10.1021/acs.jchemed.9b00351.s010 Petrus C. M. Laan Petrus C. M. Laan Mareena C. Franke Mareena C. Franke Richard van Lent Richard van Lent Ludo B. F. Juurlink Ludo B. F. Juurlink Heterogeneous Catalytic Oxidation of Ammonia by Various Transition Metals American Chemical Society 2019 catalyst surface power supply butane flame Sabatier principle Various metal catalyst wires Active catalysts Various Transition Metals Heterogeneous Catalytic Oxidation oxidation illustration Thermal heating 10 elements Rh metal wires ammonia-to-oxygen ratio grayish smoke group 9 2019-07-31 13:29:50 Media https://acs.figshare.com/articles/media/Heterogeneous_Catalytic_Oxidation_of_Ammonia_by_Various_Transition_Metals/9199097 A well-known demonstration is adapted to simplify the illustration of heterogeneous catalytic oxidation of ammonia. Various metal catalyst wires are placed above the liquid level in a flask containing concentrated ammonia. After brief preheating, some metal wires continue to glow, providing visual evidence of an overall exothermic reaction taking place at the catalyst surface. Thermal heating by a butane flame prior to insertion and <i>in situ</i> resistive heating using a power supply yield identical results. Active catalysts are the group 9 and 10 elements Rh, Ir, Pd, and Pt. Besides the illustration of the Sabatier principle, the effect of the ammonia-to-oxygen ratio can also be visualized, and active metals vary in the production of a grayish smoke. These observations provide a starting point to discuss catalytic selectivity, a topic of great relevance to industrial catalytic oxidation of ammonia.