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Impregnation Method (impregnation + method)
Selected AbstractsAblation Resistance of Different Coating Structures for C/ZrB2,SiC Composites Under Oxyacetylene Torch FlameINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2009Houbu Li C/ZrB2,SiC composites were fabricated by polymer infiltration and pyrolysis combined with slurry impregnation method. Three kinds of coating structures for these composites were applied in order to improve their ablation resistance: pure silicon carbide coatings, ZrB2,SiC mixture coatings, and ZrC,SiC alternating multilayer coatings. The ablation experiments were carried out on an oxyacetylene torch flame with a temperature of about 3000°C. The ZrC,SiC alternating multilayer showed the best ablation resistance. The linear erosion rate for ZrC,SiC alternating multilayer coatings is half of that for ZrB2,SiC mixture and pure SiC coatings. A model was put forward to account for such a result. [source] Catalytic performance of Brønsted acid sites during esterification of acetic acid with ethyl alcohol over phosphotungestic acid supported on silicaJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2007Abd El-Aziz A Said Abstract Different ratios of phosphotungestic acid supported on silica gel were prepared by an impregnation method with PWA loadings ranging from 1 to 30% w/w and calcined at 350 and 500 °C for 4 h in a static air atmosphere. The catalysts were characterized by thermogravimety (TG), differential thermal analysis (DTA), X-ray diffraction, FT-IR spectroscopy and N2 adsorption measurements. The surface acidity and basicity of the catalyst were investigated by the dehydration,dehydrogenation of isopropanol and the adsorption of pyridine (PY) and 2,6-dimethyl pyridine (DMPY). The gas-phase estrification of acetic acid with ethanol was carried out at 185 °C in a conventional fixed-bed reactor at 1 atm using air as carrier gas. The results clearly revealed that the catalyst containing 10% w/w PWA/SiO2 is the most active and delivers reaction selectively to ester with 85% yield. The Brønsted acid site resulting from hydroxylation of tungsten oxide plays the main role in the formation of ester. Copyright © 2007 Society of Chemical Industry [source] Surface properties and catalytic behavior of MoO3/SiO2 in esterification of acetic acid with ethanolJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2006Abd El-Aziz A Said Abstract A series of MoO3/SiO2 catalysts was prepared by an impregnation method with Mo loadings ranging from 1 to 50 wt%. The original and calcined samples at 400 °C were characterized by thermogravimetry (TG), differential thermogravimetry (DTG), differential scanning calorimetry (DSC), X-ray diffraction (XRD), Fourier transform infra-red (FTIR) spectroscopy, and nitrogen adsorption measurements. The surface acidity and basicity of the catalysts were investigated by the dehydration,dehydrogenation of isopropanol and the chemisorption of pyridine. The catalytic esterification of acetic acid with ethanol was carried out at 220 °C in a conventional fixed-bed reactor at 1 atm using air as a carrier gas. The results clearly revealed that silica,molybdena catalysts were active and selective towards the formation of ethyl acetate. Moreover, the catalyst containing 20 wt% MoO3 was the most active and selective one. The results emphasize the importance of the surface acid sites together with the specific surface area of the prepared catalyst, towards ester formation. Copyright © 2005 Society of Chemical Industry [source] High resistance to aerial oxidation of an amorphous NiB/SiO2 catalyst: TP-XRD, TPR and related investigationsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2004Yong-Zhen Wang Abstract An amorphous NiB/SiO2 catalyst, prepared by a reductive,impregnation method, was thoroughly studied as to its behavior in air and in benzene hydrogenation in a fixed-bed reactor at atmospheric pressure. The results showed that the amorphous NiB/SiO2 catalyst possessed long life and excellent resistance to aerial oxidation. Even after calcination at 400 °C, TP-XRD and TPR measurements revealed that the amorphous NiB/SiO2 catalyst was not oxidized, and could retain its activity in benzene hydrogenation. Copyright © 2004 Society of Chemical Industry [source] Gas phase esterification of acetic acid with ethanol over MoO3 supported on AlPO4 and the effect of modification with phosphomolybdic acid and Ce4+ ionsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2003Abd El-Aziz A Said Abstract A series of AIPO4,MoO3 (APM) systems with various molybdena loadings (5,50) mol %, same modified with phosphomolybdic acid (PMA) and cerium ions, were prepared by an impregnation method and calcined at 400 °C, except for the samples modified with PMA which were calcined at 350 °C for 4 h. The catalysts were characterized by TG/DTG, XRD, IR spectroscopy, N2 adsorption and electrical conductivity measurements. The surface