Non-linear behaviour in the NO–H₂reactions over single crystals and field emitters of some Pt-group metals

Abstract

Field emission microscopy studies of the NO-H, reactions on Pt, Rh and Ir field emitters in the lo-' to lop4 mbar total pressure range exhibit nonlinear behaviour. In the cases of Ir and Rh field emitters, sustained isothermal oscillations in the form of periodic changes in the emission current from various planes present on the tips were observed. In the case of Ir, a bright wave initiated at the Ir(510) surface and moved to the (100) and surrounding planes. In the case of Rh, a bright wave initiated at the Rh(533) surface moved around the (1 11) plane essentially parallel to the steps around that plane. Subsequently, in both cases, the emission from these bright planes decreased slowly, until the cycle began again. The dynamic behaviour of the NO-H, reactions over a number of selected large single-crystal surfaces of Pt, Rh and Ir, as studied by mass spectrometry and Auger electron spectroscopy, showed a rich variety of non-linear behaviour. The reaction over Pt(100) and various (111)-terraced Rh planes with (100) steps showed sustained isothermal oscillations in product formation when the temperature was held constant on the cooling branch of a heat-cool heating cycle. In both cases, N, and NH, were formed, but for Rh, formation of these products occurred out of phase with each other, whereas for Pt, it occurred in phase. The Ir(100) surface showed a hysteresis in N, production. Models for the observed non-linear behaviour and the differences in behaviour between Pt, Rh and Ir will be discussed.

Stochastic Models of Physicochemical Processes in Catalytic Reactions - Self-Oscillations and Chemical Waves in CO Oxidation Reaction

“…In addition to being of fundamental interest, this reaction is of great environmental significance as a means of removing carbon monoxide from exhaust gases. CO oxidation under far-from-equilibrium conditions can be accompanied by critical phenomena, such as multiple steady states, self-oscillations, traveling waves, and chaos [1,[9][10][11][12][13][14][15][16][17][18]. The successful attempts of searching for new catalytic reactions with this type of dynamic behavior resulted in the situation that presently we know more than fifty different oscillation systems [19] occurring under different experimental conditions on various types of catalysts.…”

“…Various oscillation mechanisms have been discovered and investigated to date. They include surface structure transitions [1,11], the formation of a "subsurface" oxygen layer [12][13][14][15][16][17], and the "explosive" interaction between adsorbed species [18]. A common feature in all these mechanisms is the spontaneous periodical transition of the metal surface from inactive to highly active catalytic state.…”

Heterogeneous Catalysis and High Electric Fields

“…Cobden et al [162] mentioned transient oscillations in FEM, close to the (001) plane, but not on the plane itself. Cobden et al [162] mentioned transient oscillations in FEM, close to the (001) plane, but not on the plane itself.…”

“…Cobden et al [162] mentioned transient oscillations in FEM, close to the (001) plane, but not on the plane itself. [162] and ∼520 K in Ref. Whereas the reactant partial pressures were similar in both FEM and FIM studies, the temperatures were fairly different, i.e.…”

From single crystals to supported nanoparticles in oscillatory behavior of CO+O2 reaction on platinum and palladium surfaces: Experiment and stochastic models

“…Recently, we have started to perform field electron microscopy (FEM) experiments on a sharp tips (∼1000 Å) that are in many cases only about one order of magnitude larger than nanoparticles size in a supported catalyst. Sharp tips have been used to carry out in situ investigations of real dynamic surface processes where different crystallographic nanoplanes of the tip with a lateral resolution of ∼20 Å are simultaneously exposed to the reacting gas and for which it is possible to study the interaction and the coupling of adjacent nanoplanes [8,9]. Many of the oscillatory reactions seen on Pt-and Pd-tip surfaces are examples of interplay of the different nano-sized plain surfaces [9].…”