CO探针原位红外光谱研究Pt/Sn双金属重整催化剂

In Situ FTIR Study of CO Adsorption on Pt-Sn/Al_2O_3 Reforming Catalyst

催化重整是生产芳烃原料和高辛烷值清洁汽油调和组分的重要工艺。以目前应用广泛的铂锡工业重整催化剂金属含量为参比,用工业剂制备方法合成了Pt含量为0.6%的一系列铂锡重整催化剂,建立CO探针原位红外的表征方法,并对其进行系统表征,首次获得了1%以下低含量助剂Sn的CO探针红外谱图。研究结果表明,系列剂的金属Pt的CO吸附特征峰主要以线式吸附状态存在。0.6%纯Pt剂上1 826cm^(-1)处CO桥式吸附特征峰,因添加助剂Sn后,强度下降,而CO线式吸附特征峰的强度则增加,说明Sn的加入使得Pt的分散度增加。变温CO探针吸附原位红外研究表明,对负载质量分数0.3%的纯Sn催化剂,当脱附温度升高至120℃时,吸附在Sn上的CO特征峰会完全消失。对负载质量分数0.6%的纯Pt催化剂,当脱附温度升高至300℃时,吸附在Pt中心上的CO特征峰会完全消失。当Pt-Sn双金属负载质量分数Pt为0.6%、Sn为0.3%时,CO的脱附温度明显提高达350℃。与纯Pt剂相比,随着Sn助剂的加入,使得CO的脱附温度稍有提升,Pt-Sn催化剂Pt的CO特征峰向高波数方向移动,说明Sn的加入一定程度上减弱了活性金属Pt中心上的电荷密度。因而,CO探针原位红外是表征低金属铂锡工业重整催化剂的有效手段,为阐明多金属重整催化剂的助剂作用和研究反应机理提供重要信息。

Catalytic reforming,which produces raw material of aromatic hydrocarbon and high-octane clean-gasolineblending component,is a principal technology.According to the content of platinum and tin loading on industrial reforming catalyst,platinum loading was kept constant at 0.6 Wt%and the amount of tin was variedfrom 0 to 1 Wt%in the catalysts.A series of Pt-Sn/Al 2O 3 reforming catalysts were characterized with in situ FTIR of adsorbed CO method which is established in this study.And the adsorbed CO infrared peaks were obtained at room temperature on Sn/Al 2O 3 catalysts that the mount of tin was under 1 Wt%in thefirst time.At room temperature the CO species of Pt sites adsorbed on the surface of Pt-Sn/Al 2O 3 reforming catalysts mainly on linearly-bonded CO species.It was found that there was a general trend that the amount of bridge-bonded CO species was decreasing and the amount of linearly-bonded CO species was increasing,with increasing amounts of tin in the catalyst.It was stated that the dispersity of platinum atoms was increasing.The temperature increasing desorption processwas used to show that the CO band of Pt sites disappeared completely at 300℃on 0.6%Pt/Al 2O 3,and the CO band of Sn sites disappeared completely at 120℃on 0.3%Sn/Al 2O 3.The CO band of Pt sites and Sn sites disappeared completely at 350℃on 0.6%Pt-0.3%Sn/Al 2O 3.Compared reforming catalysts Pt-Sn/Al 2O 3 with Pt/Al 2O 3,the linearly adsorbed CO band of Pt sites shiftto high frequencies.This suggests that the electronic density of Pt increaseddue to the loading of Sn.Therefore,in situ FTIR is an effective tool for characterization of low metal reforming catalysts,which provides important informationof interactions between tin and platinum.