摘要
固定SnO2 含量为 60 % ,采用不同沉淀方法和在不同沉淀条件下制备了锡锆固溶体催化剂Sn0 4 5Zr0 55O2 ,考察了沉淀过程对其结构和性能的影响 .控制尿素浓度为总金属离子 (Sn4 ++Zr4 +)浓度的 2 0倍 ,采用均相沉淀法制备的锡锆固溶体Sn0 4 5Zr0 55O2 对催化NO还原具有最高活性和较好的重复性 ,在 3 5 0℃下最大NO转化率达到 74% .XRD ,Raman ,XPS ,BET比表面测定和孔结构分析表明 ,沉淀条件不同 ,沉淀物的成核及生长过程不同 ,对SnO2 与ZrO2 之间的固溶度、催化剂表面元素分布、比表面和孔道结构以及催化活性都有较大的影响 .ZrO2 在SnO2 (r)晶格中较高的固溶度。
Lean NO_x catalysis can be viewed as a process in which two oxidants, NO_x and O_2, compete for hydrocarbon reductants with limited concentration. SnO_2 still has too high catalytic activity for complete combustion of propene, and its relative low melting point ( 1?630 ℃) and low specific surface area are also disadvantages to the catalytic performance. By adding a less active metal oxide with high thermal stability and large surface area,such as ZrO_2, into SnO_2, we first got Sn_xZr_ 1-xO_2 solid solution catalysts exhibiting high activity for NO reduction and good hydrothermal stability. Among them,the sample containing 60% SnO_2 showed the highest NO conversion of 71% at 350 ℃, which suggested that Sn_ 0.45Zr_ 0.55O_2 had the best composition. The influence of precipitation process on the structure, surface property and NO reduction activity of the catalysts was studied. A series of Sn_ 0.45Zr_ 0.55O_2 solid solution catalysts with the best composition were prepared by different precipitation methods and under different reaction conditions. The sample prepared by the urea-based homogeneous precipitation method with n(urea)/n( Sn 4++ Zr 4+)=20 showed the best performance in NO selective reduction,having the highest NO conversion of 74%. The insert of zirconia into tin dioxide with rutile structure was much influenced by the precipitation process and most of the samples with good performance in NO selective reduction were well-formed. The surface element distribution was varied owing to the inconsistent nucleation and growth process under different precipitation conditions. A proper segregation of tin on the surface was of advantage for NO selective reduction. The samples prepared under different precipitation conditions had different specific surface area and pore size distribution, and the large pore showed a promoting effect on NO selective reduction.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2003年第2期137-142,共6页
基金
国家重点基础研究发展规划项目 (G2 0 0 0 0 775 0 3)
国家 863项目 ( 2 0 01AA6430 30 1)
关键词
固溶催化剂
结构
一氧化氮
还择催化还原
锡
锆
沉淀过程
催化活性
tin, zirconium, solid solution, precipition process, nitrogen monoxide, selective catalytic reduction
