Cobalt oxides, deposition

It has been established from these studies that the different catalytic properties of transition metal oxides (chromium, cobalt) on zirconium dioxide are attributed to their different acidic properties determined by TPDA and IR-spectroscopy. The most active catalyst is characterized by strong acidic Bronsted centers. The cobalt oxide deposited by precipitation on the zirconium-containing pentasils has a considerable oxidative activity in the reaction N0+02 N02, and for SCR-activity the definite surface acidity is necessary for methane activation. Among the binary systems, 10% CoO/(65% H-Zeolite - 35% Z1O2)... 

Temperature programmed reduction (TPR) is a valuable method for gathering information about the reduction process. The reduction properties of cobalt oxide deposited on different support materials have been extensively investigated. According to most reports [6-10], unsupported, as well as supported C03O4, are reduced to cobalt metal in two-steps ... 

Cyclodextrin Inclusion Complexes as Novel MOCVD Precursors for Potential Cobalt Oxide Deposition Appl. Organometal. Chem., Vol. 24, p>p. 112-121... 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

FIG. 10 Hysteresis magnetization loops obtained at T = 3 K. (A) Diluted liquid solution of cobalt nanoparticles in hexane. (B) Cobalt nanoparticles deposited onto freshly cleaved graphite (HOPG) and dried under argon to prevent oxidation. Substrate parallel (—) and perpendicular (—) to the field. 

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. 

S) Reduction of the Oxide with Carbon Monoxide.—Reduction of cobalto-cobaltic oxide to the metal takes place rapidly, and is quite complete at 900° C. Between 350° and 450° C. the reaction is very interesting. At first some oxide is reduced to metallic cobalt after a time the finely divided metal decomposes the carbon monoxide, depositing solid carbon, presumably in the same way as its analogue, iron, namely ... 

Like its ferrous analogue, cobalt hydroxide readily absorbs oxygen, yielding a brown mass. When dissolved in acids stable cobaltous salts are obtained, but when dissolved in hot, concentrated aqueous potassium hydroxide and allowed to cool, cobaltous oxide gradually crystallines in microscopic prisms 5 which are deposited as a violet powder. The crystals are pleochroic, of density 3-597 at 15° C-, permanent in air and insoluble in ammonium hydroxide. They are soluble in acetic acid, in sodium hydroxide, and in hot solutions of ammonium chloride. 

Our recent studies of cobalt oxides catalyst deposited on y-alumina indicate unexpected activity of C0-O/AI2O3 in oxidative cracking of n-butane at low temperature. High yield of olefins 30% (mostly ethylene and propylene) was reached at 550°C and WHSV - 4.5h" [8]. Furthermore varying of oxygen concentration affects olefins distribution. Such essential features of cobalt oxide catalyst render it interesting as a base for catalyst development. 

In these cases, the majority of the Pt metals would be deposited on to the alumina surface rather than on the top of nickel or cobalt oxide particles as mentioned by Oh and Carpenter (26). 

Products of incomplete combustion have been shown to increase as the catalyst deactivates. Agarwal et al. report that the oxidation of a mixed stream of trichloroethylene and C5-C9 hydrocarbons over a chromia alumina catalyst produced CO equal to 32% of the total CO + CO2 with fresh catalyst. With a deactivated catalyst, CO had risen to 54% of the total carbon oxides produced. Pope et al. report products of incomplete combustion for the oxidation of 1,1,1-trichloroethane over a cobalt oxide catalyst. The cause of the catalyst deactivation has not been established, but both Agarwal et al. and Michalowiczl reference evidence of carbonaceous deposits on the catalyst after oxidation of halogenated hydrocarbons. ESCA studies by Hucknall et al. O have always shown a carbon residue on palladium alumina catalysts in addition to adsorbed halogen. 

Chemical vapor deposition (CVD) was applied to produce homogeneous thin films of pure and doped spinel cobalt oxide with similar morphology on the surface of planar and monolithic supports. The planar substrates were used to investigate the thermal stability and the redox properties of the spinel using temperature-programmed methods monitored by emission-FTIR spectroscopy, while the monolithic substrates were used to test the catalytic performance of the deposited films toward the deep oxidation of methane and to evaluate its durability. The high performance of cobalt oxide to oxidize methane in diluted streams was demonstrated at 500 °C. Furthermore, controlled doping of cobalt oxide layers with suitable cations was demonstrated for nickel as an example, which resulted in substantial increase of electric conductivity. 

In this study, the CVD process is used to deposit cobalt oxide as planar model layers and as working monolithic catalysts to enable accurate characterization and test of performance. 

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