NEXAFS identification of a catalytic reaction intermediate: C4H4 on Pd(111)

Hydrocarbon conversion on palladium catalysts

“…It has also been demonstrated, by adsorbing dichlorocyclobutene that benzene forms by reaction between acetylene and an intermediate having a stoichiometry C 4 H 4 [70,71]. Near-edge X-ray Adsorption Fine Structure (NEXAFS) results, in conjunction with theoretical analyses of these data, allow this species to be identified as a metallacycle [72]. The "template" effect of the hexagonal (1 1 1) face correctly orients the adsorbed C 2 H 2 and C 4 H 4 species to form benzene [21].…”

Mimicking Aspects of Heterogeneous Catalysis: Generating, Isolating, and Reacting Proposed Surface Intermediates on Single Crystals in Vacuum

“…134 (111) and Cu (110) to produce benzenesan observation which supports its role as an intermediate in acetylene trimerization to benzene on this surface. 134,135,358 In addition to these studies in which metallacycles have been generated via halohydrocarbon precursors, metallacycles have also been proposed as intermediates in the decomposition of thiophene on Pt, Ni, Rh, Ru, 6 in the decomposition of 1-butene on Pt(111), 337,338 and in the aromatization of cyclohexane on Pt(111). 359…”

Uptake of acetylene on cosmic dust and production of benzene in Titan's atmosphere

“…Jungwirthova and Kesmodel (2000) and Ramirez-Cuesta et al (1995)). In this case, cyclo-trimerization seems to occur through the rapid formation of the C4H4 metallocyclic intermediate species (Ormerod et al, 1993a;Pacchioni and Lambert, 1994;Ramirez-Cuesta et al, 1995). This species can then react with another adsorbed C2H2 species to form C6H6 (Hoffmann et al, 1992;Janssens et al, 1998;Ormerod et al, 1991;Patterson and Lambert, 1988;Patterson et al, 1989) or 2 C4H4 molecules react together to form cyclo-octatetraene (C8H8) which then thermally decomposes to yield C6H6 and C2H2 (Pacchioni and Lambert, 1994;Ramirez-Cuesta et al, 1995).…”

“…In contrast, cyclo-trimerization studies of C2H2 on palladium and copper surfaces have detected C4H4 by using techniques which directly probe the surface e.g. near-edge X-ray absorption fine structure (Ormerod et al, 1993b), laser-induced thermal desorption spectroscopy (Abdelrehim et al, 1995), temperature programmed reaction (Kyriakou et al, 2005), and sum frequency generation (Öberg et al, 2012).…”