Catalysts For Aromatization Research Articles

The Effect of Water Co-Feeding on the Catalytic Performance of Zn/HZSM-5 in Ethylene Aromatization Reactions.

During the methanol-to-aromatics (MTA) process, a large amount of water is generated, while the influence and mechanism of water on the activity and selectivity of the light olefin aromatization reaction are still unclear. Therefore, a study was conducted to systematically investigate the effects of water on the reactivity and the product distribution in ethylene aromatization using infrared spectroscopy (IR), intelligent gravitation analyzer (IGA), and X-ray absorption fine structure (XAFS) characterizations. The results demonstrated that the presence of water reduced ethylene conversion and aromatic selectivity while increasing hydrogen selectivity at the same contact time. This indicated that water had an effect on the reaction pathway by promoting the dehydrogenation reaction and suppressing the hydrogen transfer reaction. A detailed analysis using linear combination fitting (LCF) of Zn K-edge X-ray absorption near-edge spectroscopy (XANES) on Zn/HZSM-5 catalysts showed significant variations in the state of existence and the distribution of Zn species on the deactivated catalysts, depending on different reaction atmospheres and water contents. The presence of water strongly hindered the conversion of ZnOH+ species, which served as the active centers for the dehydrogenation reaction, to ZnO on the catalyst. As a result, the dehydrogenation activity remained high in the presence of water. This study using IR and IGA techniques revealed that water on the Zn/HZSM-5 catalyst inhibited the adsorption of ethylene on the zeolite, resulting in a noticeable decrease in ethylene conversion and a decrease in aromatic selectivity. These findings contribute to a deeper understanding of the aromatization reaction process and provide data support for the design of efficient aromatization catalysts.

The process of obtaining aromatic hydrocarbons by catalytic aromatization of normal hexane on the (2%LA*2%CU*8%ZN/Н-HSZ-30) catalyst

This study of the aromatic production process by catalytic aromatization of normal hexane on (2%LA*2%CU*8%ZN/Н-HSZ-30) catalyst is presented. Laboratory studies were conducted on High catalytic activity (2%LA*2%CU*8%ZN/H-HSZ-30) catalysts for catalytic aromatization of linearly structured hexane at 400, 450, and 500°C, atmospheric pressure to produce aromatic hydrocarbons. Catalytic aromatization of normal hexane at 400 °C showed high activity of the catalyst for iso-compound formation reactions and high hydrogen cyclization ability at 500°C. Based on the study of the characteristics of the high-catalytic-activity catalyst used to catalytically aromatize regular hexane to produce aromatic hydrocarbons, the used catalyst shows the structural properties, the reduction in the number of active metals in the catalyst used for the catalytic aromatization of regular hexane to produce aromatic hydrocarbons, which has a high catalytic activity. shown and aromatic hydrocarbons, which are the main components of the fuel, were found to form a catalyst with a high octane number.

Effect of mesopore spatial distribution of HZSM-5 catalyst on zinc state and product distribution in 1-hexene aromatization

1-hexene aromatization is a promising technology to convert excess olefin in fluid catalytic cracking (FCC) gasoline to high-value benzene (B), toluene (T), and xylene. Besides, the increasing market demand of xylene has put forward higher requirements for new generation of catalyst. For increasing xylene yield in 1-hexene aromatization, the effect of mesopore structure and spatial distribution on product distribution and Zn loading was studied. Catalysts with different mesopore spatial distribution were prepared by post-treatment of parent HZSM-5 zeolite, including NaOH treatment, tetra-propylammonium hydroxide (TPAOH) treatment, and recrystallization. It was found the evenly distributed mesopore mainly prolongs the catalyst lifetime by enhancing diffusion properties but reduces the aromatics selectivity, as a result of damage of micropores close to the catalyst surface. While the selectivity of high-value xylene can be highly promoted when the mesopore is mainly distributed interior the catalyst. Besides, the state of loaded Zn was also affected by mesopores spatial distribution. On the optimized catalyst, the xylene selectivity was enhanced by 12.4% compared with conventional Zn-loaded parent HZSM-5 catalyst at conversion over 99%. It was attributed to the synergy effect of mesopores spatial distribution and optimized acid properties. This work reveals the role of mesopores in different spatial positions of 1-hexene aromatization catalysts in the reaction process and the influence on metal distribution, as well as their synergistic effect two on the improvement of xylene selectivity, which can improve our understanding of catalyst pore structure and be helpful for the rational design of high-efficient catalyst.

