Template-free ZSM-5 Research Articles

Synthesis of Template-Free ZSM-5 from Rice Husk Ash at Low Temperatures and Its CO2 Adsorption Performance.

In this paper, a green synthesis method for ZSM-5 zeolite is explored to reduce the synthesis cost, environmental hazard, and reaction temperatures. For the ZSM-5 samples prepared at low temperatures, the influence of factors such as the hydrothermal temperature, crystallization time, and the number of seeds is systematically investigated. The adsorption isotherm of CO2 is used for fitting analysis of adsorption models and determination of the adsorption selectivity. The results show that the best one among the three samples presents the highest CO2 adsorption capacity of 2.39 mmol/g at 273 K and 15 bar. It is prepared with a hydrothermal temperature of 393 K, crystallization time of 7 days, and a seed crystal of 1 wt %. The dual-site Langmuir model can well describe the experimental data, indicating that double adsorption sites rather than the simple single-layer adsorption are dominant in samples. As the pressure increases, the adsorption capacity calculated by the model is much lower than the actual value with a deviation index of 12.5%. At a pressure of 1 bar, the optimal selectivity is attained with sample L-20, viz., CO2/N2 of 34.3 and CO2/O2 of 70.2. The green synthesis method reported in this research can be used to successfully prepare ZSM-5 zeolite, and it shows excellent CO2 adsorption performance. In addition, the use of low-cost raw materials and template-free synthesis methods will facilitate the large-scale application of green synthesis processes in the future.

Template-free ZSM-5 membrane preparation on alumina support by secondary hydrothermal synthesis

Zeolite membranes stand out for presenting molecular sized uniform pores. The current work aimed to optimize supported template-free ZSM-5 zeolite membrane preparation by evaluating the effect of two parameters: successive synthesis cycles of the zeolitic film and aging time of the synthesis solution. The zeolitic film synthesis was carried out by secondary hydrothermal treatment using α-alumina tubes as support, commercial zeolite as seeds and SiO2: 0.3 Na2O: 0.01 Al2O3: 114 H2O as molar composition of the synthesis solution. The aging time tested for the dissolution of silicon and aluminum was 30, 60, 120 or 180 ​min; whilst for the silicon and aluminum mix was 60 or 15 ​min. Hydrothermal synthesis was performed at 180 ​°C for 24 ​h. This procedure was executed 1, 2 or 4 times. One synthesis cycle was already capable of producing a homogeneous zeolitic film on the support with crystal interconnection. This finding was corroborated by gas permeation tests, in which the membrane did not show any apparent defects. The aging time had an effect on the type of zeolite formed. Only the aging time conditions of 180 and 60 ​min and 180 and 15 ​min prompted the exclusive formation of zeolite ZSM-5.

Synthesis of ZSM-5 and its application in butylene catalytic cracking

The template-free ZSM-5 was prepared by hydrothermal synthesis and then modified by tetramethoxysilane (TMOS). The structure, morphology, and acidity of all samples were studied by various techniques, such as XRD, SEM, 29Si MAS NMR, 27Al MAS NMR, NH3-TPD, BET and UV-vis DRS. Comparing with the zeolites synthesized by traditional method, the template-free ZSM-5 exhibited the analogical acidity, morphology and structure, but obvious difference in acid distribution. Due to the absence of the structure directing agent, the template-free ZSM-5 possessed more acid sites situated at pore channels of catalyst and less acid sites stayed at the intersection of straight and sinusoidal channels. Consequently, the shape selectivity enhanced significantly. After TMOS modification, the non-shape acid sites located at the external surface were covered by a single SiO2 layer. The template-free ZSM-5 achieved the highest total yield of ethylene and propylene, longest working life-span and lowest level of coke deposition among the studied catalysts, ascribing to the suppression of the side reactions.

