H-beta Zeolite Research Articles

Highly selective production of renewable p-xylene from bio-based 2,5-dimethylfuran and ethylene over Al-modified H-Beta zeolites

H-Beta zeolite with further dealumination and modification with alumina shows excellent and durable performances in the synthesis of renewable p-xylene (PX) via bio-based 2,5-dimethylfuran and ethylene with a PX yield of 97% and much less coke content.

Interplay of the adsorption of light and heavy paraffins in hydroisomerization over H-beta zeolite

Hydroisomerization: controlling selectivity by tuning the Pt/zeolite properties.

Understanding the Nature of Transition States in the Confined Nanospace of Different Acidic Zeolites on the Desulfurization Mechanism of Thiophene

We have presented a two-layer ONIOM study on the unimolecular and bimolecular hydrodesulfurization (HDS) mechanisms of thiophene catalyzed by H-Beta, H-MCM-22, H-ZSM-5, and H-FAU zeolites. The rate...

A novel and environmental friendly synthetic route for hydroxypyrrolidines using zeolites

A critical step in the synthesis of the hydroxypyrrolidines, 1,4-dideoxy-1,4-imino-l-lyxitol and 1,4-dideoxy-1,4-imino-d-lyxitol, from the corresponding d-sugars is the synthesis of O-methyl 2,3-O-isopropylidenepentofuranoses. Instead of applying homogeneous catalysis process with conventional inorganic acid catalysts like HCl and HClO4, it was found that heterogeneous catalysis using zeolites could be used for the one-pot synthesis of O-methyl 2,3-O-isopropylidenepentofuranoses directly from d-sugars, MeOH and acetone at mild condition. The best catalyst was H-beta zeolite containing a Si/Al molar ratio of 150, where a yield of >83% was obtained. The overall yields of the five-step procedure to 1,4-dideoxy-1,4-imino-l-lyxitol and 1,4-dideoxy-1,4-imino-d-lyxitol were 57% and 50%, respectively. This synthetic procedure has several advantages such as competitive overall yield, reduced number of steps, and mild reaction conditions. Furthermore, the zeolite catalyst can be easily recovered from the reaction mixture and reused with no loss of activity.

High-efficiency toluene alkylation with tert-butyl alcohol catalyzed by Ce2O3-modified H-beta zeolites

A series of xCe2O3/H-beta catalysts with different Ce2O3 loadings were prepared and the catalytic performances were investigated through toluene butylation as the probe reaction. The xCe2O3/H-beta catalysts showed high para-selectivity due to their improved structural and acidic properties, which were confirmed by XRD, SEM, ICP-OES, BET, Py-IR and TG. Compared with the parent H-beta zeolite, the xCe2O3/H-beta catalysts showed slightly lower toluene conversion and significantly higher para-tert-butyl toluene (PTBT) selectivity. Loading of Ce2O3 firstly narrowed the pore size of H-beta zeolite, which benefited the shape-selectivity, and secondly increased the PTBT selectivity by suppressing the isomerization on acid sites of outer surface of the catalysts. Under comparable conditions, the 5%Ce2O3/H-beta exhibited the maximum PTBT selectivity (82.7%) at 180 °C after 4 h. The optimum reaction conditions over xCe2O3/H-beta zeolites were molar ratio of tert-butyl alcohol to toluene = 3:1, reaction temperature = 180 °C, and reaction time = 4 h.

Mesoporous Beta zeolite functionalisation with FexCry oligocations; catalytic activity in the NH3SCO process

Abstract In the presented study, H-Beta zeolite and H-Beta/meso (mesoporous Beta zeolite obtained by a mesotemplate-free method) were modified with Fe3, Fe2Cr, FeCr2 and Cr3 triple-metallic aggregates (oligocations) by ion-exchange method (for comparison modification with isolated Fe cations was also done). Successful synthesis of mesoporous Beta zeolite was confirmed by several techniques such as N2-sorption, PXRD, AAS or NH3-TPD. Modified porosity and acidity of the Beta zeolite, as well as the source of metals used, influenced the form (coordination and aggregation), content and reducibility of Fe and Cr-species in the samples (UV–vis-DRS, AAS, H2-TPR). The obtained samples were tested as catalysts in the process of selective catalytic oxidation of ammonia to dinitrogen (NH3 SCO). The highest activity and selectivity for nitrogen was obtained for the bimetallic Fe Cr samples prepared by deposition of suitable oligocations.

