Synthesis Of Hierarchically Porous SAPO-11 Zeolite For The Hydrogenolysis Of Glycerol To 1, 2-propanediol

The rapid development of biodiesel industry has brought about a large surplus of by-product glycerol.How to make rational use of these excess by-product glycerol and find a reasonable and effective way to convert it into more commercially valuable chemical products is a focus of global concern.Among them,hydrogenolysis of glycerol to form propanediol is considered to be the most promising.The design and preparation of catalyst is the key to hydrogenolysis of glycerol.Therefore,a series of metal-acid bifunctional catalysts with hierarchically porous SAPO-11 zeolite?M-SAPO-11?as support and transition metal as active component were prepared and used to catalyze hydrogenolysis of glycerol.Firstly,from the aspects of the preparation parameters of the M-SAPO-11,the texture properties and acidic characteristics of the prepared support were investigated.Secondly,Cu,Ni and Co transition metals as active components,their metal properties were studied.Finally,the catalytic activity and hydrothermal stability of the prepared catalysts for hydrogenolysis of glycerol were systematically tested.The experimental results show that M-SAPO-11 with flower crystallites has a smaller particle than the conventional microporous SAPO-11 zeolite.M-SAPO-11 was synthesized by using a cationic surfactant.The loading of the transition metal Cu or/and Ni catalyst does not change the zeolite structure,but the metal affects the pore structure and acidic properties by occupying some porous channels or acid sites.The experimental results also show that M-SAPO-11 supported Cu catalyst?Cu/M-SAPO-11?has a higher activity in the hydrogenolysis of glycerol,compared to SAPO-11,hierarchically porous Beta and hierarchically porous ZSM-5 zeolite.The mesoporous structure of M-SAPO-11 alleviates the diffusion barrier present in the channels of conventional microporous SAPO-11 zeolites,and the medium strength acid sites of M-SAPO-11 avoid the formation of by-products.The M-SAPO-11 supported metal Cu/Ni atomic ratio of 2/1 catalyst?Cu₂Ni/M-SAPO-11?exhibits superior catalytic performance in the Cu or/and Ni catalysts supported on M-SAPO-11.The main reason is the formation of Cu-Ni alloy in bimetallic catalyst,which makes it has the better metal-acid synergistic effect.In addition,longer reaction time and higher H₂ pressure are found to favor glycerol conversion.Besides,the reaction temperature has a great influence on the catalytic reaction.When the temperature reaches 240°C,about 93.0%of theglycerol is converted.Finally,after the circular tests,it is seen that the Cu₂Ni/M-SAPO-11catalyst still has high catalytic stability.Additionally,a highly active Co doped hierarchically porous SAPO-11 catalyst?Co-M-SAPO-11?was successfully prepared and used for hydrogenolysis of glycerol to1,2-propanediol.Directly synthesized Co-M-SAPO-11 has more L acid sites and larger mesopores than conventional supported Co catalysts.Co-M-SAPO-11 with more L acid site facilitates the dehydration of glycerol to produce the intermediate acetol.The characteristic mesoporous structure of M-SAPO-11 mitigates the diffusion barrier of the reactants or/and products and also provides a more efficient space for the dispersion of Co metal.A suitable amount of Co introduction?5 wt.%?can provide highly dispersed metal active sites without clogging the pores of the catalyst.Under optimized conditions?4.0 MPa H₂,220°C and 8 h?,Co-M-SAPO-11 catalyst has outstanding catalytic performance of 90.9%glycerol conversion and 87.6%selectivity to 1,2-propanediol.After several cycles of reaction,the surface of the catalyst may accumulate organic compounds to cause a decrease in catalytic activity,but the process of high-temperature calcination may regenerate the partially deactivated catalyst.Besides,the possible structural model of Co-M-SAPO-11 is proposed for the first time.