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Study on The High Aluminum-content Sulfated Zirconia: The Influence of Aluminum Contents and Washing Zhiming Ma, Xuan Meng, Chao Yang, Naiwang Liu, Yuting Zhang, and Li Shi Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 27 Apr 2017 Downloaded from http://pubs.acs.org on April 28, 2017

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Industrial & Engineering Chemistry Research

Study on The High Aluminum-content Sulfated Zirconia: The Influence of Aluminum Contents and Washing Zhiming Ma, Xuan Meng, Chao Yang, Naiwang Liu, Yuting Zhang, Li Shi* State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China

ABSTRACT: A high aluminum-content sulfated zirconia was perpared by kneading method, and washing process has been considered as a key factor. Catalysts were characterized by XRD, BET, SEM, TG, FT-IR, pyridine-IR, NH3-TPD, H2-TPR,

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Al-NMR, and the reactivity was evaluated

by n-hexane isomerization. Results showed that the high aluminum-amount sulfated zirconia has a high activity after washed by water. Besides, the aluminum content could influence the crystal form, catalyst structure and acidity obviously, as well as the anchoring effect on the labile sulfates. Actually, the more the aluminum content was, the more sulfates would be left in the catalyst samples after washing. The O-H and S=O stretching vibration would be shifted in the existence of aluminum or water. With the support of aluminum coordination state, the hydrolysis model has been deduced for different aluminum contents of the catalysts, and it can explain the formation of more Brønsted acid sites and Al-O-S bands. KEYWORDS: sulfated zirconia, n-hexane isomerization, aluminum promoter, hydrolysis model

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1. INTRODUCTION SO42-/ZrO2(SZ) has attracted huge attention for its superacidity and excellent activity in many catalytic reactions. It has been widely used in hydroisomerization1, alkylation reaction2, glycerol dehydration3 and acroleic acid esterification4,5 et al. Unlike the zeolite-based catalysts (like Pd/Pt-Mordenite), sulfated zirconia is active for light paraffin isomerization under a lower temperature: the reaction temperature for Pd/Pt-Mordenite is usually from 260 oC to 280 oC, while for SZ catalysts, the temperature is around 200 oC.6 As a kind of high surface area and activity catalyst promoter, alumina has been widely used in different catalyst field. The recent researches have pointed that catalyst prepared by Atomic Layer Deposition on γ-Al2O3 could show higher activity.7-9 Rapid deactivation of sulfated zirconia is always observed during catalytic reactions, and many researchers introduce alumina as the promoter and binder.10-12 Canton et al.13 pointed out that addition of alumina could increase the surface area of the catalysts and decrease the ZrO2 particle sizes. Yu et al.1 explored the method of alumina introduction, and considered that it was a crucial step in catalyst preparation process. Hua et al.14 concluded that adding an appropriate amount of Al2O3 before sulfation could enhance acidity, activity and stability for isomerization. Kim et al.15 considered Al2O3 promoter could increase the concentration of surface intermediates, leading to the increased activity. However, almost all the researches adopt coprecipitation method to introduce the Al2O3, and the concentration of aluminum is focused on 2.5-5%(wt). Therefore, the catalyst is in a powdered form and its mechanical strength is rather poor, which prevents its application and promotion in commercial processes. 2 ACS Paragon Plus Environment

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There is still a controversy that which kinds of acid center(Lewis acid or Brønsted acid) works in the SZ catalyzed reaction and the effect of Al2O3 on formation and transformation of acid sites. Volkova et al.16 considered that the reaction rate of isomerization was controled by the Lewis acid center, while others thought SZ was only active when Brønsted acid sites were present.17 Song et al.18 concluded that Al2O3 could enhance both the acid strength and proportion of acid sites, strengthen the S=O stretching vibration at the same time. Chen et al.19 took the views that different promoters had different promotive effects on differentt kinds of acid center, and the alumina may decrease the total acid content. Nevertheless, nearly no essay points out the relationship between Lewis acid and Brønsted acid in the isomerization of light paraffin, and the form mechanism of acid center in the presence of Al promoter is inavailable either. On the other hand, washing with water often has effects on the structure and chemical property of SZ. Li et al.20 considered water washing could remove around 40% of the sulfates, and had an enormous influence on the activity. Song et al.18 concluded that washing the catalyst before or after calcination stage had different results, and washing after calcination had no impact on the catalysts. Whereas, almost no research focused on how the washing could affect the sulfates and the function of alumina in the washing process. In this paper, the object of the work is to prepare a high aluminum-amount SZ catalyst by kneading method, and compare the reactivity of n-hexane isomerization with traditional samples at a rather low temperature(150 oC). Then the transformation of Lewis/Brønsted acid sites is investigated by NH3-TPD and pyridine-IR in the presence of aluminum. The role of water washing in the properties of catalysts and the hydrolysis mechanism are also researched in detail. 3 ACS Paragon Plus Environment


