Conventional Microporous ZSM-5 Research Articles

Alkaline modified Zr-loading on nanosheet zeolite towards production of γ-valerolactone from levulinic acid through catalytic transfer hydrogenation

A self-pillared nanosheet ZSM-5 zeolite (SP) loading Zr catalyst is prepared for conversion of levulinic acid (LA) to produce γ-valerolactone (GVL). The hierarchical pore by nanosheet aggregates promotes Zr dispersion with establishment of strong interaction between Zr and zeolite. Moreover, Na ions are introduced to modify the chemical environment of Zr on nanosheet zeolite (Zr/NaSP). In catalytic transfer hydrogenation of LA using isopropanol as H-donor, uniformly dispersed Zr species on SP zeolite is conducive for both conversion of LA as well as production of GVL, in comparison with samples using conventional microporous ZSM-5 as supports (Zr/CZ). More importantly, different from protonated zeolite sample (Zr/HSP), the introduction of alkali sites could attract protons in hydroxyl groups of isopropanol, which accelerates the generation rates of GVL. The as-designed Zr/NaSP catalyst delivers GVL generation rates of 31.9 mmol·g-1·h-1, which provides a potential catalyst for GVL production.

Synthesis of layered ZSM-5 zeolites with stable self-supported structure for enhanced catalytic cracking of cycloalkane aromatics

High diffusion resistance of conventional microporous ZSM-5 zeolites greatly inhibits the effective conversion of cycloalkane aromatics into BTX, ethylene, and propylene over acid sites during the catalytic cracking of diesel. Herein, we successfully synthesized self-supported layered ZSM-5 with enhanced diffusion ability and specific acid site distribution through pre-crystallization and hydrothermal synthesis to boost the catalytic cracking of tetralin. Assisted by pre-synthesized crystal seeds as nuclei and quaternary ammonium salts, a unique 2 nm thick layer was stably spread over the surface of the crystal seeds. Even after the templating agents are removed at high temperatures, the robust self-supported layered structure could still maintain the thermal stability of MFI structure with excess 50 % acid sites distributed on the external surface. Such specific acidic distribution greatly resisted the formation of coke in the zeolite pore channels. Moreover, thanks to the reduced diffusion resistance of the mesoporous structure, the self-supported layered ZSM-5 zeolites exhibited enhanced tetralin conversion of 47.3 %, nearly 38 % higher than that of traditional ZSM-5 zeolites (9.7 %). This work could provide a reference for the design of efficient zeolite catalysts with multi-level pore structure for catalytic cracking of diesel.

Hydrothermal liquefaction of food waste to bio-oil over hierarchical Fe-Co-ZSM-5 catalyst for the circular economy

Food waste is an important wasted resource needs to be utilized for fuel production towards achieving circular economy. Hydrothermal liquefaction (HTL), a fast and energy efficient method of transforming wet food waste to bio-oil whose yield depends on catalyst. In the present study hierarchical Fe-Co-ZSM-5 was synthesized by steam assisted crystallization, characterized and evaluated for the HTL of model food waste. Highest bio-oil yield of 41.8% was obtained at 250 °C, 80 bar using 1 g of hierarchical Fe-Co-ZSM-5 catalyst of crystallinity of 84% for 2 h. Hierarchical Fe-Co-ZSM-5 catalyst is less prone to deactivation compared to conventional microporous ZSM-5 catalyst.

Catalytic fast pyrolysis of beech wood lignin isolated by different biomass (pre)treatment processes: Organosolv, hydrothermal and enzymatic hydrolysis