acidity and basicity of the catalysts were determined by adsorption of pyridine and the dehydration,dehydrogenation of isopropyl alcohol. The catalytic esterification of acetic acid with ethanol was carried out in a convention fixed bed reactor. The results clearly revealed that the catalyst with a composition of 10 mol % MoO3 (APM10) was the most active and selective catalyst for the production of ethyl acetate. Moreover, the yield of ethyl acetate increases on addition of PMA into APM10 while it decreases on the addition of Ce4+ ions. These results were correlated with structure, semiconductivity and the acid,base properties of the prepared catalysts. Copyright © 2003 Society of Chemical Industry [source] Novel microfibrous-structured silver catalyst for high efficiency gas-phase oxidation of alcoholsAICHE JOURNAL, Issue 6 2010Jiping Mao Abstract Novel microfibrous-structured silver catalysts were developed for gas-phase selective oxidation of mono-/aromatic-/di-alcohols. Sinter-locked three-dimensional microfibrous networks consisting of 5 vol % 8-,m-Ni (or 12-,m-SS-316L) fibers and 95 vol % void volume were built up by the papermaking/sintering processes. Silver was then deposited onto the surface of the sinter-locked fibers by incipient wetness impregnation method. At relatively low temperatures (e.g., 380°C), the microfibrous-structured silver catalysts provided quite higher activity/selectivity compared to the electrolytic silver. The microfibrous Ag/Ni-fiber offered much better low-temperature activity than the Ag/SS-fiber. The interaction at Ag particles and Ni-fiber interface not only visibly increased the active/selective sites of Ag+ ions and Agn,+ clusters but also significantly promoted their low-temperature reducibility and ability for O2 activation. In addition, the microfibrous structure provided a unique combination of large void volume, entirely open structure, high thermal conductivity and high permeability. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Transesterification of dimethyl oxalate with phenol over TiO2/SiO2: Catalyst screening and reaction optimizationAICHE JOURNAL, Issue 12 2008Xia Yang Abstract Physicochemical properties of silica-supported titanium oxide catalysts as well as their performances for transesterification of dimethyl oxalate (DMO) with phenol to methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO) have been investigated systematically. Various wt % of TiO2 were loaded on SiO2 by a two-step wet impregnation method. The surface properties of TiO2/SiO2 catalysts were explored by various characterization techniques (BET, SEM, ICP, XPS, XRD, FTIR of pyridine adsorption, and NH3 -TPD). Catalytic performances of TiO2/SiO2 catalysts were found to be strongly dependent on TiO2 dispersion and surface acidity. Monolayer dispersion capacity of TiO2 on silica was estimated to be about 4.0 TiO2 molecules per nm2 (SiO2) and no crystalline TiO2 was detected at TiO2 loading less than 12 wt %. FTIR and TPD analysis suggested that weak Lewis acid sites on the surface of TiO2/SiO2 were responsible for their unique selectivity to the target products, MPO and DPO. An optimization of reaction conditions for the transesterification of DMO with phenol was performed over 12 wt % TiO2/SiO2 calcined at 550°C. In addition, we studied the disproportionation reaction from MPO to DPO via a catalytic distillation process, which is highly efficient to promote formation of the desired DPO. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Identification of Helicobacter sp. in gastric mucosa from captive marmosets (Callithrix sp.; callitrichidae, primates)AMERICAN JOURNAL OF PRIMATOLOGY, Issue 2 2005Marcela Freire Vallim de Mello Abstract The aim of this study was to identify the presence of Helicobacter sp. in the gastric mucosa of captive marmosets (Callithrix sp.). Histologic specimens from the fundic, corpus, and antral gastric regions of six Callithrix jacchus, 12 C. kuhli, and 12 C. geoffroyi specimens were evaluated. The sections were stained with hematoxylin-eosin (H&E) and the Warthin-Starry silver impregnation method, and immunostained with rabbit anti- H. pylori polyclonal antibody. Helicobacter -like organisms (HLOs) and coccoid forms were present in silver-stained sections from 29 stomachs, whereas immunohistochemistry (IHC) tests revealed bacterial aggregates in 15 stomachs. No statistical difference relative to the presence of Helicobacter sp. was found among the gastric regions or marmoset species. Gastric lesions were found in the groups of marmosets that had positive and negative IHC results, but no correlation between inflammation and Helicobacter sp. infection was established. These findings demonstrate that marmosets are susceptible to naturally-occurring Helicobacter sp. infection, and open the way to the development of comparative studies on Helicobacter sp. infection in humans. Am. J. Primatol. 66:111,118, 2005. © 2005 Wiley-Liss, Inc. [source] | ||||||||||