Determination of basic sites in Mg-Al mixed oxides by combination of TPD-CO sub(2) and CO sub(2) adsorption calorimetry

• Published in: Journal of thermal analysis and calorimetry Vol. 127; no. 3; pp. 1921 - 1929
• Main Authors: Smolakova, Lucie, Frolich, Karel, Troppova, Ivana, Kutalek, Petr, Kroft, Eva, Capek, Libor
• Format: Journal Article
• Language: English
• Published: 01-03-2017
• Subjects: Adsorption; Aluminum; Basic oxides; Calorimetry; Carbon dioxide; Information dissemination; Magnesium; Mixed oxides
• ISSN: 1388-6150; 1572-8943
• DOI: 10.1007/s10973-016-5851-6

We present the critical analysis of the utilization of CO sub(2) adsorption calorimetry/volumetry and TPD-CO sub(2) 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 CO sub(2) adsorption complexes are involved. Critical parts of basic sites determination are originally discussed for both methods. In TPD-CO sub(2), the process of the purging of non-specifically physisorbed CO sub(2) is stressed. In CO sub(2) adsorption calorimetry, the differential heat of CO sub(2) distinguishing CO sub(2) adsorption on weak basic sites and non-specific CO sub(2) 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-CO sub(2) does not provide complete information about basic sites since some weak sites form unstable CO sub(2) species and these species could not be involved in TPD experiments. All our TPD-CO sub(2) experiments reflect at 0-485 degree C those CO sub(2) adsorbed in the range of the differential heat of CO sub(2) above 30-32 kJ mol super(-1).