Solid Bases and Other Materials

Molecular SievesSmall pores of precise and uniform size (could serve as desiccants – silica gel, activated carbon)

Microporous sieves (pore size less than 2 nm (20 Å))Zeolites (alumosilicate materials)Porous glassActive carbonClay

Mesoporous sieves (pore diameter between 2 and 50 nm (20 -500 Å)Silicon dioxide, mesoporous silica

Macroporous sieves (pore diameter is greater than 50 nm (500 Å)

TEM (a, b, and c) images of prepared mesoporous silica nanoparticles with mean outer diameter: (a) 20nm, (b) 45nm; and (c) 80nm. SEM (d) image corresponding to (b). The insets are a high magnification of mesoporous silica particle

A.B.D. Nandiyanto; S.-G Kim; F. Iskandar; and K. Okuyama (2009). "Synthesis of Silica Nanoparticles with Nanometer-Size Controllable Mesopores and Outer Diameters". Microporous and Mesoporous Materials 120 (3): 447–453. doi:10.1016/j.micromeso.2008.12.019.

Molecular Sieves …• Able to distinguish materials on the basis of their size

• May be crystalline, non-crystalline, para-crystalline or pillared clays

• Have variable framework charge with porous structure

http://www.coolertech.co.nz/images/molecular_diagram_full.jpg http://www.wintek-corp.com/images/molecular-sieve.jpghttp://www.kofo.mpg.de/images/schmidt1.jpg+5+450+280+5.jpg

Calcinationthermal treatment process (air or oxygen present) at temperatures below the melting point

Brings about:

- thermal decomposition- phase transition- removal of a volatile fraction

ExamplesRemoval of ammonium ions in the synthesis of zeolitesRemoval of carbon dioxide from alkaline earth carbonates

http://www.tececo.com/images/graphics/chemistry/MgcarbonatetoMgO.png

Base Catalysis in Organic SynthesisGeneral Base Catalysis Mechanism

Tischenko Reaction

benzylaldehyde Benzyl benzoate

Commercial Applications of Tischenko Reaction

- Ethyl acetate from acetoaldehyde (aluminium alcoholate traditional catalyst)

- Isobutyl isobutyrate

- Hydroxypivalic acid neopentyl glycol

- Methyl formate.[6]

Other Reactions Involving Base CatalysisAldol Reaction – Formation of C-C bond

Aldol – Tischenko Reaction – Formation of 1,3-hydroxyl compounds from aldehydes and ketones

Other Reactions Involving Base CatalysisMeerwein-Ponndorfp-Verley Reduction

Knoevenagel Condensation - nucleophilic addition of activated carbon compound

Solid Phase Bases

• Potassium fluoride on alumina (KOH, weaker base)• Alkali and alkaline earth carbonates

• Hydrotalcites (general formula Mg6Al2CO3(OH)16·4(H2O)) double hydroxide carbonates

http://tresen.vscht.cz/min/sites/default/files/layer_0.jpg

What will happen to a double hydroxide carbonate during calcination?

Guests:CarboxylatesSulfatesPhosphatesPorphyrinsPolyoxometalates

Solid Phase Bases (Cont’s)

• Magnesium Oxide

• Calcium Oxide

• Hydroxyapatite Ca10(PO4)6(OH)2

• Superbases: Alumina/Magnesium Oxides +

Alkali metal hydroxide + Alkali metal (under

N2)

ZeolitesHow do molecular sieves and zeolites relate to each other?

http://www.crystalsrocksandgems.com/images3/zeoliteshealingcrystals.jpg

•Aluminosilicates as skeletal

composition

•Highly crystalline materials

•Anionic framework with microporous

and crystalline structure Could be synthetic and natural

Zeolites Have Various Frameworks

http://www.sciencemag.org/content/334/6052/72/F3.large.jpg

Zeolites Vary By…

•Silicon-to-Aluminum Ratio

•Pore diameter

•Counter ion

•Framework

Commercial Use of Zeolites

•Detergents

•Separate linear polymers from branched

•Oxygen enrichment

•Removal of carbon dioxide, hydrogen sulfide, mercaptans from air

•Petroleum cracking

•Catalysis

Metal Organic Frameworks (MOF)Organic compounds: polyphenols, difunctional carboxylic acid, sulfonic acid, phosphonic acid, hydroxamic acid, boronic acid, etc...Metal ions: Zn, Co, Ni, Eu, La, Ce, Er, Lu, Yb, Cr, V, Fe, Zr

Have more open space (60%) than zeolites (50%)

High thermal stability

http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/Articleimage/2014/CS/c4cs00041b/c4cs00041b-f1_hi-res.gif http://www.metal-organic-frameworks.de/grafiken/mof_bild1.gif

http://www.science.tamu.edu/news/story.php?story_ID=913#.VCtvvZrD8iQ

An illustration of a prototype 6-liter adsorbed natural gas (ANG) fuel tank that relies on innovative advanced porous materials and Texas A&M's proven expertise in metal-organic frameworks and porous-polymer networks to deliver low-pressure, high-density natural gas storage in vehicles

ClaysAl, Fe, Mg silicatesCrystalline inorganic polymers (may be amorphous too)

(Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2·nH2O - montmorillonite

http://ccm.geoscienceworld.org/content/60/6/599/F1.large.jpg

Applications of Clays

•Replacements for asbestos

•Molecular sieves

•Catalysts

cationic and anionic clays

could substitute for Lewis acids

Offer selectivity by size and shape

Acylation

Alkylation

Rearmaments

Montmorilloite and CO2 Sequestration

CO2 intercalation into swelling clay layers is of potential use for CO2 storage in geological formations.

CO2 intercalation into caprock dominated with clay can lead to swelling and eventual evolution of fractures due to geomechanical stress

Also valuable model systems for understanding the structure of water and water/CO2 mixtures in confined environments

Myshakin et al., Molecular Dynamics Simulations of Carbon Dioxide Intercalation in Hydrated Na-Montmorillonite, Journal of Physical Chemistry A, 2013, 117 , 11028–11039