Nanocrystalline ZSM-5 Research Articles

Highly stable boron-modified hierarchical nanocrystalline ZSM-5 zeolite for the methanol to propylene reaction

A highly stable MTP catalyst, boron-modified hierarchical nanocrystalline ZSM-5 zeolite, has been synthesized by a facile salt-aided seed-induced route. It exhibits a long lifetime (about 725 h) even at a high WHSV (4.0 h−1).

Selective production of green gasoline by catalytic conversion of Jatropha oil

A catalytic process for value addition of bio-oil derived from the Jatropha curcas plant through the production of green gasoline has been described. Four zeolite based catalysts possessing different porosity and acidity have been prepared by using Ultrastable Y (HY), Beta (BEA), micro-crystalline ZSM-5 (MZ) and nano-crystalline ZSM-5(NZ) zeolites. The textural properties of the samples have been characterized by XRD, SEM, BET surface area, pore volume, pore size distribution and micro-calorimetric ammonia adsorption studies. These catalysts have been exploited for the production of green fuel suitable for gasoline applications. Among the various catalysts, the nano-crystalline ZSM-5 synthesized in the laboratory exhibited excellent catalytic properties such as moderate acidity and stacking order of mesoporosity (which is absent in microcrystalline ZSM-5) responsible for the production of gasoline with as high as 77.4% selectivity and 95 research octane number (RON). The catalyst also exhibited enhanced time-on-stream stability supported by coke resistance ability (derived from TGA analysis of spent catalyst) when compared with the other zeolites within the studied period of 20h. The present study provides a new catalytic process for production of gasoline from J. curcas oil for biorefinery.

Enhanced production of high octane gasoline blending stock from methanol with improved catalyst life on nano-crystalline ZSM-5 catalyst

Methanol value addition reaction has been studied on lab-synthesized nano-crystalline ZSM-5, Si/Al=13 (NZ) possessing particle size of ∼29–51nm and a micro-crystalline ZSM-5 (MZ) of similar atomic ratio is also taken as standard for comparison studies. The NZ sample exhibited excellent catalytic activity to produce 50.7wt.% of high octane (Research Octane Number=137) gasoline blending stock rich in desired toluene and xylene components, while the undesired benzene is very low, suitable for fuel applications. The superior performance of NZ to MZ catalyst reflected in three fold increase in gasoline yield and considerably high time-on-stream performance.

Transition-Metal-Exchanged Nanocrystalline ZSM-5 and Metal-Oxide-Incorporated SBA-15 Catalyzed Reduction of Nitroaromatics

Nanocrystalline ZSM-5 was synthesized by a one-step synthetic route using the conventional ZSM-5 synthesis composition but in the presence of propyltriethoxysilane as an additive. Transition metal ion-exchanged nanocrystalline ZSM-5 catalysts were obtained by the ion exchange of nanocrystalline ZSM-5. The one-step direct synthetic route was used to prepare metal-oxide-incorporated SBA-15 catalysts under milder acidic conditions than are conventionally employed for the synthesis of Si-SBA-15. The catalysts were investigated in the reduction of nitroaromatics in the presence of sodium borohydride as a reducing agent. Among the catalysts investigated, copper ion-exchanged nanocrystalline ZSM-5 exhibited the highest activity. Although the copper ion-exchanged nanocrystalline ZSM-5 is recyclable, but for efficient recycling (with no loss in activity), it is better for the catalyst to be ion-exchanged once before being used in the next cycle.

