Adsorption and reaction of 1,3-butadiene on Pt(111) and Sn/Pt(111) surface alloys

Temperature-programmed desorption (TPD), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED) were used to study the chemistry of 1,3-butadiene (H2C=CHCH=CH2, C4H6) on Pt(l 11) and p(2 x 2)Sn/Pt(l 11) and (root3 x root3)R30degrees-Sn/Pt(I 11) surface alloys. All chemisorbed 1,3-butadiene completely dehydrogenated to H, and surface carbon on Pt(1 11). Alloying Sn on Pt(1 11) can completely inhibit this decomposition and 1,3-butadiene reversibly adsorbs and desorbs from the two Sn/Pt(l 11) alloys under UHV conditions. The desorption activation energy of 1,3-butadiene on the (2 x 2) and (root3 x root3)R30degrees-Sn/Pt(I 11) surface alloys is 88 and 75 kJ/mol, respectively. These values are good estimates of the adsorption energies, and also place lower limits on the activation energy barrier for dissociating vinylic C-H bonds on the (2 x 2) and root3 surface alloys. Even though 1,3-butadiene is much more strongly chemisorbed than 1-butene (H2C=CHCH2CH3, C4H8) on the (2 x 2)-Sn/Pt(I 11) alloy, 1,3-butadiene is less reactive than 1-butene because there are no allylic beta-CH bonds in 1,3-butadiene as there are in 1-butene. (C) 2004 Elsevier B.V. All rights reserved.