LaCoO_3模型催化剂SO_2中毒机理的研究

Studies of SO_2 Poisoning Mechanism for Perovskite LaCoO_3 Model Catalyst

运用 AES,XPS,XRD和 TEM等手段研究了 La Co O3模型催化剂 SO2 中毒过程表面化学状态、晶相结构及表面形貌的变化状况 ,初步推断了 La Co O3钙钛矿型复合金属氧化物催化剂的 SO2 中毒机理 .在 SO2强化中毒过程中 ,SO2 与催化剂的活性组分 La Co O3反应生成硫酸镧和氧化亚钴 ,而在催化剂膜层内部则生成硫酸镧、亚硫酸镧及氧化亚钴 . SO2 对活性组分层的侵入及硫与 La Co O3活性组分的反应破坏了催化剂的钙钛矿结构 ,使得催化剂彻底中毒 .当中毒温度较低及中毒时间较短时 ,硫在膜层中呈峰形分布 ,其浓度随中毒温度及时间的增加而增加 .随中毒温度的升高及中毒时间的增长 ,由于亚硫酸盐的分解作用 ,S在活性层中的浓度反而降低 ,中毒深度则继续增加 .

In this work, the SO 2 poisoning mechanism of model catalyst and powder catalyst of LaCoO 3 has been investigated. The changes of the structure and the chemical states of the elements have been characterized using XRD, TEM, AES and XPS. The results showed that the perovskite structure of LaCoO 3 was destroyed by the invading of S. Some La 2(SO 4) 3 and CoO species were formed on the surface of the poisoned sample, while La 2(SO 4) 3, La 2(SO 3) 3 and CoO species were the main production in the interior of the LaCoO 3 layer, which led to the loss of the catalysis activity. The content of S in the layer increased with the increase of temperature and time. After the sample was poisoned at a relatively high temperature or for a fairly long time, the distribution of S in the LaCoO 3 layer became homogeneous with the depth and the concentration being decreased, suggesting that a dynamic equilibrium was achieved between the poisoning reaction and the decomposition of the sulphurous salts.