Determination of basic sites in Mg–Al mixed oxides by combination of TPD-CO₂ and CO₂ adsorption calorimetry

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• 作者：Lucie Smoláková ; Karel Frolich…
• 关键词：Mg–Al mixed oxides ; Basicity ; CO2 adsorption calorimetry ; TPD ; CO2
• 刊名：Journal of Thermal Analysis and Calorimetry
• 出版年：2017
• 出版时间：March 2017
• 年：2017
• 卷：127
• 期：3
• 页码：1921-1929
• 全文大小：
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Physical Chemistry; Analytical Chemistry; Polymer Sciences; Inorganic Chemistry; Measurement Science and Instrumentation;
• 出版者：Springer Netherlands
• ISSN：1588-2926
• 卷排序：127

文摘

We present the critical analysis of the utilization of CO₂ adsorption calorimetry/volumetry and TPD-CO₂ for the determination of the Mg–Al mixed oxide basicity. The aim of work is the description and the evaluation of both methods with respect to the fact when the same types of CO₂ adsorption complexes are involved. Critical parts of basic sites determination are originally discussed for both methods. In TPD-CO₂, the process of the purging of non-specifically physisorbed CO₂ is stressed. In CO₂ adsorption calorimetry, the differential heat of CO₂ distinguishing CO₂ adsorption on weak basic sites and non-specific CO₂ physisorption is stressed. Both methods are applied on series of selected Mg/Al mixed oxides varying in Mg/Al molar ratio and alkali co-cation. We show that the generally used TPD-CO₂ does not provide complete information about basic sites since some weak sites form unstable CO₂ species and these species could not be involved in TPD experiments. All our TPD-CO₂ experiments reflect at 0–485 °C those CO₂ adsorbed in the range of the differential heat of CO₂ above 30–32 kJ mol−1.