Platinum, ammonia conversion wires

P11-7b The oxidation of ammonia is to be carried out over platinum gauze. The molar flow rate of ammonia is 10 mol/min at a temperature of 500 K and a pressure of 202.6 kPa. Is one 250-mesh screen 10 cm in diameter sufficient to achieve 60% conversion The wire diameter is 0.044 mm. Assume 25% excess air, and ignore the effects of volume changes on the Reynolds number. 

The anhydrous ammonia and process air used must be free from catalyst poisons, dust, and oil. Platinum catalysts can be poisoned by such elements as As, Bi, P, Pb, S, Si, and Sn. Fortunately, synthetic ammonia is normally of high purity unless it is accidentally-contami -nated. However, since air can be contaminated by dust or many other pollutants, thorough air cleaning is necessary. Location of the air intake in an area relatively free from contaminants will help. If poisoning by impure ammonia or air ould arise, deep penetration may occur, leading to the formation of inactive compounds in the catalyst wires and, perhaps, to the extent of ruining the catalyst, fri other instances, contamination by traces of Cr, Fe, or Ni may temporarily reduce conversion efficiency, but this can often be restored by treatment with hydrochloric acid or certain sails. 

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