Development and application of oxygen permeable membrane in selective oxidation of light alkanes

In this paper, oxygen permeable membrane used in membrane reactor for selective oxidation of alkanes will be discussed in detail. The recent developments for the membrane materials will be presented, and the strategy for the selection of the membrane materials will be outlined. The main applications of oxygen permeable membrane in selective oxidation of light alkanes will be summarized, which includes partial oxidation of methane (POM) to syngas and partial oxidation of heptane (POH) to produce H-2, oxidative coupling of methane (OCM) to C-2, oxidative dehydrogenation of ethane (ODE) to ethylene and oxidative dehydrogenation of propane (ODP) to propylene. Achievements for the membrane material developments and selective oxidation of light alkanes in membrane reactor in our group are highlighted.

The role of Sn in Pt-Sn/CeO2 catalysts for the complete oxidation of ethanol

The structural features and catalytic properties of Pt-Sn/CeO2 catalysts prepared by modified polyol method were extensively investigated for the complete oxidation of ethanol. CO chemisorption, TPR, DTA and XPS measurements identically indicated that the electronic configuration of Pt by Sn as well as the formation of PtSn alloy were the key factors in determining the nature of the active sites, A strong Pt/Sn atomic ratio dependence of catalytic perfortmances was observed. which was explained in terms of the change., in the Surface structure of metal phases and the electronic Pt-Sn interaction. (c) 2005 Elsevier B.V. All rights reserved.

Low-temperature oxidation of CO over Pd/CeO2-TiO2 catalysts with different pretreatments

A comprehensive study of the low-temperature oxidation of CO was conducted over Pd/TiO2, Pd/CeO2, and Pd/CeO2-TiO2 pretreated by a series of calcination and reduction processes. The catalysts were characterized by N-2 adsorption, XRD, H-2 chemisorption, and diffuse-reflectance infrared Fourier transform spectroscopy. The results indicated that Pd/CeO2-TiO2 has the highest activity among these catalysts, whether in the calcined state or in the reduced state. The activity of all of the catalysts can be improved significantly by the pre-reduction, and it seems that the reduction at low temperature (LTR. 150 degrees C) is more effective than that at high temperature (HTR, 500 degrees C), especially for Pd/CeO2 and Pd/TiO2. The catalysts with various supports and pretreatments are also different in the reaction mechanisms for CO oxidation at low temperature. Over Pd/TiO2, the reaction may proceed through a surface reaction between the weakly adsorbed CO and oxygen (Langmuir-Hinshelwood). For Ce-containing catalysts, however, an alteration of reaction mechanism with temperature and the involvement of the oxygen activation at different sites were observed, and the light-off profiles of the calcined Pd/CeO2 and Pd/CeOi-TiO2 show a distortion before CO conversion achieves 100%. At low temperature, CO oxidation proceeds mainly via the reaction between the adsorbed CO on Pd-0 sites and the lattice oxygen of surface CeO2 at the Pd-Ce interface, whereas at high temperature it proceeds via the reaction between the adsorbed CO and oxygen. The high activity of Pd/CeO2-TiO2 for the low-temperature CO oxidation was probably due to the enhancements of both CO activation, caused by the facilitated reduction of Pd2+ to Pd-0, and oxygen activation, through the improvement of the surface oxygen supply and the oxygen vacancies formation. The reduction pretreatment enhances metal-support interactions and oxygen vacancy formation and hence improves the activity of CO oxidation. (c) 2005 Elsevier Inc. All rights reserved.

Reaction path for oxidation of ethylene to acetic acid over Pd/WO3-ZrO2 in the presence of water

Pd-supported on WO3-ZrO2 (W/Zr atomic ratio=0.2) calcined at 1073 K was found to be highly active and selective for gas-phase oxidation of ethylene to acetic acid in the presence of water at 423 K and 0.6 MPa. Contact time dependence demonstrated that acetic acid is formed via acetaldehyde formed by a Wacker-type reaction, not through ethanol by hydration of ethylene.

