Acidic ZSM-5 Zeolite Research Articles

Impacts of ball-milling on ZSM-5 zeolite properties and its catalytic activity in the two-phase glycerol ketalization with acetone

A series of acidic ZSM-5 zeolites were mechanically ball-milled for different periods and further applied as catalysts in the liquid-phase glycerol ketalization with acetone. Structural and textural characterizations showed that the samples had considerable crystallinity and micropore volume loss due to amorphization. On the other hand, due to a comminution effect, the external surface area increased and particle size reduced. TPD and FTIR analyses with probe molecules with different sizes, such as ammonia, pyridine (Py), and 2,6-di-tert-butylpyridine (DTBPy) chemisorbed on the catalyst acid sites, aided in quantifying the various levels of accessibility of chemicals. The treated materials lost acidity due to amorphization or blockage of pores, but the milling enabled higher accessibility of bulkier chemicals to acid sites, as revealed by the chemisorption of Py and DTBPy. A crucial balance of acidity, accessibility, and hydrophobicity was tailored by milling time. The one-hour grounded zeolite had a glycerol conversion 35 % greater than the pristine sample and 67 % greater than the eight-hour milled sample. The results showed that ball milling is a tool to improve the catalytic activity of zeolites with bulky chemicals by fine-tuning the milling time.

Oxidation of 1,2-diarylalkynes to 1,2-diketones on acidic mesoporous ZSM-5 supported palladium catalyst

1,2-diketones are important compounds in natural products and bioactive molecules. Current synthesis methods are involved the use of various environmentally hazardous additives and expensive organic ligands in homogeneous catalysis, which limited their practical application. Acidic mesoporous ZSM-5 zeolite supported palladium (Pd/HMZSM-5) was found to be able to transform 1,2-diarylalkynes to 1,2-diketones without any additives. The CC bond of 1,2-diarylalkyne coordinated with PdII sites to form a metal-π complex that was easily nucleophilic attacked by DMSO to form final product. The acidic sites on the catalyst can promote the adsorption and coordination of 1,2-diarylalkyne with PdII and improve the reaction activity.

Front Cover: Fine‐Tuning Texture of Highly Acidic HZSM‐5 Zeolite for Efficient Ethanol Dehydration (ChemCatChem 9/2023)

The Front Cover illustrates how different morphologies of highly acidic ZSM-5 zeolite control the product distribution of ethanol dehydration. In their Research Article, E. J. M. Hensen, C. Wattanakit and co-workers demonstrate that very thin nanolayers of this zeolite with a large external surface area and abundant mesopores enhance the ethylene yield up to 95% with a high longevity. In contrast, nanoplate and bulk structures of ZSM-5 result in low ethanol conversion, high selectivity to diethyl ether, and rapid deactivation. Reducing the crystal size of highly acidic zeolites to ultra-thin nanosheets can shorten the residence time of ethanol and its intermediates in the shape-selective environments, significantly suppressing the formation of coke precursors and achieving high and stable yield of the important chemical building block ethylene. More information can be found in the Research Article by E. J. M. Hensen, C. Wattanakit and co-workers.

Catalytic pyrolysis of olive mill wastes towards advanced bio-fuels and bio-chemicals using metal oxide catalysts

