MFI composite zeolite using isopropylamine as a structure-directing agent

Journal Pre-proof Synthesis of FER/MFI composite zeolite using isopropylamine as a structure-directing agent Kaixu Shen, Xin Huang, Jia Wang, Zhen Chen, Yunkai Yu, Zhimou Tang, Yueming Liu PII:

S1387-1811(20)30030-5

DOI:

https://doi.org/10.1016/j.micromeso.2020.110027

Reference:

MICMAT 110027

To appear in:

Microporous and Mesoporous Materials

Received Date: 8 August 2019 Revised Date:

9 January 2020

Accepted Date: 13 January 2020

Please cite this article as: K. Shen, X. Huang, J. Wang, Z. Chen, Y. Yu, Z. Tang, Y. Liu, Synthesis of FER/MFI composite zeolite using isopropylamine as a structure-directing agent, Microporous and Mesoporous Materials, https://doi.org/10.1016/j.micromeso.2020.110027. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Elsevier Inc. All rights reserved.

Credit Author Statement

K. X. Shen carried out the synthesis and characterizations of the zeolite samples. K. X. Shen and X. Huang carried out the catalytic tests and temperature-programmed desorption of ammonia (NH3-TPD). K. X. Shen and Z. Chen collected and analyzed the scanning electron microscopy (SEM) images. K. X. Shen and J. Wang collected and analyzed the transmission electron microscopy (TEM) images and EDS mapping images. K. X. Shen, X. Huang, and Z. M. Tang collected and analyzed the X-ray diffraction (XRD) and ICP data. K. X. Shen and Y. K. Yu collected and analyzed the FT-IR data. K. X. Shen, X. Huang and J. Wang collected and analyzed N2 adsorption-desorption measurements and solid-state MAS NMR data. Y. M. Liu was responsible for the overall direction of the project and preparation of the manuscript, with contributions from all authors.

FER/MFI composite zeolites with an unique aluminium distribution that Al atoms prefer to enrich in the dominated phase was synthesized successfully using isopropylamine as a single structure-directing agent.

Synthesis of FER/MFI composite zeolite using isopropylamine as a structure-directing agent

Kaixu Shen, Xin Huang, Jia Wang, Zhen Chen, Yunkai Yu, Zhimou Tang, Yueming Liu*

Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, North Zhongshan Rd. 3663, Shanghai 200062, P. R. China

Corresponding author: Profs. Yueming Liu Tel/Fax: +86-21-6223-2058 E-mail: [email protected] (Y.M. Liu)

Abstract

A comprehensive investigation into the synthesis of the FER/MFI composite zeolite based on the isopropylamine-silica sol-NaAlO2-H2O system has been carried out. Parameters such as the Na2O/SiO2 molar ratio, SiO2/Al2O3 molar ratio, water concentration, and structure-directing agent (SDA) concentration were of great importance in the crystal phase transition and the morphology control. FER/MFI composite zeolites could be successfully prepared under the conditions of the SiO2/Al2O3 molar ratio ranging from 20 to 30 in the gel mixture. SEM and TEM images showed that the two different crystals (FER and MFI frameworks) in FER/MFI composite zeolites had a state of co-existence and staggered growth, which was typical of composite zeolites. Among these factors influencing the synthesis process, adjusting the Na2O/SiO2 molar ratio was easy to control the relative contents of each phase in the composite zeolites. The higher Na2O/SiO2 molar ratio was, the more content of the FER phase was. NH3-TPD and FT-IR of adsorbed pyridine results showed the acidity properties of composite zeolites were significantly different from those of corresponding physical mixtures. Interestingly, the distribution of aluminum between the FER and MFI structures in the composite zeolites was unequal, and aluminum atoms tended to enrich in the phase predominating in the FER/MFI composite zeolites. The catalytic performance in the cracking of olefins like butene and pentene of the FER/MFI composite zeolite was superior to that of the pure ZSM-5 zeolite. The FER/MFI composite zeolite after further modification is expected to become an excellent catalyst for the catalytic cracking of low carbon olefins to

ethylene and propylene. Keywords composite zeolite; FER/MFI; isopropylamine; synthesis; catalytic cracking

1. Introduction

In recent years, as ethylene and propylene are fundamental chemical raw materials for the synthesis of some high-value polymers, organic intermediates and other chemicals, researches about their high selectivity production have attracted extensive attention [1]. However, there is still an urgent need to improve the current situation of imbalance between supply and demand of ethylene and propylene. Therefore, catalytic cracking of olefins, which were largely produced by traditional catalytic cracking and steam pyrolysis, into ethylene and propylene is aimed to deal with this problem and draws growing interest from academic and industrial domains [2]. As we all know, a catalyst is a very important factor in the olefin catalytic cracking reactions. ZSM-5 zeolite catalysts have been widely applied in this reaction process due to their unique properties [3, 4]. ZSM-5 zeolite, which has an MFI topology, is a typical three-dimensional zeolite containing two types of interconnecting channels composed of straight channels (5.6×5.3 Å) and sinusoidal channels (5.5×5.1 Å). This kind of 3-D (three-dimensional) framework can provide a wide space to inhibit coke formation which can result in catalyst deactivation [5, 6]. It has a high conversion of olefins and a longer life compared to other types of catalysts [7]. Nevertheless, its wide space contributes to more side reactions such as hydrogen transfer and aromatization reactions [8, 9]. Besides ZSM-5 zeolite, another catalyst called ZSM-35

zeolite is promising. It is acknowledged that ZSM-35 zeolite with FER framework possesses a main 10-MR channel with a pore size of 5.4×4.2 Å along the [001] direction and a perpendicular 8-MR channel with a pore size of 4.8×3.5 Å further to build a two-dimensional channel structure [10, 11]. Spherical cavities named as FER cage are formed by the intersection of the 8-MR channels and the 6-MR channels. Different from ZSM-5 zeolite, ZSM-35 zeolite can promote the monomolecular cracking of pentene, and inhibit side reactions such as hydrogen transfer and oligomerization to produce macromolecular products, but its low conversion rate, easy carbon deposition, and short life have become its weaknesses [12]. Considering a single catalyst cannot meet the actual need and own some disadvantages, composite zeolites have attracted increasing interest from research specialist staff. Speaking of composite zeolites, there are two main construction modes. One is that the infinite component units of two or more zeolites produce a new complete crystal structure due to stacking faults or disordered arrangements [13]. The other is that the original crystal structures can be maintained without producing a new structure after the two or more zeolites are combined by phase adjustment or surface treatment [14]. Based on these two different modes, composite zeolites are divided into two categories corresponding to intergrowths and co-existences, respectively. Due to their synergistic performances in catalytic reactions, composite zeolites have become a new trend in research. For example, ZSM-5/ZSM-11 composite zeolite is one of the good cases for industrial application, which gives evidence of high activity, favorable selectivity and prominent resistance to side-reactions for alkylation reaction

of benzene with the dilute ethylene in FCC off-gas [15]. ZSM-22/ZSM-23 zeolite, which is an intergrowth of MTT (ZSM-23) and TON (ZSM-22) frameworks, has shown the suppression of BTX selectivity and improved resistance to deactivation in hexane cracking [16, 17]. And FER/MOR composite zeolite contributes to its enhanced catalytic ability in DME carbonylation reaction [18]. Such composite zeolites generally maintain the properties of each structure while also producing unique pore structure and acidity, and exhibit special properties different from a single framework in catalytic reactions. In addition to the examples mentioned above, there are

other

reported

composite

zeolites

such

as

MCM-49/ZSM-35

[19],

MCM-22/ZSM-35 [20], etc. Our previous work indicated that ZSM-35, ZSM-5, and ZSM-23 zeolite could be successfully synthesized using only isopropylamine (IPA) as a structure-directing agent (SDA) [21]. And the single-crystal phase of ZSM-5 or ZSM-35 zeolite shows sufficient advantages in the olefin cracking reaction. Accordingly, it is inspiring to carry a detailed investigation of the synthesis of FER/MFI composite zeolite. Moreover, to the best of our knowledge, few studies about FER/MFI composite zeolite have been reported. In this contribution, the exploration of optimal synthesis conditions for FER/MFI composite zeolite prepared in the isopropylamine system was focused, and characterizations of the composite zeolites with different components in terms of shape properties, pore structure, acidity, and catalytic performance were also investigated. The differences between FER/MFI composite zeolites and the physically

mixed counterparts were also discussed. The results showed that FER/MFI composite zeolites with special physicochemical properties were obtained successfully, and this kind of composite zeolites exhibited superior catalytic performance relative to pure ZSM-5 zeolite in catalytic cracking of olefins.

