Sequential Impregnation Research Articles

Simultaneous IСP-MS determination of trace metals in natural water and snow after their preconcentration on novel adsorbent based on Al2O3 impregnated with Alizarin Complexone

ABSTRACTA simple and available method for on-line preparation of the adsorbent and solid phase extraction procedure for multi-element determination by inductively coupled plasma mass spectrometry (ICP-MS) has been proposed. The adsorbent (Al2O3-PB-AC) was synthesised by sequential impregnation of Al2O3 with Polybrene (PB) and Alizarin Complexone (AC). Cd(II), Cr(III), Ni(II), Pb(II) and Zn(II) were quantitatively recovered using Al2O3-PВ-AC from aqueous solutions at pH 6.5 and at a flow rate of 1.0 mL min−1. All the elements can easily be eluted by 3.0 mL 0.5 M HNO3. A mini-column packed with 0.100 g Al2O3-PB-AC retained all elements quantitatively from up to 50 mL multi-element solution with an enrichment factor of 16.7. The relative standard deviation for five replicate determinations was 3.5%, 7.3%, 6.2%, 7.4% and 4.7% for Cd(II), Cr(III), Ni(II), Pb(II) and Zn(II), respectively, for determination of 5 μg L−1 level. The developed method was applied for SPE-ICP-MS determination of Cd, Cr, Ni, Pb, Zn in snow and river waters.

Enhanced HDN Performance of Al, Zr and Ti Modified NiW Catalysts by Using Co-Impregnation Method

The Al, Zr, and Ti modified MCM-41 materials were prepared by the post-synthesis method, and then the Ni-W species were introduced on them by using the co-impregnation method in order to obtain high-performance hydrodenitrogenation (HDN) catalysts. The activity of the catalysts was evaluated by the HDN reaction of quinoline. The optimum HDN activity was observed on the catalyst supported on the Al modified MCM-41. The high performance of the NiW/Al catalyst was due to the higher dispersion of Ni, W species, the more density of acid sites, the more appropriate nature of W species, and the lower reduction temperature of W species. Moreover, the catalysts prepared by co-impregnation method showed better performance than the catalysts prepared by the sequential impregnation method in the HDN of quinoline.

Oxidation of Carbon Monoxide on Co−Ce‐Modified ZSM‐5 Zeolites: Impact of Mixed Oxo‐Species

AbstractThe main idea of the present work is the creation of new types of redox active sites by using zeolite as a matrix. Structure and catalytic activity in CO oxidation were studied for catalysts based on Co−Ce‐modified ZSM‐5 synthesized by sequential incipient wetness impregnation. Synergy of action of the two additives is observed. The most active is the catalyst with the ratio Co : Ce=3 : 1. According to TEM, XPS, UV‐vis‐DRS, DRIFTS and in situ CO‐reduction studies, the interaction of metals occurs in the channels of the zeolite with the formation of previously unknown joint structures in which CoIII and CeIII are stabilized. Apparently, these structures are represented by mixed Co−Ce oxo‐cations [CoxCeOy]n+. A new absorption band at 2179 cm−1 appearing in the DRIFT spectra of adsorbed CO is associated with mixed species. The catalytic activity in the oxidation of CO correlates with amount of these structures.

Effects of Cerium Doping on Pt–Sn/Al2O3 Catalysts for n-Heptane Reforming

A series of trimetallic Pt–Sn–Ce catalysts supported on chloride Al2O3 was prepared by a sequential impregnation method and applied for n-heptane reforming and characterized by several techniques, including N2 physiosorption, transmission electron microscopy, X-ray diffraction, hydrogen temperature-programmed reduction, CO chemisorption, ammonia temperature-programmed desorption, pyridine desorption Fourier-transform infrared spectroscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy. We have demonstrated that the introduction of Ce can promote isomerization reactions by suppressing undesirable hydrogenolysis reactions, whereas it does not significantly influence the dehydrocyclization reactions. The characterization results show that CeOx can enhance the reducibility of Pt species via enhancing the Pt dispersion. In addition, Ce increases the proportion of medium-strength acid sites, which does not only promote isomerization activity, but also suppresses the undesirable reactions such as hydrogenolysis and cracking.

