Abstract
An adsorption microcalorimeter was designed and built in our laboratory and used for the determination of differential adsorption heats in different samples of porous solids: activated carbon granules, activated carbon pellets, an activated carbon monolith and a zeolite sample. This work shows the relationship between adsorption heat and the pore size of different porous solids using adsorption of NH3, CO and N2O. The result shows that the thermal effect can be related with textural properties and superficial chemical groups of the studied porous solids. The values of differential heats of N2O adsorption in the investigated systems have shown that this interaction is weaker than that with CO. Small amounts of N2O are chemisorbed in the investigated systems. For the room temperature adsorption of N2O, the strongest active sites for the interaction with Brönsted acid groups in the ACM structure were identified. The values determined are between −60 kJ/mol and −110 kJ/mol for ZMOR and ACM, respectively, for the adsorption of N2O and −95 kJ/mol and −130 kJ/mol for the adsorption of CO.
Highlights
It is widely accepted that knowledge of adsorption heats is vital in the description of gas-solid interactions
In this work we present the synthesis and characterization of porous solids and use of adsorption calorimetry for establishing the relationship between the adsorption heat and the pore size of different porous solids
The results presented so far are a clear indication that samples with higher surface area and minor diameter pore have stronger active sites in CO adsorption that in N2O adsorption
Summary
It is widely accepted that knowledge of adsorption heats is vital in the description of gas-solid interactions. These obviously provide information about the energetics of surface processes. Inferences can be made from the adsorption heats on the structure of the surface itself. Chemisorption and catalysed reactions, like any chemical reaction, are associated with changes in enthalpy and can be studied by means of calorimeters. Adsorption calorimeters are convenient for these studies [2]. They offer a number of advantages which will be illustrated by means of selected examples
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