Auto-reduction

It has been found that sulphurous acid liberated in solution from its salts at temperatures of 100° to 120° C. or lower, may undergo instantaneous auto-reduction with production of hydrogen sulphide ... 

It appears, moreover, that this rapid auto-reduction occurs only with sulphurous acid liberated from its salts and not with gaseous sulphur... 

The reducibility of nickel and copper cations in Nb- and Al-containing MCM-41 It is known that transition metal cations, which occupy extra lattice positions in zeolites, are reduced while activated under vacuum or in an inert gas flow [20], The same occurs while applying mesoporous matrices for metal cations. The species formed during the auto reduction depend on the nature of a matrix, the conditions of cation modification, and activation They can be identified by H2-TPR, ESR, and NO/FTIR measurements. 

The auto reduction of copper in the Cu-exchanged MCM-41 materials depends on the nature of a matrix and occurs according to ... 

In a preliminary step of the separation, the cadmium radioactivity (with 1 mg Cd carrier) was reduced onto a copper foil or into a mercury drop by electrolysis, and the mercury radioactivity (with 16 pg Hg carrier) was reduced onto a copper foil by auto-reduction. In the second step, these radioactivities were separated by vacuum distillation. In the separation of the In11 m, granule tin metal was irradiated in a nuclear reactor and then vacuum distillation immediately applied. 

Figure 27 Proposed structure for the binuclear Fe complexes in Fe-MFI-300 obtained by CVD of FeCli upon (a) washing (b) mild calcination and treatment in He at 30°C (c) mild calcination and moderate heating (up to 150°C) in He or 02/He (50 50) desorption of water (d) mild calcination and heating in He to 350°C auto-reduction of iron, ascribed to the removal of the Fe-O-Fe bridging oxygen atom (e) mild calcination and heating to 350°C in a 02/He (50 50) gas mixture the presence of oxygen in the gas phase inhibits the removal of the Fe-O-Fe bridging oxygen atom ...

Knight shifts have been measured for Cu and Cu in metallic copper. NMR techniques have been used for the determination of electric field gradients in relation to point defects in metallic copper. Copper-65 NMR and Cu- AJ spin-echo, double-resonance measurements from Cu-exchanged ZSM-5 catalysts have shown the presence of Cu cations. Upon heating, auto-reduction of Cu to Cu was observed, with further reduction to the metal upon exposure to CO at high temperatures. Copper NMR was used to investigate the nanostructure of. ../Cu/CO/Cu... layers which had been prepared by different methods. ... 

Overexchanged versus Underexchanged Cu-ZSM-5. In their study on direct NO decomposition, Iwamoto et al found that the catalytic activities of Cu-ZSM-5 increase with copper ion exchange level and level off over 100% exchange capacity(7). This observation was confirmed by Li and Hall in their kinetics study(T). They also observed that oxygen desorption rate for Cu-ZSM-5-166 is higher than that of Cu-ZSM-5-76. From the exchange site distance analysis and UV spectroscopic study, Iwamoto et aL proposed that a dimeric copper species, possibly in the form of Cu -O -Cu, is the precursor for auto-reduction of the complete redox cycle. 

Keilin performed experiments to determine this dissociation constant. No mention of the auto-reduction reaction which we observed is made in his paper. 

Pages and Pages and Haissinsky found that the rate of reduction depended very strongly on the nature of the anion in a study of external gamma-radiation induced reduction of PufVI). The rates of reduction decreased in the order CIO4 "= SO4 > Cl NO3. These results presumably also apply to auto-reduction... 

Mihalyi, M. R. and Beyer, H. K., Direct evidence for the incorporation of univalent indium into high-sUica zeohte, H-ZSM-5, by thermal auto-reductive solid-state ion exchange, Chemical Communications (Cambridge, United Kingdom)(21), 2242-2243 (2001). 

The mechanism of auto-reduction of Cu + in zeolites has been studied by a number of groups that used Cu-ZSM-5. Two main mechanisms are... 

It appeared that the second mechanism was appropriate for the auto-reduction of Cu(II)Y to Cu(I)Y (Takahashi et al., 2001a). 

Figure 8.12. Pure-component equilibrium isotherms at 120°Cfor 1,3-butadiene and 1-butene on Cu-Y and Ag-Y. Samples were prepared by reduction of Cu(ll)Y by either CO or auto-reduction (in He) (Takahashi et al., 2001a, with permission). Lines are fitted isotherms with various models.

Silver cation (Ag+) exhibits very strong (but reversible) interactions with N2. It has been shown that LiLSX mixed with only 1-3% Ag+ can out-perform pure LiLSX in O2 production from air by PSA/VSA. Upon heat-treatment, Ag+ undergoes auto-reduction, resulting in unique cation sites that are favorable for interactions with gas molecules. The interesting properties of Ag+-containing zeolites are potentially useful for air separation as well as for other applications. Because of this, some details will be given for these zeolites. 

Cu(l)Y can be fully regenerated by first air oxidation (e.g., at 350 °C) followed by auto-reduction in an inert atmosphere (Hemandez-Maldonado and Yang, 2003a). 

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