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

    Modification and Sequential Treatment of EU-1 Zeolite in Mild Alkali and Alkaline-acid Conditions Xiaofeng Li, Xiaotao Sun, Yanting Zhang, Junliang Zhang, Pengchao Ren, Xiaozhen Liu, Tao Dou PII: DOI: Reference:

S1004-9541(16)30537-7 doi: 10.1016/j.cjche.2016.08.020 CJCHE 657

To appear in: Received date: Revised date: Accepted date:

4 June 2016 20 August 2016 22 August 2016

Please cite this article as: Xiaofeng Li, Xiaotao Sun, Yanting Zhang, Junliang Zhang, Pengchao Ren, Xiaozhen Liu, Tao Dou, Modification and Sequential Treatment of EU-1 Zeolite in Mild Alkali and Alkaline-acid Conditions, (2016), doi: 10.1016/j.cjche.2016.08.020

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Catalysis, kinetics and reaction engineering

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Modification and Sequential Treatment of EU-1 Zeolite in Mild

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Alkali and Alkaline-acid Conditions 1**

Xiaofeng LI (李晓峰)

, Xiaotao SUN (孙晓涛)1, Yanting ZHANG (张燕挺)1, Junliang ZHANG (张军亮)2, 1

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1,2 **

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Pengchao REN (任鹏超) , Xiaozhen LIU (刘晓臻) and Tao DOU (窦涛)

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Research Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan 030024, China

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Key Laboratory of Catalysis of CNPC, China University of Petroleum-Beijing, Changping, Beijing 102249, China

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Abstract EU-1 zeolites were sequentially treated with low-concentration sodium carbonate (Na2CO3) and

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hydrochloric acid (HCl) solutions. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption/desorption, temperature programmed desorption of NH3 (NH3-TPD), 27

Al nuclear magnetic resonance (27Al NMR) , and the catalytic performances of the treated samples

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solid state

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 Na2CO3 and 0.1 mol/L HCl solutions reached 73.9

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m2·g-1 and 0.162 cm3·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 from 85.09% 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.

Keywords EU-1 zeolite, mesoporous, catalysis

1 INTRODUCTION

Acid and alkali post-treatments to zeolites can modify the compositions and produce mesopore, specifically the treatment methods contain alkali, acid and alkali-acid treatments[1-5]. Both inorganic and organic acids and alkalies can be used in the treatment process. Alkali

ACCEPTED MANUSCRIPT treatment is mainly used to create mesopores by dissolving part of silicon atoms in zeolite framework [6-8]. Under optimal conditions, the microporous framework structure of the zeolite did not collapsed, and the catalytic performance of zeolite can be improved, because the

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new-created mesopores among microcrystallines and within microcrystallines can strengthen diffusion of reactant molecules. The acid treatment to zeolite can remove part of the aluminum

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atoms contained in zeolite framework, and improve the Si/Al ratio, acid strength and hydrothermal stability, and introduce some intercrystalline mesopores [9]. The acid and alkaline treatment also affect the acidity of zeolite to some extent. Generally, the acid-alkali combined treatment is used

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to adjust acidity and Si/Al ratio of zeolites, and create mesopores in order to promote the catalytic performances zeolites.

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EU-1 zeolite is an important catalytic material, which possesses one-dimensional topology structure [12]. Due to its special structure,

it has been demonstrated that EU-1 zeolite showed

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higher activity and selectivity in xylene isomerization reaction [13,14]. According to the literature

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[10,11], the diffusion properties of EU-1 zeolite with mesopores which induced by sequential sodium hydroxide (NaOH) and nitric acid (HNO3) treatments was improved in dimethyl ether to

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propylene (DTP) reaction, and the treated sample exhibited a higher conversion of dimethyl ether. However, there is a great change in composition and acidity of treated samples, because the high-concentration NaOH was used to treat the parent sample.At present, our research group’s