Lignin is one of the three main structural components of lignocellulosic biomass and is considered as the most abundant source of aromatic and phenolic compounds. Lignin is produced as side-stream in the pulp/paper industry or as residue in the production of second-generation bioethanol. More recently, novel biomass fractionation processes in biorefineries have been developed aiming at the production of high quality/purity lignin towards its more efficient down-stream catalytic conversion to chemicals, monomers, and fuels. Within this context, in this work, we studied the thermal (non-catalytic) and catalytic fast pyrolysis on a Py/GC–MS system and a fixed-bed reactor unit of three types of lignin, all originating from the same biomass (beech wood sawdust) but with different isolation processes: organosolv lignin derived by the organosolv pretreatment/fractionation of biomass, surface extracted lignin derived by the mild Soxhlet extraction (with ethanol or acetone) from the hydrothermally (HT) in pure water pretreated biomass, and the enzymatic hydrolysis lignin derived as a lignin-rich solid residue from the enzymatic hydrolysis of the HT pretreated biomass. Conventional microporous ZSM-5 and mesoporous ZSM-5 zeolites (with intracrystal mesopores, ˜ 9 nm) were used as catalysts in the pyrolysis experiments. Both zeolites were very active in converting the initially produced via thermal pyrolysis methoxy-substituted phenols, benzenes and benzaldehydes mainly towards BTX mono-aromatics, such as 1,3-dimethylbenzene/p- and o-xylenes, toluene and trimethylbenzenes, as well as polycyclic aromatic hydrocarbons (PAHs, mainly naphthalenes). The mesoporous ZSM-5 induced higher dealkoxylation reactivity compared to the microporous ZSM-5 leading to higher concentration of BTX aromatics without a consequent increase of PAHs. The pronounced dealkoxylation/aromatization reactivity of both ZSM-5 zeolites resulted to lower yields (but highly aromatic) organic bio-oils (e.g. from 32−35 wt.% to 15−22 wt.%) compared to thermal pyrolysis, increased non-condensable gases (mainly CO, CO2, methane, ethylene and propylene) and formation of relatively low amounts of coke on catalysts (e.g. 3−5 wt.% on lignin) in addition to thermal pyrolysis char. The observed moderate variations in the characteristics of the three types of beech wood lignin, i.e. molecular weight (GPC), S/G ratio, inter-unit linkages (2D HSQC NMR) and elemental composition, did not induce a systematic/substantial differentiation in the thermal and catalytic fast pyrolysis product yields and composition.

In-situ synthesis of hierarchical lamellar ZSM-5 zeolite with enhanced MTP catalytic performance by a facile seed-assisted method

A seed-assisted route has been applied to prepare the hierarchical lamellar ZSM-5 zeolite with good porosity and catalytic performance in methanol to propylene (MTP) reaction. In this method, ZSM-5 crystal seeds instead of organic quaternary ammonium were used to direct the formation of ZSM-5 nuclei and conventional surfactant cetyltrimethylammonium bromide (CTAB) employed as the mesoporogen. The process for the formation of hierarchical lamellar ZSM-5, including the effect of the ratio of CTAB/SiO2, initial gel aging temperature, synthesis temperature and synthesis time were discussed in detail. The results suggested that mesoporous structure was first obtained and then transformed into MFI structure in-situ during the hydrothermal synthesis process. The obtained hierarchical lamellar ZSM-5 zeolite displays an organized flack-like nanosheet stacks morphology with regular intercrystal mesopores of 3–7 nm, possessing large surface area and mesopore volume. Moreover, the synthesized hierarchical ZSM-5 zeolite has perfect catalyst lifetime in methanol to propylene (MTP) reaction than conventional microporous ZSM-5 zeolite, which could be ascribed to the hierarchical mesoporous structure accommodating more bulky molecules and accessible acid sites in the catalytic reaction.

Guaiacol hydrodeoxygenation over Pd catalyst with mesoporous ZSM-5 support synthesized by solid-state crystallization

Mesoporous structure is important to promote mass transport and active site utilization of zeolites when used in reactions involving bulky molecules. However, their conventional hydrothermal synthesis is energy and labor intensive, requiring high-pressure operation, and lengthy heating a huge amount of alkaline liquid. We successfully synthesized new mesoporous zeolites, Meso-ZSM-5, via solid-state crystallization of dry aluminosilicate nanogels. Neighbor developing nanocrystals further joint at edges, creating connected, inter-lattice mesoscale pathway in the finished single crystalline zeolites. Palladium was further loaded on these zeolites to form a bi-functional catalyst (Pd/Meso-ZSM-5). When used in the hydrodeoxygenation (HDO) of guaiacol, a major bio-oil compound with disappointing conversion and severe coking issue over many HDO catalysts, Pd/Meso-ZSM-5 exhibits superior guaiacol conversion and product distribution when compared with those supported on conventional microporous ZSM-5 counterparts. This is attributed to the improved diffusion and accessibility of active sites inside Meso-ZSM-5 with its unique hierarchically porous structure. Ring saturated hydrocarbons are largely produced at 200 °C when hydrogenation dominates while alkaylated aromatics become major HDO products as deoxygenation becomes favorable at 250 °C. These encouraging results may ignite the wide use of these mesoporous zeolites in many other reactions in both traditional fossil fuel and emerging renewable energy fields.

