(621h) Synthesis, Characterize And Catalytic Performance Of Highly Dispersed Co Sba-15 Catalyst

Authors: 
Wang, C., Yale University
Du, G., Yale University
Li, N., Yale University
Zoican, C., Yale University
Lim, S., Yale University


Highly dispersed cobalt SBA-15 was synthesized by a post synthesis method. This method is comprised of two steps: first, pure silica SBA-15 was synthesized using tri-block polymer template. Then, different cobalt precursors were applied by grafting onto the surface of silica SBA-15 by refluxing in a toluene solution of the precursor. Co(II) acetylactonate proved to be the best cobalt source for this method. The newly discovered Co SBA-15 was characterized with different techniques: N2 physisorption, XRD, TPR, TEM and X ray adsorption analysis. From N2 physisorption and XRD results, the physical structure of the silica SBA-15 was retained after cobalt was grafted with up to 10 wt.% Co on the surface. No large cobalt particles are formed as demonstrated by both XRD and TEM photographs, which indicates that all the cobalt metal particles are highly dispersed on the surface following reduction. This high dispersion of cobalt particles also resulted in a high reduction temperature (850 °C, Co+2 to metal) in TPR. This reduction temperature of cobalt on the Co SBA-15 sample was even higher than the Co+2 cation incorporated Co-MCM-41, where Si was substituted by Co+2, that means cobalt ions are very stably fixed on the surface of SBA-15. We believe that cobalt cations are bonded with several O to form a very stable dispersion on the surface. X-Ray absorption analysis exhibited Co-O bond coordination number is 3.58 +/- 0.48 and the EXAFS indicates that the cobalt was in a distorted tetrahedral environment.

The catalytic behavior of Co SBA-15 catalyst was tested for the synthesis of carbon SWNT. Incorporated Co-MCM-41 has proven to be a good catalyst for growing carbon SWNT. However, the cobalt loading has a limit to 4 wt.%, beyond which structural order and complete Co incorporation is lost. One of the advantages of the Co SBA-15 is that cobalt loading can be as high as 10 wt% without lost of pore structure of silica SBA-15. Another advantage is the pore diameter of SBA-15, which is much larger (7nm) than MCM-41 (<3nm). That means that there will be less diffusion limitation on reaction in the pores. Raman spectroscopy and TEM images showed Co SBA-15 is also a good catalyst for growing carbon SWNT. Additionally, it has much higher yield of carbon SWNT compared to C16 MCM-41.