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 gsulfur kgcat.–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.