Study On The Catalytic Performance Of B-doped NiPB/H? Catalyst For N-hexane Isomerization

At present,most of the catalysts of light alkane isomerization used in industrial are noble metal catalysts.Although noble metal catalysts have the advantages of high catalytic activity and good stability,such catalysts are expensive and are very sensitive to impurities such as sulfur in raw materials.In order to maintain the acidity of the catalyst,it is necessary to continuously replenish the halogen,which not only corrodes the equipment but also pollutes the environment.In order to reduce the cost of the isomerization catalyst and improve the applicability of the catalyst,our research group has previously studied the non-noble metal nickel-based isomerization catalysts which have a good performance of catalytic isomerization.However,there are still some problems in the synthesis process of the active component NiP,for example,the synthesis yield of NiP is low,and the washing solvent pollutes the environment.Therefore,based on the previous research,this paper continues to study in-depth on the nickel-based catalysts,and it is expectd to obtain a green catalyst with improved catalytic performance.Firstly,the effects of nickel source,washing solvent type and washing time on the yield of NiP were studied.NiP/H?catalyst was further prepared by NiP synthesized with improved method.The catalytic performance for n-hexane isomerization was investigated.The results show that the yield of NiP synthesized by the improved method is 57%,and the washing solvent and trinpropylamine in the waste liquid can be recycled and reused.The conversion and isoparaffin selectivity of n-hexane isomerization catalyzed by NiP/H?catalyst is 81%and97%,respectively.The results of XRD,BET,NH₃-TPD and TG showed that the NiP/H?catalyst has good thermal stability and structural stability,and the acidity of the catalyst is suitable,which can reduce the cracking reaction.Then,the active component NiPB were synthesized by doping element B into NiP.The effects of the amount of substance ratio of Ni,P and B in the raw material,the washing mode on the NiPB and synthesis yield were studied.The results showed that the suitable ratio of Ni,P and B in the raw material was 1:1:1,whereby the yield of the amorphous NiPB synthesized by the suitable ratio was 82%.The results of XRD,BET and SEM showed that the NiPB/H?catalyst prepared by the amorphous NiPB has a large specific surface area.The active component of NiPB is uniformly dispersed on the support,and the NiPB/H?catalyst exhibits excellent catalytic isomerization performance.The influence of preparation conditions and reaction conditions on the catalytic performance of the NiPB/H?catalyst were studied.The optimized preparation conditions are:NiPB loading is 10%,calcination temperature is 200 ^oC and calcination time is 2 h;and the optimized reaction conditions are:reaction temperature is 300 ^oC,reaction pressure is 2 MPa,H2-to-n-hexane molar ratio is 4 and WHSV is 1 h^-1.The catalyst has a large surface area and pore volume,and NiPB is uniformly dispersed on the surface of the carrier.The suitable acidity is favorable for the skeletal isomerization of the intermediate.The conversion,isoparaffin yield and selectivity of n-hexane isomerization catalyzed by NiPB/H?catalyst is80%,78%and 98%,respectively.Finally,the effects of reaction atmosphere,metal active site and acid sites on the catalytic performance of the catalyst were studied,and the catalytic isomerization mechanism was analyzed.The H2 atmosphere can inhibit the occurrence of cracking reaction,and the metal active site provides the dehydrogenation-hydrogenation center,meanwhile the acid site provides the skeletal isomerization center of the intermediate produced in the isomerization process.In addition,the deactivated catalyst was regenerated by coke burning,the conversion of n-hexane isomerization catalyzed by regenerated catalyst is 63%.