The Reactivity of Surface Defects on the MoS2(0001)
Basal Plane: Methanethiol Reactivity Studies
Christopher G. Wiegenstein and Kirk H. Schulz
Department of Chemical Engineering
Michigan Technological University
Houghton, Michigan 49931
Electronic Mail: khschulz@mtu.edu
Submitted to:
Molybdenum disulfide (MoS2) based materials are important industrial catalysts for the
removal of aromatic organosulfur compounds from petroleum feedstocks. The removal
of sulfur compounds is important since sulfur is both a known catalyst poison and an
environmental pollutant. Although there have been significant amounts of study on the
structure of the industrial hydrodesulfurization catalysts, there is still a significant amount
of uncertainty as to the surface chemistry and reactivity of organosulfur compounds on
the catalyst surface. The high pressures used in commercial HDS reactors hinder
experimental studies on surface intermediates and adsorbate structures on industrial
catalysts. A frequently used approach to gain insight into possible surface reaction
pathways and intermediate species is to use highly characterizable single crystals as
model catalysts.
MoS2 grows large sheets of sulfur terminated <0001> planes which are not catalytically
active towards aromatic organosulfur compounds such as thiophene. Wiegenstein and
Schulz (Surface Science, 396 (1998) 284) attempted to prepare basal surfaces with large
defect densities using deuterium adsorption but were not successful. Although defects
were produced via the extraction of surface sulfur by adsorbed deuterium, no significant
changes were observed in the reactivity of ethanethiol on surfaces prepared by repeated
exposures to atomic deuterium.
However, reactive MoS2(0001) surfaces have been prepared using short ionbombardment times. Three different surface preparation treatments were used: a freshly
cleaved surface; a 30-second ion-bombarded surface; and a 60-second ion-bombarded
surface. On all surfaces, two major desorption features were observed, with desorption
temperature ranges of 110-140 K and 280 - 350 K. An increase in the
population of the higher temperature state was observed as ion-bombardment time was
increased. AES results demonstrated that surface sulfur was preferentially removed via
ion-bombardment, and thus, the higher temperature state has been identified as arising
from methyl-thiolate adsorption at defect sites thought to be sulfur vacancies.
This paper will give the details of these studies, and will address the usefulness of the
defective basal plane as a model HDS catalyst.