Qiwen Sun

Effects of the ratio of Fe to Co over Fe-Co/SiO2 bimetallic catalysts on their catalytic performance for Fischer-Tropsch synthesis

Abstract The Fe-Co/SiO 2 bimetallic catalysts with different ratios of Fe to Co were prepared by aqueous incipient wetness impregnation. The catalysts of 10%Fe:0%Co/SiO 2 , 10%Fe:6%Co/SiO 2 , 10%Fe:2%Co/SiO 2 , 10%Fe:10%Co/SiO 2 , 6%Fe:10%Co/SiO 2 , 2%Fe:10%Co/SiO 2 and 0%Fe: 10%Co/SiO 2 by mass were tested in a fixed reactor by the Fischer-Tropsch synthesis. Activity and hydrocarbon distribution were found to be determined by the ratio of iron to cobalt of the catalysts. Higher iron content inhibited the activity, whereas higher cobalt content enhanced the activity of the Fe-Co/SiO 2 catalysts. On the other hand, for the catalysts of 10%Fe:6%Co/SiO 2 , 10%Fe:10%Co/SiO 2 , 6%Fe:10%Co/SiO 2 , and 2%Fe:10%Co/SiO 2 , the total C 2 –C 4 fraction increased (from 10.65% to 26.78%) and C 5+ fraction decreased (from 75.75% to 57.63%) at 523 K. Temperature programmed reduction revealed that the addition of cobalt enhanced the reducibility of the Fe-Co/SiO 2 catalyst. Metal oxides were present in those catalysts as shown by XRD. The Fe-Co alloy phase was found in the 2%Fe:10%Co/SiO 2 , 6%Fe:10%Co/SiO 2 , 10%Fe:10%Co/SiO 2 , 10%Fe:6%Co/SiO 2 catalysts and their crystals were perfect.

Effects of the Different Supports on the Activity and Selectivity of Iron-Cobalt Bimetallic Catalyst for Fischer-Tropsch Synthesis

Abstract Silica, alumina, and activated carbon supported iron-cobalt catalysts were prepared by incipient wetness impregnation. These catalysts have been characterized by BET, X-ray diffraction (XRD), and temperature-programmed reduction (TPR). Activity and selectivity of iron-cobalt supported on different carriers for CO hydrogenation were studied under the conditions of 1.5 MPa, 493 K, 630 h −1 , and H 2 /CO ratio of 1.6. The results indicate that the activity, C 4 olefin/(C 4 olefin+C 4 paraffin) ratio, and C 5 olefin/(C 5 olefin+C 5 paraffin) decrease in the order of Fe-Co/SiO 2 , Fe-Co/AC1, Fe-Co/A1 2 O 3 and Fe-Co/AC2. The activity of Fe-Co/SiO 2 reached a maximum. The results of TPR show that the Fe-Co/SiO 2 catalyst, is to some extent different. XRD patterns show that the Fe-Co/SiO 2 catalyst differs significantly from the others; it has two diffraction peaks. The active spinel phase is correlated with the supports.

Effects of promoters on catalytic performance of Fe-Co/SiO2 catalyst for Fischer-Tropsch synthesis

Abstract 2%Fe-10%Co/SiO2 catalysts with different potassium or zirconium loadings were prepared by aqueous incipient wetness impregnation and tested for Fischer-Tropsch synthesis in a flow reactor, using H2/CO = 1.6 (molar ratio) in the feed, under the condition of an overall pressure of 1 MPa, GHSV of 600 h−1 and temperature of 503 K. The zirconium and potassium promoters remarkably influenced hydrocarbon distribution of the products. CO conversion increased on the catalysts with the increase of zirconium loadings, which indicated that zirconium enhanced the activity of iron-cobalt catalysts. Low potassium loadings also enhanced the activity of the catalysts. However, high potassium loading made CO conversion on the catalysts decrease and weakened the secondary hydrogenations. The catalyst was characterized by BET, XRD and TPR. The catalyst characterization revealed that the Co3O4 phase was presented on the fresh catalyst, whereas the spinel phase of Fe-Co alloy and CoO existed on the used catalyst.

Product distributions and olefin-to-paraffin ratio over an iron-based catalyst for Fischer–Tropsch synthesis

An iron-based catalyst was prepared by the co-precipitation method. The product distributions and olefin-to-paraffin ratio (O/P ratio) with chain length of Fischer–Tropsch synthesis over the iron-based catalyst were investigated under different reaction conditions in an integral fixed bed reactor. It is found that the product distributions are non-ASF situation, and the deviation from ASF law was analyzed by taking the physisorption, solubility, volatility of products and the subsequent secondary reactions into consideration. It is noted that the contents of hydrocarbons decline with increasing carbon number and higher temperature, space velocity, H2/CO in feed gas and lower pressure is preferential for the formation of light hydrocarbons but against the chain propagation. The O/P ratio shows an exponential decrease with chain length except for ethylene and ethane because of the special adsorption character of ethylene. The O/P ratio is also affected by operating conditions. The results indicate that higher reaction temperature, space velocity of feed gas, lower pressure and higher H2/CO in the feed gas are preferential for the formation of olefins and the enhancement of O/P ratio.

