Nanoparticle engineering for catalytic applications requires both a synthesis technique for the production of well-defined nanoparticles and measurements of their catalytic performance. In this paper, we present a new approach to rationally engineering highly active Ni–Mo–S nanoparticle catalysts for hydrodesulfurization (HDS), i.e., the removal of sulfur from fossil fuels.
Nanoparticle catalysts are synthesized by the sputtering of a Mo75Ni25 metal target in a reactive atmosphere of Ar and H2S followed by the gas aggregation of the sputtered material into nanoparticles. The nanoparticles are filtered by a quadrupole mass filter and subsequently deposited on a planar substrate, such as a grid for electron microscopy or a microreactor. By varying the mass of the deposited nanoparticles, it is demonstrated that the Ni–Mo–S nanoparticles can be tuned into fullerene-like particles, flat-lying platelets, and upright-oriented platelets. The nanoparticle morphologies provide different abundances of Ni–Mo–S edge sites, which are commonly considered the catalytically important sites. Using a microreactor system, we assess the catalytic activity of the Ni–Mo–S nanoparticles for the HDS of dibenzothiophene. The measurements show that platelets are twice as active as the fullerene-like particles, demonstrating that the Ni–Mo–S edges are more active than basal planes for the HDS. Furthermore, the upright-standing orientation of platelets show an activity that is six times higher than the fullerene-like particles, demonstrating the importance of the edge site number and accessibility to reducing, e.g., sterical hindrance for the reacting molecules.
Anders Bodin, Ann-Louise N. Christoffersen, Christian F. Elkjær, Michael Brorson, Jakob Kibsgaard, Stig Helveg and Ib Chorkendorff
NANOLetters, April 17, 2018
DOI:10.1021/acs.nanolett.8b00472
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