The formation of isocyanic acid and ammonia during the reduction of NO over supported platinum group metals

The formation of isocyanic acid (HNCO) by reaction of NO and CO with sources of hydrogen has been investigated along with its subsequent hydrolysis on oxides. High HNCO yields are possible with H2 itself using Pt/SiO2 and Pd/SiO2 with Rh/SiO2 less effective. The H2 forms NH3 and H2O initially but they are recycled to HNCO as the temperature is increased. The NH3+NO+CO reaction is equally as effective as a generator of HNCO. Oxides other than silica catalyse complete hydrolysis of HNCO to NH3 and CO2. The combination of HNCO formation from NH3 and subsequent hydrolysis back to NH3 allows the amplification of ammonia by a factor of 3 when using a combination of Pd/SiO2 followed by CeO2–SiO2. Multiplication by 6 is possible with Pt/SiO2 ahead of CeO2–SiO2 since additional HNCO is generated on Pt by the reaction of NO and CO with surface hydrogen derived through the water-gas shift reaction. The reaction of a H2O/NO/CO mixture over a Pt/Al2O3 catalyst forms NH3 with >80% yield in this way.