Redox oxygen vacancies

Therefore, a bifUnctional mechanistic scheme, including the participation of both the metal (via the adsorption of CO) and the support (via the formation of "oxygen vacancies" which are active sites for the H2O dissociative adsorption) seems quite relevant to explain the specific behavior, for the NO r uction in the presence of water, of samples containing Zr02 Such active sites would be located at the met -support interface and are linked to the redox properties of the support... 

We shall mainly consider, in the present chapter, non-precious transition metals, but the model can be extended to precious metals presenting an oxidation state higher than zero [10,11], such as Rhx+, Pdx+, Ptx+ and tix+. The model also applies to some oxides alone, such as ceria (Ce02) [19] or mixed oxides such as ceria-zirconia (CeZr02) able to present redox properties and oxygen vacancies during catalytic reactions. 

The perovskite structure is stable to relatively large amounts of dopant ions on either A or B sites. Oxygen vacancies are introduced into the lattice, either through transition-metal redox processes or by doping on the A or B sites with lower valence cations. 

The electrochemical reduction of nitric oxide in solid-state electrochemical cell is an interesting field surveyed in [95]. The working principle of the cells is the cathodic reduction of NO to nitrogen and oxygen anions. In [95], the properties of various types of solid-state electrochemical cells used for NO reduction are presented and discussed. It is shown that the cathode materials with a high redox capacity and oxygen vacancies are most active for the electrochemical reduction of nitric oxide, whereas noble metal-based electrodes show a much lower selectivity. As an alternative route, the promotion of the reduction with a reductive agent is also considered. 

Toward bioapplications Since cerium occurs in both trivalent (+ 3) state and tetravalent (+4) state, it may switch between these two states in a redox reaction in ceria to make excellent oxygen buffers. Therefore, ceria NPs with increased surface area and oxygen vacancies exhibit excellent catalytic activities. In biological systems, reports indicated that ceria NPs... 

Four different routes were employed for the synthesis of iron-oxide-based redox water-sphtting materials Solid-State Synthesis (SSS), Self-Propagating High-Temperature Synthesis (SHS), Gel Combustion (GC) and Aerosol Spray Pyrolysis (ASP) [8]. These synthesis methods were chosen with the rationale to exploit particular characteristics of each one for the synthesis of products with tunable oxygen vacancies concentration. The synthesis details have been reported previously [8], therefore only the general reaction concepts are reported below, where A and B denote the bivalent dopant metals Ni, Mn or Zn. 

The extent of lattice oxygen incorporation into the decomposition products is linked to the surface redox properties of the oxide. Recent SSIMS and FT-RAIRS studies have provided initial evidence for the transient formation of oxygen vacancies on the surface of TiO2(110). Henderson has proposed that surface oxygen vacancies may explain the formation of trace amounts of formaldehyde from formic acid on Ti02(l 10) (figure 3) [41]. Both reactions (6) and (7) are proposed to occur below 500 K the water produced from formic acid exposure desorbed at 475 K, before the onset of formate decomposition to form CO. Formaldehyde and CO2 were produced in minor quantities relative to the production of CO [41]. Formaldehyde was formed from formic acid on reduced... 

As deduced from the magnetic balance results commented on above, also confirmed by XAS data (205), the use of chlorine-containing metal precursors may deeply modify the redox properties of ceria. The reversible contribution plays a minor role, thus suggesting that the presence of chlorine heavily disturbs the H2-CeC>2 interaction (209). This has also been confirmed by some volumetric (209) and TPD studies (166), Likewise, the above results show the existence of a new very important contribution to the total reduction degree reached by ceria. It is specifically related to the Cr ions incorporated into the ceria lattice. Though it does not revert on outgassing, no oxygen vacancies would be associated with this third contribution (52,163,193,195). 

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