Promoting Xylene Production in Benzene Methylation using Hierarchically Porous ZSM-5 Derived from a Modified Dry-gel Route

Methylation of benzene is an alternative low-cost route to produce xylenes, but selectivity to xylene remains low over conventional zeolitic catalysts. In this work, a combined dry-gel-conversion and steam-assisted- crystallization method is used to synthesize hierarchically porous zeolite ZSM-5 with varied Si/AI malar ratios. X-ray diffraction （XRD）, N2 physisorption, NH3-temperature programmed desorption （TPD）, scanning electronic microscopic （SEM） measurement and Fourier transform infrared （FT-IR） are employed to characterize the struc- ture and acidity of both hierarchically porous zeolites and their conventional counterparts. The method is found to be applicable to ZSM-5 with molar ratios of Si/A1 from 20 to 180. The ZSM-5 zeolites are used as catalysts for benzene methylation at 460 ℃ to investigate the effect of additional porosity and Si/A1 ratios. At low Si/AI ratios, the benzene conversions over conventional and hierarchical ZSM-5 are close, and selectivity to toluene is high over hierarchical ZSM-5. It is found that hierarchical porosity markedly enhances the utility of zeolite and the se- lectivity towards xylenes via improved mass transport at higher Si/Al ratios. Under an optimized hierarchical ZSM-5 catalvst, xvlene selectivity reaches 34.9% at a Si/AI ratio of 180.

Preparation of hierarchical ZSM-5 zeolite and its application in synthesis of tributyl citrate

First,the hierarchical ZSM-5 zeolite was prepared by hydrothermal method using mesoporous template cetyltrimethylammonium bromide(CTAB).The physical and chemical properties of the hierarchical ZSM-5 zeolite were characterized by X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR)and N2 adsorption-desorption and Scanning electron microscope(SEM).Then,the as-prepared hierarchical ZSM-5 zeolite and ion exchange resin were used as catalysts to evaluate the reaction performance of the synthesis of tributyl citrate.Compared with the ion exchange resin,the as-prepared ZSM-5 has a microporous and mesoporous composite structure and a large specific surface area,so that significantly improving the catalytic performance of synthesizing tributyl citrate and increasing the esterification rate of the reaction 8.7%.

Hierarchically Structured Monolithic ZSM-5 through Macroporous Silica Gel Zeolitization

The hierarchically structured ZSM-5 monolith was prepared through transforming the skeletons of the macroporous silica gel into ZSM-5 by the steam-assisted conversion method. The morphology and monolithic shapes of macroporous silica gel were well preserved. The hierarchically structured ZSM-5 monolith exhibited the hierarchical porosity, with mesopores and macropores existing inside the macroporous silica gel, and micropores formed by the ZSM-5. The products have been characterized properly by using the XRD, SEM and N2 adsorption–desorption methods.

Construction of monodispersed single-crystalline hierarchical ZSM-5 nanosheets via anisotropic etching

Hierarchical zeolites and single-crystalline zeolite nanosheets(NSs)have been recognized as two separate types of targeting porous materials to overcome the diffusion limitations of traditional bulk zeolites.The synthesis of uniform single-crystalline hierarchical zeolite NSs featured with NS morphology and interconnected mesoporosity,remains rarely reported.In this work,we prepared ZSM-5 zeolites with the above microstructural features via simple alkaline etching.Moreover,both their microstructure and acid strength could be accurately tuned with this approach,resulting in not only higher conversion rate and BTX selectivity but also superior anti-coking performance in the subsequent methanol aromatization reaction.

Synthesis of ZSM-5 Monoliths with Hierarchical Porosity

A new route to synthesize ZSM-5 monoliths with hierarchical pore structure has been referred to in this study. The successful incorporation of the macropores and mesopores within the ZSM-5 struc- ture was achieved through transforming the skeleton of the macroporous silica gel into zeolite ZSM-5 using carbon materials as the transitional template. The ZSM-5 crystal covered part of the macroporous material, and provided micropores to the macroporous silica gel. The structure of carbon monolith was studied after dissolving the silica contained in the carbon/silica composite.

