Complex Oscillation Patterns During the Catalytic Hydrogenation of NO₂ over Platinum Nanosized Crystals

Abstract

We studied the catalytic reduction of NO2 with hydrogen on platinum model catalysts by means of field emission techniques. Atomic resolution field ion microscopy (FIM) was used to characterize Pt samples conditioned as tips. The catalytic reaction was investigated with video frequency resolution using field electron emission microscopy (FEM). Kinetic instabilities eventually merging into self-sustained periodic oscillations were observed. Data analyses revealed monomodal and bimodal oscillations as well as the coexistence of both mono- and bimodal regimes. Fourier transforms and interpeak intervals were used to characterize these different modes. We propose a mechanism that qualitatively explains the emergence of oscillations and the appearance of bimodal oscillations.