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The need to reduce the lifecycle greenhouse gas emissions of fuels and lubricants has renewed interest in hydroisomerization processes. Here it is shown how recognizing the signature of individual alkane hydrocracking pathways enables delineating changes to the alkane hydroisomerization and hydrocracking networks as a function of catalyst pore topology. Spacious pores allow indiscriminate access to both kinetically favored alpha,alpha,gamma-trialkyl alkane hydrocracking pathways and thermodynamically favored alpha,alpha- and alpha,gamma-dialkyl alkane hydrocracking pathways. Narrower pores enhance isomerization by slowing down access to the kinetically favored hydrocracking pathways. The narrowest pores enhance isomerization further by narrowing down the remaining hydrocracking pathways: MTT-and TON-type zeolites limit hydrocracking to only a low concentration of the few isomers that are commensurate with their respective topologies. This improved understanding of how catalyst pore topologies impact hydroconversion networks is guiding the design of more carbon efficient industrial hydroisomerization processes.

Atomically dispersed supported platinum catalysts were synthesized by the reaction of Pt(acac)2 (acac = acetylacetonato) with the silicoaluminophosphate molecular sieve SAPO-37, with infrared spectra showing that the reaction involved SAPO OH groups. Extended X-ray absorption fine structure (EXAFS) spectra show that, after heating in air to 623 K, each platinum atom on average was bonded to approximately two oxygen atoms of the SAPO support, with no evidence of platinum clusters. X-ray absorption near edge spectra (XANES) indicate a platinum formal oxidation state of approximately +2. These supported mononuclear species lacked catalytic activity for ethylene hydrogenation at 1 bar and room temperature, but activity arose during catalysis in a once-through flow reactor/X-ray absorption spectroscopy cell, as the XANES white line intensity decreased, indicating reduction of the platinum, and the EXAFS-determined Pt–Pt coordination number (CN) increased from essentially zero to 2.7 ± 0.5 after 2 h, indicating the formation of platinum clusters of only a few atoms each. The data indicate the almost instantaneous formation of the clusters and identify them as the catalytically active species. Subsequent exposure of the catalyst to ethylene as in situ EXAFS and XANES data were recorded led to a decrease in the Pt–Pt coordination number to 1.6 ± 0.3 and an increase in the white line intensity, indicating partial oxidative fragmentation of the clusters by ethylene. Platinum clusters in SAPO-37 formed in separate experiments by exposure to H2 prior to catalysis were also catalytically active for ethylene hydrogenation. The data thus show how to dial in the catalytic activity by forming platinum clusters by exposure of mononuclear platinum to H2 and how to dial back the activity by oxidative fragmentation of the clusters by reaction with ethylene, all under mild conditions; the ethylene : H2 ratio of the reactant gas determines the average platinum nuclearity and thus the catalytic activity.

Zeolites are widely applied supports for metal catalysts, but molecular sieves with comparable structures-silicoaluminophosphates (SAPOs)-have drawn much less attention and been overlooked as supports for atomically dispersed metals. Now, we report SAPO-37 as a support for atomically dispersed rhodium in rhodium diethylene complexes, made by the reaction of Rh(η2-C2H4)2(acetylacetonate) with the support and anchored by two Rh-O bonds at framework tetrahedral sites, as shown by infrared and extended X-ray absorption fine structure spectra. The ethylene ligands were readily replaced with CO, giving sharp νCO bands indicating highly uniform supported species. A comparison of the spectra with those of comparable rhodium complexes on zeolite HY shows that the SAPO- and zeolite-supported complexes are isostructural, providing an unmatched opportunity for determining support effects in catalysis. The two catalysts had similar initial room-temperature activities per Rh atom for ethylene conversion in the presence of H2, but the SAPO-supported catalyst was selective for ethylene hydrogenation and the zeolite-supported catalyst selective for ethylene dimerization; correspondingly, the catalyst on the SAPO was more stable than that on the zeolite during operation in a flow reactor.

