Molecular Sieve Catalysts Research Articles

Effective synergistic interaction between InZnZrOx ternary metal oxides and SAPO-34 molecular sieve catalysts for CO2 hydrogenation to light olefins

Effective synergistic interaction between InZnZrOx ternary metal oxides and SAPO-34 molecular sieve catalysts for CO2 hydrogenation to light olefins

Uncovering the roles of Ce and Mn for NH3-SCR over Mn-Ce/IM-5 with extraordinarily superior wide-temperature performance

The development of wide-temperature catalyst with glorious activity and the resistance of SO2 for NH3-SCR reaction are of great importance. However, the preparation of wide-temperature catalyst with outstanding NH3-SCR performance and the resistance of SO2 is still challenging. In this work, Mn and Ce modified IM-5 molecular sieve catalyst (MC-5) was synthesized by incipient wetness impregnation method and the relationship of structure-activity was studied. MC-5 exhibited superior NOx conversion and it was more than 87% in the temperature range of 150-500 °C and ca. 100% at 225 °C due to the high concentration of Mn4+ and chemisorbed oxygen, the excellent redox ability and the synergistic effect of Mn and Ce. Meanwhile, the redox cycle of Mn4++Ce3+↔Mn3++Ce4+ promoted the electron transfer. 27Al NMR spectra and NH3-TPD confirmed Mn ion was mainly located on the bridge hydroxyl group (Brønsted acid sites). The localization energies ΔE of (Al, Mn) for IM-5 was determined by theoretical calculation and the reaction mechanism of M-5 catalyst on Brønsted acid sites was proposed. The reaction mechanism of M-5 catalyst on Brønsted acid sites followed L-H mechanism. And interestingly enough, the NH3-SCR activity of MC-5 significantly increased in the presence of SO2 at 200 °C. One of the reasons was that Ce binded more easily to SO42- and thus protected the active site Mn from sulfation. The other reason was the generation of more acid sites.

Selective Oligomerization of Isobutylene in Mixed C4 with Co/BETA-Loaded Molecular Sieve Catalysts

This paper investigates the use of loaded Co/BETA molecular sieve catalysts for the selective oligomerization of isobutylene. The physicochemical properties of Co/BETA molecular sieves were characterized using XRD, BET, NH3-TPD, FT-IR, XPS, and Py-FTIR. The effects of different active component loadings, reaction temperatures, and reaction air velocities on the selective oligomerization of isobutylene were investigated in a fixed-bed reactor. The results showed that the catalytic effect was optimal when the Co loading was 6%, the reaction temperature was 60 °C, the reaction pressure was 1 MPa, and the reaction air speed was 1 h−1. The isobutylene conversion was greater than 74%, the C8= selectivity was approximately 70%, and the C8= yield reached 51.69% with minimal loss of n-butene, providing good catalytic capacity and efficiency.

Mechanism of methanol-to-olefin (MTO) reaction

The full name of MTO is methanol to olefin, which is a new chemical reaction process to gain an important chemistry industry raw material. In this paper, we mainly talk about several general reaction process as well as the mechanism of the reaction. The use of molecular sieve catalytic process is a key point where the new MTO process different form the original simple petroleum cracking in order to again olefin. In this work we mainly discuss how the MTO process could happen with the assist of the molecular sieve catalyst. There are direct mechanism Carbene mechanism and Methane-formaldehyde mechanism. The effect of the direct mechanism is to gain some simple and short Carbon-Carbon product. And then the indirect mechanism will take on to control the rate of the reacting process and the ration of different products. By studying on the mechanism of the MTO reaction, we can figure out how a powerful catalyst, molecular sieve catalyst, works in the reaction. Also, the MTO process is a meaningful way to take place of the origin cracking process to gain olefin, as the storage of petroleum is decreasing fast recently.

