Zeolites and Zeolitic Materials Molecular sieves = highly organized matrices of tunable pore shape, size, and polarity for separation, recognition, and organization of molecules with precision of about 1 A. detergent builders adsorbents size-shape selective catalysts supramolecular chemistry nanotechnology Chemical composition Silica Aluminosilicates Aluminophosphates Metallophosphates Silicoaluminophosphates SiO2 MxIAlxSi2-xO4 . nH2O AlPO4 (isoelectronic with Si2O4) MPO4 MxISixAlPl-x O4 Zeolites and Zeolitic Materials >40 naturally occurring zeolites >139 structure types many hundreds of zeolite compounds Nomenclature www.iza-structure.org/databases Structure types - three capital letter codes (Most well known zeolite archetypes: SOD, LTA, FAU, MOR, MFI ) Four-connected frameworks Interrupted frameworks (denoted by a hyphen: -CLO, cloverite) Structure types do not depend on: chemical composition, element distribution, cell dimensions, symmetry Several zeolite compounds can belong to the same structure type: FAU - faujasite, Linde X, Y, Beryllophosphate-X, SAPO-37, Zincophosphate-X 3 Zeolites and Zeolitic Materials Names of zeolite materials: trivial names - Alpha, Beta, Rho chemical names - Gallogermanate-A mineral names - Chabazite, Mordenite, Stilbite, Sodalite codes - AlPO4-5, 8, 11, 54, ZSM-4, 18, 57, ... brand names - Linde A, D, F, L, N, Q , R, T, W, X, Y university names VPI-5 (Virginia Polytechnical Institute) ULM (University Le Mans) 4 Zeolites and Zeolitic Materials Primary building units: Al(III)O4, P(V)O4 and Si(IV)O4 tetrahedra Isoelectronic relationship (SiO2)2 [AlSiO4 ]- AlPO4 5 6-2 2-6-2 6= l (C6R) Chain composite building units la) it: ■-■ (tQ ffl (g) (a) zig-zag unbranched single chain, periodicity of two (b) sawtooth unbranched single chain, periodicity of three (c) crankshaft unbranched single chain, periodicity of four (d) natrolite branched single chain (e) double crankshaft chain, an unbranched double chain (f) narsarsukite chain, a branched double chain (g) a pentasil chain Polyhedral composite building units 8 Sodalite Unit Truncated octahedron 10 Sodalite Unit Packing of the sodalite units: SOD - bcc, sharing of 4-rings LTA - sc, 4-rings connected through O bridges FAU (faujasite) - cubic diamond, 6-rings connected through O bridges EMT - hexagonal diamond, 6-rings connected through O bridges 11 Zeolite LTA Zeolite A (a) [TO4] tetrahedra as BBU (b) four-membered single rings (c) lB fuenfer chains (d) cubes [46] (e) truncated octahedra [4668] (sodalite- or P-cages) (f) truncated cubeoctahedra [4126886] (a-cavities) 13 Pores in Zeolite A (LTA) (a) the sodalite cage [4668] (b) the a-cavity [4126886] (c) the 3-dimensional channel system (d) the 8-ring defining the 0.41 nm effective channel width 14 (a) D4R AFM growth studies of LTA S. Sugiyama et. al. Microporous and Mesoporous Materials 28 (1999) 1-7 15 Double-four ring (D4R) D4R 1.2273nm 1 7?7^nm 0.5072nm 16 Zeolite FAU (X and Y) and EMT 00 00 Fig. ]. Structure of zeolite Y: (a) cubic polymorph known ns FAU with ABC A EC . stocking, (b) hesac.onal polymorph known ns EMT witli AHAHAB... itackiT^. 