Forming pure shaped ZSM-5 zeolite bodies by a steam-assisted method and their application in methanol to aromatic reactions

For an industrial-scale catalytic process with a fixed or packed bed reactor, powder catalysts are not suitable because they may block the reaction pipe and increase the pressure of the reactor. Therefore, catalyst molding is essential for the industrial application of a catalyst. During the catalyst molding, binders are employed as indispensable additives that can achieve the mechanical strength requirements for industrial applications. However, the addition of binders may cover the activity sites of the catalyst and suppress the mass transfer of the reactants and products. So, traditional processes of catalyst molding significantly affect the catalytic performance. In this study, we proposed a vapor-phase-treatment to synthesize a pure shaped ZSM-5 zeolite with the re-crystallization of the binder incorporated silica sol and aluminum nitrate, which were converted into a part of ZSM-5 on a commercial H-ZSM-5 zeolite substrate. Subsequently, the shaped ZSM-5 catalyst was evaluated using the catalytic conversion of methanol to an aromatic (MTA reaction). The results showed that compared to the EPHZ catalyst, the SPHZ catalyst exhibited a long lifetime with a relatively high shape selectivity for methanol and aromatics. To rationalize these results and establish a structure–activity relationship, the zeolite catalysts were thoroughly characterized by XRD, NH₃-TPD, FT-IR, N₂ adsorption, TG, SEM, TEM, ICP and Al MAS-NMR. The results demonstrated that an interesting intra-particle pore structure was formed within the monoliths of the SPHZ catalyst. Moreover, the superior catalytic performance obtained for SPHZ may have also been due to the broad acid strength distribution and the conversion of the silicon aluminum adhesive agent to zeolite crystals.

The binder added during molding was re-crystallized and converted into a part of ZSM-5 via vapor-phase-treatment method. The prepared catalyst exhibited a long lifetime with high selectivity for MTA reaction.     

Synthesis of hierarchical ZSM-12 nanolayers for levulinic acid esterification with ethanol to ethyl levulinate

Hierarchical ZSM-12 nanolayers have been successfully synthesized via a one-pot hydrothermal process using dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (TPOAC) as a secondary organic structure-directing agent (OSDA). The as-synthesized ZSM-12 samples were characterized by means of XRD, SEM, TEM, N₂ physisorption, and NH₃-TPD. This clearly demonstrates that the TPOAC content and the crystallization time are crucial parameters for the formation of nanolayered structures. The presence of such a structure significantly improves the mesoporosity of ZSM-12 by generating interstitial mesopores between nanolayers, eventually resulting in enhancing external surface areas and mesopore volumes, and subsequently promoting the molecular diffusion inside a zeolite framework. To illustrate its advantages as a heterogeneous catalyst, hierarchical ZSM-12 nanolayers were applied in the catalytic application of an esterification of levulinic acid with ethanol to ethyl levulinate. Interestingly, hierarchical ZSM-12 nanolayers exhibit an improvement of catalytic activity in terms of levulinic acid conversion (78.5%) and ethyl levulinate selectivity (98.7%) compared with other frameworks of hierarchical zeolite nanosheets, such as ZSM-5 and FAU. The example reported herein demonstrates an efficient way to synthesize a unidimensional pore zeolite with hierarchical nanolayered structure via a dual template method and also opens up perspectives for the application of different hierarchical porous systems of zeolites in the bulky-molecule reactions such as in the case of levulinic acid esterification with ethanol.

Hierarchical ZSM-12 nanolayers were successfully synthesized via a dual template approach as an efficient catalyst for levulinic acid esterification.     

Rapid hydrothermal synthesis of hierarchical ZSM-5/beta composite zeolites

An innovative hydrothermal method has been successfully applied to the synthesis of hierarchical ZSM-5/beta composite zeolites with different mass ratios. Firstly, the ZSM-5 zeolites were coated with amorphous silica and aluminum species by a spray drying process. Then, the precursor powder was hydrothermally crystallized for only 1–2 days with the addition of tetraethyl ammonium hydroxide (TEAOH). The obtained products were characterized by XRD, SEM, TEM, N₂ physical adsorption–desorption, ²⁷Al MAS NMR, ICP, pyridine-IR and NH₃-TPD techniques. The characterization results imply that the ZSM-5/beta composite zeolites exhibit hierarchical-pores, higher external surface areas and larger mesopore volumes as compared to those of the pure ZSM-5 and beta zeolite. Moreover, the pore structure and acid sites of the ZSM-5/beta composite can be adjusted by changing the mass ratio of ZSM-5/beta. Finally, the ZSM-5/beta composite catalysts exhibit good catalytic performances in the cracking of 1,3,5-triisopropylbenzene (1,3,5-TIPB).

The hierarchical ZSM-5/beta composite zeolites synthesized via an innovative hydrothermal method exhibit superior catalytic performance in the cracking of 1,3,5-triisopropylbenzene.     