Nests of three silanol groups are located on the internal pore surface of calcined zeolite SSZ‐70. 2D 1H double/triple‐quantum single‐quantum correlation NMR experiments enable a rigorous identification of these silanol triad nests. They reveal a close proximity to the structure directing agent (SDA), that is, N,N′‐diisobutyl imidazolium cations, in the as‐synthesized material, in which the defects are negatively charged (silanol dyad plus one charged SiO− siloxy group) for charge balance. It is inferred that ring strain prevents the condensation of silanol groups upon calcination and removal of the SDA to avoid energetically unfavorable three‐rings. In contrast, tetrad nests, created by boron extraction from B‐SSZ‐70 at various other locations, are not stable and silanol condensation occurs. Infrared spectroscopic investigations of adsorbed pyridine indicate an enhanced acidity of the silanol triads, suggesting important implications in catalysis., Silanol defects determine adsorption and catalysis in zeolites by their hydrophilic properties, but they can also contribute to catalytic reactions through their weak acidities or cooperative effects with other active sites. Well‐defined silanol defect clusters (see structure: cyan H, red O, black Si) with distinct size in topologically related zeolites, SSZ‐70 and ITQ‐1 are identified by NMR spectroscopy.

Rh(I)(CO)2 complexes anchored to zeolite HY were converted into Rh4(CO)12 in the zeolite supercages upon exposure to flowing CO + H2O at 35 °C, and the chemistry and kinetics were characterized wit...

Rhodium gem-dicarbonyl complexes, Rh(CO)2, bonded within the pore structure of zeolite HY and formed by the reaction of Rh(CO)2(acac) (acac = acetylacetonato) with OH groups on the zeolite surface were converted in >95% yield to Rh4(CO)12 by reaction with CO + water at 308 K, and the process was reversed by treatment of the supported clusters in helium at 353 K. The chemistry of these reactions was characterized by IR and X-ray absorption spectra recorded during the changes and by density functional theory. The cluster formation is driven by the water gas shift half-reaction, leading to generation of CO2 and zeolite surface protons, and the reverse reaction proceeds via the half-reaction that completes the cycle of the water gas shift reaction. Thus, the overall process is cyclic–catalytic. The yield in the synthesis of Rh4(CO)12 is the highest reported, and the high selectivity is facilitated by the confining environment for the clusters in the zeolite supercages and the low density of OH groups on the z...

A halogen-free flame retardant containing nitrogen and phosphorus, 2-[anilino-(6-oxobenzo[c][2,1]benzoxaphosphinin-6-yl)methyl]phenol (PDOP), has been synthesized by reaction of benzo[c][2,1]benzoxaphosphinine-6-oxide (DOPO) with 2-( N-phenyliminomethyl)phenol. Halogen-free flame-retardant rigid polyurethane foams (RPUF-PDOP) were prepared using PDOP as a flame retardant. The flammability was investigated using limiting oxygen index, a vertical burning test (UL-94), and a cone calorimeter. When PDOP (10 wt%) as flame retardant was added to RPUF (RPUF-PDOP10%), the limiting oxygen index value was increased from 18% to 27%, and a UL-94 V-0 rating was achieved; meanwhile, the peak heat release rate, total heat release, and the average mass-loss rates of RPUF-PDOP10% were reduced from 246 to 207 kW m−2, from 26.9 to 21.0 MJ/m2, and from 0.043 to 0.033 g/s, respectively. Especially, the initial decomposition temperature of RPUF-PDOP10% was decreased from 228°C to 209°C. The final residual char from decomposition of RPUF-PDOP10% was significantly increased up to 35.6%. The addition of PDOP did not markedly decrease the mechanical properties of the resulting flame-retardant RPUFs.

This paper reports a method for directly determining the effective strength of those acid sites on a molecular sieve catalyst that are actually involved in reactions such as hydrodewaxing. The method is here applied to the conversion of a waxy paraffin over a catalyst containing platinum and a SAPO-11 sieve of high isomerization selectivity, as well as a catalyst containing platinum and a H-ZSM-5 zeolite (SiO2/Al2O3 = 150) of high cracking selectivity. Results are compared against the measured Bronsted acid site strength on these molecular sieves determined from temperature-programmed desorption of ammonia and Fourier transform infrared analysis of adsorbed pyridine. Characterization of acid sites showed both concentration and apparent acid strength for H-ZSM-5 higher than those for SAPO-11, with the latter having a finite but smaller amount of strong acid sites that adsorbed pyridine at 573 and 673 K. Reactions with n-hexadecane gave significantly higher conversion rates on H-ZSM-5, and it is shown that ...