2. Experimental

2.1 Preparation of zeolites The gel mixtures used for the synthesis were prepared using silica sol (30.0 wt% SiO2, 70.0 wt% H2O, Sinopec Catalyst Co., Ltd.), sodium aluminate (43.9 wt% Na2O, 53.0 wt% Al2O3, J&K Scientific Ltd.), sodium hydroxide (AR, China National Medicine Group, Shanghai Chemical Reagent Co.), deionized water and isopropylamine (AR, China National Medicine Group, Shanghai Chemical Reagent Co.) as materials. Crystallization of the zeolites proceeded under rotating synthesis conditions. The molar compositions of the synthesis gel mixtures were SiO2:Al2O3: IPA:Na2O:H2O = 1:(1/10-1/50):(0.2-1.2):(0.07-0.14):(12-30). A general synthesis procedure was as follows. Sodium hydroxide solution and sodium aluminate solution were mixed to form a solution. Then IPA was dropped into the solution followed by some silica sol under vigorous stirring until a homogeneous gel was formed. This gel was continuously stirred for 1 h and then was transferred to a 150 ml Teflon-lined stainless-steel autoclave, which was heated at 170

in an oven

for 72 h. After the crystallization, the autoclave was quenched in cold water and the product was recovered by filtration, drying, and calcination (550 ) to gain target

samples. Fully exchanged H-type zeolite samples (H-sample name) were obtained by ion exchange of the calcined zeolites with a 2 M aqueous solution of ammonium chloride at 80

for three times, followed by drying at 80

and calcination at 550 . FER/MFI

composite zeolite is denoted as FER/MFI-x-y, where x represents the mass fraction of the FER component in the composite zeolite and y corresponds to the mass fraction of MFI component. Those mechanically mixed samples are designated as Mixture-a-b, where a and b represent the mass fractions of FER and MFI, respectively. 2.2 Physicochemical characterization The catalysts were characterized by various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption measurements, inductively coupled plasma (ICP), temperature-programmed desorption of ammonia (NH3-TPD), FT-IR of adsorbed pyridine, 29Si and 27Al solid-state MAS NMR. X-ray diffraction (XRD) patterns were recorded on a Rigaku Ultima IV X-ray diffractometer (35 kV and 25 mA) using Cu Kα radiation (λ = 1.5405 Å). N2 adsorption was carried out at 77 K on a BELSORP-MAX instrument after outgassing the samples under vacuum at 573 K for 10 h. The crystal morphology and size were measured by scanning electron microscopy (SEM) on a Hitachi S-4800 microscope. Transmission electron microscopy (TEM) was taken on a JSM-2010F microscope. The amount of Si or Al was quantified by inductively coupled plasma (ICP) on a Thermo IRIS Intrepid II XSP atomic emission spectrometer after dissolving the

samples in the HF solution. Acidity was measured by temperature-programmed desorption of ammonia (NH3-TPD) with a Micromeritics tp-5080 equipment equipped with a thermal conductivity detector (TCD). Typically, 100 mg of sample was pre-treated in the helium stream (30 mL min-1) at 550 °C for 2 h. The adsorption of NH3 was carried out at 50 °C for 1 h. The catalyst was flushed with helium at 100 °C for 2 h to remove the physisorbed NH3 from the catalyst surface. The TPD profile was recorded at a heating rate of 5 °C min-1 from 100

to 550

.

The Brønsted and Lewis acid sites of the samples were investigated by FT-IR of adsorbed pyridine in an in-situ cell with CaF2 windows. Wafers with a weight of 25 mg and a radius of 6.5 mm were degassed for 1 h under vacuum at 500 °C. Then pyridine was admitted, and after equilibration, the samples were outgassed for 15 min at increasing temperatures (200, 250, 350, and 450 °C). The spectra were recorded on a Nicolet iS50 FT-IR spectrometer. 29Si and 27Al solid-state MAS NMR spectra were recorded on a VARIAN VNMRS-400WB spectrometer under one pulse condition. 2.3 Catalytic testing 1-butene and 1-pentene acted as olefin raw materials to test the catalytic performance of catalysts. Catalytic cracking of 1-butene over the zeolites was carried out in a stainless steel continuous-flow reactor (10 mm i.d.), with a thermocouple in the center of the catalyst bed. The catalyst was pressed, crushed, and sorted into grains by 40-60 meshes and then was activated at 550

for 3 h under a nitrogen flow

before starting each reaction run. Then, 1-butene (99.9%) in diluted nitrogen (N2/1-C4H8 = 7.82, mole ratio, analyzed by GC) was passed through the reactor at the

desired temperature. The output products were analyzed online by Agilent 7890A gas chromatograph. For simplicity, we grouped all types of butenes as the overall feed. The composition of products analyzed here by GC is mole results (the composition of calibration gas used to standardize GC is mole percent), and the total mole is not constant before and after reactions, but nitrogen does not change all the time; thus, we use nitrogen as a reference to calculate butene conversion. Then, the mole conversion of butenes, the mole selectivity of the products were calculated by: −

Conversion =

1 × 7.82 −

=

×

! "# %$ %& %$

1 7.82 ! "# %$ × 100% %& %$ ×

= 100% − 7.82 × Mole selectivity Here,

× 100%

,

, -$

=

. "/ %$

∑

,

1 "2 %$

,

=

$

× 100% represent the mole flow of butenes in

the feed, butenes in the output, nitrogen in the feed, and nitrogen in the output, respectively. (C4H8%)t, (N2%)t, (CxHy%)t, and (CiHj%)t represent the mole composition analyzed by GC of butene in the output, nitrogen in the output, a certain product in the output, and any product in the output, respectively [22]. The catalytic performance of 1-pentene cracking evaluated in the same reactor with the similar method that was used to calculate related data of butene above [23]. 2.4 Calculation of relative content The relative content of ZSM-5 and ZSM-35 zeolites was calculated by the

comparison method. The pure ZSM-5 and ZSM-35 were mixed mechanically in different proportions for XRD measurement. According to the relationship between the area of characteristic peak (2θ=7.9° for ZSM-5 and 2θ=25.2°, 25.7° for ZSM-35) and content of ZSM-5 and ZSM-35 zeolites, the standard curve was made (Fig. S1a,b). Then the area of the characteristic peak of each crystal phase in the composite zeolites synthesized in this study was compared with the standard curve to obtain the relative content of ZSM-5 and ZSM-35 zeolites.

3. Results and discussions

3.1 Influence of the Na2O/SiO2 molar ratio Fig. 1 shows the XRD patterns of the products for different alkalinity (gel SiO2/Al2O3 molar ratio, SDA and water concentrations were kept constant). ZSM-5 zeolite (MFI) was prepared without adding any NaOH agent, which meant the Na2O/SiO2 molar ratio (defined as the alkalinity) in the gel mixture was 0.07 (Fig. 1a). When the Na2O/SiO2 molar ratio reached 0.08, the FER phase began to appear and the co-existence of the two structures (MFI and FER frameworks) was also observed (Fig. 1b). Surprisingly, the proportion of the FER phase in the composite zeolite increased with an increasing Na2O/SiO2 molar ratio (Fig. 1b-e). When the Na2O/SiO2 molar ratio rose up to 0.12, there was only ZSM-35 zeolite (FER) in Fig. 1f. This phenomenon was very consistent with the observations of Chu et al. whose data indicated that the higher Na2O/SiO2 ratio in the synthesis mixture preferred ZSM-35 zeolite [24].

