摘要
采用XRD ,TEM和UV Vis方法研究了Ag HZSM 5催化剂中活性组分银的价态和结构变化 ,并将这种变化与其在CH4 选择性催化还原NOx 反应中的活性和选择性相关联 .结果表明 ,惰性气氛下高温处理使交换到分子筛阳离子位上的Ag+ 自还原为Ag0 ,并在热的作用下聚集成纳米尺度的银颗粒Agn.纳米银颗粒Agn 的形成提高了银催化剂在CH4 选择性催化还原NOx 反应中的活性 ,但它的长大又促进了CH4 和O2 的直接燃烧 ,使CH4 选择性催化还原NOx 反应的选择性降低 .氧气气氛下高温预处理抑制了银颗粒的长大 ,并且氧气的氧化作用使银颗粒带有一定电荷 ,形成小的荷电纳米银粒子Agy + x .荷电纳米银粒子的形成使催化剂的活性降低 ,但提高了CH4 选择性催化还原NOx
Different silver species formed over Ag-HZSM-5 catalyst have been identified by XRD, UV-Vis and TEM, and their catalytic performance was investigated through the reaction of the selective catalytic reduction (SCR) of NOx by CH4. By the pretreatment in a He stream at high temperatures, Ag+ can self-reduce to Ago and then Ago can aggregate into nano-sized silver particles. The catalytic activity of the silver catalyst is increased by the nano-silver particles formed. Much larger silver particles, formed with increasing the temperature, can accelerate the direct combustion of CK with O-2 and decrease the selectivity of SCR of NOx by CH4. High temperature pretreatment in 30% O-2/He stream depresses the growing of large silver particles, and makes silver particles charged to form Ag-x(y+). The presence of Ag-x(y+) leads the catalyst to show better selectivity but poor activity in the reaction of SCR of NOx by CH4.
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2001年第6期555-558,共4页
基金
国家自然科学基金 ( 2 0 0 0 30 11)
"973"计划资助项目