Among the environmental challenges that Mediterranean countries have to address are the abundant amounts of olive mill wastewater (OMWW) produced by olive oil agro-industry, such as those found in Greece and Tunisia, which lead to significant land and water pollution. The most common disposal method of olive mill wastewater, includes storage ponds, where most of the water is evaporated, while the residual sludge (olive mill wastewater sludge, OMWWS) is sent to landfills. Fast pyrolysis of OMWWS was investigated as an alternative approach of valorizing this waste, leading to the production of high heating value biofuel (bio-oil). Extraction of polyphenolic compounds with bioactive properties from OMWWS was additionally explored in order to provide further added value to OMWWS, considered as a source of bioactively important polyphenolic compounds, prior its use as pyrolysis feedstock towards the production of green fuel. Pyrolysis of the treated OMWWS (after extraction) led to a considerable reduction of the bio-oil yield, however in both cases the bio-oil produced exhibits a very interesting composition (predominance of aliphatic hydrocarbons and small fractions of aromatic hydrocarbons and phenols) and sufficiently low oxygen content. Exploring the effect of either an acidic (ZSM-5) or a basic (MgO) catalyst on the yield and composition of the bio-oil produced during the catalytic pyrolysis of OMWWS we observed that yield and quality of the produced bio-oils strongly depended on the catalyst used. Thus, acidic ZSM-5 zeolite catalyzed cracking and aromatization reactions, resulting in a bio-oil enriched in aromatics, while basic MgO catalyzed decarboxylation of fatty acids yielding a bio-oil composed mostly of aliphatic hydrocarbons. In addition, Co-promoted catalysts (5% Co either on ZSM-5 or MgO) led to additional variation of bio-oil quality, mostly enhancing ketonization reactions. The effect of a series of Fe and Mn oxide catalysts, based on alumina, silica and magnesia supports, was also studied for the catalytic pyrolysis of OMWWS, mainly focusing on using low-cost catalytic materials. In addition, ferric oxide, aluminum oxide, magnesium oxide, and silicon oxide, are among the major components of red mud, an effective catalyst used in the pyrolysis of OMWWS. All of these Fe- or Mn- materials exhibit very promising in situ upgrading of pyrolysis vapors (retaining organics’ yield and improving produced bio-oil). Most of these materials also tend to favor ketonization reactions, a more or less preferred route among the studied catalysts, which seems to mainly relate with their multifunctional (both acidic and basic) character.

Insights into structure–function relationships of mesoporous H-ZSM-5 zeolite catalysts for direct amination of cyclohexene with NH3

This work describes a novel strategy of employing Brønsted acidic ZSM-5 zeolites with meso–microporous architecture as a solid acid catalyst for direct amination of cyclohexene with NH3 to prepare cyclohexylamine.

Bifunctional zeolites-silver catalyst enabled tandem oxidation of formaldehyde at low temperatures

Bifunctional catalysts with tandem processes have achieved great success in a wide range of important catalytic processes, however, this concept has hardly been applied in the elimination of volatile organic compounds. Herein, we designed a tandem bifunctional Zeolites-Silver catalyst that enormously boosted formaldehyde oxidation at low temperatures, and formaldehyde conversion increased by 50 times (100% versus 2%) at 70 °C compared to that of monofunctional supported silver catalyst. This is enabled by designing a bifunctional catalyst composed of acidic ZSM-5 zeolite and silver component, which provides two types of active sites with complementary functions. Detached acidic ZSM-5 activates formaldehyde to generate gaseous intermediates of methyl formate, which is more easily oxidized by subsequent silver component. We anticipate that the findings here will open up a new avenue for the development of formaldehyde oxidation technologies, and also provide guidance for designing efficient catalysts in a series of oxidation reactions.

Lignin‐First Monomers to Catechol: Rational Cleavage of C−O and C−C Bonds over Zeolites

A catalytic route is developed to synthesize bio-renewable catechol from softwood-derived lignin-first monomers. This process concept consists of two steps: 1) O-demethylation of 4-n-propylguaiacol (4-PG) over acidic beta zeolites in hot pressurized liquid water delivering 4-n-propylcatechol (4-PC); 2) gas-phase C-dealkylation of 4-PC providing catechol and propylene over acidic ZSM-5 zeolites in the presence of water. With large pore sized beta-19 zeolite as catalyst, 4-PC is formed with more than 93 % selectivity at nearly full conversion of 4-PG. The acid-catalyzed C-dealkylation over ZSM-5 zeolite with medium pore size gives a catechol yield of 75 %. Overall, around 70 % catechol yield is obtained from pure 4-PG, or 56 % when starting from crude 4-PG monomers obtained from softwood by lignin-first RCF biorefinery. The selective cleavage of functional groups from biobased platform molecules through a green and sustainable process highlights the potential to shift feedstock from fossil oil to biomass, providing drop ins for the chemicals industry.

Ex-LDH-Based Catalysts for CO2 Conversion to Methanol and Dimethyl Ether

CO2-derived methanol and dimethyl ether can play a very important role as fuels, energy carriers, and bulk chemicals. Methanol production from CO2 and renewable hydrogen is considered to be one of the most promising pathways to alleviate global warming. In turn, methanol could be subsequently dehydrated into DME; alternatively, one-step CO2 conversion to DME can be obtained by hydrogenation on bifunctional catalysts. In this light, four oxide catalysts with the same Cu and Zn content (Cu/Zn molar ratio = 2) were synthesized by calcining the corresponding CuZnAl LDH systems modified with Zr and/or Ce. The fresh ex-LDH catalysts were characterized in terms of composition, texture, structure, surface acidity and basicity, and reducibility. Structural and acid–base properties were also studied on H2-treated samples, on which specific metal surface area and dispersion of metallic Cu were determined as well. After in situ H2 treatment, the ex-LDH systems were tested as catalysts for the hydrogenation of CO2 to methanol at 250 °C and 3.0 MPa. In the same experimental conditions, CO2 conversion into dimethyl ether was studied on bifunctional catalysts obtained by physically mixing the ex-LDH hydrogenation catalysts with acid ferrierite or ZSM-5 zeolites. For both processes, the effect of the Al/Zr/Ce ratio on the products distribution was investigated.

