N‑Doped 3D Mesoporous Carbon/Carbon Nanotubes Monolithic Catalyst for H₂S Selective Oxidation

The post-Claus selective catalytic oxidation of H₂S reaction in a continuous mode is demonstrated on N-doped 3D mesoporous carbon/carbon nanotube (N-C/CNT) monoliths at a reaction temperature higher than the dew point (>180 °C) of elemental sulfur. The N-C/CNT monoliths display a hierarchical open porous framework (an interconnected macroporous–mesoporous network) with abundant active nitrogen species at the surface and controlled macroscopic size and shape which represent prerequisites for operating in gas-phase reactions. Physical parameters such as pore size, structural defects, and surface chemical properties are investigated, and the structure–performance relationship for the selective oxidation of H₂S is discussed. The optimized monolith catalyst (N-C/CNT₈₀₀⁴⁵⁰) shows an outstanding desulfurization activity in terms of the sulfur formation rate (449 g_sulfur kg_cat.^–1 h^–1), stability (for more than 120 h on-stream time), and selectivity (81.6% sulfur selectivity), which outperforms the current state-of-the-art Fe₂O₃/SiC catalyst and other reported carbon-based catalyst. Moreover, a superior desulfurization activity could be achieved under either water steam (30 vol %) or dry conditions. Our results show that the excellent catalytic desulfurization performance of our monolithic carbon catalyst could be attributed to a combination of the hierarchical interconnected porous framework and the high active nitrogen species density at the exposed carbon surface.