John L. Robbins

Preparation of the first molecular carbon monoxide complex of uranium, (Me3SiC5H4)3UCO

Exposure of a solution of the metallocene (I) to CO at 1 atm and 20°C yields the title complex (II), which may be stored for at least 2 years at - 80°C. (I) also reversibly absorbs CO in the solid state.

Chemistry of supported Ru: CO-induced oxidation of Ru at 310 K

Abstract Infrared spectra of CO on reduced titania-supported Ru show three bands at 2060, 2085, and 2140 cm −1 . The first band saturates almost instantly in excess CO and exhibits coverage-dependent frequencies at subsaturation which are consistent with its assignment to CO in on-top sites on the anticipated Ru crystallites. The latter two bands grow slowly as a pair in several Torr CO at 310 K, and their growth rate is accelerated at 400 K. IR spectra measured in mixtures of isotopically labeled CO show the two high-frequency bands represent coupled vibrations of an Ru(CO) x ( x > 2) species. The observed frequencies correlate with those expected for a Ru(II) species and XPS shows that a fraction of the zero-valent Ru present on a reduced sample is converted to a higher valent species upon exposure to CO at 310 K. We therefore assign the 2085- and 2140-cm −1 IR bands to (TiO) 2 Ru(CO) 3 surface species. We also propose these species form via an oxidative fragmentation reaction involving zero-valent Ru, CO, and surface hydroxyls on the support.

Alkane rearrangement pathways on tellurium-based catalysts

Isotopic tracer studies and reaction pathway analyses suggest that olefins and diene and triene species are reactive intermediates in n-heptane dehydrocyclization on Te/NaX. Their concentration is limited by surface hydrogen overpressures caused by a rate-limiting hydrogen desorption step in the dehydrogenation sequence. The distribution of toluene isotopomers formed from dehydrocyclization of n-heptane-1-13C is consistent with a reaction sequence involving thermal cyclization of an equilibrated mixture of conjugated and nonconjugated heptatrienes. Methylhexanes are formed predominantly by methyl and ethyl shift reactions of heptenes, and not by hydrogenolysis of CS ring species. Alkane hydrogenolysis on Te/NaX occurs predominantly by thermal cracking pathways of n-heptane and heptenes. No catalytic function for either (1,5) or (1,6) ring closure was observed on Te/NaX; a catalytic dehydrogenation function, however, suffices for dehydrocyclization to occur with high selectivity.

Methanol synthesis over Cu/SiO2 catalysts

The rates of CO and CO/CO2 hydrogenation at 4.2 MPa and 523 K are reported for a series of Cu/SiO2 catalysts containing 2 to 88 wt.% Cu. These catalysts were prepared on a variety of silica sources using several different Cu deposition techniques. In CO/CO2 hydrogenation, the rate of methanol formation is proportional to the exposed Cu surface area of the reduced catalyst precursor, as determined by N2O frontal chromatography. The observed rate, 4.2×10−3 mole CH3OH/Cu site-sec, is within a factor of three of the rates reported by others over Cu/ZnO and Cu/ZnO/Al2O3 catalysts under comparable conditions. These results suggest that the ZnO component is only a moderate promoter in methanol synthesis. Hydrogenation of CO over these catalysts also gives methanol with high selectivity, but the synthesis rate is not proportional to the Cu surface area. This implies that another type of site, either alone or in cooperation with Cu, is involved in the synthesis of methanol from CO.

Chromatographic separations of fullerenes : discovery and characterization of C60 mono-epoxide

Abstract A semi-preparative scale high-pressure liquid chromatographic method for the separation of the fullerene extract components has been developed. During the course of these separations, a new fullerene species was isolated and characterized by mass spectrometry, 13C NMR, and infrared and UV-Vis absorption spectroscopy. Mass spectrometry identifies this component as the mono-oxygen adduct of C60 (C60O) and 13C NMR strongly supports the epoxide structure rather than the isomeric oxido-annulene structure. In addition, the effects of different solvents on the optical absorption spectra of purified C60 and C70 and crystalline properties of C60 fullerite powder are reported.

Controlling the chemistry of the micropore volume in pillared clays and micas

Pillared clays are microporous materials formed by propping apart clay layers with robust inorganic polyoxocations. The chemistry of the micropore space can be tailored by choosing suitable pillaring species, by adding various functionality to the pillar surfaces, and by incorporating small metal particles within the micropores. We have found that by using a commercially available zirconyl acetate solution as the zirconia polyoxocation precursor, zirconia-pillared micas with superior properties of crystallinity and microporosity can be produced. Catalytic tests have shown that treatment of a zirconia-pillared montmorillonite with sulfate increases the acid site strength and density of the zirconia pillars. In addition to materials with enhanced acidity, it is desirable to produce materials with little or no acidity for use as metal supports for catalysts in applications such as light alkane dehydrogenation, where support acidity leads to undesirable side reactions. Tetrasilicic fluoromica can be pillared by silsesquioxane oligimers derived from the in situ hydrolysis of an aminosiloxane reagent. After a two step calcination, the silica-pillared fluoromica produced has a high surface area and crystallinity, and the combination of the inert fluoromica layers with the non-acidic silica pillars makes this new material an interesting nonacidic support for noble metal catalysts.

C 60 And C 70 : Here’s Looking at you

In this paper we will describe the production, separation and characterization of the new all carbon molecules, C 60 and C 70 . High performance liquid chromatography HPLC is used to obtain purified samples of C 60 and C 70 , which are subsequently characterized by electron impact and chemical ionization mass spectrometry, IR and UV-visible absorption spectroscopy, NMR, ESR, scanning tunnelling microscopy, transmission electron microscopy and x-ray absorption fine structure measurements.