Supplementary Materials: the Fabrication of Ga2o3/zsm-5 Hollow Fibers for Efficient Catalytic Conversion of N-butane into Light Olefins and Aromatics Catalyst Acid Amount (a.u.) Weak Acid Strong Acid

Table S1. The NH3-TPD data of the as-prepared catalysts. Table S3. Distribution of products in catalytic conversion of n-butane on 0.1% Ga2O3/ZSM-5.


Introduction
Light olefins, including ethene, propene, butene, etc. are important basic chemical raw materials and the demand for them stays at a high level.Aromatic hydrocarbons, such as benzene, toluene, and xylene, are also significant materials for organic chemical production, which are widely used in the production of synthetic fiber, resin, and rubber.For the past few years, crude processing capacity of refinery continues to improve, resulting in the by-production of a large amount of C4 hydrocarbons.Among C4 hydrocarbons, many processes on the conversion of C4 alkenes have been reported, including catalytic cracking, disproportionation, etc.However, C4 alkanes, as important components of C4 hydrocarbons, due to their high stability, the chemical utilization efficiency is still low.Currently, they are mostly used as low-added value fuel.So, using less valuable but industrially abundant C4 alkanes as feedstock to produce light olefins and aromatics has been attracting increasing attention [1][2][3].
Compared with the current main process of steam cracking for the production of light olefins, catalytic cracking, due to the introduction of catalyst, can reduce the reaction temperature and energy consumption, and it also can improve the selectivity to light olefins, especially to that of propylene [4].Up to now, three kinds of catalysts have been proposed for catalytic cracking of hydrocarbons, including zeolites [5][6][7], metal oxides [8,9], and composite catalysts [10,11].Among various catalysts, ZSM-5 zeolite is a typical and superior candidate because of its excellent stability, adjustable acidity, and special pore structure [3,[12][13][14].To further improve the catalytic cracking performances of ZSM-5 zeolite, many modifications have been reported, including alkaline earth metal [15], transition metal [16], rare earth elements [17], phosphorus modification, etc. [18].The above modifications can modulate the amount of acidic sites and the acid strength of ZSM-5 zeolites, thus enhancing the selectivity to light olefins and promoting the catalytic performances of ZSM-5.
In addition to the regulation of acidity, the optimization of the pore structure is another effective strategy to enhance the catalytic performances of zeolite catalysts.In this context, nano ZSM-5 zeolites [19], mesoporous ZSM-5 zeolites [20], nanosheets of zeolite [21], and other hierarchical ZSM-5 zeolites [12] have been reported.Due to the introduction of pores with different levels, the accessibility of active sites of hierarchical ZSM-5 zeolites can be improved greatly.Meanwhile, the transportation capability for feedstock of large sizes could be also enhanced.Among various hierarchical ZSM-5 zeolites, hierarchical ZSM-5 fibers have received much concern because the hierarchical ZSM-5 fibers not only possess the high catalytic activity of zeolite, but also have high mass transfer performance and low pressure drop.Previously, we reported a versatile and facile method for the fabrication of hierarchical ZSM-5 zeolite fibers with macro-meso-microporosity by coaxial electrospinning, and it was found that suitable acidity and the hierarchical porosity contribute to the excellent catalytic performances in the catalytic cracking of iso-butane [12].
Although many catalysts have been proposed for catalytic cracking of C4 alkanes, there are few reports on the catalysts for efficient conversion of n-butane, the most stable component in C4 hydrocarbons.To promote the catalytic conversion of n-butane, the introduction of dehydrogenation component in the current acid-based zeolite to construct the bifunctional catalyst may provide a good solution [22,23].Many metal oxide-based catalysts have been reported for the dehydrogenation of alkanes, such as vanadia-based [24,25], chromium-based [26][27][28], gallium-based [29,30], etc.So in the present study, using n-butane as feedstock, we chose Ga 2 O 3 as the dehydrogenation component and introduced it into the ZSM-5 nanocrystals to fabricate Ga 2 O 3 /ZSM-5 hollow fiber based bifunctional catalysts.The physicochemical features of as-prepared catalysts were characterized by means of XRD, BET, SEM, STEM, NH 3 -TPD, etc., and their performance for the catalytic conversion of n-butane to produce light olefins and aromatics were investigated.

