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Chemisorbed reaction pathway

The reaction mechanism of SCR of NOx with decane on acid and iron-exchanged MFI-type zeolite was also investigated by operando FTIR spectroscopy and a special reactor cell enabling the use of water-containing gas mixtures. Brosius et al. found that water has a dramatic influence on the reaction pathway, while the formation of organic nitro and nitrite compounds does not proceed via chemisorbed states of NO, as observed in SCR with dry gases [174],... [Pg.128]

This unusual reaction needs both the reactive proton of the fresh catalyst and the activated hydrogen in allylic position. Additionally no easier reaction pathway must be available. So this reaction produces hydrogen deficient strongly chemisorbed hydrocarbons in the early stage of autocatalysis. [Pg.285]

Below 0.45 V the chemisorbed intermediates formed on methanol adsorption are stable on any smooth platinum surface, with the steady-state current for methanol oxidation being extremely small. Above this potential, oxidation of methanol takes place at a rate that increases exponentially with potential, with the product being primarily C02. In addition, above potentials of approximately 0.6 V, the surface is steadily stripped of adsorbed carbon-containing species, with the loss of such species being complete near 0.8 V. It would seem likely on most surfaces that it is oxidation of COads or =C-OH in a sequential reaction pathway that leads to C02, but more active intermediates, such as CO adsorbed at less stable sites, such as those at the edges... [Pg.678]

The anodic oxidation of chemisorbed Q also appears to follow the above reaction pathway. Evidence is provided by HREELS spectra (Fig. 22) obtained when the potentials are made progressively more positive. It can be seen that the spectral features for unimpaired Q persist, but with diminished intensities, at anodic-oxidation potentials. The new peaks above 3000 cm are due to the formation of hydrated surface oxides. Evidently, a small fraction of chemisorbed Q is also able to resist anodic oxidation Unfortunately, no acceptable EC-STM images could be obtained due... [Pg.309]

In electrocatalysis, notable cases of formation of strongly bound species that are not, however, the kinetically involved intermediates in the main reaction pathway arise in the electrochemical oxidations of HCOOH, HCHO, and CH3OH at Pt anodes for those reagents, a self-poisoning intermediate, variably identified as chemisorbed CO, in bridged or linear double bonding to the electrode, or the species- C—OH, is involved (43) this species is not a principal kinetically involved intermediate in, for example, HCOOH oxidation, which proceeds at unpoisoned sites by the mechanism discussed in Section V,B,3. [Pg.14]

The reaction between alcohols and hydrogen sulphide can proceed not only via one reaction pathway. The reaction pathway depends on the type of zeolites. It was stated that over hydrogen forms of faujasite type zeolites the Brflnsted acid sites play the role of active centres and the reaction proceeds between chemisorbed alcohol and physisorbed H2S (ref.2). However, in the absence of Brttnsted acid sites the cations seem to play the role of active centres (ref.7). It was suggested that on cationic forms of zeolites the reaction takes place between dissociatively adsorbed hydrogen sulphide and alcohol. The results obtained in this work confirm this sugge-... [Pg.401]

A variety of sulphonation agents has been used in the preparation of sultones from alkenes. These include liquid-phase sulphur trioxide, Lewis base-complexed sulphur trioxide such as S03-dioxane29 and S03-pyridine25, gaseous sulphur trioxide30 and chemisorbed sulphur trioxide31. Examples are shown in equation 7. More recently the reagent acetyl sulphate has been used in the sulphonation of ethylidenenorbornane to produce the y-sultone 732. The reaction pathway proposed for the formation of 7... [Pg.793]

The presence of oxygen can open up a number of additional reaction pathways that can control the actual surface chemistry. Madix has demonstrated that adsorbed atomic oxygen can behave as a nucleophillic center and attack surface bound hydrocarbon intermediates or as a Brqnsted base for hydrogen transfer reactions [63]. Chemisorbed atomic oxygen can also act as a poison on different transition metal surfaces. [Pg.24]

Experiments of thermal desorption and collision-induced desorption showed that gold particles (2-5 nm) supported on TiO2(110), and populated with both Ojds and 02,ads produces more CO2 than the sample populated with Ojds alone. This was interpreted as evidence that molecularly chemisorbed oxygen directly participates in the CO oxidahon reaction, and that the reaction pathway does not require the dissociation of oxygen [172]. [Pg.493]

These curves can be related to the inner-and outer-sphere reactions pathways. The full line represents the outer-sphere reaction, whereas the inner-sphere reactions are depicted by the dashed and dotted Unes. As can be seen, outer-sphere reactions are always weak overlapping reactions, that is, reactions in which the electrode is not acting as an electrocatalyst. Inner-sphere reactions can be either strong or weak overlap reactions, depending on the properties of the reactant species and electrode material. From a chemical point of view, a chemical bond between the reactant species and the electrode is formed in the strong overlap cases, that is, the reactant species are chemisorbed on the electrode surface. [Pg.976]

The surface transformations of propylene, allyl alcohol and acrylic acid in the presence or absence of NHs over V-antimonate catalysts were studied by IR spectroscopy. The results show the existence of various possible pathways of surface transformation in the mechanism of propane ammoxidation, depending on the reaction condition and the surface coverage with chemisorbed NH3. A surface reaction network is proposed and used to explain the catalytic behavior observed in flow reactor conditions. [Pg.277]

Co-adsorption experiments show a complex role of the nature and concentration of chemisorbed ammonia species. Ammonia is not only one of the reactants for the synthesis of acrylonitrile, but also reaction with Br()>nsted sites inhibits their reactivity. In particular, IR experiments show that two pathways of reaction are possible from chemisorbed propylene (i) to acetone via isopropoxylate intermediate or (ii) to acrolein via allyl alcoholate intermediate. The first reaction occurs preferentially at lower temperatures and in the presence of hydroxyl groups. When their reactivity is blocked by the faster reaction with ammonia, the second pathway of reaction becomes preferential. The first pathway of reaction is responsible for a degradative pathway, because acetone further transform to an acetate species with carbon chain breakage. Ammonia as NH4 reacts faster with acrylate species (formed by transformation of the acrolein intermediate) to give an acrylamide intermediate. At higher temperatures the amide may be transformed to acrylonitrile, but when Brreform ammonia and free, weakly bonded, acrylic acid. The latter easily decarboxylate forming carbon oxides. [Pg.285]


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See also in sourсe #XX -- [ Pg.2 , Pg.3 , Pg.7 , Pg.12 , Pg.15 ]

See also in sourсe #XX -- [ Pg.2 , Pg.3 , Pg.7 , Pg.12 ]




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