Effect of carbon surface functional groups on the synthesis of Ru/C catalysts for supercritical water gasification
Abstract
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 H2-TPR, CO pulse chemisorption, N2-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.