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main task is synthesizing of EU-1 zeolite used for xylene isomerization reaction [15-18]. Although the EU-1 zeolite manufactured based on the route developed by our research group have been commercialized, the catalytic performance of EU-1 zeolite still needs to be further improved. In the industrial practice, it is found that the amorphous silicon and aluminum species deposited in the gap among microcrystallines can not be removed thoroughly, and these species may cause diffusional limitation and side-reactions. Because the xylene isomerization reaction is a kind of diffusion controlled reaction, so improving EU-1 diffusion properties by sequential acid-alkali treatment is an effective means to upgrade its catalytic reaction performance. In order to enlarge intercrystalline mesoporous, improve the activity and selectivity of xylene isomerization reaction, retain the original EU-1 framework structure and its acid properties, we used the mild alkali (Na2CO3) and acid (low-concentration HCl) to remove the amorphous silicon and aluminum species. This process is supposed to ensure that the framework composition and

ACCEPTED MANUSCRIPT acidity of the zeolite stay stable basically, to improve catalytic activity and selectivity by increasing mesopores. The reasons of the selection for the mild condition post-treatment as follow: (1) They must be effective for easy operation; (2) The degree of treatment can not be too severe,

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otherwise, deep treatment may cause side effect in the catalytic reaction. In order to gain the optimal treatment conditions as well as the better catalytic performance of treated samples in

samples treated by acid and alkali in mild conditions.

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2 EXPERIMENT

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xylene isomerization reaction, this study mainly explores the physical-chemical properties of

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2.1 Materials and reagents

The distilled water was made by ourselves. Hydrochloric acid (AR) was obtained from

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Taihua Group Chemical Pesticide Factory. Sodium carbonate (≥99.8%) was purchased from

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Tianjin Kemiou Chemical Reagent Co., Ltd. The EU-1 zeolite (parent sample) was obtained from

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Taiyuan Da Cheng Huan Neng Chemical Technology Co., Ltd.

2.2 Post-treatment of samples

The parent EU-1 zeolite (5g) was added to the 70 ml Na2CO3 solution with different

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concentration. The concentration of Na2CO3 was 0.03mol·L-1, 0.05 mol·L-1, 0.10 mol·L-1, 1.0 mol·L-1, respectively. The suspension was kept 80℃ for 24h while stirring. The slurry was then suction-filtered and washed thoroughly with distilled water until the pH value of filtrate reach 7.0. And the products were designated S-0.03, S-0.05, S-0.10, S-1.0 according to the concentration of Na2CO3 solutions. HCl was selected for the dealumination treatment. 5g of the alkali treated sample was added to the 0.1 mol·L-1 HCl solution. The suspension was kept at room temperature for 24h while stirring. The slurry was then suction-filtered and washed thoroughly with distilled water until the pH value of filtrate reach 7.0. The treated samples were designated S-0.03-0.1, S-0.05-0.1, S-0.1-0.1, S-1.0-0.1 according to the concentration of Na2CO3 solutions.

ACCEPTED MANUSCRIPT 2.3 Characterization of samples

The structural characterization of the parent and treated samples was carried out by X-ray

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powder diffraction (XRD). The XRD patterns were obtained on a (Rigaku D) max-2500 X-ray

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diffractometer . The relative crystallinity of the samples was calculated by the sum of five peaks

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(2θ=19°, 20.8°, 22.2°, 23.2°, 23.9°). Scanning electron microscopy (SEM) was performed on a EOL/JSM-6700F microscope which was made in Japan. The temperature programmed desorption (NH3-TPD) of the samples was analyzed in TL5000-II multi-purpose adsorption apparatus.

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Nitrogen adsorption / desorption measurements were carried out on a Micromeritics/ASAP2000 nitrogen physical absorption device. The 27Al of the samples was measured with Bruker Advance

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400 MAS NMR.

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2.4 Preparation and evaluation of catalyst

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The treated EU-1 zeolite was mixed with high-purity aluminium hydroxide evenly. Then, the mixture was added with aqueous nitric acid solution (3wt%), and was made into the carrier by

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mixing, squeezing, drying, dicing and calcinating. The carrier was converted into the H-form through NH4+ exchange (with NH4Cl, C=1 mol·L-1 for 2h, at 80-90℃), and the carrier was then washed thoroughly with distilled water. After that, it was dipped into chloroplatinic acid and

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sorbent—trichloroacetic acid (TCA). Finally, the catalyst of EU-1 was made after activation and reduction [19].

