The Effect Of The Metallity And Acidity Of The Metal/SAPO-31 Molecular Sieve On The Isomerization Performance Of Normal Paraffins

In this work,using DBA as template,silicoaluminophosphate molecular sieve SAPO-31 molecule sieves were synthesized with ludox or fume SiO2 as silica specie,with aluminium isopropoxide or pseudo-boehmite as aluminum specie,and the bifunctional catalysts were prepared by the incipient wetness impregnation technique.The properties of the samples were characterized by XRD,SEM,TEM,XRF,N2 physical adsorption,Py-IR,H2 chemisorption and H2-TPR.The catalytic performance of the catalysts was evaluated in the probe-reaction of hydroisomerization of n-decane on the fixed bed micro-reaction apparatus.It exhibited that the kind of silica specie and aluminum specie had great influence on the morphology and acidity of synthesized SAPO-31 molecular sieve.The bifunctional catalyst loaded 0.5 wt.%Pd which was prepared by the SAPO-31 molecular sieve synthesized using the ludox as silica specie,pseudo-boehmite as aluminum specie,and SiO2/Al2O3 of 0.6 in the reaction gel possessed the best catalytic performance,when the conversion of n-decane equaled to 90.2%,the selectivity for i-decane reached 90.2%.Series of hierarchical SAPO-31 molecule sieves were successfully prepared with the meopourous templating method and dealumination method by acid treatment.The effect of various mesoporous template such as tetramethylguanidine,glucose,polyethyleneglycol and carbon nanotubes and their content,the kind of acids such as hydrochloride or citric acid and the treatment time on structure,acidity of the synthesized hierarchical SAPO-31 molecule sieves and their catalytic performance was discussed.It showed that the Pd dispersion on the Pd/SAPO-31 catalysts was increased due to the introduction of mesopore,which resulted in promoting generation and diffusion of branched isomers in the n-decane isomerization reaction and the increasing the selevtivity for i-decane,especially for di-branched isomers.The excellent catalytic performance was obtained over the 0.5Pd/S31-C(2h)catalyst in selectivity of 90.3%for i-decane at n-decane conversion of 92.5%,the selectivity for DMC8 in i-C10f which was raised from 25.3%to 30.11%,compred to micropore SAPO-31 molecule sieves as acid support.The influence of palladium salt precursor kind and the palladium loading on the catalytic performance in the n-decane hydroisomerization was investigated.It indicated that 0.3Pd/S31 and 0.3Pd(Cl)/S31 possessed higher selectivity for i-decane.Moreover,the effect metal sites and acid sites ratio(Cpa/CA)on the catalytic performance of n-decane isomerization over the xPd/S31 catalysts prepared using Pd(NO3)2 as precursor with various palladium loading was studied.when the CPd/CA was between 0.053?0.183,xPd/S31catalyst exhibited higher conversion of n-decane and selectivity for i-decane due to the excellent synergetic catalytic effects between the metal sites and acid sites.The bimetal bifunctional catalysts were prepared by loading noble metal palladium and various non-noble metal such as Mg,Cr or Ce.The effect of kinds of non-noble metal and the loading methods on the catalytic performance of n-decane hydroisomerization was discussed.It certified that the synergetic catalytic effect was obtaind between the metal sites and acid sites in n-decane hydroisomerization over the 0.2Mg-0.05Pd/S31 catalyst was prepared using stepwise impregnation method by loading 0.2 wt.%magnesium and 0.05 wt.%palladium which can be attributed to higher palladium dispersion on SAPO-31 molecule sieves resulting in promoting effect of MgO and suitable metal sites and acid sites ratio,the maximum of i-decane yield was raised from 62.6%to 77.6%compared to 0.05Pd/S31 loaded 0.05 wt.%palladium.