Síntesis, caracterización y evaluación catalítica de nanoestructuras metal nobletitania

Abstract

This work presents the synthesis, characterization and catalytic performance of nanostructured materials Pt/TiO2-NT (NT=nanotubes) by a new approach called vapor phase impregnation-decomposition method. This approach consisted in two steps as follows: Pt precursor [Pt(acac)2] is sublimated in vacuum at Tevap: 180 °C and this vapor interact with –OH groups at the TiO2-NT support surface. In a second stage, at Tdep: 400 °C the metalorganic precursor decomposition took place, where free Pt formed nucleus in the surface defects of the support. This process in addition with the homogeneous contact between the precursor vapors and the support, led to a uniform phase dispersion, small particle size and surface features that improved its catalytic performance. Compositional analysis was performed by atomic absorption spectroscopy (AAS) and showed that this new approach promotes an elevated dispersion fully comparable with other vapor phase methods. Pt nanoparticles incorporated onto TiO2-NT support, were founded mainly in reduced state (Pt0) in an uniformly scattered and in a particle size of 1.4 – 2.2 nm measured by XPS, TDP-H2 and HAADF-STEM microscopy, respectively. Additionally, FTIR-CO results exhibited that Pt nanoparticles were preferably founded on edge sites which, in accordance with literature, promotes the breaking of ligands for various catalytic reactions, for example, for naphthalene hydrogenation reaction. Pt/TiO2-NT system was tested in this reaction, where exhibited an elevated catalytic activity and selectivity for decaline cis formation, which is a more convenient bi-product because its ease for a subsequent for a ring-opening reaction aiming at cetane number improvement.