In most cases, zeolites composed of aluminosilicate are formed in an environment that is basic [25, 26]. Hydroxide ion (OH-), a symbol of the alkalinity of gel mixtures, is an important factor in causing the synthetic environment to be basic [27, 28]. It plays two roles in zeolite synthesis. In terms of crystallization, OH- as a mineralizing agent facilitates the dissolving of silica species and polymerization between silicate anions and aluminate anions for the crystallization of silicon-aluminium zeolites [29]. The research showed the increase of alkalinity in the initial synthesis gel of ZSM-5/ZSM-11 zeolite for some degree could enhance the crystallization rate remarkably by decreasing the induction period and result in a product with lower length/width ratio [15]. Then SiO4 or AlO4 tetrahedron, which are known as primary units to build zeolite framework, condense into a cavity for the fundamental structure unit of the zeolite framework and their existing states in the synthesis solution are sensitive to the alkalinity of the mixture makes it possible to direct different zeolites [30]. In short, the alkalinity plays an important role in crystallization and phase transformation. In particular, the product compositions are much sensitive to the alkalinity of the gel mixture. Accordingly, the alkalinity in our synthetic system also has an effect on the compositions of the FER/MFI composite zeolite. By comparing with the standard curve based on the relationship between the characteristic peak area and content of physical mixtures of ZSM-5 and ZSM-35 zeolites (Fig. S1), the compositions of some composite zeolites have been calculated and the results were collected in Table 1. There was a great relationship between the alkalinity and the crystal phase make-up of the composite zeolite. When the

Na2O/SiO2 molar ratio equalled 0.08, the composite zeolite was formed with 33% of the FER phase while the other part was the MFI phase, and then it was designated as FER/MFI-33-67. With the increase of the Na2O/SiO2 ratio, the content of the FER phase was gradually rising from 33% through 72%, 89%, 94% eventually to 100%. The results were in accordance with previous reports which showed that the Na2O/SiO2 molar ratio also had an obvious effect on the compositions of MCM-49/ZSM-35 composite zeolites [19]. It was supposed that a low Na2O/SiO2 molar ratio was beneficial to the formation or stability of MCM-49 zeolite, whereas a high Na2O/SiO2 molar ratio would promote the formation of ZSM-35 or transformation of MCM-49 into ZSM-35 [19]. Similarly, under such a gel condition we designed, it was preferable for the formation of the fundamental structure unit of ZSM-5 in a relatively low concentration of hydroxide ions; however, a high concentration was conducive for the growth of the ZSM-35 framework. So it was inevitable that the co-existence of two crystal phases would occur. In consequence, the alkalinity (Na2O/SiO2 molar ratio) must be restricted strictly in order to produce FER/MFI composite zeolites with specific phase compositions. As shown in Fig. 2 and Fig. 3, SEM and TEM were carried out to further confirm whether the MFI phase and FER phase were a kind of co-existence. Pure ZSM-5 zeolite given in Fig. 2a was an aggregation of nanocrystalline ZSM-5 particles while ZSM-35 zeolite was a morphology of irregular plates in Fig. 2f. Interestingly, it could be observed that FER and MFI phases in all these composite zeolites with different compositions were stacked and staggered together from the SEM images in Fig. 2b-e.

The part belonging to the FER phase showed plate-like crystals, whereas the part of the MFI phase was blocky crystals that were tightly stacked together and its morphology was the same as the report before [31]. Additionally, the size of the single ZSM-5 particle in the composite zeolite was seemingly smaller than that in pure ZSM-5 zeolite, which could be thought of as a different feature of composite zeolites. To further ascertain the state of the synthesized FER/MFI composite zeolites, the FER/MFI-72-28 sample was chosen as an example for analysis by TEM (Fig. 3). Then a line of lattice fringes was seen among FER frameworks through the TEM image shown in Fig. 3a. The lattice fringes were derived from the (101) crystal plane belonged to the MFI topology. Compared to the MFI phase, the FER phase showed a larger plate-like structure. Especially Fig. 3b showed two different kinds of interplanar spacing representing FER (d=0.663nm) and MFI (d=0.813nm) crystals, respectively. Hence, FER crystal was inserted into the MFI crystals that were stacked together. Namely, the two crystals had a state of co-existence and staggered growth. From the perspective of structure, FER zeolite shares the common feature with MFI zeolite in the secondary building unit (SBU) of 5-1 unit [32]. It is easily understood that MFI zeolite contains the composite building units of mfi, mel, cas and mor, whereas FER zeolite contains only the fer unit in their frameworks. However, the fer unit consists of 13 T (T for tetrahedral = Si or Al) atoms and is decomposed into the mor unit and 5R, which consist of 8 and 5 T atoms, respectively [33]. Consequently, it was concluded that there was also a common composite building unit between these two zeolites, which was a probable explanation for this co-existence of FER and MFI

zeolites. 3.2 Influence of the SiO2/Al2O3 molar ratio SiO2/Al2O3 molar ratio is also a very important parameter for the synthesis of silica-aluminium zeolites. The following study dealt with the effect of the SiO2/Al2O3 ratio on the formed composite zeolites. In our synthetic system, regulating the SiO2/Al2O3 ratio will generate several kinds of zeolite with different topologies. Nonetheless, it should be noted that the Na2O/SiO2 ratio was adjusted to accommodate the amount of Al variation. Because the raw material NaAlO2 will contribute to a certain amount of OH-, the alkalinity also changes when adjusting the SiO2/Al2O3 ratio. The detailed XRD patterns and SEM images were shown in Fig. S3, S4 and the crystal phases of all products were summarized in Table 2. For the purpose of avoiding the resulting impact, we kept the Na2O/SiO2 molar ratio constant and only changed the molar ratio of SiO2/Al2O3 in the initial gel composition. Fig. 4 shows the XRD patterns of the synthesized products from different gel SiO2/Al2O3 molar ratios. It was found that the framework structure was sensitive to the Al content in the relatively low SiO2/Al2O3 molar ratio. An amorphous phase appeared in the product at the SiO2/Al2O3 ratio of 10 in Fig. 4a instead of MOR zeolite (Fig. S2a and Fig. S3a). Pure ZSM-35 zeolite with high crystallinity was obtained with SiO2/Al2O3 molar ratios at 20 (Fig. 4b). The gel mixtures would transform into a kind of composite zeolites with a trace FER phase when the SiO2/Al2O3 molar ratio was between 30 and 40 (Fig. 4c,d). However, when the SiO2/Al2O3 molar ratio reached about 50, the product changed from ZSM-5 to

