Ni-Mg-Al mixed oxides

Hydrotalcite-type anionic clays as precursors of high-surface-area Ni/Mg/Al mixed oxides... 

This study deals with the preparation, properties and reactivity of high-surface-area Ni/Mg/Al mixed oxides featuring different Ni g ratios obtained from HT anionic clays. In HT precipitates all cations are present inside the brucite- pe layers, therefore the specific properties of each element may be evidenced without any interfraence due to phase segregation and/or physical dishomogeneity. 

This model may be considered of a more general validity, on account of the behaviours of the Ni/Mg/Al mixed oxides obtained from HT precursors, reported in this paper. However, some adaptations arc required depending on composition in particular, for the Mg-rich samples the reduction of the Ni ions inside the oxide phases is further hindered by the presence of Mg and Ap" " ions, as clearly evidenced by the increase in the apparent activation energy. 

Fig. 2a shows the XRD pattern of Mg-Al mixed oxide obtained by calcining Mg-Al HT at 1123K. Strong lines of MgO were observed in the Mg-Al mixed oxide, but the value of the lattice parameter a (0.420 nm) was smaller than that of pure MgO (0.421 nm), suggesting the formation of a Ni-Mg-O solid solution as well as the presence of Ap ion in the Ni-Mg-0 cubic lattice as reported by several researchers [2]. 

Early catalysts reported to be active for the ODH of butane were based on the molybdates of Mg, Mn, Fe, Co, and Ni. Selectivities of 52% to butadiene at a conversion rate of 27% were achievable with the Mg molybdate. Rung and coworkers (131) also reported that V-Mg-0 catalysts are also useful for this reaction. Vanadia supported upon Mg-Al mixed oxides have similarly received considerable attention (155). 

Anionic clays, such as hydrotalchite, manasseite, stichtite, etc. are layered double hydroxides (Mg/Al Mg/Fe Mg/Cr2 Ni/Al Ni/Fe, etc.). Anionic clays exhibit poor acidic properties. The thermal decomposition of anionic clays gives rise to mixed oxides of industrial importance as catalysts. 

Delay Element. This term may also be applied to a component which provides a specific delay in a blasting cap, detonator, fuze, etc Refs l)0hart (1946), 20 278 2)H.M.Kerr C.R.Hall USP 2560452 (1951) CA 46, 1259 (1952) [Delay elements for electric blasting caps consist of homogeneously mixed powdered metals (such as Mg, Al, Ni, Zn), fuels (such as Si), oxidizers (such as Pb C ) and Misch -metall . By varying the compns, burning times of 15 to 579 milliseconds were obtained] [The Misch-metall (Ger for mixed metal ) is an alloy of rare earths of the following compn ... 

The decarbonation of carbonated layered double hydroxides containing Mg with either Al, Fe or Cr bivalent cations or A1 with Mg, Ni, Cu or Zn divalent cations has been studied by thermal analysis. The enthalpy of adsorption of CO2 on the resulting calcined mixed oxides was measured by calorimetry, with initial heats of adsorption close to those reported for MgO (about lOOkJmol ) and a relatively homogeneous strength distribution [100],... 

Infrared skeletal spectroscopy may reveal the structure of defective situations in complex oxides. An example concerns Ni-Al binary nuxed oxides as well as Ni-Mg-A1 ternary mixed oxides. These materials find relevant application as the precursors of steam-reforming catalysts as well as total oxidation catalysts of VOCs. 

It has been proposed that the extent to which mixed-cation hydroxide compounds actually do form in aquatic and terrestrial environments is limited more by slow rates of soil mineral dissolution, a necessary preliminary step, than by lack of thermodynamic favorability (57). Because the dissolution rates of clays and oxide minerals are fairly slow, the possibility of mixed-cation hydroxide formation as a plausible "sorption mode" in 24 hour-based sorption experiments (and also most long-term studies) containing divalent metal ions such as Mg, Ni, Co, Zn, and Mn and Al(III)-, Fe(III)-, and Cr(III)-(hydr)oxide or silicate minerals has been ignored in the literature 16,17). This study and others recently published (77), however, suggests that metal sorption onto mineral surfaces can significantly destabilize surface metal ions (A1 and Si) relative to the bulk solution, and therefore lead to an enhanced dissolution of the clay and oxide minerals. Thus, predictions on the rate and the extent of mixed-cation hydroxide formation in aquatic and terrestrial environments based on the dissolution rate of the mineral surface alone are not valid and underestimate the true values. 

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