ChemInform Abstract: Surface‐Generated Gas‐Phase Radicals: Formation, Detection, and Role in Catalysis

Abstract

Publisher Summary This chapter discusses the formation, detection, and role in catalysis of surface-generated gas-phase radicals. The presence of surface-generated gas-phase radicals is well established for many catalytic decomposition and oxidation reactions. The radicals generally are observed at reaction temperatures in excess of 400° C, and in some cases temperatures of approximately 800°C are required. The surface-generated radicals may be significant as (1) initiators of chain reactions, (2) intermediates in gas-phase coupling reactions, (3) a means for the transport of intermediates from one surface to another, (4) experimental evidence for a radical mechanism, and ( 5 ) a means of determining the rate limiting step of a catalytic cycle. Even qualitative results are useful in several of these applications; however, more quantitative data are needed to establish whether gas-phase radical coupling is indeed a primary pathway for product formation. The practical utilization of this source of gas-phase radicals, in many cases, require the design of reactors and catalyst-bed configurations so as to maximize the desired reactions. It may, for example, be important to operate at short contact times, with the catalyst at much higher temperatures than the gas phase, or, in order to achieve high selectivity for the partial oxidation of alkanes, it may be necessary to operate in a pulse mode so that the alkyl radicals do not react with gas-phase molecular oxygen.