In this research, silicon carbide (SiC) has been confirmed to be catalytically active for the formation of polycyclic aromatic hydrocarbons (PAHs) from acetylene (C2H2). Aromatization reactions of C2H2wasexamined by gas-phase experiments in vacuo using α-SiC and β-SiC respectively, characterized with in situ time-of-flight mass spectrometry (TOF-MS)in which abundant information of intermediates was record-ed. The significance of this catalytic reaction lies in the fact that the reagents –acety-lene, the catalyst –SiC, and the PAH products are all coexisting in interstellar environment and this reaction indicates one of the possible channels for the formation of PAHs. Reaction products obtained were further confirmed by gas chromatography mass spectrometry (GCMS). The SiC catalysts were analyzed before and after the re-action using high-resolution transmission electron microscopy (HRTEM), X-ray dif-fraction(XRD) and derivative thermogravimetry (DTG).Results of experiments indicate that SiC catalyzes aromatization of C2H2starting from 400℃with activities dependent on temperature and notable difference has been observed between α and β crystal forms. For a long-time reaction at a particular temperature, the changes in productions of the four major PAH products, i.e. naphthalene, anthracene, phenan-threne and pyrene showed the transition from small PAHs to larger PAHs. Carbon deposition on the catalyst depends on temperature, which explains the deactivation of SiC catalyst at high temperatures. Based on experimental results, two new mechanisms for activation of acetylene on SiC that are closely connected with SiC surface dangling bonds have been proposed: 1)breakage of C-H bond by interaction of H with dangling bonds; 2) radical addition of hydrocarbon to form a surface ring structure which is then desorbed from the surface. Subsequent ring-growth process is suggested to follow the H abstraction / C2H2addition (HACA) mechanism. The activation effect of SiC dangling bonds was then extended to aromatization of propylene (C3H6) and propane (C3H8) starting from 650℃ and 750 ℃respectively in similar conditions. Comparison among reactions of C2H2, C3H6and C3H8provides further evidence for the proposed mechanism. / published_or_final_version / Chemistry / Master / Master of Philosophy

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In this thesis two studies of reactive metal adsorption upon a low index single crystal silicon dioxide surface are presented in addition to a study of sulphur adsorption upon a low index single crystal nickel surface. Chromium growth upon the a-quartz Si02(0001) (J84xJ84) Rll 0 surface is studied at three coverages, 0.25±O.08 ML, 0.5±O.16 ML and 1.0±0.33 ML, using surface extended x-ray absorption fine structure (SEXAFS). SEXAFS measurements, from the chromium K-edge, recorded at both grazing and normal incidence show that chromium growth proceeds via the formation of mesoscopic particles with a body centred cubic (b.c.c.) like structure having an average nearest neighbour Cr-Cr distance of 2.36±O.03 A. This represents a contraction of 5.6 % from the bulk b.c.c. lattice spacing of 2.49 A. There is no evidence of a surface reaction between chromium and the surface oxygen. SEXAFS was used to study titanium reactional growth on a-quartz (0001) (J84xJ84) Rll 0 and (lx1). Three nominal coverages were studied, 0.25±O.08 ML, 0.5±O.16 ML and 1.0±O.33 ML. Both normal and grazing incidence SEXAFS data were recorded and show the formation of a spatially extensive region in which an interfacial reaction has occurred between surface oxygen and adsorbate titanium atoms. Coupled with this is the formation of subnanometre titanium clusters. The metal oxide has nearest neighbour Ti-O distances close to those of both the anatase and rutile forms of titania with the metallic titanium clusters having a Ti-Ti distance within experimental error that of bulk hexagonal close packed (h.c.p.) titanium, 2.89 A. A re-examination of the surface geometry of Ni(1l0)c(2x2)S using SEXAFS has been performed. Data out to an electron wavevector of 9 A-I are analysed with a new code to assess the influence of multiple scattering. The first shell S-Ni distance is determined to be 2.20±O.02 A with the next nearest neighbour distance being 2.29±O.02 A, giving a top-layer Ni expansion of 14±3% relative to the bulk. The influence of multiple scattering does not significantly alter these values from earlier studies.

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Four topics are presented in this thesis. Firstly, a new design for a combinatorial electrochemical cell plate based on circuit board technology is described. The new combinatorial cell plate was tested using sputtered silicon and capacity as a function of mass was determined. The measured specific capacity was 3580 mAh/g, which corresponds to Li15Si4 stoichiometry. The irreversible capacity was measured to be less than 2% of the reversible capacity. This design reduced the spurious capacity that came from the lead pattern of the old plate. Second, the role of oxygen content on the electrochemical properties of sputtered Si1-xOx was investigated. All the prepared thin film samples had an amorphous or nanostructured nature. The measured specific capacity (first charge) suggests that Si1-xOx is made up of amorphous silicon that reacts reversibly with lithium, and SiO2 that forms inactive Li4SiO4 after the first lithiation. The current study shows that the irreversible capacity is directly proportional to the oxygen content. This study indicates clearly that in order to produce material with high capacity, oxygen should be minimized to reduce Li consumption during Li4SiO4 formation. However, the Si:O ratio should be optimized to get a reasonable active: inactive ratio. Third, a systematic study to investigate the effect of the addition of carbon on the electrochemical performance of the Sn-Si binary is reported. This study involved the preparation and investigation of three pseudobinary libraries. The addition of carbon was found to inhibit the aggregation of tin and reduce the two-phase coexistence regions as evidenced by smooth differential capacity plots. This was reflected in the improved electrochemical performance such as reversible capacity and cycleability. Fourth, an investigation of carbon-rich alloys of Fe1-xCx is reported. Both x-ray diffraction and 57Fe Mössbauer spectroscopy were employed to get insight into the structural properties of this system. X-ray diffraction revealed the amorphous or nanostructured nature of all samples with different Fe:C ratios. The distribution of hyperfine parameters extracted from the Mössbauer analysis shows the existence of two components suggesting that Fe exists in two distinct sites: (1) Fe surrounded with Fe neighbors and (2) Fe surrounded with C neighbors. The asymmetric environment was found more pronounced as carbon content increases in the films. This was reflected by high quadrupole splitting in excess of 1.0 mm/s.

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