Joseph W. Bruno

FT-IR and solid-state NMR investigation of phosphorus promoted hydrotreating catalyst precursors

The effect of phosphorus on the structure of Niue5f8Mo/Al2O3 hydrotreating catalyst precursors has been investigated. Calcined and reduced P/Al2O3, Pue5f8Ni/Al2O3, P-Mo/Al2O3, and Pue5f8Niue5f8Mo/Al2O3 (where the wt% P = 0.0 to 10.0, wt% Mo = 8.0 to 12.0, and wt% Ni = 4.0) have been studied using FT-IR, XRD, and 31P and 27Al MAS NMR techniques. Phosphoric acid reacts with alumina hydroxyls forming monomeric and polymeric phosphates. At the higher phosphorus loadings, aluminum phosphate is also formed. On calcined Pue5f8Ni/Al2O3, nickel phosphate is formed. This leads to a decrease in density of NO sites in the reduced state as measured by CO adsorption. The addition of up to 1.5 wt% P to Mo(8)/Al2O3 promotes the formation of octahedral molybdena on the alumina surface. However, the addition of > 2.0 wt% P results in the formation of bulk M003 and Al2(MoO4)3 in both Pue5f8Mo(8)/Al2O3 and Pue5f8Mo(12)/Al2O3. CO adsorption on reduced Pue5f8Ni(4)ue5f8Mo(8)/Al2O3 samples shows that the presence of 0.5 wt% P causes a significant increase in the number of sites adsorbing CO. Increasing the P loading further causes a decrease in the number of adsorbing sites; this decrease can be attributed to the formation of either nickel phosphate or nickel molybdate.

Identification of alcohol adsorption sites on γ-alumina

A novel temperature-programmed desorption technique in which the probe of a mass spectrometer is used as the reactor has been developed. FT-IR and this new technique have been used to study the adsorption and dehydration reactions of a series of aliphatic alcohols on [gamma]-alumina. It was found that the facility with which the various alkoxides undergo elimination processes is dependent on the size of the alkyl groups and the degree of branching. Reactions involving [[sup 18]O]ethanol and [[sup 18]O]methanol produce two isotopomeric ether products (R[sup 18]OR and R[sup 16]OR), which shows that bound alkoxides are formed by two routes: (a) dissociative adsorption on Lewis acid sites and (b) nucleophilic attack by a surface oxide on an alcohol that is probably activated toward C-O cleavage. Poisoning experiments using 2.6-dimethylpyridine confirm that the ether isotopomers are formed from different alkoxide species. Time studies indicate that there is no scrambling of the [sup 16]O and [sup 18]O alkoxides between the different types of surface sites.

Supercritical methanol drying as a convenient route to phenolic–furfural aerogels

Abstract Organic aerogels are prepared by the acid catalyzed cross-linking of phenolic–furfural (PF) precursors in methanol solution, and the solvent is subsequently removed at high temperature as the supercritical fluid. The resulting aerogel is a brown opaque solid and has been prepared as 30 ml cylindrical monoliths exhibiting little or no shrinkage during formation. These solids, which are routinely available with a density as low as ca. 125 mg / cm 3 , have been characterized by chemical methods (infrared spectroscopy and CP-MAS 13C NMR spectrometry) and physical techniques (Brunauer–Emmet–Teller surface area, transmission and scanning electron microscopy). In addition, thermal conductivities have been determined, and show that the PF aerogels are excellent thermal insulators. These studies establish that the materials described herein exhibit chemical and physical properties very similar to those seen for organic aerogels prepared with low temperature processing techniques. The current method constitutes a convenient and rapid route to organic aerogels.

Oxygen atom transfer with niobocene ketenes; Baeyer-Villiger chemistry with unusual Rrgioselectivities

Abstract Niobocene ketene complex 1 has been utilized as an oxygen atom transfer reagent, converting ketones and aldehydes to esters and carboxylic acids. The steric properties of compound 1 give rise to a series of relative migratory aptitudes that differs from those seen for peracids. The process may be rendered catalytic in 1 with methyltrifluoromethyldioxirane ( 4 ).

