Paul B. Venuto

Paraffin dehydrocyclization: Distribution of aromatic products obtained with “nonacidic” supported Pt catalysts

The distribution of the isomeric aromatic products from the dehydrocyclization of ten C8C9 paraffins over a 0.6% Pt catalyst supported on “nonacidic” alumina has been determined. The aromatic isomers obtained experimentally are those predicted for a direct cyclization to the six-membered ring structure. The participation of other size ring intermediates recently proposed to explain dehydrocyclization over chromia is not required to explain our results with a platinum catalyst. The very small amount of aromatic isomers not expected from direct six-membered ring formation probably arise from dual functional catalytic isomerization of the reactant prior to cyclization. The aromatic product distribution suggests that a “geminal dialkylcyclohexane intermediate” contributes to the reaction pathway when such structures are allowed by a six-membered ring closure.

Synthetic offretite: I. Physicochemical characterization

The thermochemical, crystallographic, morphologic and catalytic properties of a synthetic tetramethylammonium (TMA) offretite and its ammonium and hydrogen derivative forms have been investigated. TMA offretite crystallizes as small irregular particles (0.5μ × 1.5μ) in contrast to the more elongated crystals of natural and synthetic erionite. Thermal decomposition of TMA ions (probably located in the large intracrystalline pores along the c crystallographic axis) occurs near 483 °C. The resulting catalyst sorbs 7.8 wt % cyclohexane, 8.8 wt% n-hexane and 16.5 wt % water. Room temperature ion exchange of the parent TMA offretite with 0.1 N (NH4)2SO4 yields an ammonium derivative with one potassium per unit cell trapped in a cancrinite cage or hexagonal prism. Conversion of NH4-offretite to the acid form requires a temperature 100 °C higher than NH4Y. Acid offretite shows significant activity for the catalytic cracking of n-hexane.

Stoichiometry of thermochemical transformations of NH4Y zeolite

Abstract Quantitative aspects of thermal transformations of NH 4 Y have been investigated using thermogravimetric, temperature-programmed desorption, infrared, and pulsed NMR techniques. Results obtained for hydrated NH 4 Y agree closely with published data. Anhydrous NH 4 Y was quantitatively reconstituted from HY. Differential thermograms of ammonium ion decomposition show two distinct classes of chemisorption sites with apparent activation energies of 15 and 22 kcal/mole, respectively. The rate of dehydroxylation is apparently highly dependent on the ambient water vapor pressure. An increase in apparent activation energy from 70 kcal/mole at 10 −2 torr to 100 kcal/mole in the presence of He shows that the reaction is probably diffusion-controlled. The N Al atom ratio based on “chemisorbed” NH 3 is reduced from about 1.0 to 0.5 after dehydroxylation but some NH 3 is apparently more strongly held by Lewis-type sites produced. All attempts to reconstitute NH 4 Y or HY from dehydroxylated zeolite Y failed.

Mass spectra of benzofurans

Abstract The mass spectra of a number of substituted benzofurans are reported. Ring fragmentation as opposed to substituent fragmentation was observed in halogenated benzofurans. Initial loss of carbon monoxide was found without any evidence for loss of formyl radical (HCO). Benzocyclopropenecarboxaldehyde is proposed as a possible intermediate ion. Hydrogen scrambling observed with deuterated substrates occurred in either the molecular ion, the carboxaldehyde radical ion or the CO elimination product, the benzocyclopropene radical ion. The chlorobenzofurans and, in part, bromobenzofuran fragmented by successive loss of CO and halogen atom. The bromobenzfuran molecular ion also showed the inverted sequence of initial loss of bromine followed by loss of CO. This process was examined by use of the spectra of nitro- and methoxy-benzofurans. Fluorobenzofurans showed little fluorine loss in the early stages of the fragmentation process.

Sorption and exchange patterns of benzene-phenolic mixtures over faujasite catalyst: Relevance to phenol ethylation

Abstract Competitive sorption experiments showed that phenol (and anisole) was sorbed preferentially over benzene on hydrogen Y-zeolite at 130 °C. Using benzene- d 6 , isotopic exchange patterns of these compounds were observed. Benzene- d 6 , although less strongly sorbed, communicated with the zeolite surface as shown by isotopic exchange. The deuterium thus exchanged onto the surface was subsequently transferred into the nuclear as well as hydroxyl hydrogen positions of phenol. Further, a temperature higher than 200 °C was required to desorb the phenolic compounds. These data provide an explanation of some apparent anomalies previously observed in phenol ethylation.

