The significance of defect chemistry for the rate of gas–solid reactions: three examples

Abstract

Three examples are revisited in which the reaction rate could be reliably correlated with point defect chemistry highlighting the role of point defects as acid-base active centers. In the case of dehydrohalogenation of tertiary butyl chloride, AgCl becomes increasingly active as heterogeneous catalyst, if AgCl is homogeneously or heterogeneously doped. By such a procedure the silver vacancy concentration is adequately increased. The oxygen incorporation into SrTiO 3 offers an example in which the surface mechanism in terms of adsorbed species, oxygen vacancies and electronic centers has been elucidated. Appropriate surface coatings give rise to significant catalytic effects. Increasing iron (acceptor) doping not only changes the point defect chemistry but also the nature of the rate determining step. Lastly, the electrocatalytic function of Sr-doped LaMnO 3 is considered as regards oxygen reduction reaction and O 2) incorporation into Y-doped ZrO 2 in the context of solid oxide fuel cells. Again the defect chemistry is of prime importance for the reaction rate.

Cerium reduction at the interface between ceria and yttria-stabilised zirconia and implications for interfacial oxygen non-stoichiometry

“…26 Moreover, the varied local defect chemistry is relevant also for redox and acid-base effects in catalysis. 27 …”

Kinetics and Mechanisms of Oxygen Surface Exchange on La[sub 0.6]Sr[sub 0.4]FeO[sub 3−δ] Thin Films

“…23 The series of elementary steps that can vary from material to material are not yet well understood, and a significant number of mechanisms have been suggested by different authors. 14,[19][20][21][24][25][26][27] In the following, possible reasonable one-, two-, and three-step reaction mechanisms for the incorporation of oxygen in LSF are discussed.One-step mechanism.-In the simplest possible model, one can assume that the surface reaction, Eq. 17 is itself an elementary reaction corresponding to direct incorporation of oxygen into vacancies with the simultaneous oxidation of B ions ͑formation of electron holes on the iron site͒.…”

Doping Strategies in Inorganic and Organic Materials

“…Moreover -and to lesser degree common knowledge -is the following: as these charge carriers are usually also the decisive centers for reaction kinetics, doping is essential for varying reaction rates and in particular catalytic processes. [35] …”