An investigation into reactivity and selectivity in cycloadditions of 1,3-dipoles with formamidines

The objective of this research was to investigate the synthesis of nitrile oxides and to study their reactivity in 1,3-dipolar cycloadditions with formamidines. Chapter one looks at the literature surrounding the 1,3-dipolar cycloaddition reaction. It explores the generation of 1,3-dipoles (mainly nitrile oxides) and dipolarophiles (predominantly amidines). It discusses the potential synthetic uses of the 1,3-dipolar cycloadducts. It examines both and inter- and intra-molecular cycloaddition reactions. It recognises the use of the 1,3-dipolar cycloadditions as a successful method in building natural products and oxadiazolines. The decomposition of oxadiazolines as a route to nitriles is also outlined in this chapter. Chapter two discusses the results of this research candidate. The preparation of nitrile oxide precursors - hydroximoyl halides - is outlined at first. The generation of nitrile oxides is then demonstrated, followed by the preparation of furoxans. Methods for preparing the reference materials (nitriles and ureas), which result from decomposition of oxadiazolines, then follow. The preparation of series of Δ2-1,2,4- oxadiazolines via the 1,3-dipolar cycloaddition reaction is illustrated in this chapter. The selectivity of the addition of nitrile oxides to dipolarophiles was tested by competition reactions, which are also described in this chapter. NMR techniques were used in the study of the kinetics of the 1,3-dipolar cycloadditions used for the preparation of a series of Δ2-1,2,4-oxadiazolines, which is addressed in this chapter. Chapter three charts the experimental procedures followed to gain results which are discussed in chapter two. It also outlines all analytical data produced during the course of this research.

The Influence of 1,25-Dihydroxyvitamin D3 on the Cross-Priming of Lymphocytic Choriomeningitis Virus Nucleoprotein

Biologically active 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) binds the vitamin D receptor (VDR) to exert its effect on target cells. VDR expression is found in a number of immune cells including professional antigen-presenting cells such as dendritic cells. It has been found that the actions of 1,25-(OH)2D3 on the immune system are mainly immunosuppressive. The cross-presentation pathway allows for exogenously derived antigens to be presented by pAPCs on MHC-I molecules to CD8+ T cells. CD8+ T cell activation results in the expansion of epitope-specific T cell populations that confer host protection. These epitopes can be organized into an immunodominance hierarchy. Previous work demonstrated that introducing LCMV-NP via the cross-priming pathway significantly alters the immunodominance hierarchy of a subsequent LCMV infection. Building upon these observations, our study assessed the effects of LCMV-NP cross priming in the presence of a single dose of 1,25-(OH)2D3. Treatment with 1,25-(OH)2D3 was found to have biological effects in our model system. In vitro pAPCs were demonstrated to up-regulate IL-10 and CYP24A1 mRNA, in addition to the transactivation of cellular VDR, as demonstrated by a relocalization to the nuclear region. Mice treated with 1,25-(OH)2D3 were found to produce up-regulated IL-10 and CYP24A1 transcripts. Expression of VDR was increased at both the transcript and protein level. Our results demonstrate that a single dose of 1,25-(OH)2D3 does not affect the cross-priming pathway in this system. Treatment with 1,25-(OH)2D3 did not influence the ability of differentiated pAPCs to phagocytose or cross-present exogenous antigen to epitope-specific CD8+ T cells. Furthermore, 1,25-(OH)2D3 did not alter cross-priming or the establishment of the LCMV immunodominance hierarchy in vivo. By confirming that 1,25-(OH)2D3 does not suppress cross-priming in our model, our study helps to expand the understanding of the immunomodulatory role of exogenous 1,25-(OH)2D3 on the outcome of virus infection. Collectively, our data supports the observation that the role of 1,25-(OH)2D3 in the immune system is not always associated with suppressive effects.