Mesoporous zeolites as efficient catalysts for oil refining and natural gas conversion

Zeolites have been regarded as one of the most important catalysts in petrochemical industry due to their excellent catalytic performance. However, the sole micro- pores in zeolites severely limit their applications in oil refining and natural gas conversion. To solve the problem, mesoporous zeolites have been prepared by introducing mesopores into the zeolite crystals in recent years, and thus have the advantages of both mesostructured materials （fast diffusion and accessible for bulky molecules） and micro- porous zeolite crystals （strong acidity and high hydro- thermal stability）. In this review, after giving a brief introduction to preparation, structure, and characterization of mesoporous zeolites, we systematically summarize catalytic applications of these mesoporous zeolites as efficient catalysts in oil refining and natural gas conversion including catalytic cracking of heavy oil, alkylation, isomerization, hydrogenation, hydrodesulfurization, methane dehydroaromatization, methanol dehydration to dimethyl ether, methanol to olefins, and methanol to hydrocarbons.

Synthesis of mesoporous high‐silica zeolite Y and their catalytic cracking performance

Mesoporous high‐silica zeolite Y with advantages of improved accessibility of acid sites and mass transport properties is highly desired catalytic materials for oil refinery,fine chemistry and emerg‐ing biorefinery.Here,we report the direct synthesis of mesoporous high‐silica zeolite Y(named MSY,SiO_(2)/Al2O_(3)≥9.8)and their excellent catalytic cracking performance.The obtained MSY mate‐rials are mesoporous single crystals with octahedral morphology,abundant mesoporosity and ex‐cellent(hydro)thermal stability.Both the acid concentration and acid strength of H‐form MSY are obviously higher than those of commercial ultra‐stable Y(USY),which should be attributed to the uniform Al distribution of MSY zeolite.The H‐MSY displays an obviously reduced deactivation rate and improved catalytic activity in the cracking reaction of bulky 1,3,5‐triisopropylbenzene(TIPB),as compared with its mesoporogen‐free counterpart and USY.In addition,H‐MSY was investigated as catalyst for the cracking of industrial heavy oil.The MSY‐based catalyst(after aging at 800 oC in 100%steam for 17 h)exhibits superior conversion(7.64%increase)and gasoline yield(16.37%increase)than industrial fluid catalytic cracking(FCC)catalyst under the investigated conditions.

Mesoporous zeolites for biofuel upgrading and glycerol conversion

With the recent emphasis and development of sustainable chemistry, the conversion of biomass feed- stocks into alternative fuels and fine chemicals over various heterogeneous catalysts has received much attention. In particular, owing to their uniform micropores, strong acidity, and stable and rigid frameworks, zeolites as catalysts or co-catalysts have exhibited excellent catalytic performances in many reactions, including hydrodesulfurization, Fischer-Tropsch synthesis, and hydrodeoxygenation. However, the relatively small sizes of the zeolite micropores strongly limit the conversion of bulky biomolecules. To overcome this issue, mesoporous zeolites with pores larger than those of biomolecules have been synthesized. As expected, these mesoporous zeolites have outperformed conventional zeolites with improved activ- ities, better selectivities, and longer catalyst lives for the upgrading of pyrolysis oils, the transformation of lipids into biofuels, and the conversion of glycerol into acrolein and aromatic compounds. This review briefly summarizes recent works on the rational synthesis of mesoporous zeolites and their superior catalytic properties in biomass conversion.

Enhanced Ultraviolet Resistance of Polypropylene Random Copolymer Filled by ZnO-supported Mesoporous Zeolite

To enhance the ultraviolet resistance of ZnO based polymer materials, ZnO-supported mesoporous zeolite（M-ZnO） was prepared and characterized by atomic absorption spectroscopy and scanning electron microscopy. The ultraviolet resistance, crystallization behavior and melting characteristics of ZnO and M-ZnO filled PPR composites were compared by FTIR spectra and differential scanning calorimetry. The ultraviolet resistance of M-ZnO filled PPR composites is higher than that of ZnO filled PPR composites, indicating higher ultraviolet resistance of M-ZnO than that of ZnO. The crystallization temperatures of mesoporous zeolite filled PPR were higher than those of M-ZnO and decreased with increasing UV-irradiation time. But the crystallization temperatures of M-ZnO filled PPR composites were not influenced by UV-irradiation time. The ZnO supported on the surface of zeolite is effective in enhancing the ultraviolet resistance of ZnO based polymer materials.

Preparation of Core-Shell Composite of Y@Mesoporous Alumina and Its Application in Heavy Oil Cracking

A well core-shell composite of Y@meso-Al with a mesoporous alumina shell and a Y zeolite core was synthesized. The mesoporous alumina shell has a wormhole-like structure with large mesopores. The prepared catalytic cracking catalyst using this composite has exhibited excellent catalytic performance for heavy oil cracking thanks to its favorable physicochemical properties, such as high surface area, large pore volume and outstanding acid sites accessibility for large molecules provided by the composite. In comparison with the reference catalyst using pure Y zeolite, the oil conversion achieved by the above-mentioned catalyst increased by 2.73 percentage points, while the heavy oil yield and coke yield decreased by 2.23 percentage points and 1.28 percentage points, respectively, with the light oil yield increasing by 2.27 percentage points.

