A carbon support was treated with HNO3 to create surface functional groups (e.g. -COOH, -OH), which were then characterized by TGA, TPD, CNS elemental analysis, and Boehm titration. HNO3 modified the carbon surface properties by adding a high amount of carboxylic groups, improved the thermal stability of the carbon support, and reduced ca. 50% of the ash. The thermal pre-treatment (723 K under He) following the HNO3 pre-treatment successfully removed the carboxylic groups. 4% Ru/C catalysts were synthesized using the surface-modified carbon supports and characterized by H-2-TPR, CO pulse chemisorption, N-2-physisorption and HAADF-STEM. The Ru dispersion was increased in the presence of the carboxylic groups. Catalytic supercritical water gasification (CSCWG) of 10 wt.% isopropanol over the 4% Ru/C catalysts was carried out at 723 K and 30 MPa for 50 hours to assess the performance of the catalysts. It was found that the Ru/C catalyst prepared involving a pre-treatment with HNO3 did not exhibit a higher catalytic activity than the catalyst whose carbon support was not pre-treated with HNO3. Hence, the activity and the selectivity during CSCWG were not influenced by the pre-treatment of the catalyst support with HNO3.