Understanding the Nanoconfinement Effect on the Ethanol-to-Propene Mechanism Catalyzed by Acidic ZSM-5 and FAU Zeolites

We have carried out a two-layer our own n-layered integrated molecular orbital and molecular mechanics (MM) study on the mechanism of ethanol to propene on H-ZSM-5 and H-FAU zeolites. The entire me...

The effect of active site distribution in bi-functional Pt-zeolite catalysts for ethane dehydroaromatization

The direct conversion of ethane to higher-valued petrochemical feedstock such as benzene, toluene and xylenes (BTX) has become more economically attractive because of the recent shale gas revolution. The selectivity towards BTX and catalyst deactivation represent significant technical challenges in this process. In this work, we synthesized a series of bi-functional Pt on acidic ZSM-5 catalysts to investigate the effect of platinum nanoparticle distribution and location on selectivity and deactivation. The best catalyst was Pt encapsulated in desilicated ZSM-5 that remained stable after 15 h of reaction resulting in 60% higher conversion and 75% higher BTX selectivity than Pt supported on conventional acidic ZSM-5 zeolite.

Cascade Deoxygenation Process Integrating Acid and Base Catalysts for the Efficient Production of Second-Generation Biofuels

An innovative cascade deoxygenation concept coupling the thermal pyrolysis of lignocellulose with two consecutive (acidic and basic) catalytic beds in a single reactor has been developed. Thereby, thermal pyrolysis vapors produced by pyrolysis of acid-washed wheat straw have been upgraded by combining an acidic ZrO2-supported ZSM-5 zeolite and a basic K-grafted USY zeolite, both being prepared in technical form by extrusion with attapulgite binder. Investigation of the different coupling alternatives has shown that the most efficient strategy relies on passing the pyrolysis vapors first by the acid catalyst followed by the basic one in a fixed-bed reactor arrangement. In this way, an enhanced degree of bio-oil deoxygenation is achieved since the K/USY catalyst promotes the occurrence of both aldol condensation and ketonization reactions, thus leading to further bio-oil upgrading by removal of oxygen in the form of CO2 and H2O while affording the formation of C–C bonds. Moreover, this second basic catalyst promotes the further conversion of the oligomers still present in the bio-oil. Accordingly, the sequential integration of the two catalytic systems leads to a clear synergetic effect, improving the efficiency of the bio-oil deoxygenation process and affording the production of liquid organic fractions with oxygen content as low as 12 wt % and energy yield of 32% regarding the raw lignocellulosic biomass.

Activation of Mo and V oxides supported on ZSM-5 zeolite catalysts followed by in situ XAS and XRD and their uses in oxydehydration of glycerol

This paper describes the activation and catalytic performance of a multifunctional catalyst consisting of mixed oxides of vanadium and molybdenum supported on an acidic ZSM-5 zeolite. The zeolite was wet-impregnated with an aqueous solution containing a mixture of NH4VO3 and (NH4)6Mo7O24 precursors at a V/(Mo+V) molar ratio of 0.6. Evolution of the phases during activation (by calcination under 20% O2/He) was followed by synchrotron X-ray diffraction (XRD), but detection of mixed oxides of MoxVyOz was difficult, due to the high degree of dispersion on the zeolite surface. On the other hand, X-ray absorption spectroscopy (XAS) performed simultaneously at the Mo and V K-edges enabled confirmation of formation of the MoV2O8 phase on the acidic ZSM-5 zeolite. The combination of the MoV2O8 phase and the zeolite acid sites produced a highly active catalyst for gas phase glycerol dehydration-oxidation coupled reactions in which acrylic acid was the main product. The multifunctional catalyst presented only 6% of deactivation during a period of 8 h under glycerol stream, while the activities of the bulk mixed oxide and the pure ZSM-5 zeolite decreased by almost 20 and 31%, respectively.