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2. EXPERIMENTAL SECTION 2.1. Catalyst Preparation. The hydrous zirconia supports were prepared via a conventional precipitation method. 25% ammonia solution was dropwise added into 0.4mol/L ZrOCl2▪8H2O with vigorously stirring and the final pH of the slurry was kept at about 10. After precipitation, the hydroxide suspension was stirred for additional 0.5h and then aged in the mother liquor at room temperature for 15h. The obtained white precipitate Zr(OH)4 was filtered and thoroughly washed with deionized water until the chloride ions were disappeared(AgNO3 test). The Zr(OH)4 hydrogel was then dried at 110 oC for 24h. The dried sample was crushed to very fine powder and then mixed with quantitative pseudo boehmite powder(AlOOH•nH2O, n=0.08~0.62). Sulfation was carried out by impregnating the mixed powder with 0.5mol/L H2SO4 solution (15ml/g) at room temperature for 6h, then the samples were filtered without washing and dried at 110 oC for 24h. The dried sample was mixed with enough 10% HNO3 solution and the obtained mixture was extruded by the catalyst extruding machine. The cylindrical catalyst pellet was dried again at 110 oC for 24h, then calcined at 650 oC for 3h under dry air(30ml/min). The samples were denoted as SZ(Al2O3-free), SA(ZrO2-free) and SZAX, respectively, where X corresponding to the weight ratio of pseudo boehmite in the sample (SZA25 means dried zirconium hydroxide : pseudo boehmite = 10 : 2.5 ). Parts of the samples were washing with deionized water(15ml/g), and this procedure was repeated 3 times. Then the samples were dried at 110 oC for 24h, which was denoted as SZW, SAW and SZAXW, respectively. All the samples were impregnated in Pd(NH3)4Cl2 solution to loaded with 0.5%wt Pd, dried at 110 oC and calcined at 500 oC for 3h, respectively. Thus, the 4 ACS Paragon Plus Environment

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catalysts were denoted as PSZ, PSA, PSZAX, PSZW and PSZAXW. γSA means impregnating the calcined pseudo-boehmite with 0.5mol/L H2SO4 for 6h, filtering and drying, then calcinating this sample at 650oC for 3h again. As reference system, the coprecipitation method13 was used. Al(NO3)3 ▪9H2O was considered as the alumina source and guaranteed the sample has corresponding alumina amounts to PSZAX. Thus, the samples were denoted as c-PSZAX and c-PSZAXW. 2.2. Catalyst Characterization. Powder X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) were used to analyze the morphology of catalyst. XRD was performed by a D8 Advance polycrystalline diffractometer equiped with Cu Kα radiation, and the step was 0.02° at a rate of 1°/min in the range from 20° to 70°. SEM analysis was performed on a JSM-6360LV scanning electron microscope. The surface area of the samples were measured by Micromeritics ASAP 2020 surface-area analyser. In order to characterize the S content of the samples, an element analyzer (Vario Macro Cube) was used in this paper, the element contents of C, H, N, S can be detected using the CHNS mode. Thermogravimetric experiment was carried out in a TG instrument(SDT Q600 V20.9 Build 20) under air condition, temperature range from 50oC to 1200oC. The weight loss between 600 oC to 1200 oC can be considered as the loss of sulfates. Fourier transform infrared spectra (FTIR) was recorded using a Nicolet IS-10 infrared instrument by mixing the sample powder with the dried KBr in a fixed ratio. The acid property was also measured by the FT-IR using pyridine as probe molecule. NH3-TPD and H2-TPR were carried out in a quartz tube matched TCD detector, using helium as carrier gas, ammonia or 5 ACS Paragon Plus Environment


hydrogen-nitrogen as probe, respectively.

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Al MAS-NMR was recorded on a Bruker MSL-300

spectrometer with a resonance frequency of 104.34 MHz. 2.3. Catalytic Test. The n-hexane isomerization catalytic performance of Al-promoted Pd-SO42-/ZrO2 catalysts was carried out in a continuous flow fixed-bed stainless reactor (i.d.=8mm). Before reaction, the prepared catalyst (1.0g, 40-60 mesh) was pretreated in flowing dry air(30ml/min) at 450 oC for 2.5h, then the system was cooled to 100 oC and catalyst was reduced with flowing hydrogen(30ml/min) for 1.5h. After the reduction, the temperature was decreased to a seted point, then hydrogen and n-hexane were simultaneously introduced into the reactor. The reaction conditions were as follows: the reaction temperature= 150 oC, the reaction total pressure= 2.0Mpa, n-hexane weight hourly space velocity(WHSV)= 2.0h-1, H2/C6 molar ratio= 8. The products were analysed by an on-line GC-9800, equipped with an Flame Ionization Detector and SE-30 capillary column. 3. RESULTS AND DISCUSSION 3.1. Structure and Composition Characterizations Figure 1 displays the XRD patterns of PSZAX and PSZAXW. And the crystallite size is calculated by Scherrer equation24, shown in Table 1. The non-aluminum catalyst (Figure 1.a) shows the diffraction peaks of the ZrO2 tetragonal phase(t-ZrO2) at 2θ ≈ 29.8°, 34.1°, 50°, 59.4°; and the ZrO2 monoclinic phase(m-ZrO2) at 2θ ≈ 28.2°, 31.43 °, respectively.18 It can be seen that the monoclinic phase decreases with the increase of aluminum contents, and eliminated when aluminum is up to 25%. Mercera et al.21 proposed that the crystal form of ZrO2 was affected by 6 ACS Paragon Plus Environment

