The aim of this work was to study the how various heterogeneous catalysts perform upon lignosulfonate decomposition reactions. The main target of the study was to obtain extractable phenolic compounds as potential renewable chemicals for the production of fuel components and chemicals. The nature of the heterogeneous catalyst was found to have a great impact on the obtained product yields and the composition of the product mixture. Initially, a nickel–tungsten on alumina (NiW/Al2O3) reference catalyst was applied upon screening the influence of catalyst particle size and various reaction parameters. Significantly increasing product yields with decreasing catalyst particle size indicated that the lignosulfonate transformation takes place on the external catalyst surface due to large macromolecular structure of the feedstock. The contact time (space time velocity) and catalyst particle size were the most important factors influencing the selectivity profiles towards various products as well as the yields observed. The highest conversion to phenolics was obtained over in-house-prepared NiO/Al2O3 and NiMo/Al2O3 catalysts with various NiO and MoO3 loadings.