Refuse-derived fuel (RDF) produced from the processing of municipal solid waste is a promising raw material for waste-to-energy processes such as gasification. Several catalysts were used to improve the performance of RDF in this process. The study aims to understand the thermal decomposition of pellets made from a mixture of RDF and biomass in the presence of waste-based catalysts by simulating a CO2 gasification process in a thermogravimetric analyzer (TGA) instrument. Marble and eggshells, which are low-cost bio-based sources of calcium carbonate, were investigated as catalysts. Dolomite was used as a reference for comparison. In general, all samples showed two significant decomposition phases and an attenuated decomposition phase (pyrolysis), between 250 and 700 ºC, corresponding to the degradation of hemicellulose, cellulose, lignin, and mixed plastics, before the onset of gasification. It was concluded that dolomite may degrade more during the pyrolysis compared to the marble and eggshells, as it was not calcined, hindering the gasification reaction, and subsequently resulting in a lower char conversion. The catalysts based on marble and eggshells favored the reactivity of the RDF: B pellets during gasification, resulting in faster decomposition of the char. In general, the waste-based catalysts performed well, suggesting they have potential for application in waste gasification.