A small-sized fixed-bed reactor was used to evaluate catalytic performance of EU-1 catalyst in xylene isomerization reaction. The raw material for reaction was prepared with ethylbenzene and m-xylene at a molar ratio of 3:17, and the filling amount of catalyst was 1g. At first, the catalyst was activated for two hours by pumping in H2 at 400 oC, and then the temperature was reduced to 360 oC for reaction. The H2 pressure was 0.5 MPa，the H2 flow rate was 4.2 L·h-1, the material feeding rate for reaction was 5.4 ml·h-1，and the weight hourly space velocity (GHSV) was 4.5h-1. The sample was taken once every 3 hours after the material was charged, the gas chromatography with a FID detector was used for analyzing the products. The column furnace temperature was 60 oC, and the detector temperature was 250 oC. The Agilent capillary-column chromatography (60m×0.320mm×0.25μm) was used.

ACCEPTED MANUSCRIPT The balanced mass fraction of p-xylene (PX) was used as activity index, and the selectivity of C8 aromatic hydrocarbon was used as selectivity index. According to the literature [20], both reaction activity and selectivity are defined as follows:

Selectivity of C8 aromatic hydrocarbon = WPX+MX+OX+EB×100%

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The yield of p-xylene (PX) = WPX×100%

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Catalyst activity = WPX / WPX+MX+OX×100%

Where, W is the mass fraction of components in the product, for example, WPX represents the mass

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fraction of PX in the product.

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3. Results and discussion

3.1 Effect of sequential treatment on EU-1 crystallinity

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The XRD results as shown in Figure 1 and 2 elucidate the preservation of crystallinities of

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EU-1 zeolites after the sequential alkaline and acid treatment. It can be known that the treated samples still have the characteristic diffraction peaks of EU-1 zeolite, and the post-treatment does

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not change the topological structure of the EU-1 zeolite. The crystallinity of samples change between 85% and 105%, and its lattice structure is still stable. It can be found in Table 1 that the crystallinity change of samples treated by different concentrations of Na2CO3 has certain

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regularity, with the increase of sodium carbonate concentration, the crystallinity increases first and then decreases.

The crystallinity of S-0.05 goes up to 106.5%, while the S-0.1’s goes down to 94%. This is because the amorphous material is removed, which is equivalent to the purification for the zeolite, and resulting in increasing first in crystallinity. The crystallinity decreases with the concentration of Na2CO3 solution increased, indicating Na2CO3 solution with high alkalinity destroyed part of EU-1 zeolite framework. In the sequential alkaline-acid treatment, the crystallinity of the samples changes less than the single alkaline treatment due to the continuous application of low-concentration HCl solution .

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Intensity

S-1.0 S-0.10

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S-0.03

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S-0.05

s

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2()20

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Intensity

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Fig. 1 XRD patterns of samples by alkaline treatment in different concentrations

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S-1.0-0.1 S-0.1-0.1

S-0.05-0.1

S-0.03-0.1

S

20

30

2()

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Fig. 2 XRD patterns of samples modified by sequential alkaline-acid treatment

Table 1 Relative crystallinity and SiO2/Al2O3 ratios of parent EU-1 zeolite and sequentially treated samples

Sample S

Relative crystallinity/% S-alkali 100

S-alkali-acid --

SiO2/Al2O3 ratio S-alkali

S-alkali-acid

38

--

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103.7 105

32 30

32.8 30.5

S-0.1 S-1.0

94 88

92 87

28.1 26

28.6 26.6

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3.2 Effect of sequential treatment on EU-1 SiO2/Al2O3 ratio

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S-0.03 S-0.05

It is known that alkaline solution can selectively dissolve the framework and silica-alumina amorphous species of zeolite. Desilicication can affect the SiO2/Al2O3 ratio of EU-1 zeolite to

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some extent. The changes of SiO2/Al2O3 ratio of EU-1zeolite were listed in Table 1. It is found that the SiO2/Al2O3 ratio decreases continuously with the increasing of Na2CO3 concentration, the

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SiO2/Al2O3 ratio of S (parent sample), S-0.05, S-0.10 is 38, 30 and 28.1 respectively, indicating the alkaline treatment has different desilicication rates to EU-1 zeolite, the desilicication rate is greater than the dealumination rate, which agrees with the regularity reported in literature [10].

