Oxygen preadsorbed

Thermochemical Cycles Testing the Formation of Gaseous (Cycle 1) or Adsorbed (Cycle 2) Carbon Dioxide by the Interaction of Carbon Monoxide with Oxygen Preadsorbed on Gallium-Doped Nickel Oxide ... 

Fig. 29. Differential heats of interaction of carbon monoxide, at 200°C, with samples of nickel oxide containing excess oxygen, preadsorbed rapidly (A) or slowly (B).

A variety of reactions have been observed to be produced by oxygen preadsorbed on Ag(llO) 137,144). In general these reactions do not proceed on clean silver under the conditions normally utilized in studies of surface reactivity. These reactions are listed below ... 

The same sequence of adsorptions has been studied on NiO(200) (8, 20). The interaction between oxygen preadsorbed on NiO(200) and carbon monoxide yields only adsorbed carbon dioxide. Therefore, on NiO(200), gaseous carbon dioxide is produced during the catalytic reaction through Mechanism I (8, 20), whereas on NiO(250) two reaction paths are probable (Mechanisms I and II). These results show clearly... 

A related oxidative rearrangement of cephem dioxides has been reported in which an alkene is oxidized stereospecifically with rearrangement to the allylic alcohol in good yield by simple exposure to a palladium/cartxin catalyst, as depicted in equation (12). Adventitious oxygen preadsorb on the catalyst seems the likely oxidant. The reaction fails on the parent cephem or its monoxide, or on the free acid of the dioxide. This reaction would seem to hold some promise for further utility in the cephem field and other related systems. 

Figure 9.16. Ethylene hardly adsorbs on clean silver, but it does interact with preadsorbed oxygen atoms. At low coverages, the O atoms preferably interact with the C-H bond of ethylene, leading to its decomposition into fragments that oxidize to CO2 and H2O but at higher coverages the oxygen atoms become electrophilic and interact with the n-system of ethylene to form the epoxide. [After R.A. van Santen and H.P.C.E. Kuipers, Ac/v, Catal. 35 (1987) 265.]...

In this section we present preliminary results of CH-jOH reactions with preadsorbed oxygen. Of primary interest is the mechanism for the removal of the hydroxyl hydrogen during formation of the methoxy (CH3O) intermediate. Fig. 4 shows TPRS curves for CH3OH, and... 

Figure 2.2 Reactivity of oxygen states chemisorbed at Ni(210) (a) at 295 K and (b) at 77 K to water adsorbed at 77 K. The oxygen concentration ct is calculated from the 0(1 s) spectra. The oxygen state preadsorbed at 295 K is unreactive with water desorption complete at 160K whereas that at 77 K is reactive, resulting in surface hydroxylation.37 (Reproduced from Refs. 37, 42).

Support for the special reactivity of hot oxygen adatoms also came from Matsushima s temperature-programmed desorption study4 of CO oxidation at Pt(lll), when CO and 02 were coadsorbed at low temperature with C02 desorbed at 150 K, the temperature at which 02 dissociates. This temperature is some 150 K lower than that for C02 formation when oxygen is preadsorbed (thermally accommodated) at the Pt(lll) surface. 

The interaction of hydrogen with preadsorbed oxygen at Pt(lll) led to hexagonal and honeycomb structures to develop at 131 K, which could be associated with OH phases with also evidence for water formation. The front (bright ring) consisted mainly of OH(a) and the area behind the front of H20(a). The mechanism suggested is that H(a) reacts first with 0(a) to form OH(a) and then H20(a) the water is mobile and reacts with O(a) to form OH(a) it is therefore an autocatalytic reaction. 

Other authors also determined by FTIR that organic nitrocompounds are formed as primary products of the NO CH4-SCR reaction on ZSM-5-based catalysts [121-124], They preadsorbed nitromethane on the sample placed in the IR cell and followed by IR its transformation into other intermediates under 02 and NO versus time at different temperatures. For Cu- and Co-ZSM-5, it was shown that around 300°C adsorbed nitromethane is easily converted into isocyanates and then melamine via polymerization of the former species. Both species easily interact with molecular oxygen, while no reaction with NO is observed and the reactivity depends on the temperature and the nature of the transition metal cation. 

I] Prediction of the temperature where DeNOx can take place, by TPD of NO preadsorbed with or without oxygen. In the absence of oxygen, check the formation of N2, N20, N02 and NO during TPD. If N20 and/or N2 are formed, it means that the reaction already took place. If not, the system needs the reductant to take place. This experiment also means that function 3 can work [10,25],... 

Fig. X. Hydrogen adsorption at 78° and 300°K as a function of preadsorbed amount of oxygen on nickel.

Fig. 2. Typical curves of the relative changes of the electrical resistance of nickel films as a function of time (a) adsorption of one dose of hydrogen on the surface, partially covered by preadsorbed oxygen (b) adsorption of one dose of oxygen on the surface, covered by preadsorbed hydrogen (both at 300°K).

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