The Reduction of NO by CO in the Presence of Water Vapour on Supported Platinum Catalysts:Formation of Isocyanic Acid (HNCO) and Ammonia

摘要

The reaction of NO with excess CO in the presence of water vapour has been studid for silica-and alumina-supported platium.With Pt/SiO_2,HNCO is the dominant nitrogen-containing product between 300 and 400 deg C,with a yield of up to 50%.Higher tempratures favour NH_3 formation due to HNCO hydrolysis and shifts in surface populations that can be interpreted in terms of the NO+CO and water-gas shift readtions.When excess water is present,the hydrolysis activity of Pt/Al_2O_3 is sufficient to convert all HNCO to NH_3.The yield of NH_3 exceeds 75% at tempratures above 280 deg C,where conversion of NO becomes complete.Insufficient water lads to the formation of Al-NCO groups and a loss of activity that can be reversed by additional water.Pt/CeO_2 behaves similarly to Pt/Al_2O_3.Pd/SiO_2 also generates some HNCO,but the concentrations made are much less than that over Pt/SiO_2 due to a higher activity for the NO+CO reaction and a lower activity for the CO+H_2O one.