The effects of various synthesis conditions on the structure and composition of ferrisilicate analogs of zeolite ZSM-5 were considered. Scanning electron microscopy (SEM) was used to determine the particles size distributions and morphologies. Particle sizes vary from tenths of a micron to several microns, depending on degree of agitation during crystal growth, while morphology is additionally dependent on the concentration of iron in the gel during crystallization.

X-ray emissive spectroscopy (XES) performed in the transmission electron microscope (TEM) was used to determine their composition variation. The distribution of iron amongst the crystals is more homogeneous if the gel is stirred and it does not depend on particle size.

Zeolite Beta, synthesized in 1967 (1), is the first example of a large pore, high silica zeolite (SiO2O3 > 20) prepared in the presence of an organic template (Tetraethylammonium Hydroxide). Zeolite NU-2, whose synthesis has been reported in 1982 (2) seems to be related to the zeolite Beta. Although Zeolite Beta has been claimed as useful catalyst in hydrocracking (3), cracking (4), dewaxing (5), hydrotreating (6), shale oil (7) and Fisher-Tropsh products (B) conversions and as a selective adsorbent in the separation of alkylaromatics (9); this zeolite has not been extensively characterized in the open literature.

Catalytic isomerization of paraffines of low molecular weight is a very important process in petrochemical refination and zeolites like mordenites and erionites are used frequently as supports, due to acid properties, neccesary for a dual action in hydroisomerization processes(1–3). In the present work, we analyze the behavior of erionites interchanged with Pt at low weight concentrations, using test reaction for n-pentane hydrodesintegration. At several stages of the process, small quantities of the samples were studied using TEM,AEM, IR, ESCA and Auger methods.

High resolution electron microscopy has proven to be a powerful technique to determine structural characteristics of zeolites (l–2),symmetry variations and identification of several kind of defects.Together with ideal projected potential images, the microscopist usually finds in electron micrographs the influence of electro-optical parameters and alterations of the crystallinity of the material under electron irradiation. One of the purposes of this workis to contributetothe understanding of the degradation process of zeolites under electron irradiation in the electron microscope and in this way, discriminate when it is possible, what is reliable information recorded in the images obtained in high resolution conditions.

A model describing the propagation of a rhombohedral distortion in platelet CSZ–1 zeolites is presented. It is proposed that internal stress gradients grown into CSZ–1 platelets at synthesis are responsible for this distortion of the cubic FAU framework, where the spacings of 111 planes parallel to the platelet surfaces are elongated relative to the {111} planes. The presence of inhomogeneities is suggested by the presence of thin bands of twin faults which are invariably observed near the central layers of each platelet. Elastic modelling confirms that the effects of any stress associated with such twin faults will be most pronounced in the thinnest platelets, where the effects of elastic relaxation are minimal, and where the width of the fault zone relative to the platelet thickness is maximal. Platelet CSZ–3 and Y-type zeolites, which are considerably thicker, are therefore not expected to show significant rhombohedral distortion despite the presence of similar twin fault bands.

The distribution of nickel and copper between crystallites supported on high surface area silica (Cabosil HS5) has been studied using a Philips 400 series transmission electron microscope equipped with super twin lenses, a field emission gun and EDAX energy dispersive X-ray spectroscope. The same Ni-Cu catalysts have previously been characterized and used in cyclopropane hydrogenolysis kinetics. The good intercrystallite homogeneity found in a well reduced sample having 31% nominal copper validates a critical assumption made in these previous studies. Limited data on unreduced and partially reduced samples also highlight the need to carefully control the degree of reduction in kinetic and characterization studies.

The effects of temperature of oxygen exposure on metal dispersion were determined for platinum deposited on Al2O3, ZrO2, 12 wt% Y2O3–ZrO2, and MgO. Platinum on zirconia and on magnesia showed higher thermal stability than platinum on alumina.

Pt particles in a highly dispersed Pt/γ-A12O3 catalyst have been found to undergo ordering following the removal of chemisorbed oxygen with hydrogen at room temperature. The very small Pt particles are found to be disordered following an initial reduction at 500°C. Treating the ordered phase of Pt at 500°C in hydrogen is found to restore the disordered phase.