Hierarchical ZSM-5 nanocrystal aggregates: seed-induced green synthesis and its application in alkylation of phenol with tert-butanol

Hierarchical ZSM-5 zeolite aggregates were synthesized in an organic-template-free system via seed-induced crystallization. The obtained samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption–desorption, NH₃ temperature-programmed desorption (NH₃-TPD) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The prepared ZSM-5 nanocrystalline aggregates possessed open/accessible hierarchical pores and active sites, showing significant advantages in the catalytic alkylation of phenol with tert-butanol. The obtained materials could maintain the activities of the nanocrystal zeolites and meanwhile could be easily separated or recovered during the preparation and reactions. This approach was simple and also overcame the commonly-seen drawbacks such as the exceeded use of specific templates or secondary templates during the synthesis of the hierarchical zeolites.

Hierarchical ZSM-5 zeolite aggregates were synthesized in an organic-template-free system via seed-induced crystallization.     

Enhanced resistance to calcium poisoning on Zr-modified Cu/ZSM-5 catalysts for the selective catalytic reduction of NO with NH3

Ca/ZrCu/ZSM-5 catalysts containing different Zr contents were prepared by incipient wetness impregnation. The catalysts were tested for the selective catalytic reduction (SCR) of NO_x with ammonia and characterized by N₂-BET, N₂O titration, XRD, NH₃-TPD, H₂-TPR, and XPS techniques. In the temperature range of 100–170 °C, after calcium impregnation, NO_x conversion over the Cu/ZSM-5 catalyst decreased by 11.3–24.3%, while that over Zr_0.10/Cu/ZSM-5 only decreased by 3.8–12.2%. The improvement of the calcium poisoning resistance of the ZrCu/ZSM-5 catalyst is mainly attributed to an increase in the dispersion and the surface concentration of Cu. Moreover, the addition of zirconium promotes the reduction of CuO by decreasing the interaction between CuO and CaO, which also contributes to the improvement of resistance to CaO poisoning. The apparent activation energy and turnover frequency for the SCR reaction over the Ca/Zr_xCu/ZSM-5 catalysts were calculated and discussed.

After calcium impregnation, NO_x conversion over the Cu/Z catalyst decreased by 11.3–24.3%, while that over Zr_0.10/Cu/Z only decreased by 3.8–12.2%.     

The β-cyclodextrin-modified nanosized ZSM-5 zeolite as a carrier for curcumin

Herein, the nanosized ZSM-5 zeolite was synthesized based on a fractional factorial experimental design by a hydrothermal method to study the optimum conditions for the synthesis and formation of the ZSM-5 zeolite by employing different conditions. The samples were synthesized without any organic template, and different conditions, such as the molar composition of the synthesis gel and reaction time, were applied in a wide range. Then, the samples were analysed by X-ray diffraction to investigate the formation of the zeolite ZSM-5, and the results were compared to obtain the optimum conditions for its synthesis. The obtained samples were characterized by SEM, FTIR spectroscopy and TGA. Then, the functionalization of nano zeolite ZSM-5 crystals with β-cyclodextrin (β-CD) was investigated. The zeolite surface was first functionalized with amino groups using an amino alkoxysilane. Then, toluene diisocyanate was reacted with the amino-terminated ZSM-5 zeolite crystals and used for the incorporation of β-CD via its remaining isocyanate groups. After this, a drug delivery system (DDS) was prepared based on the cyclodextrin-modified zeolite with the curcumin anticancer drug, and its formation was studied under experimental conditions. The results of in vitro studies show that this drug delivery system has better characteristics than free curcumin in terms of stability and anti-proliferative and anti-inflammatory effects.

Herein, the nanosized ZSM-5 zeolite was synthesized based on a fractional factorial experimental design by a hydrothermal method to study the optimum conditions for the synthesis and formation of the ZSM-5 zeolite by employing different conditions.     

Synthesis of micro–mesoporous ZSM-5 zeolite with microcrystalline cellulose as co-template and catalytic cracking of polyolefin plastics

Micro–mesoporous ZSM-5 with different Si/Al ratios (MZ-X, X = 27, 80, 150) were synthesized by adding microcrystalline cellulose (MCC) as co-template into the hydrothermal synthesis process of zeolites. The resultant ZSM-5 were used for catalytic cracking of high density polyethylene (HPDE) and polypropylene. It was found that introduction of MCC significantly enhanced the formation of mesopores and strong acid sites. MZ-27 achieved the highest oil yield: 21.5% for HPDE and 32.1% for polypropylene, and the light aromatics (BTEX) selectivity therein were 87.6% and 79.7%, respectively. HZ-150 (MCC-free ZSM-5, Si/Al = 150) achieved the highest gas yield: 85.4% for HDPE and 76.7% for polypropylene, and the light olefins (C _2–4) selectivity therein were 44% and 48.3%, respectively. The dense acidic sites and mesoporous structure of MZ-27 were responsible for its better activity for producing aromatic products. The moderate acidity and microporous structure of HZ-150 were helpful for producing light olefins from catalytic cracking of polyolefin plastics.

Microcrystalline cellulose as co-template enhances the formation of mesopores and strong acid sites in ZSM-5 zeolites.     