A green route for the synthesis of nano-sized hierarchical ZSM-5 zeolite with excellent DTO catalytic performance

Nano-sized hierarchical ZSM-5 zeolite with high crystallization was prepared by a novel green strategy, that is, the consecutive freezing and vacuum drying route. In comparison with the traditional synthesis process, only 1/5 amount of TPAOH (tetrapropylammonium hydroxide) template was involved. Moreover, hierarchical structured zeolites can be formed even in the absence of mesoporous template (e. g. cetyltrimethylammonium bromide, CTAB). Moreover, the hierarchical ZSM-5 with a wide range of SiO2/Al2O3 ratio (25–200) can be modulated. The effects of the consecutive freezing and vacuum drying methods on the formation process, pore characteristics, crystallinity, morphology and acidity of the ZSM-5 zeolites were explored. It is noted that the abundant intra-crystal mesopores and nanoparticles structure were generated from the porous structure on the surface of the freeze-dried powder. The constructed nano-sized and hierarchical ZSM-5 catalyst exhibits a prolonged lifetime of 110 h in dimethyl ether-to-olefin (DTO) reaction, which is around 3.7-fold lifetime compared to the conventional microporous ZSM-5.

Catalytic Fast Pyrolysis of Kraft Lignin With Conventional, Mesoporous and Nanosized ZSM-5 Zeolite for the Production of Alkyl-Phenols and Aromatics.

The valorization of lignin that derives as by product in various biomass conversion processes has become a major research and technological objective. The potential of the production of valuable mono-aromatics (BTX and others) and (alkyl)phenols by catalytic fast pyrolysis of lignin is investigated in this work by the use of ZSM-5 zeolites with different acidic and porosity characteristics. More specifically, conventional microporous ZSM-5 (Si/Al = 11.5, 25, 40), nano-sized (≤20 nm, by direct synthesis) and mesoporous (9 nm, by mild alkaline treatment) ZSM-5 zeolites were tested in the fast pyrolysis of a softwood kraft lignin at 400–600°C on a Py/GC-MS system and a fixed-bed reactor unit. The composition of lignin (FT-IR, 2D HSQC NMR) was correlated with the composition of the thermal (non-catalytic) pyrolysis oil, while the effect of pyrolysis temperature and catalyst-to-lignin (C/L) ratio, as well as of the Si/Al ratio, acidity, micro/mesoporosity and nano-size of ZSM-5, on bio-oil composition was thoroughly investigated. It was shown that the conventional microporous ZSM-5 zeolites are more selective toward mono-aromatics while the nano-sized and mesoporous ZSM-5 exhibited also high selectivity for (alkyl)phenols. However, the nano-sized ZSM-5 zeolite exhibited the lowest yield of organic bio-oil and highest production of water, coke and non-condensable gases compared to the conventional microporous and mesoporous ZSM-5 zeolites.

Enhanced Phenol Hydrodeoxygenation Over a Ni Catalyst Supported on a Mixed Mesoporous ZSM-5 Zeolite and Al2O3

Developing highly active catalysts for bio-oil hydrodeoxygenation is of great importance in the low cost production of conventional transport alkane fuels. Toward this goal, a Ni catalyst supported on mesoporous ZSM-5 zeolite mixed with 25 wt% γ-Al2O3 (Ni/Al-HMZSM-5) was designed for hydrodeoxygenation of phenol as model compound. For comparison, the catalytic activities of Ni catalysts on conventional microporous ZSM-5, mesoporous ZSM-5 and γ-Al2O3 were also investigated. It was found that almost complete phenol conversion (99.6%) was achieved over the Ni/Al-HMZSM-5 catalyst along with a high cyclohexane selectivity (98.3%) under a relatively mild condition (170 °C, 4 MPa H2). The open mesopores, stronger acid sites and synergism effect of Bronsted and Lewis acidities are jointly responsible for the excellent hydrodeoxygenation performance. In addition, it was shown that the catalyst was recycled several times with little loss of activity and selectivity.

