Alkali Titanate Nanotube-Supported Platinum Catalyzed Carbon Monooxide Oxidation Reaction ─ A DRIFTS Study

• Main Authors: Wei-Yi Chen, 陳煒益
• Other Authors: Chiu-Hsun Lin
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/55423210044538120349

碩士 === 國立彰化師範大學 === 化學系 === 100 === Pt nanoparticles (around 1-2 nm) were deposited onto the surfaces of the alkali metal titanate nanotubes (MTNTs = M2Ti3O7, M=Li+, Na+, K+, Cs+) by ion exchange of Pt(NH3)2Cl2 salt followed by H2 reduction 423 K. XPS showed that the binding energies of Pt 4f7/2 that were supported on these MTNTs oxide nanotubes were systematically reduced from 70.74 eV to 70.31 eV when the support was changed from LiTNTs to CsTNTs. These binding energies were lower than that of Pt0 metallic state at around 71 eV. The results suggested that electrons were transfer from the MTNTs to Pt particles, yielding Ptδ- oxidation state. DRIFTS was used to study the adsorption and complete oxidation of CO over these Pt/MTNTs catalysts. The results indicated that when CO was adsorbed on 3% Pt/MTNTs at 303 K, DRIFTS indicated that linear (a-top and interfacial) and bridge forms of CO (B-CO and 3FC-CO) were generated and their vibration frequencies shifted downward when the charge density on Pt in these Pt/MTNTs increased. In the absence of oxygen, the adsorbed CO interacted with the hydroxyl group near the interface of the Pt particle to generate bidentate formate group, through which a fair amount of CO2, surface water and unidentate carbonate was produced (WGS mechanism). These surface formate and carbonate, however, seem quite thermally stable at lower than 373 K. In the presence of oxygen, more CO2 was produced over these Pt/MTNTs, suggesting that traditional Langmuir-Hinshelwood mechanism is operating. The amount of CO2 produced was positively related to the charge density on Pt, Pt/CsTNTs >Pt/KTNTs >Pt/NaTNTs > Pt/LiTNTs. On the other hand, the amount of carbonate produced followed the opposite order, Pt/CsTNTs <Pt/KTNTs <Pt/NaTNTs < Pt/LiTNTs. The rate of disappearance of CO, however, seems insensitive to the charge density on Pt. Bridge form of CO disappeared at a lower temperature of 325 K than LCO, but the rate of disappearance of LCO was greater than that of the Bridge CO.