Continuous and controllable synthesis of MnO₂ adsorbents for H₂S removal at low temperature

H₂S is an extremely noxious impurity generated from nature and chemical industrial processes. High performing H₂S adsorbents are required for chemical industry and environmental engineering. Herein, α-, γ-, and δ-MnO₂ adsorbents with high sulfur capacity were synthesized through a continuous-flow approach with a microreactor system, achieving much higher efficiency than hydrothermal methods. The relationship between crystal structure and synthesis conditions such as residence time, reaction temperature, concentration of K⁺ in solution and reactant ratio is discussed. According to the H₂S breakthrough tests at 150 °C, continuously prepared α-, γ-, and δ-MnO₂ exhibited sulfur capacities of 669.5, 193.8 and 607.6 mg S/g sorbent, respectively, which was at a high level among the reported adsorbents. Such enhanced performance is related to the large surface area and mesopore volume, high reducibility, and a large number of oxygen species with high reactivity and mobility. Manganese sulfide and elemental sulfur were formed after desulfurization, which indicated the reaction consisted of two steps: redox and sulfidation of the sorbents. This study provides an innovative design strategy for the construction of nanomaterials with high H₂S adsorption performances.