硅溶胶粒径对沉淀铁催化剂费托合成性能的影响

在相同的制备条件下,采用相同SiO_2浓度、不同粒径的硅溶胶作为硅源制备费托合成沉淀铁Fe/Cu/K/SiO_2催化剂,考察了硅溶胶粒径对沉淀铁催化剂费托合成反应性能的影响。实验结果表明,硅溶胶的粒径在7~18 nm范围内时,硅溶胶粒径的不同会对沉淀铁催化剂的反应性能产生影响;随硅溶胶粒径的增加,催化剂的费托合成反应CO转化率明显下降。采用XRD、N_2吸附-脱附和H_2-TPR等方法表征了硅溶胶粒径对费托合成沉淀铁催化剂的织构和性能。表征结果显示,硅溶胶的粒径越小,催化剂主物相α-Fe_2O_3晶粒和比表面积越大,越有利于催化剂的还原和碳化,因而有利于催化剂CO反应性能的提高。     

陈化时间对沉淀铁催化剂的费托合成性能影响

采用连续共沉淀方法制备了Fe-Cu-K-SiO_2催化剂,并考察了陈化时间对催化剂的结构和织构性质的影响。采用X射线衍射、N_2吸附和程序升温还原(H_2-TPR)和X射线荧光光谱(XRF)等表征手段研究了不同陈化时间的催化剂样品的织构。结果表明,陈化时间在0.5～3.0h时,催化剂的主要物相是α-Fe_2O_3。随着陈化时间的缩短,催化剂的α-Fe_2O_3晶粒减小,比表面积逐渐增加,并且助剂铜趋于表面,使催化剂中α-Fe_2O_3易于还原。催化剂在n(H_2)/n(CO)=1.5、GHSV=3000 h~(-1)、p=1.6MPa、T=240℃下的固定床费托(F-T)合成反应评价结果表明,缩短陈化时间可明显提高催化剂的CO转化率。     

F-T合成沉淀铁催化剂的研究

采用共沉淀的方法制备了Fe-Cu-K-Si催化剂,并用低温氮气吸附、脱附,X射线衍射方法对催化剂进行了表征。考察了温度和空速对该催化剂上F-T合成过程的影响,进行了1000h以上的稳定性实验。结果表明,在反应温度250~300℃,压力2.6MPa,进料比V(H2)/V(CO)=2/3,空速400~1360 h-1操作条件下,催化剂显示了较高的F-T合成反应活性以及良好的稳定性。     

K_2CO_3溶液处理对费托合成熔铁催化剂性能的影响

以高频感应炉制备了熔铁催化剂,并进行了K2CO3溶液处理,采用ICP、XRD和H2-TPR等手段,对费托合成熔铁催化剂的物相与组成进行表征。于固定床积分反应器中进行催化剂的费托合成性能评价,反应条件为220℃~350℃,2.0MPa,V(H2)/V(CO)=2,GHSV=3000h-1。结果表明,由于石墨坩埚的使用,使得感应炉制备的熔铁催化剂中引入了大量的Si和Al元素,这些元素与铁氧化物形成固熔体,造成催化剂难以被还原、表面碱度严重被削弱、产物以低碳烃为主。经K2CO3溶液处理后,催化剂中固熔体部分被溶解,还原难度逐步降低。同时,随着K2CO3溶液浓度的增加,催化剂的表面碱度逐渐增强,产物中CH4选择性由44.82%降到28.82%,C2~C4烯烃选择性也逐渐增加。     

浆态床反应器中熔铁催化剂的费托合成反应性能

研究了浆态床反应器中熔铁催化剂的费托合成反应性能,并与固定床反应器进行了比较。实验结果表明,熔铁催化剂在浆态床反应器中具有较好的费托合成反应活性和良好的稳定性;与固定床反应器相比,浆态床反应器中CH4和CO2的选择性明显降低。考察了反应温度、反应压力、合成气空速、合成气n(H2)∶n(CO)对浆态床反应器中熔铁催化剂费托合成反应性能的影响。实验结果表明,适当调变反应条件,可有效提高熔铁催化剂的费托合成反应活性,并使产物分布得到优化。在n(H2)∶n(CO)=1.6、2.0M Pa、250℃、GHSV=3 000h-1的条件下运行900h,浆态床反应器中CO的转化率达92%左右,CH4的选择性为5%左右,CO2的选择性为40%左右。     