Ag powder is activated by pulsing it with NO2 gas which forms fresh Ag microclusters. This powder is then exposed to subsequent pulses of C2H2 or CH3C2H (3.7% in N2 ). The surface enhanced Raman scattering (SERS) spectra show dramatic intensity variations due to rapid changes in adatom concentration. Normalization of these time-dependent SERS spectra to the background scattering intensity, which is proportional to the adatom concentration, provides spectra which represent adsorbate coverage if major surface reconstruction does not occur. The temporal development of the SERS spectra of C2H2 shows rapid degradation with no evidence for adsorbed species. In contrast, propyne reacts more slowly, as evidenced by the behavior of the intensity at 1980cm−1 due to adsorbed -C2-. The reactions observed are in accord with the models developed by Barteau and Madix[1] and Vohs, Carney, and Barteau[2]. Exposure to both alkynes results in the appearance of SERS active NO, an adsorbant not previously observed at room temperature. Ellipsometric measurements are consistent with the presence of a carbon overlayer, which may stabilize the NO and render the system inert to further chemical reaction.

We report observations by high resolution electron microscopy of model catalysts produced by impregnating MgO smoke particles with inorganic clusters. With the use of very low beam currents the substrates are of sufficiently low noise that we have been able to image cleanly both single atoms and very small clusters of size l-2nm in sufficient detail to determine their atomic structure. Two types of metal structures are observed: single atoms decorating atomic steps and in a few cases two-dimensional surface rafts, and a population of mainly single crystal with a few multiply twinned particles. The single crystal particles are pseudomorphically epitaxed on the MgO substrates.

The state of iridium in highly dispersed bimetallic Pt-Ir catalysts supported on amorphous silica was studied by 193Ir Mössbauer spectroscopy, after deposition via ion exchange, as well as after calcination, reduction in hydrogen, and on exposure to carbon monoxide. Characteristic patterns and relative contributions of adsorbed [Ir(NH3)5Cl] complexes, IrCl3, IrO2 and Pt-Ir alloy particles have been identified. The composition of bimetallic particles indicates a strong tendency for segregation of Pt and Ir.

The Raman spectra of ion intercalated Vermiculites have been studied. The torsional mode frequencies exhibit a shift to higher energy with increasing basal spacing d. Using a van der Waals type force model, and the nearest neighbor approximation, we have successfully derived the formula for the torsional mode frequency as functions of basal spacing d and other physical parameters. The calculation results are quite consistent with the experimental observations.

Structural and dynamical properties of intercalated solids in general [1], and layered silicates of the type AxB1−x -Vermiculite in particular, are of both fundamental and practical interest. In these systems, two types of ions A and B with different ionic radii occupy the space between two silicate layers. On the fundamental side, one is interested in studying the average interlayer spacing as a function of (1) the concentration x of the large ion, (2) sizes and compressibilities of the intercalated ions and (3) the transverse rigidity of the silicate layers. In addition, one is interested in the dynamic properties of these solids. On the practical side, when the size difference between the two intercalants is large, one obtains pillared clays which are characterized by widely spaced silicate layers that are propped apart by sparsely distributed larger interlayer cations (sometimes referred to as pillars) [2]. The enormous free volume of accessible interior space that is derived from such an open structure has significent practical application in the field of catalysis and sieving.

The nitrogen and argon adsorption isotherms of three different zeolites, calcium A, ZSM-5, and sodium Y were obtained at 77.3 and 87.5 K. Using a continuous volumetric technique high resolution data was obtained in the Henry's Law region of the isotherm at relative pressures below 10−1 P/Po. The data for the two adsorbates indicates that nitrogen, due to its quadrupole moment, shows a high degree of localized adsorption, which makes it difficult to differentiate among zeolites of different pore sizes. Argon, on the other hand, can be used to identify zeolites of different pore sizes. The argon data was used in conjunction with the Horvath-Kawazoe model to obtain a pore size distribution of the zeolite.