Comprehensive study of alkali lignin pyrolysis catalyzed by composite metal-modified molecular sieves for the preparation of hydrocarbon liquid fuels

Catalytic lignin pyrolysis for hydrocarbon liquid fuel production offers a viable alternative to fossil fuels. This study investigated the effects of transition metal (Fe, Co, Ni, Cu) modified composite molecular sieve catalysts on the pyrolysis product distribution and behavior of alkali lignin (AL). AL pyrolysis achieved the highest liquid product yield of 24.50 % at 600 °C, with high temperatures favoring hydrocarbon product formation. Volatile gaseous products from AL pyrolysis included H2, CO, CO2, phenolic compounds, heteroatomic compounds, and hydrocarbons. Molecular sieve catalyst additions were all favorable to the increase in hydrocarbon content. Compared with ZSM-5 and SBA-15, catalysts processed through acid etching and metal modification exhibited optimized pore structure, acid site distribution, and catalytic performance. Metal-modified composite molecular sieve catalysts (FeZS, CoZS, NiZS, and CuZS) generated more liquid products and promoted hydrocarbon formation. Notably, Cu-modified ZS catalysts exhibited superior acid site distribution and specific surface area, considerably reducing oxygenated compounds in the products. A higher catalyst-to-feedstock ratio increased the number of catalytically active sites, facilitating the cracking and deoxygenation of oxygenated components and generating more hydrocarbon products. The highest hydrocarbon yield for AL with a catalyst-to-biomass ratio of 10:1 under CuZS was 92.25 %, with 66.07 % being monocyclic aromatic hydrocarbons (MAHs) and 61.72 % benzene, toluene, ethylbenzene, and xylenes (BTEX). Additionally, kinetic and thermodynamic analyses revealed a substantial decrease in the average activation energy (Eα) of AL and a reduction in entropy value with the CuZS catalyst, indicating enhanced pyrolytic reactivity of AL. Therefore, the proposed method is highly effective for producing highly selective hydrocarbons through catalytic pyrolysis of AL.

Catalytic pyrolysis of torrefied biomass with molecular sieve catalysts to produce hydrocarbon rich biocrude

AbstractThe downstream processing of biocrudes obtained from direct biomass pyrolysis poses significant challenges due to stability issues, necessitating costly upgrading for further coprocessing with refinery feeds. This study examines the impact of torrefaction pretreatment on pyrolysis product distribution and biocrude composition using sawdust (SD) and groundnut shell (GS) feeds. Torrefaction was conducted at varying temperatures (200, 250 and 300°C) for 30 min under different reactor conditions. Increasing the severity of torrefaction resulted in decreased biocrude yields with reduced water content and gas formation, particularly evident with GS. A torrefaction temperature of 250°C and 30 min of pretreatment yielded higher phenolics and hydrocarbons. This increase in phenolics can be attributed to lignin enrichment during torrefaction, which, in the presence of a catalyst, undergoes deoxygenation leading to hydrocarbon formation. The influence of feed particle size, whether in powder or pellet form, on biocrude yield and composition was found to be minimal. Catalytic pyrolysis of SD using molecular sieve catalysts yielded the highest hydrocarbon (42%) and aromatic content (44%) at catalyst to biomass ratios of 1:1 and 2:3. The combination of torrefaction and pyrolysis was shown to enhance the quality of biocrude by increasing its hydrocarbon content, but at the expense of lower liquid yields. Experimental observations were supported by statistical analysis tools such as principal component analysis, which assessed pyrolysis product yields and composition.

Efficient ozone decomposition in high humidity environments using novel iron-doped OMS-2-loaded activated carbon material.