Enhanced stability of Pt@S-1 with the aid of potassium ions for n-hexane and n-heptane aromatization

As a typical high-efficient alkane aromatization catalyst, Pt/KL is prone to deactivation due to the sintering growth of Pt on the outer surface of KL and the channel blockage caused by carbon deposition, which is further exacerbated by the one-dimensional channel structure of KL. Therefore, a series of encapsulated catalysts combining the three-dimensional channel structure advantages of S-1 with the role of potassium are prepared and evaluated. It is shown that the encapsulated catalyst KPt@S-1-02 modified by moderate potassium exhibits extremely superior stability and no significant deactivation is observable after n-heptane aromatization for 180 h under harsh conditions. On the one hand, encapsulation structure enables a strong anti-agglomeration ability of Pt and the topological structure of S-1 endows the encapsulation catalysts less susceptible to channel blockage, which has been demonstrated by HAADF-STEM and N2-adsorption. On the other hand, characterizations involving NH3-TPD, CO-DRIFT and HAADF-STEM verify that the modification by an appropriate amount of K can inhibit acid sites of catalysts and improve Pt dispersion and electron density, thus enhance the stability of catalysts. However, excessive K can serve as weak acid sites, poison of active sites and inhibitor of H2 adsorption on Pt surface, leading to deactivation of the catalyst.

Enhanced stability of CO2-assisted shale gas aromatization through the introduction of Mg promoter on Mo/ZSM-5

CO2-assisted shale gas aromatization is an effective method for directly producing benzene, toluene, and xylene (BTX) and H2 as well as for suppressing coke formation compared to non-oxidative conversion. However, Mo/ZSM-5, the conventional catalyst for aromatization, should be improved to make it more resistant to coke formation and enhance the BTX yield further for practical applications of the proposed reaction system. This study proposes Mg-promoted Mo/ZSM-5, labeled as Mg/Mo/ZSM-5, to enhance the efficiency of CO2-assisted shale gas aromatization by controlling the acidic and basic properties of Mo/ZSM-5. The addition of Mg on Mo/ZSM-5 selectively removed its Brønsted acid sites and increased its base site density, resulting in the enhanced catalytic stability by suppressing hard coke formation and protecting the active phase of Mo. Thus, the modified catalyst showed a higher BTX production than conventional Mo/ZSM-5, with the complete conversion of CO2 over a longer period than with Mo/ZSM-5. These benefits were maximized at a CO2 concentration of 10 %; moreover, the Mg/Mo/ZSM-5 catalyst improved regeneration efficiency.

Intensified shape selectivity and alkylation reaction for the two-step conversion of methanol aromatization to p-xylene

Two-step conversion of methanol to aromatics via light hydrocarbons can significantly improve the conversion stability compared with direct aromatization of methanol, but it remains a challenge to achieve a high p-xylene (PX) selectivity. Herein, silica coating was firstly used to passivate external acid sites of ZSM-5 catalyst for the aromatization of light hydrocarbons by the chemical liquid deposition method. With the increase of SiO2 deposition, the density of the external acid sites of the catalyst was decreased from 0.1 to 0.03 mmol·g−1, which inhibited the surface secondary reactions and increased the PX/X from 34.6% to 60.0%. In view of the fact that the aromatization process in the second step was partly inhibited as methanol was consumed in advance in the upper methanol-to-light hydrocarbons catalyst layer, part of methanol was directly introduced into the lower aromatization catalyst layer to promote the alkylation process during the aromatization, which decreased the toluene selectivity from 34.5% to 14.3% but increased the xylene selectivity from 40.0% to 55.3%. It was also found that an appropriate external acid density was needed for aromatization catalyst to strengthen the alkylation process and improve the selectivity of xylene under the conditions of methanol introduction.

