Selectivity To Light Olefins Research Articles

Modeling the Effect of Magnesia Nanoparticles on CO Hydrogenation to Light Olefins in a Continuous Flow Reactor Using Fine Gaussian Support Vector Machine

The effect of utilising energy derived from fossil sources on the environment has aroused research interest in alternative and sustainable energy sources. Synthesis gas, a mixture of carbon monoxide (CO) and hydrogen can be used as starting materials in hydrogenation reactions to produce chemical intermediates that can be used in various processes. This study investigates the robustness of applying a fine Gaussian support vector machine algorithm for predicting light olefins from catalytic CO hydrogenation using magnesia nanoparticles-based catalysts. The datasets obtained from the CO hydrogenation reaction consist of input parameters such as magnesia nanoparticles contents, reaction temperature, and reactor pressure, and the output parameters which include CO conversions and the selectivity of light olefins (CH4, C2H6, C2H4 C3H8, C4H8, and C3H6). The dataset was trained and employed for the prediction of the light olefins using a support vector machine with an inbuilt Fine Gaussian Kernel function. The performance of the support vector machine was evaluated using the coefficient of determination (R2), root mean squared error (RMSE), mean square error (MSE), and the mean absolute error (MAE). The support vector machine showed significant potential in the prediction of CO conversion, CH4 selectivity, C2H6 selectivity, and C2H4 selectivity as indicated by R2 of 0.770, 0.800, 0.730, and 0.930, respectively. While less predictive performance was obtained for the prediction of C3H8 selectivity, C4H8 selectivity and C3H6 selectivity as indicated by R2 of 0.630, 0.610, and 0.320, respectively.

Generating nanocrystalline SAPO-34 through bead-milling and porogen-assisted recrystallization: Structural evolution and catalytic consequence in dimethyl ether-to-olefin conversion

Mechanochemical bead-milling is a promising post-synthetic way to generate nanocrystalline zeotype materials with promoted catalytic performance. Post-milling recrystallization is often entailed to remedy the damaged framework but leads to crystal growth. Herein, using SAPO-34 (ca. 20 µm) derived from inexpensive morpholine as an example, we showcase that secondary growth can be suppressed by porogen-assisted recrystallization, resulting in formation of tiny crystals (100–200 nm) with better mass transport property. The presence of porogen (polydiallyldimethylammonium chloride) also induced a reduction of acid site density owing to a re-distribution of Si across the crystal, which alleviated zoning of Si at the external surface. The catalytic advantages, with respect to a control sample recrystallized in the absence of porogen, have been experimentally verified in dimethyl ether-to-olefin conversion, exhibiting an exaggerated light olefin selectivity and prolonged catalyst lifetime. This advancement of mechanochemical synthesis opens an avenue to better tailor crystal size for zeotype materials.

Tuning the density of Brønsted acid sites on mesoporous ZSM-5 zeolite for enhancing light olefins selectivity in the catalytic cracking of n-octane

A molecular template (tetrapropylammonium hydroxide, TPAOH) and a phosphorus-containing template (tetrabutylphosphonium hydroxide, TBPOH or tetrabutylphosphonium bromide, TBPBr) were used as dual templates to prepare the mesoporous ZSM-5 zeolites. The physicochemical properties of the as-prepared ZSM-5 catalysts were characterized by means of XRD, N2 adsorption, NH3-TPD, FT-IR spectra of adsorbed pyridine, 27Al MAS NMR, etc., and their performances for the catalytic cracking of the n-octane to light olefins were investigated. The results indicated that the acidity of ZSM-5, especially the concentration of strong Brønsted acid sites (SBAS) can be finely modulated by tuning the molar ratio of TPA+/TBP+. The charge-compensation effect of TBP+ and the phosphorus species played critical roles in regulating the SBAS concentrations of ZSM-5. Consequently, the as-prepared ZSM-5 catalysts with suitable strong Brønsted acid sites density was favorable for enhancing the selectivity to light olefins. At the temperature of 600 °C, the selectivity of propene and light olefins over MFI-9/2.5 catalyst were achieved 34.7% and 70.4%, which were higher than those over conventional ZSM-5 by 2.4% and 5.1%, respectively. Selectivity to C2=∼C4= light olefins was found to be decreased with increasing the concentration of strong Brønsted acid sites due to the reduction of SBAS which inhibited the hydrogen transfer reaction. This work will provide insights and new platforms for the design of high-efficiency zeolite catalysts for important industrial reactions.

