Abstract
Adsorption of NO 2 on carbon black has been examined for different NO 2 concentrations (400 or 600 ppm) and temperatures (50 or 100 °C). The influence of chemisorption of oxygen on the carbon surface at 300 °C before exposure to NO 2 has been reported. Temperature programmed desorption (TPD) was performed after NO 2 adsorption to identify the adsorbed species by measuring the amounts of evolved gases NO, NO 2, CO and CO 2. During the exposure of the carbon black to NO 2, both adsorption and reduction of NO 2 to NO has been observed. From the oxygen and nitrogen balance data, it is shown that the NO 2 adsorption step leads to the formation of both oxygen and nitrogen surface complexes such as C(O) and C(ONO 2). Based on the TPD results, a desorption process has been proposed. Chemisorption of oxygen before exposure to NO 2 leads to an increase, during the adsorption step, of both nitrogen adsorbed and NO evolved species. This behaviour has been attributed to already existing oxygen complexes resulting from O 2 chemisorption. In fact, NO 2 adsorbs mainly on preexisting oxygen complexes. A relationship between the additional adsorbed NO 2 during the adsorption step and the excess of CO 2 released during the TPD below 500 °C has been established.
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