Acid Sites Of ZSM-5 Research Articles

Production of Jet Fuel Range Aromatics by Alkylation of Benzene with Olefins over Bifunctional Ga/ZSM-5 Catalyst.

Aromatic components of C8-C15 are playing indispensable roles in multi-functional properties of jet fuel. Here, we reported the controllable alkylation of benzene with mixed olefins of ethylene and propylene toward C8-C15 aromatic hydrocarbons for jet fuels over the bifunctional Ga/ZSM-5 catalyst. The resultant 2Ga/ZSM-5 exhibited a superior selectivity of 86.4% (yield of 55.5%) to C8-C15 range aromatics, at benzene conversion of 40.3%, ethylene and propylene conversion of 99.5% and 99.2%, respectively. The incorporation of Ga species could effectively weaken the strong acid sites of ZSM-5 and endow 2Ga/ZSM-5 catalyst with appropriate acidity, therefore facilitating the benzene alkylation process and suppressing the undesired hydrogen transfer or aromatization side reactions as well, thus improving the yield of desired C8-C15aromatics for jet fuels. This work provided insight into the development of promising bifunctional catalyst for the oriented transformation of biomass-derived chemicals to aviation fuels.

Response of Hydrogen-Bonded Brønsted Acid Sites in ZSM-5 to Adsorption and H/D Exchange of Hydrocarbons

Response of Hydrogen-Bonded Brønsted Acid Sites in ZSM-5 to Adsorption and H/D Exchange of Hydrocarbons

Aromatics production from catalytic pyrolysis of waste cassava residue using La and P modified ZSM-5: Experimental and kinetic study

In the present study, selective transformation of waste cassava residues into aromatics via catalytic pyrolysis over as-prepared La and P modified ZSM-5 was systematically investigated, especially in the aspects of product regulation and kinetic analysis. Comprehensive physicochemical characterizations were undertaken for unveiling the essential structural properties of La and P modified ZSM-5. The introduction of La and P species significantly enriched the Lewis and Brønsted acid sites in ZSM-5, thus facilitating the directional pyrolysis of waste cassava residues into aromatics. Higher apparent activation energy for aromatics formation from waste cassava residues pyrolysis in the presence of La and P modified ZSM-5 might be due to the fact that the catalytic pyrolysis belonged to diffusion-controlled gas-solid reaction. In comparison with that of the parent ZSM-5, LaP2/ZSM exhibited better performance towards aromatics formation in waste cassava residues pyrolysis, wherein the relative content of aromatics reached 83.3% at a temperature of 650 °C. Gratifyingly, the relative content of aromatics was increased to 90.5% for the catalytic pyrolysis of acid pretreated cassava residue, in the case of LaP1/ZSM catalyst.

Boosting diethylamine selective oxidation over CuO/ZSM-5 catalyst by CeO2 modification

Selective catalytic oxidation of nitrogen containing volatile organic compounds (NVOCs) is very meaningful but still remains big challenge because it is very difficult to balance the oxidation activity and N2 selectivity of available catalysts. In order to develop excellent catalysts with high N2 selectivity in wide temperature window (△T) during NVOCs oxidation, CeO2 modified CuO/ZSM-5 catalysts with different CeO2 addition order were prepared for diethylamine (DEA) oxidation. Detailed characterizations of catalysts such as XRD, XPS, H2-TPR and NH3-TPD were conducted, it is found that addition of CeO2 obviously changes the geometrical and electronic states of CuO active sites in the catalyst, and CeO2 addition order affects the Ce3+ ratio on the catalyst surface. Promotion of CeO2 species enables the generation of more highly active Cu species (Cu+ species and finely dispersed CuO clusters) for DEA oxidation; and synergistic catalysis of the Ce3+ species, active Cu species and acid sites in ZSM-5 leads to the high N2 selectivity in wide temperature window (△T). Compared to the CeO2/CuO/ZSM-5 and CuO-CeO2/ZSM-5 catalysts, the CuO/CeO2/ZSM-5 catalyst exhibits moderate high oxidation activity with T99 of 230 °C and the widest △T of 150 °C for high N2 selectivity. Our primary results in this work provide the efficient strategy for improving catalyst employed for NVOCs selective oxidation.

