Abstract
The synthesis and the catalysis in the HDS of DBT reaction of nanostructured self-supported catalyst containing MoS2+x nanoplatelets have been investigated. Enhancement of higher activity observed in sulfide catalyst sample (d) with respect to the ex situ and in situ references is more closely related to the morphology change of particles (nanoplatelets). In this work, we suggest that certain structures present in model catalysts maybe related to low dimensional structures and present a theoretical study of two MoS2 clusters (one made of 34 atoms/cluster and the second one made of 41 atoms/cluster), to these clusters seven sulfur atoms were randomly located at the surface of the sulfur layer, in order to simulate certain structures resembling arrow shaped nanoplatelets that were found in a High Resolution TEM analysis performed in some MoS2 samples. Additionally, one of the goals is to enquire about the electronic properties presented in such structures when the clusters terminated as Moor S-edge and if it could be correlated to the catalyst behavior of these compounds. To the 34 atoms/cluster Mo-edge yielded metallic behavior while the second cluster the 41 atoms/ cluster S-edge yielded a semiconductor behavior with a forbidden energy gap Eg of the order of @ 3.6 eV between the Valence and Conductions bands respectively. Moreover, to the same clusters enunciated formerly, when the sulfur atoms were located at the surface of the S-layer, for the first cluster (34 atoms/cluster) yielded a more metallic behavior, while the second one (41 atoms/cluster) yielded an isolator behavior. Our results agree with the experimental and theoretical results presented by several groups in different laboratories arriving to the conclusion that the S-Mo-S Mo-edge arrow heads structures could be responsible to the enhancement of the catalytic activity on the MoS2 studied samples.
Highlights
The most commonly used industrial hydro treating catalysts for sulfur removal from heavy oils are based on cobalt or nickel promoted MoS2 [1].Atom-resolved scanning tunneling microscopy (STM) studies of catalyst model systems have recently given the first direct insight into the atomic-scale structure of model MoS2 nanoclusters and the promoted CoMoS structures [2,3]
We have shown the synthesis and the catalysis in the HDS of DBT reaction of a nanostructured self-supported catalyst containing MoS2+x nanoplatelets
The enhancement of higher activity observed in sulfide catalyst d with respect to the ex situ and in situ references is more closely related to the morphology change of particles
Summary
The most commonly used industrial hydro treating catalysts for sulfur removal from heavy oils are based on cobalt or nickel promoted MoS2 [1]. These model systems consisted of a few nanometer wide, gold-supported MoS2 and CoMoS nanoclusters, and with the STM, it was possible to characterize their geometrical and electronic structure in great detail On this basis, new important insight was obtained on the nanocluster morphology, on the atomic-scale structure of the catalytically important edges, and on the formation of sulfur vacancies. This behavior may be attributed to metallic states at the edges of the nano wires. We demonstrate a new way to simulate the platelet arrow head structures that appear in some MoS2 samples and to investigate if the platelet-like structures show a special type of behavior (metallic, semiconductor or insulator) depending on how the cluster terminates Moor S-edge
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