Timothy R. Felthouse

Zeolite-encapsulated platinum catalysts: Preparation, characterization by transmission electron microscopy, and their shape selective behavior toward various nitrogen base poisons during the catalytic oxidation of aqueous formaldehyde

Abstract Procedures are described for the encapsulation of Pt metal crystallites by the hydrogen forms of zeolite Y, mordenite, and ZSM-5. The Pt metal crystallite size and distribution in these well-encapsulated Pt/zeolite samples have been established through the use of transmission electron microscopy. Particle size ranges for the Pt crystallites are as follows: Pt/HY, 10–20 A; Pt/H-MOR, 6–15 A; and Pt/H-ZSM-5, 5–20 A. Supported Pt metal crystallites effectively catalyze the oxidation of aqueous formaldehyde to carbon dioxide and water in an autoclave reactor at 95 °C and 207 kPa O 2 . The rate of this oxidation is extraordinarily sensitive to the presence of nitrogen bases that effectively poison the Pt sites. Nitrogen bases investigated in this study include glycine, ethylenedi-aminetetraacetic acid, pyridine, quinoline, and 4-methylquinoline. Reactor evaluation of well-encapsulated Pt/zeolite catalysts for formaldehyde oxidation in the presence of small amounts of these nitrogen bases demonstrates clearly that the Pt crystallites reside in regions of the zeolite structure accessible only through the crystalline zeolite pore structure. Nitrogen bases too large to penetrate the zeolite pores are found to have little or no effect on the formaldehyde oxidation rate. In the case of Pt/ZSM-5, poisoning by quinoline occurs rapidly but 4-methylquinoline shows little effect on the rate of formaldehyde oxidation even in high concentrations and for prolonged periods of exposure to the catalyst. Complete details will be given for these selective poisoning experiments with the encapsulated Pt/zeolite catalysts.

Expanded lattice ruthenium pyrochlore oxide catalysts I. Liquid-phase oxidations of vicinal diols, primary alcohols, and related substrates with molecular oxygen

Abstract Ternary ruthenium oxide oxidation catalysts are reported that function directly with molecular oxygen for the conversion of oxygenated hydrocarbon substrates to carboxyl-containing products. The oxide catalysts have an expanded lattice pyrochlore structure with the general composition A2+xRu2−y(A = Pb, Bi; 0 1,2-diol > primary alcohol) over these oxide catalysts closely follows that reported previously when these oxides are used as anodic electrocatalysts suggesting common surface intermediates. Trickle bed reactor operation provides the highest product selectivity: trans-1,2-cyclohexanediol is oxidatively cleaved to adipate in NaOH solutions with 74 to 95% selectivity at contact times of 0.042 to 0.784 hr and temperatures of 26 to 95°C. The bismuth-containing oxides, Bi2+xRu2−xO7−y, show stable catalyst performance under trickle bed reactor operation for over 180 hr. Complete details of these catalytic oxidations are provided along with a discussion of substrate reaction pathways and oxygen activation by these novel expanded lattice ruthenium pyrochlore oxide catalysts.

Expanded lattice ruthenium pyrochlore oxide catalysts II. Catalyst surface investigations by electron microscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction and oxidation

Abstract Five expanded lattice ruthenium pyrochlore oxide powders with the general formula A 2+ x Ru 2− x O 7− y ( A = Pb: x = 0.06, 0.15, 0.62; y = 0.5 and A = Bi: x = 0.39, 0.86; 0 y ≤ 0.5) were investigated using high-resolution electron microscopy (HREM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction/oxidation (TPR/TPO) to ascertain factors that contribute to their low-temperature catalytic oxidation activity toward 1,2-diols and alcohols in aqueous alkaline solution. HREM data find small crystallites that vary from about 25 to 200 A in diameter. Image analysis techniques applied to one 100-A crystallite of Pb 2.62 Ru 1.38 O 6.5 reveal a 5% range of lattice spacings about the exterior portions of the particle. XPS data were collected in both the valence-band and core-level regions. XPS valence-band spectra for samples with higher levels ( x > 0.15) of Ru-site substitution by the A -site atoms display a less intense band near the Fermi energy level indicating a reduced Ru 4 d character compared to the more stoichiometric analogues. Core level XPS bands contain contributions from two different valence states for each of the Pb, Bi, and Ru atoms in the A 2+ x Ru 2− x O 7− y series. XPS-derived compositions show a higher A /Ru ratio for Pb 2.62 Ru 1.38 O 6.5 than the bulk whereas the other four oxides have A /Ru ratios that are similar in the surface (XPS) and bulk (XRD) compositions. TPR using H 2 of the A 2 + x Ru 2 − x O 7 − y oxides reveals remarkable reactivity below 200°C that is in line with loosely bound oxygen in these oxides. A sample of Pb 2.62 Ru 1.38 O 6.5 with a lead-rich surface shows markedly less reactivity toward H 2 below 100°C than the other oxides. No distinct differences are seen in TPR data for all five expanded lattice ruthenium pyrochlore oxides between the surface and bulk oxygen. Reduced oxides reoxidize reversibly with oxygen after up to 20 mol% reduction (based on oxygen content) but at rates that are slow compared to H 2 reduction. The lack of a correlation between the TPR/TPO data and the liquid-phase catalytic activities toward 1,2-diols and alcohols is explained through differences in the active site preferences by the various substrates.

Catalytic amination of methyl tertiary-butyl ether to tertiary-butylamine over pentasil molecular sieves

Abstract Pentasil molecular sieves Catalyze the addition of ammonia to methyl tertiary-butyl ether to give tertiary -butylamine. By-products include methylamines, isobutene (IBE), methanol, and trace amounts of other organic producta. All analyzed products were confirmed through gas chromatography-mass spectrometry identification. The ether amination reaction proceeds under supercritical conditions (> 300 ° C and > 19.3 MPa) in a batch autoclave reactor. A description of the supercritical state reaction thermodynamics is given and compared to that for ammonia and IBE, two other low-cost raw materials for a new Catalytic commercial route to TBA. Details of the reactor and analytical system are reported. The molecular sieve Catalysts are characterized through elemental analyses, powder X-ray diffraction, and variable-temperature Fourier transform infrared spectroscopy with adsorbed ammonia. A plausible Catalytic cycle is presented for amination of a C 4 substrate to give TBA mediated by a molecular sieve surface.