Large-pore microporous materials are of great interest to process bulky hydrocarbon and biomass-derived molecules. ITQ-27 (IWV) has a two-dimensional pore system bounded by 12-membered rings (MRs) that lead to internal cross-sections containing 14 MRs. Investigations into the catalytic behavior of aluminosilicate (zeolite) materials with this framework structure have been limited until now due to barriers in synthesis. The facile synthesis of aluminosilicate IWV in both hydroxide and fluoride media is reported herein using simple, diquaternary organic structure-directing agents (OSDAs) that are based on tetramethylimidazole. In hydroxide media, a zeolite product with Si/Al=14.8–23.2 is obtained, while in fluoride media an aluminosilicate product with Si/Al up to 82 is synthesized. The material produced in hydroxide media is tested for the hydroisomerization of n-hexane, and results from this test reaction suggest that the effective pore size of zeolites with the IWV framework structure is similar to but slightly larger than that of ZSM-12 (MTW), in fairly good agreement with crystallographic data.

Three-dimensional 10-ring zeolites TUN, IMF, –SVR, MFI and MEL were investigated as for their acid properties, adsorption of 2,2-dimethylbutane and in toluene disproportionation and its alkylation with isopropyl alcohol. The results were compared against zeolite *SFV, the structure of which consists mainly of MEL zeolite with some additional 12-ring channel system. With exception of –SVR synthesized with high Si/Al ratio, all other zeolites provided Si/Al ratios in a narrow region. Novel zeolites TUN, IMF, and –SVR exhibited higher conversions than MFI and MEL in toluene alkylation. TUN and IMF were substantially more active in toluene disproportionation indicating less diffusion restrictions of channel structure on the disproportionation reaction. *SFV showed a similar catalytic behavior to MEL with much lower selectivity to p-xylene and p-cymene. This could indicate that both toluene disproportionation and alkylation proceed in reaction space of *SFV being similar to those of MFI and MEL. *SFV and TUN exhibited much faster adsorption of 2,2-dimethylbutane than MFI, MEL, IMF, and –SVR. It was concluded that the presence of some larger transport pores in *SFV than in other zeolites is responsible for fast adsorption of 2,2-dimethylbutane and transport of products resulting in a low selectivity to p-xylene and p-cymene.

A series of small-pore zeolites are synthesized and investigated as catalysts for the methanol-to-olefins (MTO) reaction. Small-pore zeolites SSZ-13, SSZ-16, SSZ-27, SSZ-28, SSZ-52, SSZ-98, SSZ-99, SSZ-104, SSZ-105 and an ITQ-3-type material are synthesized, and the results from their use as catalytic materials in the MTO reaction compared to those obtained from SAPO-34. The production of propane that tends to correlate with catalytic material lifetime (higher initial propane yields lead to shorter lifetimes) declines with increasing Si/Al (as has been observed previously for SSZ-13), and a larger cage dimension leads to higher propane yields at a fixed Si/Al. Data from these materials and others reported previously, for example, SSZ-39 and Rho, that were tested at the same reaction conditions, revealed four different patterns of light olefin selectivities: 1) ethylene greater than propylene with low butene, for example, SSZ-17, SSZ-98, SSZ-105, 2) ethylene equal to propylene and low butene, for example, SAPO-34, SSZ-13, SSZ-16, SSZ-27, SSZ-52, SSZ-99, SSZ-104, 3) propylene greater than ethylene with butene similar to ethylene, for example, SSZ-28, SSZ-39, and 4) ethylene equal to propylene equal to butene, for example, Rho. No clear relationships between zeolite cage architecture and light olefin selectivity emerged from this investigation, although several trends are presented as suggestions for further study.

Images of La-exchanged NaY zeolite obtained with aberration-corrected scanning transmission electron microscopy (STEM) show that about 80% of the La cations were present as site-isolated species, with the remainder in pair sites. The observed distances between La cations in the pair sites ranged from 1.44 to 3.84 A, consistent with the presence of pairs of cations tilted at various angles with respect to the support surface. The actual distance between La cations in the pair sites is inferred to be approximately 3.84 A. The results suggest the presence of dimeric structures of La cations bridged with O anions, and the presence of such species has been inferred previously on the basis of X-ray photoelectron spectroscopy (W. Grunert, U. Sauerlandt, R. Schlogl, H.G. Karge, J. Phys. Chem., 97 (1993) 1413).