Synthesis and characterization of hierarchical nanoporous HY zeolites from acid-activated kaolin

Hierarchical nanoporous HY zeolites were synthesized from acid-activated kaolin. The hierarchical factor （HF） was maximized by varying the aging and crystallization time. This was achieved by maximizing the external surface area without greatly reducing the micropore volume. The resulting products were characterized using X-ray diffraction （XRD）, X-ray fluorescence, N2 adsorption, and NH3 temperature-programmed desorption. The nanoporous HY zeolite with the highest HF was obtained by aging for 48 h and a crystallization time of 24 h. The acidiW and crystallinity varied depending on the operating parameters. Incorporation of an appropriate amount of NaCI was also vital in maximizing the HF, crystallinity, and acidity. The sample crystallinities were determined by comparing their XRD peak intensities with those of a conventional Y zeolite. The results show that optimizing this process could lead to a widely acceptable commercial route for FIY zeolite production.

Modification and sequential treatment of EU-1 zeolite in mild alkali and alkaline-acid conditions

EU-1 zeolites were sequentially treated with low-concentration sodium carbonate(Na_2CO_3) and hydrochloric acid(HCl) solutions.The obtained samples were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),N_2 adsorption/desorption,temperature programmed desorption of NH_3(NH_3-TPD),solid state^(27)A1 nuclear magnetic resonance(^(27)A1 NMR),and the catalytic performances of the treated samples were tested in the xylene isomerization reaction.The results showed that the external surface area and mesoporous volume of the sample sequentially treated with 0.05 mol·L^(-1) Na_2CO_3 and 0.1 mol·L^(-1) HCl solutions reached73.9 m^2·g^(-1) and 0.162 cm^3·g^(-1),respectively.The catalytic performances of EU-1 zeolites were significantly improved,that the activity of the probe reaction increased from 23.03%to 23.61%and the selectivity increased from85.09%to 87.14%compared with those of parent sample.Furthermore,it was found that only amorphous silica and alumina species was dissolved during the post-treatment process,but the framework structure and the acidic properties of EU-1 zeolite remained intact.

Synthesis of atomically dispersed cationic nickel-confined mesoporous ZSM-48(ANMZ-48)directed by metal complexes in amphiphilic molecules

The synthesis of mesoporous zeolite-anchored atomically dispersed metal catalysts(ADCs)is a considerable challenge in chemistry and materials science.Here we report the synthesis of atomically dispersed cationic nickel-confined mesoporous ZSM-48(ANMZ-48)by in situ hydrothermal reaction employing a designed tri-functional metal complex template,by which the triquaternary ammonium groups in the hydrophilic region direct the formation of ZSM-48 zeolite;the aromatic groups in the hydrophobic tail generate the mesopores through π-π stacking;and the complexes formed by nickel ions coordinated with terpyridyl groups generate atomically dispersed Ni2+confined in zeolite frameworks due to the strong sintering resistance generated by the strong coordination interaction.The ANMZ-48 is consisting of stacking of sheet-like ZSM-48 domains connected by multiply crystal twinning sharing the common(011)plane,generating abundant of imbedded mesopores with the uniform thickness of~2.4 nm and with the width of 10-50 nm.The excellent catalytic activity and stability of ANMZ-48 were also reflected in the dry reforming of methane(DRM)reaction.

Additive-free synthesis of mesoporous FAU-type zeolite with intergrown structure

Hierarchical porous zeolites attract great at- tention because of their porosity on different scales to improve molecular diffusion. Here, we report mesoporous Faujasite （FAU） zeolite nanosheets with intergrown structure synthe- sized in an additive-free system. The sample was composed of uniform nanosheets with a slice thickness of -50 nm, which held a honeycomb-like structure with abundant mesopores. This material exhibits both microporous and mesoporous structure： the intrinsic micropores with a diameter about 0.74 nm in the zeolite framework and the mesopores with a diameter about 10 nm existing within the zeolite nanosheets. The Si/AI ratios can be adjusted from I.I to 1.9 （zeolites X or Y）. In addition, this simple and environment-friendly method may provide inspiration to the synthesis of other hierarchical zeolites.

Direct synthesis of ordered mesoporous ZSM-5 zeolites from in situ crystallization of carbonaceous SBA-15

Two types of ordered mesoporous ZSM-5 zeolites with different mesopores were synthesized by a two-step method. First, carbonaceous SBA- 15 was produced by in situ carbonization of SBA- 15/P 123 composite. Then the obtained SBA- 15/C composite was transformed into crystallized mesoporous ZSM-5 by impregnation TPAOH followed by steam-assisted crystallization. The final calcined samples synthesized with typical SBA-15/P 123 precursor showed a wormlike morphology with the mean mesopore size of 4.6 nm, while samples synthesized with the addition of trimethylbenzene as swelling agent in the precursor exhibited the morphology of microsphere with the mesopore size of about 9.5 nm. Both two types of mesoporous ZSM-5 zeolites exhibited large surface area and mesopore structure. The steam-assisted crystallization （SAC） was performed with lower consumption of solvents. This two-step method may also be suitable for synthesizing other ordered mesoporous zeolites used as catalysts in some catatytic processes.

Trimodel hierarchical yolk-shell porous materials TS-1@mesocarbon:Synthesis and catalytic application

Trimodal hierarchical yolk-shell materials consisting of TS-1 core and mesoporous carbon shell （YS-TS- I@MC） was successfully synthesized by using TS-l@mesosilica as hard template, sucrose as carbon source and organic base tetrapropylammonium hydroxide （TPAOH） as silica etching agent. The resultant YS-TS-I@MC contains the micropores （0.51 nm） in TS-1 core, the mesopores （2.9 rim） in carbon shell as well as a void or a stack pore between TS-1 fragements （TS-1 intercrystal mesopores, -18.4 nm）. Under the rigorous etching conditions, the crystalline structure of TS-1 core was well retained. The YS-TS- I@MC served as a good support for palladium nano-particles （Pd NPs） or Rh（OH）x species, giving rise to efficient bifunctional catalysts for the tandem reactions including one-pot synthesis of propylene oxide or amides.