Preparation Of Delaminated Zeolite For Fischer-Tropsch Synthesis Over Cobalt

The bifunctional catalysts,prepared by intergrating F-T metals of Co with zeolites,is an effective strategy to control the distribution of F-T products and synthetic the target liquid fuels with high selectivity.However,there are some problems such as low F-T reactivity and high CH4 selectivity,because of the negative impact of microporous structure of the traditional molecular sieve and the micron-size particles.According to the high surface area,acidic sites easier to access,short channel of microporous,it is expected to obtain liquid fuels with high activity in one step by prepared the bifunctional catalysts with nano-thin layer molecular sieves.Therefore,in this dissertation,the delaminated zeolite was prepared by swelling and delaminating the MCM-22(P)with different surfactants as the swelling agent under different temperatures.In the meanwhile,ITQ-2 molecular sieves were synthesized by using the novel surfactant as the interlayer blockers agents in one-pot way.Cobalt catalysts were prepared with these zeoltes as the carrier and studied for F-T synthesis.The characterization of molecular sieves and catalysts revealed the influence of the pore structure,the acidity and its accessibility of the zeolite,the interaction between active component and carrier of the catalyst to the performance of F-T synthesis.The main research and results content are as follows:(1)The influence of pH and water content on MCM-22 molecular sieve structure was studied systematically.And three different Si/Al ratio of MCM-22(P)zeolite has been synthesized by hydrothermal synthesis method.Meanwhile,its cobalt catalyst was studied on F-T synthesis.The results show that the Co/MCM-22 catalysts could improve the selectivity of C5-C12 hydrocarbons component due to the cracking reaction of the F-T synthesis product on the acid sites compared to Co/SiO2.Howere,the CO conversion is significantly reduced and the CH4 selectivity is increased,which is mainly attributed to the diffusional limitation of the microporous structure to the synthesis gas and the H2/CO ratio near the active site is higher than that of synthesis gas.The other one reasons is the strong interaction between Co species and carrier,which eventually lead to a low reduction degree.As a result,the F-T reactivity decreased and the CH4 selectivity increased.(2)The delaminated zeolite has been prepared by the process of swelling and delamination of MCM-22(P)with different Si/Al ratio.CTAB and CPAB were respectively used as the swelling agent.The effects of different swelling methods and Si/Al ratio on the pore structure and acidity of the products were investigated.Meanwhile,cobalt catalysts were prepared and studied for F-T synthesis.Results showed that the swelling process with CPAB as the swelling agent can really reduce the temperature.And it could keep the original pore structure and acidity of the zeolite better than the old.Moreover,Co/ITQ-2 catalysts get a higher CO conversion,a similar CH4 selectivity and a high selectivity to C5-C12 liquid fuels compared to Co/MCM-22.Because its high surface areas could offer more accessible acidity.However,using CPAB instead of CTAB as the swelling agent,the former shows no more superior performance of the F-T synthesis.This could be attribute to its partial delamination with CPAB as the swelling agent,which could not provide sufficient accessible acidity.(3)The delaminated zeolite has been directly prepared by one-pot synthesis method with HMI as the dual-templatend and CPAB as interlayer blockers agents.The influence of pH,the dosage of CPAB,the reaction time on the structure and the acidity of the zeolite were investigated.Results showed that:1)The range of pH to the synthesis system is relatively narrow.With low pH the product is tend to be a kind of amorphous materials and with high pH it is tend to turn to MCM-22.2)The concentration of CPAB in the hydrothermal system has a significant effect on the product.With smaller concentration it can not block the ordered arrangement of the molecular sieve effectively.With higher concentration it may inhibit the crystallization of the zeolites and only amorphous substances can be obtained.3)The crystallinity of the zeolite is low when the reaction time is too short,however long time will make the zeolite turn to MCM-22.4)Compared with alkaline treatment method,the cobalt catalysts based on one-pot synthesis method showed a similar performance on F-T synthesis.