The chemistry of post-synthetic modification of borosilicate zeolites, and their understanding and use in catalytic applications are reviewed. First, a survey is given on the practical application of solid state NMR to follow the structural properties of boron. Then, the hydrolytic chemistry of boron in zeolites is summarized with a focus on selective reactivities of trigonal boron created by counterions, and stepwise extraction of boron from the framework. The reinsertion of other heteroatoms (mainly Al is discussed here) can be carried out by three different methods with different selectivities. First, the extent of Al reinsertion can be tailored quantitatively by controlling boron removal and vacancy formation with appropriate counterions. Secondly, the substitution of Al for B can be kinetically retarded by using uncalcined as-made zeolites with organic structure directing agents still occluded in the pores. Although these zeolites are not porous, quantitative replacement of framework atoms (Al for B) is possible, most likely by a solid state diffusion mechanism. Finally, Al reinsertion can be efficiently achieved in aqueous Al(NO3)3 solution under acidic conditions and is pore selective. This is due to the finding that the hydrated aluminum cations are too bulky for medium-sized pores, so that preferably 12-membered ring pores can be aluminated, and 10-membered ring pores do not substitute Al for B. This substitution can be quantitatively followed by the pH change in the zeolite/Al(NO3)3 slurry. A variety of catalytic test reactions are used to characterize the catalytic properties of the aluminosilicate zeolites prepared via post-synthetic treatment of their borosilicate counterparts.

The mole fraction solubilities of 1,3,2-dioxaphosphorinane-2-methanol-α,5,5-trimethyl-α-phenyl-2-oxide in different organic solvents including acetonitrile, acetone, ethyl acetate, 1,2-dichloroethane, methanol, ethanol, and chloroform were measured at a designated temperature range of (278.15 to 343.15) K and at atmospheric pressure by the gravimetrical method. The compound’s structure and thermal stability were characterized by infrared spectroscopy, nuclear magnetic resonance (1H NMR and31P NMR), mass spectroscopy, elemental analysis, and thermogravimetric analysis. The mole fraction solubilities of 1,3,2-dioxaphosphorinane-2-methanol-α,5,5-trimethyl-α-phenyl-2-oxide in the above-mentioned organic solvents were correlated as the Apelblat equation, and the calculated values with equations showed good consistency with the experimental values. The root-mean-square deviation was less than 0.010 % and the average relative error was less than 0.11 % in all the experiments.

A novel intumescent flame retardant (IFR) containing ferrocene and caged bicyclic phosphate groups, 1-oxo-4-[4'-(ferrocene carboxylic acid phenyl ester)] amide-2, 6, 7-trioxa-1-phosphabicyclo- [2.2.2] octane (PFAM), was successfully synthesized. The synthesized PFAM were added to flammable polyurethane (PU) as flame retardants and smoke suppressants. The structure of PFAM was characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (1H NMR) and elemental analysis. Thermal stability of PFAM was tested by themogravimetric analysis (TGA). The results revealed that PFAM had good thermal stability and high char weight, the char weight up to 54% at 600 °C. Flammability properties of PU/PFAM composites were investigated by limiting oxygen index (LOI) test and UL-94 test, respectively. The results of LOI tests showed that the addition of PFAM enhanced flame retardancy of PU. When the content of PFAM reaches to 3%, the LOI value is 22.2. The morphologies of the char for PU and PU/3% PFAM composite can be obtained after LOI testing were examined by SEM. The results demonstrated that PFAM could promote to form the compact and dense intumescent char layer. Experiments showed that, the PFAM application of polyurethane showed positive effect.

Dealuminated zeolite HY was used to support Ir(CO)_2 complexes formed from Ir(CO)_2(C_5H_7O_2). Infrared and X-ray absorption spectra and atomic resolution electron microscopy images identify these complexes, and the images and ^(27)Al NMR spectra identify impurity amorphous regions in the zeolite where the iridium is more susceptible to aggregation than in the crystalline regions. The results indicate the value of electron microscopy in characterizing the amorphous impurity regions of zeolites and a significant stability limitation of metals in these regions of zeolite catalyst supports.

