(361f) Role of Mo on Single-Walled Carbon Nanotubes Nucleation Catalyzed By MgO-Supported Co

Co has been shown to produce single-walled carbon nanotubes (SWCNTs) although without selectivity toward specific chiralities. In the presence of Mo however, it has been shown that chemical vapor deposition (CVD) methods yield a majority of near-arm chair SWCNTs with a small range of chiral indices. In CVD synthesis, Mo oxides and Cu oxides are used in the CVD process to synthesize the Co catalysts. However, the location of Mo at the end of the process is not known. It has been speculated that could exist as Mo-carbide, or distributed in the MgO support. One way to better understand the role of Mo, is to add Mo atoms to the support in controlled amounts and study its effects.

In this work, we use DFT calculations to study the interactions of a cobalt cluster with the MgO support in the presence and absence of Mo, and the effects of C addition to the system. First, we conduct ab initio thermodynamics simulations to find the most stable oxidation state of Mo in bulk MgO. We use this oxidation state of Mo in our subsequent calculations. The doping of 2^nd and 3^rd layer of MgO by Mo, and in both cases near and far positioning of Mo atoms with respect to each other is studied. Next, a small nanotube cap represented by a graphene fragment is brought into contact with the cobalt carbide cluster to study the energetics and influence of Mo on nucleation and first stage of SWCNT formation. In addition, we also investigate the effect of oxygen on the SWCNT nucleation and formation from a cobalt carbide supported by MgO, in the presence and absence of Mo.