Hierarchically Macroporous Zeolite ZSM-5 Microspheres for Efficient Catalysis

Hollow zeolite microspheres have recently attracted much attention for their applications in catalysis,microreactors and biomedicine.Herein,we present hierarchically structured zeolite ZSM-5 microspheres with unique,abundant macropores that allow more efficient use for catalysis.The hierarchically macroporous zeolite ZSM-5 microspheres are synthesized under the assistance of water/oil emulsions and using polystyrene nanospheres as templates.The zeolite microsphere is assembled by uniform hollow zeolite nanospheres.Their large inner cavities and thin zeolite shells lead to smaller diffusion channel and higher improved accessibility to active sites,contributing to high catalytic performance in the catalytic conversion of benzyl alcohol in mesitylene.Such novel zeolite microspheres with impressive performance will be applied to numerous other industrial catalytic reactions.

改性多级孔ZSM-5催化裂解MTP副产烃性能研究

围绕甲醇制丙烯(MTP)副产烃的综合利用,选择其中较难裂解的C_4-C_6低碳混合烃为研究对象,开展了Ce、Fe、La、P改性多级孔ZSM-5的催化性能研究。元素改性后多级孔ZSM-5表面酸分布发生了较大变化。P改性样品具有最大的B/L值,丙烯及双烯(乙烯和丙烯)选择性达到最大;P含量增加降低了表面B酸量及强酸强度,同时增加了B/L值,丙烯及双烯选择性增加,但转化率下降。在500℃及1850h^(-1)条件使用3.5P/MZ催化剂,丙烯及双烯选择性达到39.4%和65.5%,收率分别为25.6%和42.6%。

Hierarchical Porous ZSM-5 Zeolite Synthesized by in situ Zeolitization and Its Coke Deposition Resistance in Aromatization Reaction

Hierarchical ZSM-5 zeolites with micro-, meso- and macroporosity were prepared from diatomite zeolitization through a vapor-phase transport process on solid surfaces. The aromatization performance of the catalysts was in- vestigated on a fixed bed reactor by using FCC gasoline as feedstock. The crystal phase, morphology, pore struc- tures, acidity and coke depositions of the hierarchical ZSM-5 zeolites were characterized by means of X-ray diffrac- tion （XRD）, scanning electron microscope （SEM）, N2 adsorption/desorption, Fourier transform infrared （FT-IR） and thermogravimetry-mass spectrogram （TG-MS）, respectively. The results show that the prepared hierarchical ZSM-5 zeolite possesses excellent porosity and high crystallinity, displaying an improved aromatization performance and carbon deposition resistance due to its meso- and macroporous structures.

Hierarchical ZSM-5 zeolite with radial mesopores:Preparation,formation mechanism and application for benzene alkylation

Hierarchical ZSM-5 zeolite with radial mesopores is controllably synthesized using piperidine in a NaOH solution.The piperidine molecules enter the zeolite micropores and protect the zeolite framework from extensive desilication.The areas containing fewer aluminum atoms contain fewer piperidine protectant molecules and so they dissolve first.Small amounts of mesopores are then gradually generated in areas with more aluminum atoms and more piperidine protectant.In this manner,radial mesopores are formed in the ZSM-5 zeolite with a maximal preservation of the micropores and active sites.The optimal hierarchical ZSM-5 zeolite,prepared with a molar ratio of piperidine to zeolite of 0.03,had a mesopore surface area of 136 m·g and a solid yield of 80%.The incorporation of the radial mesopores results in micropores that are interconnected which shortened the average diffusion path length.Compared to the parent zeolite,the hierarchical ZSM-5 zeolite possesses more accessible acid sites and has a higher catalytic activity and a longer lifetime for the alkylation of benzene.

Mesoporous ZSM-5 Crystals Synthesized by a Novel Amphiphilic Organosilane Soft Template

Hierarchical ZSM-5 zeolite was hydrothermally synthesized by a novel silicone quaternary ammonium salt surfactant as a mesopore director.The crystallinity and the morphology of sample were characterized by X-ray diffraction(XRD),field-emission scanning electron microscope(FE-SEM),and transmission electronic microscope(TEM).Results indicated that the prepared ZSM-5 zeolites had good crystallinity,ellipsoid structure morphology and rough surface.Moreover,the pore size was enlarged to about 4 nm measured by nitrogen sorption,which indicated positive function of the synthesized template.

