To control the fine structure of Co species on calcined Co/SiO2 catalyst, especially to depress the formation of Co silicate-like species after the calcination, the present study has investigated effects of some preparation conditions (pH of the impregnating solution, and heating rate during calcination) on the fine structure of Co species on the calcined catalysts prepared with trans-1,2-diamino-cyclohexane-N,N,N',N'-tetraacetic acid (CyDTA) or nitrilotriacetic acid (NTA), and their Fischer-Tropsch synthesis (FTS) activities. Characterization results by Co K-edge EXAFS and TPR showed that the fine structure of Co species on calcined Co/SiO2 and NTA-Co/SiO2 is not affected by these preparation conditions, and Co3O4-like species is mainly formed after the calcination. On the contrary, the fine structure of Co species on calcined CyDTA-Co/SiO2 depended on these preparation conditions. An irreducible α-Co2SiO4-like species is formed after the calcinations when CyDTA-Co/SiO2 catalyst was prepared from the impregnating solution with higher pH (>9.1), and/or was calcined at the rate above 1.0 K min-1, whereas Co3O4-like species was formed when prepared from the impregnating solution with lower pH (<3.1), and/or calcined at lower heating rate (0.1 K min-1). TG-DTA measurements during the calcination of CyDTA-Co/SiO2 showed that the pH of the impregnating solution and heating rate during calcinations affect the decomposition temperature of the CyDTA-Co complex formed in the impregnating solution. The reducibility of Co species became 6-8 times greater when the complex was decomposed at lower temperatures. Therefore, it is suggested that the fine structure of Co species after the calcination is affected by the decomposition temperature (stability) of CyDTA-Co complex during the calcination. The FTS activity of CyDTA-Co/SiO2 was ca. two times greater than that of Co/SiO2 catalyst, when the catalyst was prepared from the impregnating solution with lower pH, and then calcined at a lower heating rate.
In order to make clear the promoting effects of modification of an aqueous Co nitrate solution with some chelating agents reported previously, the present study has investigated the FTS activity and surface structure of the catalysts prepared by a stepwise impregnation of the aqueous nitrilotriacetic acid (NTA) and Co nitrate solutions. The order of the stepwise impregnation of these reagents was varied, and obtained results were compared with those for the catalysts prepared by the co-impregnating method. Promoting effects of modification with NTA were clearly observed, irrespective of the order of the stepwise impregnation of the aqueous NTA and Co nitrate solutions. In particular, the catalyst prepared by the stepwise impregnation of the aqueous NTA solution followed by the aqueous Co nitrate solution showed an identical FTS activity to the catalyst prepared by the co-impregnating method. In temperature programmed reduction profiles of these catalysts after calcinations, both low temperature (ca. 500 K) and high temperature (900-1100 K) peaks were observed irrespective of the impregnating methods. The intensity of the high temperature peak, however, was evidently weaker for the catalyst prepared by the stepwise impregnation of the aqueous NTA solution followed by the aqueous Co nitrate solution. Furthermore, diffuse reflectance FT-IR measurement on the catalysts after the drying step showed that NTA forms a complex with Co2+ except for the catalyst prepared by the stepwise impregnation of the aqueous NTA solution followed by the aqueous Co nitrate solution. Some of NTA were free from the complex formation on this catalyst. Besides, unlike the catalyst prepared by the co-impregnating method, Co loading was able to be changed when the catalyst was prepared by the stepwise impregnation method, which resulted in higher FTS activities. From these results, it was suggested that the promoting effect of modification with NTA is brought by the formation of highly dispersed Co species after the calcinations, which is originated from the NTA-Co2+ complex.
The quantitative co-relationships between the time series of Liquid Natural Gas (LNG) CIF (Cost, Insurance and Freight) prices and those of crude oil prices were estimated for Japan, EU and USA based on the monthly price data in the time period from early of 1998 to 2006 of the three regional markets. Since both prices of LNG CIF and crude oil appear to be non-stationary, the cointegration and the Error Correction Model (ECM) techniques were applied to obtain the long-run elasticity coefficients between both prices of LNG CIF and crude oil for these three markets. The obtained results suggest that 100 percent changes of the crude oil prices of Japan, EU and USA have 49 percent, 76 percent and 96 percent impacts on the respective LNG CIF prices in a long term when the crude oil price in a relative high era. The obtained long-run elasticity coefficients can be used to explain the different price changes of LNG CIF in each market with responding to dramatically changing high crude oil price in recent years.