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the crystallite size: crystal size smaller than the critical size can result in t-ZrO2 form, while transformation from tetragonal to monoclinic ZrO2 occured when crystallite size became larger. As shown in Table 1, m-ZrO2 disappears when the crystallite size of t-ZrO2 is smaller than 90 Å, which perfectly matchs with Mercera’ research. While, adding Al2O3 results in the formation of smaller ZrO2 crystallites (as shown in Table 1, the crystallite size of PSZA5 is 107 Å, while PSZA25 is 84 Å), and it can stabilized the metastable t-ZrO2.22 Moreover, PSZW has more m-ZrO2 than that of PSZ (Figure 1.a and Figure 1. d), while the high Al-amount samples(PSZA15W, PSZA25W and PSZA35W) are characteristic of pure tetragonal zirconia. In consideration of the S amounts in those samples (Table 1), we conclude that Al2O3 has an effect on grappling the sulfates. And sulfates can restrain crystal structure transformation in the second calcination stage (500 oC, 3h).14 In the above Al-promoted samples, no characteristic peaks of Al2O3 are detected, implying that Al2O3 is absolutely homogeneously mixed with ZrO2. On the other hand, compared with Figure 1.b and Figure 1.i, Figure 1.c and Figure 1.j, there are different results with different methods in adding Al2O3. Low Al-amount sample prepared by coprecipitation shows pure t-ZrO2 structure, while small amounts of m-ZrO2 phase are presented in PSZA5 along with the t-ZrO2 phase. It can be explained by below: the promoter added by coprecipitation is combined close with Zr(OH)4 sol in the mother liquor, and can get into the crystal structure more easily in the calcination stage; while Al2O3 and Zr(OH)4 powder are just mechanical mixed by the kneading method. No obvious diffraction peak signal is detected in the c-PSZA25, demonstrated that excess Al2O3 can hinder the formation of zirconia crystal. Two 7 ACS Paragon Plus Environment


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reasons are involved for this difference: (1) excess aluminum can act as a filler among the zirconia crystallites, which can prevent the growth and the diffusion of the zirconia particles;13 (2) Al-O-Zr bonds may be formed during the calcination process, which would “tie down” the zirconia and restrict the crystal growth. From all above, we can concluded that the Al-promoter makes great contribution in forming t-ZrO2 crystal, and kneading method is suitable for high Al-amount catalysts. Table 1 also shows the surface area and pore volume of the samples, calculated by the BJH method. In a certain range of Al2O3 contents, the surface area increases with the increase of Al2O3 amount, indicating that structural changes have been caused by the promoter, which is in agreement with the literatures.19, 23 The PSA has a surface area of around 233.455 m2/g, and as a hierarchical porous structure, the Al2O3 can provide numorous active sites for the isomerization. After washing process, the surface area increases slightly, which differs from the Song’ conclution.24 The pore size distribution of prepared catalysts(seen in the Supporting Information) shows that the average pore size decreases slightly with the addition of Al2O3, and the most frequent pore diameter is around 3.5 nm. Moreover, nearly all the samples hold bimodal pore-size distribution, owing to the formation of Zr(SO4)2 with small pores.25 The PSZA35W has a broader pore-size distribution, indicates that the excess pseudo boehmite are located in the surface of ZrO2. More surface structure information can be seen in the SEM patterns(seen in the Supporting Information). It can be seen that both PSZ and PSZA25 have irregular surface structures, and those porous surface structures can lead to good activities. While washing treatment has no 8 ACS Paragon Plus Environment

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significant influence on the surface structure. The c-PSZA25 has a more regular surface structure like zeolites, indicated that Al2O3 added by coprecipitation are more likely to form “blends melt” with ZrO2, and it can also explain the difference in XRD patterns. Figure 2 shows the TG curve of SA, SAW and γSA. It can be found that the S contents calculated by the TG is accordance with the results of elemental analysis. The S contents of γSA is less than the SA’s, which illustrates the formation of Al-O-S is owing to the dehydration condensation between AlOOH and HSO4- under high temperature calcination. 3.2. Catalytic Activity for N-hexane Isomerization Figure 3 shows the conversion rate versus time on stream for n-hexane isomerization at 150 o