Conversion of methane to C2 and C3 hydrocarbons over TiO2/ZSM-5 core–shell particles in an electric field

Catalytic conversion of methane (CH₄) to light olefins is motivated by increasing recoverable reserves of methane resources, abundantly available in natural gas, shale gas, and gas hydrates. The development of effective processes for conversion of CH₄ to light olefins is still a great challenge. The interface of ZSM-5 zeolite and TiO₂ nanoparticles is successfully constructed in their core–shell particles via mechanochemical treatment with high shear stress. The oxidative coupling of methane at a low temperature under application of an electric field may be induced by the O₂ activation via electrons running through the surface of TiO₂ located at the interface of TiO₂ and zeolite particles. Moreover, C₃H₆ was also produced by the ethylene to propylene (ETP) reaction catalyzed by Brønsted acid sites in the ZSM-5 zeolite within core–shell particles.

A TiO₂/ZSM-5 composite catalyst efficiently works for the oxidative coupling of methane and the subsequent ethylene-to-propylene reactions in an electric field.     

Pervaporation separation of ethyl acetate from aqueous solutions using ZSM-5 filled dual-layer poly(ether-block-amide)/polyethersulfone membrane

In the present study, dual-layer mixed matrix membranes (MMMs) were prepared by incorporating ZSM-5 zeolite into poly(ether-block-amide) (PEBA) as an active layer on the polyethersulfone (PES) membrane as a support layer for pervaporation separation of ethyl acetate (EAc) from EAc/water mixtures. The ZSM-5 zeolite nanoparticles were synthesized by the hydrothermal technique and characterized using XRD, XRF and FESEM analysis. The ATR-FTIR, SEM, DSC and contact angle tests were used to characterize the fabricated MMMs. The effect of ZSM-5 concentration on the performance of the membranes was investigated by the pervaporation experiments and the results showed that loading 10% wt% ZSM-5 into the PEBA matrix had the best separation performance. The effect of feed concentration (1–5 wt%) and operating temperature (30–50 °C) on the separation factor and permeation flux of the neat PEBA/PES and PEBA/PES membranes containing 10 wt% ZSM-5 were studied at laminar and turbulent feed flow regimes. Analysis of variance was used to investigate the interaction effect of EAc concentration and temperature on the performance of the prepared membranes. It was observed that both feed concentration and temperature had positive effects on the total permeation flux and separation factor. The ZSM-5/PEBA/PES membrane containing 10 wt% ZSM-5 showed a separation factor and total flux of 124.94 and 1882 g m⁻² h⁻¹ at laminar flow and 134.22 and 1985 g m⁻² h⁻¹ at turbulent flow, respectively for a feed concentration of 5 wt% and temperature of 50 °C.

Dual-layer mixed matrix membranes were prepared by incorporating ZSM-5 zeolite into PEBA as an active layer on the PES membrane as a support layer for pervaporation separation of EAc from the EAc/water mixtures.     

Hierarchical micro-/mesoporous zeolite microspheres prepared by colloidal assembly of zeolite nanoparticles

A novel template-free colloidal assembly method that combines colloidal zeolite (silicalite-1) suspensions in a water-in-oil emulsion with an evaporation-induced assembly process has been developed for preparing hierarchical micro-/mesoporous zeolite microspheres (MZMs). Such particles have an interconnected mesoporosity and large mesopore diameters (25–40 nm) combined with 5.5 Å diameter micropores of the zeolite nanoparticles. The method developed has the advantages of employing mild synthesis conditions, a short preparation time, and not requiring the use of a mesoporogen template or post-treatment methods. The method provides a new range of micro-/mesoporous zeolites with tunable mesoporosity dictated by the size of the zeolite nanoparticles. It also offers the possibility of combining several zeolite particle sizes or optionally adding amorphous silica nanoparticles to tune the mesopore size distribution further. It should be generally applicable to other types of colloidal zeolite suspensions (e.g. ZSM-5, zeolite A, beta) and represents a new route amenable for cost-effective scale-up.

Evaporation-driven colloidal assembly of silicalite-1 nanoparticles into well-defined micro-sized spheres at low temperature and preparation times.     

Effect of H2SiF6 modification of IM-5 on catalytic performance in benzene alkylation with ethylene

Ethylbenzene (EB) is an important bulk chemical intermediate. The vapor-phase process is considered to be more efficient than the liquid-phase process when using dilute ethylene (e.g. FCC or DCC off-gas) as the feed due to its high ethylene space velocity. However, realizing a balance between reducing the xylene formation and enhancing the EB selectivity is still a challenge due to the poor performance of ZSM-5 at low reaction temperature. This study concerns an IM-5 zeolite (IMF topology) modified by H₂SiF₆, with 89% ethylbenzene selectivity, 98.6% total EB + DEB selectivity and only 540 ppm of xylene at 330 °C. IM-5 zeolites with different Si/Al₂ ratios (40–170) were prepared by H₂SiF₆ modification and their catalytic performance in vapor phase alkylation of benzene with ethylene was investigated. There was an obvious decrease in the acid sites and acid strength of IM-5 in the H₂SiF₆ treatment process, which led to a slight decrease in ethylbenzene selectivity and a significant decline in xylene yield. Under the conditions of complete ethylene conversion, the selectivity to EB + DEB increased from 96.1% to 98.6% in the parent I-40 and modified IM-5. Compared with ZSM-5 that has a similar acidity, the slightly bigger channel opening makes IM-5 more conductive to the formation and diffusion of DEB while xylene may present adverse effects. The 120 hour-lifetime test showed that IM-5 (I-110) has superior activity, equivalent stability, higher DEB selectivity and a much lower xylene selectivity in comparison with ZSM-5. The catalytic performance of the IM-5 zeolite in the vapor phase process provides a new choice for the production of ethylbenzene.