Effects of impregnation sequence for Mo-modified V-based SCR catalyst on simultaneous Hg(0) oxidation and NO reduction

A series of molybdenum (Mo)-modified vanadium (V)-based selective catalytic reduction (SCR) catalyst samples were prepared by incipient impregnation method for the simultaneous removal of elemental mercury (Hg(0)) and nitrogen oxide (NO) under a simulated sub-bituminous coal combustion gas. The Hg(0) oxidation performances of the modified SCR catalysts significantly varied in terms of different formulations and impregnation sequences while NO reduction performance was quite stable. When Mo and tungsten (W) were sequentially doped onto titanium dioxide (TiO2) support followed by V, the modified SCR catalyst showed the best Hg(0) oxidation performance compared to those firstly doped with V onto TiO2 followed by Mo and W or V, Mo and W simultaneously doped onto TiO2. TEM, XPS and XANES results showed that the different impregnation sequences could result in the different particle sizes of MoO3 and the oxidation states of V and Mo speciation, which could lead to different Hg(0) oxidation performances.

Effect of impregnation sequence of Pd/Ce/γ-Al2O3 sorbents on Hg0 removal from coal derived fuel gas

This study attempted to investigate the effect of impregnation sequence of the Pd/Ce/γ-Al2O3 sorbents on Hg0 removal. To this end, five kinds of sorbents were prepared and tested in simulated coal derived fuel gas (N2–H2–CO–H2S–Hg), including Pd/γ-Al2O3, Ce/γ-Al2O3 and three kinds of Pd-based sorbents with Ce impregnation on γ-Al2O3 substrate. The tests were conducted at 250 and 300 °C respectively. According to the results, bimetallic Ce–Pd/γ-Al2O3 sorbent prepared by simultaneously impregnating Pd and Ce showed much higher and more stable removal efficiency of Hg0 than the other three kinds of sorbents. The Hg0 removal efficiency of Ce–Pd/γ-Al2O3 sorbent reached above 98% within 480 min at 250 °C and 91% within 200 min at 300 °C. Characterization results indicated that the sorbent Ce–Pd/γ-Al2O3 prepared by the co-impregnation method had bigger specific surface area (216.6 m2/g) than the other three kinds of Pd-based sorbents. The content Pd and Ce on the sorbent Ce–Pd/γ-Al2O3 surface is 0.21% and 0.61%, which proved higher than that of the other three kinds of Pd-based sorbents, and observation from STEM-XEDS maps showed it demonstrated the highest dispersion. It is found that Ce is likely to promote the dispersion of Pd on the support surface during the preparation of the sorbent under the co-impregnation method. Meanwhile, Ce enhanced the H2S resistance of the sorbent. Thereby, Ce–Pd/γ-Al2O3 sorbent is found to have the optimal performance of mercury removal. In this study, the Hg0 removal mechanism of the Pd/Ce/γ-Al2O3 sorbents in the simulated coal derived fuel gas was also elaborated.

The Catalytic Performance of Ni-Co/Beta Zeolite Catalysts in Fischer-Tropsch Synthesis

The influence of nickel introduction on the catalytic performance of cobalt micro- and mesoporous Beta zeolite catalysts in Fischer–Tropsch Synthesis was studied. Catalysts containing 3 wt% of nickel and 10 wt% of cobalt were prepared by co-impregnation and sequential impregnation and comprehensively characterized by XRD, XPS, NH3-TPD, TPR-H2 and TEM EDX techniques. Neither the dealumination of Beta zeolite nor the incorporation of Co and Ni affected its structure, as shown by XRD and BET investigations. The presence of nickel results in the decrease in the temperature of the cobalt oxide reduction, evidenced by TPR-H2 and the increase of CO conversion. Among all the tested catalysts, the best catalytic properties in FTS showed that based on microporous dealuminated zeolites with a very high CO conversion, near 100%, and selectivity to liquid products of about 75%. In case of dealuminated samples, the presence of Ni decreased the selectivity to liquid products. All catalysts under study showed high resistance to deactivation during the whole time of synthesis (24 h). The very high stability of nickel-cobalt based Beta catalysts was probably due to the hydrogen spillover from metallic nickel particles to cobalt oxides, which decreased re-oxidation of the active phase, sintering and the creation of the carbon on the catalyst surface. Moreover, the presence of Ni on the surface of cobalt-based Beta catalysts could obstruct the formation of graphitic carbon and, in consequence, delay the deactivation of the catalyst.

