Display omitted •HP-DSC to evaluate catalyst behavior and performance under hydrothermal conditions.•Mixtures of cellulose and heterogeneous catalysts tested at 250 °C.•Siralox and FeCl3 showed the highest catalytic activities.•Investigation of synergies among acid and basic sites. Catalysts are usually employed in hydrothermal processes for different purposes, such as enhancing quality and yield of produced biofuels. However, assessing catalyst performances can be time consuming and expensive. For this reason, in this work, a technique based on high pressure differential scanning calorimetry was applied to study heterogeneous catalyst behavior under hydrothermal conditions at the micro-scale. Heterogeneous catalysts were mixed with distilled water and cellulose, selected as substrate, and tested at 250 °C. The heat release profiles obtained were deconvoluted in three Gaussian peaks, each associated with a set of reactions. Siralox and iron chloride showed the highest catalytic activities impacting the development and the enthalpy of the reactions. Selected samples were further characterized to investigate synergies among acid and basic sites and emphasize the importance of the spatial distribution of the components inside the catalysts. This study highlights the crucial role of advanced techniques in optimizing catalyst performance for more efficient biofuel production.