Catalyst Characterization
Figure 1 shows the XRD patterns of the as-synthesized catalysts.From Figure 1 the characteristic diffraction peaks of ZSM-5 could be seen, showing that the catalysts are typical of MFI topology and the introduction of gallium on ZSM-5 does not change the crystalline structure of ZSM-5.No obvious diffraction peaks corresponding to gallium species are observed in the XRD patterns of Ga/ZSM-5, indicating that gallium species may be well dispersed on the surface of ZSM-5 zeolite [31] or the amount of them is too low to show obvious diffraction peak.According to the Ga 2p 3/2 XPS spectra (Figure 2), the Ga 2p 3/2 binding energy value (BEs) for the as-prepared Ga/ZSM-5 (1118.3eV) is consistent with that for Ga 2 O 3 , indicating that the gallium exists on the surface of ZSM-5 in the form of Ga 2 O 3 .In comparison with that of the single bulk Ga 2 O 3 , the broadening of the half peak width of Ga 2p 3/2 of the as-prepared Ga 2 O 3 /ZSM-5 occurs, which is connected with the increase of the Ga dispersion [32].Figure 3A shows the SEM image of the synthesized Nano-ZSM-5 with the average particle size of 137 nm.After the introduction of Ga2O3 on Nano-ZSM-5 by impregnation (Figure 3B), the morphology and particle size of Ga2O3/ZSM-5 do not show obvious change.Then, Ga2O3/ZSM-5 was used as building blocks for the preparation of Ga2O3/ZSM-5 hollow fibers via coaxial electrospinning.Specifically, a suspension of Ga2O3/ZSM-5 nanocrystals in polyvinylpyrrolidon (PVP)/ethanol solution used as the outer fluid, and paraffin oil acted as the inner liquid.The addition of PVP in the suspension was to provide appropriate viscosity for the fluent electrospinning, and paraffin oil, the inner liquid, was to present hollow structure via calcination.The Ga2O3/ZSM-5/PVP composite fibers were successfully prepared (Figure 3C), and after temperature-programmed calcination, the PVP and paraffin oil were removed, and hierarchical Ga2O3/ZSM-5 hollow fibers were obtained (Figure 3D).From Figure 3D, hollow structure and comparatively uniform diameter of the as-prepared fibers could be well seen.Figure 3E presents the high magnification SEM image of the red square in Figure 3D, and it clearly shows that the wall of the Ga2O3/ZSM-5 zeolite hollow fibers is composed of Ga2O3/ZSM-5 nanoparticles, with uniform macropores on the hollow fiber level.The TEM image (Figure 3F) of the fibers further proves the continuous hollow structure character of the fibers.Figure 3A shows the SEM image of the synthesized Nano-ZSM-5 with the average particle size of 137 nm.After the introduction of Ga2O3 on Nano-ZSM-5 by impregnation (Figure 3B), the morphology and particle size of Ga2O3/ZSM-5 do not show obvious change.Then, Ga2O3/ZSM-5 was used as building blocks for the preparation of Ga2O3/ZSM-5 hollow fibers via coaxial electrospinning.Specifically, a suspension of Ga2O3/ZSM-5 nanocrystals in polyvinylpyrrolidon (PVP)/ethanol solution used as the outer fluid, and paraffin oil acted as the inner liquid.The addition of PVP in the suspension was to provide appropriate viscosity for the fluent electrospinning, and paraffin oil, the inner liquid, was to present hollow structure via calcination.The Ga2O3/ZSM-5/PVP composite fibers were successfully prepared (Figure 3C), and after temperature-programmed calcination, the PVP and paraffin oil were removed, and hierarchical Ga2O3/ZSM-5 hollow fibers were obtained (Figure 3D).From Figure 3D, hollow structure and comparatively uniform diameter of the as-prepared fibers could be well seen.Figure 3E presents the high magnification SEM image of the red square in Figure 3D, and it clearly shows that the wall of the