The Preparation And Study On The Regeneration Performance Of Catalyst For Hydrogen By Methane Catalytic Cracking

With the aggravation of global energy crisis,the quality of crude oil becomes worse and worse day by day,and the requirement of environmental protection is being strict increasingly,therefore seeking for renewable alternative energy resources,and improving the refining capacity of crude oil have come to the top priority.Hydrogen,as a kind of clean and efficient energy,not only can be used as an energy source directly,but also is an important raw material for hydro-treatment process which is an important processing method of crude oil in refinery.Therefore,how to generate hydrogen in a stable and efficient way has become a urgent problem to be solved.In this thesis,based on a two-step catalytic decomposition of methane for hydrogen production process,we have prepared catalysts based on aluminium oxide using nickel as active metal,explored the effect of magnesium and lanthanum donation on the catalytic performance,and the catalytic performance of catalysts in reaction-regeneration cycles has also been investigated.Besides,we have prepared a new kind of catalyst which was nickel based on molecular sieve using hydrothermal synthesis method.We used the synthetic catalysts in experiment of methane catalytic cracking and compared their catalytic performance with the catalysts prepared by conventional impregnation method.In this thesis,We have prepared NiO/Al2O3 catalysts with different nickel loading using a sol-gel method,different Ni O loading could lead to different exist conditions of nickel species on the catalyst.The methane conversion rate increased and the hydrogen selectivity reduced gradually with the increase of NiO loading.In the experiments,we found that catalyst with 40wt% of NiO loading could achieve best catalytic performance.The introduction of magnesium and rare earth elements like cerium,lanthanum and zirconium could raise the methane conversion rate,the addition of magnesium could form MgAl2O4 with Al2O3,so can inhibit the formation of NiAl2O4.The reduction of nickel species would become more easily attribute to the weaken of the interaction between the active component and support.Besides,We have prepared nickel based ZSM-5 zeolite catalysts for methane catalytic decomposition reaction using a hydrothermal synthesis method.We have found that the nickel atoms have existed as a part of molecular sieve skeleton through a UV-vis characterization when the NiO loading was below 10wt%.Compared with the catalysts prepared by conversional impregnation method,the catalysts made by hydrothermal synthesis method could achieve better dispersion of nickel atoms.The catalytic performance of the hydrothermal synthesis catalysts were better than the impregnated catalyst at the same NiO loading.A reaction-regeneration experiment has been carried out on the 40wt%NiO-5wt%MgO-3wt%La2O3/Al2O3 catalyst,we have gotten the conclusions follow.The conversion of methane increased and the hydrogen selectivity decreased with the extension of regeneration time.After the part regeneration of catalyst,there still remained part of the carbon deposition,this would consume the lattice oxygen on the catalyst due to its reducing capacity,that would lead to the increase of hydrogen selectivity.With the increase of reaction and regeneration cycles,the hydrogen selectivity gradually increased while the conversion of methane decreased.The increase of regeneration temperature was advantageous to the combustion of deposited carbon on the catalyst,and would lead to the increase of methane conversion rate,while decreased the hydrogen selectivity.