\bibitem{Sahimi90}      M.~Sahimi, G.R.~Gavalas, T.T.~Tsotsis, \hskip 2mm
                        {\it Statistical and Continuum Models of Fluid-Solid Reactions in Porous Media},
                        Chem. Engng. Sci. {\bf 45} (6), 1443-1502, 1990.