LaMnAl11O19催化剂上生物质气化气燃烧中NH3-NOx的转化特性

采用共沉淀法制备了LaMnAl₁₁O₁₉六铝酸盐催化剂，采用XRD、BET和XPS对样品结构进行了表征，并通过模拟生物质气化气的燃烧实验和NH₃单独氧化实验，分别考察了催化燃烧和均相燃烧过程中NH₃的转化特性。利用原位漫反射红外光谱（in-situ DRIFT）法在线研究了NH₃在催化剂表面的吸附和氧化信息。结果表明，焙烧后催化剂形成磁铅石（MP）结构的六铝酸盐晶体，且具有较大的比表面积，Mn以+2、+3价形式存在晶体中。均相燃烧下模拟气中的NH₃在500℃开始反应，随之就有NO生成。催化燃烧工况下NH₃氧化曲线和模拟气中NH₃的转化曲线相差不大，NH₃的起燃温度为310℃，反应后随之就有NO生成，NO在350℃~800℃保持一个较高的浓度。NO₂的生成温度较高，并仅在较窄的温度区间内出现，在整个燃烧过程中仅检测到几个10^-6的N₂O,反应过程中有40%以上的NH₃转化成NO。DRIFT结果表明，催化剂作用下NH₃的转化遵循 -NH反应机理，即催化剂表面吸附的NH₃分解产生 -NH，-NH与氧原子（O）反应生成HNO，再进一步反应生成N₂或N₂O，或是 -NH直接与氧分子（O₂）反应生成NO。

Conversion of NH_3-NO_x in gasified biomass over LaMnAl_(11)O_(19) catalyst

LaMnAl₁₁O₁₉ catalysts were prepared by co-precipitation method and characterized with XRD, BET and XPS. The conversion of NH₃ at the conditions of catalytic combustion and homogeneous combustion were studied by combustion of simulated biomass gasification gas and NH₃ oxidation, respectively. Moreover, the NH₃ adsorption and oxidation on the surfaces of the catalyst samples were examined by in-situ DRIFT experiments. It was found that calcination of the percursors at 1200℃ led to the formation of a final monophasic materials with MP structure and high surface area, while the Mn ions were either divalent or trivalent. Under homogeneous combustion condition, NH₃ at simulated biomass gasification gas started to react at 500℃, then NO was formed. Under catalytic combustion condition, the curves of NH₃ oxidation with and without addition of simulated gasification gas showed no obvious differences. NH₃ started to react at 310℃, and NO exhibited higher concentration in the temperature range of 350℃~800℃. However, NO₂ was generated at higher temperature within a narrow temperature range. The concentration of N₂O during the reaction was less than 10 ×10^-6. More than 40% of the NH₃ converted to NO during the experiments. The results of in-situ DRIFT indicated that the reaction of ammonia conversion followed the imide (-NH) mechanism, that is, the ammonia adsorbed on the catalyst surface was decomposed to -NH firstly, then the -NH reacted with atomic oxygen (O) to further form nitroxyl (HNO) and N₂ or nitrous oxide (N₂O), or -NH reacted with molecular O₂ to produce nitric oxide (NO) directly.