Method of providing a controlled atmosphere containing nitrogen or a mixture of nitrogen and hydrogen

摘要

A controlled atmosphere of nitrogen or nitrogen and hydrogen is obtained by passing a mixture of gaseous ammonia and free oxygen - containing gas, wherein the molecular ratio of NH3 to O2 is greater than 4:3, over a supported catalyst comprising at least one metal of the platinum group, e.g. 0.5 per cent by weight platinum, rhodium, ruthenium and/or iridium deposited on dehydrated alumina or zirconium dioxide. A proportioned mixture of ammonia and air containing at least 21.83 per cent ammonia is passed into the top of the catalyst chamber 16 through a bed of catalyst 29. The frusto-conical shape 30 ensures that regardless of the amount of ammonia feed there is always a zone in which optimum oxidation efficiency is obtained. After condensation of water, the exit gases are mixed with a controlled amount of air and passed over a supported palladium catalyst bed 33, heated to 100 DEG C or more by heat exchange with the gases coming from bed 29, to remove any nitrogen oxides and adjust the hydrogen content. Water is again condensed out. Where nitrogen alone is the product the catalyst metal is essentially platinum for combustion, but where a nitrogen-hydrogen mixture is the product then rhodium, ruthenium, and/or iridium are also used for cracking and the catalysts may be in single or separate beds.