IM-5 zeolite modified by H₂SiF₆ has superior activity, equivalent stability, higher DEB selectivity and a lower xylene selectivity in comparison of ZSM-5 with similar Si/Al₂ ratio. The process provides a new way to make ethylbenzene in the vapor phase.     

Enhanced production of aromatics from propane with a temperature-shifting two-stage fluidized bed reactor

A temperature-shifting two-stage fluidized bed reactor technology was used to convert propane and its intermediate products into aromatics. The first stage served for the aromatization of propane with a Ga/ZSM-5 catalyst at 570 °C. The second stage served for the alkylation of the intermediates of olefins at 300 °C. The increased yield of aromatics was attributed to the effective transformation of C₂–C₃ olefins as well as due to the suppression of the hydrogen transfer effect of the olefins.

High-yield production of aromatics from propane with a temperature shifting, two-stage fluidized bed reactor technology.

The production of aromatics from propane with zeolite-based catalysts (e.g. HZSM-5, Zn/ZSM-5, and Ga/ZSM-5) is an important route, exhibiting a combined effect of dehydrogenation with a metal and oligomerization, ring formation with Lewis/Brønsted acids, and a shape selective effect inside the channel of the zeolite.^1–4,6,7 Increasing the temperature in the range 500–550 °C or above is thermodynamically and kinetically favorable for the conversion of propane in such a slow and endothermic reaction.^8–10 However, the dehydrogenation of propane as well as the complicated transformation in the dual hydrocarbon pool cycle inside the zeolite, produces olefins as intermediates.⁵ These are rapidly converted into paraffins with the same carbon number at a high temperature by an effect of hydrogen transfer, rather than ring formation to aromatics, which is similar to those in methanol-to-aromatics (MTA) or methanol to olefins (MTO) processes.^11–13 Such a drawback is difficult to overcome for the case with a long residence time between the catalyst and the gases, for example, in a large reactor with isothermal operation. On the other hand, a multistage fluidized bed reactor was adopted in the MTA process, offering the flexibility of temperature shifting and a variation of catalysts in different stages. As a result, the backmixing of gases could be suppressed effectively to achieve a high conversion of feedstock and a high selectivity of the desired aromatics products.^14–17 However, due to the differences in the catalysts, operating temperature, partial pressure of hydrogen or water, and coke type, such a multistage reactor strategy has not been applied to propane to aromatics conversion yet.Herein, we propose a temperature-shifting second-stage fluidized bed concept for the consecutive conversion of propane and its intermediate products, as illustrated in Fig. 1. The technology allows for the high conversion of propane with a Ga/ZSM-5 catalyst in the first stage of the reactor (close to the entrance of propane). The as-produced light paraffins and olefins with the as-produced benzene (B) and toluene (T) are further converted into C₈–C₉ aromatics with an HZSM-5 catalyst in the second stage at a low temperature. As a result, the content of the C₂–C₃ olefins decreased by 8% from the first stage to the second stage. Meanwhile, the yield of the aromatics after the second stage increased by 6–12% compared with that after the first stage. Our strategy provides new insights into the consecutive conversion chains in the conversion system of propane to aromatics.Open in a separate windowFig. 1(a) Proposed temperature shifting, two stage-fluidized bed reactor to prepare aromatics from propane using different zeolite-based catalysts. (b) Time-dependent production distribution of components in the exit of 1^st and 2^nd stage (hydrocarbon base). (c) Time-dependent volume ratio of hydrogen in the exit of 1^st and 2^nd stages.Experimentally, 340 g of Ga/ZSM-5 catalyst was used in the first stage of the fluidized bed, where the temperature was 570 °C (ESI, SI-1^†). Next, 34 g of HZSM-5 catalyst was packed in the second stage of the fluidized bed, where the temperature was 300 °C. The temperatures in different stages were controlled separately and there was a condenser between them. The feedstock of propane diluted with N₂, entering into the fluidized bed from the bottom, was first converted on the Ga/ZSM-5 catalyst in the first stage. Then, the as-produced intermediate product, entering into the second stage, was further converted on HZSM-5. Reactions in the two stages were both carried out in the gaseous state. The pressure of the exit of the reactor was 0.35 MPa. The space velocity of propane on the catalyst in the first stage was 0.01 h⁻¹. In this case, the sampling of gases and catalysts in different stages was performed to understand the process efficiency.The product distribution after flowing out of the reactor is shown in Fig. 1b. The weight ratio of propane was 30–31% in the first stage and changed to 32–33% for longer times. This suggested that the conversion of propane was close to 70% at 570 °C in the first stage, suggesting that high temperature was favourable for the conversion of propane. For the production of aromatics, there was an apparent induction period of 1–5 h, where the yield of aromatics increased from 28% to 34% in the first stage. This was due to the building of a hydrocarbon pool inside the zeolite, as reported in many other studies.