Reactive intermediates of the reduction of SO2 on activated carbon

The reduction of SO2 on activated carbon was studied in the range of 600-700degreesC in a differential reactor under steady-state conditions and under chemically controlled kinetics. Initial rates of carbon conversion and gas reagent were calculated from the mass balance of the gaseous products. The kinetics was first-order with respect to carbon and first-order with respect to the partial pressure of SO2. The activation parameters were AHO = 21.5 kcal mol(-1) and DeltaS not equal = -211 cal mol(-1) K-1. The activated carbon was ca. 10(5) times more reactive than graphite, and determined by the enthalpy of activation. The main reaction products were CO2 and sulfur. CO and COS were produced from consecutive reactions of the primary products. During the pre-steady state, the sulfur content of the carbon increased to a plateau where the reaction reached the steady state condition. This sulfur was shown to be chemically bound to the carbon matrix and represents the stable reactive intermediates of the reduction Of SO2. The XPS spectrum of the residual carbon C(S) showed two forms of sulfur bound to carbon: non-oxidized sulfur (sulfide and/or disulfide) and oxidized sulfur (sulfone, sulfoxide, sulfenate, sulfinate). The sulfur intermediates C(S) reacted with SO2 at the same rate as pure activated carbon and with CO2 to produce SO2 by the reverse reaction. The reaction of C(S) with CO produced COS. Copyright (C) 2003 John Wiley Sons, Ltd.