Modification of nanocrystalline HZSM-5 zeolite with tetrapropylammonium hydroxide and its catalytic performance in methanol to gasoline reaction

Nanocrystalline ZSM-5 zeolite was modified with tetrapropylammonium hydroxide (TPAOH) solution. The effect of the TPAOH treatment time on the catalytic performance of HZSM-5 was investigated in methanol to gasoline (MTG) reaction. The modified samples were characterized using X-ray diffraction, scanning electron microscopy, 27 Al and 29 Si magic-angle spinning nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, N 2 adsorption, and NH 3 temperature-programmed desorption. The HZSM-5 structure was basically unchanged after modification, but the relative crystallinity increased and the crystal morphology was more regular. The Brunauer-Emmett-Teller surface area, the micropore surface area, the surface Si/Al ratio, and the amount of strong acid sites increased; this might be caused by desilication and dealumination, and secondary crystallization of the zeolite during the treatment. The stability of the catalyst was significantly improved after modification, as reflected by the increased lifetime from 70 h to above 170 h in MTG reaction. The catalyst lifetime increased with increasing TPAOH treatment time. Hydrogen transfer reactions became faster and led to more isoparaffins and less olefins in the liquid products. 采用四丙基氢氧化铵(TPAOH)溶液对纳米ZSM-5分子筛进行改性, 运用X射线衍射/扫描电镜/ 27 Al和 29 Si固体核磁/X射线光电子能谱/N 2 物理吸附脱附法和NH 3 程序升温脱附等手段对所制样品进行了表征, 并评价了其催化甲醇制汽油反应性能. 结果表明, 改性后的HZSM-5相对结晶度增加, 晶体形貌更加规整, 表面硅铝比增加, 比表面积和微孔表面积增大, 强酸位酸量增多. 同时, TPAOH改性不仅可以使分子筛脱硅脱铝, 而且伴有二次晶化补硅补铝, 改变了分子筛的硅铝分布. 改性的HZSM-5在甲醇制汽油反应中的稳定性大幅度提高, 其寿命由70 h增至170 h以上, 随着TPAOH处理时间的增加, 催化剂寿命增加, 氢转移反应加快, 导致油相产品中异构烷烃增多, 烯烃减少. Tetrapropylammonium hydroxide treatment of the HZSM-5 zeolite improved the diffusion capacity and coke tolerance through desilication, dealumination, and secondary crystallization, reflected by the significantly increased catalyst lifetime.

Catalytic conversion of rapeseed oil for the production of raw chemicals, fuels and carbon nanotubes over Ni-modified nanocrystalline and hierarchical ZSM-5

Catalytic conversion of rapeseed oil has been investigated over nanocrystalline and hierarchical ZSM-5 zeolites aimed to the production of both raw chemicals and fuels. Ni has been added to some of the samples in order to induce bifunctional properties in the catalysts. Almost total rapeseed conversion and deoxygenation degree were achieved with all the catalysts. The main products were gaseous olefins (mostly ethylene and propylene) and aromatic compounds (benzene, toluene and xylenes), which have high interest as raw chemicals. Likewise, high hydrogen contents are found in the gaseous stream since the operating conditions employed (high reaction temperature and atmospheric pressure) favor the occurrence of dehydrogenation reactions. The introduction of hierarchical porosity in ZSM-5 increases the production of light olefins at the expense of aromatic compounds, showing the close relationship between these two types of hydrocarbons. Hierarchical zeolites exhibit enhanced accessibility and diffusion rates, which hinders secondary reactions of the primary cracking products. Ni-containing catalysts show an enhanced dehydrogenation activity as denoted by the increased hydrogen, light olefins and coke production. Important changes were observed in the catalytic activity along time on stream, with a progressive increase in the fraction of aliphatic hydrocarbons. Interestingly, the coke formed over the Ni-containing ZSM-5 samples is in the form of carbon nanotubes, which grow causing a segregation of the Ni particle from the zeolite support. This effect is attenuated in the hierarchical zeolites because the secondary porosity stabilizes the metal particles. In summary, rapeseed oil can be transformed into valuable products (hydrogen, light olefins, aromatic hydrocarbons and carbon nanotubes) by using tailored Ni-containing nanocrystalline and hierarchical ZSM-5 zeolites.