Highly robust and efficient MnZnFe2O4 decorated fibrous KCC-SiO2 catalyst for the synthesis of light olefins from syngas

In this study, high light olefin (C2–C4) selectivity is obtained through FTS reaction and using a novel and robust catalyst of KCC-SiO2 fibrous nanospheres decorated with MnZnFe2O4 NPs.

Metal–organic framework-assisted synthesis of Zr-modified SAPO-34 zeolites with hierarchical porous structure for the catalytic transformation of methanol to olefins

Zr-Modified SAPO-34 zeolites with hierarchical porous structure were synthesized in the presence of UiO-66. The Zr0.50-SAPO-34 zeolites exhibited long lifetimes (>1500 min) and excellent selectivity for light olefins (98.66%) in the MTO reaction.

Facile synthesis of hierarchical macro/microporous ZSM-5 zeolite with high catalytic stability in methanol to olefins

Hierarchical macro/microporous ZSM-5 zeolite (defined as ZSM-5(MM)) was successfully synthesized by using silica spheres as silica source. The effects of template, sodium ions, hydroxyl ions, aluminum and water contents as well as crystallization temperature on the morphology and pore structure of ZSM-5 were investigated in detail. The formation mechanism was studied by XRD, SEM, N 2 sorption, ICP-AES, XPS, 27 Al MAS NMR and 29 Si MAS NMR, confirming that the silica spheres during synthesis process were served as not only silica nutrients to accelerate the generation of crystal nucleus, but also morphology guiding agents that induce the formation of macro/microporous structure followed by quasi solid hydrogel transformation mechanism. The prepared ZSM-5(MM) zeolite exhibited much longer catalytic lifetime and higher light olefins selectivity in the methanol to olefins (MTO) than those of the conventional microporous sample. This is because the hierarchical macro/microporous structure can effectively improve the diffusion of feedstocks and products, suppressing the rapid coke deposition. Meanwhile, the contribution of alkene cycle in MTO is enhanced and it produces more propene and butene. ● A facile strategy has been developed to synthesize hierarchical macro/microporous ZSM-5 zeolite ● The silica spheres not only serve as silica source, but also play a morphology-oriented role ● The formation of hierarchical structure is related to the dissolution rate of silica spheres. ● Macro/microporous ZSM-5 exhibited longer catalytic lifetime and higher olefin selectivity in MTO

Effect of Rb promoter on Fe3O4 microsphere catalyst for CO2 hydrogenation to light olefins

Alkali metals have been widely studied to improve the efficiency of CO2 hydrogenation to light olefins on iron-based catalysts. Herein, a series of Rb-promoted Fe3O4 microsphere catalysts were developed to understand the effects of Rb promoter on the catalytic performance. The 3wt%Rb/Fe3O4 catalyst showed high selectivity of light olefins (C2–C4, 47.4%) with a high olefin/paraffin ratio (10.7). XRD, H2-TPR, CO2-TPD, XPS analyses show that the proper Rb loading rate may adjust carbonaceous species content and ferric oxide content on the surface of the catalyst which is help for the synergistic effect to produce light olefins.

Ge‐Substituted Hierarchical Ferrierite for n‐Pentane Cracking to Light Olefins: Mechanistic Investigations via In‐situ DRIFTS Studies and DFT Calculations

AbstractThe development of heterogeneous catalysts for light olefin production via a catalytic cracking has been crucially important due to the high demand of related products in industrial applications. Herein, we report the structural analysis of a germanium‐substituted hierarchical ferrierite zeolite obtained by one‐pot synthesis. This is the first report on an investigation of the synergistic effect of hierarchical structures and the one‐pot Ge‐substitution in a ferrierite framework on the catalytic cracking mechanism. Our findings exhibit that the existence of germanium in a hierarchical ferrierite framework can indeed reduce the Brønsted acid strength, facilitating a catalytic reaction with high light olefin selectivity (63 %) due to the elimination of side reactions, such as dimerization and aromatization, confirmed by in‐situ DRIFTS and DFT studies. This opens up the perspective of the development of metal substitution in an interconnected 8‐ and 10‐pore framework with hierarchical structures on the catalytic behaviors of light olefin production.