This study effectively addresses the rapid deactivation of manganese-based catalysts in humid environments during ozone decomposition by introducing iron-doped manganese oxide octahedral molecular sieve (Fe-OMS-2) catalysts supported on activated carbon (AC). By optimizing the doping ratio of Fe-OMS-2, the Fe-OMS-20.5/AC catalyst achieves nearly 100% ozone decomposition efficiency across a wide range of relative humidity levels (0 to 60%), even at elevated air flow rates of 800 L·g-1·h-1, outperforming standalone AC, Fe-OMS-2, or a simple mixture of OMS-2 and AC. The Fe-OMS-20.5/AC catalyst features a porous surface and a mesoporous structure, providing a substantial specific surface area that facilitates the uniform distribution of the Fe-OMS-2 active phase on the AC surface. The incorporation of Fe3+ ions enhances electron transfer between valence state transitions of Mn, thereby improving the catalyst's efficiency in ozone decomposition. Additionally, the AC component protects catalytic sites and enhances the catalyst's humidity resistance. In conclusion, this research presents a novel strategy for developing highly efficient and cost-effective ozone decomposition catalysts that enhance dehumidification, significantly contributing to industrial ozone treatment technologies and advancing environmental protection.

Research progress of molecular sieve supported catalysts in catalytic oxidation of chlorine-containing volatile organic compounds

Chlorinated Volatile Organic Compounds (CVOCs) come from a wide range of sources and are common precursors of PM2.5 and ozone pollution, which pose a serious threat to the environment and have adverse effects on human health. Catalytic degradation is one of the effective methods to solve CVOCs pollution, which has the advantages of low operating temperature, less chlorine-containing by-products and high degradation efficiency. The core of this technology is to design and develop catalyst materials with excellent stability and catalytic performance. At present, molecular sieve catalysts have attracted extensive attention because of their acidity and unique pore structure. In this paper, the current research status of catalysts supported by molecular sieve, such as noble metals, transition metal oxides and perovskites, and their activity, acidity, stability and selectivity in CVOCs catalytic reactions were summarized and analyzed, and the future development direction of CVOCs molecular sieve supported catalysts was prospected.

Molecular sieve-like wood achieves efficient chiral catalysis

Molecular sieve catalysts have been adopted in chiral catalytic reactions due to their high specific surface area, nano-scaled pores and effective separation, however, the problems like low utilization ratio of channels, difficult modification, long period and complex preparation, and no economic benefits reduce its widely application. In this paper, natural wood was employed as raw material to preserve the cellulose skeleton rich in poly‑hydroxyl and the multistage porous channels of nanometer, micron and millimeter by simple treatment. A low-cost, high-yield and high-selectivity chiral catalyst could be obtained from wood with chiral catalytic sites. The in situ grafting method retains the well-developed multistage pore structure of wood, enhances the mass transfer and possesses universal applicability to different aldol condensation reactions. The asymmetric reaction of cyclohexanone and p-nitrobenzaldehyde is catalyzed by grafting readily available amino acids such as threonine, with a yield of 82% and selectivity of 57%. Molecular sieve-like wood possesses the advantages of low economic cost and good catalytic performance, which provides a potential possibility to replace traditional molecular sieve catalyst.

Structure sensitivity of Cu supported on manganese oxide catalysts in levulinic acid hydrogenation

Different synthesis methods were used to prepare a series of size-controlled copper nanoparticles supported on manganese oxide octahedral molecular sieves (OMS-2) catalysts.

Potassium-promoted Ru-MCM-41 catalyst via in situ loading for effective low-temperature ammonia decomposition

A potassium (K)-promoted Ru-based siliceous molecular sieve catalyst, K-nRu-MCM-41, was successfully synthesized via a hydrothermal method.

Synergistic low-temperature plasma (DBD) treatment of n-hexane gas

The experiment is based on a single dielectric barrier discharge (DBD) plasma generator, using micro-discharge to produce non-equilibrium plasma synergizing with two different catalysts (TiO2, 4A molecular sieve) to decompose n-hexane gas. In the n-hexane degradation experiment, the study investigates the influence of factors such as the type of catalyst, discharge voltage, and flow rate on the degradation rate of n-hexane. The experiments revealed that in all synergistic experiments with catalysts, the degradation rate of n-hexane increased with the decrease in flow rate and with the increase in voltage. Among the four catalysts selected, the 4A molecular sieve catalyst showed the best removal effect for n-hexane gas, reaching 73.2%.

