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A literature survey reveals a prominent reduction in the concentration of Brønsted acid sites in hierarchically organized zeolites with increasing mesoporous or external surface area independent of the framework type or synthesis route; this suggests a common fundamental explanation. To determine the cause, nature, and impact of the underlying changes in aluminum speciation, this study combines a multitechnique analysis that integrates basic characterization, a detailed synchrotron XRD and multiple-quantum NMR spectroscopy assessment, and catalytic tests to correlate evolution of the properties with performance during successive steps in the preparation of hierarchical MFI-type zeolites by desilication. The findings, subsequently generalized to FAU- and BEA-type materials, identify the crucial impact of calcination on the protonic form, which is an integral step in the synthesis and regeneration of zeolite catalysts; on aluminum coordination; and the associated acidity trends. [ABSTRACT FROM AUTHOR]

The structure of the as-synthesized borosilicate zeolite SSZ-87 has been solved by combining high-resolution X-ray powder diffraction (XPD) and rotation electron diffraction (RED) techniques. The unit cell and space group symmetry were found from the XPD data, and were essential for the initial analysis of the RED data. Although the RED data were only 15% complete, this proved to be enough for structure solution with the program Focus. The framework topology is the same as that of ITQ-52 (IFW), but for SSZ-87 the locations of the structure directing agent (SDA) and the B atoms could also be determined. SSZ-87 has large cages interconnected by 8- and 10-rings. However, results of hydroisomerization and Al insertion experiments are much more in line with those found for 12-ring zeolites. This prompted the structure analyses of SSZ-87 after calcination, and Al insertion. During calcination, the material is also partially deboronated, and the location of the resulting vacancies is consistent with those of the B atoms in the as-synthesized material. After Al insertion, SSZ-87 was found to contain almost no B and to be defect free. In its calcined and deboronated form, the pore system of SSZ-87 is more flexible than those of other 10-ring zeolites. This can be explained by the fact that the large cages in SSZ-87 are connected via single rather than double 10-ring windows and that there are vacancies in some of these 10-rings. [ABSTRACT FROM AUTHOR]

The synthesis of the high-silica zeolite SSZ-61 using a particularly bulky polycyclic structure-directing agent and the subsequent elucidation of its unusual framework structure with extra-large dumbbell-shaped pore openings are described. By using information derived from a variety of X-ray powder diffraction and electron microscopy techniques, the complex framework structure, with 20 Si atoms in the asymmetric unit, could be determined and the full structure refined. The Si atoms at the waist of the dumbbell are only three-connected and are bonded to terminal O atoms pointing into the channel. Unlike the six previously reported extra-large-pore zeolites, SSZ-61 contains no heteroatoms in the framework and can be calcined easily. This, coupled with the possibility of inserting a catalytically active center in the channel between the terminal O atoms in place of H+, afford SSZ-61 intriguing potential for catalytic applications. [ABSTRACT FROM AUTHOR]

The white-beam Laue diffraction experiment is an attractive alternative to the more conventional monochromatic one for single-crystal structure analysis, because it takes full advantage of the X-ray energy spectrum of a synchrotron source and requires no rotation of the crystal in the beam. Therefore, it could be used for structural characterizations under in situ or operando conditions. The potential of Laue diffraction was recognized and exploited by the protein community many years ago, and the methodology, which involved positioning and rotating the crystal in the beam, has been successfully applied to the determination of both protein and small-molecule crystal structures. Here, it is proposed that the specificities of Laue diffraction are exploited to study randomly oriented stationary microcrystals of inorganic materials. In order to determine the best strategy for collecting a reasonable quantity of data from stationary crystals, a series of simulations on four model structures for three experimental setups have been performed. It is shown that the structures of the four samples can be solved with the dual-space method in SHELX, even though the data sets are highly incomplete and much of the low-resolution part is missing. The experimental setup and data collection strategy for measuring such microcrystals have been developed on BL12.3.2 at the Advanced Light Source in Berkeley. The intensities of reflections with one and two harmonics can be extracted reliably by exploiting the tunable low-energy threshold of a Pilatus detector. In this way, the number of usable reflections can be increased from 75 to 95%. Such Laue microdiffraction data have been measured and used successfully to refine the structures of the model samples. [ABSTRACT FROM AUTHOR]

