Conversion of NO to isocyanic acid and ammonium cyanate over Pd, Ir, and Pt-10% Rh catalysts

• Published in: Journal of catalysis 1978, Vol.54 (2), p.269-280
• Main Authors: Voorhoeve, R.J.H., Trimble, L.E.
• Format: Article
• Language: English
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/0021-9517(78)90049-0

The formation of HNCO and NH 4OCN was studied over unsupported Pd, Ir, and Pt-10% Rh catalysts. The reactions studied are 2NO + 3CO + 2H 2 → NH 4OCN + 2CO 2, 2NO + 4CO + H 2 → 2HNCO + 2CO 2, and 2NO + 2NH 3 + 4CO + H 2 → 2NH 4OCN + 2CO 2. The yields of NH 4OCN in the first reaction were 97% for the Pt-10% Rh catalyst. The best yield of HNCO in the second reaction was 75% over the Ir catalyst, with an additional 22% of the NO reacting according to the first reaction, for an overall NO → NCO conversion of 86%. The third reaction was carried out with a yield of 86% over Pt-10% Rh. These reactions may be attractive synthetic routes to ammonium cyanate, or its isomer urea, and to isocyanic acid or its trimer isocyanuric acid. The effects of H 2O and H 2 in the inlet gas of the reaction were found to depend on the temperature and on the H 2O H 2 ratio. The results were explained by a reaction scheme which places central importance on the adsorbed NCO intermediates. Hydrogenation and hydrolysis of NCO are shown to lead to HNCO and NH 3. It is argued that the mechanistic reaction scheme presented accounts for the observed product distributions for Pt, Rh, Ru, Os, and Cu-Ni in addition to Pd, Ir, and Pt-10% Rh.