Tailoring perovskite surface composition to design efficient lean NOx trap Pd–La1-xAxCoO3/Al2O3-type catalysts (with A = Sr or Ba)

Here we report the influence of surface composition on the NOx removal efficiency of lean NOx trap Pd–La1-xAxCoO3/Al2O3-type catalysts. Three catalysts were prepared by the sequential impregnation of 30 wt.% of La1-xAxCoO3-type perovskites and 1.9 wt.% of Pd over alumina. The following perovskite compositions were used: La0.7Sr0.3CoO3, La0.7Ba0.3CoO3 or La0.5Ba0.5CoO3. The results of X-Ray diffraction, N2 adsorption-desorption at −196 °C, electron microscopy, temperature programmed techniques, and Raman and X-ray photoelectron spectroscopies demonstrated that lanthanum partial substitution by barium promoted the presence of Ba-based phases homogeneously distributed at the surface. This fact together with the higher basicity of Ba than Sr led to an increase of the surface basicity for Ba-doped samples. Likewise, Ba doping also favors the formation of small PdO particles homogenously distributed over the surface in close contact with the perovskite phase. Hence, the interactions between Pd and surface basic sites were also promoted. As a result, 1.9 wt.% Pd–30 wt.% La0.5Ba0.5CoO3/Al2O3 catalyst exhibited the highest NOx adsorption and reduction efficiency. Specifically, the NO global conversion and nitrogen production were as high as 90 % and 72 % at 350 °C, respectively. The enhancement of NOx storage capacity during the lean period is mainly assigned to the displacement of gas/solid equilibrium between NO2 and the available NOx adsorption sites due to the presence of higher concentration of basic sites at the surface. Meanwhile, the promotion of the NOx reduction capacity is due to the higher strength of NOx adsorbed species, which slows down the decomposition rate of NOx adsorbed species. Furthermore, the high proximity of Pd and perovskite phase favors the intermediate compounds diffusion. These results confirmed the excellent NOx removal efficiency of the 30 wt.% La0.5Ba0.5CoO3-based catalyst, even above than Pt-based model catalyst.

Pd Modification and Supporting Effects on Catalytic Dehydration of Ethanol to Ethylene and Diethyl Ether over W/TiO2 Catalysts.

In the present work, the palladium (Pd) modification and supporting effect of W/TiO2 catalysts on catalytic ethanol dehydration to ethylene and diethyl ether were investigated. The Pd modification with different sequence of Pd and W impregnation on the catalysts was prepared by the incipient wetness impregnation technique. The catalyst characterization and activity testing revealed that the different sequence during impregnation influenced the physicochemical properties and ethanol conversion of catalyst. The differences in structure and surface properties were investigated by XRD, BET, SEM, EDX, XPS and NH3-TPD. Upon the reaction temperature between 200 to 400°C, it was found that the conversion increased with increasing of temperature for all catalysts. The Pd incorporated into catalysts enhanced the ethanol conversion depending on the sequence of impregnation. At low temperature (ca. 200 to 300°C), diethyl ether is a major product and the Pd modification over W/TiO2 catalyst resulted in increased diethyl ether yield. This is because an increase of ethanol conversion was obtained with Pd modification, while diethyl ether selectivity did not change. This can be attributed to the higher amount of weak acids sites present after Pd modification into catalyst. Among all catalysts, the PdW/TiO2 catalyst (coimpregnation) achieved the highest diethyl ether yield of 41.4% at 300℃. At high temperature (ca. 350 to 400°C), ethylene is the major product. The W/Pd/TiO2 catalyst (with sequential impregnation of Pd on TiO2 followed by W) exhibited the highest ethylene yield of 68.1% at 400°C. It can be concluded that the modification of Pd onto W/TiO2 upon different sequence of Pd and W impregnation can improve the diethyl ether and ethylene yield in catalytic ethanol dehydration.

Effect of alkali promoters (Li, Na, K) on the performance of Ru/Al2O3 catalysts for CO2 capture and hydrogenation to methane

The impact of alkali promotion on the CO2 hydrogenation activity and selectivity over 1 %Ru/Al2O3 catalyst was investigated varying the type of metal (Li, Na, K) and precursor salt (carbonates vs. nitrates) while keeping constant the equivalent weight load. Catalysts prepared by sequential impregnations of Ru and alkali precursors on highly resistant γ-Al2O3 spheres (1 mm) were characterized by XRD, BET, H2 chemisorption, PSD, FT-IR, CO2-TPD, H2-TPRx and CO2 catalytic hydrogenation tests at atmospheric pressure under continuous flow conditions in the temperature range 200–430 °C. It was found that both CO2 capture capacity and methanation activity of Ru/Al2O3 catalyst were simultaneously increased only via doping with Li (nitrate), which largely reacted with alumina to form a mixed spinel phase. Therefore, Li-Ru/Al2O3 catalyst was successfully tested as a dual functional material operating the cyclic chemical looping process of CO2-capture followed by its methanation under alternating flow conditions at a fixed temperature as low as 230 °C.

