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Zeolite catalysts were prepared by carrying out an ion-exchange process of transition metals and impregnation to incipient-wetness method of metal catalyst using a chlorine free gold precursor, KAu(CN)2. The instability of Au/Y (3.74wt%Au) resulted in low CO oxidation activity (~ 18 % conversion at 450 0C), suggesting that the reduced gold metal atoms are bound to the zeolite by a weak interaction. This is subject to migration within the passages of the zeolite during use. The presence of proton stabilized most of Au clusters (electron deficient species) within the HY zeolite, resulting in small amounts of gold species migrating to the outer surface. Interestingly the CO oxidation activity of Au/HY is half that of Au/Y, which clearly indicate that the presence of metallic gold plays a significant role during CO oxidation. The loading of Au/M-Y (M = Ni2+, Fe3+, Co2+ or Cr3+) were varied from 1.67- 7.48wt%Au and from 1.76-5.45wt%M. Modification of this Y structure with transition metals has been found to be beneficial for both activity and stability of smaller gold clusters, by strengthening the interaction between gold and zeolite exchange sites and by large magnitude in maintaining the dispersion of gold. This suggests that the unreduced chromium ions function as a chemical anchors for reduced Au metal and that the reduced atoms of gold may form small clusters with the anchoring metal. TPR profile has confirmed that the introduction of 1.67wt%Au on Fe-Y (1.88wt%Fe) increased the stability of Fe ions as stabilizer metal. However, as the gold loading of Au/Fe-Y catalyst increases the TPR profile shows that the stability of Fe ions decreases and hence the activity of catalysts. An increase in transition metal content, above 1.88wt%Fe was found to lower the CO oxidation activity. A TPR profile has confirmed that as the reduction potential became more negative, the activity of supported Au increases following the sequence: Ni2+, 0.23 << Fe3+, -0.41 < Cr3+, -0.56. The estimated particle sizes of gold by X-ray diffraction were found to be ~ 12 nm for Ni2+, ~ 7 nm for Fe3+, and ~ 5 nm for Cr3+ stabilized metal. Samples of Au/HY (3.77wt%Au) have been prepared by an ion-exchange method using Au(III) ethylenediamine complex-ions, [Au(en)2]3+. Following a pretreatment in an O2 atmosphere, the catalyst showed the existence of an induction period before reaching a steady state activity; suggesting the need for activating gold prior to catalyzing CO oxidation reaction. As-prepared catalyst contained 85% of gold in the Au3+ valence state as confirmed by Mössbauer spectroscopy. The catalyst was treated with various reducing agents (such as NaBH4); to yield stable and active smaller gold clusters (< 2 nm) inside the HY cavities, as revealed by X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD) and Uv- Vis Spectrophotometer. DRIFTS revealed that electron-deficient particles (Auó+- CO species) of gold clusters, inside the HY framework and in contact with protons are active species for CO oxidation. CO activity and formation of smaller gold clusters depends on the nature and molar ratio of reducing agents, and the source of gold. The induction period observed for unreduced Au catalyst is a slow step in the activation of gold active sites. Treatment of Au/Y (3.46wt%Au) with sodium borohydride enhanced the activation of gold active species and hence improves the catalytic activity. The NaBH4 treated Au/Y (3.73wt%Au) catalyst has shown, for the first time, activity of approximately 28% CO conversion. The catalyst showed almost the same activity and induction period as that of the untreated Au/HY (3.77wt%Au) catalyst, which leaves much to be investigated about the behaviour of Au on Y zeolite upon treatment with a proper reducing agent. The protons have been found to stabilize the smaller Au nanoparticles within the zeolite cavities. The modification of zeolite-Y was carried out by treatment with different alkali metal nitrates such as LiNO3, NaNO3 and KNO3 before introducing gold from different sources, (i.e. gold ethylenediamine complex ion, Au(en)2Cl3; chloroauric acid, HAuCl4; or potassium dicyano aurate, KAu(CN)2 complex). The CO oxidation activity of the catalysts was found to depend on the nature of the gold source and on the type of alkali metal nitrate used. The order of activity was as follows: HAuCl4 >> KAu(CN)2 > Au(en)2Cl3. It was found that the activity of catalysts prepared by deposition of Au from an aqueous solution of chloroauric acid on Na-modified zeolites-Y, increased as a result of an increase in the amount of Au deposited as confirmed X-ray fluorescence spectroscopy (XRF). The Kmodified zeolite-Y had a smaller amount of Au deposited (i.e. Au/KY, 0.454wt%Au; Au/NaY, 0.772wt%Au and Au/LiY, 0.212wt%Au) and hence the CO oxidation activity was lower than that of Na-modified zeolites-Y. Thus, the order of the catalytic activity is as follows: Na > K > Li. The XRD studies have revealed that metallic gold particles sizes do not depend on the nature of alkali metal nitrates used to modify the zeolite-Y surface and the zeolite-Y crystallinity has been maintained. Monometallic Au/NaY (0.772wt%Au, treated with NaNO3) was found to be active in ethylene hydrogenation with ~5% conversion. Treatment of catalysts with NaBH4 was found to lower the catalytic activity of the catalysts, contrary to activities observed on CO oxidation and these concluded that cationic gold are responsible for the observed activity. The activity was found to depend on the source of Au used, and the order is as follows; HAuCl4 >> KAu(CN)2 > Au(en)Cl3. Bimetallic catalysts of Au/M-Y (where Au represent gold from KAu(CN)2, and M = Ni2+, Fe3+, or Cr3+) were found to be more active compared to monometallic catalysts due to promotional effect of transition metal. The order of activity of the bimetallic system at 260 0C was as follows; Ni2+ >> Fe3+ > Cr3+, and at 150 0C, was Ni2+ >> Cr3+ > Fe3+, contradicting the order of activity observed on CO oxidation. Formation of carbonaceous deposits on the surface of the catalyst at temperature higher than 260 0C has been confirmed. Cu modified Au/TiO2 (anatase, 200m2/g) has been prepared by incipient-wetness method by either introducing the modifier, before or after Au loading. Such catalysts were found to give high and stable activity for the water-gas shift (WGS) reaction, when compared to unmodified Au/TiO2 catalysts. It has been suggested that an increase in activity on modified Au/TiO2, is mainly due to the existence of a synergetic interaction between Cu and Au, since the activity of both Cu/TiO2 and Au/TiO2 is lower than that of bimetallic system. The presence of nitrates on Cuc-Au/TiO2 (c Cu precursor is Cu(NO3)2*2.5H2O) has been found to be detrimental to the activity of Au on TiO2; due to the poisoning of Au active sites and enhancement of Au agglomeration by NO2 - formed during the reaction. An increase in Cu loading lowers the activity of Au. A XANES spectrum has confirmed that gold exists as either Au+/Au0 during WGS reaction and Cu exists as copper ions (Cu+/Cu2+) before and during WGS reaction. Formation of bimetallic particles was not detected by EXAFS data analysis. The observed effects are interpreted as a mutual influence of gold and copper ions and reduced species of gold and copper due to their competing for ion exchange sites. Cu has no promotional effect on low temperature CO oxidation and on preferential CO oxidation in excess of hydrogen.