C with catalysts. It has been confirmed that adding a small quantity of Al2O3 (usually by the

coprecipitation method) can improve the activity and stability of isomerization vastly,26 and kneading method has shown the same effects based on the activity of PSZA5 in this study. Meanwhile, c-PSZA25 is not active for isomerization, declaring that excess aluminum introduced by the coprecipitation is harmful, which can be explained by the XRD and SEM patterns. Compared PSZ with PSZW, PSZA5 with PSZA5W, PSZA25 with PSZA25W, respectively, an interesting phenomenon can be found. Contrasted with the no-washing samples, both pure SO42-/ZrO2 and low aluminum sample show lower activity and stability, while the high aluminum sample (PSZA25W) shows higher conversion and stability than PSZA25. Li et al.20 has confirmed that labile sulfates as key components could be removed by water and lead to inactivation. Meanwhile, Song et al.24 indicated that washing the calcinated PSWZA had no influence on the activity of isomerization. The sulfate content listed in Table 1 shows that 9 ACS Paragon Plus Environment


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aluminum has a grappling effect on the surface of sulfates, and sulfates have a crucial role in activity. Figure 4 and 5 provide the formation ratios of multi-branched (2,2-DMB and 2,3-DMB) to mono-branched isomers (2-MP and 3-MP) and isomers to cracking products (I/C) of these samples. This two activity indicators can show the the rate of the secondary reaction and cracking. As can be seen that both PSZA5 and PSZA25W have high multi/mono and low I/C ratios, meaning that more mono-branched isomers have transformed into multi-branched isomers, thus, more cracking products are formed. Compared PSZA25 with PSZA25W, iso-olefin intermediates can reach the acid sites more easily after washing, according to bifunctional mechanism.25 While for the PSZA5 and PSZA5W, washing leads to a decrease on conversion and multi/mono ratio, the reason is that small amounts of aluminum can not grapple enough sulfates in the washing process. 3.3. Acidity And Reducibility Analysis 3.3.1. PY-IR Analysis To further explore the influence of aluminum promoter and washing on the catalysts, In-situ FTIR technology is used to characterize the acidity, using pyridine as the probe molecule. In general, IR adsorption bands observed at around 1445 cm-1 can be assigned due to Lewis(L) acid sites, while bands observed at around 1540 cm-1 are attributed to a pyridine molecule interacting with Brønsted(B) acid sites. Another strong band located at around 1490 cm-1 is attributed to a combined effect of L-acid sites and B-acid sites.27, 28 Figure 6 shows the FT-IR spectras of these samples at 200 oC and 450 oC, which represent the total acid contents and strong acid contents, 10 ACS Paragon Plus Environment

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respectively. And the quantitative results are given in Table 2, including the acid strength, acid types and ratios, according to the Lambert–Beer law and the relevant empirical equations.29, 30 Föttinger et al.17 pointed out that L-acid sites were dominant in the low sulfate contents SO42-/ZrO2, which has low activity in n-alkane isomerization. Meanwhile, Al2O3 can increase the catalyst acidity and adjust the L/B ratio dramaticlly, which has been confirmed by many researchers.13, 18, 23, 25 Figure 6 and Table 2 depict that the total acid contents increase by 11.5%, compared with PSZ and PSZA25, and the ratio of L/B at 200 oC and 450 oC decrease greatly, indicating that more B-acid sites are formed with the addition of Al2O3. We can explain it as follow. First, Al2O3 offers weak acid sites, and it can interact with S-Zr bands to generate new acid sites owing to the electronic absorption effect; second, sulfates prefer to reacting with zirconia to form L-acid sites in the non-promoted system, and with the aluminum added, the formation of Al-O-Zr bands in the binary oxides are responsible for the enhancement of B-acid sites;14 third, more sulfates are retained by the Al2O3 promoter, and sulfate content is important to the formation of acid centers. At the same time, washing is another key factor for the distribution and strength of the acid center. From Table 2, it can be concluded that the total acid contents of PSZ and PSZA25 decrease after washing with water, caused by the loss of labile sulfates. On the other hand, for the non-promoted system, more strong B-acid sites and weak L-acid sites are formed by washing, but for PSZA25, L/B ratio at 450 oC doesn’t change obviously. Chen et al.19 concluded that L-acid sites may react with water and translate to B-acid sites easliy, and we think it can be restrained by the Al promoter. Manoilova et al.31 considered that water washing could strongly weaken the 11 ACS Paragon Plus Environment


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B-acid sites while slightly influence the L-acid sites, which is different from our results. And the reason may be the introduce of Al2O3 promoter and the different preparation methods. All in all, both L-acid sites and B-acid sites play an important role in the isomerization, and a suitable L/B ratio is necessary for a better reactivity. 3.3.2. NH3-TPD Analysis In order to explore the acidity of the catalysts better, NH3-TPD was used to measure the strength and distribution of the acid sites, shown in Figure 7. The peaks in the ranges of 130-250 o