Effect of Fe, Ni, and Co on the hydrothermal liquefaction of Chinese herb residue for bio-oil production

This study investigated the effects of reaction temperature (300–360 °C), reaction time (0–60 min), and the ratio of raw materials to solvent (1:5–1:15; g/mL) on the HydroThermal Liquefaction (HTL) of Chinese Herb Residues (CHR) for Bio-Oil (BO) production. Optimal HTL conditions for CHR were determined. To enhance both the yield and quality of BO, metal-modified catalysts including Fe/MCM-41, Co/MCM-41, and Ni/MCM-41 were prepared. These catalysts, after hydrogen reduction, loaded metal elements in their elemental state onto the carrier. Subsequently, CHR catalytic HTL experiments were conducted at 330 °C for 15 min with a ratio of 1:10 (g/mL). BO analysis was performed using EA, GC-MS, and FT-IR. Under the optimal HTL conditions (330 °C/15 min/1:10), the BO yield reached 24.57 wt.%, with a Higher Heating Value (HHV) of 25.96 MJ/kg. The major components of the BO included phenols, ketones, acids, and esters. In the catalytic HTL, Fe/MCM-41 (26.15 wt.%), Ni/MCM-41 (26.2 wt.%), and Co/MCM-41 (27.05 wt.%) catalysts each achieved higher BO yields. When using Ni/MCM-41 catalyst, the highest HHV of BO reached 32.01 MJ/kg, representing an 81% improvement over CHR HHV of 17.66 MJ/kg. Additionally, with Fe/MCM-41 catalyst, the lowest oxygen content in BO was 9.68%, and the selectivity for phenols and ketones was the highest, showing increases of 15.22% and 33.15%, respectively, reaching 44.13% and 24.5%. The results indicate that HTL can effectively convert high-moisture CHR into valuable products. Hydrogen-reduced metal-modified catalysts contribute significantly to increasing BO yield, promoting deoxygenation and hydrogenation reactions, and markedly improving HHV and the selectivity of chemical components, thereby effectively enhancing both the yield and quality of BO.

Functional Catalyst Molecular Sieves in Green Chemical Applications

With the development of green chemical industry and the continuous improvement of environmental awareness, the application of various catalysts in environmental protection has been widely concerned. As a green catalyst, molecular sieve catalyst has superior environmental performance, which is mainly reflected in its ability to improve the selectivity of reaction products, can be reused, good thermal stability and strong adaptability. This paper mainly introduces the types, development history, synthesis technology and application of zeolite catalysts, due to the development of science and technology, a large number of new synthetic zeolite catalysts are used in the field of catalysis and meet the requirements of green chemistry, and its synthesis technology is gradually trending towards environmental protection with the development of green chemistry. Zeolite catalysts are widely used in chemical industry and other fields, and their green environmental protection performance promotes the development of chemical processes in the direction of green chemicals.

Catalytic reforming of polypropylene to produce hydrogen: Influence of support characteristics and active metal type in catalyst

Hydrogen production by catalytic pyrolysis of waste plastics has attracted extensive attention in recent years. This paper takes hydrogen production as the starting point. A variety of supported nickel catalysts were developed for the catalytic pyrolysis of polypropylene using a two-stage fixed bed reactor. Based on the better characteristics of bimetallic catalysts, calcium, magnesium, iron doped nickel bimetallic catalysts were prepared to explore the improvement effect of catalytic hydrogen production performance. The micromorphology, structure composition and active substance distribution of different supported catalysts and bimetallic catalysts were measured. The experimental results show that the catalyst with powdered activated carbon as the support has the best catalytic performance of hydrogen production. In a series of molecular sieve catalysts, the smaller the Si/Al ratio of the support, the higher the catalytic performance. Among the bimetallic catalysts, Fe-Ni bimetallic catalysts have better catalytic advantages than Ca-Ni and Mg-Ni bimetallic catalysts, which is closely related to the stable Fe-Ni alloy structure formed on the catalyst surface. In conclusion, the differences in catalytic performance between catalyst support and active metal discussed in this paper will provide theoretical support for the catalytic pyrolysis technology of plastics to produce hydrogen.