^12,13 After that, the yield of aromatics remained very constant at 34–35.5% in the first stage for 5–20 h. Moreover, the yield of olefins remained constant at 13% in the first stage for 20 h. Also, further conversion of olefins in the second stage was also very stable, resulting in a decrease in the yield of olefins to 5% in the second stage for 20 h. The transformation of olefins in the second stage contributed to the increase in the yield of aromatics to 36–39.5% for 20 h. The steady changing trend validated the effectiveness of the enhanced production of aromatics from olefins in situ in the second stage for such a temperature shifting two-stage fluidized bed technology. In addition, the transformation of propane into aromatics yielded hydrogen in a large amount (Fig. 1c). The volume ratio of hydrogen in 1–5 h was smaller than 8%, also confirming the presence of an induction period for the catalyst. After that, the volume ratio of hydrogen exceeded 8–10% in the first stage. The volume ratio of hydrogen only dropped a very small bit in the exit of the second stage, validating the effective suppression of the side reactions at low temperature in the second stage.As follows, we analysed the distribution of aromatics in detail (Fig. 2a). The ratio of B was the largest, T was the second largest and xylene (X) was very small. This suggested that the high temperature condition favoured the formation of B and T with few methyl groups on the benzene ring, indicating a dealkylation effect.^16,17,20 The yields of B and T showed a much more rapid increasing trend compared to that of X in the induction period, where the coke amount was low and didn''t exert a diffusion barrier on these molecules. In this case, the increased yields of B and T were attributed to the altering of the acidic sites with the increased dealkylation ability. The following reactions in the second stage resulted in the decrease in the yields of B and T, but an increase in the yields of X, ethylbenzene (EB) and trimethylbenzene (TriMB). The latter two were apparently the products of alkylation between olefins with B and T.^16–19 Quantitatively, the yields of B and T decreased by 2–2.5% and 0.5%, respectively. The yields of X, EB and TriMB increased by 1–1.5%, 2% and 2.5%, respectively. The increased part of X, EB and TriMB was larger than the decreased part of B and T. From the changing trend of olefins (Fig. 2b), it can be found that the yield of ethylene decreased by 4% from the 1st stage to the 2nd stage, while the yield of propene dropped by 2% at 1 h and by 4.5% at 19 h, The yield of butene, however, increased by 1% from the 1st stage to the 2nd stage. This suggested that except for the dominant alkylation of olefins with B and T, the self-aromatization of olefins and the transformation to other intermediates (butene) still occur at low temperatures in the second stage. Although the components of gases entering into the second stage differed with the reaction time, the combined effect of the alkylation and self-aromatization of olefins made the gross yield of aromatics in the second stage nearly constant with the reaction time (Fig. 1a).Open in a separate windowFig. 2(a) Time-dependent distribution of aromatics in the exit of 1^st and 2^nd stages (hydrocarbon base). (b) Time-dependent distribution of olefins in the exit of 1^st and 2^nd stages (hydrocarbon base). (c) Time-dependent distribution of paraffins in the exit of 1^st and 2^nd stages (hydrocarbon base).In addition, we also compared the hydrogen transfer effect in the different stages (Fig. 2c). The yields of methane, ethane and butane all increased by 1–2% after the transformation in the second stage. Ethane and butane were both the products from ethylene and butene via the hydrogen transfer effect, respectively. As compared to the formation of aromatics from ethylene and the ratio of butene in the second stage, we would like to state that the hydrogen transfer effect still existed but was insignificant in the present study. This validated the effectiveness of the suppression of the hydrogen transfer effect by the use of temperature shifting in the two-stage fluidized bed.In addition, it is very interesting that the activity of the catalyst for the formation of aromatics was stable for around 20 h, but the activity of produced methane was suppressed sustainably. Quantitatively, the TGA pattern indicated that the catalyst in the first stage and second stages contained 4.5% coke and 5.8% coke, respectively (Fig. 3a). This suggested that both the decreased yields of methane were due to the coke deposition of the catalysts in the different stages. Nearly 5% coke deposition on the catalyst resulted in a decreased yield of methane by 15% within 20 h. This, we think, is therefore a very good method to suppress the undesirable methane, which is inert to further transform and is of low cost in all hydrocarbons. Coke, sometimes, is desirable for the circulating fluidized bed reactor since its burning in the reactor of a regenerating catalyst by air provides the necessary heat for the high temperature for this endothermic reaction.^14,21,22 In addition, the derivative thermogravimetric (DTG) pattern (Fig. 3a inset) indicated that there was an apparent peak centre at 537 °C for the coke on the catalysts in the first stage (Fig. 3b). The value was higher than that for the burning temperature of poly-aromatics but close to that for the activated carbon or carbon filaments. In addition, this burning temperature of the coke was higher than the temperature (centre at 476 °C) of the coke at the second stage. This apparently suggests that the coke in the first stage and second stage is significantly different.Open in a separate windowFig. 