Functionalized Hierarchical ZSM-5 Zeolites for the Viscosity Reduction of Heavy Oil at Low Temperature

Herein,we propose a novel approach to reduce the viscosity of heavy oil by functional hierarchical CTMS-ZSM-5-PTMS zeolites.CTMS-ZSM-5-PTMS zeolites synthesized by asymmetric modification and selective alkali etching can reduce the viscosity of heavy oil through adsorbing asphaltenes.This method can reduce the viscosity of heavy oil from hundreds of thousands mPa·s to about ten thousand mPa·s.The work provides an economical and environmentally friendly candidate for heavy oil viscosity reduction under low-temperature conditions.

Comparative study of microwave-assisted versus conventional heated reactions of biomass conversion into levulinic acid over hierarchical Mn_(3)O_(4)/ZSM-5 zeolite catalysts

Conversion of delignified cellulose from rice husk biomass,and model compounds of cellobiose and glucose to levulinic acid(LA)over hierarchical Mn_(3)O_(4)/ZSM-5 catalyst was carried out using a household microwave method,and then compared to the established conventional thermos-reaction method.The hierarchical ZSM-5 was prepared using a double template method,aiming for micro and mesoporous systems developed in the structure.The as-prepared ZSM-5 were modified with Mn3O4 through incipient wetness impregnation with Mn2+solution followed by calcination at 550℃.The catalysts were characterized using various techniques such as powder XRD,SEM,BET,AAS,and FT-IR which indicated the hierarchical structure of MFI zeolite(Si/Al of 30-34)with Mn loading of 2.14 wt%.The conversion products were analyzed using HPLC,1H NMR,and 13C NMR instruments.The microwave-assisted reaction using 600 W for 180 s using delignified cellulose,cellobiose,and glucose gave conversion of 37.27%,46.35%,and 54.29%,respectively which is close to the conversion given by the conventional reaction carried out at 130◦C for 4 h(36.75%,55.62%,and 60.9%,respectively).Interestingly,the LA yield from the microwave-assisted reaction(4.33%,6.12%,and 9.57%)is higher than the yield from the conventional reaction,which only produced 5.2%,4.88%,and 6.93%respectively.The microwaveassisted method is also shown to give less by-products compared to the thermochemical reaction.Therefore,it could be considered an alternative method for converting cellulose to LA.

Solid-conversion synthesis of three-dimensionally ordered mesoporous ZSM-5 catalysts for the methanol-to-propylene reaction

A facile synthesis of hierarchical ZSM-5 with the three-dimensionally ordered mesoporosity(3DOm ZSM-5)was achieved by solid conversion(SC)of SiO_(2)colloidal crystals to high-crystalline ZSM-5.The products of 3DZ5_S/C and 3DZ5_S,which were severally transformed from the carbon-padded SiO_(2)colloidal crystals and the initial SiO_(2)colloidal crystals,exhibited not only a similar ordered structure and acidity but also higher crystallinity and more balanced meso-/micropore combination in comparison with 3DZ5_C obtained by the conventional confined space crystallization approach.All three synthesized 3DZ5 catalysts showed improved methanol-to-propylene performance than the commercially microporous ZSM-5(CZ5),embodied in five times longer lifetime,higher propylene selectivity and S_(propylene)/S_(ethylene) ratio(P/E),and superior coke toleration with lower formation rate of coke(R_(coke)).Moreover,the 3DZ5_S catalyst in situ converted from SiO_(2)colloidal crystals presented the highest selectivities of propylene(42.51%)and light olefins(74.6%)among all three 3DZ5 catalysts.The high efficiency in synthesis and in situ utilization of SiO_(2)colloidal crystals demonstrate the proposed SC strategy to be more efficiently and eco-friendly for the high-yield production of not only 3DOm ZSM-5 but also other types of hierarchical zeolites.