Hierarchical zeolites obtained by alkaline treatment for enhanced n-pentane catalytic cracking

This study manufactured various hierarchical ZSM-5 zeolites using NaOH, NaAlO2, Na2CO3, K2CO3 and NaHCO3 solutions through post-treatment. Later, X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), X-ray fluorescence (XRF), N2 adsorption and desorption, solid state 29Si and 27Al MAS NMR, ammonia temperature programmed desorption (NH3-TPD) as well as pyridine adsorption infrared spectra (Py-FTIR) were carried out to characterize their structure properties and acidities. Further, this study investigated n-pentane catalytic cracking for producing the light olefins over hierarchical nano-sized ZSM-5 zeolites. Alkaline treatment with milder NaHCO3 was much more controllable and reasonable than treatment with other alkalis, which not only adjusted the acidity to promote n-pentane activation, but also formed hierarchical structures combing micropores and mesopores to reduce diffusion resistance and suppress secondary reaction contributing to an enhanced catalytic ability and anti-coke deposition performance. Among the catalysts, ZNaHCO3 exhibited ∼92% the highest n-pentane conversion and ∼50% light olefins selectivity during n-pentane catalytic cracking under 590 °C for 300 min, simultaneously, and these figures markedly increased relative to those for the parent ZSM-5 zeolite. Most importantly, it was also proved that HTC values are relevant to the degree of effectiveness of NaHCO3 desilication, and that mesopore formation contributes to the desirable selectivity of light olefins and coke amount.

Light olefins synthesis from CO2 hydrogenation over mixed Fe–Co–K supported on micro-mesoporous carbon catalysts

Recycling CO2 into light olefins is a promising approach to reduce CO2 emissions. To promote this technology, an efficient catalyst with high activity and selectivity towards light olefins is imperative. In this work, a series of Fe–Co–K supported on micro-mesoporous carbon (MMC) and microporous carbon (MC) with different metal loading contents (20–80 wt%) were prepared for CO2 hydrogenation to light olefins. Impregnating mixed metal oxides on both MMC and MC reduced particle sizes and enhanced their dispersion and reducibility, yielding a higher CO2 conversion compared to the unsupported Fe–Co–K catalyst. The metal oxides were highly dispersed inside the micropores of MC support, achieving the highest CO2 conversion. However, the high dispersion of metal oxides inside micropores led to the formation of isolated particles with a low interfacial contact with each other, resulting in a low light olefins selectivity. The MMC support provided a lower degree of metal dispersion, creating more interfacial contact area, promoting the selectivity towards olefins. Overall, the 60 wt% Fe–Co–K supported on MMC catalyst exhibited the highest light olefins yield of 10.8% at 400 °C and 20 bar and excellent stability.

Improvement of light olefins production over the Co‐Ni‐Mn nano‐catalyst: modeling and optimization of process by RSM

AbstractThe co‐precipitated Co‐Ni‐Mn nano‐catalysts were evaluated for carbon monoxide hydrogenation. The influence of Al2O3, SiO2, Zeolite, Active carbon, MgO supports and then the effect of best chosen support loading on the catalytic behavior and structure of ternary Co‐Ni‐Mn nano‐catalysts were studied. The Co‐Ni‐Mn/20 wt%SiO2 sample has shown highest selectivity toward light olefins production. Furthermore the influence of process conditions was investigated. Evaluation tests were performed under process conditions of P = 1–10 bar, T = 523‐623 K, and H2/CO = 0.67–3. The Response Surface Methodology (RSM) method was used for modeling and optimization process and the best conditions for catalyst evaluation were determined (T = 598.16 K, P = 1 atm and H2/CO = 2.19). Under these conditions the highest selectivity of light olefins, higher CO conversion % and lower selectivity toward methane were achieved. Catalysts characteristics were investigated using XRD, BET, TEM, TGA, DSC, SEM, XPS, and TPR techniques. © 2021 Society of Chemical Industry (SCI).