Vanadium oxide modified H-beta zeolite for the synthesis of polyoxymethylene dimethyl ethers from dimethyl ether direct oxidation

The bifunctional H-beta zeolite supported vanadium oxide catalysts were prepared at different calcination temperatures and investigated for dimethyl ether (DME) direct oxidation to polyoxymethylene dimethyl ethers (DMMx). The impact of the nature of VOx species and the acid properties controlled by the calcination temperature on the DMMx formation has been studied in detail. Vanadium oxide species dispersing well on the H-beta zeolite offer suitable redox sites. Meanwhile, the acid strength and distribution of H-beta zeolite are modulated by the interaction between VOx species and zeolite framework. The acid properties of the catalysts with different calcination temperatures are analyzed by pyridine-Fourier transform infrared spectra and NH3 temperature-programmed desorption measurements, and the selectivity to DMMx shows a linear relationship with the Brønsted/Lewis acid sites ratio, indicating that the catalysts with higher B/L ratio are effective for the DMMx formation. In addition, the NH3-TPD results confirm that more acid sites with strong strength for the catalysts are in favor of the C–O chain growth to synthesize larger DMMx molecules. These results above are helpful for us to well understand the active sites and design the effective catalysts to synthesize DMMx with longer C–O chain.

High-silica Hβ zeolites for catalytic hydration of hydrophobic epoxides and alkynes in water

We investigated the hydration of hydrophobic epoxides and alkynes in water using 24 types of heterogeneous and homogeneous catalysts and found that Hbeta (Hβ) zeolite with a relatively high Si/Al ratio (Si/Al = 75), Hβ-75, is an effective catalyst. Hβ-75 showed wide substrate scope, good reusability, and applicability in gram-scale synthesis for both types of reactions. The effects of hydrophobicity, acidity, and the size of zeolite pores were also comprehensively studied through the hydration of hydrophilic and hydrophobic epoxides and alkynes with different molecular sizes using two types of zeolite (Hβ and HZSM5). The high yields obtained using the Hβ-75 catalyst in the hydration of hydrophobic epoxides and alkynes are attributed to the hydrophobic interaction between zeolite pores with the substrates, as well as the relatively large pore size.

Excellent Performances of Dealuminated H-Beta Zeolites from Organotemplate-Free Synthesis in Conversion of Biomass-derived 2,5-Dimethylfuran to Renewable p-Xylene.

Direct synthesis of renewable p-xylene (PX) by cycloaddition of biomass-derived 2,5-dimethylfuran (2,5-DMF) and ethylene was achieved over Al-rich H-beta zeolites synthesized by an organotemplate-free approach and their dealuminated counterparts with different Si/Al ratios. Among them, H-beta zeolite with an Si/Al ratio of 22, obtained from an Al-rich parent by dealumination, was found to be an excellent catalyst for the synthesis of PX. A PX yield of 97 % and 2,5-DMF conversion of 99 % were obtained under optimized conditions. These results are even better than those of a commercial H-beta zeolite prepared using a organotemplate synthesis with a similar Si/Al ratio of 19. The excellent performance of the H-beta zeolite with Si/Al ratio of 22 is closely related to its acidity and porous structure. A moderate Brønsted/Lewis acid ratio can improve the conversion of 2,5-DMF to as high as 99 %. Furthermore, dealuminated H-beta zeolite has a secondary pore system that facilitates product diffusion, which increases the selectivity to PX. In addition, this catalyst shows better regeneration. After five successive regeneration cycles, the yield of PX was still as high as 85 % without obvious dealumination. This work provides a deeper understanding of the more general Diels-Alder cycloaddition of furan-based feedstocks and olefins and significantly improves the potential for the synthesis of chemicals from lignocellulosic biomass.

Ethylene Conversion over Catalysts Based on Solid Superacids and Heteropoly Acids

Catalytic properties of solid superacids (WO3/ZrO2 and SO4/ZrO2), and monolith and H-Beta zeolite-supported phosphotungstic heteropoly acid in gas-phase alkylation of benzene with ethylene to ethylbenzene and in the side reaction of ethylene oligomerization are studied. It was found that H-Beta zeolite had the highest activity and selectivity to ethylbenzene. The use of solid superacid (WO3/ZrO2) was shown to be more efficient in low-temperature oligomerization of ethylene.

Synthesis of Ethyl-4-ethoxy Pentanoate by Reductive Etherification of Ethyl Levulinate in Ethanol on Pd/SiO2 -C Catalysts.

