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

在Pt/TiO_2上添加M_xO_y（M= Li，Na，K，Cs，Sr，Bo，La）等碱性氧化物，制备了耐硫NO吸收剂。碱性氧化物添加剂在无SO_2和含SO_2气氛下均能有效提高Pt/TiO_2的NO吸附容量。在SO2气氛下，Pt-Li_2 O/TiO_2对NO的吸收没有影响，但对NO的吸收有明显的影响。在含SO_2气氛中吸附反应6 h后，H_2S在H_2中的TPD谱表明，Pt-Li_2 O/TiO_2上储存的SO_2在最低温度释放。Pt-Li_2 O/TiO_2上形成的Li_2TiO_3除了使锂的碱性较弱外，还使Pt-Li_2 O/TiO_2上的硫酸盐不稳定，导致含硫物种在最低温度下脱附。原位FT-IR分析表明，Pt-Li_2 O/TiO_2催化剂上硫酸盐的生成缓慢，且硫酸盐的分解需要高温，这也是Pt-Li_2 O/TiO_2具有优异的耐SO_2性能的原因。通过一系列实验确定了模型中的模型参数。实验结果表明：（1）随着W/F（催化剂重量/气体流量）的增加，NO和NO_2浓度的增加，NO_x的吸收量增加;（2）由于NO氧化为NO_2的限制，NO_x的吸收量增加;（3）NO_x的吸收量与W/F成正比。模型成功地模拟了NO和NO_2的吸附曲线，并对各种操作条件下的NO_x吸收进行了较好的预测。反应器轴向距离x处的NOx浓度（Vx，t）与反应器表面覆盖度θ（t）和NOx入口浓度V（x，t）的关系式<in>为：Vx，t = exp（-1.75 θ）<in>V1-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.