Sodium alanate hydride

The sodium alanate hydride NaAlH is so far the most investigated and promising hydrogen storage material, at least on a short time scale (for reviews see [1-7]). 

The pyridine ring is easily reduced in the form of its quaternary salts to give hexahydro derivatives by catalytic hydrogenation [446], and to tetrahydro and hexahydro derivatives by reduction with alane aluminum hydride) [447], sodium aluminum hydride [448], sodium bis 2-methoxyethoxy)aluminum hydride [448], sodium borohydride [447], potassium borohydride [449], sodium in ethanol [444, 450], and formic acid [318]. Reductions with hydrides give predominantly 1,2,5,6-tetrahydro derivatives while electroreduction and reduction with formic acid give more hexahydro derivatives [451,452]. 

Reduction of unsaturated ketones to unsaturated alcohols is best carried out Nit v complex hydrides. a,/3-Unsaturated ketones may suifer reduction even at the conjugated double bond [764, 879]. Usually only the carbonyl group is reduced, especially if the inverse technique is applied. Such reductions are accomplished in high yields with lithium aluminum hydride [879, 880, 881, 882], with lithium trimethoxyaluminum hydride [764], with alane [879], with diisobutylalane [883], with lithium butylborohydride [884], with sodium boro-hydride [75/], with sodium cyanoborohydride [780, 885] with 9-borabicyclo [3.3.1]nonane (9-BBN) [764] and with isopropyl alcohol and aluminum isopro-... 

High yields of amines have also been obtained by reduction of amides with an excess of magnesium aluminum hydride (yield 100%) [577], with lithium trimethoxyaluminohydride at 25° (yield 83%) [94] with sodium bis(2-methoxy-ethoxy)aluminum hydride at 80° (yield 84.5%) [544], with alane in tetra-hydrofuran at 0-25° (isolated yields 46-93%) [994, 1117], with sodium boro-hydride and triethoxyoxonium fluoroborates at room temperature (yields 81-94%) [1121], with sodium borohydride in the presence of acetic or trifluoroacetic acid on refluxing (yields 20-92.5%) [1118], with borane in tetrahydrofuran on refluxing (isolated yields 79-84%) [1119], with borane-dimethyl sulflde complex (5 mol) in tetrahydrofuran on refluxing (isolated yields 37-89%) [1064], and by electrolysis in dilute sulfuric acid at 5° using a lead cathode (yields 63-76%) [1120]. 

It can be summarized that of all the complex aluminum hydrides presented in this chapter only NaAlH4 up till now partially fulfils the requirements for a storage material for mobile fuel cell applications. Over the last decade, the kinetics as well as the cycle stability of doped sodium alanates has been improved. Nevertheless, for application in a low-temperature fuel cell the storage capacity seems to be too low because only the first decomposition step (3.6 wt.% hydrogen) can be used. 

Sodium alanate (NaAll-14) remains so far the most studied complex hydride. It is found that NaAlH4 decomposes in several steps ... 

Recently, metal-doped aluminium hydrides have been proposed as further potential hydrogen storage materials [107, 123]. Among lightweight metal hydrides the lithium and sodium alanates (NaAfflU, LiAlH4) have been widely... 

The calculations presented here are consistent with many models and measurements described in the literature [11-14, 17, 20, 21], Models and measurements indicate that the effective thermal conductivity of particles loaded in a packed bed is generally limited to values below 5 W/m K, even with significant increases in the particle thermal conductivity (Fig. 4.4(b)). More clever methods must be employed to enhance thermal conductivity to levels above 5 W/m K. Additionally, the models discussed above have been developed for distinct particles typical of classic/interstitial hydride materials. These classic/interstitial beds are generally characterized as unsintered powders while complex hydrides, such as sodium alanates, can become porous sintered solids as seen in Fig. 4.5. Application of packed particle models have not been directly applied to sintered solid materials. 

In this section, we will explore the safety properties of a specific set of complex hydrides, sodium alanates. These materials represent the most advanced solid-state hydrogen system developed to date and allow us to understand the safety properties associated with this class of materials. 

Sodium alanates prototypical complex metal hydrides... 

One attractive feature of alanates is that lithium and sodium salts are readily available commercially. Magnesium alanate can be readily prepared with sodium alanate and magnesium hydride via a metathesis reaction. The mixed metal alanate, Na2LiAlH6, is prepared through ball milling of sodium hydride, lithium hydride, and sodium alanate. Potassium alanate can be prepared by the direct synthesis of potassium hydride and aluminum under high temperature and pressure." ... 

Some of the highest storage capacities are for complex hydrides and because of this there has been considerable research on alanates, borohydrides and amides/imides. One of the most successful systems (in terms of reversibility) has been that of sodium alanate, although the cyclable capacity is low at... 

Improve the kinetics of absorption and desorption and thermodynamic plateau pressures of Ti-doped sodium alanate metal hydrides. 

Find new complex metal hydrides and catalysts using procedures and techniques developed during the sodium alanate investigations. 

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