C, 250-380 oC and 380-520 oC are normally attributed to NH3 chemisorbed on weak, medium

and strong acid sites, respectively.32 Obviously, the order of total acid contents is: PSZA25> PSZA5≈ PSZ, which is in accordance with the result of pyridine-IR. In addition, aluminum has a more remarkable effect on the weak acid sites (130-250 oC) and medium acid sites (250-380 oC), and PSZA25 has a stronger acid sites at around 500 oC. Besides, water processing can decrease the total acid sites, and significantly influence the acid distribution. 3.3.3. H2-TPR Analysis The reduction properties are characterized by H2-TPR, as shown in Figure 8. Apparently, only one peak is observed on the pattern of both PSZ and PSZW, which is ascribed to the reduction of sulfates.18 It can be seen that Al-promoted catalysts have a stronger reduction peak than that of the non-promoter ones, which can be attributed to the introduction of more sulfates grasped by Al2O3. A shoulder reduction peak can be seen in the PSZA25 and PSZA25W, around 30 oC higher than the sulfates reduction in PSZ. It can be considered that a charge transfer from zirconium to the neighboring aluminum strengthens the Al-O bands between Al and sulfates.14 12 ACS Paragon Plus Environment

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Washing can decrease the reduction peak intensity slightly, because some sulfates can be washed out by water. However, no peaks of PdOx reduction to metallic state are debected by the TPD detector, the reason may be the lower contents of Pd in the catalyst or the reduction properties of PdOx.33 3.4. IR Analysis The IR spectra of samples are shown in Figure 9 and Figure 10, which are normalized by the thickness of the wafers. In the O-H stretching region (3800-3600cm-1), all the samples show similar spectral features: a higher frequency strong symmetrical band at 3738cm-1 with a shoulder at 3750cm-1, and a weak band at 3763cm-1 are attributed to terminal OH groups, which are single-coordinated to the ZrO2 surface; the lower band at 3680cm-1 is attributed to the bridging OH groups.20, 34 In the sulfate groups stretching region(1500-900cm-1), a band at 994cm-1 is assigned to the symmetric O-S-O stretching vibration in the ZrO2 surface, and the bands observed at higher frequency

1042cm-1, 1137cm-1, 1222cm-1 are corresponded to the antisymmetric

O=S=O stretching vibration.29, 35 Compared with PSZ, the decrease of terminal and bridged hydroxy groups after aluminum added(seen in Figure 9), indicates that fractional aluminum can occupy the binding sites for generating zirconia surface OH groups. At the same time, the S=O stretching bands of the PSZA5 and PSZA25 are located at a rather high frequency (from 1042cm-1 to 1072cm-1, and from 1137cm-1 to 1142cm-1), which can be explained by the modification of the sulfates. From Figure 9, it can also be found that the dominant shoulder peak has transformed from 994cm-1 and 1042cm-1 to 1072cm-1 and 1142cm-1 after adding Al2O3, indicating that these bands are very 13 ACS Paragon Plus Environment


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sensitive to sulfates,31 and the combining form of sulfates have been transformed from a chelating bidentate structure to a bidentate persulfate ion on ZrO2 surface. Consequently, more acid sites can be formed. Vishwanathan et al.36 considered that the asymmetric S=O stretching vibrations at higher frequency played a key point in the formation of acid sites, while Song et al.18 concluded that the increase of higher frequency S=O bands indicated the proportion of strong acid sites, which are well accordance with the results of acidity property. Figure 10 shows the influence of washing on catalysts with or without alumina promoter. In the O-H stretching region, the higher wavenumber of terminal OH groups shifts from 3738cm-1 to 3741cm-1 in non-alumina sample indicates the removal of the water soluble sulfates, leading to a lower acidity of OH groups.20, 31 And it is well verified by the sulfate amounts in Table 1 and the acidity in Table 2. In the S=O stretching region, the same phenomenon is found: compared PSZAW with PSZ, the S=O band also shifts from 1042cm-1 to 1048cm-1. For the PSZA25 and PSZA25W, however, no obviously change can be detected, and it can verify the grappling effects of Al2O3 on sulfates. Moreover, the different activity tendency in the n-hexane isomerization after washing can be explained by the IR spectras. 3.5. 27Al MAS-NMR And Hydrolysis Model Analysis In order to examine the coordination state of aluminum, the

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Al MAS-NMR of PSZA5,

PSZA25 and PSZA25W were carried out, as shown in Figure 11. The signals are described as below:23,

37, 38

the intense resonance line at 0.2ppm assigns to Al3+ species in octahedral

coordination; the sharp peak at 34ppm and 59ppm can be contributed to the presence of pentacoordinated Al Ⅴ and tetrahedral Al Ⅵ species, respectively; the signal at 8ppm can be 14 ACS Paragon Plus Environment