USE OF A LOW-COST TEMPLATE-FREE ZSM-5 FOR ATMOSPHERIC PETROLEUM RESIDUE PYROLYSIS

To understand the physicochemical properties and catalytic activity during the pyrolysis of atmospheric petroleum residue, a template-free ZSM-5 zeolite was synthesized using a direct method without additional seeds or an organic structure director and compared with conventionally synthesized ZSM-5. The crystallinities of the two zeolites were evaluated by XRD and FTIR and were quite similar; however, structural analyses using SEM and argon physisorption revealed that the zeolites diverged in particle diameter and in the external surface area of the micropores. The synthesis procedure without a template incorporated additional aluminum into the crystalline network, according to ICP-AES and TPD NH3 experiments. The catalytic pyrolysis performed over the template-free ZSM-5 generated results comparable to those for pyrolysis performed over the conventional ZSM-5 according to its hydrocarbon distribution. The selectivity to aromatics compounds was exactly the same for both ZSM-5 zeolites, and these values stand out compared to thermal pyrolysis. The template-free ZSM-5 produced 20% of light hydrocarbons (C4-C6), where such compounds are olefins and paraffins of great interest to the petrochemical industry. Therefore, template-free ZSM-5 is promising for industrial use due to its lowered synthesis time, low-cost and significant distribution to light hydrocarbons.

Fabrication of a non-enzymatic Ni(ii) loaded ZSM-5 nanozeolite and multi-walled carbon nanotubes paste electrode as a glucose electrochemical sensor

A template-free ZSM-5 nanozeolite was synthesized and then carbon paste electrode (CPE) was modified by ZSM-5 nanozeolite, multi-walled carbon nanotubes and Ni2+ and was used as catalyst for the electrooxidation of glucose (EC′ mechanism).

Inductive effect of various seeds on the organic template-free synthesis of zeolite ZSM-5

A comprehensive investigation into the effect of seed on the crystallization of ZSM-5 in the absence of template was performed by introducing seeds with different frameworks and pore structures into the gel mixture. It was found that the crystallization behavior of template-free ZSM-5 was strongly governed by three key factors in a synergetic way. Firstly, the common composite building units contained in the seed and product zeolites crucially promoted the nucleation and subsequent crystal growth of target zeolites. Secondly, the terminal TOH units on the surface of seed crystals strengthened their recognition capacity to the composite units formed in systems, which significantly accelerated the crystallization process. Thirdly, the external surface area provided by seeds offered specific sites for composite building units to attach to and pile up to form new zeolitic layer. Thus, in this work, ZSM-5 or ZSM-11 zeolites with terminal TOH were viewed as the preferable seeds to induce the formation of ZSM-5 in a short period (12–16 h) without template addition and the crystal size could be easily controlled just by using seeds with different external surface area.

ChemInform Abstract: Treatment of Boron-Containing Pentasil-Type Zeolites Under “Boron- Extracting” Conditions.

Thermal or hydrothermal treatments of boron-containing pentasil-type zeolites, as well as acid-leaching procedures, lead to the partial or full removal of the framework boron atoms from the material. Resulting from this removal, the boron-stimulated lattice contraction is nearly completely cancelled. Catalytic properties of the ‘deborated’ material in acid-catalysed reactions are very close to those measured on comparable boron-free samples. This fact can be utilized in the production of template-free ZSM-5 of enhanced SiO2/Al2O3 molar ratio.

Template free ZSM-5 from siliceous rice hull ash with varying C contents

Green technology or use of environmentally friendly chemical process is now gaining popularity because of the demand from the conscientious consumers and strict environmental regulations. For manufacturing ZSM-5, tetrapropylammonium cations are used as a template. The use of toxic tetrapropylammonium hydroxide for templating ZSM-5 is a common practice and it also adds to the production costs. In this paper, a template free synthesis of ZSM-5 with various C contents using siliceous rice hulls, a byproduct of rice milling industries, is discussed. These ZSM-5 zeolites composited with amorphous C could be commercially exploited for the removal of volatile organic compounds (VOCs) from either wastewater or air. Carbon free ZSM-5 was also produced by pyrolyzing the C-containing ZSM-5 at 773 K for 3 h.