Ga2O3/ZSM-5 zeolite hollow fibers is composed of Ga2O3/ZSM-5 nanoparticles, with uniform macropores on the hollow fiber level.The TEM image (Figure 3F) of the fibers further proves the continuous hollow structure character of the fibers.Figure 3A shows the SEM image of the synthesized Nano-ZSM-5 with the average particle size of 137 nm.After the introduction of Ga 2 O 3 on Nano-ZSM-5 by impregnation (Figure 3B), the morphology and particle size of Ga 2 O 3 /ZSM-5 do not show obvious change.Then, Ga 2 O 3 /ZSM-5 was used as building blocks for the preparation of Ga 2 O 3 /ZSM-5 hollow fibers via coaxial electrospinning.Specifically, a suspension of Ga 2 O 3 /ZSM-5 nanocrystals in polyvinylpyrrolidon (PVP)/ethanol solution used as the outer fluid, and paraffin oil acted as the inner liquid.The addition of PVP in the suspension was to provide appropriate viscosity for the fluent electrospinning, and paraffin oil, the inner liquid, was to present hollow structure via calcination.The Ga 2 O 3 /ZSM-5/PVP composite fibers were successfully prepared (Figure 3C), and after temperature-programmed calcination, the PVP and paraffin oil were removed, and hierarchical Ga 2 O 3 /ZSM-5 hollow fibers were obtained (Figure 3D).From Figure 3D, hollow structure and comparatively uniform diameter of the as-prepared fibers could be well seen.Figure 3E presents the high magnification SEM image of the red square in Figure 3D, and it clearly shows that the wall of the Ga 2 O 3 /ZSM-5 zeolite hollow fibers is composed of Ga 2 O 3 /ZSM-5 nanoparticles, with uniform macropores on the hollow fiber level.The TEM image (Figure 3F) of the fibers further proves the continuous hollow structure character of the fibers.The EDAX elemental maps present the element distribution of Si, O, Al, and Ga (Figure 4), and bright green dots indicates that Ga element is well dispersed on the as-prepared Ga 2 O 3 /ZSM-5 hollow fibers.
The EDAX elemental maps present the element distribution of Si, O, Al, and Ga (Figure 4), and bright green dots indicates that Ga element is well dispersed on the as-prepared Ga2O3/ZSM-5 hollow fibers.Figure 5 shows the nitrogen adsorption-desorption isotherms and BJH pore size distribution (inset) of the Ga2O3/ZSM-5 hollow fibers.According to the nitrogen adsorption-desorption measurement, the Brunauer-Emmett-Teller (BET) surface area of 377 m 2 /g and the pore volume of 0.275 cm 3 /g were determined.From Figure 5, it can be seen that the present isotherms exhibit a typical hysteresis loop at p/p0 > 0.1, indicating mesopores are formed, arising from the interparticle voids of Ga2O3/ZSM-5.Hence, the as-prepared Ga2O3/ZSM-5 hollow fibers exhibit a good hierarchical macro-meso-microporosity, with micropores in ZSM-5 nanoparticles, mesopores formed by the stacking of the Ga2O3/ZSM-5 nanoparticles, and continuous macropores on the hollow fibers.The EDAX elemental maps present the element distribution of Si, O, Al, and Ga (Figure 4), and bright green dots indicates that Ga element is well dispersed on the as-prepared Ga2O3/ZSM-5 hollow fibers.Figure 5 shows the nitrogen adsorption-desorption isotherms and BJH pore size distribution (inset) of the Ga2O3/ZSM-5 hollow fibers.According to the nitrogen adsorption-desorption measurement, the Brunauer-Emmett-Teller (BET) surface area of 377 m 2 /g and the pore volume of 0.275 cm 3 /g were determined.From Figure 5, it can be seen that the present isotherms exhibit a typical hysteresis loop at p/p0 > 0.1, indicating mesopores are formed, arising from the interparticle voids of Ga2O3/ZSM-5.Hence, the as-prepared Ga2O3/ZSM-5 hollow fibers exhibit a good hierarchical macro-meso-microporosity, with micropores