Quantitative Assessment of Pore Blockage in Supported Catalysts: Comparing Differential Scanning Calorimetry and Physisorption

Abstract

Mesoporous materials are commonly used as supports for a guest phase, such as catalytically active transition metal nanoparticles. N2 physisorption at 77 K is the standard technique to characterize mesoporosity; however, it is not always suitable to assess pore blockage caused by the guest phase. Here we report on the qualitative and quantitative assessment of pore blockage comparing N2 physisorption with two alternative techniques: differential scanning calorimetry (DSC) of the freezing and melting of confined water and physisorption of Ar at 77 K. A set of well-defined model catalyst nanostructures with varying degrees of pore blockage was synthesized using ordered mesoporous supports and different nanoparticle sizes. Pore blockage was detected with sorption techniques by analyzing the delayed gas desorption. For the first time we report the analysis of nanoparticle induced constrictions with DSC by studying the delayed freezing of water in the constricted pores. Both DSC and argon sorption provided information which cannot be accessed by standard N2 physisorption. Therefore, both techniques are advocated for the analysis of complex porous structures.