Student Number : 9502913H - PhD thesis - School of Chemistry - Faculty of Science / Alkyl-transfer (transalkylation, disproportionation) reactions of alkylaromatics were studied for the purpose of finding out the principles that governs them. Alkyl-transfer of simpler alkylaromatics ranging from mono to polyalkyl-benzenes and alkylnaphthalenes were studied in a fixed bed reactor system on solid acid catalysts (zeolites) at temperatures up to 400 °C. Results showed that alkyl-transfer reactions are reversible reactions with disproportionation favoured at lower temperatures while transalkylation seemed to be dominant at higher temperatures. The outlined mechanism showed that the catalyst pore sizes and the type of pores as well as the feed composition of binary mixtures play important roles in the transfer of alkyl groups between aromatic molecules. In alkyl-transfer reactions, the ease of conversion depends on the number of alkyl groups on the aromatic ring/s, the chain length, the type of alkyl substituent/s and the ring conjugation of the aromatic moiety. Zeolitic catalysts are rapidly deactivated by carbonaceous material deposition during alkyl-transfer reactions especially at higher temperatures while deactivation through molecular retention is dominant at lower temperatures. Nevertheless, zeolites can be regenerated by high temperatures in oxidizing atmospheres. Bulkier alkylaromatics (those found in coal and petroleum liquids) can be transformed through alkyl-transfer reactions if a suitable catalyst with the required strength and appropriate pore sizes can be developed, preferably a tri-dimensional arrangement as shown by the results of this study. Thus the alkyl-transfer process has promising future applications in petrochemical and related industries; especially those interested in the transformation of coal to chemicals.

Thesis (Ph.D.)--University of Delaware, 2005. / Principal faculty advisor: Raul F. Lobo, Dept. of Chemical Engineering. Includes bibliographical references.

<p>The objectives of this project was to ameroliate two waste materials, namely Acid Mine Drainage and Fly Ash and recover the solid residues for conversion into an adsorbent to treat brine. The solid residues were then converted into zeolite P through low temperature hydrothermal treatment. The adsorption capacity of the solid residues, zeolite P derived from the solid residues was compared to the commercial zeolite Y and fresh Arnot fly ash. The quality of the resulting water was assessed using different analytical methods before the reaction with adsorbents and after the reaction and a comparison was done based on the removal efficiency of elements Zeolite P from solid residues was successfully synthesized as confirmed by XRD, BET and FTIR. Brine treatment with fly ash, solid residues, zeolite P and commercial zeolite Y adsorbents was done concentration on the following major elements Na, K, Mg, Ca and Si. Zeolite P had higher or similar removal efficiency that the commercial zeolite Y for the following elements K, Ca and Mg. Fly ash is the only adsorbent that managed to reduce the concentration of Na in brine and also had a good removal efficiency of Mg. Si leached out of all the adsorbents which could be ascribed to Si being the major component of these adsorbents which could indicate some dissolution of these adsorbents under the conditions tested. Overall, zeolite P did not completely remove the major elements, especially for Na, but did result in a cleaner waste stream which would improve brine processing.</p>