LUMINESCENCE STUDIES OF CERIUM(III) INCORPORATED IN SILICA GELS PREPARED USING SOL-GEL METHODS

Abstract Sol-gel methods have been adapted for the incorporation of cerium(III) into a silica gel network, and the resulting gels have been prepared either with or without the use of formamide as a drying control chemical additive (DCCA). The use of formamide and Ce(III) has been found to result in lanthanide-assisted hydrolysis of the amide, leading to crystallization phenomena during gelation. We describe strategies to avoid this, as well as the results of luminescence studies on the Ce/ silica gels. The latter have been used to observe the characteristics luminescence of gel-supported cerium, and have also been employed as a probe of the gelation process. This has been found to lead to increasing luminescence intensity, with the most significant increases occurring after gelation and during the drying stage.

Preparation, luminescence studies, and solution behaviour of a cerium–tungsten heterobimetallic compound

The crystal structure determination of cerium–tungsten compound (2)[Cp″2Ce-(µ-OC)W(CO)(Cp)(µ-CO)]2[Cp″= C5H3(SiMe3)2, Cp = C5H5] shows it to consist of a 12-membered ring in which Ce and W centres are linked by Σ-carbonyls; intact (2) is virtually non-emissive (presumably due to cerium–tungsten excited state energy transfer), but in acetonitrile solvent it serves as a source of the luminescent cerium cation [Cp″2Ce(NCMe)x]+.

Sterically Congested Bisphosphite Ligands for the Rhodium(I)-Catalyzed Hydrosilation of Ketones

Sterically congested bisphosphites were shown to be effective ligands for the Rh-catalyzed hydrosilation of ketones with diphenylsilane. The hydrosilation of 4-alkylcyclohexanones and ( m )-menthone led to a significant proportion of the less stable (axial) alcohol, which suggests that these reactions are under kinetic, rather than thermodynamic, control.

FT-IR Analysis of Toluene Hydrogenation Reactions on Reduced Alumina Supported Catalysts

Abstract An IR technique has been developed to study toluene adsorption and hydrogenation on supported metal catalysts (M/Al 2 O 3 ). IR analysis of toluene adsorbed on reduced P/Al 2 O 3 samples shows that there is an interaction between the proton of the acidic P-OH groups and the pi electrons of the toluene. Hydrogenation typically occurs at characteristic temperatures between 25°C and 150°C on reduced Rh(1.5)/Al 2 O 3 , Ni(15)/Al 2 O 3 and Ni(4)-Mo(8)/Al 2 O 3 . Repeated toluene hydrogen cycles on reduced Al 2 O 3 , Ni(4)-Mo(8)/Al 2 O 3 and Ni(15)/Al 2 O 3 demonstrate that there are several carbonaceous species being formed on the Al 2 O 3 surface, and that the relative amounts of each species change with time. Furthermore, additives such as phosphate prevent the build-up of carbonaceous species on the Al 2 O 3 surface.

Mechanistic studies on the oxidation of an anionic rhenium polyhydride complex: generation and reactivity of the transient radical [ReH6(PMePh2)2]

Abstract The anionic polyhydride [ReH6P2][K] (1) (P = PMePh2) undergoes facile one-electron oxidation when treated with either ferricinium ion or [Fe(bpy)3]3+; the ultimate products are ReH7P2 (2) and dimer Re2H8P4 (3). Mechanistic studies are consistent with the intial production of the 17-electron intermediate [ReH6P2]; while the proposed intermediate is not trapped by added phosphines, it reacts with an added hydrogen atom source (1,4-cyclohexadiene) to form 2 at the expense of 3. The [ReH6P2] is proposed to proceed in the absence of trapping reagents to 2 and 3 via two distinct pathways, hydrogen abstraction and condensation with another rhenium hydride species. This competition is concentration dependent; while 2 is always observed as the major product, the percentage of 3 formed is greater at higher concentrations.

Regiochemical and mechanistic studies of the addition of tin hydride and oxide to substituted ketenes

Abstract The reactions of aryl-substituted ketenes with tri-n-butyltin hydride give rise to O-bound tin enolates. With unsymmetrically-substituted methyl phenyl ketene this process exhibits little or no stereoselectivity. The kinetic mixture consists of virtually equal proportions of E and Z enolate isomers, which then equilibrates to a 71 29 Z/E mixture under thermodynamic control. Mechanistic studies are not consistent with either radical or polar mechanisms, and a concerted pathway with differential rates of bond formation is proposed. With dimethyl ketene a similar reaction gives a vinyl ester enolate, which presumably results from an initially-formed aldehyde enolate. Finally, the reaction of diphenyl ketene with tri-n-butyltin oxide results in a tin carboxylate which adopts a polymeric structure in the solid state.