Activation by Thermal Decomposition of Metallic Oxides

The surface of alumina, AI2O3, may be activated by employing laser or UV irradiation to decompose AI2O3 [61]. Decomposition 

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Activation by Thermal Decomposition of Metallic Oxides. The surface of alumina, AI2O3, may be activated by employing laser or ultraviolet irradiation to decompose AI2O3 (68). Decomposition of AI2O3 results in the generation of aluminum particles that are catalytic for electroless deposition of Cu (the first reaction probably is displacement deposition). 

Sintered Electrodes In these electrodes the active materials are present in pores of a sintered nickel support plate. This plate is manufactured by sintering of highly disperse nickel powder produced by thermal decomposition of nickel pentacarbonyl Ni(CO)5. The plates are filled by impregnating them in alternation with concentrated solutions of salts of the corresponding metals (Ni or Cd) and with an alkali solution serving to precipitate insoluble oxides or hydroxides. 

Various active nickel catalysts obtained not via reduction of nickel oxide with hydrogen have been described in the literature. Among these are the catalysts obtained by the decomposition of nickel carbonyl 10 by thermal decomposition of nickel formate or oxalate 11 by treating Ni-Si alloy or, more commonly, Ni-Al alloy with caustic alkali (or with heated water or steam) (Raney Ni) 12 by reducing nickel salts with a more electropositive metal,13 particularly by zinc dust followed by activation with an alkali or acid (Urushibara Ni) 14-16 and by reducing nickel salts with sodium boro-hydride (Ni boride catalyst)17-19 or other reducing agents.20-24... 

The third route is defined as substractive (lUPAC), in that certain elements of an original structure are selectively removed to create pores. Examples include the formation of porous metal oxides by thermal decomposition of hydroxides, of porous glasses by chemical etching, of activated carbons by controlled pyrolysis, of ceramic foam membranes by burning off a polymer (e.g. polyurethane), of alumina by anodic oxidation of aluminium to give oriented cylindrical pores with a narrow size distribution. 

Palladium is one of the most versatile and efficient catalyst metals in organic synthesis. Solubility in water is achieved by utilization of simple palladium(II) salts or water-soluble ligands, such as TPPTS and TPPMS. The active catalysts for Heck-type reactions are zerovalent palladium(O) species [3], which are often generated in situ by thermal decomposition of a Pd(II) precursor or by the application of a reducing agent, e.g., 1-6 equiv. of a phosphine in the presence of base generates Pd(0) and the phosphine oxide (Eq. 3) [4],... 

Oxides of metals exhibiting low basicity may be obtained by thermal decomposition of their salts with volatile or readily decomposed acids. Such salts include nitrates, carbonates, formates and oxalates. In order to obtain active preparations, the decomposition conditions should be as mild as possible. The decomposition proceeds faster in vacuiun than in air, so that the reaction temperature may be lower (for the same yield per imit time). An even stronger influence on the reaction rate is sometimes exerted by an appropriate gaseous ataiosphere (see below). 

The previous examples are all supported gold catalysts. Supported bimetallic catalysts have been explored as well. Scurrell and coworkers developed a series of Au-M/ Fe Oj (M=Ag, Bi, Co, Cu, Mn, Ni, Pb, Ru, Sn, Tl) catalysts for WGS [70,71], These catalysts were prepared by deposition-coprecipitation using HAuCl, FeCNOjjj, and metal salts as precursors, followed by calcination in air at 400°C. Au-Ru/Fe Oj showed the highest activity. However, there is no evidence showing that the so-called bimetallic catalysts are bimetallic. The thermal decomposition of metal salts in air usually leads to the formation of metal oxides instead [61]. 

Of great interest is the use of intermetallic compounds of platinum with rare-earth metals such as cerium and praseodymium for anodic methanol oxidation, known from the work of Lux and Cairns (2006). This combination is attractive inasmuch as it involves two metals that differ strongly in their own electrode potentials Pt with = -1-1.2 V and Pr with = —2.3 V(SHE), and thus in their electronic structure. However, for the same reason, traditional methods of preparing joint disperse deposits of these metals by chemical or electrochemical reduction in a solution of the corresponding salts fail in such a situation. Lux and Cairns developed a new technology for preparing disperse powders of such compounds by thermal decomposition of complex cyanide salts of these metals. The catalyst obtained had some activity in ethanol oxidation (although somewhat... 

Zinc oxide is made either by the oxidation of the metal in oxygen (the indirect, IP, or French process), by the direct decomposition of zinc ores in air (the direct or American process) or by the thermal decomposition of zinc salts (TD zinc oxide). IP zinc oxides differ from TD zinc oxides in that their surfaces do not contain absorbed water. Also, whereas TD zinc oxide reacts with plain eugenol, IP zinc oxide hardly reacts unless activated by an acetic add or zinc acetate accelerator (Table 9.2). 

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