The slit-smeared intensity of X-radiation scattered from carbon-supported metal catalysts behaves as clh−1 + c2h−3 for higher h-values in the small-angle region (h+4πλ−1 sinθ, λ + X-ray wavelength,θ + half of scattering angle, c1, c2 are constants). For three-phase systems with sharp phase boundaries, uniform electron-densities in the metal and void phases, and lamellar electrondensity fluctuations in the carbon phase, the small-angle X-ray scattering (SAXS) can be described in terms of inter- and intraphase electron-density correlation functions, and can be shown to yield the observed behavior. Further assumptions are required to separate these contributions and calculate interfacial specific surfaces. SAXS measurements on Pt, Ru, Pd, and Rh/C are presented.

We consider a three-state lattice-gas with nearest-neighbor interactions on a triangular lattice as a model for multicomponent chemi- and physisorption. By varying the lateral interaction constants between the adsorbate particles, this model can be made to exhibit either enhanced adsorption or poisoning (inhibited adsorption). We discuss here the conditions on the interaction constants that lead to poisoning. We present the results of a ground-state calculation and detailed numerical study of the phase diagram for a set of interactions that exhibits poisoning. We calculate the phase diagrams and adsorption isotherms by the finite-size scaling transfer-matrix method. We consider the result as a simple model for the coadsorption of Sulphur and Hydrogen on a Platinum (111) surface, with interaction constants estimated from experimental data. The resulting adsorption isotherms are in good agreement with experimental results.

The interest in the petroleum industry in converting heavier feeds to liquid fuels has led to a search for microporous materials with pore sizes larger than those found in the faujasitic zeolites which form the basis of many petroleum processing catalysts. Materials with zeolite-like pores in the 10 Å range can be synthesized by intercalating large polyoxocations between the layers of smectite clays. Subsequent calcination dehydrates the cations and converts them into oxide pillars that prop the clay layers apart, resulting in permanent microporosity in the interlayer region. Pillared clays have been studied extensively during the last decade due to their potential use in petroleum processing as cracking and hydrocracking catalysts. Previous workers have primarily utilized smectite clays such as montmorillonite and hectorite as the starting layered material for pillared clay. We now report that synthetic fluoromicas, clay-like materials of layer charge density higher than that of smectites, can also be pillared with polyoxoaluminum cations to form aluminapillared fluoromicas that are thermally stable up to 700°C.

This paper reports a novel family of aluminophosphate based molecular sieves denoted as VPI-5. These molecular sieves are the first to contain pores larger than 10 Å. The large pores of the VPI-5 sieves consist of long channels circumscribed by eighteen membered rings and are capable of adsorbing molecules excluded from other molecular sieves.

Diffusion and reaction of large organic molecules in pillared clays, a new class of catalysts capable of converting gas oil into transportation fluids, is investigated. We first discuss some recent experimental data and point out the possible difficulties for obtaining accurate data. We, then, discuss a new model for describing diffusion and reaction of large organic molecules in pillared clays. The model employs stochastic and random walk concepts to model the diffusion process, and a dynamic Monte Carlo method for predicting various properties of interest, such as the effective diffusivity of the molecules.

The long-range order of pillared interlayered clays (PILCs) after acid activation with 0.05N HCl has been investigated by X-ray diffraction (XRD) methods. The data show that long-range order in PILCs decreases as AlCH-PB = ZrCH-PB » Zr/AlCH-PB - Cr/AlCH-PB (PB - pillared bentonite; MCH = metal chlorohydroxy pillaring agent, where M - Al, Zr or Cr). Apparently, pure oxide clusters are more stable than mixed oxide clusters. Treatment of PILCs with dilute HCI at 25°C is less damaging than at reflux temperature, and calcined PILCs are more stable than air-dried materials. More structural damage occurs with 3M sulfuric acid treatment than with dilute HCI. Treatment with a weak base also causes some degradation of the pillars. 27AI-MAS NMR has been used to study pillared hectorite (PH), as well as other clay systems. The large increase of the observable octahedral aluminum (AI(VI)) resonance seen after pillaring is explained by loss of water from the [Al13O4 (OH) 24 (H2O)12] 7 +(Al13 ) cation. 27A1 spectra of PILCs derived from different pillaring agents and exposed to various heat and acid treatments are remarkably similar.