Kai Qi

Coke oven gas (COG) is considered to be one of the most likely raw materials for large-scale H₂ production in the near or medium term, with membrane separation technologies standing out from traditional technologies due to their less energy-intensive structures as well as simple operation and occupation. Based on the "MOF-in/on-COF" pore modification strategy, the COF membrane (named the PBD membrane) and ZIF-67 were used as assembly elements to design advanced molecular sieving membranes for hydrogen separation. The composition and microstructure of membranes before and after ZIF-67 loading as well as ZIF-67-in-PBD membranes under different preparation conditions (metal ion concentration, metal-ligand ratio, and reaction time) were investigated by various characterizations to reveal the synthesis regularity and microstructure regulation. Furthermore, H₂/CH₄ separation performances and separation mechanisms were also analyzed and compared. Finally, a dense, continuous, ultrathin, and self-supporting ZIF-67-in-PBD membrane with a Co²⁺ concentration of 0.02 mol/L, a metal-ligand ratio of 1:4, and a reaction time of 6 h exhibited the largest specific surface area, micropore proportion, and the best H₂/CH₄ separation selectivity (α = 33.48), which was significantly higher than the Robeson upper limit and was in a leading position among reported MOF membranes. The separation mechanism was mainly size screening, and adsorption selectivity also contributed a little.

The characteristics and preparation methods of zeolite-based adsorbents and membranes were reviewed and their applications in gas separation and purification were introduced according to classification. The effects of framework structure, equilibrium cations and pore size of zeolites as well as temperature and pressure of the system on gas adsorption and separation were discussed, and the separation mechanisms were also summarized. The main defects and improved methods of zeolite-based adsorbents and membranes were briefly described, and their future trend for gas separation and purification was finally prospected.

The samples of MnO_x/TiO₂ catalysts supported on cordierite honeycomb ceramics were prepared by a sol-gel-impregnation method, and evaluated for low-temperature (353-473 K) selective catalytic reduction (SCR) of NO_x with NH₃. The influences of pretreatment on cordierite and catalyst dosage were investigated at first and optimized as follows: pickling for cordierite honeycomb ceramics with 1 mol/L HNO₃ for 3 h prior to loading procedure as well as the catalyst dosage of 3-5 wt.%. The activity results indicated that there was an optimum working condition for MnO_x/TiO₂/cordierite catalysts: NH₃/NO molar ratio=1.1, [O₂]=3 vol.%, GHSV=5514 h^-1, the highest activity of nearly 100% NO conversion could be obtained. As a comparison, the performances of commercialized vanadium-based honeycomb catalyst were also employed, which revealed the narrower scope of application of GHSV and the higher active temperature window. In conclusion, it turns out that the prepared MnO_x/TiO₂/cordierite catalysts are more applicable as a low-temperature SCR catalyst for NO_x removal in a more complicated application environment.