Some industrial waste gases, such as the exhaust air from the paint booth, are difficultly treated by the catalytic combustion system, since the heavy metals contained in these gases rapidly poison the catalyst. A simple reactivation process is presented as follows : platinum catalysts poisoned with heavy metals are soaked with the solution of chelating ragents such as EDTA at ordinary or elevated temperature. The recovery of the activity was found remarkable by this treatment on lead, copper, zinc, titanium, and lead chromate contaminated catalysts. Chromium, probably existing on the catalysts as its stable oxide (Cr₂O₃), was, however, hardly removed even by the treatment at 130°C.

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