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After further acid treatment, it is found that the SiO2/Al2O3 ratio of alkali-acid treated sample

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is lower than that of the samples treated only by alkali. It is also found based on comprehensive analysis that a certain amount of Al species is still deposited on the EU-1 surface. At this time, the

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SiO2/Al2O3 ratio of EU-1 zeolite is really not the true framework SiO2/Al2O3 ratio. The HCl solution can remove this part of non-framework aluminum, resulting in the increase of SiO2/Al2O3 ratio [21]. It is significant to suppress the rate of the side reactions by removing the

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non-framework aluminum. It is stated in details in the following sections.

3.3 Effect of sequential treatment on EU-1 morphology

Figure 3 shows the SEM images of sequentially treated samples. It can be seen from SEM images that there are big particles piled up densely by small particles on the surface of parent EU-1 sample (S), and these big particles are different in size. The surface of treated samples is irregular and deformed a little. This phenomenon becomes quite obvious with the increase of Na2CO3 concentration. The morphology of S-0.05 and S-0.03 changeed little, and some particles of S-0.1 have been dissolved and damaged, which are not evident. It is thus seen that the Na2CO3 treatment is a more mild alkaline treatment method, and has a sight effect on EU-1 morphology relative to that of

ACCEPTED MANUSCRIPT caused by the strong alkali—NaOH [10]. The SEM images of S, S-0.05 and S-0.05-0.1 are different to some extent. Relative to the parent sample (S), the particles in S-0.05 do not pile up tightly with a greater gap. It is found that

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S-0.05 and S-0.05-0.1 change less in morphology, indicating the mild acid treatment can’t change

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the EU-1 particle pile-up state.

Fig. 3 The SEM images of sequentially treated samEU-1 zeolites

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Fig. 4 Mechanism diagram of EU-1 zeolite in sequential alkaline-acid treatment

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Obviously, the effects of posttreatment under mild condition with lower concentration of Na2CO3 and HCl solutions to the morphology of EU-1 zeolite are different from those caused by

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strong alkali and acid [11]. Figure 4 gives the mechanism diagram in alkali-acid conditions. In this diagram, low-concentration Na2CO3 alkaline solution can remove amorphous silica-alumina species. In addition, it can enlarge mesopore volume and specific surface area without causing

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great damage of EU-1 framework. But part of the non-framework aluminum exposed by

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desilicication, and it can be formed Al(OH)3 with the CO32- anion. The deposited Al species can be

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moved by further acid treatment, so the mesoporous volume can be increased.

3.4 Effect of sequential treatment on EU-1 specific surface area and pore volume

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3.4.1 Sequential alkaline treatment Figure 5 shows the N2 adsorption/desorption isotherms and the pore diameter distribution of alkaline treatment samples. It is seen from Figure 5 that adsorption/desorption curves of all samples are IV-type isotherm, where there is a hysteresis loop at the high P/P0 areas, indicating the samples have mesoporous structure. The finding shows that total BET surface area is in a downtrend after alkaline treatment, and goes down continuously with increasing of Na2CO3 concentration. Both external specific surface area and mesopore volume firstly increase, then decrease (Table 2). The external specific area and mesopore volume of sample treated by 0.05 mol·L-1 Na2CO3 is 76.3m2·g-1 and 0.155cm3·g-1 separately, increasing 9.8% and 6.9% respectively compared with the parent sample (S). It can be seen that the low concentration of Na2CO3 treatment can remove the amorphous silicon aluminum species, dredge the occluded channel, increase the surface of the

ACCEPTED MANUSCRIPT mesoporous surface and the volume of the mesopore. It is also found that total specific surface area and total pore volume decrease in the study which is sililar to the desilicication of

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one-dimensional ZSM-22 [21].

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Fig. 5 Isotherms of N2 adsorption/desorption and pore size distribution of parent sample and alkali treated samples

Table 2

N2 adsorption datas of parent sample and treated samples with alkaline

Sample name

BET surface area/m2·g-1

Micropore surface area / m2·g-1

External surface area /m2·g-1

Total pore volume / cm3·g-1

Micropore volume /cm3·g-1

S

406.3

336.8

69.5

0.153

0.145

S-0.03

403.2

330.9

72.3

0.145

0.152

S-0.05

395.5

319.2

76.3

0.139

0.155

S-0.10

351.0

292.4

58.6

0.138

0.145

S-1.0

234.5

181.4

53.1

0.09

0.13

3.4.2 Sequential alkali-acid treatment Table 3 shows the N2 adsorption data of sequentially alkali-acid treated samples and parent sample. As compared with those of the parent sample, the BET surface area and micropore surface

ACCEPTED MANUSCRIPT area of S-0.05-0.1decrease little, but the micropore volume increases and mesopore volume decreases. Moreover, the mesopore volume of S-0.05-0.1 increase 11.7% compared to the parent sample. The mesopore volume increases because the HCl can remove Al species inside of pores.