Synergistic Catalysis of Brønsted Acid, Al-Lewis Acid, and Zn-Lewis Acid on Steam-Treated Zn/ZSM-5 for Highly Stable Conversion of Methanol to Aromatics

The development of stable and selective ZSM-5 catalysts for methanol aromatization remains an ongoing challenge. Here, we demonstrate highly stable aromatization on ZSM-5 by preliminary steam treatment before Zn introduction. Steam treatment destroyed part of frameworks, which decreased acid density from 0.5 to 0.25 mmol g–1 and increased Al-Lewis acid sites (Al-LAS) at the expense of Brønsted acid sites (BAS). However, aromatization activity was further increased and the lifetime was still kept at 100 h. A comparative experiment found that increasing the SiO2/Al2O3 ratio from 60 to 240 also decreased acid density to 0.25 mmol g–1, but BAS-based acid sites aggravated coke formation and reduced lifetime to 50 h. This reflected that Al-LAS and BAS on steam-treated ZSM-5 provided synergistic catalysis for stable aromatization. Introducing Zn into steam-treated ZSM-5 further transformed part of BAS to Zn-LAS but not changed acid density, which determined increased aromatics selectivity and a quite different well-maintained stability.

Coke Formation over Zeolite Catalysts in Light Alkanes Aromatization and Anti-Carbon-Deposition Strategies and Perspectives: A Review

The price of light aromatics, which are important chemical intermediates, is greatly affected by fluctuations in the oil market, and there is a gap in the supply. It is urgent to expand the source of aromatics to match the market demand. Being highly accessible, oxygen-free aromatization of light alkanes (C1–C4), with high product selectivity and high cost-effectiveness, has attracted widespread interest from both academia and industry. However, the rapid deactivation of catalysts due to carbon deposition has seriously hindered the industrialization process. This Review presents the bifaciality of coke on catalysts and proposes a coke formation mechanism related to the dynamic migration of intermediates according to the type of catalyst active site. An emphasis is placed on creating a reaction microenvironment that resists carbon deposition by improving the mass-transfer efficiency, controlling the interaction between intermediates and active sites, adjusting silanol defects, and looking forward to future directions for development.

Propene transformation on Cu-modified ZSM-5 zeolite: Aromatization and oxidation

Propene transformation on copper-modified ZSM-5 zeolite has been studied by 13C MAS NMR and FTIR spectroscopy. Two major reaction pathways are identified, aromatization to the simple aromatic hydrocarbons (benzene, toluene) and oxidation to acrolein. Copper-allyl species is inferred to be the key intermediate in both processes. π-Complex of propene with copper sites is the primary intermediate, preceding the formation of copper-allyl species. The role of different active sites is established. Cu2+–O2– Lewis acid-base pairs are responsible for the allylic species formation, whereas [Cu3(μ-O)3]2+ oxo-clusters provide the oxidation of copper-allyls. The results obtained are of importance for developing zeolite-based catalysts for propene aromatization to the simple aromatic compounds and partial oxidation to acrolein.

Possibility of application of high silicon keolitic catalyst with thermal and mechanochemical treatment for catalytic flavoring of the propane-butane fraction

The studies were carried out in a flow catalytic device in the stationary phase of the catalyst (catalyst volume 6 cm3), at 450–6000C, at normal atmospheric pressure (P = 0.1 MPa), was carried out under conditions in which the volumetric velocity of the initial gas mixture was 600–1000 h-1. Qualitative and quantitative composition of propane-butane fraction and reaction products were analyzed on the chromatograph “Chromatic-Crystal 5000M” under the following favorable conditions: separation of gaseous products was carried out in a column thermal conductivity detector (TCD) with a length of 3 m and a diameter of 3 mm filled with 8% NaOH / Al2O3. The separation of liquid products was carried out in a DV-1 capillary quartz column (30 m x 0.25 μm), and detection was carried out in a flame ionization detector. Check the acidity of the catalysts. The acid characteristics of the samples were studied by the method of the programmed desorption of ammonia in the automatic chemisorption analyzer “USGA-101”. X-ray phase analysis: X-ray examination of the samples (X-ray phase analysis) was performed on a diffractometer XRD-6100 (Shimadzu, Japan). Phase identification was performed based on radiographs of individual components (JSPDS card index) based on data from the literature. The purpose of this work is to study the possibility of using thermally and mechanochemically treated high-silicon zeolite catalysts in the catalytic aromatization of the propane-butane fraction and acid properties.