We describe a new zeolite catalyst where we develop only a portion of the structure for strong acid sites. This is achieved using zeolite SSZ-57 in boron lattice substitution (weak acid sites) and then replacing the boron sites in the large pore segments of this novel zeolite, while the intermediate pores (with MEL topology) remain unchanged. We can achieve the creation of such a novel catalyst system due to the inherent structure of SSZ-57 (repeat domains of MEL topology, periodically interrupted by a short segment of large pores) because the re-insertion of aluminum for boron requires that the pores be large to effect substitution. In this work, we describe the preparation and characterization of the novel material designated as SSZ-57LP. We use three model compound reactions to demonstrate the unique behavior for this novel large pore (but short path) zeolite and contrast it with intermediate pore zeolite Al-ZSM-11 (MEL topology) and the Al-SSZ-57 where the strong acid sites are in both intermediate and large pore regions (from direct zeolite synthesis with aluminum in the gel). The reactions studied are the Constraint Index probing reactant selectivity for cracking n-hexane and 3-methylpentane, the hydroisomerization of n-hexane where the formation of dimethylbutanes is examined for large pore space within a zeolite, and then finally, the isomerization and disproportionation of 1,3-diethylbenzene, again as a probe for large enough transition state selectivity within a given zeolite.

The solubilities of 1,3,2-dioxaphosphorinane-2-methanol-α,α-5,5-tetramethyl 2-oxide (DMTO) were measured in different solvents including ethyl acetate, methanol, ethanol, chloroform, acetonitrile, acetone, 1,2-dichloroethane, and water at temperature ranging from 278.15 K to 343.15 K by the gravimetrical method. The structure of DMTO was characterized by nuclear magnetic resonance (1H NMR and 13P NMR), infrared spectroscopy (IR), and mass spectroscopy (MS). The thermal stability of DMTO was characterized by thermogravimetric analysis (TGA). The modified Apelblat was used to correlate the measured solubility data. The results showed that the calculated solubilities were in good agreement with experimental values in all selected solvents. The root-mean-square deviation was less than 0.091 %, and the average relative error was less than 0.22 % in all of the experiments.

Researchers at Chevron recently discovered a route for making high silica stilbite (STI), a zeolite with intersecting 10- and 8-ring channels. This zeolite, named SSZ-75, provides an interesting comparison to two other two-dimensional 10/8-ring zeolites, namely, ferrierite (FER) and ZSM-57 (MFS). The catalytic properties of these zeolites are characterized here using the Constraint Index test, adsorption measurements, and toluene disproportionation and its alkylation with isopropyl alcohol. Results are then compared to ZSM-5 (a well-characterized 3-dimensional 10-ring zeolite) and TON (a 1-dimensional 10-ring zeolite). While the micropore volumes for several of these five materials are similar, the Constraint Index, which considers the competitive cracking of n-hexane and 3-methylpentane, differs greatly. On the other hand, toluene conversions along with selectivity to p-xylene for MFI and STI are remarkably similar. This indicates that the reaction volume available at the intersections of the 10- and 8-ring channels in STI is comparable with that of the 10-ring channel intersections in MFI. However, in toluene alkylation with isopropyl alcohol, differences in intersection volume between MFI and STI are revealed. These results nicely demonstrate how the size of the pores and geometry of the channel intersections (rather than just the size of the individual pores) impact the catalytic properties of zeolites with multidimensional channel systems.

Paraffin disproportionation via molecular redistribution (MR) and molecular averaging (MA) couples paraffin dehydrogenation and olefin hydrogenation to olefin metathesis and presents a unique example of bifunctional catalysis. In this paper we will present a series of applications of the MR/MA chemistry in refining and petrochemical industries. The thermodynamic aspects of the MR/MA chemistry and parameters influencing the catalyst performance will be discussed. We will also report the catalyst regeneration related to coke deposition and sulfur poisoning. Furthermore, the MR technology for upgrading liquid petroleum gas is scaled up in pilot plant. MR/MA provides a simple process of paraffin disproportionation which can be accomplished otherwise only via complex combinations of other existing technologies.