Synergistic Effect of ZSM-5 Zeolite in Pt–CeO2–TiO2/ZSM-5 Catalysts for Highly Efficient Catalytic Oxidation of VOCs

A series of Pt–CeTi/ZSM-5 catalysts (0.5 wt % Pt) with different CeO2–TiO2/ZSM-5 mass ratios were synthesized and used for the catalytic oxidation of 1,2-dichloroethane and benzene. The results reveal that the strong Pt/CeO2–TiO2 interaction can be evidently enhanced by introducing proper amounts of CeO2–TiO2 mixed oxides, resulting in the improvement of Pt dispersion and redox properties as well as the production of more defective oxygen and Pt2+ species. The synergistic effect between abundant ZSM-5 acid sites (especially strong acid sites) and strong Pt/CeO2–TiO2 oxidizing sites facilitates the deep oxidation of benzene, intermediates, and byproducts generated from the 1,2-dichloroethane oxidation process at lower temperature. Among the catalysts, Pt–CeTi/ZSM-5(1/10) with the CeO2–TiO2/ZSM-5 mass ratio of 1/10 exhibits the greatest activity for benzene and 1,2-dichloroethane oxidation, showing the T90% of 145 and 245 °C, respectively. Moreover, the catalyst also possesses satisfactory adaptability for the oxidation of various VOCs and durability for 1,2-dichloroethane oxidation.

Sustainable Aromatic Production from Catalytic Fast Pyrolysis of 2-Methylfuran over Metal-Modified ZSM-5

The catalytic fast pyrolysis (CFP) of bio-derived furans offers a promising approach for sustainable aromatic production. ZSM-5 modified by different metal species (Zn, Mo, Fe, and Ga) was employed in the CFP of bio-derived furans for enhancing aromatic production. The effects of metal species, metal loadings, and the weight hourly space velocity (WHSV) on the product distributions from the CFP of 2-methylfuran (MF) were systemically investigated. It is found that the introduction of Zn, Mo, Fe, and Ga on ZSM-5 significantly increases the MF conversion and aromatic yields. The maximum MF conversions of 75.49 and 69.03% are obtained, respectively, by Fe-ZSM-5 and Ga-ZSM-5, which boost the aromatic yield by 34.5 and 42.7% compared to ZSM-5. The optimal loading of Fe on ZSM-5 is 2%. Additionally, the highest aromatic yield of 40.03% is achieved by 2%Fe-ZSM-5 at a WHSV of 2 h−1. The catalyst characterization demonstrates that the synergistic effect of Brønsted and Lewis acid sites in Fe-ZSM-5 is responsible for achieving the efficient aromatization of MF. The key to designing improved zeolite catalysts for MF aromatization is the introduction of large numbers of new Lewis acid sites without a significant loss of Brønsted acid sites in ZSM-5. These findings can provide guidelines for the rational design of better zeolite catalysts used in the CFP of biomass and its derived furans.

Enhancing high selectivity production of light aromatics from in-situ catalytic upgrading of cellulose pyrolysis vapors by regulating hierarchical core-shell ZSM-5@MCM-41

The catalytic upgrading of cellulose pyrolysis vapors is one of the effective methods to realize its high value utilization. Tuning the pore structure and acid sites of ZSM-5 (Z5) is a necessary strategy to develop effective catalysts for the production of light aromatics and the inhibition of carbon formation. In this study, a core-shell structure ZSM-5 @MCM-41 was developed and used for the first time in catalytic fast pyrolysis (CFP) of cellulose to prepare light aromatic hydrocarbons. The successful synthesis of the hierarchical core-shell ZSM-5 @MCM-41 was confirmed by nitrogen physisorption, X-ray diffraction (XRD), and transmission electron microscope (TEM) analysis. In aromatic hydrocarbon production, 1.0SH-Z5 @ M41 (1.0 mol/L, ZSM-5 @MCM-41) has the highest relative content of 98.76%. The relative content of BTEX (benzene, toluene, ethylbenzene, and xylene) is up to 89.83%, which is 2.39 times that of traditional microporous Z5. The quadratic polynomials were developed to correlate the Brønsted-to-Lewis acid site strength ratio (BLR) and mesopore-to-micropore volume ratio (MMR) with the relative content of BTEX. The mechanism of in-situ catalytic upgrading of cellulose pyrolysis vapor over ZSM-5 @MCM-41 was revealed. Due to high selectivities and low coke formation, ZSM-5 @MCM-41 offers an improved option for making monocyclic aromatics from cellulosic biomass.

