The objective of the present work is the evaluation, modeling, and optimization of heterogenic autocatalytic reactions that show the Langmuir-Hinshelwood kinetics with accompanying external diffusion for nonporous catalyst pellets or intraparticle diffusion and external energy transport for porous pellets in a fixed-bed tubular reactor. Both cases studied are closely related to industrial applications. It was proved that there is an opportunity to increase the yield of the process through the controlled change in mass transfer resistance (catalyst pellet size) along the length of the chemical reactor.