17 Molecular Sieves Zeolite Cation Code Pore diameter Zeolite A: Na Ca Na, K 4A 5A 3A 0.42 nm 0.48 nm 0.38 nm Zeolite X: Na Ca 13X 10X 0.8-1.0 nm 0.7 nm Zeolite Y contains more Si 18 Framework Density Framework density (FD) Defined as the number of tetrahedral atoms (T-atoms) per cubic nanometer (1000 A3) FD is related to the void volume of the crystal: as the FD value decreases, the void volume and capacity for adsorption increases FD < 20 are characteristic of microporous structures the minimum known FD is 12.5 with the void occupying just over half of the crystal volume FD U 14 - a -» -u - 16 -14 -11 - quartz ft ■SB-Y HS1- -19 5f 4 SbaorSmllNtRlqg Pores Various sizes (4 -13 A), shapes (circular, elliptical, cloverleaf-like), and connectivity (1-3D) The size of the rings formed by the TO4 tetrahedra ranges from 4 to 18 of the T-atoms and determines the pore aperture Extraframework charge-balancing cations Ion-exchangeable, size, charge, positions, distribution, ordering, coordination number Si-to-Al ratio Influences cation content, hydro-phobicity/-philicity, acidity Lowenstein rule: absence of the Al-O-Al moieties, in aluminosilicates Si/Al > 1 Linde A (LTA) Si/Al = 1 ZK-4 (LTA) Si/Al = 2.5 ZSM-5 Si/Al = 20 - 00 Pure SiO2 Si/Al = 00 Pentasils ZSM-5 Zeolite Synthesis Synthesis - an empirical and heuristic process, new phases are often discovered by serendipity Aluminosilicates - high pH & Mixing NaAl(OH)4(aq) + Na2SiO3(aq) + NaOH(aq), 25 °C, condensation-polymerization, gel formation a Ageing Na(H2O)n+ template effect Naa(AlO2)b(SiO2)c.NaOH.H2O(gel) 25-175 °C & Hydrothermal crystallization of amorphous gel, 60-200 °C Nax(AlO2)x(SiO2)y.zH2O(crystals) A Separation of the solid product by filtration & Calcination - occluded water, removed by 25-500 °C vacuum thermal dehydration -template removal - calcination in O2 at 400-900 °C removes the guest molecules from the framework without altering it - extraction (neutral templates) 1t 21 Zeolite Synthesis Structure of the zeolite product depends on: - Composition - Concentrations and reactant ratios - Order of mixing - Temperature - Ageing time (hours to weeks) - Crystallization time (days to weeks, kinetics of the structure-directing process is slow) -pH - Stirring/no stirring - Pressure - Seeding - Reactor material (PTFE, glass, steel) - Templates Templates: Organic cationic quaternary alkylammonium salts, alkylamines, aminoalcohols, crownethers, structure-directing, space-filling, charge-balancing Vary the template - discover new structures ! 22 ^ , * * , Templates lemplate or guest compounds A Three levels of the guest action with increasing structure-directing specificity: ■ Space-filling - the least specific, observed, for example, in the synthesis of AlPO4-5, 23 different, structurally unrelated compounds, could be employed, they pack in the channels of the structure thereby increasing its stability. ■ Structure-directing - a higher degree of specificity, only tetramethylammonium hydroxide is effective in the synthesis of AlPO4-20 -elongated molecules, such as linear diamines, initiate the formation of channels -nondirectional-shaped guests leads to the formation of cage-like cavities, the size of these cavities correlates with the size of freely rotating guests ■ True templating - very rare, it requires even more precise host-guest fit which results in the cessation of the free guest-molecule rotation A curiosity: aluminophosphate VPI-5 does not require any guest for its formation! 