Rational design of hierarchical zeolite encapsulating FeMnK architecture to enhance light olefins selectivity in Fischer-Tropsch synthesis

Construction of core–shell catalysts is generally considered as an effective strategy for regulating hydrocarbon distribution in Fischer-Tropsch synthesis. Rational design of core–shell catalysts to enhance olefins selectivity is greatly desirable but still challenging. Herein, a series of FeMnK@H-S-1(x) catalysts (FeMnK oxide encapsulated in hollow silicalite-1 zeolite) featured with hierarchical shell were elaborately fabricated by “desilication-recrystallization” method in a mixed alkaline solution (x = NaOH/(TPAOH + NaOH)). Hierarchy factor was introduced to quantitatively describe variety of hierarchical zeolite encapsulating structures. In catalytic performance, it was found that the light olefins selectivity attained the maximum at 50.6% over FeMnK@H-S-1(0.20) catalyst with space–time yield of light olefins up to 26.7 µmolC2=-C4=.gFe−1.s−1 and performed a monotonicity increase relation with the hierarchy factor. Maximizing the hierarchy factor was beneficial to the formation of light olefins on the as-synthesized catalysts, which may result from the well coordination of shape-selective function and transport efficiency due to the optimally orchestrated porosities. Additionally, the moderate H2 activation capacity, relatively lower olefins desorption energy and the suppressed olefins secondary reaction over FeMnK@H-S-1(0.20) catalyst also contribute to the boosted light olefins selectivity. This study sheds new clues for rational catalyst design in direct light olefins synthesis from Fischer-Tropsch synthesis.

Evaluation of Fischer-Tropsch synthesis to light olefins over Co- and Fe-based catalysts using artificial neural network

Currently, energy transition due to fossil fuel negative side effects is taking place. This transition impacts the chemical industry based on light olefins reactions. Plastics, detergents, polymers, and others are mostly produced from such hydrocarbons, which are mainly originated from oil-based and highly energy-consuming processes. Fischer-Tropsch Synthesis (FTS) is a strategic technology capable to transform a given carbon source, including natural gas and biomass, into high added-value hydrocarbons. It is affected by several conditions, such as catalyst design and operating conditions and its feasibility requires a good selection of relevant process variables to optimize light olefins yield. In this work, Machine Learning models were used to predict adequate reaction conditions from the catalytic literature data. Three-layer feedforward neural networks were adjusted using a careful selection of operating conditions and catalyst composition as inputs and carbon monoxide conversion, light olefins selectivity, and carbon dioxide yield as outputs. The results indicate neural network prediction efficacy for FTS most relevant variables, such as temperature and catalyst composition. This work presents the novelty of including more variables in the model compared to recent similar studies, such as catalyst support, active phase, and promoters as inputs; and light olefins selectivity and CO2 yield as outputs. Overall, Fe-based catalyst (standard Fe (1.6 wt%) K/TiO2) presented the highest light olefins selectivity and yield at optimal conditions (T = 500 °C and 20 wt% of active phase), despite showing the highest emission of carbon dioxide.

A Hydrophilic Supported Fe3O4 Catalyst with Enhanced Light Olefins Selectivity in the Fischer‐Tropsch Synthesis

AbstractA series of Fe3O4 catalysts supported on chitosan (CTS) were prepared through successive hydrothermal synthesis, cross‐linking, and mechanical mixing of CTS. The prepared catalysts were characterized by SEM, XRD, N2 adsorption‐desorption, XPS, FT−IR, TG, H2−TPR, CO−TPD, C3H6−TPD, and contact angle (CA) analysis, then evaluated for their performance in the Fischer‐Tropsch synthesis (FTS). CTS supported Fe3O4 catalyst increased the hydrophilicity of the pristine un‐supported Fe3O4. Results revealed that the catalysts exhibit high activity with tuned product distribution in FTS. The water gas shift reaction is facilitated over the Fe3O4/CTS catalysts, and their selectivity for light olefins is significantly improved by inhibiting the secondary reaction of the initial olefins, which was confirmed by C3H6−TPD experiments. The Fe3O4 particle size has a significant influence on product distribution, with larger Fe3O4 particles being beneficial to the formation of light olefins. The 30 % Fe3O4/CTS catalyst has light olefin selectivity of 35 % with an O/P value of 2.19, which are higher than those of 21 % and 0.62 over the pristine Fe3O4.