On the Mesoporogen-Free Synthesis of Single-Crystalline Hierarchically Structured ZSM-5 Zeolites in a Quasi-Solid-State System.

Hierarchically structured zeolites (HSZs) have gained much academic and industrial interest owing to their multiscale pore structures and consequent excellent performances in varied chemical processes. Although a number of synthetic strategies have been developed in recent years, the scalable production of HSZs single crystals with penetrating and three-dimensionally (3-D) interconnected mesopore systems but without using a mesoscale template is still a great challenge. Herein, based on a steam-assisted crystallization (SAC) method, we report a facile and scalable strategy for the synthesis of single-crystalline ZSM-5 HSZs by using only a small amount of micropore-structure-directing agents (i.e., tetrapropylammonium hydroxide). The synthesized materials exhibited high crystallinity, a large specific surface area of 468 m(2) g(-1) , and a pore volume of 0.43 cm(3) g(-1) without sacrificing the microporosity (≈0.11 cm(3) g(-1) ) in a product batch up to 11.7 g. Further, a kinetically controlled nucleation-growth mechanism is proposed for the successful synthesis of single-crystalline ZSM-5 HSZs with this novel process. As expected, compared with the conventional microporous ZSM-5 and amorphous mesoporous Al-MCM-41 counterparts, the synthesized HSZs exhibited significantly enhanced activity and stability and prolonged lifetime in model reactions, especially when bulky molecules were involved.

Hierarchical mesoporous Pd/ZSM-5 for the selective catalytic hydrodeoxygenation of m-cresol to methylcyclohexane

Mesopore incorporation into ZSM-5 enhances the dispersion of Pd nanoparticles significantly accelerating m-cresol conversion relative to a conventional microporous ZSM-5, and dramatically increasing selectivity towards the desired methylcyclohexane deoxygenated product.

Production of Renewable Petrochemicals from Catalytic Co-Pyrolysis of Beech Wood and Low-Density Polyethylene with Mesoporous Bifunctional ZSM-5 Zeolites

This study investigated catalytic fast pyrolysis (CFP) of beech wood, low-density polyethylene (LDPE), and their mixture (mass ratio of 1) with a conventional microporous ZSM-5 and mesoporous bifunctional Zn/ZSM-5meso zeolite prepared by desilication of the conventional ZSM-5 with NaOH solution and then impregnation with Zn.The generation of mesopores by desilication improved the diffusion property of the zeolite, which decreased the formation of undesired polyaromatic hydrocarbons from secondary polymerization reactions of monoaromatics in CFP. In addition, the impregnation of Zn increased the dehydrogenation activity of the zeolites, and thus enhanced the conversion of low-value alkanes to valuable olefins. As a result, Zn/ZSM-5meso produced higher yields (56.0 C%) of valuable petrochemicals (monoaromatic hydrocarbons and olefins) and lower yields of undesired polyaromatics (1.70 C%) and alkanes (10.2 C%) in co-feed CFP of the beech wood and LDPE mixture than ZSM-5 (48.2 C%, 4.18 C%, and 18.7 C% for petrochemicals, polyaromatics, and alkanes, respectively).ZSM-5 desilication and impregnation with Zn thus have a beneficial effect on improve the product distribution in CFP of biomass and plastic mixtures. In addition, the results suggest that CFP may provide a promising technology for producing renewable petrochemicals from municipal and agricultural solid wastes, which usually contain high contents of biomass and waste plastics.

