Synthesis and characterization of new ordered nanoporous carbon molecular sieves CMK-3 modified with Pt

JULIANA M. JUÁREZ; MARCOS B. GÓMEZ COSTA; OSCAR A. ANUNZIATA

Cancún

Congreso; XXIII International Materials Research Congress; 2014

MRC

Ordered nanoporous carbon CMK-3 was synthesized via two impregnation step of the siliceous mesopores SBA-15, using a solution of sucrose by incipient wetness method. The sucrose?silica composite was then heated at 1173 K for 4 h under nitrogen flow. The silica template was dissolved with 5 wt% hydrofluoric acid in order to remove the silica. The template-free carbon product obtained was filtered, washed with deionized water and ethanol, and dried [1]. Pt-CMK-3 was prepared by wet impregnation using a solution of cloroplatinic acid as source of Pt. Porous carbon CMK-3 and the sample modified with Pt were characterized by XRD, FTIR, BET and TEM. The structure of CMK-3 material, synthesized using silicon SBA-15 as template, was found to be an exact negative replica of the template. The main indication of the structural transformation was the appearance on the X-ray diffraction (XRD) patterns of CMK-3 that was consistent with the symmetry of SBA-15 [2]. CMK-3 shows two broad diffraction peaks which can be indexed as [0 0 2] and [1 0 0] Miller indices defining the orientation of the plane for typical graphite carbons [3]. The pattern of Pt-CMK-3 shows metallic Pt signals [4], indicating the successful reduction of platinum.  The surface areas are 904 m2/g, 950 m2/g and 500 m2/g for SBA-15, CMK-3 and Pt-CMK-3, respectively.  While the nanomaterial area is significantly smaller with the incorporation of the metal, CMK-3`s characteristic structure is maintained after Pt is within the host, in agreement with the XRD studies. The TEM micrographs of Pt-CMK-3 show Pt nanoparticles with average diameter of ~2-8 nm, probably located into the pores of the host. The metals particles average diameters obtained by Scherrer?s formula were 5 nm. Hydrogen chemisorption was carried out to the samples. The Hydrogen chemisorption at room temperature was 0.19 ml/g for Pt-CMK-3. The metal dispersion was 33% and the average crystallite size of platinum was 4 nm. On the other hand, the capacity of hydrogen uptake was evaluated at low and high pressures and cryogenic temperatures (77 K). At low and high pressures the amount of hydrogen uptake is higher in Pt-CMK-3 than CMK-3 sample (3.3 and 2.2 wt% respectively at 10 bar).