The acid properties of H-ZSM-5 as studied by NH₃-TPD and ²⁷Al-MAS-NMR spectroscopy

详细信息	查看全文 | 推荐本文 |

• 作者：Luz Rodr&#xed ; guez-Gonzá ; lez ; Florian Hermes ; Marko Bertmer ; Enrique Rodr&#xed ; guez-Castell&#xf3 ; n ; Antonio Jimé ; nez-L&#xf3 ; pez ; Ulrich Simon
• 关键词：NH₃-TPD ; H-ZSM-5 ; ²⁷Al-MAS-NMR ; Br&#xf8 ; nsted acidity ; Zeolite
• 刊名：Applied Catalysis A ; General
• 出版年：2007
• 期刊代码：4_0926860x
• 类别：ch
• 出版时间：10 September 2007
• 卷：328
• 期：2
• 页码：174-182
• 文件大小：912 K

摘要

The acid properties of H-ZSM-5 zeolites with different SiO₂/Al₂O₃ ratios (30, 50, 80, 150, 280 and 1000) were examined by means of the temperature programmed desorption of ammonia (NH₃-TPD). Different pretreatments together with a comparison of different curve-fitting methods after desorption of ammonia were used to differentiate between different adsorption sites. ²⁷Al-MAS-NMR spectroscopy was applied to distinguish the framework (Al_F) from the extra-framework aluminum (Al_EF). Both techniques reveal that the concentration of Brønsted acid sites is lower than expected when considering the aluminum content. The strength of the Brønsted acid sites, determined by a theoretical model assuming the free readsorption of ammonia, is found to be in the range of ΔH = 129–161 kJ mol⁻¹ and shows variations in the acid strength to be less than σ = 12 kJ mol⁻¹.