uniformly add hydrogen into theSAPO-34 framework based oncurrent data and determine trends.

Increase silicon substitutionconcentrations and double SAPO-34

supercell to detect siliconincorporation trends (i.e. increasingthe non-unformity)

Determine the acid site strengths forfurther CH3OH adsorption


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Acknowledgements

WVU HPC Supercomputering Facility Prof. Zhongmin Liu Dr. Yingxu Wei

Dalian Institute of Chemical Physics, P.R.C

Thank you!

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