Hydrogen activating magnesium

Fernandez and Sanchez [18] investigated the kinetics of hydrogen absorption and desorption by activated magnesium powder (several cycles of hydrogen absorp-tion/desorption at 375°C) using a volumetric technique. They pointed out that for-mation/decomposition of metal hydrides comprises a number of steps taking place in series transport to the surface, dissociation, H chemisorption, surface-... 

Indeed, on Pd/SiO adsorbed formaldehyde was characterized with dimethyl- or diethylsulfate in the form of formaldehyde dimethyl or diethyl acetal, respectively. The highest concentration of formaldehyde (10 mol.(g of cat) )) was observed when only CO was added to the prereduced Pd catalyst (42). With an excess of hydrogen as well as on more active magnesium containing catalyst, only trace amounts of adsorbed formaldehyde were detected. Its low concentration on these catalytic surfaces may result from rapid conversion of adsorbed formaldehyde into methoxy moieties (Table I). 

Activated magnesium is quenched by the addition of isopropyl alcohol until hydrogen gas is no longer evolved. Caution Hydrogen gas is flammable and should be vented into a fume hood. 

Caution. The residual material contained in the reaction flask and fritted funnel includes highly activated magnesium metal and metallic mercury. The residual material must not come into contact with water, since the hydrogen that is generated would ignite. The magnesium should be decomposed by reaction with 2-propanol. The metallic mercury should be disposed of properly. 

Rank the activities of copper, zinc, hydrogen, and magnesium from most active to least active. 

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