Basic Sorption-Desorption Characteristics of NOx and SOx by Mixed Oxide Sorbents

通过添加M_xO_y （M= Li, Na， K, Cs, Sr, Bo, La）等碱性氧化物，制备了Pt/TiO_2型耐硫NO吸附剂。在无so_2和含so_2气氛下，碱性氧化物添加剂均能有效提高Pt/TiO_2对NO的吸附能力。在so_2气氛下，Pt-Li_2O/TiO_2对6 h的NO吸收量没有影响，而对其他吸收量则有明显的影响。在含SO_2气氛中吸附6h后，H_2中H_2S的TPD光谱显示，储存在Pt-Li_2O/TiO_2上的SO_2在最低温度下被释放。在Pt-Li_2O/TiO_2上形成的Li_2TiO_3会导致Pt-Li_2O/TiO_2上的硫酸盐不稳定，导致含硫物质在最低温度下脱附。原位傅里叶变换红外光谱表明，Pt-Li_2O/TiO_2上形成块状硫酸盐需要高温才能分解，这也是Pt-Li_2O/TiO_2耐so_2性能优异的原因。采用连续搅拌槽式反应器模型模拟了NO和NO_2的吸附特性。模型中包含的模型参数是通过一系列实验确定的。实验结果表明：1)增加催化剂重量/气体流量和NO、NO_2浓度可以提高NO_x的吸收率；2)添加NO_2可以提高NO_x的吸收率，因为NO氧化为NO_2受到限制；3)NO_2吸附过程中NO_x的吸收率与W/F成正比。该模型成功地模拟了NO和NO_2的吸附曲线，并很好地预测了不同工况下NO_x的吸收量。反应器内轴向距离x位置的NO_x浓度和运行时间t表示为V_x， t表示为NO_x入口浓度V_<in>和表面覆盖率θ(t)的函数，V_<x, t>= exp(- 1.75θ)V_<in>(1-θ)-0.0242 exp(2.00θ)θ。

Sulfur-tolerant NO sorbents based on Pt/TiO_2 were developed by adding base oxide additives such as M_xO_y (M= Li, Na, K, Cs, Sr, Bo, La). The base oxide additives were effective in improving the NO sorption capacity of Pt/TiO_2 under both SO_2-free and SO_2-containing atmosphere. Under SO_2-containing atmosphere, the NO uptake during sorption reaction for 6 h was not affected over Pt-Li_2O/TiO_2, whereas it was significantly deteriorated over the other sorbents. TPD spectra of H_2S in H_2 after sorption reaction of 6h in SO_2-containing atmosphere showed SO_2 stored on Pt-Li_2O/TiO_2 was released at the lowest temperature. In addition to weak basicity of lithium compared to other additives, Li_2TiO_3 formed over Pt-Li_2O/TiO_2 could lead to instability of the sulfates on Pt-Li_2O/TiO_2, giving rise to desorption of sulfur-containing species at the lowest temperature. In situ FT-IR indicated formation of bulk-like sulfate that needs high temperature to decompose was slow over Pt-Li_2O/TiO_2, which also contributed to the excellent SO_2-tolerance of Pt-Li_2O/TiO_2.NO and NO_2 sorption characteristics were simulated using continuously-stirred tank reactor model. Model parameters included in the model were determined by series of experiments. In these experiments, the following findings were obtained : 1) NO_x uptake was raised by increasing W/F (catalyst weight/gas flow rate) and the concentration of NO and NO_2, 2) NO_x uptake was increased upon feeding NO_2 due to limitation of oxidation of NO to NO_2, 3) NO_x uptake was proportional to W/F during NO_2 sorption reaction. NO and NO_2 sorption curves were successfully simulated by the model, and NO_x uptake was well predicted for various operating conditions. The NO_x concentration at position x in the axial distance in the reactor and operation time t, represented as V_x, t, was expressed as a function of NO_x inlet concentration V_<in> and surface coverage θ(t), V_<x, t>= exp(- 1.75θ)V_<in>(1-θ)-0.0242 exp(2.00θ)θ.