Jerry R. Ebner

Ethylene oxidation on silver powder: A tap reactor study

Abstract The oxidation of ethylene over silver powder catalysts was studied between 475 and 575 K at pressures of circa 10 Torr under transient conditions that allowed reactions of atomic and molecular oxygen to be distinguished. Dioxygen and d 4 -ethylene were pulsed separately over silver powder in a microreactor with pulse durations of 200 μs, and the products were detected by a multiplexed mass spectrometer. This method, denoted as temporal analysis of products, allows either simultaneous pulsing of the reactants or pulse delays ranging from a few milliseconds to minutes. In these experiments both ethylene oxide and carbon dioxide were detected as products. Ethylene oxide formed instantaneously on the time scale of the reactant pulse, but carbon dioxide formed with a much slower time constant, characteristic of the decomposition of surface carbonate, indicating the importance of secondary interactions of CO 2 with surface oxygen in the kinetics of CO 2 formation. Pulse-probe experiments, in which the catalyst was first loaded with adsorbed atomic oxygen and then reacted with anaerobic ethylene pulses or ethylene-oxygen mixtures, showed that the adsorbed species giving rise to ethylene oxide is atomic, not molecular, oxygen.

Nature of active species of (VO)2P2O7 for selective oxidation of n-butane to maleic anhydride

TEM, EXAFS, FTIR, temporal analysis of products (TAP), stopped-flow desorption (SFD) and catalytic measurements of (VO)2P2O7 are reported. The reduced interaction between (020) planes of (VO)2P2O7 in samples prepared in an organic medium induces a charge localization on the V atoms of the coupled trans-vanadyl present in this plane, enhancing their catalytic reactivity in butane oxidation. Contiguous surface Bronsted sites (P—OH) also participate in the mechanism of selective oxidation. C-containing residues are present in relevant amount on the surface during catalytic experiments and give rise to a specific fouling of the active sites, but their possible role as co-catalysts in the transfer mechanisms of single activated species is also discussed.

Butane Oxidation in A Transport Bed Reactor – Redox Characteristics of The Vanadium Phosphorus Oxide Catalyst

Redox properties of vanadium phosphorous oxide (VPO) catalysts have been measured using butane and hydrogen as reductants and molecular oxygen as an oxidizing agent. These redox measurements indicate vanadium phosphorous oxide catalysts can vary markedly in oxygen capacity and redox rates. The VPO systems selected for this study range in oxygen carrying capacity from surface oxygen participation only to involvement of subsurface oxygen. The stability of the operative redox chemistry of a VPO catalyst is illustrated by a 30000 cycle butane reduction test. Butane oxidation results in a transport bed reactor are explained by fundamental redox properties of vanadium phosphorous oxide catalysts.

Process for preparing carboxylic acid salts and methods for making such catalysts and catalysts useful in such process

A process to manufacture a carboxylic acid salt is disclosed wherein an aqueous solution of a primary alcohol is contacted with a base hydroxide in the presence of an effective amount of a catalyst consisting essentially of an alkali resistant support, from about 0.05 wt. % to about 10 wt. %, based on the total weight of the catalyst, of an anchor metal is selected from the group consisting of platinum, palladium, ruthenium, and gold, and between about 1 wt. % and about 50 wt. %, based on the total weight of the catalyst, of an element selected from the group consisting of copper, cobalt, nickel, and cadmium combined with the anchor metal.

Tetrahydrothiophene desulfurization on Co-Mo/γ-Al2O3: A temporal analysis of products (TAP) investigation

The catalytic reactions of tetrahydrothiophene, thiophene, 1-butene, 1,3-butadiene, and n-butane with hydrogen were studied at low pressure over a commercial cobalt molybdate catalyst. The formation sequence of tetrahydrothiophene desulfurization products was monitored with submilli-second time resolution using the temporal analysis of products (TAP) transient microreactor technique. The TAP experiments showed that butene and butadiene were the only hydrocarbon desulfurization products formed, although rapid dehydrogenation to thiophene was also observed. The exceptional time resolution of the TAP spectrometer provided evidence that the butene formed could not be accounted for by a mechanism involving butadiene hydrogenation. The results suggested a desulfurization mechanism for tetrahydrothiophene wherein C4 hydrocarbon formation proceeds via a surface butene thiolate intermediate produced by a single β-hydride elimination. It is proposed that 1,3-butadiene is formed by a slow subsequent β-hydride elimination of the intermediate, while rapid C-S bond hydrogenolysis involving surface hydrogen is responsible for butene formation.

