Fixed-bed Microreactor Research Articles

Study on the Acidic Modification of Mesoporous HZSM-5 Zeolite and Its Catalytic Cracking Performance

Mesoporous HZSM-5 zeolites with nanocrystal stacking morphology were directly synthesized via hydrothermal methods without mesoporous templates. The synthesized mesoporous HZSM-5 was subjected to hydrothermal–citric acid washing treatment. The structural and acidic properties of the samples before and after modification were characterized using various techniques. The catalytic performance for butene conversion to propylene was investigated under atmospheric pressure, 500 °C, and a butene weight hourly space velocity (WHSV) of 10 h−1 in a continuous-flow micro-fixed bed reactor. The results show that propylene selectivity increased significantly from 24.7% before modification to 44%, and propylene yield increased from 22% to 38%. After 2 h of hydrothermal–citric acid washing modification, the catalyst maintained a butene conversion rate of 76% and a selectivity of 47% at 525 °C and a WHSV of 10 h−1 after 130 h of continuous reaction, with a propylene yield of 37%. The results indicate that moderate hydrothermal–citric acid washing modification leads to the removal of aluminum from the zeolite framework, reducing the amount and strength of acid but increasing the mesopore quantity. This helps control the reaction pathways and diffusion of intermediate products, suppresses some side reactions, and improves the selectivity and yield of the desired product, propylene, while significantly enhancing catalytic stability.

Activity of CuCoCe layered double hydroxides catalysts and mechanism for C3H6-SCR

CuxCoyCez-LDH prepared with layered double hydroxides (LDHs) as precursors was calcined to form CuxCoyCezO catalysts which were experimentally investigated for the selective catalytic reduction of NO by C3H6 (C3H6-SCR) in a fixed bed micro-reactor in the presence of O2. The physical–chemical properties of the catalysts were characterized and analyzed with respect to the SCR reactivity. In situ DRIFTS study was conducted to investigate the intermediate species during the SCR reaction. Results showed that NO conversion was as high as 95 % at 225 °C over Cu0.21Co0.48Ce0.31O catalyst. The excellent activity of the catalyst could be attributed to the synergistic effect between Cu, Co, and Ce. The XRD results showed that the synergistic effect between the metals was because of the formation of the solid solution between Cu, Co, and Ce, which promoted the interaction and dispersion of the three active components. EDS mapping further proved this point. According to the XPS data, Cu and Co had a redox reaction that increased the number of oxygen vacancies favorable for NO adsorption and dissociation. The redox properties between Cu and Co was further confirmed to improve the catalytic activity by H2-TPR. Additionally, the results of BET and NH3-TPD demonstrated that the SCR catalytic activity was promoted by the right quantity of acidic sites and the specific surface area. In situ DRIFTS experiments provided a mechanism for the C3H6-SCR reaction on the catalyst and confirmed the formation of reaction intermediates such as bidentate and monodentate nitrate, formate, and acetate.

Enhanced light olefin production from CO2 over potassium promoted Fe–Co bimetallic ZrO2 supported catalysts

Over 1300 tons of carbon dioxide (CO2) is emitted into the earth's atmosphere every second, threatening to breach the limiting global temperature increase of 1.5 °C set under the Paris Agreement. It is considered as sustainable feedstock that ensures season-wide availability for producing oxygenates and olefins. Likewise, CO2 hydrogenation to lower olefins was performed using bimetallic Fe-Co catalysts, processed in situ in a fixed-bed catalytic microreactor at 280–380 °C and a pressure of 0.5–3 MPa. A MOF framework (UIO-66) was used to fabricate ZrO2 NPs. In addition, a series of potassium-promoted Fe-Co bimetallic catalysts over the ZrO2 NPs were prepared, characterised and studied for the hydrogenation of carbon dioxide to light olefins. With increasing K content, the selectivity of C2-C4 increased under all operating conditions. The spent catalyst exhibits the bimodal size distribution of Fe3C, Fe2O3 and Fe° after a modified Fischer-Tropsch synthesis (M−FTS) reaction. The XANES data shows that the energy of the Fe K-edge and the Zr K-edge are shifted in a positive direction compared to the respective foil, indicating the presence of oxides in the fresh catalyst. Under the optimised reaction conditions, the H2-pretreated K promoted Fe-Co catalyst (K5Co3Fe10/ZrO2) showed remarkably low methanation with an olefin (C2-C4) selectivity of 38 %. In addition, the catalyst exhibits excellent stability and activity, providing nearly constant CO2 conversion and selectivity of (C2−C4=) lower olefins, CO and paraffin over the 100 h time-on-stream.

