N-doped porous carbocatalyst engineering via modulating the crystalline size of ZIF-8 for continuous H2S selective oxidation

Nitrogen-doped porous carbon (NPC) has been considered as an efficient metal-free catalyst for selective oxidation of H2S, but the key factors affecting the reaction performance most are hard to identify due to that the carbocatalyst is usually derived from the complex and uncontrollable synthesis methodology. Herein, we report on the synthesis of NPC derived from the carbonization of high-quality ZIF-8 nanocrystals as the robust carbocatalysts for H2S selective oxidation. By tuning MEIM (2-Methylimidazole)/Zn (II) molar ratio, the precise size of ZIF-8 nanocrystals can be easily controlled and resulted in the NPC particle size range from 0.12 to 1.06 μm. Benefit from the rapid diffusion pathway and full exposure of active N sites, the obtained NPC-8 with particle size of ∼ 0.31 μm exhibits superior catalytic performance on H2S selective oxidation, achieving an excellent catalytic conversion rate of 99% as well as stability (> 100 h) at 190 °C. Combined with characterization results and reaction parameter experiments, it could be induced that the catalytic activity of H2S selective oxidation could be mainly affected by the size of ZIF nanocrystals, beside that, the developed micro-/mesopores framework and abundant N sites also contribute to improve the intrinsic activity of NPC.