(633c) Synthesis of, Characterization of and Catalytic SWNT Synthesis on Pt-Co-Mcm-41
Pt supported on carbon nanotubes has been demonstrate to be a good catalyst for fuel cell anodes, and different methods have been attempted to utilize base metals in the Pt-CNT system to decrease the cost of the catalyst, while maintaining high reactivity. Recently we have synthesized C10-Co-MCM-41 mesoporous catalyst, which provides high yield and good diameter selectivity in single walled carbon nanotube (SWNT) synthesis. In this contribution, Pt-Co-MCM-41 was synthesized based on a modified procedure of the Co-MCM-41 hydrothermal synthesis. The catalyst has been characterized by nitrogen absorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature programmed hydrogen reduction (H2-TPR), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies. The results indicated that the Pt was reduced and formed Pt nanoparticles during the hydrothermal treatment during the synthesis of the catalyst, while Co (II) was atomically dispersed in the MCM-41 matrix. TPR results showed that the Pt nanoparticles can facilitate the reduction of Co (II).
SWNT was produced by first pre-reducing the catalyst at the TPR maximum rate of reduction temperature, following by the carbon deposition from carbon monoxide (CO) disproportionation. The Pt-Co-MCM-41 maintained a high yield similar to that of the Co-MCM-41 catalyst, however, the introduction of Pt enhanced the production of smaller diameter (0.64nm) SWNT. The analysis of EXAFS results showed that although there is no Pt-Co bimetallic species in the fresh calcined catalyst, during the pre-reduction stage, Pt-Co bonds were formed. There are three phases in the reduced catalyst: Pt, Co and Pt-Co bimetallic phases. Since Pt is not an active catalyst for SWNT synthesis, the increased smaller diameter SWNT selectivity is attributed to the Pt-Co bimetallic phase. The selectivity can also be correlated with the Pt/Co ratio in the catalyst.