ZSM-23 comparing Fig. 4e with Fig. S2g. Indeed different SiO2/Al2O3 molar ratios will result in different crystallinities and morphologies of zeolites. For instance, when using piperazine as an organic structure-directing agent for zeolite synthesis, it was observed that ZSM-4, mordenite, ZSM-35, ZSM-5 and ZSM-12 zeolites in pure phase could be obtained successively in the product in the process of changing the SiO2/Al2O3 ratio [34]. In particular, different zeolites preferably incorporate a certain amount of aluminium into their frameworks on the basis of their unique topologies, then finishing crystallization in a specific SiO2/Al2O3 range [35]. When the SiO2/Al2O3 molar ratio was at 25 and 30 as shown in Table 2, there existed a composite phase containing FER and MFI frameworks in the zeolites. In addition, in the production of all the zeolites, the SiO2/Al2O3 molar ratio in the products was almost the same as the ratio in the initial gel (Table 2). It was attributed to the excellent integration capacity for Si and Al atoms into the zeolite framework. A similar phenomenon has been reported in the synthesis of other zeolites, in which ZSM-5+MOR and ZSM-35+MOR crystal phases were observed at the SiO2/Al2O3 molar ratio of 20 [15, 36]. The intersection of such different crystal phases was similar to the competitive growth of MOR, ZSM-5, and ZSM-35 in our gel system, which provided the base for the successful synthesis of FER/MFI composite zeolites. All data in Section 3.1 and 3.2 show that not only the change of SiO2/Al2O3 molar ratio but also the Na2O/SiO2 molar ratio has a great influence on the transformation of the product phase. Based on the synthesis results, a schematic representation of phase

selectivity related to SiO2/Al2O3 ratio and Na2O/SiO2 ratio was shown in Fig. 5 for simplicity. So in order to synthesize the desired composite zeolites, it is necessary to select a gel condition with suitable SiO2/Al2O3 ratios (20-30) and Na2O/SiO2 ratios. 3.3 Influence of the water concentration Fig. 6 shows the XRD patterns of the products formed with different gel water concentrations (gel SiO2/Al2O3 molar ratio, template content, and Na2O/SiO2 molar ratio were kept constant). It was found in Fig. 6a that the composite zeolite appeared as a product in the system on condition that the H2O/SiO2 molar ratio was 12. The proportion of the MFI phase increased when the H2O/SiO2 molar ratio rose up to 20 (Fig. 6b). As seen in Fig. 6c, only the MFI phase was obtained when the H2O/SiO2 molar ratio was 21. The further increase of water concentration would lead to the formation of amorphous products (Fig. 6d-f). So the lower water concentration was, the higher relative content of FER phase was. These results showed that water concentration also played an important role in crystal phase transformation. In many cases, the studies have attributed the influence of water to that of alkalinity. So the water-sodium ratio was used as a parameter of the synthesis conditions of zeolites. Under this system of hydrothermal synthesis of mixtures of NaA zeolite and sodalite, decreasing n(H2O)/n(Na2O) made well-crystallized NaA zeolite be converted to SOD zeolite [37]. As for the effect of water concentration, other authors believed in their research that a decrease in the H2O/SiO2 molar ratio in the reaction mixture led to a decrease in the size of nanocrystal aggregates, while the sizes of the primary crystallites remained unchanged [38]. Compared with these previous researches, a

water-poor environment in our reactant mixture, which meant that the alkaline gel was condensed and had strong alkalinity, would certainly lead to the crystallization of the FER phase. Meanwhile, an environment with adequate water and relatively weak alkalinity would favor the formation of the MFI phase. Therefore, the variations of the amount of water could adjust the crystal phase composition of the composite zeolites. 3.4 Influence of the SDA concentration The influence of the SDA concentration was investigated. Fig. 7 shows the XRD patterns of the products for different structure-directing agent concentrations (gel SiO2/Al2O3 molar ratio, Na2O/SiO2 molar ratio, and water concentration were kept constant). The ZSM-35 phase appeared in the product when the IPA/SiO2 ratio was 0.2 and dominated the crystalline phase until the IPA/SiO2 ratios were up to 0.6 where there was no ZSM-5 phase (Fig. 7a-d). Excessive isopropylamine (IPA/SiO2=0.8) would promote the formation of ZSM-5 crystal phase exhibited in Fig. 7e, while continuing to increase the SDA concentration would not bring a rise of the proportion of MFI phase but a drop in Fig. 7f,g. The competitive growth of the two frameworks, MFI and FER existed during the whole crystallization period. As known, IPA is a small amine molecule and more likely to promote the forming of ZSM-35 instead of ZSM-5 zeolite in the low SiO2/Al2O3 molar ratio conditions. According to the previous research [39], small amines played a “pH-stabilizing” role as well as their well-known “structure-directing” role. A suitable IPA/SiO2 ratio in the gel had a stronger positive effect on the growth of pure ZSM-35 zeolite than on that of ZSM-5 zeolite. The above results showed that the increase of IPA concentration would cause

a small amount of ZSM-5 phase to appear. It meant that a higher concentration of IPA would direct the growth of the ZSM-5 phase. However, different SDA concentrations did not regularly adjust the crystal phase composition of the composite zeolites as the same as changing the alkalinity. During the synthesis process of composite zeolites, many studies proved the importance of using mixed amines as SDAs [40, 41]. Clearly, the bi-amine has played a synergistic directing function to zeolite synthesis such as the synthesis of MCM-49/ZSM-35 composite zeolites in the hexamethyleneimine and cyclohexamine system and ZSM-22/ZSM-23 ones in the mixed N-isopropyl-1,3-propanediamine (IPD) and 1-methylbutylamine (MBA) system [16, 19]. Unlike the above reports, however, FER/MFI composite zeolites using a single organic amine- isopropylamine as an SDA was successfully synthesized, which displayed the uniqueness of the synthetic system. 3.5 Pore structures and acidity properties of FER/MFI composite zeolites and corresponding physical mixtures The SEM and TEM results have confirmed the formation of FER/MFI composite zeolites, so what are the differences between their pore structures and acid properties and

those

of

corresponding

mechanical

mixture?

First

of

all,

nitrogen

adsorption-desorption measurements were applied to detect the textural properties of a series of zeolite samples synthesized with different Na2O/SiO2 molar ratios. Fig. 8a shows that pure ZSM-5 zeolite has type I isotherms. The main adsorption of this sample was at ultra-low relative pressure, with no obvious adsorption at mediate

relative pressure (0.4

distributions

of

H-ZSM-5,

H-FER/MFI-33-67,

H-FER/MFI-72-28,

H-FER/MFI-89-11, H-ZSM-35 and some physically mixed samples were then investigated by NH3-TPD method and FT-IR of adsorbed pyridine. Fig. 9a-c exhibits that there are two peaks of ammonia desorption for all the samples. The peak temperature centered at high temperature (300-550 ) rises upon the increasing content of FER phase in the samples, and the peak temperature located at low temperature (100-300 ) is similar in all the samples. This implies that H-ZSM-35 zeolite possesses much stronger acid sites than H-ZSM-5 zeolite and total acid sites all present a tendency of increase with the content of the FER phase. It is advantageous for developing the catalytic application of FER/MFI composite zeolites, since a series of composite zeolites with different acid distribution can be obtained by changing the ratio of MFI to FER phase. When the proportion of FER phase in the composite zeolite was relatively high, the total acid amount of the composite samples such as H-FER/MFI-72-28 and H-FER/MFI-89-11 was higher than that of the corresponding physically mixed samples (Fig. 9a-b). Unexpectedly, these two composite zeolites and pure H-ZSM-35 zeolite had more similarities in the acid properties. It is definite that the physically mixed samples are hybrids of two zeolites with identical SiO2/Al2O3 molar ratio of 20 in each ingredient. Therefore, their NH3-TPD curves illustrate a simple combination of acid sites of the two pure phases. For the composite zeolites, their acid distributions are more similar to that of the pure H-ZSM-35 zeolite, which means that the SiO2/Al2O3 ratio of each component is no longer 20. In other words, it is more likely that the SiO2/Al2O3 ratio of the FER phase is lower than 20 and the MFI phase has a