in ZSM-5 nanoparticles, mesopores formed by the stacking of the Ga2O3/ZSM-5 nanoparticles, and continuous macropores on the hollow fibers.Figure 5 shows the nitrogen adsorption-desorption isotherms and BJH pore size distribution (inset) of the Ga 2 O 3 /ZSM-5 hollow fibers.According to the nitrogen adsorption-desorption measurement, the Brunauer-Emmett-Teller (BET) surface area of 377 m 2 /g and the pore volume of 0.275 cm 3 /g were determined.From Figure 5, it can be seen that the present isotherms exhibit a typical hysteresis loop at p/p 0 > 0.1, indicating mesopores are formed, arising from the interparticle voids of Ga 2 O 3 /ZSM-5.Hence, the as-prepared Ga 2 O 3 /ZSM-5 hollow fibers exhibit a good hierarchical macro-meso-microporosity, with micropores in ZSM-5 nanoparticles, mesopores formed by the stacking of the Ga 2 O 3 /ZSM-5 nanoparticles, and continuous macropores on the hollow fibers.The temperature-programmed desorption of ammonia (NH3-TPD) experiments were conducted to obtain the acidic properties of the as-prepared Ga2O3/ZSM-5.Figure 6 presents NH3-TPD profiles of Ga2O3/ZSM-5.From Figure 6, it can be seen that there are two desorption group peaks for ZSM-5, one is in the range of 150-250 °C, corresponding to the weak acid sites, and the other, i.e., the strong acid sites, reside in the range of 300-450 °C.After the introduction of Ga2O3, there is no shift of the diffraction peaks, indicating that the strength of acidic sites does not change.Among the samples, except 0.2% Ga2O3/ZSM-5, the amount of weak acid does not show apparent change, and only the amount of strong acid shows a slight decrease (Table S1).

Catalytic Preformances
Before investigating the catalytic performance of Ga2O3/ZSM-5 hollow fibers, to check whether an optimal introducing of Ga2O3 on ZSM-5 exists, Ga2O3/ZSM-5 catalysts with different Ga2O3 loading were evaluated.Figure 7 shows the conversion of n-butane (A), yield of ethene and propene (B), and yield of C2 = , C3 = , C4 = plus BTX (C2 = , C3 = , C4 = plus BTX refer to ethene, propene, butenes, butadiene and benzene, toluene, xylene) (C) as a function of reaction temperature.From Figure 7, it is apparent that The temperature-programmed desorption of ammonia (NH 3 -TPD) experiments were conducted to obtain the acidic properties of the as-prepared Ga 2 O 3 /ZSM-5.Figure 6 presents NH 3 -TPD profiles of Ga 2 O 3 /ZSM-5.From Figure 6, it can be seen that there are two desorption group peaks for ZSM-5, one is in the range of 150-250 ˝C, corresponding to the weak acid sites, and the other, i.e., the strong acid sites, reside in the range of 300-450 ˝C.After the introduction of Ga 2 O 3 , there is no shift of the diffraction peaks, indicating that the strength of acidic sites does not change.Among the samples, except 0.2% Ga 2 O 3 /ZSM-5, the amount of weak acid does not show apparent change, and only the amount of strong acid shows a slight decrease (Table S1).The temperature-programmed desorption of ammonia (NH3-TPD) experiments were conducted to obtain the acidic properties of the as-prepared Ga2O3/ZSM-5.Figure 6 presents NH3-TPD profiles of Ga2O3/ZSM-5.From Figure 6, it can be seen that there are two desorption group peaks for ZSM-5, one is in the range of 150-250 °C, corresponding to the weak acid sites, and the other, i.e., the strong acid sites, reside in the range of 300-450 °C.After the introduction of Ga2O3, there is no shift of the diffraction peaks, indicating that the strength of acidic sites does not change.Among the samples, except 0.2% Ga2O3/ZSM-5, the amount of weak acid does not show apparent change, and only the amount of strong acid shows a slight decrease (Table S1).

