Palladium beta-hydride

After catalyst deposition, the membranes are placed in reactors, and both sides of the membranes are exposed to oxygen [60]. Reaction with oxygen presumably removes carbon and sulfur impurities from the palladium catalyst surfaces as well as from the reactor wall surfaces. If not removed these could poison the palladium catalysts and limit hydrogen flux. Palladium forms a coherent oxide, which expands only by about 1.6% relative to metallic palladium. This expansion is less than that of the beta-hydride, which expands by about 3.2%. 

Fleischmann M., Graves P.R., Robinson J., The Raman-spectroscopy of the ferricyanide ferrocyanide system at gold, beta-palladium hydride and platinum-electrodes, J. Electroanal. Chem. 1985 182 87-98. 

It follows from the work of Darling and others that formation of the beta phase palladium hydride must be avoided to prevent embrittlement, cracking and delamination of thin catalytic films of unalloyed palladium used on composite membranes of Nb, Ta, Ti, V, and Zr. This also holds true for alloys of palladium susceptible to hydrogen embrittlement. Likewise, transformation of Nb, Ta, Ti, V and Zr substrates into brittle hydrides at low temperatures or at high hydrogen partial pressures must also be avoided. 

The above sequence was extended to a preparation of 6-epicorynoline. Performic acid oxidation of deoxycorynolone, followed by treatment with alkali, afforded a mixture of diols 3, epimeric at C-5. Lithium aluminum hydride reduction of diols 3, followed by palladium hydrogenolysis of the benzylic C-5 hydroxyl, gave rise to 6-epicorynoline. It will be noted that in this instance performic acid oxidation, followed by hydrolysis, furnished C-6 beta hydroxyl derivatives. ... 

Other seleetivity issues can arise during P-hydride elimination. If there is more than one sp -bonded hydrogen atom beta to the palladium group in the olefin adduct, then a mixture of geometric isomers may result. Also, if the hydridopalladium(II) species is not scavenged fast enough by the... 

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