Modulating multi-active sites in CeO2-modified MnOx/ZSM-5 catalyst for selective catalytic oxidation of diethylamine

An efficient MnOx/CeO2/ZSM-5 catalyst was developed for selective oxidation of diethylamine (DEA) with high N2 selectivity in a wide temperature window (ΔT = 140 °C), owing to the existence of oxidation and selective catalytic reduction (SCR) active sites. MnOx species prefer to locate on the surface of CeO2 compared to ZSM-5, and the presence of CeO2 is beneficial to form more Mn4+ species, the active sites for oxidation reaction. The mechanistic investigation suggests that internal SCR of NOx generated from the over-oxidized DEA is the crucial pathway for N2 generation. The high SCR activity of the MnOx/CeO2/ZSM-5 catalyst in oxidation conditions is mainly attributed to the synergistic catalysis of Mn4+ species and acid sites of ZSM-5, the active sites for SCR reaction. Thus, it has been clearly clarified that addition of CeO2 and its addition sequence could modulate the surface active sites of MnOx/ZSM-5 catalyst for the selective catalytic oxidation of DEA.

Tailoring Co3O4 active species to promote propane combustion over Co3O4/ZSM-5 catalyst

Co3O4 species in Co3O4/ZSM-5 catalyst can be tailored to smaller particle size and higher content of surface lattice O2− and Co3+ species by pre-reduction and pre-oxidation (labeled as Co3O4/ZSM-5-A catalyst), resulting in the enhanced catalytic activity for propane combustion. The 25Co3O4/ZSM-5-A catalyst gives a high reaction rate of 0.379 μmol gcat−1 s−1, which is over two folds higher than that of the 25Co3O4/ZSM-5 catalyst (reaction rate of only 0.177 μmol gcat−1 s−1). The higher content and reducibility of surface lattice O2− in the Co3O4/ZSM-5-A catalyst facilitated its activity for propane combustion through the Mars-Van Krevelen mechanism as evidenced by in-situ diffuse reflectance infrared spectra. The 25Co3O4/ZSM-5-A catalyst (Ea = 37.1 ± 2.9 kJ mol−1) gives much lower apparent activation energy than 25Co3O4/ZSM-5 catalyst (Ea = 85.5 ± 6.7 kJ mol−1), suggesting the easier occurrence of propane combustion over the 25Co3O4/ZSM-5-A catalyst. The atmospheres (2% O2 + 0.2% C3H8 + N2; 9% O2 + 0.2% C3H8 + N2; Air) for pre-oxidation process also significantly affect the catalytic activity of the finally obtained catalysts (labeled as 25Co3O4/ZSM-5-A, 25Co3O4/ZSM-5-B, 25Co3O4/ZSM-5-C), which is attributed to their differences in Co3O4 species (nanoparticle size, and the content of surface lattice O2− and Co3+). Besides, the acid sites of ZSM-5 also play important role on the catalytic combustion propane.

Precisely regulating acid density and types to promote the stable two-step conversion of methanol to aromatics via light hydrocarbons

Acidic properties of ZSM-5 zeolites for the aromatization of light hydrocarbons strongly determined the final catalytic selectivity and stability for two-step methanol conversions of aromatics via light hydrocarbons. Herein, the density and types of acid sites of ZSM-5 were precisely adjusted to explore their influences on the final catalytic performance. Different from the indistinctive effect of SiO2/Al2O3 ratios on traditional one-step methanol conversion to aromatics, decreasing acid density by increasing SiO2/Al2O3 ratios from 36 to 70 decelerated coke formation and significantly extended the catalytic lifetime from 46.5 to 190.8 h. Further modification with low Zn loading decreased B/L ratio from 19.0 to 1.7 and established a good catalytic synergy between Zn-Lewis and Brønsted acid sites for aromatization of light hydrocarbons, which increased the aromatics selectivity from 27.5% to 31.4%. The decreased catalytic stability after introducing Zn species was attributed to the coke coverage on acid sites but not the final blockage of pore channels as mentioned in previous studies, which was indicated by the similar coke rate of the deactivated catalyst and their gradually increased surface area with increasing Zn content. This work provides more insights into the regulation of acid properties for aromatization catalyst to boost the conversion of methanol to aromatics.

