The kinetics of the oxidation of methanol to formaldehyde in the presence of Pb0.88 Bi0.06 La0.02 Mo/SiO2 catalyst was described by the Redox mechanism. When the particles of catalyst were increased to 3mm in diameter

the effect of intraparticle diffusion depended greatly on the oxidation rate of methanol to formaldehyde. The effectivenese factor of the catalyst was determined to be 0.28-0.12 and was interpreted with the kinetics of the Redox mechanism. The kinetic equation of the Redox mechanism in the presence of the intraparticle diffusion of methanol molecules was interpreted by the theory of diffusion and was proved experimentally. The apparent activation for the oxidation of methanol in the presence of intraparticle diffusion was determined by kinetic experiments and interpreted by a theoretical equation. The effective coefficients of intraparticle diffusion of methanol and the tortuosity factor of the catalyst were determined by kinetic experiments conducted with reaction conditions investigated.