23 Templates The ratio TO2/(C + N + O) is a measure of space-filling of the framework by the guest molecules, characteristic for a specific guest and structure. Existence of primary and secondary units in a synthesis mixture 4R, 6R, 8R, D4R, D6R, 5-1, cubooctahedron 24 Zeolite Synthesis Mechanisms (a) gel dissolution and solution mediated crystallization (SBU in solution) (b) "in situ" rearrangement of the gel 25 Zeolite Synthesis Mechanisms Mechanism of structure-directing action of the TPA template Crystallization Mechanism crystallization mechanism of FAU-type zeolite under ambient conditions 27 Zeolites and zeolitic materials Wide range of solid state characterization methods for zeolites: diffraction, microscopy, spectroscopy, thermal, adsorption and so forth Zeolite post modification for controlling properties of zeolites Tailoring channel, cage, window dimensions: -^Cation choice (Ca2+ exchanged for Na+) -^Larger Si/Al decreases unit cell parametrs, window size decreases number of cations, free space increases hydrophobicity -^Reaction temperature, higher T, larger pores 28 Stability Rules Lowenstein rule: never Al-O-Al Dempsey rule: NNN-principle Al-O-Si-O-Si-O-Al is more stable than Al-O-Si-O-Al 29 Bronsted Acidity Tuning Bronsted acidity: + Ion exchange for NH4 Pyrolysis to expel NH3 Calcination to expel H2O Solid acid for the hydrocarbon cracking The larger the Si/Al ratio,the more acidic is the zeolite Na ® Na .0 OO O /S\ A\ /Si O ooooooooo Ion Exchange +NH4 ® -Na ® ® © NH4 NH4 oooooo /S\ O OOOOOOOOO Heating -NH3 H ^ H Si Al Si Al Si OOO 0 ooooooooo Bronsted acid ,0 Calcination 600 oC -H2O Lewis acid Si Al Si O V /V A A A 0 000000000 Si Al 30 Brensted Acidity Size-Shape Selectivity Size-shape selective catalysis, separations, sensing Selectivity at: •Reactants •Products •Transition state 32 Separation of xylene isomers by pervaporation thru a MFI membrane 33 Zeolite Applications Odor control, adsorbents Ion exchange capacity, water softening, detergents (25wt% zeolite) Host-guest inclusion, atoms, ions, molecules, radicals, organometallics, coordination compounds, clusters, polymers (conducting, insulating) Nanoreaction chambers Advanced zeolite devices, electronic, optical, magnetic applications, nanoscale materials, size tunable properties, QSEs 34 Aquaculture Ammonia filtration in fish hatcheries Biofilter media Agriculture Odor control Confined animal environmental control Livestock feed additives Horticulture Nurseries, Greenhouses Floriculture Vegetables/herbs Foliage Tree and shrub transplanting Turf grass soil amendment Reclamation, revegetation, landscaping Silviculture (forestry, tree plantations) Medium for hydroponic growing Household Products Household odor control Pet odor control Industrial Products Absorbents for oil and spills Gas separations Radioactive Waste Site remediation/decontamination Water Treatment Water filtration Heavy metal removal Swimming pools Wastewater Treatment Ammonia removal in municipal sludge/wastewater Heavy metal removal Septic leach fields 36 Aluminophosphates +Isoelectronic relationship of AlPO4 to (SiO2)2 clonic radius of Si4+ (0.26 A) is very close to the average of the ionic radii of Al3+ (0.39 A) and P5+ (0.17 A) Many similarities between aluminosilicate and AlPO4 molecular sieves Dense AlPO4 phases are isomorphic with the structural forms of SiO2: quartz, tridymite, and cristobalite Aluminosilicate framework charge balanced by extraframework cations Aluminophosphate frameworks neutral (AlO2-)(PO2+) = AlPO4 3 Aluminophosphates Some AlPO4 structures are analogous to zeolites while other are novel and unique to this class of molecular sieves. Only even-number rings = the strict alternation of Al and P atoms Incorporation of elements such as Si, Mg, Fe, Ti, Co, Zn, Mn, Ga, Ge, Be, Li, As, and B into the tetrahedral sites of AlPO4 gives a vast number of element-substituted molecular sieves (MeAPO, MeAPSO, SAPO) important heterogeneous catalysts M1+, M2+, and M3+ incorporate into the Al sites M5+ elements incorporate into the P sites This substitution introduces a negative charge on these frameworks. Si4+, Ti4+, and Ge4+ can either replace P and introduce a negative charge or a pair of these atoms can replace an Al/P pair and retain the charge neutrality. 