Low-temperature hydrodesulfurization of thiophene on Ni/Pt(111) bimetallic surfaces with monolayer Ni coverage

The low-temperature HDS of thiophene was investigated over Ni/Pt(111) bimetallic surfaces using Auger electron spectroscopy, temperature-programmed desorption, and low-energy electron diffraction. The reactivity of the bimetallic surface, with Ni coverages at approximately one monolayer (ML), was compared to those of a Pt(111) surface and thick Ni(111) film. All surfaces decomposed thiophene; however, Ni/Pt(111) and thick Ni(111) produced butene. More importantly, the desorption of butene from the monolayer Ni/Pt(111) surface occurred at a significantly lower temperature (similar to230 K) than that of the Ni(111) film (similar to280 K). In addition, the Ni/Pt(111) and Pt(111) surfaces also produced butadiene. The selectivity to produce C-4 hydrocarbon molecules on the Ni/Pt(111) surface remained similar to that of the Pt(111) surface. However, the overall activity toward the decomposition of thiophene increased from 0.053 thiophene per metal atom on Pt(111) to 0.077 thiophene per metal atom on the monolayer Ni/Pt(111) surface. The preadsorption of atomic hydrogen at liquid nitrogen temperatures on the ML bimetallic Ni/Pt surface further enhanced the activity toward the production of gas-phase butene by a factor of 2.2. We propose that this increase in the HDS activity on the monolayer Ni/Pt(111) surface results from the weak M-H bond, not seen on either pure metal surface. (C) 2002 Elsevier Science.