Study On Preparation And Catalytic Performance Of Ni-based Catalyst Supported On Molecular Sieve

With the rapid development of economic globalization,energy is increasingly attracting people's attention.Among them,the efficient and clean hydrogen energy is one of the best choices to replace traditional energy sources and improve the environment.The ethanol steam reforming for hydrogen?ESR?technology of ethanol is mature,and the key to its wide application lies in the development of a catalyst with excellent low-temperature activity and high selectivity of hydrogen.In this study,an all-silicon MCM-41 molecular sieve and an antimony-doped C_x-M-T molecular sieve were prepared by a hydrothermal reaction method,N/C_x-M series and N-C_x-M series catalysts were prepared by impregnation method and co-precipitation method,respectively,by loading active component Ni onto MCM-41molecular sieve and doped C_x-M-T molecular sieve carrier.The effects of the doping amount of cerium ions and the calcination temperature on the structure and properties of the silica-based MCM-41 zeolite support were investigated in detail.At the same time,the influence of the loading method of Ni active component on the structure and properties of its series catalysts was also investigated in detail.X-ray power diffraction?XRD?,temperature-programmed reduction?TPR?,thermal analysis?TG-DTA?,N₂ adsorption-desorption isotherms?BET?,X-ray photoelectron spectroscopy?XPS?and transmission electron microscopy?TEM?techniques were used to characterize the molecular sieve support and catalyst.The reaction of ethanol steam reforming for hydrogen was carried out in the minitype active evaluation device to evaluate the activity and selectivity of the catalyst.To investigate the effect of calcination temperature on the structure and properties of molecular sieves,It was found that the molecular sieves calcined at550�C possess hexagonal ordered regular mesoporous structures and slit-like mesoporous structures,with good crystallinity and large specific surface area.The specific surface area of the MCM-41 molecular sieves was 1032.04 m²/g;When the calcination temperature was 650�C,the hexagonal ordered regular mesoporous structure was destroyed,its long-range orderability was reduced,and the calcination temperature was 750�C.The diffraction peaks of the XRD features of the MCM-41molecular sieve completely disappeared.It showed that the hexagonal regular channel of the molecular sieve has completely collapsed,and at the same time,the specific surface area became 711.83 m²/g.That is,the specific surface area of the all-silicon molecular sieve decreased as the calcination temperature increased during preparation.The specific surface area of the molecular sieves prepared from the doped cerium also decreased as the calcination temperature increased.In addition,when examing the relationship between the structure and properties of the doped MCM-41 molecular sieve and the amount of cerium doped,at the calcination temperature of 550�C,the characteristic peaks of the?100?crystal planes of the C_0.5-M-550,C₁-M-550,and C₂-M-550 molecular sieves doped with cerium elements shifted to large angle directions,respectively.cerium ion doping has entered the molecular sieve lattice framework;However,as the amount of cerium increased,the characteristic peaks of the?100?crystal surface of the molecular sieve became weaker and weaker,indicating that the regularity of hexagonal regular pores decreased with the increasing of the amount of doped cerium;However,the samples prepared by calcining at 750�C had no hexagonal mesoporous structural feature diffraction peaks,indicating that the molecular sieve framework collapsed more severely.In summary,it can be seen that when the calcining temperature in the preparation process was too high,or the amount of doped cerium was too large,hexagonal ordered mesopores were not easily obtained.In the research of preparation of series catalysts with Ni active component supported by molecular sieve as carrier it was found that the influence of co-precipitation loading Ni and impregnation loading Ni on the pore structure of the molecular sieves is not much different,in which the ratio of N-M catalyst prepared by co-precipitation method The surface area of the N/M catalyst prepared by the impregnation method reached 953.08 m²/g,and the specific surface area of the fully-siliconized MCM-41molecular sieve reached 915.90 m²/g after impregnation.The extent of the decrease in surface area caused was not significant,and the main reason for the decrease in specific surface area was caused by the molecular sieve being wetted with the solvent,re-dried,and re-fired.When examining the redox properties of the catalyst,it was found that the higher the roasting temperature during sample preparation,the more severe the destruction of the molecular sieve framework,and the more lattice cerium oxide precipitates out of the molecular sieve framework.These precipitated cerium oxides were exposed on the surface of the molecular sieve and were more easily exposed.N/C_x-M catalysts showed the reduction peaks of Ni O at about 400�C and about 500�C;Ni O reduction peaks appear at 400-450�C for N-C_x-M catalysts,at 650-800�C.Between the two methods,the catalysts prepared by the two methods all showed the reduction of cerium oxide on the surface of the molecular sieve framework?about 650�C?and the reduction of cerium oxide in the framework lattice of the molecular sieve?around730�C?;compared with C_x-M-550,the reduced nickel species The presence of the active component on the surface of the molecular sieve facilitates the reduction of cerium oxide.The XPS characterization results of the catalysts showed that,as the doping amount of cerium increasing,the cerium element was partially doped into the molecular sieve framework and partially existed in the free oxidation state(Ce³⁺and Ce⁴⁺)on the surface of the molecular sieve.When the doping amount of cerium was too large,free oxidation of cerium agglomeration and molecular sieve surface,reducing the effective surface area of the molecular sieve,so that the dispersion of Ni on it decreased,resulting in reduced activity of the catalyst;XPS results show that Si,O element binding energy both tend to decrease when the calcination temperature increased,resulting in the loss of more lattice oxygen and an increase in its reduction temperature.The performance evaluation of Ni-C_x-M series catalysts showed that the appropriate amount of cerium element doping can improve the reactivity and selectivity of the catalyst.When cerium doping amount is 4.0%,the catalytic effect was best,the ethanol conversion rate reacheed 100%,and the percentage of hydrogen can reach 100%in the lower temperature range?400-500�C?.No CO was detected in the ethanol steam reforming reaction product completed on the series of catalysts,which may benefit from the catalyst prepared by doping cerium has a good ability to store oxygen and release oxygen,reducing the production of CO.