FeMn@HZSM-5 capsule catalyst for light olefins direct synthesis via Fischer-Tropsch synthesis: Studies on depressing the CO2 formation

For Fe-based Fischer-Tropsch synthesis catalyst, how to decrease CO2 formation is a big challenge. In this work, a capsule catalyst (FeMn@HZSM-5) with FeMn as core and HZSM-5 as shell was prepared and used for Fischer-Tropsch to olefins (FTO) reaction, compared with bare FeMn catalyst and several hybrid catalysts by physically mixing FeMn and HZSM-5 in different ways. Among these catalysts, the FeMn@HZSM-5 capsule catalyst showed the best catalytic performance with the highest light olefins selectivity and the lowest CO2 selectivity. Compared with FeMn catalyst, the CO2 selectivity of FeMn@HZSM-5 catalyst decreased more than 10%. However, the CO2 selectivity of other physically mixing catalysts was similar to that of bare FeMn catalyst, indicating that randomly adding HZSM-5 had no effect on depressing the CO2 formation. Benefiting from the HZSM-5 shell, the FeMn@HZSM-5 capsule catalyst could effectively affect the diffusion of H2O and thus suppress the water-gas shift reaction in FTO reaction.

Syngas to light olefins over ZnAlOx and high-silica CHA prepared by boron-assisted hydrothermal synthesis

Transformation of syngas into light olefins (STO) over bifunctional oxide and zeolite (OX-ZEO) composite catalysts requires rational design of zeolites with moderate to low acid density and strength. As a promising zeolite component in OX-ZEO towards olefins production, the synthesis of CHA with desirable acidity remains to be a challenging task. Herein, high-silica CHA zeolite with Si/Al ranges from to 20 to ∞ were prepared via a boron-assisted hydrothermal synthesis method. The influence of Si/Al ratio on the acidity and textural properties of boron-containing CHA (BAl-CHA) was systematically studied. The syngas to olefin performance over ZnAlOx/BAl-CHA was explored. The roles of acidity, framework boron and reaction parameters in determining the olefin selectivity as well as catalyst stability were revealed. The 85.1% selectivity of light olefins was achieved over the BAl-CHA catalyst with Si/Al ratio over 300. The boron played a vital role in directing the formation of CHA structure (Si/Al > 100) and reduced the strong acid sites. The H2/CO ratio, reaction temperature, total pressure and proximity of the two components also played crucial role in determining the light olefins selectivity. A DME/methanol involved aromatic-cycle is proposed to play a predominant role in the olefin production. The residual CO and H2 are likely involved in the aromatic-cycle, and then affect the product distribution, with CO promoting the ethene selectivity while H2 enhancing the alkane selectivity.

Catalytic and deactivated behavior of SAPO-34/ZSM-5 composite molecular sieve synthesized by in-situ two-step method

This work aims at revealing the reaction and carbon behavior of SAPO-34/ZSM-5 composite molecular sieve (SZ-TS) in MTO reaction, which is synthesized via in situ two-step crystallization method. Several tests are used to explore the structure–activity relationship of the SZ-TS. The results show that the strength of weak and medium-strong acid is suitable, the particle size of two-phase molecular sieve is decreased, the hierarchical pore structure with abundant mesoporous is formed. By using the SZ-TS in MTO reaction, the methanol conversion and light olefins selectivity are 98% and 92.7%, respectively. These results can be attributed to the interface phase effect produced by etching and dissociation on the skeleton of the nuclear phase SAPO-34. The result of in situ IR and analysis of carbon deactivation indicate that polymethylbenzene is generated as the active intermediate of MTO reaction.SZ-TS with appropriate acid sites and rich mesoporous distribution could alleviate the formation rate of methyl-substituted benzene and polycyclic aromatic hydrocarbons, smaller particle size can avoid the occurrence of secondary reactions of olefins, therefore displaying the excellent resistance to the carbon deposition inactivation, with a catalytic lifetime up to 1380 min.

