H2PtCl6H_2PtCl_6-derived Pt nanoparticles on USY zeolite: A qualitative and quantitative electron tomography study

The structural details of a bifunctional Pt/USY catalyst were studied using electron tomography. As a part of a fundamental study on the synthesis of Pt/USY catalyst, H2PtCl6 precursor was used for the impregnation of USY zeolite support as a source of negatively charged PtCl62− ions in order to restrict interaction with acidic sites of USY zeolite. After heat treatments, it was visualized in 3D that some Pt particles were 3–4 nm in size, while the majority maintained the size of 1.2–1.5 nm which corresponds to the diameter of the zeolite Y micropore cavities (1.2 nm). Electron tomography further revealed that 3–4 nm Pt particles seem to be entrapped in the zeolite crystal, without preferential location in mesopores or at the surface of the crystals. Quantitative image analysis provided the diameters (compared with EXAFS results) and the nearest neighbor distances of hundreds of imaged Pt particles

Heterogeneities of the Nanostructure of Platinum/Zeolite Y Catalysts Revealed by Electron Tomography

To develop structure-performance relationships for important catalysts, a detailed characterization of their morphology is essential. Using electron tomography, we determined in three dimensions the structure of Pt/zeolite Y bifunctional catalysts. Optimum experimental conditions enabled for the first time high-resolution 3D imaging of Pt particles as small as 1 nm located inside zeolite micropores. Semiautomated image analysis of 3D reconstructions provided an efficient study of numbers, size distributions, and interparticle distances of thousands of Pt particles within individual zeolite crystals. Upon extending this approach to a number of zeolite crystals of one batch of Pt/zeolite Y catalyst, heterogeneities were revealed. The Pt loading, an important parameter for catalyst performance, varied between zeolite crystals up to a factor of 35. This discovery calls for re-evaluation of catalyst preparation methods and suggests potential for lowering the nominal loading with noble metals