Cobalt surface reduction

Co catalyst Co content (%) Cobalt surface density, Nco/(100 A ) Sbet (mVg) TPV (cmVg) Pore diameter (A) C03O4 crystallite diameter from XRD (A) Extent of reduction measured by TGA (%)... 

The effect of Mn as promoter for CNF-supported cobalt catalysts was studied by impregnating a parent 9.5 wt% Co catalyst with different amounts of MnO (ranging from 0.03 to 1.1 wt%) [124]. It was found that manganese hindered cobalt reduction, the cobalt surface remaining more oxidic in character in the presence of Mn. The catalytic performance was affected differently in tests carried out at 1 and 20 bar. At atmospheric pressure, the chain growth probability increased, and the product distribution shifted toward olefinic products... 

Because of the excellent catalytic performance of the ceria-based C03O4 and CuO catalysts, a combination of the two systems was investigated by preparing, through co-precipitation, mixed Cu-Co-Ce-O oxides with different compositions. The mixed oxides had a larger surface area with respect to the Co-Ce-O and Cu-Ce-O composite oxides. Moreover, the addition of cobalt to the Cu-Ce-O catalyst enhanced thermal stability because the particle size was unchanged on calcination at 850 °C. According to the H2-TPR patterns, the peaks due to cobalt oxide reduction and those for copper oxide reduction were reciprocally affected and shifted towards lower temperatures. The interaction between cobalt and... 

The present study revealed effects of various rutile/anatase ratios in titania on the reduction behaviors of titania-supported cobalt catalysts. It was found that the presence of rutile phase in titania could facilitate the reduction process of the orbalt catalyst. As a matter of fact, the number of reduced cobalt metal surface atoms, which is related to the overall activity during CO hydrogenation increased. 

The present research showed a dependence of various ratios of rutile anatase in titania as a catalyst support for Co/Ti02 on characteristics, especially the reduction behaviors of this catalyst. The study revealed that the presence of 19% rutile phase in titania for CoATi02 (C0/RI9) exhibited the highest number of reduced Co metal surface atoms which is related the number of active sites present. It appeared that the increase in the number of active sites was due to two reasons i) the presence of ratile phase in titania can fadlitrate the reduction process of cobalt oxide species into reduced cobalt metal, and ii) the presence of rutile phase resulted in a larger number of reduced cobalt metal surface atoms. No phase transformation of the supports further occurred during calcination of catalyst samples. However, if the ratios of rutile anatase were over 19%, the number of active sites dramatically decreased. 

The surface analyses of the Co/MgO catalyst for the steam reforming of naphthalene as a model compound of biomass tar were performed by TEM-EDS and XPS measurements. From TEM-EDS analysis, it was found that Co was supported on MgO not as particles but covering its surface in the case of 12 wt.% Co/MgO calcined at 873 K followed by reduction. XPS analysis results showed the existence of cobalt oxide on reduced catalyst, indicating that the reduction of Co/MgO by H2 was incomplete. In the steam reforming of naphthalene, film-like carbon and pyrolytic carbon were found to be deposited on the surface of catalyst by means of TPO and TEM-EDS analyses. 

Reduction of the 00 04 Catalysts. For all three samples the reduction of the surface of the 00 04 particles to metallic cobalt was observed by XPS following reaction in one atmosphere of flowing H2. After one hour at 350"C bulk C03O4 was completely reduced, while for CO304/Si02 2 the reduction was only about 80% complete. The COj04/Si02-923 sample was about 60% reduced at... 

Some of the transition metal macrocycles adsorbed on electrode surfaces are of special Interest because of their high catalytic activity for dloxygen reduction. The Interaction of the adsorbed macrocycles with the substrate and their orientation are of Importance In understanding the factors controlling their catalytic activity. In situ spectroscopic techniques which have been used to examine these electrocatalytlc layers Include visible reflectance spectroscopy surface enhanced and resonant Raman and Mossbauer effect spectroscopy. This paper Is focused principally on the cobalt and Iron phthalocyanlnes on silver and carbon electrode substrates. 

Of special Interest as O2 reduction electrocatalysts are the transition metal macrocycles In the form of layers adsorptlvely attached, chemically bonded or simply physically deposited on an electrode substrate Some of these complexes catalyze the 4-electron reduction of O2 to H2O or 0H while others catalyze principally the 2-electron reduction to the peroxide and/or the peroxide elimination reactions. Various situ spectroscopic techniques have been used to examine the state of these transition metal macrocycle layers on carbon, graphite and metal substrates under various electrochemical conditions. These techniques have Included (a) visible reflectance spectroscopy (b) laser Raman spectroscopy, utilizing surface enhanced Raman scattering and resonant Raman and (c) Mossbauer spectroscopy. This paper will focus on principally the cobalt and Iron phthalocyanlnes and porphyrins. 

Figure 11.8 Formation of ordered nanoparticles of metal from diblock copolymer micelles, (a) Diblock copolymer (b) metal salt partition to centres of the polymer micelles (c) deposition of micelles at a surface (d) micelle removal and reduction of oxide to metal, (e) AFM image of carbon nanotubes and cobalt catalyst nanoparticles after growth (height scale, 5 nm scan size, lxl pm). [Part (e) reproduced from Ref. 47].

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