Hydrodesulfurization of Thiophene in n-Heptane Stream Using CoMo/SBA-15 and CoMo/AlSBA-15 Mesoporous Catalysts

Heterogeneous catalysts containing cobalt and molybdenum supported on mesoporous materials types SBA-15 and AlSBA-15 were synthesized for application in the HDS reactions of thiophene in the n-heptane stream. The materials were synthesized by the hydrothermal method using Pluronic P123 as a template. The calcined SBA-15 and AlSBA-15 supports were submitted to co-impregnation with solutions of cobalt nitrate and ammonium heptamolybdate, aiming for the production of 15% in mass of metal loading with an atomic ratio of [Co/(Co + Mo)] = 0.45. The obtained materials were dried and calcined to obtain the mesoporous catalysts in the forms of CoMo/SBA-15 and CoMo/AlSBA-15. The catalysts were characterized by XRD, TG/DTG, SEM, and nitrogen adsorption. From XRD analysis, it was verified that after the decomposition of the cobalt and molybdenum salts, MoO3, Co3O4, and CoMoO4 oxides were formed on the supports, being attributed to these chemical species, the activity for the HDS reactions. The catalytic activity of the obtained catalysts was evaluated in a continuously flowing tubular fixed-bed microreactor coupled on-line to a gas chromatograph, using an n-heptane stream containing 12,070 ppm of thiophene (ca. 5100 ppm of sulfur) as a model compound. The synthesized catalysts presented suitable activity for the HDS reaction, and the main obtained products were cis- and trans-2-butene, 1-butene, n-butane, and low amounts of isobutane. The presence of 1,3-butadiene and tetrahydrothiophene (THT) was not detected. A mechanism of the primary and secondary reactions and subsequent formation of the olefins and paraffins in the CoMo/SBA-15 and CoMo/AlSBA-15 mesoporous catalysts was proposed, considering steps of desulfurization, hydrogenation, dehydrogenation, THT decyclization, and isomerization.

Tailored design of novel Co0-Coδ+ dual phase nanoparticles for selective CO2 hydrogenation to ethanol

Catalytic hydrogenation of CO2 to ethanol is a promising solution to address the greenhouse gas (GHG) emissions, but many current catalysts face efficiency and cost challenges. Cobalt based catalysts are frequently examined due to their abundance, cost-efficiency, and effectiveness in the reaction, where managing the Co0 to Coδ+ ratio is essential. In this study, we adjusted support nature (Al2O3, MgO-MgAl2O4, and MgO) and reduction conditions to optimize this balance of Co0 to Coδ+ sites on the catalyst surface, enhancing ethanol production. The selectivity of ethanol reached 17.9% in a continuous flow fixed bed micro-reactor over 20 mol% Co@MgO-MgAl2O4 (CoMgAl) catalyst at 270 °C and 3.0 MPa, when reduced at 400 °C for 8 h. Characterisation results coupled with activity analysis confirmed that mild reduction condition (400 °C, 10% H2 balance N2, 8 h) with intermediate metal support interaction favoured the generation of partially reduced Co sites (Coδ+ and Co0 sites in single atom) over MgO-MgAl2O4 surface, which promoted ethanol synthesis by coupling of dissociative (CHx*)/non-dissociative (CHxO*) intermediates, as confirmed by density functional theory analysis. Additionally, the CoMgAl, affordably prepared through the coprecipitation method, offers a potential alternative for CO2 hydrogenation to yield valuable chemicals.

