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Sorption of S02 on MgO at 25 °C, and thermal decomposition at the sorbed layer in vacuum at temperatures up to 775 °C, were studied using infrared spectra recorded with a Fourier transform spectrometer. S02 was sorbed in at least four forms. The main interaction of S02 with degassed MgO resulted in the formation of monodentate-and bidentate-like surface sulfites which could only be removed by degassing at high temperatures. A reversible chemisorption occurred at high degrees of surface coverage. S02 was then physically adsorbed on top of the more tightly bound species. Heating in vacuum at temperatures below about 300 °C resulted in the removal of a large portion of the bidentate-like species, while at temperatures above 300 °C the monodentate species was desorbed. Temperatures of up to 775 °C were used to remove completely all of the sorbed material. Heating in

rn The sorption of SOz on CaO at 25°C and the thermal decomposition of the sorbed layer in vacuum at temperatures up to 75OoC were studied by use of infrared spectra recorded with a Fourier transform spectrometer. SOz is sorbed in at least three forms. The main interaction of SO2 with degassed CaO is irreversible and leads to the formation of a surface sulfite. A reversible chemisorption occurs at high degrees of surface coverage. SO2 is then physically adsorbed on top of the more tightly bound species. On heating in vacuum, some surface sulfite is converted to surface sulfate at 550OC; at higher temperatures, conversion to sulfate and polymerization occur, a mixture of species being formed. Heating in oxygen converts the mixture to species resembling bulk CaS04. fforts to remove SOZ from power-plant stack gases have E included a variety of processes based on gas-solid interactions, such as catalytic oxidation or the injection of powdered limestone into the stack stream. Being of actual or potential technological importance, suitable gas-solid interactions have been studied. However, much of the work in this area seems oriented to the development of commercial processes, the fundamental aspects of the gas-solid interactions being neglected somewhat. Specifically, judging from the literature, nothing definite appears to be known about the surface species produced in many such reactions. As information about the nature and structure of surface species would be of mechanistic significance and also of potential utility, we have started a program of study with the intent of obtaining such information.The present paper deals with the reaction of SOZ with CaO, studied by means of the infrared spectroscopic techniques which have been so successfully applied to adsorption and heterogeneous catalysis. CaO was of interest because of the reported use of calcium compounds for SOn removal (Arai et al., 1960;Wickert, 1963; Pechkovskii and Mal'tseva, 1964;BASF 1965). Experirnen talCaO powder (Baker and Adamson Co.) was formed into self-supporting sample disks of 3/4-in. diameter by pressing 55-75 mg of powder in a steel die at a pressure of 80-100 tons/in.2 A sample disk was tied with thin platinum wire to a quartz carriage bearing a quartz-enclosed magnet. The carriage and specimen were then placed within the body of a quartz cell, shown schematically in Figure 1. The sample was To whom correspondence should be addressed. positioned within the furnace during heat treatments. A calibration procedure permitted estimation of the temperature at the sample position by means cf an external thermocouple. After installation in the cell, a sample was subjected to one of two degassing procedures by use of conventional high-vacuum equipment capable of 10-6 torr. Some samples were degassed at 80OOC for three hr and cooled to 25OC in vacuum. Others were degassed for two hr at 800°C, heated for one hr at 800°C in 15 torr oxygen, degassed for one hr at 8OO0C, and then cooled in vacuum. Identical results were obtained with the two types of sa...

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