Continuous and controllable synthesis of MnO adsorbents for HS removal at low temperature.

HS is an extremely noxious impurity generated from nature and chemical industrial processes. High performing HS adsorbents are required for chemical industry and environmental engineering. Herein, α-, γ-, and δ-MnO 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 HS breakthrough tests at 150 °C, continuously prepared α-, γ-, and δ-MnO 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 HS adsorption performances.