Simultaneous production of aromatics-rich bio-oil and carbon nanomaterials from catalytic co-pyrolysis of biomass/plastic wastes and in-line catalytic upgrading of pyrolysis gas

An integrated process that includes catalytic co-pyrolysis of biomass/plastic wastes and in-line catalytic upgrading of pyrolysis gas were conducted to simultaneously produce aromatics-rich bio-oil and carbon nanotubes (CNTs). The influences of feedstocks blending ratio on the characteristics of bio-oil and CNTs were established. The reaction mechanism of carbon deposition during the system was also probed. The results showed that co-feeding plastic to biomass siginificantly enhanced the selectivity of monoaromatics (benzene, toluene, and xylene) from 5.6% for pure biomass to the maximum yield of 44.4% for 75.0% plastic ratio, and decreased naphthalene and its derivates from 85.9 to 41.7% correspondingly. The most synergistic effect on BTX selectivity occurred at 25% of plastic ratio. The multi-walled CNTs were successfully synethsized on Ni catalyst by utilizing prolysis gas as feedstocks. For pure biomass, the least CNTs yield with ultrafine diameters of 3.9–8.5 nm was generated via disproportionation reaction of CO which was derived from decarboxylation and decarbonylation of oxygenates on the ZSM-5 acid sites. With the rise of plastic ratio, sufficient hydrocarbons were produced for CNTs growth, endowing CNTs with long and straight tube walls, along with uniform diameters (~16 nm). The CNTs yield increased as high as 139 mg/g-cata. In addition, the decreased CO2 inhibited dry reforming with C1-C4 hydrocarbons and deposited carbon, avoiding excessive etching of CNTs. Thereby, high-purity CNTs with less defects were fabricated when plastic ratio was beyond 50% in the feedstock. The strategy is expected to improve the sustainability and economic viability of biomass pyrolysis.

Tuning of Magnesium Distribution in ZSM-5 via Different Impregnation Methods and Its Effect on Methanol to Propene Reaction

Two modified zeolites, ZSM-5-Mg(OH)2 and ZSM-5-Mg(NO3)2, were achieved by Mg(NO3)2 impregnation methods with or without NH3·H2O as a precipitator, respectively. The Bronsted acid sites of ZSM-5 can...

An ONIOM Study of Catalytically Active Brønsted Acid Sites of ZSM-5

An ONIOM Study of Catalytically Active Brønsted Acid Sites of ZSM-5

Role of Brønsted acid site during catalytic combustion of methane over PdO/ZSM-5: Dominant or negligible?

ZSM-5 zeolites (NaZSM-5, HZSM-5 and Silicalite-1) with different acid nature were synthesized and used as supports of Pd catalysts for catalytic combustion of methane. Moreover, the acid property of the as-synthesized Pd/NaZSM-5 catalyst was adjusted by a NH4+ ion-exchange process to post-generate Brønsted acid sites and different preparation methods were investigated. The potential roles of Brønsted acid sites (anchoring Pd species or activating methane molecules) were discussed, and the experimental results indicated that the anchoring effect of Brønsted acid sites on Pd species was not directly observed. However, the acid properties of supports (the presence of Al3+ as Lewis acid sites, especially coordinatively unsaturated Al3+) were crucial for the preparation of Pd/ZSM-5 catalysts with high Pd dispersion. Additionally, although Brønsted acid sites of ZSM-5 was contributed to the activation or even cracking of long-chain alkanes (such as n-decane), the direct adsorption/dissociation of methane on Brønsted acid sites was difficult and depended more on the dispersion and particle size of PdOx. Pd/NaZSM-5 catalyst presented an outstanding durability at low-temperature (350 °C) and high-temperature (800 °C), and the high Si/Al ratio could improve the water-resistance due to its good hydrophobicity, but the reversible deactivation owing to the formation of PdO into Pd(OH)2 under high concentration of water vapor was still unavoidable.