Catalytic conversion of methanol to propylene over high-silica mesoporous ZSM-5 zeolites prepared by different combinations of mesogenous templates

The effects of mesoporosity on catalytic performance of methanol to propylene (MTP) reaction have been investigated by using a series of high-silica nanosized hierarchical ZSM-5 zeolites with different degrees of mesoporosity, which were hydrothermally synthesized in the presence of different mesogenous templates, i.e., TPOAC, CTAB, and their combinations. The results were compared with a conventional microporous ZSM-5 catalyst. The prepared catalysts were characterized by XRD, FE-SEM, BET, NH3-TPD and FT-IR techniques. Meanwhile, their catalytic activities were evaluated in a fixed-bed reactor under atmospheric pressure, 460 °C and WHSV of 1h−1. Compared with conventional catalyst, the nanosized hierarchical porous ZSM-5 templated with a mixture of 75% TPOAC and 25% CTAB displayed reliable MTP catalytic lifetime (76 h) as well as sufficiently high propylene selectivity (43.65%) and propylene to ethylene (P/E) ratio (4.05), which were predominately attributed to its optimal combination of acidity and porosity.

ZSM-5 Zeolite with Micro-Mesoporous Structures Synthesized Using Different Templates for Methanol to Propylene Reaction

ZSM-5 zeolites with different pore structures were synthesized using different templates(tetrapropyl ammonium hydroxide(TPAOH), cetyltrimethylammonium bromide(CTAB) and C18-6-6Br2). The obtained nanosized(NZ), mesoporous(MZ), and nanosheets(NSZ) ZSM-5 samples were compared with conventional microporous ZSM-5 zeolite(CZ). The physicochemical properties of these samples were characterized using X-ray diffraction(XRD), scanning electron microscopy(SEM), N2 adsorption-desorption,and temperature-programmed desorption of ammonia(NH3-TPD). The results showed that the mesopore volumes and surface areas of the four samples increased in the order NSZ MZ NZ CZ, and the ratio of strong/weak acidity increased in the order CZ MZ NZ NSZ. In the methanol to propylene(MTP) reaction,the catalyst porosity played an important role on the product selectivity and catalytic stability. The selectivities for propylene and total olefins improved with increasing mesoporosity; NSZ, with the largest mesopore volume, gave the highest propylene selectivity, i.e., 47.5%, and 78.4% total olefins. Meanwhile, the introduction of mesopores into the ZSM-5 zeolite extended the catalytic lifetime. The NZ sample displayed reliable MTP catalytic activity for 200 h, which was predominately attributed to its optimal combination of acidity and porosity.

Aromatics from biomass pyrolysis vapour using a bifunctional mesoporous catalyst

Zeolites with uniform intracrystal mesopores, designated MSU-MFI, were prepared using silane-modified polymers as mesopore-generating agents. X-ray diffraction analysis of this catalyst showed Braggs peaks representative of MFI structure. Catalyst characterization by nitrogen physisorption revealed a mesoporous structure with high surface area, pore size and volume. The MSU-MFI catalysts developed in this study were selective toward aromatic chemical production from poplar pyrolysis vapour. Yields of generalized products and aromatics were comparable to those obtained from conventional microporous ZSM-5 analogs as demonstrated by pyroprobe-gas chromatography/mass spectrometry and thermogravimetric analysis. While ZSM-5 was more selective to smaller C6 aromatics and naphthalenes, MSU-MFI catalysts were more selective to C8 and C9 monoaromatics. The incorporation of gallium(III) ions in MSU-MFI using the incipient wetness method increased aromatic yields by up to 15% over Ga-free catalysts and decreased the coke production by up to 6% (p < 0.05). Due to high yields and low coke formation, Ga-MSU-MFI offers an improved option for making non-oxygenated aromatic chemicals from photosynthetic biomass.

Catalytic fast pyrolysis of biomass with mesoporous ZSM-5 zeolites prepared by desilication with NaOH solutions

This study investigated the effects of desilication of ZSM-5 zeolite on its catalytic properties in catalytic fast pyrolysis (CFP) of lignocellulosic biomass. A series of mesoporous ZSM-5 zeolites were prepared by desilication of a conventional microporous ZSM-5 zeolite with NaOH solutions of varying concentrations (0.1–0.5M). The creation of mesopores improved the diffusion property of the desilicated ZSM-5 zeolites and their catalytic activity for cracking bulky oxygenates (e.g., syringols derived from the lignin component of biomass). Consequently, the desilicated zeolites produced more aromatic hydrocarbons (carbon yields of 26.2–30.2%) and less coke (39.9–41.2%) in CFP of beech wood than the parent microporous ZSM-5 (23.2% aromatics and 44.4% coke). The highest aromatic yield (30.2%) and lowest coke yield (39.9%) were obtained in CFP of beech wood with mildly desilicated zeolite treated with 0.3M NaOH solution. However, desilication with a greater concentration, 0.5M NaOH, decreased the aromatic yield to 26.2% due to a considerable loss of microporosity in the severely desilicated zeolite. The results indicate that carefully controlled desilication of zeolite can improve the conversion of lignocellulose to valuable aromatic hydrocarbons and decrease the formation of undesired coke, thus improving the product distribution in CFP of lignocellulose.