Synthetic offretite: II. Decomposition of organic cations and generation of acidity

Abstract The organic transformations and associated structural changes during thermal decomposition of a tetramethylammonium (TMA) offretite have been investigated. In the aluminosilicate structure, lattice associated hydroxyl groups, confirmed as protonic in nature by interaction with NH 3 , were generated from TMA cations, an unusual proton precursor. Dehydroxylation of acid offretite at approximately 500 °C occurred to give electron acceptor (Lewis) sites which coordinated with NH 3 . A complex mixture of coke, trimethylamine, and twenty-one low molecular weight molecules, including methanol, carbon monoxide, methyl ether, C 3 -C 4 olefins, and hydrogen can be formed from vacuum fragmentation of the bulky TMA cations within the narrow offretite channels. A mechanistic interpretation, which includes superimposition of many “classical” reaction patterns rationalizes the observed product distributions.

Formation of stilbenes and related compounds from reaction of benzyl-type mercaptans over zeolites

Abstract Trans-Stilbene is formed with 60–70% selectivity when benzyl mercaptan is passed over Na 13X and Linde 4A at 250 °C and one atmosphere. Appreciable amounts of analogous olefin dimers are also formed from reaction of a number of other aralkyl mercaptans, RCH2SH, over zeolites where the structure of R does not permit simple β-elimination of H2S. Possible operation of α-eliminations is suggested.

Synthetic offretite: III. Physicochemical aspects of crystallization

Abstract The progress of crystallization of tetramethylammonium (TMA) offretite from an alumina-silica gel at 97 °C has been monitored by sorptive, thermochemical, spectroscopic, and other physicochemical probes. Initial ordering of gel particles into large agglomerates and onset of crystallization occurred within the first 20 hr. During the critical interval of 20–44 hr, the gel was transformed into a crystalline phase, with incorporation of aluminum and TMA cations into the aluminosilicate lattice, and after this period showed all characteristics of crystalline offretite, including maximum sorption capacity and typical crystal morphology.

In-Situ Leaching of Crownpoint, New Mexico, Uranium Ore: Part 1 Mineralogical Frame of Reference

Before assessing potential for in-situ leaching, it is advantageous to identify the nature of probable reactants in the ore horizon, including both the uranium species and those in the gangue material. We report mineralogical data on a broad suite of samples from the Westwater Canyon member of the Jurassic Morrison formation in the Crownpoint area of the Grants mineral belt. Optical microscope, electron microprobe, X-ray diffraction, and spectroscopic and wet chemical analyses were conducted. In these samples, the uranium occurs predominantly as either coffinite or uraninite. The host rock is arkosic sandstone comprising mainly detrital quartz and feldspar. Kaolinite and chlorite are present in claystone clasts, and calcite occurs as a cement. Major trace elements include molybdenum, vanadium, iron, selenium and sulfur. There is carbonaceous organic material in the ore, and it is intimately associated with the uranium mineral when it is coffinite. Geochemical, pyrolytic and /sup 13/C nuclear magnetic resonance (NMR) analyses indicate that the organic material is probably a very mature, coaly kerogen derived from plant components.

Synthesis, Reactions and Interactions of Olefins, Aromatics and Alcohols in Molecular Sieve Catalyst Systems

Publisher Summary This chapter discusses the synthesis, reactions, and interactions of olefins, aromatics, and alcohols in molecular sieve catalyst systems. There exists a hierarchy of olefin–zeolite and aromatic zeolite interactions that ranges from diffusion and the mildest adsorption effects to bimolecular condensation, cracking, and severe reorganizations of molecular structure. Because the pores of zeolites are uniform and of sizes characteristic of simple organic molecules, diffusion and chemical reaction are greatly influenced by variation in size, shape, and polarity of the guest molecule and in the configuration and geometry of the host crystal. Olefins and aromatics also play major role—over a wide range of conditions—in the formation of coke. Pore mouth catalysis and reverse molecular size selectivity (“the faujasite trap”) have been observed in the reactions of low molecular weight olefins at relatively low temperatures. The critically important role of olefins in intermolecular hydrogen transfer reactions and in formation of coke over a wide range of conditions cannot be overemphasized.