38 Aluminophosphates AIKV5 AlPOr3l 39 Aluminophosphate Synthesis Aluminophosphates prepared by the hydrothermal synthesis Source of Al: pseudoboehmite, Al(O)(OH), Al(O/-Pr)3 Mixing with aqueous H3PO4 in the equimolar ratio - low pH ! Forms an AlPO4 gel, left to age One equivalent of a guest compound = template Crystallization in a reactor Separated by filtration, washed with water Calcination Other zeolite materials Oxide and non-oxide frameworks, sulfides, selenides Coordination frameworks, supramolecular zeolites The quest for larger and larger pore sizes 40 Cobalto-Aluminophosphate ACP-1 (Co/Al 8.0) bcc arrangement of the double 4-ring units (D4R) Ethylenediamine molecules are located inside 8-ring channels At the centre of each D4R, there is a water molecule, 2.31 A away from four metal sites Al(O-iPr)3, CoCO3.H2O, 85% H3PO4, ethylene glycol, ethylenediamine, pH 8.4 Heated in a Teflon-coated steel autoclave at 180 °C for 4 d 41 Synthesis of Double 4-ring Units (D4R) 42 Metallo-Organic Framework (MOF) Structures 4000 structures known (2008), 1000 new per year Metal centers • Coordiantive bonds • Coordination numbers 3-6 • Bond angles Polytopic Ligands Organic spacers Flexible - rigid Variable length 43 Polytopic Organic Linkers 44 Polytopic N-bound Organic Linkers Cationic framework structures Evacuation of guests within the pores usually results in collapse of the host framework Molecular Complexes Extended Solids Expanded Framework 45 46 Metallo-Organic Framework Structures Scheme 4. Self-Assembly of Dodecahedra Polytopic carboxylate linkers 48 Polytopic Carboxylate Linkers Aggregation of metal ions into M-O-C clusters form more rigid frameworks frameworks are neutral no need for counterions Decorated-Expanded Framework 49 MOF-5 Zn4O(BDC)3.(DMF)8(C6H5Cl) •Zn(NO3)2 + H2BDC in DMF/PhCl •Addition of TEA: deprotonation of H2BDC •Addition ofZn2+ • Addition of H2O2: formation of O2- in the cluster center Z^O Cavity diam. 18.5 A Nature, 1999, 402, 276 a primitive cubic lattice MOF-5 MOF-5 Stable even after desolvation at 300 °C in air gas sorption isotherms for MOF-5 w o (fl o £ 1600 -J ^ ■ • • ■ • 1200 1 800 t ♦ ♦ ♦ ♦♦♦ ♦ ♦ ♦ ♦ 400 ■Ar • CCU • CHCI3 0 1 •N2 ♦CeHe ♦ CeHi2 0.2 0.4 0.6 P/P 0.8 MO F M O F MOF MOF MOF MO F MOF -2 -3 -4 -5 -6 -0 -11 pore diameter (ä) surface area pore volume (cm3/g) 7 8 14 12 4 8 7 270 140 2900 127 560 0.094 0.038 0.612 1.04 0.099 0.035 0.20 51 Interpenetration 53 Metallo-Organic Framework Structures 54 Basic Nets coordination coordination figures net 3 triangle triangle SrSi2 a 3 triangle triangle ThSi2 3 triangle triangle 63 honeycomb 3,4 triangle square Pt304 4 square square NbO 4 tetrahedron tetrahedron diamond (C) 4,4 square tetrahedron cooperite (PtS) 4 square square 44 square lattice ii octahedron octahedron primitive cubic cube cube body-centered cubic d P1304 NbO Diamond (C) i I i r—r 1 j g *— n ■ -1/ f ■— 3 t — —11 U—J, Cooperite (PtSj 44 Square lattice ríf "s "1 it i v$ bio Inorganic and Metallo-Organic Quartz 56 MIL-lOO and MIL-lOl MIL-lOl Record Surface area 5 900 m2/g 57 Covalent Organic Frameworks