Catalytic Preformances
Before investigating the catalytic performance of Ga 2 O 3 /ZSM-5 hollow fibers, to check whether an optimal introducing of Ga 2 O 3 on ZSM-5 exists, Ga 2 O 3 /ZSM-5 catalysts with different Ga 2 O 3 loading were evaluated.Figure 7 shows the conversion of n-butane (A), yield of ethene and propene (B), and yield of C 2 = , C 3 = , C 4 = plus BTX (C 2 = , C 3 = , C 4 = plus BTX refer to ethene, propene, butenes, butadiene and benzene, toluene, xylene) (C) as a function of reaction temperature.From Figure 7, it is apparent that with increase of the reaction temperature, the conversion of n-butane, the yield of ethene and propene and the yield of C 2 = , C 3 = , C 4 = plus BTX on all catalysts markedly increase.And at the same temperatrue, increasing the Ga 2 O 3 loading results in the increase of the conversion and the yield of C 2 = , C 3 = , C 4 = plus BTX.As for the yield of ethene and propene, when the reaction temperature is lower than 600 ˝C, it increases with the increasing loading of Ga 2 O 3 , while when the temperature is above 625 ˝C, the yield of ethene and propene decreases with increasing the loading of Ga 2 O 3 .Such a result could be attributed to the synergistic effect of the dehydrogenation and aromatization properties of Ga 2 O 3 [33] and the cracking function of ZSM-5.At lower temperatures, due to the dehydrogenation property, the presence of Ga 2 O 3 contributes to the activation and dehydrogenation of n-butane.Hence n-butane may undergo dehydrogenation to produce butene, which is much easier to be converted than n-butane, and then, butene will undergo catalytic cracking reaction to produce ethene and propene as primary products.When temperature is above 625 ˝C, the produced ethene and propene will undergo oligomerization to produce higher olefins (C2-C9), and then, C7-C9 alkylcyclohexenes would be formed by cyclization and dehydrogenation.Finally, C7-C9 alkylcyclohexenes are converted to corresponding aromatics [34].Thus, although the increase of the yield of ethene and propene flattens out with the increase of the temperature, the generation of the benzene, toluene, and xylene results in the yield of C 2 = , C 3 = , C 4 = plus BTX continuing to increase.From Figure 7, it is can be seen that when the Ga 2 O 3 loading amount is above 0.3%, the enhancing capacity of the conversion of n-butane and the yield of C 2 = , C 3 = , C 4 = plus BTX is not obvious.
According to the literature [35], one possible explanation is that a very small amount of gallium is sufficient to cause a marked enhancement in the activity of ZSM-5, and too much gallium loading will lead to excessive dehydrogenation and secondary reaction, resulting in no beneficial improvement in catalytic conversion of n-butane.In addition, according to the NH 3 -TPD results (Figure 6), the introduction of Ga 2 O 3 slightly decreased the amount of strong acid of ZSM-5, so with the increase of the Ga 2 O 3 loading, the decreased acidity property results in the decrease of cracking performance.The present result indicates that excellent catalytic activity could be obtained by regulating of the Ga 2 O 3 , leading to a good balance between the dehydrogenation of Ga 2 O 3 and the cracking function of ZSM-5.Given that 0.3% Ga 2 O 3 /ZSM-5 was chosen as building blocks for the preparation of Ga 2 O 3 /ZSM-5 hollow fibers via coaxial electrospinning, and their catalytic conversion of n-butane into light olefins and aromatics was further investigated.
