Solid Bases and Other Materials

Molecular Sieves Small 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 glass Active carbon Clay 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.kofo.mpg.de/images/schmidt1.jpg+5+450+280+5.jpg http://www.coolertech.co.nz/images/molecular_diagram_full.jpg http://www.wintek-corp.com/images/molecular-sieve.jpg

Calcination thermal treatment process (air or oxygen present) at temperatures below the melting point Brings about: thermal decomposition phase transition removal of a volatile fraction Examples Removal of ammonium ions in the synthesis of zeolites Removal of carbon dioxide from alkaline earth carbonates http://www.tececo.com/images/graphics/chemistry/MgcarbonatetoMgO.png

Base Catalysis in Organic Synthesis General 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 Catalysis Aldol Reaction – Formation of C-C bond Aldol – Tischenko Reaction – Formation of 1,3-hydroxyl compounds from aldehydes and ketones

Other Reactions Involving Base Catalysis Meerwein-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 Guests: Carboxylates Sulfates Phosphates Porphyrins Polyoxometalates What will happen to a double hydroxide carbonate during calcination? http://tresen.vscht.cz/min/sites/default/files/layer_0.jpg

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)

Zeolites Aluminosilicates as skeletal composition How do molecular sieves and zeolites relate to each other? Aluminosilicates as skeletal composition Highly crystalline materials Anionic framework with microporous and crystalline structure Could be synthetic and natural http://www.crystalsrocksandgems.com/images3/zeoliteshealingcrystals.jpg

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

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

Clays Al, Fe, Mg silicates Crystalline 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