(621bj) Calorimetric and Manometric Measurements for the Study of Sorption Properties and Surface Energetics of Catalysts

Authors: 
Lilova, K., Setaram Inc.
Brown, L., Setaram Inc.

Developing energy efficient and environmental friendly materials with better adsorption properties than the currently existing ones became a crucial matter. Both experimental studies and theoretical modelling have been focused on many classes of porous materials: i.e zeolites, germanosilicates, aluminophosphate and gallophosphate zeotypes, mesoporous silica, etc. As a relatively new class of porous materials, the meta-organic frameworks (MOFs) attracted a significant interest during the last decade because of their low density and promising potential as catalysts.

Understanding the thermodynamics of both physi and chemisorption as well as the capacity and cyclic life is essential for the practical application of the catalysts. The energetics of interaction between the guest species and the host framework is another critical factor for determining the properties of different materials, particularly those involved in heterogeneous catalysis. The surface energetics studies allow to predict the possible reactions and processes, and at the same time to modify the structure accordingly.  

The combination of Sievert’s manometric technique and calorimetry were successfully used to determine directly the integral heat of adsorption, the isosteric heat of adsorption, and the differential heat of adsorption as a function of the surface coverage. Several examples including Cu-BTC, MOF-5, and CD-MOF2 were selected to demonstrate the technique. The thermodynamic stability (formation enthalpy) of three new large-porous zeolites catalysts was studied using high temperature oxide melt solution calorimetry. Solution and immersion calorimetry were used to obtain the enthalpies of confinement of organic molecules in a microporous framework. As an example, the energetics of confinement of n-hexane in ion exchange zeolite A will be shown. Combining different calorimetric techniques with surface measurements is the most direct experimental way to determine the surface energetics of nanomaterials and predict their properties and stability as a function of the surface area. The results on several nano oxides will be presented.