摘要
基于原位傅里叶变换红外光谱(DRIFTS)法对柴油机选择性催化还原(SCR)后处理铜基菱沸石(Cu-CHA)催化剂Cu-SSZ-13的储氨机理进行试验研究。试验结果表明,NH_3主要吸附在Cu-SSZ-13催化剂表面的Lewis酸性位和Br?nsted酸性位上,其中Br?nsted酸性位有4种,分别是Si-OH、Cu-OH、Al-OH和Ai-OH-Si,而Lewis酸性位主要是两种Cu交换位,分别是六元环上的孤立铜离子和CHA笼子中的铜离子。在程序升温脱附(TPD)过程中,Br?nsted酸性位上吸附的铵离子比Lewis酸性位上吸附的配位氨更稳定,吸附在Lewis酸性位上的配位氨在350℃时基本完全脱附,而吸附在Br?nsted酸性位上的铵离子,其中Si-OH和Cu-OH上的铵离子在350℃时基本全部脱附,Al-OH和Ai-OH-Si上的铵离子在350℃时仍然吸附于催化剂表面,且二者为主要的Br?nsted酸性位。此外,当温度从150℃升到300℃过程中,Ai-OH-Si上吸附氨红外特征峰有增强的趋势,部分从Lewis或弱Br?nsted酸性位上脱附下的NH3再吸附于Ai-OH-Si上,这种再吸附现象对于减少柴油机瞬态工况下氨泄漏具有重要意义。
In situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)was employed to study ammonia storage mechanism of a Cu-chabazite(CHA)catalyst Cu-SSZ-13 for diesel selective catalytic reduction(SCR)after-treatment system.The results show that NH 3 mainly adsorbed on the surface of Cu-SSZ-13 on both Bronsted and Lewis acidic sites.There are four types of Bronsted acidic sites:Si-OH,Cu-OH,Al-OH and Al-OH-Si.Cu^2+located in six-membered rings and CHA cages form Lewis acidic sites on Cu-SSZ-13.Temperature programmed desorption(TPD)results show that NH 4+ions on Bronsted acidic sites are much more stable at high temperature than the ammonia ad-species on the Lewis acidic sites.Ammonia adsorbed on Lewis acidic sites and NH4^+on Si-OH and Cu-OH almost desorbed at 350℃,while NH4^+on major Bronsted acidic sites Al-OH and Al-OH-Si still existed at 350℃.When the temperature increased from 150℃to 300℃,the IR bands of Al-OH-Si enhanced.This result indicates that some NH3 desorbed from Lewis acid sites or weak Br?nsted acidic sites may re-adsorb onto Al-OH-Si.These findings are of great significance for reducing NH 3 slip of diesel engine under transient conditions.
作者
刘彪
姚栋伟
吴锋
魏铼
李杏文
何华定
LIU Biao;YAO Dong-wei;WU Feng;WEI Lai;LI Xing-wen;HE Hua-ding(Power Machinery&Vehicle Engineering Institute,Zhejiang University,Hangzhou 310027,China;Zhejiang Liming Engine Parts Co.,Ltd.,Zhoushan 316000,China)
出处
《高校化学工程学报》
EI
CAS
CSCD
北大核心
2019年第1期103-109,共7页
Journal of Chemical Engineering of Chinese Universities
基金
国家重点研发计划课题(2017YFC0211103)
中央高校基本科研业务专项资金(2016QNA4014)
能源清洁利用国家重点实验室(浙江大学)自主课题(ZJUCEU2016006)