Influence of Nature of Silica Source on Template-Free Synthesis of ZSM-5

Synthesis of ZSM-5 from template-free batches which preceded the preparation of template-free ZSM-5 layers on porous supports was studied to ascertain the effect of nature of silica source on the purity of template-free ZSM-5. Silicic acid and two colloidal silica sols were used as silica sources to prepare the template-free batches with a molar composition of 6.5Na2O:Al2O3:80SiO2:3196H2O. One of the colloidal silica sols contained methanol as stabilizer while the other did not. The product purity and rate of crystallization increased when colloidal silica sols were used as silica source, however, use of silicic acid led to low purity and slow crystallization rate. The methanol in the colloidal silica sol appeared to act as template to promote the crystallization and was occluded in the resultant ZSM-5 pores. The dissolution of the meta-stable ZSM-5 phase and formation of quartz was observed regardless of the nature of the silica source in case of prolonging the crystallization time more than 90 h at 200°C.

Possibilities and limitations of the prediction of the Si/Al ratios of zeolites from the batch composition

In earlier studies, it was shown that the Si/Al ratio of faujasite and some related zeolites crystallizing from batches with the composition NaAlO 2: n(Na m H 4– m SiO 4): pH 2O can be described by (A) ( Si/ Al) zeolite =1+b([ SiO 2]/[ OH −]) Solution , where [OH −] is the total alkali content and [SiO 2], the silica content of the solution phase in the batch. From Eq. (A) with some assumptions (B) ( Si/ Al) Product ≈ (b+m)n b+nm can be obtained, containing only the parameters n and m of the batch composition and the fitting parameter b from Eq. (A). For a large number of faujasite batches and for other large pore zeolites with four- and six-membered rings in the structure, a good agreement was obtained between the experimental Si/Al ratios and the values obtained from Eq. (B) using b=2. For zeolites with five-membered ring structures values of b=7–10 proved to be suitable. For high template contents, no common description can be obtained by Eq. (B). It could, however, be shown that this equation would be a good help for planning syntheses of mordenite, template-free ZSM-5 and BETA. The experiments with BETA were best described with b=14. From kinetic studies, Eq. (A) and the parameter b can be at least qualitatively explained by a model assuming that an amorphous layer is formed in an equilibrium reaction at the crystallizing surface. The formation of the final structure occurs by a reorganization of this layer under the influence of cations and templates. This reaction step is rate determining. The Si/Al ratio is determined in the attachment reaction. From an analysis of the alkalinity in the solution phase, it can be seen that, for the zeolites with four- and six-membered rings, the attachment of monomer silicate and the silico-aluminate species with about one silicate ligand can be expected. For the five-membered ring zeolites oligomer silicates and silico-aluminate complexes with two or more ligands are more probable. A borderline between the two situations can be drawn at about ( nm) 55.5/p≈[ OH]≈1 mol/l .

Treatment of boron-containing pentasil-type zeolites under ‘boron-extracting’ conditions

Thermal or hydrothermal treatments of boron-containing pentasil-type zeolites, as well as acid-leaching procedures, lead to the partial or full removal of the framework boron atoms from the material. Resulting from this removal, the boron-stimulated lattice contraction is nearly completely cancelled. Catalytic properties of the ‘deborated’ material in acid-catalysed reactions are very close to those measured on comparable boron-free samples. This fact can be utilized in the production of template-free ZSM-5 of enhanced SiO2/Al2O3 molar ratio.

Cation Assisted Lattice Improvement of Highly Siliceous ZSM-5 upon Prolonged Heat Treatment

Abstract Prolonged heat treatment of highly siliceous, template-free ZSM-5 containing Na+ or K+ causes improvement of the lattice structure, migration of alkaline ions to the outer layers of the zeolite particles as shown by XPS and an increased isolation of ≡ Si–ONa sites from ≡ Si–OH sites, as shown by 29Si CP MAS NMR analyses of silylated products.