Enhanced performance of nano-crystalline ZSM-5 in acetone to gasoline (ATG) reaction

Two ZSM-5 zeolites exhibiting micro (MZ) and nano (NZ) range crystal size have been synthesized and evaluated for their activity towards acetone to gasoline (ATG) reaction. The NZ possessed comparable acidity with that of MZ, but a significant increase in porosity (twofold increase in pore volume) was observed in case of NZ. The hierarchical pore system in NZ was observed to be responsible for enhanced catalytic activity of this material in terms of higher aromatic yields, higher octane number and increased time-on-stream stability in acetone to gasoline reaction.

Catalytic conversion of rapeseed oil into raw chemicals and fuels over Ni- and Mo-modified nanocrystalline ZSM-5 zeolite

The conversion of rapeseed oil has been investigated using Mo oxide- and Ni-modified nanocrystalline ZSM-5 zeolites as catalysts in a nitrogen atmosphere. The incorporation of metals into the HZSM-5 support causes significant changes in their acid and textural properties, modifying also its catalytic behavior. For all the catalysts, an almost total deoxygenation of the rapeseed oil takes place as denoted by the formation of CO and in a lesser extension of CO2 and H2O. The main reaction products were light olefins (mainly ethylene and propylene) and aromatic hydrocarbons (BTX). Ni/HZSM-5 catalysts exhibit a higher selectivity toward the formation of light olefins, whereas for Mo/HZSM-5 catalysts the product distribution is shifted toward aromatics. Differences in the evolution of the product distribution along the time on stream were also observed as a result of the formation of different types of coke over the catalysts. A great amount of highly polyaromatic coke was formed over the Ni/HZSM-5 samples, whereas a less structured coke is deposited over the parent zeolite and the Mo/HZSM-5 catalysts. These results show that the incorporation of metals over nanocrystalline ZSM-5 leads to catalysts with interesting properties for the conversion of vegetable oils into raw chemicals and fuels.

NANOCRYSTALLINE ZSM-5: AN EFFICIENT CATALYST FOR REGIOSELECTIVE ACETOLYSIS OF EPICHLOROHYDRIN

Acetolysis of epichlorohydrin (ECH) with acetic acid yields the product 1-acetoxy-3-chloro-2-propanol, which is used for the manufacture of various polyepoxy materials. The conventional method of producing 1-acetoxy-3-chloro-2-propanol uses sulfuric acid, p-toluenesulfonic acid, or BF3Et2O as a catalyst. These processes suffer from problems associated with the use of highly corrosive liquid acids. It is thus clear that there is tremendous scope for developing a new catalytic process for the acetolysis of ECH. In the present study, acetolysis of ECH with acetic acid was studied over nanocrystalline ZSM-5 catalysts and was found to be very active for the selective formation of 1-acetoxy-3-chloro-2-propanol. The catalyst was fully characterized. The best parameters for the acetolysis of ECH were established.

Catalytic performance of nano crystalline H-ZSM-5 in ethanol to gasoline (ETG) reaction

HZSM-5 zeolites of varying acidity and porosity were prepared under various synthesis conditions, and the effect of catalyst properties on the conversion of ethanol to gasoline reaction was investigated. Special emphasis is given to understand the role of strong acidity in effective oligomerization of olefin intermediates and their effective conversion to gasoline range hydrocarbons (most of it contains aromatics and isoparaffins) through hydrogen transfer (HT) reactions. The nano crystalline ZSM-5 (NZ) catalyst having high acidity and stacking order of mesoporosity showed high gasoline yields. The micro crystalline ZSM-5 (Catalyst Z) also exhibited comparable acidity with NZ, but could not give higher gasoline yields due to the absence of mesopores in the catalyst. Where as, catalyst ZA (micro crystalline) with low acidity and absence of mesopores produced considerable amount of propylene along with less gasoline. The studies envisioned the need of strong acidity and mesoporosity for effective conversion of olefin intermediates into C5+ oligomers and their conversion to gasoline through HT reactions.