The program FOCUS [Grosse-Kunstleve, McCusker & Baerlocher (1997). J. Appl. Cryst. 30, 985-995] was originally developed to solve zeolite structures from X-ray powder diffraction data. It uses zeolite-specific chemical information (three-dimensional 4-connected framework structure with known bond distances and angles) to supplement the diffraction data. In this way, it is possible to compensate, at least in part, for the ambiguity of the reflection intensities resulting from reflection overlap, and the program has proven to be quite successful. Recently, advances in electron microscopy have led to the development of automated diffraction tomography (ADT) and rotation electron diffraction (RED) techniques for collecting three-dimensional electron diffraction data on very small crystallites. Reasoning that such data are also less than ideal (dynamical scattering, low completeness, beam damage) and that this can lead to failure of structure solution by conventional direct methods for very complex zeolite frameworks, FOCUS was modified to accommodate electron diffraction data. The modified program was applied successfully to five different data sets (four ADT and one RED) collected on zeolites of different complexities. One of these could not be solved completely by direct methods but emerged easily in the FOCUS trials. [ABSTRACT FROM AUTHOR]

The crystal structure of a novel open-framework gallogermanate, SU-66 {|(C6H18N2)18(H2O)32|[Ga4.8Ge87.2O208]}, has been solved from laboratory X-ray powder diffraction (XPD) data by using a direct-space structure solution algorithm and local structural information obtained from infrared (IR) spectroscopy. IR studies on 18 known germanates revealed that the bands in their IR spectra were characteristic of the different composite building units (CBUs) present in the structures. By comparing the bands corresponding to Ge-O vibrations in the IR spectra of SU-66 with those of the 18 known structures with different CBUs, the CBU of SU-66 could be identified empirically as the Ge10(O,OH)27 cluster (Ge10). The unit cell and space group (extinction symbol P-- a; a = 14.963, b = 31.593, c = 18.759 Å) were determined initially from the XPD pattern and then confirmed by selected-area electron diffraction. The structure of SU-66 was solved from the XPD data using parallel tempering as implemented in FOX [Favre-Nicolin & Černý (2002). J. Appl. Cryst. 35, 734-743] by assuming P21 ma symmetry and two Ge10 clusters in the asymmetric unit. Rietveld refinement of the resulting structure using synchrotron XPD data showed the framework structure to be correct and the space group to be Pmma. The framework has extra-large (26-ring) one-dimensional channels and a very low framework density of 10.1 Ge/Ga atoms per 1000 Å3. SU-66, with 55 framework atoms in the asymmetric unit, is one of the more complicated framework structures solved from XPD data. Indeed, 98% of the reflections were overlapping in the XPD pattern used for structure solution. Tests on other open-framework germanates (SU-62, SU-65, SU-74, PKU-12 and ITQ-37) for which the XPD data, unit cell, space group and IR spectra were available proved to be equally successful. In a more complex case (SU-72) the combination of FOX and powder charge flipping was required for structure solution. [ABSTRACT FROM AUTHOR]

A new zeolite (SSZ-52, ∣(C14H28N)6Na6(H2O)18∣[Al12Si96O216]), related to the DeNOx catalyst Cu-SSZ-13 (CHA framework type), has been synthesized using an unusual polycyclic quaternary ammonium cation as the structure-directing agent. By combining X-ray powder diffraction (XPD), high-resolution transmission electron microscopy (HRTEM) and molecular modeling techniques, its porous aluminosilicate framework structure (R3̅m, a = 13.6373(1) Å, c = 44.7311(4) Å), which can be viewed as an 18-layer stacking sequence of hexagonally arranged (Si,Al)6O6 rings (6-rings), has been elucidated. The structure has a three-dimensional 8-ring channel system and is a member of the ABC-6 family of zeolites (those that can be described in terms of 6-ring stacking sequences) like SSZ-13, but it has cavities that are twice as large. The code SFW has been assigned to this new framework type. The large cavities contain pairs of the bulky organic cations. HRTEM and XPD simulations show that stacking faults do occur, but only at the 5–10% level. SSZ-52 has considerable potential as a catalyst in the areas of gas conversion and sequestration. [ABSTRACT FROM AUTHOR]

The new X-ray free-electron laser source (SwissFEL) that is currently being developed at PSI will provide a broad-bandpass mode with an energy bandwidth of about 4%. By using the full energy range, a new option for structural studies of crystalline materials may become possible. The proof of concept of broad-bandpass diffraction presented here is based on Laue single-crystal microdiffraction and the experimental setup on BL12.3.2 at the Advanced Light Source in Berkeley. Diffraction patterns for 100 randomly oriented stationary crystallites of the MFI-type zeolite ZSM-5 were simulated assuming several bandwidths, and the statistical and structural results are discussed. With a 4% energy bandwidth, the number of reflection intensities measured in a single shot is significantly higher than with monochromatic radiation. Furthermore, the problem of partial reflection measurement, which is inherent to the monochromatic mode with stationary crystals, can be overcome. [ABSTRACT FROM AUTHOR]