Eu助剂对费托合成FeCuSi催化剂的影响

采用共沉淀法制备了不同铕(Eu)含量的铁基催化剂,并用N_2低温吸附、XRD、H_2-TPR、CO-TPD和H_2-TPD等技术进行表征,在固定床反应器中评价催化剂费托合成反应催化性能。结果表明,在FeCuSi催化剂中,Eu的添加能够明显增加Fe物种的分散度,改善催化剂的还原性能,促进CO及H_2在催化剂表面的吸附,从而影响催化剂的催化效果。在325℃、1.0MPa、9000h~(-1)的反应条件下,nEu:nFe为0.02的催化剂100Fe_6Cu_3Si_2Eu,CO转化率为94.9%,烃分布中甲烷为13.1%、C_2～C_4烯烃为21.2%。     

费托合成催化剂的研究进展

围绕费托合成反应产物分布的有效调控这一关键科学问题,综述了近年来在该反应催化剂的设计和研制方面所取得的重要研究进展针对载体(特别是具有规则孔道结构的分子筛或碳材料等)的孔道效应、各类助剂的本质等催化剂方面的关键因素对铁、钴和钌基催化剂的活性及产物选择性的影响进行了系统分析,并探讨了相关体系中的活性金属尺寸效应。还概述了最近在费托合成反应中涌现的新催化材料、新催化剂制备方法和新反应体系。     

助催化剂对费-托合成熔铁催化剂影响的研究

通过正交实验,在固定床反应器中研究了助剂对熔铁催化剂费托合成(FTS)反应性能的影响,并利用BET,SEM,XRD,TPH-MS等表征手段分析了助剂对催化剂的织构、还原行为、碳化行为及物相变化的影响。结果表明:Al2O3对费托反应用的熔铁催化剂的性能的影响最为显著,随着Al2O3含量的增加,FTS反应活性提高,C2+产率增加。正交实验最优组合为Al3/K3/B1/Ca2.5/Fe100催化剂,在n(H2)/n(CO)=1.6,温度523K,压力2.0MPa,空速3000h-1反应条件下,合成气转化率为74.5%,CH4选择性为5.9%,C2+的收率为145.0g/m3。同时,发现在FTS反应后催化剂表面上的主要碳物种是碳化铁γ1和γ2,且随着Al2O3的加入,α态原子碳(最活泼的碳化物形式)和碳化铁γ1、γ2的含量增加,而β、δ1和δ2含量减少,Al2O3能促进最活泼的α碳物种的形成。     

费托合成钴基催化剂研究进展

综述了费托合成钴基催化剂及其失活原因的研究进展,阐述了催化剂的活性组分、载体、催化助剂等对反应活性和产物选择性的影响,分析了钴基催化剂失活原因,认为中毒、钴晶粒烧结、碳效应、钴再氧化、钴—载体形成化合物、机械磨损都会不同程度造成催化剂失活。     

碳纳米管表面化学结构对Co基费托合成催化剂性能的影响

在Co基费托合成反应中,碳载体因其表面化学惰性而与金属Co的相互作用较弱,有利于Co物种的还原,但同时因为缺少锚定位点而导致金属分散性不佳。采用酸化预处理的方式在碳纳米管表面引入缺陷和含氧官能团,可以改善Co与载体之间的相互作用,促进Co物种的分散,从而提高反应性能。拉曼光谱(Raman)、X射线光电子能谱(XPS)等表征结果表明,用34%(质量分数,下同)的硝酸在120℃条件下,可以获得缺陷度相近且表面含氧量提升的碳纳米管载体(oCNT-M),用68%的硝酸在140℃条件下,可以获得缺陷度和含氧量同时提升的碳纳米管载体(oCNT-H)。H₂程序升温还原(H₂-TPR)、透射电子显微镜(TEM)和CO化学吸附(CO-chemisorption)等表征结果表明,含氧量和缺陷度的增加可以改善Co物种的还原和分散,有利于形成更多的活性Co位点。通过高浓度强氧化性硝酸处理得到的碳纳米管载体oCNT-H,其表面含氧量和缺陷度同时得到提高,获得的Co基催化剂与Co/CNT-L相比,在费托反应测试中CO转化率从10.9%提高到41.9%,C_5+<...     