The synthesis of biomass-derived ethers to be used as biofuels or biofuel additives has attracted much attention. Following the recently reported synthesis of etherified ester ethyl-4-ethoxy pentanoate (EEP) from γ-valerolactone (GVL) in ethanol catalyzed by H-beta zeolite, an alternative route to prepare EEP in high yield has been developed by reductive etherification of ethyl levulinate (EL) in ethanol at 140 °C under 0.5 MPa H2 with a silica-modified Pd/C catalyst. The ether production likely follows a tandem acetalization-hydrogenolysis process with ethyl-4,4-diethoxy pentanoate (EDEP) as the intermediate. The acetalization step can be favored by introducing acidic materials, such as SiO2 -carbon or beta zeolite, as a cocatalyst. The combination of the Pd/SiO2 -C and beta zeolite mixture leads to 100 % EL conversion and 93 % EEP selectivity under optimized reaction conditions. For the first time, the standard molar combustion enthalpy of as-prepared EEP is measured by using a static oxygen bomb, and the value of which is determined to be about -5658 kJ mol-1 , which is much larger than that of GVL (-2650 kJ mol-1 ).

Profiling the short-lived cationic species generated during catalytic dehydration of short-chain alcohols

Short-chain alcohols are important products of biomass conversion and can be further converted into platform chemicals via catalytic dehydration. Although cationic species are believed to be intermediates in the alcohol-to-hydrocarbon processes, directly observing them is still a challenge due to the lack of efficient tools to deal with their instability and short lifetimes. Here we integrate a micro catalytic reactor onto the ion inlet of an Orbitrap mass spectrometer for high-speed, high-sensitivity, and high-throughput detection of the short-lived cationic species generated during dehydration of short-chain alcohols over heterogeneous catalysts. Hundreds of cationic species can be feasibly observed within the catalytic alcohol dehydration on acidic zeolites H-Beta and H-ZSM5. It is demonstrated that these cationic species may feasibly reveal the catalytic reaction activity and selectivity. This strategy has the potential to inform catalyst development and to help refine reaction conditions in the future.

Characteristics of H-beta Zeolite Catalyst for Catalytic Decomposition of <i>t</i>-Butyl Mercaptan

Characteristics of H-beta Zeolite Catalyst for Catalytic Decomposition of <i>t</i>-Butyl Mercaptan

Aluminum Fluoride Modified Beta Zeolite as Highly Selective Catalyst for the Esterification of sec-Butanol with Acetic Acid

This article describes a simple but effective method to dealuminate and realuminate H-Beta zeolite as a catalyst for removing organic acids from bio-oils via their esterification reactions with alcohols. A series of modified Beta zeolites were prepared by mechanically mixing an oxalic acid leached Beta zeolite with different amounts of solid-phase aluminum fluoride (AlF3) and calcinating the resulting mixtures. The structure, texture property, and acidity of the oxalic acid leached Beta zeolite can be finely adjusted by simply changing the amount of AlF3 used. Dealumination and realumination could simultaneously take place via the interaction of Beta zeolite with AlF3 when the content of AlF3 was between 1.5 and 3.0 wt %. Only dealumination happened when the content of AlF3 was lower than 1.0 wt % or higher than 4.0 wt %. The catalytic activities for esterification reaction of sec-butanol and acetic acid showed that the modified Beta zeolite with a suitable amount of AlF3 exhibited much higher selectivity than the oxalic acid leached H-Beta zeolite.

Insight into the reaction mechanism and charge transfer analysis for the alkylation of benzene with propylene over H-beta zeolite

The reaction mechanism of alkylation of benzene with propylene to produce cumene over H-beta zeolite was investigated by density functional theory (DFT) using a 5T cluster model at the B3LYP/6-31G* level. The Mulliken population analysis was conducted to investigate the charge transfer analysis. Two possible reaction pathways, i.e., consecutive (stepwise) and associative (one-step) mechanism, were proposed. DFT simulation results revealed that the activation energy of associative mechanism (106 kJ/mol) is much lower than that of consecutive reaction pathway (294 kJ/mol). That is, the formation of cumene over H-beta zeolite is more preferred through associative mechanism, wherein the protonation and alkylation occur simultaneously without isopropoxide formation. Then, Mulliken charge transfer (CT) analysis for the two reaction mechanisms was conducted. Both reaction mechanism and CT analysis results proved that it is the H proton connected to benzene ring transferred back to zeolite framework during the formation of cumene from transition state in the alkylation step, not the original active center H atom of H-beta zeolite. Finally, it was found that the electric properties of zeolite framework play an important role in the alkylation of benzene with propylene.

