Production and regeneration of platinum carrier catalysts for the synthesis of hydroxylamine from nitric oxide and hydrogen

摘要

Platinum catalysts, for the synthesis of hydroxylamine from nitric oxide and hydrogen in the presence of dilute mineral acids, are produced or regenerated by a process wherein an aq. PtIV salt solution is first reduced to the PtII stage in presence of graphite or activated charcoal (as carrier) at a chloride ion concentration which is a multiple of (e.g. 20-50 times) the molar Pt concentration of the initial solution and at pH 3-7, by a selective reducing agent, the Pt being then precipitated on the carrier at pH 2,3-4,0 by a strong reducing agent. The selective reducing agent is preferably sodium dithionite or its reaction product obtained by hydrolysis and addition of formaldehyde (e.g. sodium hydroxymethanesulphinate), or sulphurous acid and its compounds such as the sodium and calcium salts. The strong reducing agent is preferably formic acid or its sodium or calcium salt. The PtIV solution may be formed by the action of aqua regin on Pt , e.g. in a catalyst requiring regeneration. Specifications 624,353, 667,870, 714,226, 720,796, 736,632, 772,693 and U.S.A. Specifications 2,658,028, 2,767,147, 2,798,791, 2,834,740 and 2,861,960 are referred to.