摘要
采用双股并流共沉淀方法制备了SnO2含量从10%至90%的锡锆体系DeNOx催化剂,用XRD、微区电子衍射、FT-Raman及FT-IR等技术深入研究了锡锆体系氧化物的结构及其随组成的变化规律.结果表明,由于Sn4+与Zr4+离子半径接近,SnO2与ZrO2易于形成固溶体,并随组成变化表现出不同的结构特征.纯ZrO2为单斜相,当少量Sn4+(SnO2≤20%)进入ZrO2晶格时形成四方相富锆固溶体,Sn4+起到稳定ZrO2四方相的作用;随着SnO2含量的增大,结构从无定形或微晶态的富锆固溶体(含SnO230～50%)经富锆固溶体与金红石结构的富锡固溶体在55%SnO2含量的共存状态变化到具有金红石结构的富锡固溶体(SnO2≥60%).FT-Raman和FT-IR光谱测试证明,Zr进入SnO2晶格使得Sn-O键的结合减弱,Sn离子上的有效正电荷减小,降低了SnO2对丙烯的燃烧能力,从而提高了对NO的还原活性.
A series of SnxZr1-xO2 solid solution catalysts with SnO2 content varied from 10% (w) to 90% ( w) were prepared by co-current coprecipitation method (CCP method) using ammonia solution as precipitating agent and calcined at 500degreesC for 4 h in air. The structure variation with SnO2 content was investigated by XRD, electron diffraction, FT-Raman and FT-IR. Tin dioxide and zirconia can react with each other to form solid solutions within a large composition range. In the present work, zirconia prepared by CCP method and calcined at 500degreesC was monoclinic, and tin dioxide prepared by the same way possessed rutile structure. The experiment results showed the following dependence of the solid solution structure on SnO2 content. First, less than 20% SnO2 inserted into the lattice of ZrO2 could stabilize the tetragonal structure of zirconia and form the zirconia-rich solid solutions. Then, amorphous zirconia-rich solid solutions were formed in the SnO2 content region from 30% to 50%. Furthermore, a rutile structure tin dioxide-rich solid solution existed as SnO2 content over 60%. Finally, the zirconia-rich solid solution and tin dioxide-rich solid solution could co-exist while the SnO2 content maintained at 55%, which exhibited a structure transition between zirconia-rich and tin dioxide-rich solid solutions. Because the Sn-O bond was weakened and the effective electropositivity of Sn4+ was decreased as Zr4+ inserted into SnO2 lattice as proved by FT-Raman and FT-IR measurements, both the activation and the complete combustion of propene were restrained by Zr4+, as a result, the catalytic performance for NO selective reduction was promoted.
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
2003年第6期498-503,共6页
Acta Physico-Chimica Sinica
基金
国家重点基础研究发展规划(G2000077503)
国家863(2001AA643030-1)资助项目~~
