The use of XPS spectra for the study of reaction mechanisms: the atom inventory method

X-ray photoelectron spectroscopy (XPS) allows the analysis of the surface atomic composition of a solid and can be used for mechanistic studies of solid-gas and solid-liquid reactions. The change of atomic composition of a surface after a reaction can be calculated considering hypothetical mechanisms based on the known reactivity of the organic moieties bound to the solid surface. Atom inventory of the elements involved in the reactions was used to quantify the components of the XPS spectrum after the reaction and consequently the change of concentration in at%. The method was used to study the basic hydrolysis and photolysis of the intermediates bound to the carbon matrix after the reduction of SO(2) on activated carbon. Consistent mechanisms were postulated for these reactions. Basic hydrolysis hydrolyzed the sultine intermediate, and the attack of hydroxide ion on the episulfide formed a sulfide anion, eliminating S(2-) in a consecutive step. Laser photolysis of modified activated carbon in t-butanol showed the insertion of the organic moiety in the carbon matrix with expulsion of an SO(2) radical anion that oxidized to SO(4)(2-). Copyright (C) 2008 John Wiley & Sons, Ltd.