Effect of Aging on the Precursor Sol for the Synthesis of Nanocrystalline ZSM-5

Nanocrystalline ZSM-5 (Si/Al = 100) is synthesized from an initial clear solution of TEOS-TPAOH-AIP-H2O system. The method comprises three stages: (i) concentration of an initial clear solution, (ii) low-temperature aging (25°C, 50°C, 75°C, or 100°C), and (iii) high-temperature hydrothermal treatment (180°C for 90 min). The average size of the crystals is almost the same when the aging temperature is in the range from 25°C to 75°C, i.e., around 48 nm. However, the average size of the zeolite crystals increases as the aging temperature reached 100°C, to 85 nm.

Facile synthesis of hierarchical nanocrystalline ZSM-5 zeolite under mild conditions and its catalytic performance

Hierarchical nanocrystalline ZSM-5 zeolite (NZ5) was synthesized at 100°C under atmospheric pressure using methylamine as a mineralizing agent. The crystallization process of NZ5 was characterized by dynamic light scattering (DLS), X-ray diffraction (XRD), and infrared spectroscopy (FTIR). The results of contrastive experiments showed that evaporation of the solvent promoted the aggregation of primary particles, and the addition of methylamine accelerated the crystallization process. The NZ5 aggregate consisted of 20nm individual particles, as shown in scanning electron microscope (SEM). The lattice fringes in the transmission electron microscope (TEM) images and the XRD results indicated that individual particles of NZ5 were highly crystalline. N2 adsorption-desorption isotherms showed that NZ5 had high BET surface areas with mesopores having a mean diameter of about 9nm. NZ5 exhibited a long lifetime, a stable and high yield of liquid hydrocarbons, and a high anti-coking performance in methanol-to-hydrocarbons reaction. Catalytic testing and TGA results showed that the lifetime of NZ5 was about ten times longer than that of micro-sized ZSM-5 zeolite (MZ5), and the average coking rate with NZ5 was one fifth over that of MZ5.

Influences of Mesoporosity Generation in ZSM-5 and Zeolite Beta on Catalytic Performance During n-Hexane Isomerization

Catalytic performance of Pt impregnated parent and desilicated nano-crystalline zeolites, ZSM-5 and Beta for n-hexane isomerization was studied. Difference in channel systems of the zeolites and absence/presence of mesopores therein were found to be reflected in product distributions. ZSM-5 was desilicated by NaOH and zeolite Beta with tetramethylammonium hydroxide (TMAOH.) Desilication was found to afford comparable catalytic performance to that of the parent counterpart at reaction temperature lower by 25 °C. Observed product distributions could be substantiated with characterizations such as ammonia TPD, surface area determination and SEM. Desilicated zeolite Beta was seen to be less prone to coking as deduced from the TGA study. Location of Pt with reference to proton sites within the channels and that inside the pores viz a viz external surface also have been discussed briefly. Pt impregnated Zeolite Beta desilicated by TMAOH affords comparable isomer yields at temperature lower by 25 C to that by the parent zeolite. The modification also led to improved catalyst life.

Acidic and catalytic properties of hierarchical zeolites and hybrid ordered mesoporous materials assembled from MFI protozeolitic units

Two types of MFI zeolitic materials with improved accessibility, hierarchical zeolites and hybrid ordered mesoporous materials are here compared in terms of textural, acidic and catalytic properties. In both cases, protozeolitic units were employed as starting building blocks, the growth of which was perturbed by a silanization agent (hierarchical ZSM-5) or controlled by assembling around surfactant micelles (hybrid ordered mesoporous material, HZM). Likewise, two standard samples (nanocrystalline ZSM-5 and Al-MCM-41) were used as reference. Nitrogen adsorption measurements confirmed the presence of a secondary porosity and a high share of non-microporous surface area in hierarchical ZSM-5, whereas no significant amount of micropores was detected in the hybrid HZM sample. However, 27Al MAS NMR measurements indicated that zeolitic fragments are present within the walls of the latter sample. The acidic properties of the materials under study were extensively investigated by adsorption–desorption of different base probe molecules. Specifically, FTIR spectra taken after pyridine adsorption show the presence of a high population of strong Lewis acid sites in both hierarchical ZSM-5 and HZM samples. This fact, along with a high accessibility to the active sites, is proposed to be mainly responsible for the enhanced catalytic activity exhibited by these materials in 1,2-epoxyoctane rearrangement and anisole acylation. The results obtained clearly indicate the strong and positive influence of the textural and acidic features of the hierarchical materials on their catalytic properties.

