Catalysis Today, Vol.323, 159-165, 2019
Catalytic oxidation of nitrogen containing compounds for nitrogen determination
The high temperature catalytic oxidation (HTCO) performance of Al2O3 supported Pt, Cu, Cu-Ce and Fe catalysts were systematically studied with a perspective of selective oxidation of nitrogenous compounds to nitric oxide for quantitative determination of bound nitrogen. The catalyst samples were prepared via impregnation and characterized by XRD and BET. In addition, temperature programmed reaction experiments with acetonitrile and oxygen were conducted to evaluate the catalytic activity and selectivity toward N-2, N2O and NO. The catalyst samples were also tested for model components; urea, EDTA, pyridine, glutamic acid and ammonium sulfate representing different functional groups. The conversion of acetonitrile was tended to increase in the order of Cu-Ce/Al2O3> Cu/Al2O3> Pt/Al2O3> Fe/Al2O3 at around 500 degrees C and almost complete conversion of acetonitrile was achieved at 700 degrees C over the all catalyst samples studied. Temperature programmed reaction experiments indicated that two reaction routes, direct oxidation of cyanide species and oxidation of ammonia formed by hydrolysis of cyanide species determine NO selectivity. Direct oxidation of cyanide species is favored over Pt/Al2O3 catalyst which exhibit highest NO yield (93%) at 700 degrees C. The second route, hydrolysis of cyanide species to ammonia which is further oxidized to N-2, NO and NO2 was evidenced by TPR-FTIR analyses over Fe/Al2O3, Cu/Al2O3 and Cu-Ce/Al2O3 catalysts. Among these catalysts, highest NO yield (90%) was observed over Fe/Al2O3 at 700 degrees C which is comparable to Pt/Al2O3 catalyst. For Cu and Cu-Ce/Al2O3 catalyst, lower yields were obtained due to higher N-2 selectivity. Similar results were obtained from benchmark tests performed by model nitrogen components representing different functional groups. Pt/Al2O3 and Fe/Al2O3 catalysts possessed higher oxidation activities and nitrogen recoveries than Cu and Cu-Ce catalysts. As a result, Fe/Al2O3 catalyst is highly effective, lower cost alternative to existing Pt based catalysts which are used for bound nitrogen determination.