Zeolite HSSZ-53, which has 1-dimensional channels with 14-ring extra-large pores, was used as a support for a molecular iridium complex synthesized from Ir(C2H4)2(C5H7O2) and characterized with infrared (IR) and extended X-ray absorption fine structure (EXAFS) spectroscopies and atomic-resolution aberration-corrected scanning transmission electron microscopy (STEM). The spectra show that Ir(C2H4)2(C5H7O2) reacted readily with the bridging OH groups of the zeolite, leading to the removal of C5H7O2 ligands and the formation of mononuclear Ir(C2H4)2 complexes bonded to the zeolite by Ir–O bonds at the framework aluminum sites. STEM images confirm the spectra, showing site-isolated iridium centers within the zeolite channels, with no evidence of iridium clusters. The samples constitute a highly uniform, well-defined array of essentially molecular catalytic species in a highly uniform, confined environment, allowing precise investigations of the chemistry of the iridium complex in the absence of solvents. IR s...

Using aberration-corrected scanning transmission electron microscopy (STEM), we imaged iridium atoms in isolated iridium complexes in the one-dimensional nonintersecting 14-ring channels of zeolite SSZ-53. STEM allows tracking of the movement of atoms in the channels, demonstrating the interaction of iridium with the zeolite framework (channel confinement) and providing a direct visualization of the initial steps of metal nanocluster formation. The results demonstrate how STEM can be used to help design improved catalysts by identifying the catalytic sites and observing how they change in reactive atmospheres.

In this paper, we report our studies on adsorption of 2,2-dimethylbutane as adsorbate in various zeolites. The time dependence of the adsorption capacity provides valuable information on the structure characteristics of zeolites to distinguish between large and medium pore zeolites. Novel zeolites IM-5 and SSZ-57 will be used as examples to demonstrate how to employ this technique to gain useful input for the determination of new zeolite structures. The effects of external surface on the adsorption behavior of zeolites will be discussed.

The chemistry of post-synthetic modification of borosilicate zeolites, and their understanding and use in catalytic applications are reviewed. First, a survey is given on the practical application of solid state NMR to follow the structural properties of boron. Then, the hydrolytic chemistry of boron in zeolites is summarized with a focus on selective reactivities of trigonal boron created by counterions, and stepwise extraction of boron from the framework. The reinsertion of other heteroatoms (mainly Al is discussed here) can be carried out by three different methods with different selectivities. First, the extent of Al reinsertion can be tailored quantitatively by controlling boron removal and vacancy formation with appropriate counterions. Secondly, the substitution of Al for B can be kinetically retarded by using uncalcined as-made zeolites with organic structure directing agents still occluded in the pores. Although these zeolites are not porous, quantitative replacement of framework atoms (Al for B) is possible, most likely by a solid state diffusion mechanism. Finally, Al reinsertion can be efficiently achieved in aqueous Al(NO3)3 solution under acidic conditions and is pore selective. This is due to the finding that the hydrated aluminum cations are too bulky for medium-sized pores, so that preferably 12-membered ring pores can be aluminated, and 10-membered ring pores do not substitute Al for B. This substitution can be quantitatively followed by the pH change in the zeolite/Al(NO3)3 slurry. A variety of catalytic test reactions are used to characterize the catalytic properties of the aluminosilicate zeolites prepared via post-synthetic treatment of their borosilicate counterparts.

© 2015 American Chemical Society. 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.

A stable site-isolated mononuclear platinum catalyst with a well-defined structure is presented. Platinum complexes supported in zeolite KLTL were synthesized from [Pt(NH3)4](NO3)2, oxidized at 633 K, and used to catalyze CO oxidation. IR and X-ray absorption spectra and electron micrographs determine the structures and locations of the platinum complexes in the zeolite pores, demonstrate the platinum-support bonding, and show that the platinum remained site isolated after oxidation and catalysis.

The synthesis, structure solution, and characterization of the high-silica zeolite SSZ-55 are described. SSZ-55 was synthesized under hydrothermal conditions using a [(1-(3-fluorophenyl)cyclopentyl...