Effect of temperature on deactivation models of alumina supported iron catalyst during Fischer-Tropsch synthesis

Determination of catalyst deactivation model plays prominent role in process controlling. The aim of this study is to investigate deactivation models of Fe/Al₂O₃ catalyst at different temperature during the Fischer-Tropsch synthesis. Data analysis determined the suitability of second-order GPLE model to describe deactivation behavior of the catalyst. Comparing model parameters at different conditions demonstrated that the catalyst deactivation rate increased by temperature elevation. Analysis of the models also revealed that the catalyst deactivation involves two stages, the first stage occurs at high temperatures while the next step happens at low temperatures, and the deactivation energy of both stages was calculated.     

Formation of carbon dioxide in the Fischer-Tropsch synthesis on nanosized iron catalyst particles

The formation of carbon dioxide in the Fischer-Tropsch synthesis performed in a three-phase system in the presence of a nanosized catalyst was studied. The synthesis temperature was found the main parameter responsible for the yield of CO₂. At a constant conversion of CO, pressure has almost no effect on selectivity for the formation of CO₂, whereas a decrease in the H₂/CO ratio and an increase in the contact time or the concentration of an active component in the reaction zone lead to a decrease in the selectivity.     

Effect of the support nature on the catalytic properties of iron in benzene benzylation

The effect of the support nature on the dispersion, structure, and catalytic activity of iron oxides supported on ZrO₂, TiO₂, ZnO, Al₂O₃, and silicas of different structures has been analyzed using the example of benzene benzylation. The structure and electronic properties of the catalysts prepared from iron acetylacetonate have been studied by Mössbauer spectroscopy. It has been shown that the use of SiO₂, ZrO₂, and ZnO supports characterized by weak oxide–oxide interaction leads to the formation of small iron oxide clusters of a 2–10 nm size, which exhibit the highest activity in catalysis.     

Fischer-Tropsch synthesis in a three-phase system with iron catalyst nanoparticles

The features of the Fischer-Tropsch synthesis in the presence of 100Fe: 8Al₂O₃: 3K₂O (parts by weight) catalyst nanoparticles under the slurry reactor conditions have been studied. The catalyst is prepared in situ and activated in the reactor. It has been found that during the preparation process, the catalyst reacts with the dispersion medium to form a structured system that is not liable to sedimentation. It is shown that the use of CO as a reducing agent makes it possible to increase the yield of liquid hydrocarbons by a factor of 1.5. An increase in the syngas pressure has almost no effect on the yield of liquid hydrocarbons; however, it gives the possibility of enhancing the catalyst efficiency up to 700 g/(kg Fe · h) at 40 atm. In conditions of a three-phase system, gasoline-fraction hydrocarbons, half of which consist of olefins, are mostly formed on the nanosized catalyst.     

Formation of alcohols on nanosized iron catalysts under Fischer-Tropsch synthesis conditions

Regularities of the alcohol formation in a three-phase system in the presence of the nanosized 100Fe: 8Al₂O₃: 3K₂O (parts by weight) iron catalyst under the Fischer-Tropsch synthesis conditions have been determined. It has been found that the molecular-weight distribution of alcohols does not follow the Anderson-Schulz-Flory law. The principal product is ethanol; its proportion in the mixture can be as high as 78 wt %. It has been supposed that the formation of alcohols can follow the mechanism including the CO insertion in the metal-carbon bond. It has been shown that the highest ethanol yield (78 wt %) is obtained using 20 atm, 300°C, and H₂/CO = 2.5 (mol/mol), an iron-containing catalyst charge in the reactor of 2 wt %.