Kirk D. Schmitt

THE ROLE OF DIQUATERNARY CATIONS AS DIRECTING AGENTS IN ZEOLITE SYNTHESIS

The formation of various zeolitic phases using diquaternary cations was monitored. The chain length of the diquats was found to play a key role in the nature of the final products. In a specific composition regime, it was found that, by varying the diquat chain length, the uni-dimensional 10-ring zeolite ZSM-23 or a 12-ring containing system, i.e., ZSM-50, NU-87, or ZSM-12, was obtained. Molecular modeling studies led to a proposed orientation of the respective diquats in the 12-ring pores/channels of ZSM-50 and NU-87. It is concluded that specific chain lengths provide an ideal fit for the formation of these “2-dimensional” pore systems. When the fit is less than ideal, ZSM-23 appears as the default phase under the conditions studied.

Development of a formation mechanism for M41S materials

1. Summary The influence of surfactant/silica molar ratio(Sur/Si) in M41S syntheses was studied in the simple synthesis system consisting of tetraethylorthosilicate(TEOS), water, and the cetyltrimethylammonium(CTMA) cation at 100°C. As the Sur/Si increased from 0.5 to 2, the siliceous products obtained were identified and could be classified into four separate groups: MCM-4 1(hexagonal), MCM-48(cubic), thermally unstable M4 1 S, and a molecular species, the organic octamer [(CTMA)SiO2, 5]8. One of the thermally unstable structures has been identified as a lamellar phase. These results are consistent with micellar phase transformations that occur at various surfactant concentrations and reinforce the concept that micelle structures serve as templating agents for the formation of M41S type materials.

Toward the rational design of zeolite synthesis: The synthesis of zeolite ZSM-18☆

Abstract ZSM-18 has, until now, only been made using one trisquaternary ammonium ion, 2,3,4,5,6,7,8,9-octahydro-2,2,5,5,8,8-hexamethyl-1 H -benzo[1,2-c:3,4-c′:5,6-c″]tripyrrolium, 1 . This trisquaternary is difficult to make and destabilizes the zeolite during calcination. We used modeling to aid the design and selection of new templates for ZSM-18. The geometry and charge distribution of these templates were chosen to best fit our estimate of “templating.” Template 2 , tris -(2-trimethylamonioethyl)amine, is easy to synthesize in high yield and can be routinely calcined to produce highly sorptive ZSM-18. Template 3 , tris -(2-trimethylamonioethyl)methane, produces ZSM-18 only when seeded. Si n.m.r. and Al n.m.r, indicate that aluminum is not located exclusively in the three rings as has been predicted theoretically. [H]-ZSM-18 can be steam-dealuminated. The Si n.m.r, of the dealuminated material agrees with the number of sites and relative occupancies expected.

Determination of carbon centre types in solid fuel materials by CP/MAS n.m.r.

Abstract Methyl, quaternary aliphatic and aromatic, and hydrogen-bearing aliphatic and aromatic carbon centres in solid fuel samples have been determined quantitatively by pulse-programmed 13 C n.m.r. coupled with elemental analysis. The method may be used for unaltered samples of oil shales, coals, etc., and has been tested on model compounds representative of components in these materials.

Characterization of zeolites and amorphous silica—aluminas by means of aluminum-27 nuclear magnetic resonance spectroscopy: A multifield, multiparameter investigation

Abstract We have obtained the aluminum-27 nuclear magnetic resonance (n.m.r.) spectra of a large number of ZSM-5 (MFI) zeolites and amorphous silica aluminas by using static, spin-echo, and “magic-angle” sample-spinning (MAS) techniques, at various magnetic field strengths in the 2.35–11.7 Tesia range. Our results give the mean nuclear quadrupole coupling constants (QCC), the static and MAS line widths, the chemical shifts and shift distributions, the spin—spin relaxation times (T2H), as well as the effects of hydration on T2H. We show that such a multiparameter analysis permits an unambiguous differentiation between framework and nonframework (ZSM-5 and amorphous silica—alumina) aluminum sites, which is of use in characterizing the structures of complex commercial zeolite catalysts. We present a theoretical approach to the determination of the QCC values in zeolites and silica—aluminas based upon the field dependence of the MAS or static line widths, which also yields an approximate bond-angle distribution that is found to be in accord with that deduced from X-ray diffraction and 29Si n.m.r.