Steam-assisted synthesis of SAPO-34@ZSM-5 core-shell zeolite for enhancing the synergies of n-hexane-Methanol Co-Reaction to light olefins

An alternative and promising route for the production of light olefins which realizes the objective of effective resource usage is the coupling conversion of n -hexane-methanol. The SAPO-34@ZSM-5 core-shell composite has been designed and fabricated by the steam-assisted crystallization (SAC) method for boosting the n -hexane-methanol synergies. SAC avoids the undesired phase transformation/dissolution of SAPO-34 caused by exposure to harsh basic conditions of the ZSM-5 precursor solution. In comparison with the nanosized ZSM-5 or physical mixture, the SAPO-34@ZSM-5 core-shell zeolite demonstrates a 32–38 wt% increase in the light olefin selectivity, a 28–67 wt% increase in the n -hexane conversion, and an 89–143% improvement in the catalyst lifetime under identical reaction conditions. With the aid of GC-MS analysis of carbonaceous deposits in spent catalysts, higher polymethylbenzenes concentration and lower polycyclic aromatic hydrocarbon (PHA) concentration are obtained from the extracted species of spent SAPO-34@ZSM-5 in comparison with that of other samples, which suggests the aromatic-based route to light olefins is enhanced and the carbonaceous deposition is slowed down. The core-shell configuration of the SAPO-34@ZSM-5 composite diminishes the diffusion rate of methanol towards the SAPO-34 core layer and increases the coupling of n -hexane derivatives with methanol in the hydrocarbon pool (HCP) route. The decreased number of acidic sites on the external surface of the SAPO-34 core layer may also be accounted for the inhibited carbon deposition. • SAPO-34@ZSM-5 is synthesized firstly by a steam-assisted crystallization method. • Core-shell structure of SAPO-34@ZSM-5 enhances the synergistic effect of reactants. • Core-shell structure of SAPO-34@ZSM-5 slows down coking inside the SAPO-34 core layer. • A synergistic path for n-hexane-methanol co-reaction on SAPO-34@ZSM-5 is proposed.

Synthesis of low-silica SAPO-34 at lower hydrothermal temperature by additional pressure and its enhanced catalytic performance for methanol to olefin

A low hydrothermal temperature, short crystallization time and green strategy is developed for the synthesis of low-silica SAPO-34. The samples were prepared by adjusting the additional pressure with N 2 using TEA as the sole template. The pure SAPO-34 (SP-C4) was obtained only under pressure of 2.7 MPa which possessed the smaller crystal size and moderate acidity and showed enhanced the lifetime and light olefins selectivity in methanol to olefins. And the possible formation mechanism of low-silica SAPO-34 was proposed. • A green strategy is developed for the synthesis of SAPO-34 by additional pressure. • Synthesis of low-silica SAPO-34 at low hydrothermal temperature for short time. • The obtained SAPO-34 possesses the smaller crystal size and moderate acidity. • Enhanced the lifetime (520 min) and light olefins selectivity (85.0%).

Surface modification of g-C3N4-supported iron catalysts for CO hydrogenation: Strategy for product distribution

Surface modified g-C3N4 supported iron catalysts were prepared using ultrasonic-assisted impregnation and employed as model catalysts to investigate the surface modification effects on product distribution in Fischer–Tropsch synthesis. Characterizations evidenced that both hydroxyl and amino groups were grafted on the g-C3N4 surface. Results showed that the selectivity of light olefins in hydrocarbons was increased from 12.3% on pure Fe3O4 to 31.5% on Fe/C3N4 further to 38.4% on Fe/AMC3N4 under same reaction condition as well as elevated activity owing to electron transfer of amino groups. But high CO2 selectivity was inevitable via the enhanced water gas shift reaction. H2O2 treatment increased the hydrophilicity of g-C3N4, resulting in predominance of water-assisted pathway promoted the chain growth. Compared with Fe/C3N4, the CH4 selectivity for Fe/OHC3N4 was significantly reduced from 38.4% to 22.8%. The Fe/OHC3N4 also exhibited lower CO2 selectivity of 11.4% than Fe/AMC3N4 of 24% due to the enrichment of surface hydroxyl. Surface modification played a critical role in tuning the product distribution and promoting the formation of light olefins with low C1 by products (CH4 and CO2).