Zeolite Supported Bimetallic Catalyst System: The Effect of Metal Loading for Catalytic Pyrolysis of Jatropha Residue

Two transition metals were loaded on H-ZSM-5 zeolite to produce bimetallic zeolite supported catalysts for catalytic pyrolysis reaction. Ni and Co metal were loaded on H-ZSM-5 via wet impregnation method. The loading sequence was applied using one-step and two-step loading method. The different loading sequence affect surface properties of catalyst and catalytic activity in pyrolysis reaction. The bimetallic catalysts were prepared at Ni+Co metal loading content of 10+10 wt% (Ni:Co=1:1) to 10+20 wt% (Ni:Co=1:2 or 2:1). All bimetallic catalysts supported on H-ZSM-5 were calcined and characterized by X-ray Diffraction (XRD), Surface area analysis (BET) and Temperature Programmed Desorption of ammonia (NH3-TPD). The XRD patterns of bimetallic zeolite supported catalysts revealed that loading of two metals at high content affect crystalline structural of ZSM-5 support. All XRD patterns illustrated peaks characteristic of ZSM-5, cobalt oxide and nickel oxide. The NH3-TPD results showed number of acid sites of the catalyst which revealed that the acid sites of ZSM-5 support was weakened with transition metal added. The two-step loading of 10+20 wt% metals on ZSM-5 reduced the peak intensities of NH3 desorption due to the metal particles aggregate on acid sites of ZSM-5. The two-step 10+20 wt% bimetallic catalysts has the lowest surface acidity, followed by the one-step 10+20 wt%, the two-step 10+10 wt% and the one-step 10+10 wt% bimetallic catalysts, respectively. Jatropha residue was used for catalytic pyrolysis study. Jatropha residue and bimetallic catalyst was pyrolyzed at 500 °C in a pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The product vapor was analyzed by GC/MS for the different groups of organic products such as fatty acid, aldehydes, ketones, aliphatic hydrocarbons, aromatic hydrocarbons and nitrogen compounds. The product from catalytic pyrolysis of jatropha residue with bimetallic zeolite supported catalysts enhance deoxygenation reaction that resulted in high aliphatic and aromatic hydrocarbons product. The one-step loading at ratio Ni:Co = 1:1 (10+10 wt%) gave the highest hydrocarbons product yield at 57.81%.

Conversion of propionic acid and 3-pentanone to hydrocarbons on ZSM-5 catalysts: Reaction pathway and active site

Conversion of propionic acid to gasoline-range molecules was investigated at 350°C on a series of ZSM-5 catalysts with varying density of Brønsted acid sites (BAS), achieved by ion exchange of proton with Na+. Ketonization of propionic acid to 3-pentanone is the primary reaction, with the sequential aldol condensation to dipentanone alcohol being the secondary. The major reaction pathway for forming the aromatics involves dehydration, cyclization, dehydration and hydride transfer from dipentanone alcohol, leading to the formation of C10 aromatics before being dealkylated to lighter aromatics. Temperature programmed desorption of propionic acid indicates that the reaction initiates with acylium cation formation on BAS through dehydration. Comparing the turnover frequencies of ketonization and aldol condensation on ZSM-5 with varying density of BAS indicates that BAS is the active site for both reactions. The propionic acid feed deactivates the catalyst faster than the 3-pentantone feed due to a stronger adsorption of propionic acid on the acid sites of ZSM-5.

Enhanced catalytic performance in butylene cracking by hierarchical surface silicon-rich ZSM-5

In the process of butylene catalytic cracking, the amount, location and strength of acid sites of the catalyst play an important role in suppressing the undesired reactions. Hydrothermal dealumination is widely used to adjust the acidity of catalyst. Also, the steaming treatment has a significant impact on the physico-chemical properties of the catalyst, such as leading to mesoporosity at the perimeter of zeolite crystals through dealumination process. The mesoporosity is beneficial to long working life-span of catalyst, while it can increase the external surface acid sites of ZSM-5, subsequently resulting in non-shape selective catalytic reactions on the external surface of the catalyst. Coke and large-molecular hydrocarbons or intermediates can be produced relatively easily at external surface acid sites because of the absence of spatial constraints. The external acid sites of catalyst can be deactivated through chemical liquid deposition of SiO2 onto the surface of catalyst using the tetramethoxysilane (TMOS) as silica source. Combing hydrothermal treatment and TMOS modification, a hierarchical surface silicon-rich ZSM-5 zeolite without pore-opening narrowed was prepared. Compared with the catalytic performance of untreated catalyst, this new catalyst has achieved a high total yield of propylene and ethylene and showed excellent hydrothermal stability. Side reactions and coking were restrained simultaneously during the butylene cracking process.