Preparation of nano-crystalline MFI zeolite via hydrothermal synthesis in water/surfactant/organic solvent using fumed silica as the Si source

The preparation of nano-crystalline MFI zeolites (Silicalite-1 and ZSM-5) was carried out by hydrothermal synthesis in a water/surfactant/organic solvent using fumed silica and aluminum sulfate as the Si and Al source, respectively. It was confirmed that the surfactant in the solution affected the nucleation rate of the MFI zeolite. Moreover, the crystal size of the MFI zeolite decreased with increasing surfactant concentration, and nanometer-sized MFI zeolites was obtained at a surfactant concentration of 0.25–0.5 mol/L. The successful preparation of MFI zeolite nanocrystals was ascribed to the stabilization of the MFI zeolite precursors and/or crystals by the adsorbed surfactant on their surface. This method was applied to the preparation of nano-crystalline ZSM-5 zeolite. ZSM-5 zeolite with a crystal size of approximately 50 nm was obtained. The nano-crystalline ZSM-5 zeolite was well-crystallized without octahedral Al atoms in the external framework, and exhibited almost the same acidity as a reference ZSM-5 zeolite.

Catalytic properties in polyolefin cracking of hierarchical nanocrystalline HZSM-5 samples prepared according to different strategies

Two series of hierarchical nanocrystalline ZSM-5 zeolites prepared by different synthesis strategies (at low temperature and from silanized seeds) and with external surface areas ranging from 150 to 250 m 2 g −1 were tested in the cracking of pure LDPE and HDPE at 340 °C and of waste polyethylene at 360 °C. Hierarchical zeolites showed quite higher activity, with values even six times higher than a standard nanocrystalline sample used as reference ( n-HZSM-5). The activity values decreased from LDPE to HDPE due to the occurrence of some degree of branching in the former polymer, which act as preferential cracking sites. The major products were C 1–C 4 hydrocarbons (in the range 30–70%, mostly C 3–C 4 olefins) and C 5–C 12 hydrocarbons (20–60%), whose share depends on both the polyolefin and the catalyst. The amount of C 13–C 40 hydrocarbons was practically negligible (<1%) due to the high acid strength of the zeolites which promotes end-chain cracking reactions. Likewise, hierarchical nanocrystalline HZSM-5 zeolites prepared from silanized protozeolitic units showed higher activities than the hierarchical nanocrystalline HZSM-5 samples synthesized at low temperature and atmospheric pressure. The differences were especially remarkable in the case of waste polyethylene cracking. These results were ascribed to the stronger acidity of the hierarchical zeolite samples prepared from silanized seeds.

Synthesis of hierarchical nanocrystalline ZSM-5 with controlled particle size and mesoporosity

Development of new zeolite based materials is essential for a variety of applications in catalysis, separations, and medicine. Increasing the specific surface area and decreasing the micropore diffusion pathlength in zeolites are important factors for improving the performance of zeolites in catalytic applications and these factors can be optimized by decreasing the zeolite particle size. Creation of a hierarchical zeolite material that possesses both micro- and mesopores with very large surface areas and improved mass transport properties is an effective solution. In this study, a facile approach to a one step synthesis of nanocrystalline ZSM-5 zeolite from a single template system in 12–24 h at 140 °C and with high yield is presented. ZSM-5 zeolite crystals as small as 6 nm which form mesoporous aggregates of approximately 200 nm in diameter were synthesized using this method. The mesopore volume and size distribution showed a dependence on particle size such that smaller particles lead to higher mesopore volumes and narrower pore size distributions. The size of individual crystals, as well as mesopore surface area and pore volume can be controlled by adjusting the pH of the reaction mixture, as well as the hydrothermal treatment temperature and duration.

