Temporal Analysis Of Products Studies Research Articles

Aldol condensation of acetaldehyde for butanol synthesis: A temporal analysis of products study

The catalytic upgrading of CO2-based ethanol into valuable products, such as higher alcohols, is of increasing interest. Carbon-neutral n-butanol can substitute major fractions of conventional gasoline in the transport sector of the future. A promising synthesis path towards n-butanol is the Guerbet reaction, in which the homo aldol condensation of acetaldehyde constitutes an important intermediate step, which was investigated using the Temporal Analysis of Products methodology. This investigation employed the lanthanide oxides Dy2O3, Eu2O3, and Er2O3, supported on activated carbon due to their varying basic characteristics. In addition to the aldol condensation of acetaldehyde yielding butanol, its decomposition into CO, CH4, and H2 also occurred. Furthermore, acetaldehyde pulsing onto the catalyst surface of Dy2O3/C also lead to the formation of carbonaceous deposits. Fortunately, catalyst regeneration by means of O2 pulsing was successful. Other reaction routes yielding acidic acid, ethyl acetate, or diethyl ether could be experimentally excluded.

Combined near-ambient pressure photoelectron spectroscopy and temporal analysis of products study of CH4 oxidation on Pd/γ-Al2O3 catalysts

Vehicles that run on natural gas must be equipped with an exhaust gas after-treatment system to burn their unavoidable CH4 slip, which must not be released into the environment as CH4 is a potent greenhouse gas. Pd is known as a highly active catalyst material for CH4 oxidation. For this study, Pd was deposited on a γ-Al2O3 support and the as-received samples were pre-reduced and pre-oxidized, respectively. Near-Ambient Pressure Photoelectron Spectroscopy and the Temporal Analysis of Products methodology were combined to understand that both electronic states, namely PdO and Pd°, are active for the CH4 oxidation reaction, whereby the superior activity of the pre-reduced Pd/γ-Al2O3 catalyst was ascribed to the spill-over of OH-groups from the support to Pd. It was found that the reaction products, CO, CO2 and H2, were strongly and, to a large extent, adsorbed on the catalyst surface and were involved in reversible chemical interactions on the catalyst surface during the CH4 oxidation reaction on the Pd/γ-Al2O3 catalyst.

Isotopic Temporal Analysis of Products study of anaerobic NO reduction by NH3 on Pt catalysts

A Temporal Analysis of Products (TAP) study was carried out of the anaerobic NO+NH3 reaction system on Pt sponge and Pt/Al2O3 catalysts. Temperature, pulse timing, and feed composition were varied to quantify the conversion and product selectivities. Isotopically labeled nitric oxide (15NO) was used to follow reaction pathways to molecular nitrogen and nitrous oxide. A variation in the delay time between sequential pulses of 15NO and NH3 had a significant effect on the reaction path to molecular nitrogen. A mixed feed (no delay time) above the light-off temperature resulted in a product mixture nearly balanced between the mixed product 15NN, and the two single-source products 15N2, and N2. With increased delay time the selectivity of 15NN decreased significantly in favor of 15N2 and N2. The data suggest at least two major routes to nitrogen formation, one involving direct NO decomposition on reduced Pt sites and the other involving reaction between NHx species and NO. There is also kinetic evidence for a slower, third minor route involving an unidentified surface complex, possibly HNOad. The alumina support is shown to suppress this effect of delay time through ammonia adsorption, serving as a source-sink. The trends are interpreted with a mechanistic model constructed from a sequence of elementary steps.

Temporal Analysis of Products Study of HCl Oxidation on Copper- and Ruthenium-Based Catalysts

The use of in situ approaches to study mechanisms of experimentally demanding and complex reactions under conditions of practical relevance opens doorways to discover new or improved heterogeneous catalysts. A representative example within this category of reactions is the gas-phase oxidation of HCl to Cl2 (Deacon process). Studies in the temporal analysis of products (TAP) reactor complemented by flow experiments at ambient pressure evidenced pronounced mechanistic differences between copper catalysts (CuO, CuCl, and CuCl2, that is, Deacon-like catalysts) and RuO2 (the basis of the recent Sumitomo’s catalyst for large-scale Cl2 production). RuO2 is 1 order of magnitude more active than the copper-based materials. HCl oxidation on RuO2 obeys a Langmuir−Hinshelwood mechanism in the presence of adsorbed species over a partially chlorinated surface. HCl oxidation on the copper catalysts is more complex: all the samples experience bulk changes, namely, chlorination, resulting in multiphase materials. Besides, lattice species also participate in the reaction. In particular, fresh CuO follows a Mars−van Krevelen mechanism, in which lattice oxygen is active for Cl2 and H2O production, leading to bulk chlorination, whereas for copper chlorides activated upon exposure to the Deacon mixture and used CuO, a combination of Mars−van Krevelen and Langmuir−Hinshelwood mechanisms seems to be a better description. Investigations over the copper-based phases and characterization of the fresh and used samples by X-ray diffraction indicate that a copper (hydr)oxychloride is the main active phase. Our mechanistic study suggests that a more active and particularly stable copper catalyst can be achieved by controlling the degree of surface chlorination. This is more or less a self-regulated process on the ruthenium-based catalyst.

A temporal analysis of products study of the mechanism of VOC catalytic oxidation using uranium oxide catalysts

A temporal analysis of products (TAP) reactor is used to investigate the mechanism of oxidation of volatile organic compounds by uranium oxide catalysts. Continuous flow studies indicated that butane, benzene and chlorobutane VOCs were oxidised to carbon oxides and no partially oxidised products were observed. A combination of TAP pulse experiments with oxygen present and absent in the gas phase has indicated that the lattice oxygen from the catalyst is responsible for the total oxidation activity. This has been confirmed by studies using isotopically labelled oxygen. It is proposed that the catalysts operates by a redox mechanism utilising lattice oxygen and the high activity shown by U 3O 8 is due to the facile uranium redox couple and the non-stoichiometric nature of the oxide.