SiOCN ceramic aerogels with lightweight, high surface areas, and macro-meso pores have been synthesized by a facile method combining freeze-drying technique and polymer-derived ceramic route. The wet gels are synthesized via the hydrosilylation reaction between polysilazane and divinylbenzene with cyclohexane as solvent. The solvent is then removed by a freeze-drying process to form pre-ceramic aerogels. The SiOCN ceramic aerogels are finally obtained by pyrolyzing the pre-ceramic aerogels at 1000°C in ultrahigh purity N 2 . The thermogravimetric and mass spectrometry system (TG/DSC-MS) is used to investigate the polymer-to-ceramic conversion process during pyrolysis. The phase composition, structure, and morphology of the SiOCN ceramic aerogels are investigated by XRD, FT-IR, XPS, and SEM. The results show that SiOCN ceramic aerogels are composed of amorphous matrix phase and "free carbon" phase. The SiOCN aerogels possess three-dimensional (3D) network porous structure with low density (0.19 g/cm 3 ), high specific surface area (134 m 2 /g), large pore volume (0.49 cm 3 /g), and hierarchical pore structures of both macro and meso pores. The formation mechanism and evolution process of SiOCN ceramic aerogels are discussed. K E Y W O R D S3D porous structure, freeze-drying, polymer-derived ceramic, SiOCN aerogel

Membrane gas absorption (MGA) is of great interest for SO 2 capture from ship exhaust, as it has high separation efficiency and, more importantly, is comprised of a separator that can be flexibly installed and operated on ships. Here, we report a class of hydrophobic tubular asymmetric ceramic membranes for SO 2 absorption. To find the membranes with reasonable microstructure and geometry, we used a numerical 2D model to simulate SO 2 absorption process and verified the model by comparing its results with experimental data. Simulations showed that most of the SO 2 mass transfer resistance existed in membrane phase, indicating that the optimization of membrane parameters, rather than operational conditions, should be the primary consideration to enhance the overall SO 2 mass transfer performance. Furthermore, simulations indicated that the SO 2 separation performance depended negligibly on membrane pore sizes, but can be significantly improved by optimizing the thickness and inner diameter of membrane tubes. Results and Discussion Characterization of ceramic membrane propertiesFollowing our previous work, 27 the asymmetric membranes that are listed in Table 1 were modified with HTDMS. Among them, M2, with the top layer's pore size of 0.2 μm, was