3(a) Thermal gravimetric analysis of coke on the catalysts for 20 h; the inset is the DTG result of (a). (b) NH₃-TPD analysis of the Ga/ZSM-5 catalyst before and after the reactions for 20 h. (c) NH₃-TPD analysis of the HZSM-5 catalyst before and after the reactions for 20 h.We compared the acidic properties (NH₃-TPD data) of the catalyst used in the different stages (Fig. 3b and c). There was a strong peak of weak acids for the Ga/ZSM-5 catalyst centred at 213–216 °C, but they remained nearly unchanged before and after the deposition of coke. The difference between the fresh and the coke-deposited Ga/ZSM-5 catalysts mainly comes from the peak intensity between 400–550 °C, assigned to the middle strength or strong acids. This result is reasonable considering the dehydrogenation of propane and the formation of a benzene ring require high temperature and strong acidic sites. In comparison, the HZSM-5 catalyst used in second stage mainly exhibited a difference in the low temperature region (centred at 208–220 °C), assigned to the weak acids.^15,18–20 The acid amount of these weak acids dropped significantly after the deposition of coke. This result is also reasonable considering the alkylation of olefins with B/T is relatively easy, for which the weak acids on the catalyst are enough.We used CH₂Cl₂ to extract the coke in the different stages and used GC-MS to analyze the solutions (Fig. 4a). It was clear that there were various peaks observed for the coke in the second stage, which contained sing-, double-, triple-, even tetra-benzene ring derivates. In sharp contrast, there was nearly none of these organic compounds observed with the coke in the first stage. This suggested that the coke was formed by the gradual dehydrogenation of poly-aromatics in the second stage at low temperature with the increase in reaction time.^25,26 However, the high temperature in the first stage resulted in a quick dehydrogenation of the poly-aromatics to further become a graphite-type product or amorphous carbon. This well explains the strange trend in the present work that the coke amount at low temperatures (second stage) was higher than that found at high temperature (first stage). In addition, as the remaining temperature was nearly the same in the second stage, olefins in a dry condition (the present study) tended to become coke, compared to that in a wet condition (where the partial pressure of water is very high) in the MTA process.¹⁶Open in a separate windowFig. 4(a) GC-MS chromatograms of the organic species in the catalysts (used for 20 h) extracted by CH₂Cl₂. (b) Raman spectra of the coke-deposited catalyst for 20 h.Raman spectroscopy further confirmed this trend (Fig. 4b). For the coke deposited on the catalyst in the first stage, the intensity ratio of the D band to G band was 0.534, larger that (0.455) at the second stage. This suggested the formation of highly graphitized carbon by a serious dehydrogenation. In addition, the peaks of the D band and G band for the coke in the second stage were also very wider compared to those in the first stage, providing direct evidence of the presence of non-crystalline poly-aromatics in the second stage.Considering the time-dependent total conversion of propane, total selectivity of aromatics, total selectivity of olefins and paraffins, the catalysts in the first and second stages were all very stable within 20 h reaction. It is hard to say that the catalyst was seriously deactivated. Many previous studies have confirmed the low deposition rate of coke on the Ga/ZSM-5 catalyst with high stability.^1–4,27 The active sites responsible for the formation of aromatics, for the dehydrogenation of propane and for the surface alkylation of olefins and B/T were all less influenced by the deposition of coke with the increase in the reaction time in the present study, probably owing to the deposition position of the coke.²⁸ However, the coke deposited process changed the profile of ethylene and propene, via different hydrocarbon pools inside the zeolite channel.^24,29–33 Further investigation is needed. In addition, the technology is not only useful for the suppression of the hydrogen transfer effect in propane to aromatics, but also for the selectivity control of propene in similar MTA and MTO processes.^{12,14–17,20–23,26,32} We also summarized the results of the conversion of propane and selectivity of BTX (Table S2, SI-2^†). The results were apparently dependent on the operating condition and catalyst. Even though our results (conversion of propane: 70%, selectivity of BTX: 50%) in a fluidized bed with large quantities of catalysts (340 g Ga/ZSM-5 and 34 g HZSM-5) rank in the middle among many data obtained in packed beds with small quantities of catalyst (1 g), they suggest the flow mode of the gases in a two-stage fluidized bed is close to that in a packed bed, validating our original purpose.In summary, we validated the temperature-shifting second-stage fluidized bed technology for the deep conversion of propane to achieve a high yield of aromatics. Here, two stages served for propane aromatization and the alkylation of olefins (C₂–C₃) with aromatics in sequence. Olefins were successfully converted into aromatics. Characterization of the coke suggested different dehydrogenation effects in different stages by the temperature effect. The deposition of coke on the catalyst suppressed the formation of methane, but did not influence the gross conversion of propane and the gross yield of aromatics. These results provide new insights into the process intensification technology for propane-to-aromatics conversion.     