Ce-Doped V2O5-WO3/TiO2 with Low Vanadium Loadings as SCR Catalysts and the Resistance of H2O and SO2

The promoting effect of Ce on V-W/Ti catalyst for selective catalytic reduction (SCR) of NOx by NH3 was studied. Compared with the original V-W/Ti samples, addition of Ce contributed better NH3-SCR performance. The H2O and SO2 resistance of Ce modified V-W/Ti catalyst was improved by the different impregnation sequence of Ce. The catalysts were characterized by NH3-temperature programmed desorption (NH3-TPD), X-ray photoelectron spectroscopy (XPS), and H2-temperature programmed reduction (H2-TPR) techniques. The results showed that the impregnation sequence of W and Ce influenced the NH3 adsorption capacity of the catalysts. In comparison to 0.2V-5Ce-5W/Ti and 0.2V-(5Ce5W)/Ti, 0.2V-5W-5Ce/Ti catalyst contributed better H2O and SO2 resistance, with the highest Ce3+/(Ce4+ + Ce3+) value of 36.6%. Besides, a catalytic mechanism of SCR reactions over Ce-doped V-W/Ti catalysts was proposed.

Effect of Cu/CeO2 catalyst preparation methods on their characteristics for low temperature water−gas shift reaction: A detailed study

• Cu/CeO 2 catalysts were prepared using different impregnation orders for Cu and Ce. • Cu–Ce/CeO 2 (prepared by co-impregnation) exhibited the highest catalytic activity. • Cu dispersion and Cu particle size are important factors in reaction < 280 °C. • Oxygen vacancy concentration and active Cu species are important factors > 360 °C. To investigate the effect of Cu/CeO 2 catalysts preparation methods for low temperature water−gas shift reaction, Cu/CeO 2 catalysts were prepared with various impregnation sequences and applied to the water−gas shift reaction at a high gas hourly space velocity of 36,080 mL/g·h. The catalyst preparation method affected both the Cu−Ce synergistic effect and the physico−chemical properties of the Ce promoted Cu/CeO 2 catalysts, such as specific surface area, Cu particle size, Cu dispersion, amount of active Cu species and oxygen vacancy concentration. Among the prepared catalysts, Cu–Ce/CeO 2 showed the highest CO conversion because of the high contents of active Cu species and high concentration of oxygen vacancies.

Defining nickel phosphides supported on sodium mordenite for hydrodeoxygenation of palm oil

Palm oil is largely produced in Thailand and sufficient to utilize as a biofuel feedstock through hydrodeoxygenation (HDO). In this work a new bifunctional catalyst consisting of nickel phosphide supported on zeolite mordenite in sodium form (Ni-P/NaMOR) was prepared by sequential impregnation and characterized extensively by several techniques to understand the reduction behavior, phases and distribution of nickel phosphides on the support. Nickel and phosphate precursors were transformed to Ni2P2O7 species by calcination and to a mixed phase between Ni12P5 and Ni2P by reduction. The phosphide species distributed in the zeolite cavities and external surface. The HDO of palm oil was tested in a down-flow stainless steel trickle bed reactor and the atmosphere was hydrogen. The mixed phase of nickel phosphides enhanced the HDO reaction. When tested by various temperatures and pressures, the optimum condition in this work was at 425 °C and 50 bar in which a complete of palm oil conversion, the largest HDO yield and selectivity toward C15-C18 alkanes were obtained. The green diesel and HDO yields from reduced Ni-P/NaMOR were larger than those from pure Ni2P and mixed Ni2P-Ni12P5. Interestingly, a small amount of isoparaffins was also observed likely due to the contribution of NaMOR support.