Catalytic fast pyrolysis of biomass over Mg-Al mixed oxides derived from hydrotalcite-like precursors: Influence of Mg/Al ratio

In this work we examine a series of Mg-Al mixed oxides derived from hydrotalcite-like precursors prepared with different Mg/Al ratios i.e. Mg/Al = 2, 3, and 4, as catalysts for the catalytic fast pyrolysis (CFP) of wheat straw. Characterization of the Mg-Al mixed oxides by N2 adsorption, X-ray diffraction and CO2 temperature programmed desorption revealed a decrease in the surface area and a higher number and proportion of basic sites corresponding to an increase in the Mg concentration in the hydrotalcite precursors. The Mg-Al mixed oxides derived from hydrotalcite precursors are active materials for the catalytic fast pyrolysis of biomass. The removal of oxygen during the catalytic fast pyrolysis of biomass over the Mg-Al-mixed oxides depends on their Mg/Al ratio, and an increase in gas production with a strong improvement in the decarboxylation capacity as the Mg concentration in the mixed oxides decreased, was observed. The Al-Mg mixed oxide catalyst with the lowest Al concentration (Mg/Al = 4.0) maintained the deoxygenation and bio-oil energy yield at levels comparable to those achieved over an acidic ZSM-5 zeolite widely used in the CFP of biomass. A moderate increment in ketone formation for the catalyst with Mg/Al = 4.0 suggests that these basic materials promote the aldol condensation and ketonization of pyrolytic compounds by removing the oxygen in the form of H2O and CO2.

Cultivation, characterization, and properties of Chlorella vulgaris microalgae with different lipid contents and effect on fast pyrolysis oil composition.

A systematic study of the effect of nitrogen levels in the cultivation medium of Chlorella vulgaris microalgae grown in photobioreactor (PBR) on biomass productivity, biochemical and elemental composition, fatty acid profile, heating value (HHV), and composition of the algae-derived fast pyrolysis (bio-oil) is presented in this work. A relatively high biomass productivity and cell concentration (1.5g of dry biomass per liter of cultivation medium and 120 × 106 cells/ml, respectively) were achieved after 30h of cultivation under N-rich medium. On the other hand, the highest lipid content (ca. 36wt.% on dry biomass) was obtained under N-depletion cultivation conditions. The medium and low N levels favored also the increased concentration of the saturated and mono-unsaturated C16:0 and C18:1(n-9) fatty acids (FA) in the lipid/oil fraction, thus providing a raw lipid feedstock that can be more efficiently converted to high-quality biodiesel or green diesel (via hydrotreatment). In terms of overall lipid productivity, taking in consideration both the biomass concentration in the medium and the content of lipids on dry biomass, the most effective system was the N-rich one. The thermal (non-catalytic) pyrolysis of Chlorella vulgaris microalgae produced a highly complex bio-oil composition, including fatty acids, phenolics, ethers, ketones, etc., as well as aromatics, alkanes, and nitrogen compounds (pyrroles and amides), originating from the lipid, protein, and carbohydrate fractions of the microalgae. However, the catalytic fast pyrolysis using a highly acidic ZSM-5 zeolite, afforded a bio-oil enriched in mono-aromatics (BTX), reducing at the same time significantly oxygenated compounds such as phenolics, acids, ethers, and ketones. These effects were even more pronounced in the catalytic fast pyrolysis of Chlorella vulgaris residual biomass (after extraction of lipids), thus showing for the first time the potential of transforming this low value by-product towards high added value platform chemicals.

Brönsted and Lewis acid ZSM-5 zeolites for the catalytic dehydration of glucose into 5-hydroxymethylfurfural

Three different acid ZSM-5 zeolites (H-, Fe- and Cu-ZSM-5) have been prepared and tested in the catalytic dehydration of glucose into 5-hydroxymethylfurfural (HMF). A commercial NH4-ZSM-5 zeolite (MFI) was modified by thermal or ion-exchange treatments in order to create Brönsted and Lewis acid sites. The zeolitic structure is preserved, and the resulting acid zeolites have demonstrated to be active in the glucose dehydration. The influence of different experimental variables, such as reaction time and temperature, substrate:catalyst molar ratio, volume of the organic solvent and aqueous phase, as well as the density and nature of acid sites, on the catalytic behaviour was investigated. Under the optimal reaction conditions, by using a biphasic NaCl (20wt%) aqueous solution/methyl isobutyl ketone (MIBK) system, a glucose conversion of 80% and a HMF yield of 42% were achieved at 195°C, after only 30min, using H-ZSM-5, which has the lowest Lewis/Brönsted molar ratio among the prepared zeolites. The reutilization of this catalyst was also examined.