Pretreatment of Alumina and Its Influence on the Properties of Co/Alumina Catalysts for Fischer-Tropsch Synthesis

Abstract 16.6%Co/γ-Al2O3 catalysts prepared by incipient wetness impregnation method were used for Fischer-Tropsch synthesis. The support was pre-treated with different concentration of NH4NO3 aqueous solution. The effect of support pre-treatment on the properties of support and performance of supported-cobalt-based catalysts was investigated. To treat the support with NH4NO3 aqueous solution enlarged the pore of γAl2O3, decreased the impurity Na2O content, and weakened the surface acidity of γAl2O3. The change in the properties of the support decreased the interaction between cobalt species and support, enhanced the CO hydrogenation rate and the C5+ selectivity. For all catalysts, increasing the reaction temperature increased the CO hydrogenation rate or the CO conversion, slightly decreased the total hydrocarbon selectivity, and favored the formation of methane and light hydrocarbons, while the chain growth probability decreased. For 16.6%Co/γAl2O3 catalysts, prepared with the support treated with 100 g/L NH4NO3 aqueous solution, the CO conversion, the CH4 selectivity, and the C5+ selectivity were 83.13%, 6.86% and 82.75% respectively, and the chain growth probability was 0.83 under the condition of 493 K, 1.5 MPa, 500 h−1 and the molar ratio of H2 to CO being 2.0 in feed.

Effects of Zr and Ni promoters on the activation and deactivation of a precipitated iron-based catalyst for Fischer–Tropsch synthesis

Iron-based catalysts with or without Zr and Ni promoters were prepared by the co-precipitation method. The specific surface area, pore volume and average pore size of the fresh catalysts was analyzed by N2-physisorption, and the effects of Zr and Ni promoters on the structure, activation and deactivation were investigated by H2-TPR, XRD and Mössbauer spectroscopy techniques. The Fischer–Tropsch reaction performance of catalysts was also studied in a fixed bed reactor. The results indicated that Zr promoter inhibited the reduction and carburization of catalysts due to the strong interaction between Fe and Zr and led to a lower activity and C5+ selectivity. The addition of Ni promoter improved the activity of iron-based catalyst, but caused a lower C5+ selectivity and higher CO2 selectivity. Meanwhile, Ni was preferential for the reduction of iron phases but against the carburization of catalysts. To some extent, the addition of Zr, Ni promoters improved the stability of iron-based catalysts.

Mechanism of oxygenates formation in high temperature Fischer-Tropsch synthesis over the precipitated iron-based catalysts

Abstract In-situ DRIFTS and chemical trapping techniques were employed to investigate the adsorbed species over the surface of precipitated iron-based catalysts and the mechanism of oxygenates formation in high temperature Fischer-Tropsch synthesis. The results showed that both linear and bridged CO molecules are present on the catalyst surface, which leads the formation of numerous oxygenated precursors. Some crucial surface intermediates are detected by the in-situ DRIFTS, such as acetate, acetyl and methoxide. The surface of precipitated iron-based catalysts is characterized by following facts: alcohols are able to react with free surface hydroxyls to form alkoxy species; surface adsorbed molecules exhibit certain oxidizing ability; basic sites such as OH − and lattice oxygen may react with CH 3 OH or CH 3 CHO molecules. By chemical trapping of the CH 3 OH + CO and CH 3 I + CO + H 2 reactions, it was found that acetyl is an important intermediate for oxygenates and the hydrogenation of acetyl is a crucial step for the formation of oxygenates. On the basis of these observations, the mechanism of oxygenates formation in high temperature Fischer-Tropsch synthesis over the precipitated iron-based catalysts was then proposed.

Methanol Conversion on SAPO-34 Catalysts Synthesized by Tri-templates

The effect of different combinations of a new tri-templating agent TEAOH/DEA/TEA, namely tetraethyl ammonium hydroxide (TEAOH)/diethylamine (DEA)/triethylamine (TEA), on the catalytic performance of SAPO-34 was investigated in MTO conversion. It was found that SAPO-34 and SAPO-5 are competing phases at TEA concentrations higher than 40 %. Pure SAPO-34 with high crystallinity, large BET surface area and small crystal size (0.8~1.4μm) was obtained at a low TEA concentrations. The combination of TEAOH/DEA/TEA strongly governed the acidity of crystals. TEAOH:DEA:TEA=0.67:0.67:0.67 gave an economical catalyst active in MTO reaction with 100 % methanol conversion, 89.39 % ethylene and propylene selectivity, a longest lifetime and a high coke capability of 24.2 wt %.