Simultaneous deoxygenation, cracking and isomerization of palm kernel oil and palm olein over beta zeolite to produce biogasoline, green diesel and biojet-fuel

Drop-in fuels have aroused great interest for automotive and aeronautical use, constituting the newest area of biofuel research. These fuels do not contain oxygen, like fossil fuels, and require no modifications to engines and distribution infrastructure. In this work, biohydrocarbons were obtained in the distillation ranges of gasoline, diesel and aviation kerosene from palm kernel oil and palm olein in the form of triglycerides or their hydrolysates. A 15% ratio of the thermally activated HBeta zeolite catalyst to the mass of the fatty material was used. Deoxygenation reactions (5 h, 800 rpm, batch reactor) occurred at 350 °C under 10 bar H2 atmosphere to furnish as much as 96% conversion to liquid hydrocarbons. The products were analyzed by FTIR for a rapid quantification of the deoxygenation efficiency using a method developed for this purpose. These products were also characterized by thermal analysis and GC–MS. The freezing temperatures of the biohydrocarbons and their mixtures with fossil aviation kerosene were determined by DSC. The results obtained were very promising, especially considering the relatively mild process conditions as low H2 pressure and catalyst without noble metal and with high reusability.

Study of Confinement and Catalysis Effects of the Reaction of Methylation of Benzene by Methanol in H-Beta and H-ZSM-5 Zeolites by Topological Analysis of Electron Density

In this work we studied the host–guest interactions between confined molecules and zeolites and their relationship with the energies involved in the reaction of methylation of benzene by methanol in H-ZSM-5 and H-Beta zeolites employing density functional theory (DFT) methods and the quantum theory of atoms in molecules. Results show that the strength of the interactions related to adsorption and coadsorption processes is higher in the catalyst with the larger cavity; however, the confinement effects are higher in the smaller zeolite, explaining, from an electronic viewpoint, the reason why the stabilization energy is higher in H-ZSM-5 than in H-Beta. The confinement effects of the catalyst on the confined species for methanol adsorption, benzene coadsorption, and the formed intermediates dominate this stabilization. For the transition state (TS), the stability of the TS is achieved due to the stabilizing effect of the surrounding zeolite framework on the formed carbocationic species (CH3+) which is highe...

Catalytic conversion of beech wood pyrolytic vapors

Catalytic fast pyrolysis (CFP) of beech wood chips was undertaken in a laboratory-scale fixed bed reactor equipped with a biomass semi-continuous dispenser. During pyrolysis, chars are retained on a quartz frit and the pyrolytic vapors are entrained through a fixed-bed catalyst to be converted. Several acidic catalysts such as zeolites H-Beta, zeolite HMFI and 5% Ni supported on HMFI were screened in this equipment. The Ni/HMFI catalyst was also tested in the presence of 1 vol.% of hydrogen in the feed stream. Mass and carbon balances were carefully checked and the gas, liquids and solids fractions were analyzed in-depth to evaluate the impact of the catalyst compared to thermal conversion. In the presence of a catalyst, with a low catalyst-to-biomass ratio of 0.1, a lower amount of bio-oil was formed but it contained less oxygen. The bio-oils were characterized by bi-dimensional GC (GCxGC) coupled with MS and FID detectors. The amount of gaseous products also increased in the presence of all catalysts. In addition of the deoxygenation, gel-permeation chromatography (GPC) showed a decrease of the highest molecular masses in the bio-oil after catalytic treatment, which confirms the conversion of some oligomers. The presence of Ni enhanced the deoxygenation reactions while the addition of H2 is also beneficial to the bio-oil composition.

Characterization of Different Si- and Al-based Catalysts with Pd Modification and Their Use for Catalytic Dehydration of Ethanol.

This study aims to investigate the production of ethylene and diethyl ether from ethanol via catalytic dehydration using Si- and Al-based catalysts with Pd modification. First, six catalysts including H-beta zeolite (HBZ), mixed phases of γ-χ-Al2O3 (M-Al) and γ-Al2O3 (G-Al) with and without Pd modification (0.5 wt%) were prepared. The catalytic dehydration of vaporized ethanol at temperature ranging from 200 to 400°C was performed over the catalysts. For ethylene production, the most promising catalyst is HBZ (giving ethylene yield of ca. 99% at 400°C), whereas Pd modification has no significant effect on ethylene production. Considering the production of diethyl ether, it is produced at lower temperature (ca. 250°C) than that of ethylene. The most active catalyst to produce diethyl ether is HBZ with Pd modification (giving diethyl ether yield of ca. 48% at 250°C). Thus, increased diethyl ether yield can be achieved with Pd modification at low temperature for the HBZ catalyst. Other catalysts such as M-Al and G-Al can also produce significant amounts of ethylene. To elucidate the effect of Pd modification on these catalysts, different characterization techniques such as nitrogen physisorption (BET and BJH methods), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and ammonia temperature-programmed desorption were performed and further discussed in more detail.

A strategy of ketalization for the catalytic selective dehydration of biomass-based polyols over H-beta zeolite

A strategy is presented to control the etherification site in sugar alcohols via ketalization of the terminal vicinal-diol group with a ketone.