Insights into the reaction mechanism of propene H/D exchange over acidic zeolite catalysts from theoretical calculations

The reaction mechanisms of propene H/D exchange over deuterated acidic ZSM-5 zeolite have been theoretically revealed.

Pyrolysis and catalytic pyrolysis as a recycling method of waste CDs originating from polycarbonate and HIPS

Pyrolysis appears to be a promising recycling process since it could convert the disposed polymers to hydrocarbon based fuels or various useful chemicals. In the current study, two model polymers found in WEEEs, namely polycarbonate (PC) and high impact polystyrene (HIPS) and their counterparts found in waste commercial Compact Discs (CDs) were pyrolysed in a bench scale reactor. Both, thermal pyrolysis and pyrolysis in the presence of two catalytic materials (basic MgO and acidic ZSM-5 zeolite) was performed for all four types of polymers. Results have shown significant recovery of the monomers and valuable chemicals (phenols in the case of PC and aromatic hydrocarbons in the case of HIPS), while catalysts seem to decrease the selectivity towards the monomers and enhance the selectivity towards other desirable compounds.

Catalytic synthesis of 2,5-bis-methoxymethylfuran: A promising cetane number improver for diesel

Efficient hydrogenation of 5-hydroxymethylfurfural (HMF) into 2,5-bis-hydroxymethylfuran (BHMF) was performed using a Cu/SiO2 catalyst, obtaining as high as 97% BHMF yield. In the presence of acidic ZSM-5 zeolite (HZSM-5), the synthesized BHMF further reacted with methanol, leading to 70% yield of corresponding 2,5-bis-methoxymethylfuran (BMMF). The target product BMMF was an excellent cetane number improver for diesel, proved by its cetane number of 80 (much higher than that of the commercial diesel), high flash point (90°C) and low cold filter plugging point (<−37°C).

Abatement of hydrocarbons by acid ZSM-5 and BETA zeolites under cold-start conditions

Simulated cold-start tests have been carried out to evaluate the performance of H-ZSM-5 and H-BETA zeolites as hydrocarbon traps under simulated gasoline car exhaust gases, paying special attention to the effect of water on their behaviour. It is concluded that the hydrothermal treatment of the zeolites in the acidic form contributes to the better performance of these materials as hydrocarbon traps since the stabilization of the zeolites takes place. Moreover, the decrease of the surface acidity of the zeolites results in an increase of the Si/Al ratio, which contributes to the decrease of the water affinity for adsorption sites. Thus, the competition with hydrocarbon molecules in the exhaust for the adsorption sites is reduced which increases their trap efficiency. The stabilized H-ZSM-5 is the zeolite that showed the best performance with a propene offset temperature of 240 °C, which should be high enough for the three-way catalyst to carry out its role as catalytic converter.

Extended activity of zeolite catalysts with CO2 as reaction medium

Isooctane is a typically used vehicle fuel component. However, the synthesis of isooctane is limited due to the coking phenomenon when using zeolite catalysts. In this paper the suitability of CO2 as a solvent for zeolite based acid catalytic reactions was studied in general and isobutene dimerization in particular. The special focus of this study was to clarify whether using CO2 as a solvent reduces coking compared to propane, which was used as a reference solvent in this case. The reaction was carried out in a 50cm3 continuous stirred tank reactor with two solid acid catalysts, ZSM-5 and ZSM-23 zeolites. Besides the desired dimerization reaction, the oligomerization reaction was also considered. The study also includes determination and discussion on phase conditions. Calculations based on thermodynamic methods show that the reaction phase may change during the experiment from a single phase (liquid, gas or supercritical) to a two phase domain (coexistence of vapor and liquid). Experiments with the ZSM-23 catalyst gave initial isobutene conversion of above 80%. The conversion with CO2 was approx. 56% after ∼200h whereas with propane it was approx. 32% after about 120h. These results were similar also over the ZSM-5 catalyst. The reduced coking tendency results in lower carbon dioxide emissions as the need for burning off the coke in catalyst regeneration is decreased. The results show that carbon dioxide is a potential solvent for industrial purposes as it prolongs the catalyst activity due to a reduced coking tendency.