FUEL 28 |
| The production of clean transport fuels by hydrodesulfurization (HDS) has recently attracted increased attention due to the introduction of new environmental legislation on fuel specifications. To meet these requirements there is a need to understand and improve HDS catalysts. The active phase of the MoS2-based hydrotreating catalyst is composed of 2-3nm wide MoS2-like nanoclusters, typically promoted by Co or Ni, forming the so-called CoMoS and NiMoS nanostructures. In this talk, I present atom-resolved scanning tunneling microscopy (STM) of MoS2, CoMoS and NiMoS nanoclusters [1]. We observe a promoter-dependent morphology, which is explained by the different affinities for Co and Ni to replace Mo at the edge sites of MoS2 nanoclusters. Our finding shows that the location and coordination of the promoter atoms are different in NiMoS and CoMoS, which may explain the different selectivity observed in the industrial catalysts. Recent experiments with the unpromoted MoS2 triangles reveal that small clusters with a certain size are more stable than others, and atom-resolved images show that the most stable small clusters may be terminated by new edge configurations. Specifically, we find that clusters containing less than 21 Mo atoms prefer to be terminated by (-1010) S edges with varying sulfur coverage, as opposed to the (10-10) edges present in the larger clusters [2]. The novel findings suggest that good size control during the synthesis of MoS2 nanostructures may be used for the production of chemically or optically active MoS2 nanomaterials with superior performance. In order to include the effect of a different support, we also synthesized MoS2 nanoclusters on highly oriented pyrolytic graphite (HOPG) [3]. 1.Lauritsen, J.V et al., J. Catal, submitted 2007. 2.Lauritsen, J.V. et al., Nature Nanotechnology, 2007. 2: p. 53-58. 3.Kibsgaard, J. et al., Journal of the American Chemical Society, 2006. 128(42): p. 13950 - 13958. |
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Green Chemistry for Sustainable Energy Supply and Conversion
1:45 PM-5:40 PM, Sunday, April 6, 2008 Morial Convention Center -- Rm. 242, Oral
Division of Fuel Chemistry |