SiO2/Al2O3 ratio higher than 20. This can be inferred as well by the stronger acid sites of the composite zeolite, that is, the peak area at the high temperature is larger than that of the pure H-ZSM-35 zeolite (Fig. 9a-b). This is why the acidities of the composite zeolites differed from those of the physically mixed zeolites in the same percentage composition and were closer to that of the pure H-ZSM-35 zeolite. With the decrease of FER phase, a quite different acidic property was also obtained. The NH3-TPD curves (Fig. 9c) of the H-FER/MFI-33-67 sample (consisted of 33% FER and 67% MFI) were also distinct from that of the corresponding mechanical mixture. This difference indicated that the distribution of aluminium atoms in the two crystal phases in this composite zeolite sample was not uniformly distributed either. Combining this NH3-TPD curve which is more similar to that of pure phase ZSM-5 with the finding that the FER component does not contribute to the acidity it should have (Fig. 9c), it was concluded aluminium atoms in this composite sample were almost distributed in the MFI framework, which in turn led to a nearly pure-silica FER zeolite. FT-IR of adsorbed pyridine was carried out to further assess acidity properties. Two characteristic bands at around 1540 and 1450 cm-1 are usually assigned to pyridine adsorbed on the Brønsted acid sites and Lewis acid sites, respectively [45]. Then the strength of Brønsted acid sites is characterized with the help of a semi-quantitative method. The faster the normalized area relative to Brønsted acid sites decreases, the weaker the acid strength is [46]. As exhibited in Fig. 9d (original spectra were shown in Fig. S4), the Brønsted acid strength of the physically mixed sample is higher than

that of the composite sample indicating that the acid sites in the composite sample are concentrated more in the position where the pyridine cannot be adsorbed. This could be confirmed by previous researches that pyridine molecules can be protonated only by the acid sites located in the main 10-MR channels since it is too bulky to enter the ferrierite cage, whose biggest window is an 8-MR [47]. As a consequence, the NH3-TPD method was used to determine the acid sites in all the channels of the zeolites with FER and MFI topologies. The FT-IR of adsorbed pyridine measurement was applied to identify the acid sites in the 10-MR channels of FER plus those in all the channels of MFI zeolite. The results superficially exhibit the acid strength of the composite zeolites lower than that of the physically mixed samples, but actually, this difference between NH3-TPD and IR results is ascribed to the existence of unmeasurable 8-MR channels and the ferrierite cage. Also, the samples with more FER components have an acid strength more similar to pure FER zeolite, and the case is also analogous to the samples in which MFI is predominant. This further confirms that the ratio of silicon to aluminum contained in the two phases in the composite zeolite is not 20, but is biased. EDS analysis shown in Table 4 was carried out to further support the distribution of Al in different phases. The results illustrated that the concentration of Al in the FER phase was higher than that in the MFI phase, which was in line with the inference just mentioned. That is to say, the composite sample makes the acid sites closely related to aluminium atoms more concentrated in the 8-MR channels of the FER and the ferrierite cage. Meantime, solid state NMR and

27

29

Si MAS

Al MAS NMR were carried out in order to research the state of the

coordination of Si and Al in the ZSM-5, ZSM-35, composite zeolites and corresponding mechanical mixtures (Fig. S5, S6). It was found that the spectra of the FER/MFI-89-11 composite zeolite was just like the combination of these two pure zeolites’ spectra and there was no significant difference between the composite sample and physically mixed one. To sum up, all of these demonstrated that the composite zeolites with unique pore structures and acidity properties were synthesized for sure. 3.6 Catalytic performance of FER/MFI zeolite in olefin cracking reaction H-ZSM-5, H-FER/MFI-89-11, H-Mixture-89-11, and H-ZSM-35 as catalysts were used for the butene cracking reaction. As shown in Table 5, H-ZSM-5 exhibited a higher selectivity for paraffins, hydrogen, and aromatics. Although the total selectivity of ethene and propene was quite low over H-ZSM-5, the coke was difficult to generate, and it showed excellent stability and reactivity. It was because the pore channels of H-ZSM-5 did not favor the formation of coke [48]. In the composite zeolite H-FER/MFI-89-11 sample, the FER phase played an important role in reducing the hydrogen transfer reaction and exhibited good olefin selectivity with high conversion, which presented a combination of catalytic performance of two different zeolites. The olefin undergoes a protonation process on an H-type zeolite catalyst to form a carbenium ion, which then breaks by oligomerization or direct cracking to form ethylene, propylene and other products. Among them, β-Scission is the predominant mechanism for the cracking of carbenium ions [22, 23]. In the butene cracking

reaction, there are two modes. One is monomolecular butene cracking. The other is oligomerization cracking. A series of studies have shown that butene cracking takes place mainly based on dimerization cracking [49]. On the MFI and FER zeolites, the reaction pathway is dominated by butene dimerization to form C8+ intermediates and then cracking into other hydrocarbons. In the FER/MFI composite zeolites, the FER component causes a large amount of inhibition of the hydrogen transfer reaction, and the ratio of propene to ethene (P/E) is also improved. By-products like hydrogen and paraffins were greatly reduced, indicating the introduction of FER phase made bimolecular hydrogen transfer pathway inhibited. Benefit from the shape selectivity of the FER phase, the resulting intermediate (C8=) was carried out in such a reaction path (C8=→ C3=+C5=) that the selectivity of propylene was greatly increased [50, 51]. When comparing composite zeolites with physically mixed zeolites with the same composition in Table 5, it was seen that the conversion of butenes and selectivity of ethene of composite zeolites were higher than those of physically mixed samples, but the selectivity of propylene and pentene was lower, which could be explained by the acid amounts shown in NH3-TPD profiles. The amount of strong acid sites of the H-FER/MFI-89-11 sample is larger than that of the H-Mixture-89-11 sample, and strong acid sites promote the reaction path (C8=→ C2=+C6=) to producing more C2= [22]. On the basis of this point, the H-FER/MFI-89-11 sample possesses more reactive abilities of hydrogen transfer and aromatization because of its more strong acid sites. Such varying catalytic performance is essentially due to the difference in aluminium distribution of composite zeolites. Although the SiO2/Al2O3 molar ratio of

every composite zeolite measured by ICP is approximately 20 in Table 1, it is a bulk SiO2/Al2O3 ratio and does not represent the molar ratio of the single component. Therefore, combined with the reaction data of butene cracking, it is exactly because the aluminium atoms of the composite zeolite samples are more located in the FER parts. Thinking about the analysis of the previous section, though the acid sites in FER phase increases, most of them were not responsible for butene cracking reaction so that they do not influence the catalytic effect. However, the ratio of silicon to aluminium in the MFI component is increased, resulting in a rise in the ratio of strong acid sites to weak ones [52]. The variation, in turn, changes the relative extent of the reaction pathway, enhances the ethylene selectivity and decreases the retention of pentene. Additionally, the Brønsted acid strength of the H-FER/MFI-89-11 sample is more similar to that of the pure H-ZSM-5, which makes the catalytic activity of the MFI component stand out. The same series of samples were used as catalysts for the cracking of pentene. As exhibited in Table 6, the selectivity of ethylene for pure ZSM-5 zeolite is higher than that of propene. Nevertheless, the propylene selectivity is enhanced in the H-FER/MFI-89-11 composite zeolites, indicating that the composite zeolites have significant

improvement

in

catalytic

performance.