with increase of the reaction temperature, the conversion of n-butane, the yield of ethene and propene and the yield of C2 = , C3 = , C4 = plus BTX on all catalysts markedly increase.And at the same temperatrue, increasing the Ga2O3 loading results in the increase of the conversion and the yield of C2 = , C3 = , C4 = plus BTX.As for the yield of ethene and propene, when the reaction temperature is lower than 600 °C, it increases with the increasing loading of Ga2O3, while when the temperature is above 625 °C, the yield of ethene and propene decreases with increasing the loading of Ga2O3.Such a result could be attributed to the synergistic effect of the dehydrogenation and aromatization properties of Ga2O3 [33] and the cracking function of ZSM-5.At lower temperatures, due to the dehydrogenation property, the presence of Ga2O3 contributes to the activation and dehydrogenation of n-butane.Hence n-butane may undergo dehydrogenation to produce butene, which is much easier to be converted than n-butane, and then, butene will undergo catalytic cracking reaction to produce ethene and propene as primary products.When temperature is above 625 °C, the produced ethene and propene will undergo oligomerization to produce higher olefins (C2-C9), and then, C7-C9 alkylcyclohexenes would be formed by cyclization and dehydrogenation.Finally, C7-C9 alkylcyclohexenes are converted to corresponding aromatics [34].Thus, although the increase of the yield of ethene and propene flattens out with the increase of the temperature, the generation of the benzene, toluene, and xylene results in the yield of C2 = , C3 = , C4 = plus BTX continuing to increase.From Figure 7, it is can be seen that when the Ga2O3 loading amount is above 0.3%, the enhancing capacity of the conversion of n-butane and the yield of C2 = , C3 = , C4 = plus BTX is not obvious.According to the literature [35], one possible explanation is that a very small amount of gallium is sufficient to cause a marked enhancement in the activity of ZSM-5, and too much gallium loading will lead to excessive dehydrogenation and secondary reaction, resulting in no beneficial improvement in catalytic conversion of n-butane.In addition, according to the NH3-TPD results (Figure 6), the introduction of Ga2O3 slightly decreased the amount of strong acid of ZSM-5, so with the increase of the Ga2O3 loading, the decreased acidity property results in the decrease of cracking performance.The present result indicates that excellent catalytic activity could be obtained by regulating of the Ga2O3, leading to a good balance between the dehydrogenation of Ga2O3 and the cracking function of ZSM-5.Given that 0.3% Ga2O3/ZSM-5 was chosen as building blocks for the preparation of Ga2O3/ZSM-5 hollow fibers via coaxial electrospinning, and their catalytic conversion of n-butane into light olefins and aromatics was further investigated.
(A) Figure 8 shows the conversion of n-butane (A) and the yield of C2 = , C3 = , C4 = plus BTX (B) on the as-prepared 0.3% Ga2O3/ZSM-5 hollow fibers.For comparison, the catalytic performance of Nano-ZSM-5, 0.3% Ga2O3/ZSM-5 nanoparticles and the hierarchical ZSM-5 hollow fibers electrospun by the as-prepared Nano-ZSM-5 were also investigated.From Figure 8, it can be seen that with increasing the reaction temperature, the conversion of n-butane increases on all catalysts.Among the four catalysts, Ga2O3/ZSM-5 hollow fibers exihits the best catalytic reactivity in the whole temperature range.At the temperature of 575 °C the conversion of n-butane is almost 100%.Similar phenomenon is also reflected in the yield of C2 = , C3 = , C4 = plus BTX.When the reaction temperatures are lower than 650°C, the yield of C2 = , C3 = , C4 = plus BTX on the four catalysts follows the order of Ga2O3/ZSM-5 hollow fibers > Ga2O3/ZSM-5 > ZSM-5 hollow fibers > Nano-ZSM-5.According to the catalytic behavior of four catalysts, specifically, compared with Nano-ZSM-5 and ZSM-5 hollow fibers, the catalytic performances of Ga2O3/ZSM-5 and Ga2O3/ZSM-5 hollow fibers are enhanced, respectively, indicating that the introduction of Ga2O3 is beneficial to the dehydrogenation of n-butane and thus promotes the catalytic activity of the catalysts efficiently.Meanwhile, in comparison with the present Nano-ZSM-5 and Ga2O3/ZSM-5 as well as magnesium-containing HZSM-5 reported in the literature [15], the catalytic   S3).
Catalysts 2016, 6, 13 8 of 12 reactivities of hollow fibers of both ZSM-5 and Ga2O3/ZSM-5 are improved, indicating that the hierarchical pore structure of hollow fibers contributes to enhancing the whole catalytic performance.