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considered as octahedral AlO6 sites of residual pseudo boehmite. Hua et al.14 pointed that the surface of Al-promoted catalysts was rich in both aluminum and Al-O-Zr bands by XPS, and the sharp octahedral Al3+(0.2ppm) could be indicated the formation of isomorphs or solid solutions. Compared PSZA25 with PSZA5, excess aluminum are existed in the form of pseudo boehmite (8ppm) at PSZA25, which is in accordance with the BET analysis above. After the water processing, stronger signals for all the types of Al are detected because of the hydrolysis of portion Al-O-S bands. Based on the results above, the hydrolysis mechanisms are deduced for the non or few aluminum-amount samples and high aluminum-amount sample, displayed in Scheme 1 and Scheme 2, respectively. 4. CONCLUSIONS A high aluminum-amount sulfated zirconia was prepared by kneading method and evaluated by the isomerization of n-hexane at 150 oC. The results demonstrate that the washed PSZA25 has the highest reactivity among all the catalysts. The structure characterization analysis shows that the addition of aluminum can delay the phase transition, and improve the surface area vastly. In the presence of Al-O-S and hydrogen bonds, more B-acid sites can be formed and sulfates are difficult to washed out. Both the L-acid sites and B-acid sites play an important role in the bi-functional catalytic reforming mechanism. The FT-IR patterns indicate that both the aluminum and water have obvious effects on O-H stretching vibration and S=O stretching vibration. By 27Al MAS-NMR, the hydrolysis mechanism has been deduced, and it is useful for understanding the formation of acid sites and further application in industry. 15 ACS Paragon Plus Environment


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SUPPORTING INFORMATION Part A. Pore size distribution of prepared catalysts by BJH method. Part B. SEM patterns of samples. AUTHOR INFORMATION Corresponding Author *

E-mail: [email protected]

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(14) Hua, W. M.; Xia, Y. D.; Yue, Y. H.; Gao, Z. Promoting Effect of Al on SO42-/MxOy (M= Zr, Ti, Fe) Catalysts. J. Catal. 2000, 196, 104-114. (15) Kim, S. Y.; Lohitharn, N.; Goodwin, J. G.; Olindo, R.; Pinna, F.; Canton, P. The effect of Al2O3-promotion of sulfated zirconia on n-butane isomerization: An isotopic transient kinetic analysis. Catal. Commun. 2006, 7, 209-213. (16) Volkova, G. G.; Reshetnikov, S. I.; Shkuratova, L. N.; Budneva, A. A.; Paukshtis, E. A. n-Hexane skeletal isomerization over sulfated zirconia catalysts with different Lewis acidity. Chem. Eng. J. 2007, 134, 106-110. (17) Fottinger, K.; Zorn, K.; Vinek, H. Influence of the sulfate content on the activity of Pt containing sulfated zirconia. Appl. Catal. A. 2005, 284, 69-75. (18) Song, H.; Wang, N.; Song, H. L.; Li, F.; Jin, Z. S. Effect of Al Content on the Isomerization Performance of Solid Superacid Pd–S2O8

2−

/ZrO2–Al2O3. Chinese J. Chem. Eng. 2014, 22,

1226-1231. (19) Chen, W. H.; Ko, H. H.; Sakthivel, A.; Huang, S. J.; Liu, S. H.; Lo, A. Y.; Tsai, T. C.; Liu, S. B. A solid-state NMR, FT-IR and TPD study on acid properties of sulfated and metal-promoted zirconia: Influence of promoter and sulfation treatment. Catal. Today. 2006, 116, 111-120. (20) Li, X. B.; Nagaoka, K.; Lercher, J. A.; Labile sulfates as key components in active sulfated zirconia for n-butane isomerization at low temperatures. J. Catal. 2004, 227, 130-137.


