TAP studies on 2% Ag/gamma-Al2O3 catalyst for selective reduction of oxygen in a H-2-rich ethylene feed

Catalysts currently employed for the polymerization of ethylene have previously been found to deactivate in the presence of oxygen. It is, therefore, important that oxygen is removed from the ethylene feedstock prior to the polymerization. The Ag/gamma-Al2O3 catalyst exhibits excellent activity and selectivity toward oxygen reduction with hydrogen in the presence of ethylene. TAP vacuum pulse experiments have been utilised to understand the catalytic behaviour of the Ag/gamma-Al2O3 catalyst. TAP multi-pulse experiments have determined the types of active sites that are found on the Ag/gamma-Al2O3 catalyst, and the intrinsic activity of these sites. The lifetime of the reactive adsorbed oxygen intermediate has also been determined through TAP consecutive pulse experiments. Multi-pulse and consecutive pulse data have been combined with ethylene adsorption/desorption rate constants to provide an overview of the Ag/gamma-Al2O3 catalyst system.

Dramatic solvent effects on ring-opening metathesis polymerization of cycloalkenes

A series of metathesis polymers and copolymers have been formed and their structures were analysed by C-13 NMR spectroscopy. Noble metal and non-noble metal salt catalysts are distinguished by their behaviour in various solvents. Thus, in phenolic solvents, the former class produce alternating copolymers from cyclopentene and norbornene, while the latter are unaffected and produce random copolymers. In contrast, ether solvents have the effect of markedly increasing the cis content of polymers from the latter catalysts while the former are unaffected.

Performance and characteristics of platinum, palladium/rhodium and palladium automotive catalysts when subjected to ethanol, acetaldehyde and a synthetic E85 exhaust gas mixture

The performance optimisation of automotive catalysts has been the focus of a great deal of research for many years as the automotive industry has endeavored to reduce the emission of toxic and pollutant gases generated from internal combustion engines. Just as the emissions from diesel and gasoline combustion vary so do the emissions from combustion of alternative fuels such as ethanol; the variation is in both quantity and chemical composition. In particular, when ethanol is contained in the fuel, ethanol and acetaldehyde are present in the exhaust gas stream and these are two compounds which the catalytic converter has not traditionally been designed to manage. The aim of the study outlined in this paper was to assess the performance of various catalyst formulations when subjected to a representative ethanol exhaust gas mixture. Three automotive catalytic converter formulations were tested including a fully Pt sample, a PdRh three-way catalyst sample and a fully Pd sample. Initially the samples were tested using single component hydrocarbon light-off tests followed by a set of tests with carbon monoxide included as an inlet gas to observe its effect on each individual hydrocarbon oxidation. Finally, each formulation was tested using a full E85 exhaust gas mixture. The study was carried out using a synthetic gas reactor along with FTIR and FID exhaust gas analysers. All formulations showed selectivity toward acetaldehyde formation from ethanol dehydrogenation which resulted in negative acetaldehyde conversion across each of the samples during the mixture tests. The fully Pt sample was the most detrimentally affected by the introduction of carbon monoxide into the gas feed. The Pd and PdRh samples exhibited a tendency toward acetaldehyde decomposition resulting in methane and carbon monoxide formation. The Pt sample did not form methane but did form ethylene as a result of ethanol dehydration.

Selective hydrogenation of acetylene in ethylene rich feed streams at high pressure over ligand modified Pd/TiO2

The selective hydrogenation of acetylene from ethylene rich streams was conducted at high pressure and in the presence of CO over two 1 wt% loaded Pd/TiO2 catalysts with differing dispersions. Although, the more poorly dispersed sample did not result in high acetylene conversion only a small proportion of the total available ethylene was hydrogenated to ethane. The more highly dispersed sample was able to remove acetylene to a level below the detection limit but this was at the expense of significant proportion (ca. 30%) of the available ethylene. Modification of the catalysts by exposure to triphenyl phosphine or diphenyl sulfide and subsequent reduction at 393 K led to improved performance with increased conversion of acetylene and decreased propensity to hydrogenate ethylene resulting in an overall net gain in ethylene. The higher dispersed sample which had been ligand modified provided the best results overall and in particular for the diphenyl sulfide treated sample which was able to completely eliminate acetylene and still obtain a net gain in ethylene. The differences observed are thought to be due to the creation of appropriate active ensembles of Pd atoms which are able to accommodate acetylene but have limited ability to adsorb ethylene. Sub-surface hydrogen formation was suppressed, but not eliminated, by exposure to modifier.

Topochemical polymerization in self-assembled rodlike micelles of bisurea bolaamphiphiles

Rod-like micelles, formed from bolaamphiphiles with oligo(ethylene oxide) hydrophilic outer segments and a hydrophobic segment with diacetylene flanked by two urea moieties, were covalently fixated by topochemical photopolymerization to high degrees of polymerization by optimizing the hydrophobic core and the hydrophilic periphery of the bolaamphiphiles. Analysis of the polymerized product with dynamic light scattering in chloroform showed degrees of polymerization of approximately 250. Cryo-TEM of bolaamphiphiles before and after UV irradiation showed that the morphology of the rods was conserved upon topochemical polymerization. © 2014 The Royal Society of Chemistry.

Selective Hydrogenation of Acetylene over Pd-Boron Catalysts: A Density Functional Theory Study

Boron-modified Pd catalysts have shown excellent performance for the selective hydrogenation of alkynes experimentally. In the current work, we investigated the hydrogenation of acetylene on boron-modified Pd(111) and Pd(211) surfaces, utilizing density functional theory calculations. The activity of acetylene hydrogenation has been studied by estimating the effective barrier of the whole process. The selectivity of ethylene formation is investigated from a comparison between the desorption and the hydrogenation of ethylene as well as comparison between the ethylene and the 1,3-butadiene formation. Formation of subsurface carbon and hydrogen on both boron-modified Pd(111) and Pd(211) surfaces has also been evaluated, since these have been reported to affect both the activity and the selectivity of acetylene hydrogenation to produce ethylene on Pd surfaces. Our results provide some important insights into the Pd B catalysts for selective hydrogenation of acetylene and also for more complex hydrogenation systems, such as stereoselective hydrogenation of longer chain alkynes and selective hydrogenation of vegetable oil.

A DFT study of the transition metal promotion effect on ethylene chemisorption on Co(0001)

Transition metals are often introduced to a catalyst as promoters to improve catalytic performance. In this work, we study the promotion effect of transition metals on Co, the preferred catalytic metal for Fischer-Tropsch synthesis because of its good compromise of activity, selectivity and stability, for ethylene chemisorption using density functional theory (DFT) calculations, aiming to provide some insight into improving the alpha-olefin selectivity. In order to obtain the general trend of influence on ethylene chemisorption, twelve transition metals (Zr, Mn, Re, Ru, Rh, It, Ni, Pd, Pt, Cu, Ag and Au) are calculated. We find that the late transition metals (e.g. Pd and Cu) can decrease ethylene chemisorption energy. These results suggest that the addition of the late transition metals may improve alpha-olefin selectivity. Electronic structure analyses (both charge density distributions and density of states) are also performed and the understanding of calculated results is presented. (C) 2009 Elsevier B.V. All rights reserved.