There exists a synergistic effect between Ga2O3/ZSM-5 (or ZSM-5) and the hierarchical porosity of the hollow fibers.The unique hierarchical macro-meso-microporosity structure of the as-prepared hollow fibers can effectively enhance the accessibility of the feedstock to catalytic active sites and facilitates the mass transfer of targeted products, including ethene, propylene, aromatics, etc.Thus, the secondary reactions of ethene and propene as well as the carbon deposition could be hindered [12].Ga2O3/ZSM-5 hollow fibers, which effectively combine the cracking function of ZSM-5, the hierarchical macro-meso-microporosity of hollow fibers, and the dehydrogenation of Ga2O3, show the best catalytic behavior among the four catalysts, with the highest yield of C2 = , C3 = , C4 = plus BTX at 600 °C by 87.6%, which is 56.3%, 24.6%, and 13.3% higher than ZSM-5, ZSM-5 zeolite fibers, and 0.3% Ga2O3/ZSM-5, respectively.The stability results of Ga2O3/ZSM-5 hollow fibers show that the catalytic activity of the catalyst decreases with time on stream, and carbon deposition is the cause of catalyst deactivation since the activity of the Ga2O3/ZSM-5 hollow fibers was fully recovered after regeneration (Figures S1-S3).

ZSM-5 Nanocrystals Preparation
ZSM-5 nanocrystals were prepared by hydrothermal crystallization from a clear solution with the composition of 9TPAOH:0.125Al 2 O 3 :25SiO 2 :599H 2 O:1.3NaOH according to previous literature [12,36] except that the addition of NaOH and the synthesis was carried out at 100 ˝C for 72 h.When the synthesis was completed, the nanocrystals products were washed, dried, and calcined at 550 ˝C for 6 h in muffle furnace followed by ion-exchanged, dried, and calcined process.The zeolite prepared according to the above methods is denoted Nano-ZSM-5 (with an actual Si/Al of 55 determined by XRF).

Ga 2 O 3 /ZSM-5 Preparation
The as-prepared Nano-ZSM-5 was subsequently impregnated by the incipient wetness technique using aqueous solution of Ga(NO) 3 ¨xH 2 O, dried for 10 h at 100 ˝C, and calcined at 600 ˝C for 6 h.Catalysts prepared in this way with x wt.% of Ga 2 O 3 are denoted x% Ga 2 O 3 /ZSM-5.

Hierarchical Ga 2 O 3 /ZSM-5 Hollow Fibers Preparation
The outer fluid was prepared as follows: 1.5 g dry Ga 2 O 3 /ZSM-5 nanocrystals were added to 12.16 g absolute ethanol in a beaker (sealed by plastic wrap) and the mixture was subjected to ultrasonic treatment at 100 W for 8 h in order to the nanocrystals be fully dispersed in absolute ethanol.Then, 2.5 g PVP powder was added into the suspension followed by stirring to dissolve PVP powder completely.At last, in order to exclude bubbles in the suspension, another 0.5 h sonication treatment was conducted.
The electrospinning experimental device and the process of electrospinning are similar to that described in the literature [12] except that the flow rate of the paraffin oil is 0.8 mL¨h ´1.The as-prepared fibers are denoted x% Ga 2 O 3 /ZSM-5 hollow fibers.

Catalyst Characterization
X-ray powder diffraction (XRD) patterns in the range of 5 ˝-50 ˝were recorded on a powder X-ray diffractometer(Shimadzu XRD 6000) (Shimadzu, Tokyo, Japan) using CuKα radiation (λ = 0.15406 nm) with a scanning rate of 2 ˝/min, voltage 40 kV, and current 30 mA.Quanta 200F (FEI, Hillsboro, OR, USA) scanning electron microscpy (SEM) was used to observe morphology of the catalysts, and it was also employed for EDX line scan.TEM images were obtained by a JEOL JEM 2100 electron microscope (JEOL, Tokyo, Japan) equipped with a field emission source at an accelerating voltage of 200 kV.The BET specific surface area and pore volume of the samples were determined by adsorption-desorption of nitrogen at liquid nitrogen temperature, using a Micromeritics TriStar II 3020 porosimetry analyzer (Micromeritics, Norcross, GA, USA).X-ray photoelectron spectroscopy (XPS) was applied to analyze the change of surface composition performed on a PerkinElmer PHI-1600 ESCA (PerkinElmer, Waltham, MA, USA) spectrometer using Mg¨Ka (hv = 1253.6eV, 1 eV = 1.603 ˆ10 ´19 J) X-ray source.The binding energy values were corrected for charging effect by referring to the adventitious C1s line at 284.6 eV.