Effect of steam de-alumination on the interactions of propene with H-ZSM-5 zeolites

Steam de-alumination is used to prepare a H-ZSM-5 material representative of industrial acid zeolite catalysts. Characterisation shows extensive loss of zeolite acidity but minimal loss of framework crystallinity in the treated material. The material''s interaction with propene is probed by means of inelastic and quasielastic neutron scattering, providing information on the reactivity and mobility of the propene respectively. These results are compared to those previously obtained for propene in the untreated zeolite. The steaming treatment resulted in decreased reactivity of the zeolite toward olefin oligomerization, higher temperatures for reaction initiation, and increased mobility of the propene in the zeolite at all temperatures. Analysis of the motions of the propene revealed by QENS shows the mobility to be comparable to those previously reported for propane in similar materials but occurring at slower velocities due to the greater rigidity and polarisation of the propene molecule.

Inelastic and quasi-elastic neutron scattering are used to investigate how steaming changes the physico-chemical characteristics of the zeolite ZSM-5.     

Protective desilication of highly siliceous H-ZSM-5 by sole tetraethylammonium hydroxide for the methanol to propylene (MTP) reaction

Protective desilication of highly siliceous H-ZSM-5 was effectively realized by dissolution and recrystallization in tetraethylammonium hydroxide (TEAOH) solution. With better balance between dissolution of OH⁻ and recrystallization of TEA⁺, intracrystalline mesopores could be generated by selective dissolution of Si by the drilling effects of TEAOH on the micropores, and then Si species in the mother liquor near the external surface could be recrystallized into ZSM-5 shell. With a significantly reduced diffusion length provided by the intracrystalline mesopores, TEAOH-treated samples exhibited longer lifetime and higher propylene selectivity than the parent H-ZSM-5 zeolite. The mediumly-treated T-16 h sample possessed the longest MTP lifetime of 140 h, 5.6 times that of the parent H-ZSM-5 zeolite. Furthermore, the coke content and adsorbed methyl benzene species on the T-16 h sample were heavier than those on the parent H-ZSM-5 sample, which were related to the intracrystalline mesopore structure.

Protective desilication of highly siliceous H-ZSM-5 was effectively realized by dissolution and recrystallization in tetraethylammonium hydroxide (TEAOH) solution.     

Application of diffuse reflectance near-infrared spectrometry and chemometrics in characterization of micro and mesoporous ZSM-5 zeolites

Evaluation of porosity type of zeolites is one of the critical topics in catalysis science. The relationship between external surface area and diffuse reflectance (DR) spectra in the near-infrared spectral region has been employed to propose a method for estimation of micro or mesoporosity in ZSM-5 zeolite samples. Linear discriminant analysis (LDA) was utilized to estimate degree of porosity based on near-infrared diffuse reflectance spectra. The textural properties (surface area and pore volume) of micro and mesoporous ZSM-5 samples were measured using N₂ adsorption/desorption technique at 77 K and external surface area was calculated by t-plot as a reference method in this work. Several porous ZSM-5 samples with only microporous channels or mesoporous besides them were classified in terms of external surface area and meso pore volume derived from t-plot as “Micro” or “Micro + Meso” type samples. It was concluded that LDA using the PCA for feature selection is capable of generalization and could precisely predict the type of porosity in ZSM-5 zeolites.

Evaluation of porosity type of zeolites is one of the critical topics in catalysis science.     

Rapid synthesis of hierarchical SSZ-13 zeolite microspheres via a fluoride-assisted in situ growth route using aluminum isopropoxide as aluminum source

Hierarchical SSZ-13 zeolite microspheres were quickly synthesized by adding a small quantity of hydrofluoric acid in the starting gel using aluminum isopropoxide as aluminum source. The as-synthesized hierarchical SSZ-13 crystals with high crystallinity, pore volume and external surface area were obtained within 12 h, whereas a much longer time (144 h) was necessary to synthesize a fully crystalline zeolite in a fluorine free system. The obtained hierarchical SSZ-13 catalysts showed excellent MTO performance together with considerably prolonged catalytic lifetime and improved selectivity of light olefins in comparison with the conventional microporous SSZ-13.

Hierarchical SSZ-13 were quickly synthesized by adding a small quantity of hydrofluoric acid in the starting gel using aluminum isopropoxide as aluminum source.     

Beneficial use of ultrasound irradiation in synthesis of beta–clinoptilolite composite used in heavy oil upgrading process

A novel beta–clinoptilolite composite was prepared from beta zeolite and alkaline treated clinoptilolite by employing conventional and sonicated mixing procedures. Parent and prepared catalysts were characterized by XRD, FE-SEM, N₂ adsorption–desorption and NH₃-TPD analyses. Prepared composite of beta zeolite and treated clinoptilolite exhibited improved structural properties especially upon sonicated mixing procedure. Employing ultrasound irradiation notably improved beta distribution in the composite and increased mesoporous volume and specific surface area from 0.245 cm³ g⁻¹ and 171.3 m² g⁻¹ in conventionally mixed composite to 0.353 cm³ g⁻¹ and 232.9 m² g⁻¹ in sonicated sample. Catalytic performance of prepared composite was evaluated in heavy oil upgrading process in a continuous fixed bed apparatus. Liquid product was specified by conducting SIMDIS-GC and GC/MS analyses. Spent catalysts were characterized by TGA, FTIR and XRD. Beta–clinoptilolite composite containing only 30 wt% of beta zeolite, exhibited similar performance to beta zeolite catalyst by resulting 75.3% viscosity reduction while producing lower amount of coke. Amount of light hydrocarbons produced over beta–clinoptilolite composite was 33.51 wt% while beta zeolite catalyst produced 35.58 wt% light hydrocarbons in upgrading process. Ultrasound irradiated composite showed more stable structure in catalytic cracking procedure compared to conventionally mixed composite. After 5 h time on stream, relative crystallinity of clinoptilolite phase in the conventionally mixed composite was reduced by 34.5% while sonicated sample remarkably preserved its structure during the reaction and only 1% reduction occurred for this sample.

