Geoffrey C Bond

Selective Hydrogenation of Ethyne in Ethene‐Rich Streams on Palladium Catalysts. Part 1. Effect of Changes to the Catalyst During Reaction

The effect of various changes to the palladium catalyst during its stabilization in the course of the selective hydrogenation of ethyne‐ethene mixtures (formation of hydride and carbide phases and of carbonaceous deposits) was reviewed. The deposits in the form of a carbonaceous overlayer on the palladium surface create sites at which selective ethyne hydrogenation to ethene can occur. The carbonaceous deposit on the support increases the selectivity to ethane formation by increasing the rate of ethene hydrogenation on support sites (spillover of hydrogen from metal to the support surface) and by decreasing the effective diffusivity of ethyne in the pores.

Selective Hydrogenation of Ethyne in Ethene‐Rich Streams on Palladium Catalysts, Part 2: Steady‐State Kinetics and Effects of Palladium Particle Size, Carbon Monoxide, and Promoters

Developments in the last three decades of kinetics of selective hydrogenation of ethyne in ethene‐rich streams on palladium catalysts are reviewed. Most of the studies can be described comprehensively by a model that assumes carbonaceous deposits (i) create irreversibly on the palladium surface small A types of active site (selective to ethene) and large E types of active site (selective to ethane), and (ii) are involved in hydrogenation of ethene on E s sites on the support. The relative importance of these sites, with varying (i) reaction conditions, (ii) palladium dispersion, (iii) process modifiers, and (iv) promoters, is discussed.

The Use of Kinetics in Evaluating Mechanisms in Heterogeneous Catalysis

One of the major objectives of research in heterogeneous catalysis has been the correlation of catalytic performance with the structure and composition of the catalyst. Development of applicable general concepts has been slow, especially with supported metals, where numerous factors of the solid determine its ability to act catalytically. Progress is inhibited by the attention paid to the physical characterization of catalysts, while there is frequently an insufficiently detailed study of the reaction; a protocol is proposed to remedy this. Devising a mechanism based on measured kinetics allows the properties of the solid to be connected first to the mode of chemisorption of the reactants, and only then to the overall catalytic behavior.

Complete Catalytic Oxidation of Methane and Ethane Over Supported Platinum, Palladium and Manganese Oxide Catalysts

Activities of Pt, Pd and Pt + Pd catalysts (metal concentrations ≤ 0.4%) supported on γ-A12O3 and on TiO2 (anatase) for the complete oxidation of methane (300 ppmv) in air have been measured as a function of temperature; values of T10, T50 and T90 together with the Arrhenius parameters (activation energy and pre-exponential factor) are reported. Pt is less active than Pd when on TiO2, but more active when on γ-Al2O3, contrary to literature reports, but on both supports the Pt + Pd mixture is much more active than either metal separately, T10 for Pt + Pd/γ-Al2O3 being as low as 228°C. Possible reasons for this are briefly considered.