Neal Hickey

Automotive catalytic converters: current status and some perspectives

Automotive three-way catalysts (TWCs) have represented over the last 25 years one of the most successful stories in the development of catalysts. The aim of this paper is to illustrate the technology for abatement of exhaust emissions by analysing the current understanding of TWCs, the specific role of the various components, the achievements and the limitations. The challenges in the development of new automotive catalysts, which can meet future highly demanding pollution abatement requirements, are also discussed.

Effect of ZrO2 content on textural and structural properties of CeO2 / ZrO2 solid solutions made by citrate complexation route

Abstract Single phase homogeneous CeO 2 –ZrO 2 solid solutions with various compositions were synthesized using a citrate complexation route. Investigation of the sintering behaviour disclosed important modifications of the textural and, in particular, structural properties, which apparently create a strongly defective structure that could explain the unusual redox properties of these catalytic systems.

Promotion of reduction in Ce0.5Zr0.5O2: the pyrochlore structure as effect rather than cause?

Evidence is presented that the well-established phenomenon of promotion of Ce0.5Zr0.5O2 reduction by suitable treatment procedures may be controlled by adjusting the conditions; and that such reduction leads to the formation of the pyrochlore structure at extremely low temperature.

A comparative study of oxygen storage capacity over Ce0.6Zr0.4O2 mixed oxides investigated by temperature-programmed reduction and dynamic OSC measurements

The effects of redox-ageing on the temperature-programmed reduction and dynamic oxygen storage were investigated on two samples of Ce0.6Zr0.4O2 prepared under different synthesis conditions. It was observed that a high-temperature reduction/mild oxidation redox cycle can generate temperature-programmed reduction (TPR) profiles featuring a reduction peak at a temperature as low as 537 K. However, despite such favourable reduction behaviour, a strong deactivation of the oxygen storage is observed under dynamic conditions, indicating the limitations of the TPR method for investigation of oxygen storage.

Trans and cis influences and effects in cobalamins and in their simple models.

The interligand interactions in coordination compounds have been principally interpreted in terms of cis and trans influences and effects, which can be defined as the ability of a ligand X to affect the bond of another ligand, cis or trans to X, to the metal. This review analyzes these effects/influences in cobalamins (XCbl) and their simple models cobaloximes, LCo(chel)X. Important properties of these complexes, such as geometry, stability, and reactivity, can be rationalized in terms of steric and electronic factors of the ligands. Experimental evidence of normal and inverse trans influence is described in alkylcobaloximes for the first time. The study of simple B(12) models has complemented that on the more complex cobalamins, with particular emphasis on the properties of the axial L-Co-X moiety. Some of the conclusions reached for the axial fragment of simple models have also been qualitatively detected in cobalamins and have furnished new insight into the as yet unestablished mechanism for the homolytic cleavage of the Co - C bond in the AdoCbl-based enzymes.

Reactivation of aged model Pd/Ce0.68Zr0.32O2 three-way catalyst by high temperature oxidising treatment

A deactivated (aged under redox-cycled model TWC feed-stream) Pd/Ce(0.68)Zr(0.32)O(2) catalyst is remarkably reactivated when subjected to a high temperature oxidising treatment whereas this effect is only marginal for Pd/Al(2)O(3), which indicates the key role of such treatment in restoring the Pd-Ce(0.68)Zr(0.32)O(2) interactions leading to highly active catalysts.

Interactions of a water-soluble calix[4]arene with spermine: solution and solid-state characterisation

Abstract The octaanionic 5,11,17,23-tetrasulfonato-25,26,27,28-tetrakis(hydroxycarbonylmethoxy)-calix[4]arene (cone conformation) (C4TsTc) was investigated as a sensor for the biogenic tetracationic polyamine, spermine .(H4Spe4+). Fluorescence titration experiments of the water-soluble calixarene with spermine showed the formation of the 2:1 and 1:1 calixarene:spermine complexes in solution. The single crystal X-ray diffraction analysis of [(NaC4TsTc)4·(H4Spe)7] confirmed the formation of 2:1 and 1:1 calixarene:spermine species and showed that the water-soluble calixarene binds the spermine either by partially hosting it in the inner cavity or through the carboxylate groups on the lower rim. In order to investigate the effect of multivalent systems, supramolecular assemblies of octaanionic calixarene molecules templated by meso-tetrakis(4-N-methylpyridyl)porphyrin (H2T4) in different stoichiometric porphyrin:calixarene ratios (1:4 and 3:4) were also tested for spermine binding in solution. Fluorescence titration experiments with the 1:4 and 3:4 H2T4:C4TsTc supramolecular complexes showed that the multivalent assemblies are more sensitive to the presence of spermine than the calixarene alone.

