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.

The indirect effects of biofuels and what to do about them:The case of grass biomethane and its impact on livestock

Grass biomethane surpasses the 60% greenhouse gas (GHG) savings relative to the fossil fuel replaced required by EU Directive 2009/28/EC. However, there are growing concerns that when the indirect effects of biofuels are taken into account, GHG savings may become negative. There has been no research to date into the indirect effects of grass biomethane; this paper aims to fill that knowledge gap. A causal-descriptive assessment is carried out and identifies the likely indirect effect of a grass biomethane industry in Ireland as a reduction in beef exports to the UK. Three main scenarios are then analyzed: an increase in indigenous UK beef production, an increase in beef imported to the UK from other countries (EU, New Zealand and Brazil), and a decrease in beef consumption leading to increased poultry consumption. The GHG emissions from each of these scenarios are determined and the resulting savings relative to fossil diesel vary between -636% and 102%. The significance of the findings is then discussed. It is the view of the authors that, while consideration of indirect effects is important, an Irish grass biomethane industry cannot be held accountable for the associated emissions. A global GHG accounting system is therefore proposed; however, the difficulty of implementing such a system is acknowledged, as is its probable ineffectualness. Such a system would not treat the source of the problem - rising consumption. The authors conclude that the most effective method of combating the indirect effects of biofuels is a reduction in general consumption. © 2011 Society of Chemical Industry and John Wiley & Sons, Ltd.

An investigation of the role of surface nitrate species in the oxidation of propene on a Pt-based diesel oxidation catalyst

Enhancing the low temperature activity of diesel oxidation catalysts is important for cold-start conditions and the possible importance of nitrate species in oxidation reactions has been proposed although definitive evidence has not been reported. To investigate the possible role of surface nitrates, their adsorption and reactivity on a Pt-based diesel oxidation catalyst have been investigated using the Short Time on Stream (STOS) transient kinetic technique. The results provide for the first time definitive evidence for the oxidation of propene by some of these nitrate-type species. © The Royal Society of Chemistry 2013.

Critical role of water in the direct oxidation of CO and hydrocarbons in diesel exhaust after treatment catalysis

CO and C3H6 oxidation have been carried out in the absence and presence of water over a Pd/Al2O3catalyst. It is clear that water promotes CO and, as a consequence, C3H6oxidation takes place at muchlower temperatures compared with the dry feed. The significant increase in the catalyst’s activity withrespect to CO oxidation is not simply associated with changes in surface concentration as a result ofcompetitive adsorption effects. Utilising18O2as the reactant allows the pathways whereby the oxidationdue to gaseous dioxygen and where the water activates the CO and C3H6to be distinguished. In thepresence of water, the predominant pathway is via water activation with C16O2and C16O18O being themajor species formed and oxidation with dioxygen plays a secondary role. The importance of wateractivation is further supported by the significant decrease in its effect when using D2O versus H2O.

Air pollutant contamination and acidification of surface waters in the North York Moors, UK: Multi-proxy evidence from the sediments of a moorland pool

Despite the extensive geographical range of palaeolimnological studies designed to assess the extent of surface water acidification in the United Kingdom during the 1980s, little attention was paid to the status of surface waters in the North York Moors (NYM). In this paper, we present sediment core data from a moorland pool in the NYM that provide a record of air pollution contamination and surface water acidification. The 41-cm-long core was divided into three lithostratigraphic units. The lower two comprise peaty soils and peats, respectively, that date to between approximately 8080 and 6740 cal. BP. The uppermost unit comprises peaty lake muds dating from between approximately ad 1790 and the present day (ad 2006). The lower two units contain pollen dominated by forest taxa, whereas the uppermost unit contains pollen indicative of open landscape conditions similar to those of the present. Heavy metal, spheroidal carbonaceous particle, mineral magnetics and stable isotope analysis of the upper sediments show clear evidence of contamination by air pollutants derived from fossil-fuel combustion over the last c. 150years, and diatom analysis indicates that the naturally acidic pool became more acidic during the 20th century. We conclude that the exceptionally acidic surface waters of the pool at present (pH=c. 4.1) are the result of a long history of air pollution and not because of naturally acidic local conditions. We argue that the highly acidic surface waters elsewhere in the NYM are similarly acidified and that the lack of evidence of significant recovery from acidification, despite major reductions in the emissions of acidic gases that have taken place over the last c. 30years, indicates the continuing influence of pollutant sulphur stored in catchment peats, a legacy of over 150years of acid deposition.