A study on middle distillate hydrotreatment zeolite catalysts containing Pt/Pd and/or Ni was performed. The effect of the addition of the corresponding CoMo, CoMoPd, CoMoPtPd and CoMoNi in PdNiPt-zeolite, Pt-zeolite, Ni-zeolite, and PdPt-zeolite was studied. The catalysts were characterized physically and chemically by methods and techniques such as Brunauer-Emmett-Teller (BET), Barret-Joyner-Hallenda (BJH), and neutron activation analysis. The structures of the Ni and Pt containing zeolite were studied by X-ray Photoelectron Spectroscopy (XPS). An experimental apparatus was constructed to investigate the activity of the experimental catalysts. The catalysts activity measured in terms of conversion of dibenzothiophene (DBT), substituted dibenzothiophenes (sDBT) and phenanthrene as well as molar-averaged conversion was evaluated in a continuous flow Robinson Mahoney reactor with stationary basket in the hydrodesulfurization and hydrogenation of heavy gas oil which contains sulphur refractory compounds such as 4- methyldibenzotiophene (4-MDBT) and 4,6- dimethyldibenzothiophene (4,6-DMDBT). DBT, 4-MDBT, 3-MDBT, 1-EDBT, 3-EDBT, 4,6-DMDBT, 3,6-DMDBT, 2,8- DMDBT and 4-methylnaphtho[2,1-b]thiophene were selected to calculate the molaraveraged conversion. The conversions of the sulfur containing compounds and phenanthrene were determined as a function of the operating variables: space time (W/Fo DBT), temperature, H2/HC mol ratio and pressure. The Conversions of DBT and 4,6-DMDBT into their reaction products such as Biphenyl (BPH), Cyclohexylbenzene (CHB), Bicyclohexyl (BCH) and 3,4-Dimethylbiyphenyl (3,4-DMBPH) were determined only as a function of space time in the interval of 4000-6000 kgcath/kmol. The results of this work showed that Pt-HY and PdPt-HY are good noble metals catalysts for the hydrodesulfurization of heavy gas oil. Moreover, this study showed that CoMoPd/Pt-HY and CoMoNi/PdPt-HY catalysts are good candidates for deep HDS and hydrogenation of heavy gas oil. It was found that the conversions of sulfur compounds were higher than the conversions provided by the conventional CoMo/Al2O3 catalyst. Also higher hydrogenation of phenanthrene was observed. Deactivation of the catalysts was not observed during the operation. Finally, the study not only contributed to define the technical bases for the preparation of the noble metal catalysts for hydrodesulfurization of heavy gas oil at pilot scale, but also provided technical information for developing the kinetic modeling of the hydrodesulfurization of heavy gas oil with the noble metal catalysts.

Hierarchically ordered porous oxides have garnered much interest because of the numerous applications that can be developed from these materials. The catalytic properties, separation ability, and ion exchangeability of these materials, specifically zeolites, make them great candidates for applications. One area which has not been heavily studied is ways to control the morphology and particle size of these materials through soft chemistry approaches. This dissertation looks at two methodologies which can be used to alter zeolitic particle morphology. The first is a dual templating approach which attempts to incorporate microporous walls within a mesoporous structure. The zeolitic material, silicalite-1, is used as a siliceous precursor for the formation of the mesoporous SBA-15 material. A battery of characterization techniques were used to identify the structural properties of the material, including porosimetry, diffraction, microscopy, and spectroscopy. The overall conclusion was that a material with different properties than the parent SBA-15 were obtained, but that no characterization technique could be used to show the definitive presence of the zeolite in the walls. Another technique studied is the growth of zeolitic materials within the water domains of microemulsions. The concept of a reverse microemulsion, a confined water droplet in a continuous oil phase makes it an interesting system for morphological control. The zeolitic materials should only be able to grow within the water domain, and the reactive materials should be less available as they are trapped in separate micelles. Zeolite A (LTA) and zeolite L (LTL), two technologically important zeolites, were studied. Enhanced growth, larger particles, and unique material aggregates are just a few of the observations made for the two systems. The development of these materials should facilitate the application of zeolite in emerging technologies. In particular, preliminary work has been done on the development of large zeolite crystals with tuned orientations and particle sizes. This research shows multiple ways in which particle size and morphology can be tuned simply by altering the chemistry and reaction conditions of the system. This research has led to unique findings dealing with large zeolite crystals, and should open the door for continued research in this area.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: zeolite; advanced oxidation; TCE. Includes bibliographical references (p. 58-60).