Leeds reports

A. R. Leeds reported that a soln. of ammonium chloride forms white flecks on standing a couple of years, but it is not clear whether this was not caused by the action of the soln. on the glass. Soln. of ammonium chloride, says G. Gore, are decomposed in contact with finely divided silica. A. Bineau (1838), J. S. Stas (1865), and H. B. Baker (1894) have reported that vessels made of soft, blit not hard, glass are etched by the vapour of ammonium chloride, and F. W. Clarke has found that ammonium chloride exerts a marked action on silicates at about 350° this also is exemplified by J. L. Smith s process for the determination of alkalies in silicates. The corrosive action of ammoniacal vapours on the exposed... 

J. E. Saxton, Department of Organic Chemistry, University of Leeds Reporters... 

One series of publications initiated at the University of Leeds gives complete reviews on selected groups of reactions. They are referred to in this chapter as Leeds reports. ... 

Because of the relative simplicity of this system (8 species, at most about 40 relevant elementary steps), it is possible to give a complete picture of the reactions involved. Since complete reviews have been given by Baulch et al (1972), in this chapter only results published after 1972 are discussed, together with the recommendations given in this Leeds report. 

The scatter of the data for H + O2 OH + O given in the Leeds report (Baulch et a/., 1972) is considerable, corresponding to a factor of about 6 at flame temperatures. Because of this scatter, it was impossible to decide whether there is non-Arrhenius behavior of the temperature dependence of the reaction under consideration (as is clearly the case for O -f H2 and OH -1- H2, see below and Chapter 3). New measurements done after 1972 improve this situation (Fig. 5). Especially, the expression given by Schott (1973) results from direct and sensitive measurements. Extrapolation of his expression to lower temperatures, however, leads to incompatibilities with reliable data. The recommendation given by Dixon-Lewis (1983) provides a close match to these data. The higher values given by the Leeds expression at flame temperatures are supported by some indirect but reliable flame modeling studies. 

Since this reaction is the reverse of H + O2 OH -h O, it distinctly inhibits high-temperature combustion, and there is a moderate sensitivity of flame propagation to its rate coefficient (Fig. 4). Measurements are available only below 425 K. However, it is reasonable to assume zero activation energy for this exothermic radical-radical reaction. This leads to a temperature-independent rate coefficient of 1.8 x 10 cm /mol s (Fig. 6), in agreement with the Leeds report low-temperature recommendation (2 X 10 cm /mol s) and, roughly, with the rate coefficient determined from the reverse reaction and the equilibrium constant. 

The scatter of the data given in the Leeds report is small enough to detect non-Arrhenius behavior of the temperature dependence of this rate coefficient (Chapter 3). The recommended expression differs slightly from the Leeds report recommendation (Fig. 7). 

The scatter of the rate data in the Leeds report was too large to allow definite identification of non-Arrhenius behavior of the temperature dependence of the rate coefficient of this reaction. However, this is now possible taking into consideration measurements published after 1972 (Fig. 8 and Chapter 3). 

Again, these reactions are relatively unimportant for high-temperature combustion because of the slow H2O2 formation rate. Data for H 4 H2O2 and OH + H2O2 are presented in Figs. 20 and 21, since the rate coefficients of the Leeds report cannot be recommended any longer. 

No direct measurements are available for this reaction. The rate coefficient recommended in the Leeds report is taken here it was determined from the rate coefficient of the reverse reaction and the equilibrium constant. 

There are many studies of CO + OH CO 2 + H reported in the literature, reviewed by Baulch et al (1976) and in Chapter 3. Figures 24 and 25 present the Leeds report recommendation together with results published after 1976. Most of these studies were done at low temperature, motivated by the importance of this reaction for atmospheric chemistry. There is a definite pressure dependence of the low-temperature rate coefficient (Butler et al, 1978 Chan et al, 1977 Overend and Paraskevopoulos, 1977a), which may be coupled to the presence of trace amounts of oxygen (Biermann et al, 1978). At high temperature this complex formation should be unimportant. Nevertheless, there is need for more precise data over 1000 K, especially in view of the non-Arrhenius behavior. 

These reactions are too slow to play a considerable part in flame propagation. The recommended expressions are taken from the Leeds report (Baulch et al, 1976). 

Figure 14.2 Cyclic base voltainmograms of Ru(OOOl) in 0.1 M HCIO4, 50mVs scan range 0.1-1.05 V (solid line) and —0.12 —1.05 V (dotted Une). Also indicated are LEED patterns reported in [Zei and Ertl, 2000] after emersion at 0.35, 0.75, and 1.2 V and anodic charges per surface atom transferred at different potentials according to El-Aziz and Kibler [2002].

Similar studies6 were reported for the chemisorption of nitric oxide at Rh(lll) with at 10 8 Torr a (2x2)-3NO structure, previously reported by LEED with a different structure with a (3 x 3) periodicity observed above 10 2 Torr (Figure 7.5). The latter has an apparent height of 0.1 nm above the (2 x 2) structure, suggesting that a distortion has occurred of the top surface layer of... 

The group at Aarhus have reported carbon-induced structures at Ni(lll) and Ni(110) surfaces resulting from the dissociation of ethylene at high temperatures.27 Between 400 and 500 K, the Ni(l 10) surface is seen to form two carbidic structures with (4 x 3) and (4 x 5) domains present arising from surface reconstruction with substantial transport of nickel taking place. At higher temperatures (560 K), the surface becomes dominated by the (4 x 5) structure, which is well ordered and can be observed clearly by LEED. Ion scattering studies provide additional information which enables models to be constructed for both the (4 x 3) and (4 x 5) phases. 

Perdereau and Oudar s early paper20 reported LEED patterns and surface concentration data for the (111), (100) and (110) surface planes. For Ni(lll) a sequence of structures was observed starting with p(2 x 2), changing to ( /3 x v/3) 30° with increasing sulfur concentration and finally to a structure labelled SBAII , which Edmonds et al,21 identify as a (5 /3 x 2) structure. The low-concentration structures agree well with a model involving sulfur... 

Grant-Muller S (2004) Study of Policies regarding Economic Instruments Complementing Transport Regulation and the Undertaking of physical Measures (SPECTRUM) deliverable 6. The report can be downloaded from http //www.its.leeds.ac.uk/projects/spectrum/downloads/ D6.pdf... 

Prior to the publication in 1980 of Clavilier s historic paper (1) reporting anomalous voltammetry of Pt(lll), there had been a number of studies of the voltammetry of single crystal Pt electrodes, with some using modern methods of surface analysis (e.g., LEED or RHEED) for characterization of the structure of the crystal prior to immersion in electrolyte (2-6). and all were in qualitative agreement with the seminal work (in 1965) on Pt single crystals by Will (7.). 

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