Selective decomposition of cumene hydroperoxide into phenol and acetone over nanocrystalline ZSM-5

Phenol is an industrially important chemical, generally produced via sulphuric acid catalysed decomposition of cumene hydroperoxide (CHP). The effluent containing the acid used as catalyst has to be neutralised and extracted to avoid corrosion and environmental problems. In the current work, a simple process was developed based on the use of nanocrystalline ZSM-5 (Si/Al = 100) catalyst. The catalyst was characterised by XRD, SEM, TEM, DLS and FT-IR analyses. The activity of this catalyst was tested for the liquid-phase decomposition of cumene hydroperoxide. The effects of various parameters such as, catalyst weight, catalyst particle size, concentration of CHP, reaction temperature and reusability of catalyst were studied. It was observed that the nanocrystalline ZSM-5 with smaller particle size showed superior activity. In addition, these catalysts have excellent reusability and can be used instead of sulphuric acid for selective decomposition of CHP into phenol and acetone with 100% conversion.

Nanocrystalline ZSM-5: A catalyst with high activity and selectivity for epoxide rearrangement reactions

Abstract Nanocrystalline ZSM-5 (∼20–50 nm) has been tested as a catalyst in the liquid phase rearrangement of 1,2-epoxyoctane, 2-methyl-2,3-epoxybutane and isophorone oxide together with a microcrystalline ZSM-5 sample (∼5 μm) employed as a reference. Whereas this last material shows a low activity for the three epoxide rearrangement reactions considered, nanocrystalline ZSM-5 leads in all cases to high epoxide conversion. This different catalytic performance is attributed to the differences in the accessibility of the reactant molecules to the catalyst active sites. The smallest crystal size of the nanocrystalline zeolite contributes favourably to both the formation of a high external surface area, with no steric constraints, and to a faster intracrystalline diffusion of the epoxide molecules towards the acid sites located within the zeolite micropores. When sterically hindered epoxides are tested, the catalytic rearrangement occurs mainly on the external surface of the nanocrystalline zeolite. Moreover, it is remarkable that for the three epoxides investigated the high catalytic activity observed over nanocrystalline ZSM-5 is accompanied by the attainment of high selectivities, typically around or over 80%, towards products with commercial applications.

Friedel–Crafts acylation of anisole over hybrid zeolitic-mesostructured materials

The application of hybrid zeolitic-mesostructured materials (HZM) as catalysts in Friedel–Crafts acylation has been investigated and compared with the behaviour of standard ordered mesoporous Al-MCM-41 and nanocrystalline ZSM-5 samples. Hybrid zeolitic-mesoporous samples were prepared from zeolite seeds obtained in different stages of ZSM-5 crystallization by assembling around cetyltrimethyl ammonium bromide (CTAB) micelles to obtain materials having a combination of both zeolitic and mesostructured properties. Acylation of anisole with acetyl chloride and acetic anhydride has been investigated over this type of catalysts, the highest conversions being obtained in all cases with the former acylating agent. The activity of the hybrid materials (HZM) was found to be remarkably higher than those exhibited by Al-MCM-41 and ZSM-5 materials, which has been interpreted as a convenient combination of accessibility and zeolitic features in the former. Deactivation, re-use and regenerability of the HZM material were also investigated. With all catalysts, a decline of activity was observed along the reaction time denoted by the fact that the conversion reaches a plateau. This deactivation is caused mainly by product inhibition associated to the strong adsorption of p-MAP on the acid sites. Nevertheless, the hybrid catalysts could be regenerated by calcination and further re-used efficiently for the anisole acylation.