Over the past few years, the powder charge-flipping algorithm has proved to be a useful one for structure solution from powder diffraction data, so a semi-systematic study of the effect of the different input parameters on its success has been performed. Two data sets were studied in these tests: a zirconium phosphate framework material and D-ribose. The Superflip input parameters tested were the reflection overlap factor, the intensity repartitioning frequency, the isotropic displacement parameter, the threshold for charge flipping and the number of cycles/runs. By varying the values of these parameters within sensible ranges, an optimized set could be found for the zirconium phosphate case, but no combination of parameters allowed the D-ribose structure to be solved. Reasoning that starting with nonrandom phases might help, an approximate (but incorrect) structure was generated using the direct-space global-optimization method implemented in the program FOX. This structure was then used to calculate initial phase sets for Superflip by allowing the calculated phases to vary in a random fashion by a user-defined percentage. With such phases and reoptimized input parameters, some fully interpretable solutions with the correct symmetry could be produced, even with fairly low resolution data. Unfortunately, it was not possible to recognize these solutions using the Superflip R values, so other criteria were sought. Both cluster analyses and maximum entropy calculations of the solutions were performed, and the latter, in particular, look very promising. A set of guidelines derived from these two structures could be applied successfully to a further two inorganic and seven organic structures. [ABSTRACT FROM AUTHOR]

Zn atoms have been incorporated into the STA-1 microporous framework (SAOframework type) for the first time. Pure Zn-containing STA-1 aluminophosphate has been obtained in the presence of either (S)-(−)-N-benzylpyrrolidine-2-methanol (BPM) or benzylpyrrolidine (BP) as structure-directing agent. Characterisation results have demonstrated that the organic molecules remain intact within the microporous framework after the hydrothermal treatment. The X-ray diffraction pattern has been indexed in the tetragonal space group I4m2 (a= 13.7828(1) Å and c= 21.9444(4) Å). Chemical analysis and 31P MAS NMR spectroscopy confirm the incorporation of ca. 4.5 Zn atoms per unit cell by isomorphous substitution of Al. This large-pore aluminophosphate has one of the lowest framework densities among the known zeolite structures, and is therefore of potential interest for applications in adsorption or catalytic processes involving bulky molecules. [ABSTRACT FROM AUTHOR]

The flexible, anionic, open-framework material NaLa[(PO3H)2CH-C6H4-CH(PO3H)2]·4H2O (NaLa(H4L)) exhibits an exceptional selectivity for monovalent metal cations. This study elucidates the relationship between the ion-exchange behavior and the framework flexibility of this recently discovered material. The exchange of the Na+ ions in NaLa(H4L) with alkaline-earth, alkaline, and selected transition metal ions was studied. EDX and ICP-OES elemental analysis revealed that ion exchange was successful with monovalent ions, while higher-valent ions were rejected. An explanation for this charge selectivity could be found in the site-specific role of the guest cation. X-ray diffraction and thermogravimetric studies on the reversible hydration and dehydration behavior demonstrate that NaLa(H4L) has a flexible framework. Contraction of the channels upon dehydration leads to a decrease in the cell volume of 15%. Rietveld refinement of the structure of the dehydrated form NaLa(H4L)dehyd revealed the key role played by the guest cation in the channel-shrinking mechanism. In the hydrated, expanded form, each Na+ ion guest shares three phosphonate oxygens with a La3+ ion in a lanthanum phosphonate chain that defines part of the wall of a rhombic channel. The Na+ ion completes its octahedral coordination sphere with two water molecules and a weaker bond to a fourth phosphonate oxygen. In the dehydrated, contracted form, the Na+ ion loses the two water molecules and moves toward a second La3+ ion, which is located in an adjacent lanthanum phosphonate chain, to share two more phosphonate oxygens, and becomes 5-coordinate. This results in the formation of an -La-O-Na-O-La- chain and a concomitant shrinking of the channels. A comparison of the monovalent metal (M(I)) ion-exchanged compounds, M(I)La(H4L), reveals that both the ionic radius and the enthalpy of hydration of the guest cation affect the equilibrium between the expanded and the contracted forms, and that the framework adapts specifically to the size of the guest cation. [ABSTRACT FROM AUTHOR]

