The results of exact solution of the nonlinear equations set for the case of first order reaction rate with respect to gaseous admixture and for a particular model of the gas-porous solid reaction in flow are presented. Along with the expressions derived from an improved shrinking core model they are used to study the effect of sulphur removal catalyst granules properties on the commercial-scale bed macrokinetics. It is shown that sulphur removal catalyst bed dynamics are mainly determined by the size of granules and the value of effective diffusivity of hydrogen sulphide in sulphurized granule shell. The results allow a reasonable choice of sulphur removal catalyst to be made and to estimate bed service time under various operating conditions. They will be also useful when analysing other similar processes. (c) 2004 Elsevier B.V. All rights reserved.