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(21) Mercera, P. D. L.; Ommen, J. G. V.; Doesburg, E. B. M.; Burggraaf, A. J.; Ross, J. R. H. Zirconia as a Support for Catalysts Evolution of the Texture and Structure on Calacination in Air. Appl. Catal. 1990, 57, 127-148. (22) Zalewski, D. J.; Alerasool, S.; Doolin, P. K. Characterization of catalytically active sulfated zirconia. Catal. Today. 1999, 53, 419-432. (23) Barrera, A.; Montoya, J. A.; Viniegra, M.; Navarrete, J.; Espinosa, G.; Vargas, A.; Angel, P. D.; Perez, G. Isomerization of n-hexane over mono- and bimetallic Pd–Pt catalysts supported on ZrO2–Al2O3–WOx prepared by sol–gel. Appl. Catal. A. 2005, 290, 97-109. (24) Song, Y. Q.; Tian, J.; Ye, Y. R.; Jin, Y. Q.; Zhou, X. L.; Wang, H. A.; Xu, L. Y. Effects of calcination temperature and water-washing treatment on n-hexane hydroisomerization behavior of Pt-promoted sulfated zirconia based catalysts. Catal. Today. 2013, 212, 108-114. (25) Yang, Y. C.; Weng, H. S. Al-promoted Pt/SO42−/ZrO2 with low sulfate content for n-heptane isomerization. Appl. Catal. A. 2010, 384, 94-100. (26) Hwang, C. C.; Mou, C. Y.; Comparison of the promotion effects on sulfated mesoporous zirconia catalysts achieved by alumina and gallium. Appl. Catal. A. 2009, 365, 173-179. (27) Zhao, Q.; Yao, J. J.; Shi, L.; Wang, X. Effect of calcination temperature on structure, composition and properties of S2O82-/ZrO2 and its catalytic performance for removal of trace olefins from aromatics. RSC. Adv. 2016, 6, 84553-84561. (28) Tang, H. V.; Huang, Q. L.; Ungureanu, A.; Eic, M.; On, D. T.; Kaliaguine, S. Effect of the acid properties on the diffusion of C7 hydrocarbons in UL-ZSM-5 materials. Micropor. Mesopor. Mat. 2006, 92, 117-128. 19 ACS Paragon Plus Environment


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Page 22 of 37

Table 1. Some Physicochemical Properties of Samples Prepared by Different Methods S

Crystallite Crystallinity(%)

Catalyst

SBET

Contents

VP (cm3/g)

Size(Å) (m2/g)

(wt%)

Ta

Mb

T

M

98±2

103±1

104.849±1.674 0.184±0.012

PSZA5

2.424±0.048 68.01±0.97 91.03±1.17 107±4

123±4

110.782±2.234 0.149±0.027

PSZA25

2.527±0.016 55.54±1.19

84±2

--

126.628±1.211 0.213±0.003

PSZ

2.134±0.065 73.65±1.54 89.54±0.96

--

PSZW

1.099±0.079 81.89±1.78 84.39±1.31

86±1

104±5

106.769±2.157 0.191±0.012

PSZA5W

1.374±0.102 60.67±0.78 96.91±2.18

92±2

105±3

115.536±1.239 0.185±0.024

PSZA15W 1.923±0.095 61.93±2.21

--

84±2

--

133.283±2.081 0.224±0.009

PSZA25W 2.461±0.049 53.04±1.69

--

79±1

--

135.609±1.202 0.212±0.011

PSZA35W 2.871±0.082 53.19±0.98

--

79±3

--

141.454±2.007 0.219±0.012

PSA

4.972±0.109

--

--

--

--

230.455±3.168 0.263±0.041

PSAW

4.396±0.096

--

--

--

--

245.976±2.995 0.261±0.036

a: tetragonal structure; b: monoclinic structure.


Page 23 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 2. Amounts of Lewis and Brønsted Acidity of Catalysts Samples

T

TB

TL

SB

SL

WB

WL

L/B200 oC

L/B450 oC

PSZ

113

28

85

8

37

20

48

3.04

4.63

PSZW

93

23

70

8

22

15

48

3.04

2.82

PSZA5

113

39

74

14

32

25

42

1.9

2.92

PSZA5W

92

35

57

11

28

24

29

1.63

2.55

PSZA25

126

55

71

16

33

39

38

1.29

2.12

39

52

13

25

26

27

1.33

1.92

PSZA25W 91

Units: 10-3 mmol/g; T: total acidity; B: Brønsted acidity; L: Lewis acidity; S: strong acidity; W: weak acidity; error range: ±3%. Figure Captions Figure 1. The XRD patterns for the prepared catalysts. (a) PSZ; (b) PSZA5; (c) PSZA25; (d) PSZW; (e) PSZA5W; (f) PSZA15W; (g) PSZA25W; (h) PSZA35W; (i) c-PSZA5; (j) c-PSZA25. Figure 2. The TG curve of SA,SAW and γSA under air, temperature range from 50 oC to 1200 oC. Figure 3. The conversion rate of samples in the n-hexane isomerization at 150 oC. Figure 4. Multi-branch /mono-branch ratio over prepared catalysts in the n-hexane isomerization at 150 oC. Figure 5. Isomerization/cracking ratio over prepared catalysts in the n-hexane isomerization at 150 oC. Figure 6. Pyridine-IR spectra of samples at 200 oC and 450 oC. (a) PSZ; (b) PSZW; (c) PSZA5; (d) PSZA5W; (e) PSZA25; (f) PSZA25W. 23 ACS Paragon Plus Environment


Page 24 of 37

Figure 7. NH3-TPD pattern of samples in the range from 100 oC to 600 oC. Figure 8. H2-TPR pattern of samples in the range from 50 oC to 700 oC. Figure 9. IR patterns of no-washing samples in the range from 3800cm-1 to 3600cm-1, and from 1500cm-1 to 900cm-1. Figure 10. Contrastive IR patterns of washing and non-washing samples in the range from 3800cm-1 to 3600cm-1, and from 1400cm-1 to 900cm-1. Figure 11. Al-NMR spectra of the PSZA5, PSZA25 and PSZA25W in the range from 200ppm to -200ppm.