Unique catalytic performance of mesoporous molecular sieves containing zeolite units in transformation of m-xylene

Integrating ZSM-5 zeolite units into two different mesostructured materials, led to high p-xylene selectivity in the transformation of m-xylene. The activity and selectivity of both composite materials were compared with those of Al-MCM-41, Al-MCM-48 and the conventional microporous ZSM-5. A bimolecular pathway involving disproportionation and transalkylation, together with the presence of ZSM-5 zeolite units in the composite materials, was responsible for this high p-xylene selectivity. The catalysts were characterized by powder XRD, TGA, SEM, nitrogen sorption and FT-IR of pyridine adsorption. The selectivity towards p-xylene over the different catalysts under study follows the order: conventional ZSM-5 < ZSM-5/MCM-48 < ZSM-5/MCM-41. The highest p-xylene selectivity noticed over ZSM-5/MCM-41 composite material indicates more transalkylation of trimethylbenzene molecules with m-xylene. The apparent activation energies for the transformation of m-xylene over both composite materials were found to decrease as follows: E Z/48M-4 , E Z/41M-4 (transalkylation) > E Z/48M-3 , E Z/41M-3 (disproportionation) .

High activity in catalytic cracking of large molecules over a novel micro-micro/mesoporous silicoaluminophosphate

AbstractA novel micro-micro/mesoporous silicoaluminophosphate ZSM-5-SAPO-5/MCM-41 (define as MZS-5) composite material with regular spherical morphology was synthesized through a novel process of the self-assembly of CTAB surfactant micelles with silica-alumina source which originated from the alkaline treatment of ZSM-5 zeolite. The physical properties of the MZS-5 composite material were characterized by XRD, FT-IR, Nitrogen adsorption–desorption, SEM and Py-FTIR techniques. Catalytic tests showed that the MZS-5 composite catalyst exhibited higher catalytic activity compared with the conventional microporous ZSM-5, SAPO-5 zeolite and mesoporous Al-MCM-41 molecular sieve for catalytic cracking of 1,3,5-triisopropylbenzene (TIPB). The remarkable catalytic reactivity of TIPB molecules was mainly attributed to the presence of the hierarchical zeolite structure. In the MZS-5 structure, the mesopores provided pathways for transportation of larger molecules and the microporous ZSM-5 and SAPO-5 zeolite provided acidic sites for catalytic activity.Graphical AbstractA novel micro-micro/mesoporous silicoaluminophosphates MZS-5 catalyst exhibited higher catalytic activity than microporous ZSM-5, SAPO-5 and mesoporous Al-MCM-41 for catalytic cracking of 1,3,5-triisopropylbenzene due to its hierarchical porosity. [IMAGE]

Study of cracking of large molecules over a new type meso-ZSM-5 composite zeolite

A new type meso-ZSM-5 composite zeolite with interconnected macropores and skeletons under hydrothermal conditions was prepared through zeolite degraded method. The skeletons can be templated to the morphology of network in different conditions. The physical properties of the meso-ZSM-5 composite zeolite were characterized by XRD, IR, SEM and nitrogen sorption techniques. Catalytic tests show that the meso-ZSM-5 composite zeolite catalyst exhibits high catalytic activity compared with the conventional microporous ZSM-5 zeolites for catalytic cracking of 1,3,5-triisopropylbenzene. The high 1,3,5-triisopropylbenzene conversion are mainly assigned to the presence of the hierarchical porosity of the pore walls. The macropores offer easier transport and access to the active sites and the macroporous walls built by ZSM-5 crystals provide the acidic sites for reaction.