Supported palladium nanomaterials as catalysts for petroleum chemistry: 2. Kinetics and specific features of the mechanism of selective hydrogenation of phenylacetylene in the presence of carbon-supported palladium nanocatalyst

Abstract

The selective hydrogenation of phenylacetylene (PhA) into styrene (St) in the presence of a palladium nanocatalyst has been investigated. Salient features of this reaction have been revealed, such as independence of the PhA hydrogenation and St hydrogenation (after exhaustion of PhA) rates from the PhA and St concentrations, respectively; their nearly first-order dependence on the hydrogen pressure; and the first order in catalyst loading. The experimental results obtained according to a special plan have been processed using computer programs for various reaction mechanisms. It has been found that adequate description is achieved for the only scheme involving the adsorption one to two PhA and/or St molecules and one to two hydrogen molecules on the active site of the same type. The presence of one hydrogen molecule on the active site leads to the hydrogenation of PhA to St or St to ethylbenzene (EB). In the presence of two adsorbed hydrogen molecules, PhA is selectively hydrogenated to St and nonselectively hydrogenated directly to EB. It has been shown that the nature of the selectivity of the palladium catalyst is determined by the thermodynamics of competitive adsorption of PhA and St. The activation energies of the individual steps of the process have been determined.