Industrial Perspectives on the use of Dioxygen: New Technology to Solve Old Problems

The selective catalytic oxidation of organic molecules continues as a very important reaction pathway for the synthesis of primary and specialty chemicals in the chemical industry worldwide. Catalytic utilization of molecular oxygen using both soluble metal compounds in liquid reaction media (homogeneous catalysis) and the surfaces of metals or metal oxide compounds in gas or liquid reaction media (heterogeneous catalysis) is very important today, and will become even more important in the future as worldwide environmental policies become more stringent. This will necessitate the development of new “no-waste” technologies which will provide economically viable syntheses of molecules of commercial importance. Clearly, selective catalytic oxidation with O2 represents critical technology and will be an area in which continued research and technical breakthroughs will be required.

Key Structure-Activity Relationships in the Vanadium Phosphorus Oxide Catalyst System

Abstract The crystal structure of vanadyl pyrophosphate has been redetermined using single crystals obtained from a near solidified melt of a microcrystalline catalyst sample. Crystals that index as vanadyl pyrophosphate obtained from this melt are variable in color. Crystallographic refinement of the single crystal X-ray diffraction data indicates that structural differences among these materials can be described in terms of crystal defects associated with linear disorder of the vanadium atoms. The importance of the disorder is outlined in the context of its effect on the proposed surface topology parallel to (1,0,0). Models of the surface topology simply and intuitively account for the non-stoichometric surface atomic P/V ratio exhibited by selective catalysts of this phase. These models also point to the possible role of the excess phosphorus in providing site isolation of reactive centers at the surface.

Activation of Vanadium Phosphorus Oxide Catalysts for Alkane Oxidation Oxygen Storage and Catalyst Performance

The reaction of n-butarie with “reactor-equilibrated” (VO) 2 P 2 O 7 based catalysts activated with different oxygen treatments has been investigated using a combination of high speed transient response and temperature programmed techniques. Results indicate that (VO) 2 P 2 O 7 has a unique “storage/supply” system capable of adsorbing oxygen and efficiently channeling it to the active catalytic site. It is proposed that storage occurs via the transformation of (VO) 2 P 2 O 7 into V +5 compounds and the supply mechanism involves the reverse reaction.

Thiol protected platinum black and palladium black catalysts in oxidation catalysis

Platinum and palladium metals are common catalysts for formic acid wet oxidation, exhibiting high activity and good stability. However, in the presence of some reactive organic substances, even in low concentrations, they suffer severe deactivation. This paper demonstrates the feasibility of protecting metal catalysts from aggressive media by creating a tertiary structure over the active sites. The approach is based on the known principle of metal surface modification by self-assembled organic monolayer films. We have found that self-assembled monolayers (SAMs) fabricated from heterocyclic thiols containing nitrogen, e.g., 6-mercaptopurine (6MP), can protect platinum and palladium black catalysts for formic acid oxidation in the presence of iminobis[methylenephosphonic acid] (IDMPA). IDMPA was chosen as a model inhibitor because it displays strong chelating properties. Catalysts protected with 6MP demonstrate higher activity and stability and have significantly lower metal leaching (up to 15 times in case of palladium black) than their unprotected counterparts. The surface structure of the catalysts and their surface composition were characterized using X-ray photoelectron spectroscopy (XPS) and Scanning Tunneling Microscopy (STM).

Site isolation in vanadium phosphorus oxide alkane oxidation

Abstract Single crystal X-ray diffraction studies of vanadyl pyrophosphatc indicate that at least two polytypical structures exist for this active and selective alkane oxidation catalyst. The crystal structures of these materials differ with respect to the symmetry and direction of columns of vanadyl groups within the unit cell. Single crystals of vanadyl pyrophosphatc have been generated at extreme temperatures not often experienced by microcrystallinc catalysts. The crystallography of the system suggests that other crystalline modifications or disordered phases might also exist. Zeroth-order models of crystal surface termination of vanadyl pyrophosphate have been constructed which conceptually illustrate the ability of vanadyl pyrophosphate to accommodate varying amounts of surface phosphorus parallel to (1,0,0), (0,1,0) and (0,2,4). Pyrophosphate termination of surfaces parallel to (1,0,0) likely results in the isolation of clusters of reactive centers and limits overoxidation of the alkane substrate.