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Figure 6 gives pore diameter distribution data of sequentially treated samples and parent sample. The pore diameter distribution of S-0.05-0.1 is consistent with that of S-0.05 basically,

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indicating a less effect of sequential alkali-acid treatment on pore diameter distribution.

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Fig. 6 Isotherms plot for N2 adsorption/desorption and pore size distribution of parent sample and alkali treated samples

Table 3 N2 adsorption data of sequentially treated alkaline-acid samples and parent sample

Sample name

BET surface area/ m2·g-1

Micropore surface area /m2·g-1

External surface area /m2·g-1

Micropore volume /cm3·g-1

Mesopore volume /cm3·g-1

S

406.3

336.8

69.5

0.153

0.145

S-0.05

395.5

319.2

76.3

0.139

0.155

S-0.05-0.1

392.3

318.4

73.9

0.144

0.162

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3.5 Effect of sequential treatment on the coordination of Al

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S-0.05-0.1

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S-0.05

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60

40

20

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100

S

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Fig.7 27Al NMR spectra of the parent sample and treated EU-1 samples

Figure 7 shows the 27Al NMR spectra of parent and treated EU-1 samples. It is known from the spectra that no peak occurs at 0 of parent sample (S), indicating there is no non-framework Al

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in parent sample. But there is peak at 0 in the sample of S-0.05, indicating that the removal of part of framework silicon causes the Si-O-Si breakage, and part of Al atoms are exposed out of the framework. They are reacted with the CO32- anion, producing Al(OH)3 which are deposited on the EU-1 zeolite surface and block the pores of the zeolite. The peak at 0 of S-0.05-0.1 disappears, demonstrating the non-framework Al is removed by HCl solution. More importantly, this proves the hypothesis of the sequential alkali-acid treatment mechanism.

3.6 Effect of sequential treatment on EU-1 acidity

3.6.1 Alkaline treatment Figure 8 shows NH3-TPD of EU-1 zeolite treated by Na2CO3 solution. The NH3 desorption peak centred at 200 oC is corresponding to the weak acid site, and the NH3 desorption peak at 390 o

C is corresponding to the strong acid site of EU-1 zeolite [22]. The acid properties of treated

ACCEPTED MANUSCRIPT samples and parent sample were summarized in Table 4. It is seen that the strong acid amount of the samples treated by different concentrations Na2CO3 decreases, and the weak acid strength is unchanged nearly. The peak postions of S-0.05 is close to that of original sample(S). Weak acid

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amount, strong acid amount and total acid amount decrease with the increase of Na2CO3

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concentration. In the mild condition (0.05 mol·L-1 Na2CO3), the peak positon and acid amount

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decrease slightly, but these change greatly in rigorous condition (1.0 mol·L-1 Na2CO3)..

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S S-1.0 S-0.03 S-0.05 S-0.1

200

TemperatureC

400

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Fig. 8 NH3-TPD profiles of parent sample and alkali treated EU-1 samples

Table 4 Acid properties of different EU-1 samples

Sample

Total acid amount /mmol·g-1

Weak acid amount /mmol·g-1

Strong acid amount /mmol·g-1

Weak peak temperature /℃

Strong peak temperature /℃

S S-0.03 S-0.05 S-0.10 S-1.0

0.364 0.346 0.329 0.315 0.287

0.166 0.152 0.147 0.142 0.125

0.198 0.194 0.182 0.173 0.162

224 224 224 215 219

390 386 387 404 382

S-0.05-0.1

0.274

0.094

0.180

230

394

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3.6.2 Alkaline-acid treatment S S-0.05-0.1

200

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S-0.05

400

Temperature/C

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Figure 9 NH3-TPD patterns of sequentially treated samples and parent sample

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Figure 9 shows NH3-TPD patterns of sequentially treated samples and parent sample. It is known from the figure that acid peak position of the three samples is unchanged , but the acid amount of samples changes significantly. Strong and weak acid amount of S-0.05-0.1 decrease,

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because non-framework Al and part framework Al are removed by HCl solution and this lead to

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that total acid amount of EU-1 zeolite decreases.

