The biomass gasification is gaining attention of scientists and researchers worldwide to be an innovative and efficient method for producing clean energy. While consuming 'junk' organic, such as sugarcane bagasse or rice husk, the gas produced in the process is used for heat or electricity generation (or gas turbine engines), synthesis of liquid fuels, hydrogen production, chemical synthesis and manufacturing of fuel cells. However, a key challenge in the development and improvement of the biomass gasification process is cleaning the gas produced in order to ensure its quality and applicability. Among the main impurities found in the gasification gas, the tar is one of the worst, the presence of this kind of impurity can prejudice the performance of the process and also damage equipment. There are several methods for tar removal. Catalytic process is the most studied and the one that shows the best results. This paper presents an isothermal mathematical model that characterizes production and consumption of tar, modelled by toluene, reforming reaction using nickel- based catalyst. A computer code in FORTRAN 90 language was developed to perform the simulation, which described the concentrations of the main components (C7H8, O2, H2 and CO), as well as the reaction yield and influence of temperature on generation of products. Then the optimum conditions for carrying out the process were determined.