Microwave-assisted catalytic fast pyrolysis of spent edible mushroom substrate for bio-oil production using surface modified zeolite catalyst

In order to minimize coke yield and improve hydrocarbon production during microwave-assisted catalytic fast pyrolysis of spent edible mushroom substrate, ZSM-5 zeolite catalyst is modified with pre-coking treatment, chemical vapor deposition of SiO2, and ethylene diamine tetraacetie acid (EDTA) chemical modification method, respectively (labeled PC-ZSM-5, SiO2-ZSM-5 and EDTA-ZSM-5). Experimental results show that all the modification methods result in a loss of external acid sites of ZSM-5. Among the three modified catalysts, the maximum oil fraction yield and the minimum coke yield are obtained with SiO2-ZSM-5. The relative content of hydrocarbons in oil fraction increases in the following order: SiO2-ZSM-5>EDTA-ZSM-5>PC-ZSM-5>original ZSM-5. Moreover, SiO2-ZSM-5 shows the highest relative contents of toluene and xylene, whereas original ZSM-5 produces the lowest ones. Besides, the selectivity of benzene in aromatics follows the order of original ZSM-5>EDTA-ZSM-5>PC-ZSM-5>SiO2-ZSM-5, while the selectivity of toluene+xylene presents the opposite trend.

The role of external acid sites of ZSM-5 in deactivation of hybrid CuZnAl/ZSM-5 catalyst for direct dimethyl ether synthesis from syngas

Direct synthesis of dimethyl ether (DME) from syngas was investigated on a series of hybrid Cu–ZnO–Al2O3/ZSM-5 catalysts prepared by kneading. It was found that the initial performance of the catalysts was a function of both zeolite crystallite sizes and Si/Al ratio. The activity of the hybrid catalysts gradually decreased with time on stream because of simultaneous copper sintering, copper oxidation and ion exchange with zeolite hydroxyl groups. Copper sintering led to the decrease in the number of metal active sites, while ion exchange of Cu2+ ions with the hydroxyl groups of the zeolite resulted in lower concentration of acid sites for methanol dehydration. Copper sintering and ion exchange could be slowed down by selective neutralization of the acid sites on the zeolite outer surface by silylation. Both catalyst stability and dimethyl ether productivity were significantly improved.

Modification of acid sites in ZSM-5 by ion-exchange: An in-situ FTIR study

A study of the acid sites in Mn+-ZSM-5 zeolites (Mn+=H+, Al3+, Ca2+, and Ba2+), synthesized by ion-exchange from the NH4+ form, has been carried out using X-ray diffraction, 27Al MAS NMR, and in-situ FTIR spectroscopy. X-ray diffraction data indicate that the crystalline structure of ZSM-5 is maintained on ion-exchange. 27Al MAS NMR spectroscopy confirms that Lewis acid sites in all of the Mn+-ZSM-5 zeolites are mainly located on the tetrahedral aluminum atoms in the zeolite framework. However, octahedral extra-framework aluminum is another source of Lewis acid sites in H+-ZSM-5 and Al3+-ZSM-5. Brønsted acid sites are identified as originating from the hydroxyl groups that bridge Al and Si atoms. The acid sites in Mn+-ZSM-5 have been characterized by in-situ FTIR spectroscopy with pyridine as the probe molecule. FTIR spectroscopy demonstrated that the number of accessible acid sites and ratio of Lewis to Brønsted acid sites in Mn+-ZSM-5 can be effectively modified by ion-exchange. The number of acid sites in Mn+-ZSM-5 increases in the same order as the acidity of cations with Ba2+<Ca2+<NH4+<Al3+<H+. Though the strength of both Lewis and Brønsted acid sites is virtually identical for all Mn+-ZSM-5 zeolites, the ratio of Brønsted to Lewis acid sites varies as a result of the loaded cation. In addition, modification of acid sites in Mn+-ZMS-5 by loading different cations is discussed in terms of the accessibility of the surface of the zeolite channels and the reactivity of the cations with Brønsted acid hydroxyls. We conclude that larger cations can effectively constrict the zeolite channels and impede the ability of pyridine to access acid sites on the surface of the channels.