A SURVEY OF ACETYLENE CYCLIZATION ON SINGLE-CRYSTALS, SUPPORTED PARTICLES AND BIMETALLIC SURFACES - NEW CYCLIZATION STUDIES ON BIMETALLIC PD W(211)/

A review of acetylene cyclotrimerization to form benzene is presented. This structure-sensitive catalytic reaction is of particular interest because C-C bonds can be formed readily on certain surfaces under ult ra high vacuum (UHV) conditions. In addition, we present new results f or acetylene cyclotrimerization on a bimetallic surface, Pd deposited on W(211). Pd on W is chosen because it is a morphologically unstable system and W(211) facets develop after annealing Pd/W(III) to greater than or equal to 700 K. Temperature programmed desorption (TPD) data r eveal negligible amounts of benzene detected from acetylene adsorption on clean W(211). A monolayer (ML) Pd film on W(211) decreases the hig h reactivity towards acetylene decomposition and catalyzes the cyclotr imerization reaction; benzene desorbs with TPD peaks at 210 K and simi lar to 470 K. The use of high resolution electron energy loss spectros copy (HREELS) has shown the desorption of benzene products to be react ion rate-limited on the similar to 1.0 ML Pd/W(211) surface. (C) 1998 Elsevier Science B.V.