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3.7 Effect of post-treatment EU-1 zeolite in xylene isomerization

Table 5 gives catalytic data of EU-1 catalyst in xylene isomerization reaction. It is seen from

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Table 5 that the activity of the samples by sequential treatment becomes higher than that of original sample, it increased by 0.67 at most. Activity and selectivity of S-0.05 are improved greater, but with the further increasing of Na2CO3 concentration, the catalytic performance of treated samples is becoming worse. The selectivity of S-0.05-0.1 has a significant improvement compared with that of S-0.05. The improvement of selectivity is because the EU-1 acidity is changed and the rate of side reaction was reduced after acid treatment. In addition, it is also because the aluminum hydroxide deposited is removed by acid-treatment [11]. Alkali and sequential alkaline-acid treatment can increase mesopores of EU-1zeolite and improve diffusion properties under mild condition. More importantly, xylene isomerization is a kind of diffusion controlled reaction, the mesopore volume of treated samples increase compared with the parent sample. So the sequential alkali-acid treatment is an effective way to improve

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Table 5

S S-0.03

17.28 18.48

42.07 45.93

15.67 14.79

S-0.05

18.02

42.92

15.02

S-0.1

17.52

42.23

14.74

S-1.0

17.73

49.52

10.83

S-0.05-0.1

18.24

43.99

15.02

Ethylbenzene/

Activity/ %

Selectivity/ %

10.07 10.25

23.03 23.33

85.09 89.45

9.39

23.70

85.42

8.81

23.52

83.30

11.12

22.71

89.20

9.89

23.61

87.14

%

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o-xylene /%

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m-xylene/ %

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p-xylene/ %

Sample

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Catalytic data of xylene isomerization reaction of catalyst for sequentially treated samples

4. Conclusions

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(1) The EU-1 zeolite sequentially treated with different concentrations of alkaline solutions is

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studied in this paper. The treatment of Na2CO3 solution can adjust EU-1 pore structure and acid property in a mild condition. The EU-1 zeolite with larger mesopore volume can be created in

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alkaline treatment in the proper concentration; (2) The EU-1 topological structure is not changed in mild alkali and alkaline-acid treatment; the crystallinity of samples ranges between 85% and 105%. The rate of desilicication and

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dealumination is different in the alkali treatment, the desilicication rate is greater than dealumination rate, and the SiO2/Al2O3 ratio of samples can decreased continuously with alkaline concentration increasing; (3) The silicon species is dissolved greatly in alkaline treatment. The Al species deposited on the surface of EU-1 zeolite is a primary cause to severe side reaction. The acid treatment can further clean the EU-1 surface to improve selectivity of catalytic reaction and remove non-framework Al. This is of importance to reduce catalytic side reaction; (4) The BET specific surface area is in a downtrend after alkaline treatment, and with the increase of Na2CO3 concentration, the BET specific surface area of samples decreases continuously. The external specific surface area and mesopore volume both firstly increase, then decrease;

ACCEPTED MANUSCRIPT (5) The weak acid amount, strong acid amount and total acid amount decrease with the increase of Na2CO3 concentration; the acidity changes less in mild condition (0.05 mol·L-1 Na2CO3);

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(6) The catalytic performance of Na2CO3 treated samples improve greatly. However, the selectivity of EU-1 zeolite treated by sequential alkali-acid can be improved significantly. The

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activity and selectivity of sample treated by sequential 0.05 mol·L-1 Na2CO3 and 0.1 mol·L-1 HCl

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can be improved effectively in xylene isomerization reaction.

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Graphical abstract

The EU-1 zeolite was treated in mild condition with lower concentration of sodium carbonate and hydrochloric acid. Low-concentration sodium carbonate alkaline solution can remove

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amorphous Si/Al species in the gap among EU-1 crystallines on a targeted site. In addition, it can enlarge mesopore volume and specific surface area without causing great damage of EU-1

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framework. A little of non-framework Al species is deposited certainly after alkaline treatment. After that, the diluted hydrochloric acid is applied to remove non-framework acid center to reduce

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side reaction in xylene isomerization. The mesoporous molecular sieve was obtained by the

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alkali-acid treatment.