The synthesis, structure solution, and characterization of the high-silica molecular sieve CIT-5 (California Institute of Technology Number 5) is described. CIT-5 is synthesized at hydrothermal conditions in the presence of N(16)-methylsparteinium and preferrably lithium cations. The structural solution of CIT-5 shows that it contains one-dimensional pores circumscribed by 14 tetrahedral atoms (14 MR). Rietveld refinement of the synchrotron X-ray powder data gives a symmetry and space group assignment for the structure of Pmn2_1 (no. 31) with refined unit cell parameters of a = 13.6738(8) A, b = 5.0216(3) A, and c = 25.4883(7) A (V = 1750.1 A^3). Electron diffraction and transmission electron microscopy confirm the space group and the topology of the structure viewed along the [010] direction. Solid-state ^(29)Si NMR spectroscopy results are consistent with the space group assignment. The thermal/hydrothermal stability of CIT-5 compares well to that of other large- and extra-large-pore, high-silica molecular sieves. The acid form of CIT-5 is able to perform hydrocarbon reactions such as cracking and alkylation and shows behaviors that are different from other zeolites.

The synergy of template molecule size and hydrophobicity and the sources of inorganic reagents affecting zeolite nucleation are described. In particular, the discovery of high silica zeolites SSZ-26, 41, 42 and UTD-1 is considered in this light. Of particular value is the use of zeolites themselves as reactants; three different examples are given. Some general rules for lattice substitution and zeolite product type are given. An unexpected use of the template used in the discovery of zeolite SSZ-42 is described now that the structure of the zeolite has been resolved, largely from single crystal data. Finally some new synthetic conditions with considerable economic advantage are described for zeolite SSZ-25. Some new questions about the effect of organic cations on solution instability are raised.

The molecular sieve UTD-1 is investigated using scanning and transmission electron microscopies (TEM), solid-state NMR spectroscopy, electron (ED) and X-ray diffraction (XRD), adsorption studies, and catalytic test reactions. The results confirm that UTD-1 is the first high-silica zeolite to contain a one-dimensional, extra-large 14-ring pore system. TEM and ED show that UTD-1 is faulted along the (002) planes. Simulations of XRD patterns of faulted structures using DIFFaX indicate that the XRD pattern of a framework containing the so-called double crankshaft chains is in better agreement with the experimental pattern than a framework with the narsarsukite chains previously reported. Thermal/hydrothermal stability studies show that UTD-1 has similar stability to other medium- and large-pore, high-silica zeolites. The ratio of isomerization to disproportionation, and the distribution of trimethylbenzene isomers in the m-xylene isomerization test reaction from UTD-1 are similar to those obtained from other ...

The reactions of m-xylene are conducted over all known zeolites with intersecting medium and large pores (MCM-22, NU-87, CIT-1, SSZ-33, SSZ-26) and the results compared to those from large (SSZ-24, ZSM-12, zeolite beta, zeolite L) and medium (ZSM-5, EU-1) pore zeolites. Each of the materials MCM-22, NU-87 and CIT-1/SSZ-33/SSZ-26 reveals a unique reaction behavior in terms of the p-xyleneo-xylene and isomerization/disproportionation ratios, the distribution of formed trimethylbenzenes and the rate of deactivation. The reaction activities and selectivities of MCM-22 and CIT-1/SSZ-33/SSZ-26 are somewhat like medium and large pore zeolites, respectively, as is expected from their crystal structures. NU-87 displays a lower p-xyleneo-xylene ratio and a higher turnover frequency than predicted from the crystal structure.

The enthalpies of formation of a series of high-silica zeolites are only 8–14 kJ/mol less exothermic than that of quartz, with a very weak dependence on volume (framework density), despite a factor of two variation in those parameters. Several mesoporous silicas, with pore diameters in the range 3–5 nm, also are only 14 kJ/mol less stable energetically than quartz. Thus, in the microporous and mesoporous regime, the energy appears to level off at values only about 14 kJ/mol less stable than quartz, with the pores behaving energetically like an inert second phase. Similar trends are seen for AlPO4 zeolites, and for a dehydrated CaAl silicate zeolite. These data suggest that the synthesis of microporous materials is not limited by their energetics but by finding appropriate kinetic pathways for their formation.

A series of pure-silica or high-silica zeolites, several mesoporous silicas, moganite, and the conventional silica polymorphs (tridymite, cristobalite, coesite, glass) are energetically, at most, 15 kJ/mol higher than quartz, with the energy versus volume curve leveling off about 15 kJ per mol of SiO2 above quartz for large volumes. For AlPO4 polymorphs, a similar trend holds, with energy leading off at an even less metastable value, namely about 10 kJ per mol of Al0.5P0.5O2 above berlinite. These small energy differences are consistent with self assembly of these materials being geometrically and kinetically, rather than energetically, controlled. Thus there is very little energetic limitation to the possibility of synthesizing various micro- and mesoporous framework structures.

