A simultaneous volumetric adsorption–isothermal titration calorimetry study of small molecules on supported metallic nanoparticles

Abstract

Adsorption microcalorimetry studies can determine the energetics involved in different adsorbate–surface interactions. These measurements can be taken using various techniques such as single-crystal adsorption calorimetry, isothermal titration calorimetry and differential scanning calorimetry. The incremental dosing of a small molecule adsorbate with simultaneous calorimetric measurement enables differential heats of adsorptions to be measured at a specific temperature. In this study, an automated volumetric adsorption apparatus (Micromeritics ASAP2020) was interfaced with a Differential Scanning Calorimeter (Setaram Sensys EVO) to perform simultaneous volumetric uptake and calorimetric measurements. Heats of adsorption of small gas molecules (CO, H2) on supported metal catalysts (Pt, Pd, Au) were measured using this setup. Similar calorimetric measurements for the adsorption of CO (0.5 % Pt/SiO2; 5 % Pd/Al2O3) and H2 (0.5 % Pt/SiO2) were also taken by interfacing a Micromeritics ASAP2020 with a custom-built calorimeter. From these studies, it was observed that the initial heats of CO adsorption on supported Pt (0.5 % Pt/Al2O3, 135 kJ mol−1; 1 % Pt/SiO2, 104 kJ mol−1) and Pd (5 % Pd/Al2O3, 148 kJ mol−1) catalysts were significantly higher than the corresponding Au (1 % Au/TiO2, 57.2 kJ mol−1; 1 % Au/Al2O3, 54.1 kJ mol−1) catalysts. It was also observed that the initial heat of adsorption of H2 on the supported 0.5 % Pt/Al2O3 (~80 to 89 kJ mol−1) catalyst is higher than that on 1 % Pt/SiO2 (~61 kJ mol−1). CO and H2 adsorption studies on the 0.5 % Pt/Al2O3 and the 5 % Pd/Al2O3 catalyst using both calorimetric setups yielded similar volumetric uptakes and initial heats.