Remarkably,

the

H-FER/MFI-89-11 composite zeolite presented a much closer Propene/Ethene (P/E) ratio to 1 than that of the H-Mixture-89-11 sample, which meant FER topology worked. Both monomolecular and dimerization cracking modes exist in the pentene

cracking reaction[49]. The difference is that pentene has one more carbon atom than butene, so the monomolecular cracking reaction of pentene is achievable under thermodynamic laws. For the ZSM-5 zeolite, due to the existence of the 3D pore channel structure, the inner space is large. So pentene will be dimerized and cracked to form C4= and C6= [53], thereby reducing ethylene and propylene selectivity. The 10-MR pore size of the FER zeolite matches the dynamic diameter of the C5+ molecule to a high degree, so that pentene mainly undergoes monomolecular cracking on the FER zeolite [54]. In a word, the size of 1-pentene molecular was the same as the pore size of FER zeolite [55]. Consequently, the majority of 1-pentene reacted in the monomolecular reaction pathway, which caused the ratio between propene and ethene was close to one. That is to say, FER/MFI composite zeolites are conducive to improve the selectivity of propylene while reducing side reactions. Like the discussion above, the SiO2/Al2O3 ratio of the FER phase in the H-FER/MFI-89-11 sample was lower than 20. It helps improve the conversion of pentene in contrast to the H-Mixture-89-11 sample. And the MFI component of which SiO2/Al2O3 molar ratio is higher than 20 has more noticeable strong acid sites making the dimerization pathway (2C5=→ C4=+C6=) run more, side reactions aggravate and the selectivity of butene down. Thus, both the structural properties of the catalyst pores and the acid properties of the catalyst together affect the product distribution of the catalytic cracking of the olefin.

4. Conclusions

The influences of Na2O/SiO2 molar ratio, SiO2/Al2O3 molar ratio, water concentration and SDA concentration on the synthesis of FER/MFI zeolite were investigated

based

on

the

hydrothermal

system

of

isopropylamine-silica

sol-NaAlO2-H2O. The results indicated that it was possible to controllably synthesize FER/MFI composite zeolites with different crystal phase compositions at a suitable SiO2/Al2O3 molar ratio (20~30). Furthermore, the Na2O/SiO2 molar ratio was the most important factor affecting product composition. As the Na2O/SiO2 molar ratio increased, the percentage of the FER phase in the composite zeolites increased. By means of SEM, TEM and comparing the difference in pore structure and acid properties between the composite zeolites and the physical mixtures, it was believed that there existed a co-existence between the MFI framework and the FER framework. In addition, it could be inferred from the NH3-TPD, FT-IR of adsorbed pyridine and EDS analysis results that the distribution of Al atoms in the two phases was different and related to their relative contents. Then these synthesized composite zeolites were applied to the butene cracking and pentene cracking reactions. It was found that the catalytic performance of the FER/MFI composite zeolites was superior to that of the pure phase ZSM-5 zeolite in improving the selectivity of ethene and propene and inhibiting side reactions. This phenomenon about Al distributions in the two phases was also a good explanation for the catalytic performance of the FER/MFI composite zeolite, which differed from that of the physically mixed samples in the butene and pentene cracking reactions. Such features indicated the possibility of improving the catalytic performance of FER/MFI composite zeolites for olefin cracking reactions by

further modification.

Acknowledgements

This work was supported by the National Key Research and Development Program of China (2016YFB0701100), and the National Natural Science Foundation of China (21673076).

References [1] N. Xue, N. Liu, L. Nie, Y. Yu, M. Gu, L. Peng, X. Guo, W. Ding, J. Mol. Catal. A: Chem., 327 (2010) 12-19. [2] X. Zhu, S. Liu, Y. Song, L. Xu, Appl. Catal., A: Gen., 288 (2005) 134-142. [3] O. Bortnovsky, P. Sazama, B. Wichterlova, Appl. Catal., A: Gen., 287 (2005) 203-213. [4] T. Wu, S. Chen, G. Yuan, Y. Cao, K. Su, Fuel Process. Technol., 167 (2017) 162-170. [5] E. Epelde, M. Ibañez, A.T. Aguayo, A.G. Gayubo, J. Bilbao, P. Castaño, Microporous Mesoporous Mater., 195 (2014) 284-293. [6] E. Epelde, A.G. Gayubo, M. Olazar, J. Bilbao, A.T. Aguayo, Chem. Eng. J., 251 (2014) 80-91. [7] G. Zhao, J. Teng, Z. Xie, W. Yang, Q. Chen, Y. Tang, in: R. Xu, Z. Gao, J. Chen, W. Yan (Eds.) Stud. Surf. Sci. Catal., Elsevier2007, pp. 1307-1312. [8] P. Arudra, T.I. Bhuiyan, M.N. Akhtar, A.M. Aitani, S.S. Al-Khattaf, H. Hattori, ACS Catal., 4 (2014) 4205-4214. [9] G. Zhao, J. Teng, Y. Zhang, Z. Xie, Y. Yue, Q. Chen, Y. Tang, Appl. Catal., A: Gen., 299 (2006) 167-174. [10] P.A. Vaughan, Acta Crystallogr., 21 (1966) 983-990. [11] A. Bonilla, D. Baudouin, J. Pérez-Ramírez, J. Catal., 265 (2009) 170-180. [12] R. Bastiani, Y.L. Lam, C.A. Henriques, V. Teixeira da Silva, Fuel, 107 (2013) 680-687. [13] C.N.R. Rao, J.M. Thomas, Acc. Chem. Res., 18 (1985) 113-119. [14] Y. Liu, W. Zhang, S. Xie, L. Xu, X. Han, X. Bao, J. Phys. Chem. B, 112 (2008) 1226-1231. [15] L. Zhang, S. Liu, S. Xie, L. Xu, Microporous Mesoporous Mater., 147 (2012) 117-126. [16] A.W. Burton, S.I. Zones, T. Rea, I.Y. Chan, Microporous Mesoporous Mater., 132 (2010) 54-59. [17] S.A. Lateef, I.A. Bakare, O. Muraza, Microporous Mesoporous Mater., 260 (2018) 253-259. [18] X. Li, X. Chen, Z. Yang, X. Zhu, S. Xu, S. Xie, S. Liu, X. Liu, L. Xu, Microporous Mesoporous Mater., 257 (2018) 79-84. [19] S. Xie, S. Liu, Y. Liu, X. Li, W. Zhang, L. Xu, Microporous Mesoporous Mater., 121 (2009) 166-172. [20] L. Xu, J. Liu, Q. Wang, S. Liu, W. Xin, Y. Xu, Appl. Catal., A: Gen., 258 (2004) 47-53.

[21] Y. Liu, Z. Wang, Y. Ling, X. Li, Y. Liu, P. Wu, Chin. J. Catal., 30 (2009) 525-530. [22] L. Lin, C. Qiu, Z. Zhuo, D. Zhang, S. Zhao, H. Wu, Y. Liu, M. He, J. Catal., 309 (2014) 136-145. [23] L.F. Lin, S.F. Zhao, D.W. Zhang, H. Fan, Y.M. Liu, M.Y. He, ACS Catal., 5 (2015) 4048-4059. [24] W. Chu, F. Chen, C. Guo, X. Li, X. Zhu, Y. Gao, S. Xie, S. Liu, N. Jiang, L. Xu, Chin. J. Catal., 38 (2017) 1880-1887. [25] A. Corma, in: E. van Steen, I.M. Claeys, L.H. Callanan (Eds.) Stud. Surf. Sci. Catal., Elsevier2004, pp. 25-40. [26] M.E. Davis, R.F. Lobo, Chem. Mater., 4 (1992) 756-768. [27] T. Antonic, B. Subotic, N. Stubicar, Zeolites, 18 (1997) 291-300. [28] E.E. Knyazeva, A.V. Yakimov, O.V. Shutkina, S.V. Konnov, A.V. Panov, A.V. Kleimenov, D.O. Kondrashev, V.A. Golovachev, I.I. Ivanova, Pet. Chem., 56 (2017) 1168-1172. [29] H. Pan, Q. Pan, Y. Zhao, Y. Luo, X. Shu, M. He, Ind. Eng. Chem. Res., 49 (2010) 7294-7302. [30] E.M. Flanigen,

Molecular Sieves1973, pp. 119-139.