A reexamination of phosphorus-containing zeolites ZK-21 and ZK-22 in light of SAPO-42

Abstract The isostructural, phosphate-containing zeolites SAPO-42, ZK-21, and ZK-22 were examined by chemical analysis, X-ray diffraction, scanning electron microscopy, and nuclear magnetic resonance spectroscopy. Although the degree of crystallinity and the nature of impurities varied, significant framework substitution by phosphorus, as well as phosphate occluded in the sodalite cage, was found in samples of all three zeolites.

Insertion of aluminium into high-silica-content zeolite frameworks. Part 3.—Hydrothermal transfer of aluminium from Al2O3 into [Al]ZSM-5 and [B]ZSM-5

High-silica ZSM-5 and [B]ZSM-5 (both containing ca. 600 ppm Al) are catalytically activated by hydrothermal treatment in the presence of alumina. Aluminium is transported as an aquo-species from Al2O3 into the zeolite and enters the framework in the tetrahedral conformation. The presence of framework B induces enhanced activation, the degree of activation increasing with B content. This is due to the hydrolytic instability of framework B and hence its ready substitution by Al.

ZSM-10: Synthesis and tetrahedral framework structure

A reproducible, scaleable synthesis of ZSM-10 is reported. This synthesis is dependent on the presence of 1,4-dimethyl-DABCO cations during the nucleation/aging stage, but this directing agent is not incorporated in the final product. Analysis of the zeolite product during aging shows that offretite is formed first and then converts to ZSM-10. The framework topology of ZSM-10 (K24Al24Si84O216 · xH2O · yR) has been determined from synchrotron X-ray and electron diffraction data, model building, and X-ray powder pattern simulation. ZSM-10 has a large hexagonal unit cell with a = 31.575(7) A, c = 7.525(4) A, P6/mmm maximum topological symmetry, and a tetrahedral framework density of 16.6 T/1,000 A3. The tetrahedral framework is constructed from columns of alternating cancrinite cages and double 6-rings which also build the LTL (Linde Type L or zeolite L) and OFF (offretite) frameworks. Two different one-dimensional, 12-ring pore systems parallel the caxis in ZSM-10. One 12-ring channel is topologically identical to the undulating channel in the LTL framework, and the other is identical to the 12-ring channel in the OFF framework. ZSM-10 appears to be the first zeolite with two distinct, parallel, 12-ring channel systems that occur individually in other zeolites.

Spectral editing: A quantitative application of spin-echo nuclear magnetic resonance spectroscopy to the study of 27Al in zeolite catalysts

Abstract 27Al spin-echo nuclear magnetic resonance (n.m.r.) is used to measure the spin—spin relaxation times, T2H, for a substantial number of model compounds, and a theory (with no adjustable parameters) based on AIue5f8AI dipolar interactions combined with crystallographically determined AIue5f8AI distances is used to estimate T2H. The homonuclear magnetic dipole interaction explains the experimental data reasonably well for compounds with high Al levels, but much less well for compounds with low levels of AI, where structure-specific interactions are important. Such structure-specific interactions are exploited to edit zeolitic AI from the background binder in alumina-bound ZSM-5 and in dealuminated zeolite-Y catalysts containing nonframework (NFW) AI. Editing allows quantitative analysis of the zeolitic components. For dealuminated zeolite Y, it is concluded that peaks assigned by others to “pentacoordinate” AI may actually arise from NFW aluminum, based on the fact that their T2H is short relative to framework (FW) AI. Theory and experimental results for the technically more demanding measurement of T2H under conditions of “magic-angle” sample spinning (MAS) with synchronous sampling are also reported. Spin-echo editing of synchronously sampled 27AI MAS n.m.r. spectra are shown to be useful for determining the FW zeolitic AI content of realistically formulated (kaolinite bound) and steamed/calcined fluidized bed cracking (FCC) catalysts. The loss of framework AI in two series of steamed FCC catalysts is less precipitous than the loss in catalytic activity, as measured by the hexane cracking α parameter.

Designed Synthesis of Mesoporous Molecular Sieve Systems Using Surfactant-Directing Agents

The use of cationic surfactants as structure directing agents has resulted in the discovery of M41S, the first, ordered mesoporous molecular sieves. Herein we describe the ability of the surfactant molecules to interact with silicate counterions resulting in the formation of organosilicate-surfactant composite arrays which exhibit hexagonal, cubic or lamellar structure.