Basic functional groups were important to the catalytic oxidization of H2S by carbon-based catalysts. However, until recently, little work was focused on the specific effect of each basic group on desulfurization. To this aim, for the first time, a sewage sludge-derived catalyst was synthesized, modified to increase the number of basic groups, and applied in catalytic oxidization of H2S. As a result, the modified catalyst with enhanced basic groups (3.728 mmol/g) removed 2.08 mmol/g of H2S at 180 degrees C for 180 min. By comparison, the unmodified catalyst had 2.162 mmol/g of basic groups. Under the same reaction conditions, it removed only 1.68 mmol/g of H2S. TPD analysis showed that benzoquinone basic group played a critical role in desulfurization. In fact, it catalyzed H2S rather than a mere reaction, which was the mechanism of carbonyl basic groups. The amount of benzoquinone groups was increased from 0.224 to 0.930 mmol/g after alkali modification, resulting the enhanced desulfurization effect. Moreover, the carbonaceous material and metal components also accounted for desulfurization. The main result of this work helps to understand the nature of H2S catalytic oxidization by carbon-based catalyst.