Page 25 of 37

T M M

T

T

T

a b c

Intensity[A.U.]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


d e f g h i j 20

30

50

40

60

70

2-Theta[degree]

Figure 1



100 98 96 94 92 90

γSA

88 86 8

84

7

S contents[wt%]

Weight[%]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 37

82 80 78

SAW

6 5

5.02 4.42

4

3.42

SA

3 2 1 0

SA

76 0

100

200

SAW

300

400

γSA

500

600

700

Temperature[

800 ℃

900 1000 1100 1200 1300

]

Figure 2


Page 27 of 37

100

PSZA25W

90

PSZA5 80

PSZA25 70

Conversion[%]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


60

PSZ

50 40 30

PSZA5W

20

PSZW 10

c-PSZA25

0 1

2

3

4

5

6

7

8

TOS[h]

Figure 3



2.0

Multi-branch/Mono-branch Ratio[A.U.]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 37

PSZ PSZA5 PSZA25 PSZW PSZA5W PSZA25W

1.5

1.0

0.5

0.0 0

10

20

30

40

50

60

70

80

90

100

Conversion[%]

Figure 4


Page 29 of 37

500

Isomerization/Cracking Ratio[A.U.]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


100 50

10


5

1 0

10

20

30

40

50

60

70

80

90

100

Conversion[%]

Figure 5



200

450

℃

a

a

b

b

Absorbance[A.U.]

Absorbance[A.U.]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

c

d

Page 30 of 37

℃

c d

e e f 1560

f 1540

1520

1500

1480

1460

1440

1560

1540

-1

1520

1500

1480

1460

1440

-1

Wavenumber[cm ]

Wavenumber[cm ]

Figure 6


Page 31 of 37


Intensity[A.U.]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


100

200

300

400

Temperature[

℃

500

600

]

Figure 7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Intensity[A.U.]


Page 32 of 37

PSZA25W

PSZA25 PSZW PSZ 50

100

150

200

250

300

350

400

Temperature[

450 ℃

500

550

600

650

700

]

Figure 8


Page 33 of 37

-1

-1 3680cm -1

3750cm

1222cm

PSZ PSZ

-1

Transmittance[A.U.]

3738cm

Transmittance[A.U.]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


PSZA5

-1

3763cm

PSZA25

PSZA5 -1

-1

1137cm

PSZA25

994cm -1 1042cm

-1

1142cm

3800

3750

3700

3650

3600

-1

1072cm

1500 1400 1300 1200 1100 1000

-1

900

-1

Wavenumber[cm ]

Wavenumber[cm ]

Figure 9



-1 1042cm

-1

Transmittance[A.U.]

PSZ

Transmittance[A.U.]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

PSZW

3738cm

-1

3741cm

PSZA25

PSZ PSZW -1

1048cm

PSZA25

PSZA25W

3800

3750

3700

3650

Page 34 of 37

PSZA25W

3600

1400

1300

1200

1100

1000

900

-1

-1

Wavenumber[cm ]

Wavemunber[cm ]

Figure 10


Page 35 of 37

59

34

8 0.2 PSZA5

Intensity[A.U.]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


PSZA25

PSZA25W 200

150

100

50

0

-50

-100

-150

-200

Chemical Shift[ppm]

Figure 11



O

O

H+

O S

H

Page 36 of 37

O

O O

O

H+

Zr+

Zr

H

Washing

H+

H

O

O

O

Zr

Zr+ O

O

Scheme 1. Hydrolysis Mechanism for Non-aluminum or Little Aluminum-amount Samples.

O O

H+

O

S

H O

H H+

O

H

Zr

O O

H O

S

H O

O Zr+

O O

H+

O

O

O

Al O

H+

H

O H O

S

O

Washing

H H+

O

H

Zr

H+

H O Al O H O

O Zr+

H+

O O

H H

H O

Scheme 2. Hydrolysis Mechanism for High Aluminum-amount Samples.


Page 37 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


For Table of Contents Only

O

H

washing

S

H

Zr

H H

O

O

+

O

O Zr+ O

O O

H+

H+ O Zr +

Zr

O

O

O

Al2O3 added

H+

O O

O

O S

H O

H H+

O Zr

O

H O

O Zr +

S

O

H+

H+

O

O O

O

Al

H

O

H

O H O

O S

H O

H H

washing H

+

O H Zr

O

O Zr+

H+

O

Al

H

O

H+ O

O

H H

H O


Study of High-Aluminum-Content Sulfated Zirconia - ACS Publications

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