ALKALI ALKALINE EARTH METALS cesium used

Silver alone on a support does not give rise to a good catalyst (150). However, addition of minor amounts of promoter enhance the activity and the selectivity of the catalyst, and improve its long-term stability. Excess addition lowers the catalyst performance (151,152). Promoter formulations have been studied extensively in the chemical industry. The most commonly used promoters are alkaline-earth metals, such as calcium or barium, and alkali metals such as cesium, rubidium, or potassium (153). Using these metals in conjunction with various counter anions, selectivities as high as 82—87% were reported. Precise information on commercial catalyst promoter formulations is proprietary (154—156). 

The properties of hydrated titanium dioxide as an ion-exchange (qv) medium have been widely studied (51—55). Separations include those of alkali and alkaline-earth metals, zinc, copper, cobalt, cesium, strontium, and barium. The use of hydrated titanium dioxide to separate uranium from seawater and also for the treatment of radioactive wastes from nuclear-reactor installations has been proposed (56). 

Alkali metals lithium, sodium, potassium, rubidium, cesium, and francium. Metals such as sodium and potassium (the alkali metals) react violently with water—too violently to conduct experiments. The group 2 metals (also called alkaline earth metals) react less readily and can be used in the laboratory. Alkaline earth metals, including beryllium, magnesium, calcium, strontium, barium, and radium. 

Methacrylic acid produced from propionic acid in this process can be esterified with methanol to yield methyl methacrylate. Catalysts used in this route include alkali metal or alkaline-earth metal aluminosilicates, potassium hydroxide- or cesium hydroxide-treated pyrogenic silica, alumina, and lanthanum oxide. Both propionic acid and methyl propionate are commercially available through the Oxo process (i.e., by the carbonylation of ethylene or by the hydrofor-mylation of ethylene to propionaldehyde, followed by oxidation of the aldehyde to the corresponding acid). This alternative route has, however, shown only 50% conversion and >80% selectivity rates, and it appears that additional catalyst development is necessary in order to make this process more attractive. 

To further examine the nucleophilic side of the CH activation continuum, the our group and the Cundari group undertook a computational study [59] of alkali metal amide and alkaline earth metal amide CH activation reactions with alkanes. This study is directly related to classic superbase chemistry using cesium cyclohexylamide-type reagents to induce CH bond deprotonation of alkanes [60]. 

Impregnation followed by thermal treatment is commonly used to prepare alkali metal oxide or alkaline earth metal oxide clusters in molecular sieves in order to obtain catalysts with basic properties. A first hint at the usefulness of such procedures was published in 1984 Lacroix et al. reported that cesium-exchanged zeolite X is more active in the side-chain alkylation of toluene with methanol when left unwashed after the cation exchange [1]. Hathaway and Davis [2-4] carried out further systematic studies on the preparation of intrazeoUtic oxide clusters with basic properties. These authors described two methods for the introduction of alkali metal oxides into the pores of faujasites [2j When zeolites X and Y, ion-exchanged at room temperature with aqueous solutions of alkali metal acetates or... 

In general, alkali metal salts damp muzzle flash better than alkaline earth salts. It is also fairly certain that the flash-damping effect in the alkali metal group increases from lithium to cesium. In the First World War, bags filled with sodium chloride placed in front of the propellant charge, was used as a muzzle flash damper. 

The addition of an easily ionized substance such as cesium, which is usually not an analyte of interest in air pollution work, can reduce problems in alkali metal determination. A releasing agent, such as lanthanum, is useful for overcoming problems in analyzing for alkaline earth elements, and rare earth elements. Information on the use of these additives is given for specific cases in Table 1. 

The alkali metals are represented by the six chemical elements of group 1A(1) of Mendeleev s periodic chart. These six elements are, in order of increasing atomic number, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). The name alkali metals comes from the fact that they form strong alkaline hydroxides (i.e., MOH, with M = Li, Na, K, etc.) when they combine with water (i.e., strong bases capable of neutralizing acids). The only members of the alkali metal family that are relatively abundant in the Earth s crust are sodium and potassium. Among the alkali metals only lithium, sodium, and, to a lesser extent, potassium are widely used in industrial applications. Hence, only these three metals will be reviewed in detail in this chapter. Nevertheless, a short description of the main properties and industrial uses of the last three alkali metals (i.e., Rb, Cs, and Fr) will be presented at the end of the section. Some physical, mechanical, thermal, electrical, and optical properties of the five chief alkali metals (except francium, which is radioactive with a short half-life) are listed in Table 4.1. 

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