Anwendung der Halbleiter‐Theorie auf Probleme der heterogenen Katalyse

Abstract

Es wird d e r Stand d e r heutigen Katalyse-Fonchung aufgezeigt und die gegenseitige Beziehung zu der Halbleiter-Theorie herausgestellt. Nach Behandlung d e r Grundlagen der Randschicht-Theorie der Chemisorption wird vor allem am Beispiel des N,O-Zerfalls und d e r CO-Oxydation d e r Mechanismus des wechselseitigen Elektronenaustausches zwischen Katalysator und reagierendem Gas diskutiert. Zahlreiche weitere Beispiele zeigen, daB durch eine enge Verknupfung d e r Halbleiter-Forschung rnit der Katalyse-Forschung diese sich immer mehr von d e r reinen Empirie entfernt und syotematisch betrieben werden kann.Trotz der gro6en technischen Erfolge der heterogenen Katalyse ist ihr M e c h a n i s m u s infolge der komplizierten Vorglnge an der Phasengrenzfllche Katalysator/gasformige Reaktionspartner noch weitgehend ungeklart. Ohne auf die Wirkung der Metallkatalysatoren einzugehen, sei hier die derzeitige Situation nur bei den durch o x y d i s c h e Ka t a l y sa t o r e n katalysierten Gasreaktionen diskutiert. I ) Siehe K. Houffe Fehlordnungserschelnungen und Leltungsvorgange In ionen-h d elektronenieitenden festen Stoffen, in Ergebn. exakt. Naturwiss. 25, 193 [1951]. C ? m . 1 67. J d r g . 1955 Nr. 7 Angezc.

In Situ and Operando Spectroscopy for Assessing Mechanisms of Gas Sensing

“…[46] However, most of the studies were performed under conditions far from the real working conditions of sensors (for a summary of numerous studies on semiconducting metal oxides, see references [41,50,112]). Besides spectroscopic and catalytic (kinetic) investigations (SnO 2 : kinetic studies of CO oxidation, [132] IR spectroscopic studies of water, CO 2 , and CO adsorption, [133] (summarized in reference [134]), EPR investigations of oxygen adsorption, [135] (reviewed in references [136,137])), the improvements were concentrated on devising systems and in situ cells for combined (i.e., performed under the same conditions on "identical" samples) and simultaneous electrical, catalytic, and spectral investigations (Table 2).…”

“…As already mentioned above, the current models of gas sensing originate formally from the electronic theory of catalysis [42][43][44] and, in particular, from the boundary layer theory of chemisorption. [45,46] Electron exchange between catalysts and gaseous initial, intermediate, and end species is frequently decisive in heterogeneous catalysis, so new methods for the determination of Fermi potentials and space-charge phenomena in catalysts as well as the measurement of work functions and charge transfer levels will offer further insight into the mechanisms of catalysis. [60] Electrical techniques have been used not only as another characterization method for the catalyst, [225,226] but also for studying the mechanism of catalytic reactions in situ.…”

Interplay between O2 and SnO2: Oxygen Ionosorption and Spectroscopic Evidence for Adsorbed Oxygen

“…This model dates from about the 1950s, and originates formally from the "boundary layer theory of chemisorption" developed by Hauffe. [15,16] As early as 1955, Hauffe wrote: "due to the electron affinity of oxygen, the electron can be transferred to the chemisorbed oxygen and, consequently, there will be no chemisorbed oxygen atoms, but ions, in the surface". [16] This statement represents the quintessence of the "ionosorption model" and in the following years, Hauffe and Morrison extended the model to treat gas adsorption on semiconductors.…”

“…[16] This statement represents the quintessence of the "ionosorption model" and in the following years, Hauffe and Morrison extended the model to treat gas adsorption on semiconductors. Their early work [15][16][17] was followed by a monograph (1966, Hauffe), [18] a student textbook (1974, Hauffe and Morrison), [19] and in 1977 it was extended to a general theory of gas ionosorption on semiconductors (Morrison). [20] Tin dioxide is the most commonly used material in commercial gas sensors based on semiconducting metal oxides.…”

The Catalytic Activity of Zinc Oxides from Single Source Precursors with Additives for the C–H Acitivation of Lower Alkanes

“…This explains that no distinct difference for commercial ZnO and ZnO from single source precursors for the OCM, ODE and ODP can be observed. For lithium doped zinc oxides the sintering and therefore the deactivation should occur at even lower temperatures [15,16,17]. But below 400°C no catalyst showed any activity for the activation of a C-H bond.…”