Poly(lactic acid) synthesized from non‐food biomass feedstocks with tin‐loaded ZA molecular sieve catalysts by direct melt polycondensation

AbstractThe design and synthesis of catalysts loaded with active components has attracted considerable attention in current research owing to their exceptional catalytic performance. In this study, the focus was on the utilization of tin‐loaded ZA molecular sieves, possessing remarkable adsorption properties, alongside the catalytic activity of tin. These catalysts were successfully prepared and employed for the synthesis of poly(lactic acid) (PLA) from lactic acid derived from non‐food biomass. By modifying the treatment of ZA molecular sieves, the properties of tin‐loaded ZA molecular sieves were adjusted. The resulting catalysts exhibited a high tin capacity ranging from 2.29% to 2.81% and featured abundant mesoporous structures, providing a surface area of up to 341.2 m2 g−1. Regarding the preparation of PLA, our findings demonstrated that ZA‐III‐Sn2+ as a catalyst yielded PLA with a higher weight‐average molecular weight (Mw) up to 2.57 × 104 g mol−1 and a higher yield of 65.3% compared to other catalysts. Moreover, the most optimal catalytic effect was achieved by adding the catalyst in three separate stages. Moreover, the amount of catalyst, reaction temperature and reaction time were found to influence both the molecular weight and yield of PLA. This study not only provides a valuable strategy for the preparation of loaded catalysts for PLA production but also offers new insights into the overall preparation process of PLA. © 2023 Society of Industrial Chemistry.

Catalytic transfer hydrogenation of CO2 to formic acid with glycerol as the hydrogen donor over Ru-REUSY catalysts

In this work, a "hydrogen-free" strategy based on the ruthenium (Ru) modified REUSY molecular sieve catalysts was proposed, which can promote CO2 catalytic transfer hydrogenation using endogenous hydrogen induced by glycerol dehydrogenation. As the active component, Ru can not only act on the dehydrogenation reaction with glycerol, but also promote the hydrogenation reaction of CO2. Comparison experiments confirmed that under conditions of 200 °C, 36 h, and 7.92 g KHCO3, the reaction could obtain the highest yields over 10 wt.% Ru-deAl(5 h)-REUSY. The yields of formic acid and lactic acid were 19.81 % and 6.13 % respectively. In addition, when replacing the carbon source from KHCO3 to CO2 (dry ice), formic acid and lactic acid yields over 10 wt.% Ru-deAl(5 h)-REUSY catalysts were further improved, reaching 64.14 % and 17.13 %, respectively. This work demonstrated the feasibility of the "hydrogen-free" upgrade process realizing the catalytic transfer hydrogenation of CO2 into formic acid with glycerol as hydrogen donor.

Investigating the synergistic driving action of microwave and char-based multi-catalysts on biomass catalytic pyrolysis into value-added bio-products

A method for preparing value-added bio-products dominated by aromatic hydrocarbon bio-oil with high selectivity by fast pyrolysis of biomass under the synergistic effect of microwave and char-based multi-catalysts (CMCs) was proposed. Various CMCs were prepared, and their structural characteristics were compared in detail. Microwave pyrolysis (MWP) experiment shows that the synergistic of microwave and biochar (hot spot effect) activates the active sites of molecular sieve catalysts, which can improve the diffusion of heavy components, thus regulating the pyrolytic products. Two non-noble metal active sites were introduced into CMCs, and their pyrolysis characteristics were compared. The Zn-modified CMCs showed good selectivity to monocyclic aromatic hydrocarbons. The yield of monocyclic aromatic hydrocarbons (MAHs) increased to 28.49 %, and the content of C6 ∼ C8 aromatic hydrocarbons was obviously increased, especially in the decarbonylation reaction. The Zr-modified CMCs could inhibit the transition condensation and cyclization of aromatic hydrocarbons. The ratio of MAHs to polycyclic aromatic hydrocarbons (PAHs) reached 1.31–1.42, which optimized the distribution of liquid products, and the yield of MAHs was between 22.99–28.61 %. CMCs have the characteristics of microwave absorption and catalytic conversion of aromatic hydrocarbons with high activity.

