Correlating mechanical strain with low-temperature hydrogenation activity on submonolayer Ni/W(110) surfaces

In the current paper we report a unique low-temperature hydrogenation pathway on submonolayer Ni/W(I 10) surfaces, which does not occur on either clean W(I 10) or on Ni/W(I 10) surfaces with Ni coverages greater than one monolayer (ML). Cyclohexene (c-C6H10) is used as a probe molecule to investigate the hydrogenation activity of Ni films deposited on a W(I 10) surface. Using Auger electron spectroscopy (AES), temperature-programmed desorption (TPD), low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and high-resolution electron energy loss spectroscopy (HREELS), we have studied the reaction products and the bonding mechanisms of cyclohexene on various Ni/W(I 10) surfaces. On a clean W(I 10) surface, cyclohexene molecules undergo decomposition without producing the hydrogenation product, cyclohexane (c-C6H12). In contrast, a low-temperature (237 K) hydrogenation pathway is detected after the W(I 10) surface is covered with submonolayer coverages of Ni. The maximum hydrogenation activity occurs at approximately 0.4 ML Ni, which corresponds to a Ni coverage regime with high values of tensile strain on the Ni/W(110) bimetallic surfaces.