Air Pollution from Mobile Sources: Formation and Effects and Abatement Strategies

An overview of the issue of air pollution from mobile sources is presented in the present chapter. The chapter is divided into three sections. The first section contains a general introduction on specific aspects of air pollution from internal combustion engines. The topics covered include a description of the primary and secondary pollutants formed and their adverse effects on health and the environment; the mechanisms of pollutant formation and, consequently, the factors which affect their formation; and a historical perspective of the legislative measures progressively introduced over the years. Finally, a brief description of the abatement strategies which may be generally adopted will be given (primary methods vs. secondary methods). The second section describes the state-of-the-art pollution abatement technologies for gasoline, lean-burn and diesel engines. The third section describes aspects related to pollution abatement in the marine sector. Air pollution abatement from ships is of high current interest due to the recent and ongoing introduction of legislation in the area. The specific problems associated with the marine sector are described, along with the strategies/technologies adopted to affront these problems. Historically, thanks in part to the success achieved, there has been a shift in emphasis of the focus of the problem, which has evolved from gasoline-fuelled engines, to diesel and lean-burn gasoline engines, to, more recently, off-road vehicles and marine engines. The present contribution will centre on the development of emission abatement from road vehicles, which have been largely responsible for the technological advances made in the field, and marine engines, which have recently become the subject of attention and can be considered to represent the challenge for the future. The situation regarding off-road vehicles will not be specifically considered as related solutions are derived from the above quoted areas. The contribution is based on a seminar held at the summer school of the International PhD in Environmental Science and Engineering, Cagliari, September 2008.

Trans and Cis Effects of Axial Fluoroalkyl Ligands in Vitamin B12 Analogues: Relationship between Alkyl- and Fluoroalkyl-Cobalamins

CF2HCbl, CF3Cbl , and CF3CH2Cbl have been synthesized and characterized in solution by (1)H NMR and UV-vis spectroscopy, and their X-ray crystal structures have been determined using synchrotron radiation. The structure of CF3CH2Cbl is reported for the first time, whereas those of CF2HCbl and CF3Cbl are re-examined to obtain more precise structural data. Comparison of the structural data obtained with the alkylcobalamin analogues, MeCbl and EtCbl, indicates that the Co-C and Co-NB3 bond lengths are shorter in the fluoroalkylcobalamins. The structural data of the fluoroalkylcobalamins previously reported in the literature had been conflicting in this regard. Thus, a much less dramatic shortening of the two axial bonds was found for CF3Cbl, whereas in the case of CF2HCbl, the Co-NB3 bond length is shorter than in MeCbl. Direct comparison of the structures of CF3CH2Cbl and EtCbl indicates a large distortion of the axial fragment in the former case that can be attributed to steric effects. A number of previously reported correlations of the effect of the β-ligand on the structure and properties of cobalamins are re-examined in light of the present results. Particular emphasis is placed on the axial fragment. This analysis substantially confirms and, with the new data reported here, adjusts and expands the data set for correlations between trans and cis influences of the β-ligand of cobalamins and their structure (Co-X and Co-NB3 distances and corrin fold angle) and properties (UV-vis spectra, NMR spectra, and pK(base-off)).

Selective Binding of Spherical and Linear Anions by Tetraphenyl(thio)urea-Based Dihomooxacalix[4]arene Receptors

Three novel tetra(thio)ureido dihomooxacalix[4]arene anion receptors (phenylurea 4a, phenylthiourea 4b, and tert-butylurea 4c) were synthesized and obtained in the cone conformation in solution, as shown by NMR studies. The X-ray crystal structure of 4c is reported. The host-guest properties of these receptors toward several anions were investigated by 1H NMR titrations. Phenylurea 4a displayed a very efficient binding toward the spherical F- and Cl- anions, and the linear CN- (log Kass = 3.46, 3.50, and 4.02, respectively). In comparison to related bidentate phenylurea dihomooxacalix[4]arenes, tetraphenylurea 4a is more preorganized and the higher number of hydrogen bond donor sites provides a remarkable enhancement of its binding efficiency.