Ethanol CO2 reforming on La2O3 and CeO2-promoted Cu/Al2O3 catalysts for enhanced hydrogen production

3%Ce- and 3%La-promoted 10%Cu/Al2O3 catalysts were synthesized via a sequential incipient wetness impregnation approach and implemented for ethanol CO2 reforming (ECR) at 948–1023 K and stoichiometric feed ratio. CeO2 and La2O3 promoters reduced CuO crystallite size from 32.4 to 27.4 nm due to diluting impact and enhanced the degree of reduction of CuO → Cu0. Irrespective of reaction temperature, 3%La–10%Cu/Al2O3 exhibited the highest reactant conversions, H2 and CO yields followed by 3%Ce–10%Cu/Al2O3 and 10%Cu/Al2O3. The greatest C2H5OH and CO2 conversions of 87.6% and 55.1%, respectively were observed on 3%La–10%Cu/Al2O3 at 1023 K whereas for all catalysts, H2/CO ratios varying from 1.46 to 1.91 were preferred as feedstocks for Fischer-Tropsch synthesis. Activation energy for C2H5OH consumption was also reduced with promoter addition from 53.29 to 47.05 kJ mol−1. The thorough CuO → Cu0 reduction by H2 activation was evident and the Cu0 active phase was resistant to re-oxidation during ECR for all samples. Promoters addition reduced considerably the total carbon deposition from 40.04% to 27.55% and greatly suppressed non-active graphite formation from 26.94% to 4.20% because of their basic character and cycling redox enhancement.

The Influence of a Mesoporous Silica on Ru-Sn Catalyst Activity in the Hydrogenation of Methyl Oleate

The hydrogenation of methyl oleate on a Ru-Sn catalyst deposited on Al-HMS was studied in comparison to that conducted on the same catalyst deposited on a conventional support, i.e. g-Al2O3. The catalyst was prepared by sequential impregnation. The distribution of the acid strength of the prepared catalysts was determined by thermic desorption of diethyl amine in the temperature range from 20 to 600�C. Experiments were carried out on a laboratory echipament using a fixed bed catalytic reactor at a temperature of 275�C, pressure of 100 atm with a methyl oleate volume flow rate (VHSV) of 0.15h-1 and molar ratio hydrogen/ methyl oleate of 10/1. The main compounds identified were saturated and unsaturated fatty alcohols and saturated hydrocarbons. Ru-Sn/ Al-HMS + g-Al2O3 shows a higher conversion to liquid products that the Ru-Sn-Ba / g-Al2O3, probably due to a favorable distribution of the acid strength.

Effect of Pt pre-sintering on the durability of PtPd/Al2O3 catalysts for CH4 oxidation

Unburned CH4 is a primary component of natural gas and its contribution to the greenhouse effect is 20 times that of CO2. Durable oxidation catalysts are critical for developing natural gas vehicles (NGV). Pd-based catalysts with Pt promotion have been widely used for CH4 oxidation due to their activity, durability, and tolerance in H2O and sulfur. However, significant drawbacks including poor durability and ineffective synthesis protocols related to the Pt:Pd ratio, exist. Here, we achieve significant improvements in the activity and durability of PtPd bimetallic catalysts for CH4 oxidation by simply pre-sintering the Pt particles before the addition of Pd. Energy dispersive X-ray spectroscopy coupled with scanning transmission electron microscopy, X-ray diffraction, and diffuse reflectance infrared Fourier-transform spectroscopy studies demonstrate that sequential impregnation of Pd after pre-sintering of Pt led to a segregated PdO layer on top of the pre-sintered metallic clusters, while the co-impregnated PtPd catalysts (without pre-sintering of Pt) exhibited homogeneous distribution of Pt and Pd. Re-oxidation experiments after regeneration by fuel-rich combustion, demonstrated the rapid Pd to PdO re-oxidation behavior for the pre-sintered catalysts compared to that for the co-impregnated catalysts, which we thought important for long-term durability due to the facile catalytic cycle needed for CH4 oxidation. All results suggest that the PdO surface layer on top of the Pt clusters is critical for long-term durability of CH4 oxidation; herein, important insight on the critical nature of the molecular level design of bimetallic clusters towards the development of more durable Pd-based catalysts for CH4 oxidation, is provided.