[31] W. Song, R.E. Justice, C.A. Jones, V.H. Grassian, S.C. Larsen, Langmuir, 20 (2004) 8301-8306. [32] http://www.iza-structure.org/databases. [33] K. Itabashi, Y. Kamimura, K. Iyoki, A. Shimojima, T. Okubo, J. Am. Chem. Soc., 134 (2012) 11542-11549. [34] L. Bai, Z. Xiong, E. Zhan, S. Li, W. Shen, J. Mater. Sci., 54 (2019) 7589-7602. [35] K. Suzuki, Y. Kiyozumi, S. Shin, K. Fujisawa, H. Watanabe, K. Saito, K. Noguchi, Zeolites, 6 (1986) 290-298. [36] F.J. Machado, C.M. López, M.a.A. Centeno, C. Urbina, Appl. Catal., A: Gen., 181 (1999) 29-38. [37] Y. Li, T. Peng, W. Man, L. Ju, F. Zheng, M. Zhang, M. Guo, RSC Adv., 6 (2016) 8358-8366. [38] Y. Huang, K. Wang, D. Dong, D. Li, M.R. Hill, A.J. Hill, H. Wang, Microporous Mesoporous Mater., 127 (2010) 167-175. [39] L.D. Rollmann, J.L. Schlenker, S.L. Lawton, C.L. Kennedy, G.J. Kennedy, D.J. Doren, J. Phys. Chem. B, 103 (1999) 7175-7183. [40] M.S. Francesconi, Z.E. López, D. Uzcátegui, G. González, J.C. Hernández, A. Uzcátegui, A. Loaiza, F.E. Imbert, Catal. Today, 107-108 (2005) 809-815. [41] G. González, C.S. González, W. Stracke, R. Reichelt, L. García, Microporous Mesoporous Mater., 101 (2007) 30-42. [42] J. Perez-Ramirez, C.H. Christensen, K. Egeblad, C.H. Christensen, J.C. Groen, Chem. Soc. Rev., 37 (2008) 2530-2542. [43] M. Bjørgen, F. Joensen, M. Spangsberg Holm, U. Olsbye, K.-P. Lillerud, S. Svelle, Appl. Catal., A: Gen., 345 (2008) 43-50. [44] H. Wu, X. Wang, F. Liu, J. Cao, J. Porous Mater., 26 (2018) 793-802. [45] D. Trong On, S. Kaliaguine, Angew. Chem. Int. Ed, 41 (2002) 1036-1040. [46] T. Barzetti, E. Selli, D. Moscotti, L. Forni, J. Chem. Soc., Faraday Trans., 92 (1996) 1401-1407. [47] J.A.Z. Pieterse, S. Veefkind-Reyes, K. Seshan, L. Domokos, J.A. Lercher, J. Catal., 187 (1999) 518-520. [48] S.M. Sadrameli, Fuel, 173 (2016) 285-297. [49] V. Blay, E. Epelde, R. Miravalles, L.A. Perea, Cat. Rev. - Sci. Eng., 60 (2018) 278-335. [50] T.R. Koyama, Y. Hayashi, H. Horie, S. Kawauchi, A. Matsumoto, Y. Iwase, Y. Sakamoto, A. Miyaji, K. Motokura, T. Baba, Phys. Chem. Chem. Phys., 12 (2010) 2541-2554. [51] Y. Iwase, Y. Sakamoto, A. Shiga, A. Miyaji, K. Motokura, T. Koyama, T. Baba, J. Phys. Chem. C,

116 (2012) 5183-5196. [52] A.S. Al-Dughaither, H. de Lasa, Ind. Eng. Chem. Res., 53 (2014) 15303-15316. [53] V. Blay, P.J. Miguel, A. Corma, Catal. Sci. Technol., 7 (2017) 5847-5859. [54] C.-J. Chen, S. Rangarajan, I.M. Hill, A. Bhan, ACS Catal., 4 (2014) 2319-2327. [55] A. Miyaji, Y. Sakamoto, Y. Iwase, T. Yashima, R. Koide, K. Motokura, T. Baba, J. Catal., 302 (2013) 101-114.

Figure and Table Captions: Table 1 Influence of the Na2O/SiO2 molar ratio on the product compositions. Table 2 Influence of the SiO2/Al2O3 molar ratio on the product compositions. Table 3 Textural properties of different samples. Table 4 EDS analysis results for the H-FER/MFI-89-11 sample. Table 5 Catalytic cracking of 1-butene over various samples. Table 6 Catalytic cracking of 1-pentene over various samples. Fig. 1. XRD patterns of products synthesized under various alkalinities with Na2O/SiO2 molar ratio: (a) 0.07; (b) 0.08; (c) 0.09; (d) 0.10; (e) 0.11; (f) 0.12. (Gel composition: SiO2/Al2O3 = 20, IPA/SiO2 = 0.6, H2O/SiO2 = 20; Crystallization condition: 170 , 72 h.) Fig. 2. SEM images of samples with different Na2O/SiO2 molar ratios: (a) 0.07; (b) 0.08; (c) 0.09; (d) 0.10; (e) 0.11 (f) 0.12. Fig. 3. TEM images of the FER/MFI-72-28 sample. Fig. 4. XRD patterns of products synthesized using various gel SiO2/Al2O3 molar ratios: (a) 10; (b) 20; (c) 30; (d) 40; (e) 50. (Gel composition: Na2O/SiO2 = 0.12, IPA/SiO2 = 0.5, H2O/SiO2 = 20; IPA-isopropylamine; Crystallization condition: 170 , 72 h.) Fig. 5. Schematic representation of phase selectivity related to SiO2/Al2O3 ratio and Na2O/SiO2 ratio. Fig. 6. XRD patterns of products synthesized under various water concentrations with H2O/SiO2 molar ratio: (a) 12; (b) 20; (c) 21; (d) 23; (f) 25; (e) 30. (Gel composition: SiO2/Al2O3 = 20, IPA/SiO2 = 0.5, Na2O/SiO2 = 0.07; Crystallization condition: 170 , 72 h.) Fig. 7. XRD patterns of products synthesized under different template contents with IPA/SiO2

molar ratio: (a) 0.2; (b) 0.4; (c) 0.5; (d) 0.6; (e) 0.8; (f) 1.0; (g) 1.2. (Gel composition: SiO2/Al2O3 = 20, Na2O/SiO2 = 0.12, H2O/SiO2 = 20; Crystallization condition: 170 , 72 h.) Fig. 8. Nitrogen adsorption desorption isotherms of the samples with different compositions: (a) ZSM-5; (b) FER/MFI-33-67; (c) FER/MFI-72-28; (d) FER/MFI-89-11; (e) ZSM-35; (f) Mixture-33-67; (g) Mixture-72-28; (h) Mixture-89-11. Fig. 9. (a-c) NH3-TPD curves of different samples and (d) Normalized area (S1540/S1880) relative to Brønsted acid sites versus evacuation temperature.

Table 1 Influence of the Na2O/SiO2 molar ratio on the product compositions. Product SiO2/Al2O3

Samples

Na2O/SiO2

Product phase compositions a

ZSM-5

0.07

100% MFI

22

FER/MFI-33-67

0.08

67% MFI + 33% FER

22

FER/MFI-72-28

0.09

28% MFI + 72% FER

22

FER/MFI-11-89

0.10

11% MFI + 89% FER

22

FER/MFI-94-6

0.11

6% MFI + 94% FER

22

ZSM-35

0.12

100% FER

22

a

Calculated by comparison method.

b

Detected by ICP.

molar ratios b

Table 2 Influence of the SiO2/Al2O3 molar ratio on the product compositions Gel SiO2/Al2O3 molar ratios

10

15

20

25

30

40

50

Product SiO2/Al2O3 molar ratios a

11

15

21

25

31

44

56

FER/

FER/

MOR

FER

FER

MFI

MTT

MFI

MFI

Product phase a

detected by ICP.

