CO interaction with zeolites studied by TPD and FTIR: transition-metal ion-exchanged FAU-type zeolites

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• 作者：Rakic ; Vesna M. ; Hercigonja ; Radmila V. ; Dondur ; Vera T.
• 关键词：Carbon dioxide ; Carbon monoxide ; Fourier transform infrared spectroscopy ; Temperature-programmed desorption of CO ; Transition-metal-exchanged zeolites
• 刊名：Microporous and Mesoporous Materials
• 出版年：1999
• 出版时间：January, 1999
• 年：1999
• 卷：27
• 期：1
• 页码：27-39
• 全文大小：289 K

文摘

The interaction of carbon monoxide with the cationic Lewis acid sites of transition-metal (Fe²⁺, Co²⁺, Ni²⁺) and Cu²⁺-exchanged Y and X zeolites was investigated by Fourier transform infrared spectroscopy (FTIR) and temperature-programmed desorption (TPD). The activation of the sample, the adsorption (at room temperature) of CO and the detection of desorbed molecular species were done in situ, either with FTIR or with a mass spectrometer, in gas-flow systems. During the adsorption of CO from the gas stream, a low surface coverage (between two and seven molecules per unit cell) was achieved. In the case of CuY and CuX zeolites, the TPD/MAS spectra exhibit only CO signals. During adsorption of CO, IR absorption bands in the 2200–2000 cm⁻¹ spectral region, characteristic for symmetric stretching of CO adsorbed on zeolites, were collected in the FTIR spectra, indicating molecular adsorption of CO on Cu²⁺-exchanged samples. In the case of all other samples investigated, disproportionation of CO was noticed during its adsorption and temperature-programmed desorption. IR absorption bands near 2350 cm⁻¹, characteristic for ν₃ asymmetric stretching of weakly bound CO₂ on zeolites, and IR absorption bands in the 2200–2000 cm⁻¹ spectral region were collected during adsorption of CO on Fe²⁺-, Co²⁺- and Ni²⁺-exchanged samples. In the TPD/MAS spectra both CO and CO₂ signals were monitored. Significant amounts of carbon deposits (between two and nine carbon atoms deposited per unit cell of the zeolite) were found after adsorption and TPD procedures.