ZSM‐5@KIT‐6‐encapsulated composite molecular sieves for the catalytic cracking of waste cooking oil model compound to produce light olefins

AbstractBACKGROUNDA series of ZSM‐5@KIT‐6 composite molecular sieve catalysts was prepared by encapsulating ZSM‐5 as a substrate in the mesoporous material KIT‐6. The intent was to use these catalysts to promote the catalytic cracking of a waste cooking oil model compound (WCOMC) to produce light olefins.RESULTSThe morphology, structural characteristics and acidity of each of the resulting catalysts were characterized by X‐ray diffraction, transmission electron microscopy, N2‐Brunauer–Emmett–Teller (N2‐BET) surface area analysis and temperature‐programmed ammonia desorption. The results showed that ZSM‐5 was successfully coated with KIT‐6. The BET surface areas of these catalysts ranged from 345 to 792 m2 g−1 and the specimens had average pore sizes in the range of 2.37–5.51 nm. Total acidity increased with increases in the mass‐based proportion of ZSM‐5 in the material.CONCLUSIONThe catalytic cracking of WCOMC was studied in a lab‐scale fixed‐bed apparatus. Trials at a reaction temperature of 600 °C using the material having a mass‐based ZSM‐5 proportion of 80.0% (ZK‐80) gave the highest gas‐phase yield of light olefins of 43.8%. After 6000 min, the catalytic performance of this material remained stable, demonstrating a resistance to carbon deposits. The superior activity of the present composite catalysts can be ascribed to improvements in pore structure and acid strength distribution. © 2023 Society of Chemical Industry (SCI).

Experimental and numerical study of Cu-SSZ-13 SCR system for NOx reduction and hydrothermal aging under diesel exhaust conditions

Selective catalytic reduction (SCR) is a crucial technique for mitigating nitrogen oxides emission of internal combustion engines. Compared with vanadium-based catalysts, copper-based molecular sieve catalysts exhibit superior low-temperature catalytic performance and anti-aging properties. The catalytic characteristics of Cu-SSZ-13 catalyst in both fresh and aged states are investigated through experimental and numerical simulations. The catalytic performance of Cu-SSZ-13 catalyst with 200 g/L coating is investigated under wide inlet temperatures (180 °C–450 °C) and ANR (ammonia to nitrogen ratio) (1–1.4) conditions via an engine emission test device. Further, the apparatus is adopted to evaluate performance at various aging temperatures (600 °C, 700 °C, and 800 °C). The aging factor is introduced based on experimental results to establish and correct the kinetic model for SCR aging state. The results illuminate that the increase of ANR fails to compensate for decline of catalytic efficiency under low-temperature conditions (150 °C).The generated quantity of isocyanate acid through the side reaction of urea hydrolysis increases proportionally with ANR. And it increased supply only resulted in a marginal 1 %–3 % improvement of catalytic efficiency. As SV decreases from 60,000 h−1 to 35,000 h−1, the catalyst efficiency increases from 22 % to 45 %, resulting in an elevation of reactant concentration and its gradient on the catalyst surface. This leads to accelerated reaction rates and enhanced diffusion effects. The catalytic efficiency can be significantly enhanced at low temperatures when NO2 fraction in NOx falls within the range of 10 %–25 %. The sensitivity of SCR reactions to aging varies at low temperatures (<250 °C) due to the distinct reaction sites on catalyst for different types of SCR reactions. The NO2 SCR reactions exhibit minimal susceptibility, while the rapid SCR reactions are significantly impeded. Moreover, it has been observed that the catalyst microstructure was completely deteriorated under hydrothermal aging test at 900 °C operating condition. In general, the low-temperature catalytic performance of Cu-SSZ-13 catalyst can be further optimized by pretreating inlet gas components and optimizing the catalyst structure.