Dry reforming of methane over Co-Ce-M/AC-N catalyst: Effect of promoters (Ca and Mg) and preparation method on catalytic activity and stability

The catalytic activity of DRM reaction over 1M-1Co-1Ce/AC-N (M = Ca and Mg) catalysts was investigated at 800 °C and under atmospheric pressure. By promoting N-doped activated carbon supported Co-Ce catalysts with alkaline-earth metals to obtain catalysts with better catalytic performance is the main purpose of study. The catalysts were prepared by wet-impregnation method and the influence of impregnation sequence on catalytic performance was also studied. The characterization was conducted using TPR, TPD, XPS, TEM and Raman. The catalyst 1Ca-1Co-1Ce/AC-N promoted with Ca and prepared by co-impregnation exhibited higher catalytic activity than unmodified. This was mainly due to the stronger interaction between metal and support as well as better active metals dispersion. The 1Ca-1Co-1Ce/AC-N catalysts also displayed excellent stability and XPS results indicated that higher Ce3+/Ce4+ and Oβ/(Oα+Oβ) ratios were observed on this catalyst. However, the catalyst 1Co-1Ce/1Ca/AC-N prepared with sequential impregnation exhibited poor stability. In addition, the TEM of the spent catalysts revealed that there were a large number of carbons were generated on active metal surface.

Preparation and investigation of Pd doped Cu catalysts for selective hydrogenation of acetylene

A series of PdCu bimetallic catalysts with low Cu and Pd loadings and different Cu: Pd atomic ratios were prepared by conventionally sequential impregnation (CSI) and modified sequential impregnation (MSI) of Cu and Pd for selective hydrogenation of acetylene. Characterization indicates that the supported copper (II) nitrate in the PdCu bimetallic catalysts prepared by MSI can be directly reduced to Cu metal particles due to the hydrogen spillover from Pd to Cu(NO3)2 crystals. In addition, for the catalysts prepared by MSI, Pd atoms can form PdCu alloy on the surface of metal particles, however, for the catalysts prepared by CSI, Pd tends to migrate and exist below the surface layer of Cu. Reaction results indicate that compared with CSI, the MSI method enables samples to possess preferable stability as well as comparable reaction activity. This should be due to the MSI method in favor of the formation of PdCu alloy on the surface of metal particles. Moreover, even Pd loading is super low, < 0.045 wt-% in this study, by through adjusting Cu loading to an appropriate value, attractive reactivity and selectivity still can be achieved.

The Facile Preparation of Flexible Graphene/Carbon Nanotubes Hybrid Papers for Electromagnetic Interference Shielding

A series of flexible graphene/carbon nanotubes (CNTs) hybrid papers were prepared by a facile impregnation method using cellulose papers as substrate. The impregnation cycles and sequence have a great impact on microstructure, electrical conductivity and electromagnetic interference (EMI) shielding performance of graphene/CNTs hybrid papers. The results showed that the surface of cellulose papers was covered by graphene and CNTs, forming continuous conductive networks. The graphene/CNTs hybrid papers achieved a thickness range of 174.7-253.2 μm and areal density range of 26-35.7 g/m2, which presented a larger advantage than traditional EMI shielding materials. The electrical conductivity was increased from 0.33 S/cm to 7.63 S/cm with the increase of impregnation cycles from 1 to 5. Furthermore, graphene/CNTs hybrid papers delivered a high EMI shielding effectiveness of 22-32 dB in the frequency of 30-1500MHz, which was superior to single graphene or CNTs papers. Moreover, the electrical conductivity and EMI shielding effectiveness of as-prepared graphene/CNTs hybrid papers presented little decline after even bending 100 times at an angle of 180° owing to their excellent flexibility. The graphene/CNTs hybrid papers possess a huge application potential in electromagnetic compatibility (EMC) of electronic device. Key words: graphene; carbon nanotubes; electromagnetic interference shielding; cellulose paper; dielectric polarization

Gallium-Immobilized Carbon Nanotubes as Solid Templates for the Synthesis of Hierarchical Ga/ZSM-5 in Methanol Aromatization

Hierarchical Ga/ZSM-5 was synthesized by using a combinative method of steam-assisted crystallization (SAC) and hard templating. Ga-immobilized carbon nanotubes (GaCNTs) were used as hard templates. Compared with Ga-doped ZSM-5 catalysts made by impregnation and by sequential CNT templating and impregnation, hierarchical Ga/ZSM-5 had a moderate mesoporosity and possibly a high concentration of (GaO)+-Bronsted acid site. The moderate mesoporosity shortens residence times of products in the ZSM-5 matrix, while the high concentration of (GaO)+-Bronsted acid enhances aromatization activity. These advantages are critical to improve catalytic performance and durability of hierarchical Ga/ZSM-5 in methanol aromatization.