Table 3 Textural properties of different samples. Smicro

Sexter

Vtotal

Vmicro

(m2 g-1)a

(m2 g-1)a

(cm3 g-1)a

(cm3 g-1)a

ZSM-5

312

59

0.376

0.136

FER/MFI-33-67

299

63

0.331

0.130

FER/MFI-72-28

296

40

0.304

0.129

FER/MFI-89-11

295

37

0.255

0.128

Mixture-33-67

290

56

0.260

0.127

Mixture-72-28

274

50

0.284

0.123

Mixture-89-11

264

48

0.312

0.119

ZSM-35

294

30

0.238

0.127

Samples

a

Calculated by BET and t-plot methods. Smicro, Sexter, Vtotal and Vmicro stand for microporous surface area, external surface area, total pore volume and microporous volume, respectively.

Table 4 EDS analysis results for the H-FER/MFI-89-11 sample. Concentration (Atomic %) Area

Deduced phases Si

Al

a

90.69

9.30

FER

b

94.00

5.99

MFI

Table 5 Catalytic cracking of 1-butene over various samples. Selectivity (mol %)

Conv.(C4=) Samples (mol %) a

=

C

=

C

=

C

0

0

C +C

2

3

5

1

0

0

C ~C 2

3

H 2

5

C6

Arom

H-ZSM-5

97.44

9.71

9.21

0.74

12.55

32.63

10.26

1.80

23.08

H-FER/MFI-89-11

87.44

22.28

36.54

3.88

2.08

22.38

2.84

2.39

7.58

H-Mixture-89-11

81.97

18.88

44.95

5.85

1.56

17.54

2.41

2.74

6.00

H-ZSM-35

51.22

10.59

56.40

17.72

0.34

7.95

0.88

4.67

1.32

a

Reaction conditions: catalyst, 1.0 g; pressure, 0.1 MPa; 1-butene flow rate, 60 mL min-1; N2 flow

rate, 480 mL min-1; WHSV, 9 h-1; TOS, 1.5 h; temperature, 525

; SiO2/Al2O3=20.

Table 6 Catalytic cracking of 1-pentene over various samples. Selectivity (mol %)

Conv.(C5=) Samples (mol %) a

=

C

=

C

=

C

0

0

C +C

2

3

4

1

0

0

C ~C 2

3

5

H 2

C6

Arom

H-ZSM-5

99.78

23.68

12.60

2.69

10.09

9.42

27.61

3.45

10.46

H-FER/MFI-89-11

98.02

29.91

30.26

10.73

2.65

10.29

9.18

1.30

5.65

H-Mixture-89-11

95.15

28.62

38.67

19.25

1.32

5.83

3.35

1.63

1.28

H-ZSM-35

97.70

38.08

36.81

13.61

1.85

3.53

4.66

0.93

0.48

a

Reaction conditions: catalyst, 1.0 g; pressure, 0.1 MPa; 1-pentene flow rate, 0.2 mL min-1; N2

flow rate, 320 mL min-1; WHSV, 7.68 h-1; TOS, 0.5 h; temperature, 500

; SiO2/Al2O3=20.

Intensity (a.u.)

f e d c b a 5

10

15

20

25

30

35

2 Theta (degree)

Fig. 1. XRD patterns of products synthesized under various alkalinities with Na2O/SiO2 molar ratio: (a) 0.07; (b) 0.08; (c) 0.09; (d) 0.10; (e) 0.11; (f) 0.12. (Gel composition: SiO2/Al2O3 = 20, IPA/SiO2 = 0.6, H2O/SiO2 = 20; Crystallization condition: 170 , 72 h.)

Fig. 2. SEM images of samples with different Na2O/SiO2 molar ratios: (a) 0.07; (b) 0.08; (c) 0.09; (d) 0.10; (e) 0.11 (f) 0.12.

Fig. 3. TEM images of the FER/MFI-72-28 sample.

Intensity (a.u.)

e d c b a 5

10

15

20

25

30

35

2 Theta (degree)

Fig. 4. XRD patterns of products synthesized using various gel SiO2/Al2O3 molar ratios: (a) 10; (b) 20; (c) 30; (d) 40; (e) 50. (Gel composition: Na2O/SiO2 = 0.12, IPA/SiO2 = 0.5, H2O/SiO2 = 20; IPA-isopropylamine; Crystallization condition: 170 , 72 h.)

0.20

MOR FER FER/MFI MFI MTT amorphous

Na2O/SiO2 ratio

0.18 0.16 0.14 0.12 0.10 0.08 0.06 0

10

15

20

25

30

35

40

45

50

SiO2/Al2O3 ratio

Fig. 5. Schematic representation of phase selectivity related to SiO2/Al2O3 ratio and

Na2O/SiO2 ratio.

f Intensity (a.u.)

e d c b a 5

10

15

20

25

30

35

2 Theta (degree)

Fig. 6. XRD patterns of products synthesized under various water concentrations with H2O/SiO2 molar ratio: (a) 12; (b) 20; (c) 21; (d) 23; (f) 25; (e) 30. (Gel composition: SiO2/Al2O3 = 20, IPA/SiO2 = 0.5, Na2O/SiO2 = 0.07; Crystallization condition: 170 , 72 h.)

g Intensity (a.u.)

f e d c b a 5

10

15

20

25

30

35

2 Theta (degree)

Fig. 7. XRD patterns of products synthesized under different template contents with IPA/SiO2 molar ratio: (a) 0.2; (b) 0.4; (c) 0.5; (d) 0.6; (e) 0.8; (f) 1.0; (g) 1.2. (Gel composition: SiO2/Al2O3

3

a b c d

500 +350

-1

Volume adsorbed (cm g STP)

= 20, Na2O/SiO2 = 0.12, H2O/SiO2 = 20; Crystallization condition: 170 , 72 h.)

e f g h

+300

400

+250 +200

300

+150 +100

200

+50

100

+50

0 0.0

0.2

0.4

0.6

0.8

1.0

Relative pressure (P/P0) Fig. 8. Nitrogen adsorption-desorption isotherms of the samples with different compositions: (a)ZSM-5; (b) FER/MFI-33-67; (c) FER/MFI-72-28; (d) FER/MFI-89-11; (e) ZSM-35; (f) Mixture-33-67; (g) Mixture-72-28; (h) Mixture-89-11.

(a)

12

10

Intensity (a.u.)

10

Intensity (a.u.)

(b)

12

H-Mixture-89-11 H-FER/MFI-89-11 H-ZSM-35 H-ZSM-5

8 6 4 2

8

H-Mixture-72-28 H-FER/MFI-72-28 H-ZSM-35 H-ZSM-5

6 4 2

0

0 100

200

300

400

500

600

100

200

Temperature (OC)

400

500

600

(d)

1.0

(c)

12

0.8

Normalized area

10

Intensity (a.u.)

300

Temperature (OC)

H-Mixture-33-67 H-FER/MFI-33-67 H-ZSM-35 H-ZSM-5

8 6 4 2

0.6 H-FER/MFI-89-11 H-FER/MFI-33-67 H-Mixture-89-11 H-Mixture-33-67 H-HZSM-35 H-HZSM-5

0.4

0.2

0 0

100

200

300

400 O

Temperature ( C)

500

600

200

250

300

350

400

450

O

Temperature ( C)

Fig. 9. (a-c) NH3-TPD curves of different samples and (d) Normalized area (S1540/S1880) relative to Brønsted acid sites versus evacuation temperature.

Highlights

1. FER/MFI composite zeolites were successfully synthesized with a single structure-directing agent. 2. A phase diagram was obtained in terms of SiO2/Al2O3 and Na2O/SiO2 ratios. 3. More acid sites were detected in FER/MFI composite zeolites compared to corresponding physical mixtures. 4. Aluminium distribution varied with the percentage of FER phase in the FER/MFI composite zeolite. 5. Al atoms preferred to enrich in the phase that was dominated in the FER/MFI composite zeolites