MCM-41 and mesoporous materials derived from kanemite are synthesized and characterized by X-ray powder diffraction (XRD), N 2 adsorption-desorption, cyclohexane and water physical adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analyses (TGA), Fourier transform infrared (FTIR) and 13 C and 29 Si magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Both preparations yield mesoporous materials with narrow-pore-size distributions and somewhat similar physicochemical properties. However, due to a higher degree of condensation in the silicate walls of the materials derived from kanemite, these samples have higher thermal and hydrothermal stability than MCM-41. Additionally, the mechanisms by which these two types of materials are formed are dramatically different.

Zeolites X and Y containing intrazeolitic cesium oxide particles are synthesized and characterized by 133 Cs nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy of adsorbed CO 2 and CO 2 temperature- programmed desorption. The isomerization of 1-butene to give cis/trans ratios of 2-butene above 10 at 150°C shows that these materials are solid base catalysts. At the same reaction conditions, cesium ion-exchanged zeolites X and Y are inactive. The combined physicochemical properties are used to develop structure-property relationships and to rationalize the origin of the strong basicity achieved by the intrazeolitic cesium oxide particles. These novel catalysts offer new possibilities for shape-selective solid superbase catalysis.

In this presentation we explore the characterization and catalytic behavior of zeolite SSZ-57. It has definite structural relationships to zeolite MEL, but then significant departures in the performance details. The HREM work carried out at the Terasaki lab attempts to develop a novel theory about this seeming contradiction in structural relation and performance divergence.

The solids obtained during the synthesis of MCM-41 are investigated by X-ray powder diffraction, thermogravimetric analysis and 29Si NMR spectroscopy. These data, in combination with those obtained from in situ14N NMR spectroscopy, are used to elucidate the synthesis mechanism of MCM-41. The results shown here reveal that the liquid crystalline phase, H1, is not present in the synthesis medium during the formation of MCM-41 and therefore cannot be the structure-directing agent for MCM-41. Rather, the data suggest that randomly ordered rod-like organic micelles interact with silicate species to yield approximately two or three monolayers of silica encapsulation around the external surfaces of the micelles. Subsequently, these composite species spontaneously assemble into the long-range ordered structure (hexagonal packing) characteristic of MCM-41. With further heating, the silicate species in the interstitial spaces of the ordered organic—inorganic composite phase continue to condense. Complete condensation of the silicate species is not possible because SiO− species are necessary for charge compensation of the occluded alkylammonium ions.

The mesoporous molecular sieves MCM-41 are synthesized and characterized by X-ray powder diffraction, nitrogen adsorption/desorption, cyclohexane and water adsorption, transmission electron micrographs (TEM), thermogravimetric analysis (TGA), ammonia temperature-programmed desorption (TPD), FTIR, FT-Raman, 29Si, 27Al and 13C magic angle spinning (MAS) NMR spectroscopy. Raman spectra from these materials exhibit a common band at ∼610 cm−1 assignable to cyclic trisiloxanes (3-membered rings), indicating in combination with TEM, IR and NMR results that the inorganic portion of MCM-41 resembles amorphous silicas or aluminosilicates rather than crystalline molecular sieves in terms of the local structure and bonding. Pure-silica MCM-41 can be heated to at least 850°C in dry air or 800°C in air with 8 Torr water vapor before structural collapse begins. Using sodium aluminate as the aluminum reagent, aluminosilicate MCM-41 can be prepared with a Si/Al ratio as low as 29 without observing the presence of octahedral aluminum. Such is not the case when using Catapal alumina. Adsorption of cyclohexane and water reveals that pure-silica and aluminosilicate (Si/Al = 39) MCM-41 are both hydrophobic. Based on ammonia TPD results, aluminosilicate MCM-41 has acidity similar to that of amorphous aluminosilicates.

The framework topology of the novel zeolite SSZ-42 is determined from single crystal data (15 × 15 × 35 µm) and refined from powder diffraction data; the crystalline architecture is characterized by an undulating, one-dimensional 12-membered ring channel system.