| ZSM-5 zeolite has unique structure and is often used directly or as carrier materials in the fields of shape-selective catalysis and petrochemical industry.Traditional synthesis process of ZSM-5 zeolite is more complex and disadvantageous such as a large amount of wastewater discharging,high energy consumption and non-enviromental friendly.As we known,ZSM-5 is one of important catalyst for MTP reaction.Focus on the low selectivity of propylene and short lifetime,a simple and green solid phase method for the synthesis of[M,H]ZSM-5 is proposed in this article.HZSM-5,[B,H]ZSM-5 and[Mn,H]ZSM-5 were directly synthesized by solid phase method.The catalytic performance of Boronisomorphous substituted HZSM-5 and Mn-containing HZSM-5 for methanol to propylene was studied in detail.1.Proton-type ZSM-5 was synthesized by solid phase method and the effect of time,temperature,and alkalinity were investigated in detail.The method avoids the use of excessive water,dry gel,Na+cation and fluoride.Crystallization by using the stoichiometric amount of TPAOH at 180℃ for only 12 h gave well-structured HZSM-5 crystals with high specific surface area of 429 m2/g and high thermal stability.Moreover,HZ-12-180 shows excellent catalytic activity for methanol to propylene reaction by comparison with commercial HZSM-5.2.The crystallization dynamic kinetics of solid phase synthesis was studied.It was found it exhibits shorter induction period(t0),higher nucleation rate(Vn),faster growth rate(Vg),and low activation energies by comparison with the conventional hydrothermal method.The HZSM-5 units can be constructed quickly for the solid phase synthesis.The crystallization mechanism showed that the five member rings(5MRs)was closely relate with the formation of MFI structure.3.Boron-isomorphous substituted HZSM-5,[B,H]ZSM-5 zeolite(BHZ)was directly synthesized by solid-phase method and the properties were characterized by XRD,FESEM,N2 adsorption/desorption,FT-IR,ICP-AES,NH3-TPD,py-FTIR,TG,GC-MS,solid MAS NMR and UV-Vis of Co2+.It was found that the acid distribution was tuned and the AlF siting was changed when introduced boron into the ZSM5 framework,which significantly affected the catalytic performance of BHZ sample in MTP reaction.The preferential occupying in the channel intersections and sinusoidal channels of boron atoms caused AlF sited in the straight and sinusoidal channels,which simultaneously tuned acid distribution and weakened the acid strength in the channel intersections.These changes tuned the ducal-cycle mechanism of MTP,resulting in lower carbon deposition rate and longer lifetime for BHZ samples,especially for 2.5-BHZ,by comparison with HZ sample.4.Mn-containing HZSM-5,[Mn,H]ZSM-5 zeolite was also directly synthesized by a solid-phase method,and its physicochemical properties was characterized via XRD,N2 adsorption/desorption,FT-IR,TEM,HAADF-STEM-EDX,ICP-OES and MAS NMR.The direct evidence of tetracoordinated framework Mn(III)was authenticated by UV-Vis,Raman,XPS and H2-TPR.Meanwhile,the Mn atoms can tune and stead the acidity of ZSM-5 zeolite,which increased weak BAS and decreased the SAS,thus restrained hydrogen-transfer and aromatization reactions.27Al MAS NMR revealed that introduction of Mn lead to increase the amount of AlF siting in straight channels,thus causing the aromatic-based cycles are depressed.Meanwhile,in situ DRIFTS and GC-MS also prove that introduction of manganese significantly reduce the carbon deposition rate and the Mn-HZ produce more hydrocarbon pool species.Therefore,the Mn-HZSM-5 zeolite has longer lifetime and high selectivity to propylene and butene in MTP reaction.In addition,the reaction mechanism for MTP reaction was proposed.Ethylene was detected with high concentrations at the preliminary stage and it might be the initial HCP species.Mn-HZ more benefited for the olefin-based cycle mechanism. |
