Using environmental transmission electron microscope to study the in-situ reduction of Co3O4 supported on α-Al2O3

Cobalt nanoparticles on a porous support such as alumina are widely used in the Fischer-Tropsch process to convert natural gas into synthetic fuel. One challenge is to characterize the catalyst in as close as possible to the condition in which it functions. In-situ experiments can be performed in specialized Transmission Electron Microscope (TEM) instruments with differentially pumped columns at pressures in the range up to 20 mbar. 1-3 The objective of this work is to study the reduction of Co3O4 nanoparticles directly and observe their morphology and crystallography. The catalysts were produced through one-step incipient wetness impregnation of an α-Al2O3 metal oxide support with an aqueous solution of cobalt nitrate hexahydrate, Co(NO3)2.6H2O. After impregnation, the samples were dried at 110°C for 3 h, and finally calcined in air at 300°C for 16 h. Samples for TEM were then prepared by dispersion of crushed powder directly on steel grids and gold grids. TEM analysis was performed with an FEI TITAN E-cell electron microscope operating at 300 kV. Reduction was done at 360°C and 3.4 mbar H2 flow. The samples were studied before and after reduction by High Resolution TEM (HRTEM) imaging, high angle annular dark field Scanning TEM (STEM) imaging and Electron Energy Loss Spectroscopy (EELS) and changes were monitored dynamically during reduction. HRTEM images and EELS showed the presence of characteristic metallic Co planar spacings and the absence of O in the particles after reduction. Earlier studies have shown reduction to CoO on γ-Al2O3 support.1 Here we have obtained complete reduction of the Co nanoparticles. Figure 1 shows a metallic Co after stopping the H2 flow and cooling to room temperature. Lattice fringes show the identity of both the metal and support. References [1] P. Li, J. Liu, N. Nag, P. A. Crozier, Appl. Catal. A, 307 (2006) 212. [2] E. D. Boyes, P. L. Gai, Ultramicrosc., 67 (1997) 219. [3] P. L. Gai, E. D. Boyes, Microsc. Res.Tech., 72 (2009) 153. [4] This research was supported by Research Council of Norway and Statoil and forms a part of the inGap Centre of research-based Innovation, which receives financial supports from the Norweian Research Council under contract no. 174893. This experiment has done in center for electron Nanoscopy at Technical University of Denmark (DTU) and we specially thank Rafal E. Dunin-Borkowski support.