分子筛脱硅对其结构与吸附氨氮性能的影响

为提高分子筛吸附氨氮的能力，采用碱蚀法对4种不同硅铝比ZSM5型分子筛进行脱硅处理，对比了脱硅前后吸附氨氮性能的差异；结合X射线衍射、扫描电镜等分析手段观察了其孔隙与晶体结构、表面形貌的变化，同时借助X射线荧光光谱、傅里叶红外光谱等表征手段分析了其内部元素组成与骨架基团的变化；考察了分子筛脱硅处理对改善其吸附氨氮性能的影响机制.结果表明，分子筛经脱硅后氨氮吸附量大幅提高，硅铝比越大吸附氨氮性能改善越显著，其中，硅铝比最小的ZSM5-27型分子筛脱硅后的氨氮平衡吸附量由5.81mg/g上升至10.44mg/g，上升幅度亦达79.7%；碱蚀脱硅处理有效降低了ZSM5型分子筛的硅铝比，分子筛硅铝比越大降低越显著.分子筛脱硅后，其介孔比表面积与比孔容增加、孔径分布变得宽泛；晶体结构仍保持完整、晶粒形态变得更加清晰规整；离子交换容量增加、硅/铝氧四面体结构单元作用增强.碱蚀法对ZSM5型分子筛具有骨架脱硅补铝、疏通孔道等多重作用，脱硅后分子筛活性位点增加、氨离子扩散阻力下降，吸附性能得到改善.

Effect of molecular sieve desilication on its structure and adsorption of ammonia nitrogen

In this study, desilication treatment using alkali etching was applied to ZSM5 molecular sieves with four different silicon-aluminum ratios to investigate the difference of their ammonia nitrogen adsorption. Their changes in crystal structure, surface morphology, internal element composition and connection mode after desilication were examined with scanning electron microscopy, X-ray diffraction analysis, X-ray fluorescence spectroscopy, and Fourier transform infrared spectroscopy. The mechanism of the desilication effect on improving the adsorption of ammonia nitrogen by molecular sieves was then analyzed. The results indicated that after desilication treatment, the mesoporous specific surface area and specific pore volume of the molecular increased, and the pore size distribution was broaded, the structure of the molecular sieve remained intact and the grain morphology became clear and regular, associated with enhanced ion exchange capacity and Si/AlO₄ structure. The molecular sieve desilication by alkali etching had multiple effects such as desilication of skeleton, the aluminum supplementation of skeleton, and the tunnel dredging. These led to decreased silicon-aluminum ratio and increased number of active sites in the molecular sieve, meanwhile, decreased the diffusion resistance of ammonia ion, which then resulted in improved ammonia nitrogen adsorption performance. After desilication, the ammonia nitrogen adsorption by molecular sieve was greatly enhanced, while more significant improvement was observed for molecular sieve with originally higher silicon-aluminum ratio. while its equilibrium adsorption capacity of ammonia and nitrogen increased from 5.81mg/g to 10.44mg/g, with an increase of 79.7% being reached. In summary, the desilication treatment could provide an effective technical alternative to use molecular sieve for the deep denitrification of wastewater treatment plant effluent.