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Abstract: Carbon nanofibers (CNFs) and nanotubes (CNTs) were successfully synthesized by chemical vapor deposition using a novel catalyst CaCO3. The reaction process of C2H2 on CaCO3 surface could be classified into three stages; stage I: dehydrogenation reaction (88–129°C), stage II: dehydrogenation and hydrogenation reactions (129–686°C) and stage III: dehydrogenation reactions (higher than 686°C). It was found that the molecular weights of the crosslinked C2H2 products increase with the increase of reaction temperature. Nevertheless, the dehydrogenation reaction of C2H2 into CNFs took place only at a temperature higher than about 500°C and the highest yield of CNFs occurred at about 600°C. [Copyright &y& Elsevier]

Abstract: Most catalysts used in preparing carbon materials by chemical vapor deposition were transitional metals such as Fe, Co, Ni and only a few references were about the synthesis of carbon materials using water-soluble catalysts until now. Compared with metals, water-soluble catalysts can be conveniently removed from products. In our present works, water-soluble salt potassium iodide (KI) was found to be an efficient catalyst to grow carbon fibers and CNF under suitable conditions. Various structures of carbon fibers were synthesized by chemical vapor deposition using KI as the catalyst. And the experimental results showed that the nanostructure evolution of the fibers is strongly dependent on the temperature and history of the catalyst. [Copyright &y& Elsevier]

Abstract: The optimal calcination temperature was 600°C and the highest activities were obtained at Al:K molar ratios of 3:1, 1:1 and 1:1 for Al2O3/KNO3, Al(NO3)3/KNO3 and Al2O3/KOH precursor combinations, respectively. The active compound in the catalyst prepared by Al(NO3)3/KNO3 was KNO3 exclusively. However, the catalytic activity of the catalysts prepared by Al2O3/KOH was affected by the formation of K2Al2O4 and K2CO3 compounds. The catalysts prepared by all precursor combinations behaved a comparable thermal stability. High temperature aging of the catalysts would result in the loss of surface area and/or active compounds, and hence the deterioration of their catalytic activities. [Copyright &y& Elsevier]

Abstract: Ln/K oxide catalysts (Ln=La, Sm, Y) supported on the alumina substrate have been prepared and their catalytic activities of diesel soot oxidation were tested by TPR system. The results showed that all La/K, Sm/K and Y/K catalysts showed a similar change of catalytic activity with the variation of K content. Nevertheless, Y/K catalyst was more active for diesel soot oxidation with a soot ignition temperature of about 350°C at a loose soot/catalyst contact mode. XRD, TG/DSC analyses were employed to investigate the structures and thermal behaviors of catalysts. It was found that the oxides would react with KNO3 to form the solid solution and the K+ saturation level was related to the ionic radii of the Ln3+. The Ln/K catalysts showed a physical CO2 absorption ability that was further enhanced at higher temperature. However, when the temperature was above a critical temperature, the absorption ability was reduced. The CO2 absorption characteristics was believed to be diffusion controlled and was attributable to the lattice defects (oxygen vacancies) caused by the solid solution formation. The dynamic CO2 transportation within the catalyst could play an important role on the catalytic oxidation process. [Copyright &y& Elsevier]

Abstract: CeO2–K catalysts supported on porous alumina substrate have been prepared by using a novel water-immiscible solvent. The advantage of this method is to load the catalyst onto the filter surface by one-time coating and prevent depositing the catalyst into the porous structure of support materials. The catalytic activities of the supported catalysts were evaluated by TPR system and the results showed that the pure CeO2 displayed a poor catalytic activity for soot oxidation, while the addition of K element into CeO2 would result in the formation of CeO2–K solid solution and significant enhancement of catalytic activity. Nevertheless, the variation of K content had a limited effect on soot ignition temperature. The catalyst with a Ce:K molar ratio of 1:2 exhibited an ignition temperature of about 330°C and the oxidation rates of about 0.16 and 0.28mgmin−1 cm−2 at temperatures of 370 and 390°C, respectively. [Copyright &y& Elsevier]

Abstract: The CeO2–K catalysts loaded on porous alumina substrate have been produced by a new route. The potassium halides played an important role on the catalytic activity enhancement of CeO2 catalyst for soot oxidation. This improvement could partially originate from the catalytic production of CO by the potassium halides. Their effects on the catalytic activity promotion followed the order KF∼KCl>KBr>KI and their addition into CeO2 resulted in the CeO2–K catalysts with the lowest soot ignition temperatures of about 334, 335, 345 and 362°C, respectively, at a loose soot/catalyst contact mode. Nevertheless, the CeO2 with addition of KCl behaved a better catalytic performance. It was also found that the catalysts have a CO2 absorption capability. [Copyright &y& Elsevier]

Abstract: The CO2 absorption characteristics and catalytic oxidation activities of V/K and V/Ce/K-based catalysts were studied by temperature-programmed reactions. It was found that the V/K and V/Ce/K catalysts displayed a strong CO2 absorption characteristic that was believed to be attributable to the formation of potassium bicarbonate species and physical CO2 absorption. The experimental procedure used could precisely identify the soot ignition onset temperature (IOT) of the prepared catalysts. The V/K catalyst prepared at a V:K molar ratio of 1:2 showed the lowest IOT, but behaved a poor catalytic oxidation performance. The addition of CeO2 into the V/K catalyst with a V:K molar ratio of 1:6 could reduce the IOT from about 320 to 303°C at a loose soot/catalyst contact mode. [Copyright &y& Elsevier]

Abstract: Low cost production of carbon nanofiber and nanotube has been widely studied. Previously, these carbon materials have been synthesized by using chemical vapor deposition. In this letter, the carbon nanomaterials of various morphologies have been produced by using cesium carbonate as a catalyst and acetylene gas (C2H2) as a carbon source via chemical vapor deposition. It was found that the deposited products were mainly carbon nanotubes and nanofibers at deposition temperatures of 600 and 700 °C, respectively. Because the catalysts are water-soluble, they can be removed from the deposited products by simple water-washing instead of using highly concentrated acid for metal catalyst removal. [Copyright &y& Elsevier]