Revealing the effect of synergistic interaction between ZnO and ZnCr2O4 on the syngas aromatization

AbstractZn‐Cr‐based catalysts are widely used as oxide catalysts for syngas aromatization, and it is difficult to study the synergistic effect of ZnO and Zn‐Cr spinel due to the complex system of non‐stoichiometric Zn‐Cr spinels. In order to reveal the synergistic effect, we physically mixed ZnO and ZnCr2O4 with definite structure to avoid ambiguous structure of non‐stoichiometric Zn‐Cr spinels. The results showed that the introduced ZnO affected the oxygen vacancies generation and promoted the activation of CO and H2, leading to an increase of oxygenates compared to the sole ZnCr2O4. Due to the synergy of ZnO and ZnCr2O4, the xZZC catalysts could produce more adsorbed species than the ZnCr2O4 catalyst, while the ZnCr2O4/ZSM‐5 catalyst was more difficult to convert formate species. The ZnO in xZZC/ZSM‐5 decreased the formate adsorption strength, which favored the continued conversion of formate and further realized the enhanced pulling effect on CO conversion.

Development and catalytic mechanism of a highly efficient Pt/Kβ catalyst for n-Heptane aromatization

Development of a high-performance naphtha aromatization catalyst has been paid many attentions as this reaction is generally employed to elevate the octane number of FCC gasoline and Fischer-Tropsch-synthesized oil. Here, a hierarchical porous Pt/Kβ catalyst is developed. It shows much higher activity, selectivity and stability than conventional Pt/KL. The catalytic performance of Pt/Kβ depends on Brϕnsted acidity and mesoporosity of zeolite β and nanoparticles (NPs) size and electronic state of Pt. The catalytic mechanism was investigated by combining TPSR, GC–MS, reaction kinetic studies and DFT calculations. Pt NPs catalyze dehydrogenations of alkanes/cycloalkenes to alkenes and dienes, while Brϕnsted acid sites facilitate alkene cyclization and ring-expansion of cycloalkenes despite that they can also dehydrogenate alkanes/alkenes through hydrogen transfer reactions. The n-heptane is mainly aromatized by dehydrogenating to 1-heptene and 2-heptene, 1,6- and 1,5-cyclizing into methylcyclohexane and ethyl-cyclopentane, and successively ring-expanding and/or dehydrogenating to toluene that may be further dealkylated to benzene.

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.

Mo, Cu Bimetallic Loaded Hierarchical Pore ZSM-5 Catalysts for the Hydrothermal Aromatization of Algal Bio-Oil Model Compounds

Mo, Cu Bimetallic Loaded Hierarchical Pore ZSM-5 Catalysts for the Hydrothermal Aromatization of Algal Bio-Oil Model Compounds

Towards Extraordinary Catalysts for Aromatization of Biomass and Low-Cost C5 Streams

Towards Extraordinary Catalysts for Aromatization of Biomass and Low-Cost C5 Streams

Synergistic effect of Zn with Ni on ZSM-5 as propane aromatization catalyst: effect of temperature and feed flowrate

This work shows how propane was catalytically converted to aromatic compounds over Zn-Ni/HZSM-5 to investigate the synergistic role of nickel as a zinc stabilizer and promoter in propane aromatization. Co-impregnation method was employed for Zn-Ni/ZSM-5 synthesis fixed 2 wt% of zinc and 1, 2 and 3 wt% of nickel. Modified catalysts’ were fully characterized. Catalysts crystallinity, structure and microporosity were retained from the analysis results. The propane aromatization process was conducted at 540 °C, 1200 ml/g-h gas hourly space velocity and atmospheric pressure. The presence of Ni with Zn improved catalytic performance for all Ni loading. Aromatic selectivity and propane conversion were improved, with the best performance to be Zn-Ni/ZSM-5 with 2 wt% Zn, 2 wt% Ni on ZSM-5 averaging 88 and 60% for twelve hours’ time on stream. Aromatic selectivity on Zn-Ni/ZSM-5 is eight times better than the parent HZSM-5 and one and half times better than the Zn/ZSM-5 catalyst. The electronic interaction of zinc and nickel resulting from equality of oxidation state of +1 and +2 and metal-binding energy change synergistically improved the catalytic performance of the bimetallic Zn-Ni/ZSM-5 over the HZSM-5 and Zn/ZSM-5. Flowrate increase from 6 to 35 ml min−1 decreased propane conversion from 80–40% with increased aromatic selectivity from 55–80%. Temperature increase from 500–580 °C favours both propane conversion and aromatic selectivity increase from 50–68 and 55–92% respectively. The metallic interactions from H2-TPR and XPS analysis revealed a big improvement in propane conversion, aromatic selectivity and product distribution.