Beta–clinoptilolite composite synthesized in the presence of ultrasound irradiation exhibited high stability in heavy oil upgrading process while producing equal amount of light fuels and lower amount of coke compared to beta zeolite catalyst.     

Production of 5-hydroxymethylfurfural (HMF) from rice-straw biomass using a HSO3–ZSM-5 zeolite catalyst under assistance of sonication

This work studied the application of sulfonated ZSM-5 zeolite, a bi-functional catalyst for conversion of biomass-derived glucose to HMF. Glucose hydrolysate was obtained by enzymatic hydrolysis of rice straw, that was pretreated by sodium hydroxide. Glucose hydrolysate was then subjected to a transformation reaction to achieve HMF using HSO₃–ZSM-5 zeolite under the assistance of sonication. The reaction conditions including solvent, temperature, catalyst dosage and reaction time were studied. Suitable conditions, which gave the highest yield of HMF of 54.1% have been found. The HSO₃–ZSM-5 zeolite presented a high catalytic efficiency for conversion of glucose to HMF, an important and useful intermediate in the chemical industry.

A porous HSO₃–ZSM-5 zeolite was successfully synthesized and applied for conversion of biomass-derived glucose to HMF.     

Synthesis,characterization and n-hexane hydroisomerization performances of Pt supported on alkali treated ZSM-22 and ZSM-48

ZSM-48 and ZSM-22 zeolites with similar Si/Al molar ratio have been treated with alkali to modify the pore structures and acidity, and alkali treated ZSM-22 and ZSM-48 samples have been characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), N₂ adsorption/desorption, Nuclear Magnetic Resonance (NMR), NH₃-Temperature Programmed Desorption (NH₃-TPD) and Pyridine-Fourier Transform Infrared Spectroscopy (Py-FTIR). Characterization results indicate that NaOH treatment could improve the mesoporous structure for both ZSM-22 and ZSM-48. NaOH treatment modifies the acidity of ZSM-22 and ZSM-48 diversely. The n-hexane hydroisomerization performances of Pt supported protonic form ZSM-22 and ZSM-48 (Pt/HZSM-22 and Pt/HZSM-48) bifunctional catalysts have been evaluated in a fixed bed reactor. Catalytic results indicate that catalytic activity and selectivity depend on both pore structure and acidity of zeolites. In comparison of Pt/HZSM-22 and Pt/HZSM-48, Pt/HZSM-22 shows better n-hexane hydroisomerization performance at relatively low temperature (<300 °C), meanwhile, at relatively high temperature (>300 °C) Pt/HZSM-48 exhibits better catalytic performance. Moreover, alkali treated Pt/HZSM-48 could produce more di-branched isomer compared with alkali treated Pt/HZSM-22.

ZSM-48 and ZSM-22 zeolites with similar Si/Al molar ratio have been treated with alkali to modify the pore structures and acidity, and they have been characterized by XRD, SEM, TEM, N₂ adsorption/desorption, NMR, NH₃-TPD and Py-FTIR.     

Synthesis of ZSM-5/KIT-6 with a tunable pore structure and its catalytic application in the hydrodesulfurization of dibenzothiophene and diesel oil

Porous support materials were prepared by assembling primary and secondary ZSM-5 structural units into a well-ordered mesoporous framework. The materials possessed both ZSM-5 microporous building units and mesoporous structure were used as supports for the preparation of hydrodesulfurization (HDS) catalysts. The materials and their corresponding catalysts were characterized by XRD, FTIR, ²⁷Al MAS NMR, TEM, N₂ adsorption–desorption, Py-FTIR, H₂-TPR, Raman, and HRTEM techniques. The pore structures of the composite materials were modulated by adjusting the molar ratio of butanol/P123 (BuOH/P123) and then, the influences of BuOH/P123 on the catalytic performance in the HDS of dibenzothiophene (DBT) and diesel oil were systematically studied. The results showed that butanol has a big influence on the structure of the micro–mesoporous material, whereby different micro–mesoporous structures, such as the p6mm hexagonal structure or Ia$\bar{3}$d cubic structure, were formed with different butanol addition amounts. The composite ZK-3 (BuOH/P123 = 100) possessed the best surface area and pore structure. Therefore, the NiMo/ZK-3 catalyst showed the highest catalytic activity in the HDS of DBT with a BP selectivity of 72.1% due to its excellent textural property, moderate MSI, relatively high B/L ratios, and highly dispersed NiMoS active phases. Moreover, the NiMo/AZK-3 catalyst exhibited excellent catalytic performance in the HDS of diesel oil.

Porous material with tunable pore structure ZSM-5/KIT-6 was prepared by adjusting the addition amount of n-butanol. NiMo/ZK-3 and NiMo/AZK-3 catalysts exhibit good catalytic performances in the HDS of DBT and diesel oil, respectively.