High-resolution X-ray powder diffraction and electron microscopy techniques yield remarkably complementary information for crystal structure determination. By combining the two types of data, structures of polycrystalline materials that resist solution by more conventional methods can be tackled. In particular, crystallographic phase information extracted either from high-resolution transmission electron microscopy (HRTEM) images or from precession electron diffraction (PED) data has proven to be extremely useful in such cases. PED data can also be used to identify weak reflections in the diffraction pattern, and this information, in turn, can be exploited to improve the partitioning of the intensities of reflections that overlap in the powder diffraction pattern. The dual-space (diffraction and real space) structure determination programs Focus and pCF have been shown to be especially well-suited for combining the two different types of data. The power of this approach is illustrated with the details of the solutions of the structures of TNU-9, IM-5 and SSZ-74, the three most complex zeolite framework structures known. [ABSTRACT FROM AUTHOR]

Information derived from precession electron diffraction (PED) patterns can be used to advantage in combination with high-resolution X-ray powder diffraction data to solve crystal structures that resist solution from X-ray data alone. PED data have been exploited in two different ways for this purpose: (1) to identify weak reflections and (2) to estimate the phases of the reflections in the projection. The former is used to improve the partitioning of the reflection intensities within an overlap group and the latter to provide some starting phases for structure determination. The information was incorporated into a powder charge-flipping algorithm for structure solution. The approaches were first developed using data for the moderately complex zeolite ZSM-5, and then tested on TNU-9, one of the two most complex zeolites known. In both cases, including PED data from just a few projections facilitated structure solution significantly. [ABSTRACT FROM AUTHOR]

The article discusses the use of three dimensional (3D) electron diffraction (ED) data derived from a single-crystal x-ray diffraction (XRD) experiment to determine hydrogen atom positions, referencing an article in the issue co-authored by scientist L. Palatinuse. The realtionship between the scattering power of an atom and its atomic number is discussed. [ABSTRACT FROM PUBLISHER]

The structure of the calcined form of the high-silica zeolite SSZ-70 has been elucidated by combining synchrotron X-ray powder diffraction (XRPD), high-resolution transmission electron microscopy (HRTEM), and two-dimensional (2D) dynamic nuclear polarization (DNP)-enhanced NMR techniques. The framework structure of SSZ-70 is a polytype of MWW and can be viewed as a disordered ABC-type stacking of MWW-layers. HRTEM and XRPD simulations show that the stacking sequence is almost random, with each layer being shifted by ±1/3 along the (110) direction with respect to the previous one. However, a small preponderance of ABAB stacking could be discerned. DNP-enhanced 2D 29Si{29Si} J-mediated NMR analyses of calcined Si-SSZ-70 at natural 29Si isotopic abundance (4.7%) establish the through-covalent-bond 29Si-O-29Si connectivities of distinct Si sites in the framework. The DNP-NMR results corroborate the presence of MWW layers and, more importantly, identify two distinct types of Q3 silanol species at the surfaces of the interlayer regions. In the first, an isolated silanol group protrudes into the interlayer space pointing toward the pocket in the adjacent layer. In the second, the surrounding topology is the same, but the isolated -SiOH group is missing, leaving a nest of three Si-O-H groups in place of the three Si-O-Si linkages. The analyses clarify the structure of this complicated material, including features that do not exhibit long-range order. With these insights, the novel catalytic behavior of SSZ-70 can be better understood and opportunities for enhancement recognized. [ABSTRACT FROM AUTHOR]

Two novel zirconium phosphate compounds, l(C9H8N)4(H2O)4I[Zr8P12O40(OH)8F5] and l(C9H8N)2l[Zr2P2O8 (OH)4F4], designated as ZrPOF-Q1 and ZrPOF-Q2, respectively, have been synthesized hydrothermaiy in the presence ot quinoline and HF and characterized by elemental and tharmogravimettc analyses, UV-vis spectroscopy, and scanning electron microscopy. Their crystal structures were determined troni powder X-ray diffraction data using a charge-flipping algorithm. The ZrPOF-Q1 structure [P¯I, a=10.7567(1) A, b = 13.8502(1) Å, c = 14.8995(1) Å, α =109.6(1)°, β=101.1(1 )°, and y=100.5(1)°] consists of zirconium phosphate layers with quinounium ions in between, The layers are unusual in that isolated ZrO2F4 octahedra are anchored on both sides of the layer and protrude into the interlayer space. The ZrPOF-Q2-structure [P¯I, a=7.7058(1) Å, b=12.3547(1) Å, c=6.5851(l) Å, α=97.0(1)°, fin 89.7(1)°, and γ= 101.9(1)°] consists of zirconium phosphate chains with an unusual Zr/P ratio of 1.0, interspersed with quinolinium ions. Both materials are stable up to 250 °C and exhibit Interesting photoluminescence in the UV-vis spectral region. This is attributed to the protonated quinoiine molecules, which are an Integral part of both structures. [ABSTRACT FROM AUTHOR]