MOF derived 2.x-dimensional trimetallic catalysts for selective aromatization to p-xylene

Aromatization to p-xylene is challenging in which the catalyst should be designed and tuned. A series of layered MOF(Al, Cr, Fe)der catalysts derived from trimetallic MIL-53(Al, Cr, Fe) have been synthesized by one-pot method and systematically investigated for selective production of p-xylene from diisobutylene. The catalyst showed the p-xylene yield of 21% with p-xylene selectivity of 91% in aromatics under relative milder conditions. The highly homogenously dispersed of Al, Cr and Fe elements greatly enhanced the formation of the active monochromate species. The mesoporous 2.x dimensional structure comprised of stacking layers exposed more available active Cr species. The coordination unsaturated active sites by introduction of Fe was favorable for the aromatization of diisobutylene. The regeneration and recycle experiments showed the catalyst had fine structure stability and regeneration performance.

Role of the nonstoichiometric Zn-Cr spinel in ZnCrOx/ZSM-5 catalysts for syngas aromatization

Bifunctional catalysts composed of ZnCrOx oxide and ZSM-5 were widely used in syngas-to-aromatics (STA). The CO conversion on bifunctional catalysts was generally higher than that on oxide catalysts attributed to the pulling effect of zeolite, but the key factor for the improvement of CO conversion was still short of systematical explanation. In this work, the degree of nonstoichiometric spinel of ZnCrOx (ZxC) oxides was finely tuned through modulating the ratio of Zn/Cr, which could significantly influence the catalytic behaviors of ZnCrOx/ZSM-5 catalysts for the CO hydrogenation to aromatics. The increase of nonstoichiometric spinel corresponded to the increase of oxygen vacancies and the enhancement of Zn-Cr synergistic effect, which promoted the activation of H2 and CO, leading to a dramatic increase of CO conversion. The work revealed that the action of ZnO and oxygen vacancies was the key factor for CO pulling in ZnCrOx oxide and ZSM-5 catalyzed STA reaction.

Methanol Aromatization over Zn and Ce Modified Hierarchical ZSM-5 Catalysts: Effect of Ce as a Promoter

Zinc (Zn) and cerium (Ce) modified hierarchical ZSM-5 (HZ) catalysts were prepared by incipient wetness impregnation, and their catalytic performances in methanol to aromatics reaction were evaluated in a fixed-bed reactor operating at 400°C under 0.1 MPa and WHSV of 1.0 h−1. The structure, acidity, and state of Zn species of the Zn/Ce modified HZ catalysts were investigated via several characterization techniques, including XRD, NH3-TPD, H2-TPR, nitrogen adsorption, and XPS. The results showed that the aromatization activity of 2 wt% Zn-modified HZ (2% Zn/HZ) could be significantly enhanced by loading 0.6 wt% Ce, which was mainly attributed to the increase in surface ZnOH+ species. Moreover, it was found that Ce inhibited pore blockage caused by Zn. Consequently, compared to 2% Zn/HZ, 2% Zn-0.6% Ce/HZ exhibited higher aromatic selectivity and longer catalyst lifetime.

Catalytic performance of titanium subgroup metal oxides for syngas conversion

Titanium subgroup nanometallic oxides (TiO2, ZrO2 and HfO2), prepared via supercritical method, were combined with ZSM-5 and quartz to obtain bifunctional catalysts (Ti/HZ, Zr/HZ, Hf/HZ) and metal oxide catalysts (Ti/Si, Zr/Si, Hf/Si) respectively. The effect of crystal structure, surface oxygen vacancy and syngas adsorption of metal oxides on the catalytic CO hydrogenation was investigated. The results show that the bifunctional catalysts could directly catalyze the syngas to aromatics. The oxygen vacancy concentration, oxygen electron properties and the H/C ratios (the adsorption ratio of CO to H2) of the metal oxides synergistically determine the type of intermediates on the metal oxide surface. The CHxO* species generated on the surface of ZrO2 is beneficial for Zr/HZ catalyst to obtain higher aromatic selectivity (71.15%), while CH3* on TiO2 and HfO2 leads to higher CH4 selectivity for Ti/HZ and Hf/HZ catalysts. The results of this research could provide a valuable reference for design of syngas aromatization catalyst.