A selective catalytic reduction (SCR) monolithic reactor based on Ti-V-W-Sepiolile catalyst for removal of nitrogen oxides from Power Plant was simulated by using an approaching model which took into account interfacial and intraphase gradients. Different correlations for mass transfer between the solid and the fluid phase were compared, the best obtained results were the corresponding results for the experimentally determined correlations of Ullah (U. Ullah, P. Waldram, C.J. Bennet, T. Truer, Monolithic reactors. mass transfer measurements under reacting conditions, Chem. Eng. Sci. 47 (1992) 2413-2418) and Votruba (J. Votruba, J. Sinkule. V. Hlavacek, J. Skrivanek, Heat and mass transfer in honeycomb catalysts I, Chem. Eng. Sci. 30 (1975) 117-123; J. Votruba, O. Mikus, K. Nguen, V. Hlavacek, J. Skrivanek, Hear and mass transfer in honeycomb catalysts II, Chem. Eng. Sci. 30 (1975) 201-206). For the considered reaction, internal behavior seems to be essential. A refined study of the intraparticle behavior, calculating D-e from an experimental tortuosity factor previously obtained, was accomplished. It was shown that the amount of catalyst could be drastically reduced without changing the performance of the monolithic reactor.