Acidic properties of the catalysts were characterized by the temperature-programmed desorption of ammonia (NH 3 -TPD) method.0.1 g sample was pretreated in nitrogen at 600 ˝C for 1 h, cooled to room temperature, and adsorbed NH 3 for 30 min.After flushing with pure nitrogen gas for 45 min, TPD started at a rate of 10 ˝C/min from 100 ˝C to 600 ˝C and the signal was monitored with a thermal conductivity detector (TCD).The TG-DSC test was performed to analyze the amount of carbon deposition using METTLER TOLEDO TGA/DSC 1 (Mettler Toledo, Zurich, Switzerland), at a heating rate of 10 ˝C/min from 30 ˝C to 800 ˝C in an oxygen atmosphere.

Reaction Testing
Catalytic tests were performed in a fixed-bed flow reactor by passing a gaseous of n-butane (2 mL¨min ´1, 99.9%) in nitrogen at a flow rate of 38 mL/min, and the catalyst load was 200 mg.The products were analyzed on-line using a gas chromatograph (SP-2100) (Beifen-Ruili, Beijing, China) equipped with a 30 m GS-ALUMINA capillary column and a FID detector (Beifen-Ruili, Beijing, China), and the contents of them are calculated on hydrocarbon basis (Tables S2-S7).

Conclusions
The dehydrogenation component of Ga 2 O 3 was introduced to acid-based ZSM-5 nanocrystals, using Ga 2 O 3 /ZSM-5 nanoparticles as building blocks, Ga 2 O 3 /ZSM-5 hollow fibers with hierarchical macro-meso-microporosity were successfuly prepared by coaxial electrospinning.High conversion activity of n-butane and good yield of C 2 = , C 3 = , C 4 = plus BTX were demonstrated.Superior catalytic performances are attributed to the good banlance of the cracking function of ZSM-5 and the dehydrogenation of Ga 2 O 3 , and the synergetic effect of bifunctionality and hierarchical porosity.The present results help to cast new light on the design of bifunctional fiber-based catalysts for efficient catalytic conversion of light alkanes.

Figure 7 .
Figure 7.The conversion of n-butane (A); the yield of ethane and propene (B) and C 2 = , C 3 = , C 4 = plus BTX (C) of the catalysts with different Ga 2 O 3 loadings as a function of reaction temperatures.

Figure 8
Figure 8 shows the conversion of n-butane (A) and the yield of C 2 = , C 3 = , C 4 = plus BTX (B) on the as-prepared 0.3% Ga 2 O 3 /ZSM-5 hollow fibers.For comparison, the catalytic performance of Nano-ZSM-5, 0.3% Ga 2 O 3 /ZSM-5 nanoparticles and the hierarchical ZSM-5 hollow fibers electrospun by the as-prepared Nano-ZSM-5 were also investigated.From Figure 8, it can be seen that with increasing the reaction temperature, the conversion of n-butane increases on all catalysts.Among the four catalysts, Ga 2 O 3 /ZSM-5 hollow fibers exihits the best catalytic reactivity in the whole temperature range.At the temperature of 575 ˝C the conversion of n-butane is almost 100%.Similar phenomenon is also reflected in the yield of C 2 = , C 3 = , C 4 = plus BTX.When the reaction temperatures are lower than 650 ˝C, the yield of C 2 = , C 3 = , C 4 = plus BTX on the four catalysts follows the order of Ga 2 O 3 /ZSM-5 hollow fibers > Ga 2 O 3 /ZSM-5 > ZSM-5 hollow fibers > Nano-ZSM-5.According to the catalytic behavior of four catalysts, specifically, compared with Nano-ZSM-5 and ZSM-5 hollow fibers, the catalytic performances of Ga 2 O 3 /ZSM-5 and Ga 2 O 3 /ZSM-5 hollow fibers are enhanced, respectively, indicating that the introduction of Ga 2 O 3 is beneficial to the dehydrogenation of n-butane and thus promotes the catalytic activity of the catalysts efficiently.Meanwhile, in comparison with