Morphoology Control Of One-dimensional Zeolite Crystals

As adsorbents and catalysts,zeolites have been widely applied in industrial processes.Hydroisomerization of n-paraffins has been paid great attention in decades.As important catalysts for hydroisomeization,one-dimensional zeolites have diffusion limitations.As is all known,the catalytic property of zeolites is closely influenced by their diffusion ability.Hence,it is promising to control the morphology of one-dimensional zeolite crystals.Usually,the morphology of one-dimensional zeolites is rod-like.Relative long diffusion path tends to hinder the diffusion of reactants and products.In order to overcome the diffusion limitations,one-dimensional zeolites with morphology of nanoparticles or nanosheet are paid much more attention.In chapter two,one-dimensional zeolite SAPO-11 with nanosheet morphology is rational designed synthesis by adding PHMB in the initial gel.Comparing with conventional SAPO-11 with spherical morphology,the diffusion limitation of SAPO-11 nanosheets is less.It is reported that mono-and multi-zeolite nanosheets have much more pore mouth,which is benefit for hydroisomerization of n-paraffins.Hence,SAPO-11 zeolite nanosheets with partially block in the micropores are an ideal catalyst for hydroisomerization.The calculation results show that SAPO-11 nanosheet with 10 um thickness is relative stable,which is proved by experimental data.Besides,we have investigated the crystallization process of SAPO-11 nanosheets to understand how to form the nanosheet morphology.Notably,Pt/SAPO-11 nanosheets catalysts show higher isomer selectivity and lower cracking selectivity than Pt/Conventional SAPO-11.In chapter three,we have investigated the relationship between the crystallization time and crystallization tenmperature.We designed a rapid synthesis of Omega zeolite at higher temperature based on this relationship.The crystallization time of conventional Omega is as long as 10 d,while here is 5 h at 180 °C.Higher temperature can shorten the crystallization time and the length of the rod.Mostly,shorter length always means shorter diffusion path in one-dimensional zeolites.As we expected,the catalytic performance of Pt/Omega-180 catalyst is a little better than the conventional Pt/Omega catalyst in hydroisomerizationIn chapter four,we control the growth rate of crytal by adjusting the amount of potassium in precursors,which influence the ultimate size of crystal.As a result,we have successfully synthesized a series of zeolite L nanocrystals with different paticle sizes.Interestingly,after loading of Pt nanoparticles(0.5 wt%),the Pt/Nano L-10 catalyst exhibits relative high isomer selectivity in low temperatures,while relative high cracking selectivity in high temperatures.That is to say,we are able to obtain the target products by adjusting the reaction temperatureIn chapter five,we are able to control the length of b-axis of MFI zeolites by adjusting the amount of the template with the same amount of urea in the initial gel We have successfully obtained a series of MFI zeolites with different length of b-axis Furthermore,this method can also be applied in the synthesis of MFI zeolites with high SAR or low SAR to control their b-axis length.Interestingly,these MFI samples might be promising materials for studying the mechanisms of MTO reaction.