A DRIFT spectroscopic study of acetylene adsorbed on metal oxides

Abstract

oxides was studied. Two main types of acetylene adsorption complexes were found: first, complexes formed by weak reversible adsorption at O 2À sites and basic OH groups and, second, stable complexes formed by the dissociative adsorption of acetylene at Me d+ -O dÀ pairs with the formation of acetylide species. The position of the C-H band in weakly adsorbed complexes and C= =C bands in strongly adsorbed complexes can be used for the sensitive characterization of oxide basicity. The measurements performed at elevated acetylene pressures (10-20 Torr) give information on the total basicity of oxides, whereas the analysis of the complexes formed at low pressures ($0.2 Torr) characterizes the properties of specific absorption sites. The interaction of acetylene with surface sites was mainly reversible; however, the products of acetylene oligomerization could be observed in the long-term experiments.

On the Redox Mechanism Operating along C2H2 Self-Assembly at the Surface of TiO2

“…The same reaction, by the way, has been observed also in the case of alumina, an oxide, similar to TiO 2 in terms of acid−base properties. 22,32 The role of the initial C−H dissociative absorption in the whole process is further proved by the experiments of propyne absorption showing a marked reduction of the self-assembling reactivity at the TiO 2 surface. In this compound in fact, one of the acetylenic hydrogens is substituted by a less acid methyl group lower having propensity for the heterolytic dissociation.…”

Sites for the selective hydrogenation of ethyne to ethene on supported NiO/Au catalysts

“…As a result, the positive contribution of hydrogen from hydroxyl groups to the hydrogenation decreases. The metal cations of the supports are of importance in the adsorption and activation of reactants [39,40]. It was suggested that cooperation of coordinatively unsaturated Au atoms and the acid-base pair site (Al (Figs.…”

“…Ethyne and ethene are Lewis bases sensitive to electron acceptors [4,5,40]. An increase in the surface positive charge on Au due to electron transfer [7] improves the electron acceptor properties of gold and thereby should lead to stronger adsorption of ethyne or ethene on Au δ+ than on Au 0 and, therefore, increase the probability of the chemical reaction.…”

Acetylene oligomerization on the surface of TiO2: a step forward in the in situ synthesis of nanostructured carbonaceous structures on the surface of photoactive oxides

“…29 Concerning the doublet of weak bands at ca. 1690 and 1618 cm -1 (Figure 1), they are in a region where conjugated double bonds are expected to fall, although they do not find exact correspondence with those of the polyacetylenic species reported by Rives-Arnou and Sheppard 14 on TiO 2 or by some of us in zeolites (where they have carbocationic character).…”