Enhancement of higher alcohols selectivity in Fischer-Tropsch synthesis using Walnut and Almond shell derived biochars as Copper/Cobalt catalyst support

The production of higher alcohols from synthesis gas using biochar-supported copper-cobalt catalysts is investigated. Biochars were prepared via pyrolysis of Walnut shells and Almond shells and were subsequently activated through physical and chemical methods. A 15 wt% Copper and 5 wt% Cobalt was loaded on the activated biochars via the impregnation technique. The chemical and physical properties of the catalysts were studied using various methods. The catalytic performance of the catalysts was assessed in a fixed-bed microreactor at 20 bars, 320 °C, and, an H2/CO ratio of 2, and the results were compared with the γ-Alumina supported catalyst. Strong interaction between cobalt and copper particles and the formation of bimetallic CuCo2O4 species were observed. The catalysts' reducibility was enhanced by a factor of 1.42. The catalytic studies revealed a significant enhancement in the rate of carbon monoxide hydrogenation. The catalyst supported on low-cost Almond shell-derived biochar demonstrated the best performance. The total alcohol selectivity increased from 22.2 wt% to 34.2 wt%, and the C2+ alcohol selectivity rose from 78.3 wt% to 91.1 wt%, as compared to the industrial catalyst supported on alumina. However, the selectivity for C5+ liquid hydrocarbons decreased to 16.8 wt%. Notably, biochar-supported catalysts also exhibited good stability.

Selective deep desulfurization of liquefied petroleum gas on Ni/ZnO-based catalyst

Process of selective deep desulfurization of liquefied petroleum gas (LPG) was developed using a Ni/ZnO-based catalyst. Ethyl mercaptan, dimethyl disulfide and methyl disulfide were used as model compounds in LPG to investigate sulfides conversion over different catalysts. All three model sulfides were totally removed over the composite catalyst at above 300 °C in hydrogen atmosphere. Desulfurization of LPG from FCC unit were studied in a micro-fixed bed reactor, and scaled up in a fixed-fluidized bed reactor. Results showed that highly selective desulfurization of LPG could be achieved using the composite catalyst when the sulfur loading of catalyst was in a particular range. The sulfur content of LPG could be decreased to lower than 2.0 μg·g−1 with an olefin loss ratio of less than 1.5 %. X-ray photoelectron spectroscopy (XPS) characterization indicated that the interaction of Ni with S strengthened with the increasing of sulfur loading. Density functional theory calculations showed that the pre-coated S on Ni (111) surface increased the adsorption energy difference between propylene and sulfides which was helpful for the retention of propylene during desulfurization on Ni/ZnO-based catalyst.

Reaction mechanism study of catalytic conversion of light straight-run naphtha to light olefins over micro-spherical HZSM-5 zeolite catalyst

Catalytic conversion of naphtha has attracted attention as an alternative method to the conventional thermal cracking to produce light olefins in an environment-friendly and energy-efficient way. In this work, a reaction mechanism study of light straight run naphtha cracking over micro-spherical catalyst containing HZSM-5 was systematically investigated using single hydrocarbon feeds, and the straight run naphtha itself. The identified reaction pathways from the single feeds along with the naphtha experimental data have been utilized to investigate reaction pathways of the naphtha conversion reactions. The experimental tests were carried out in the temperature ranges of 450–650 ℃ and space-times of 0.3–1.5 min using a fixed bed micro-reactor in isothermal and isobaric conditions. The product distribution for the naphtha feed shows that light paraffins and light olefins are the primary products, which are products of monomolecular protolytic cracking of the paraffin components of the naphtha feed. The olefin interconversion reactions illustrated that oligomerization and cracking by β-scission dominate the secondary reactions of naphtha catalytic cracking conversions. The experiments conducted on cyclohexane, cyclohexene and n-hexane single feeds revealed that BTX formation proceeds through the formation of C6-C8 naphthenes, and C6-C8 cyclo-olefinic intermediates. Low temperatures and space times promote the selectivity to propylene while the selectivity of ethylene increases with temperature. The degree of thermal cracking (DTC) illustrated that thermal cracking is considerable only for temperatures of higher than 550 ℃.

Catalyst-enhanced autothermal chemical looping reforming: Intrinsic SMR kinetics and numerical simulation

In this work, we propose a catalyst-enhanced autothermal chemical looping reforming (CE-aCLR) to address the environmental concerns associated with toxic Ni-based oxygen carrier (OC) and the low fuel conversion related to the low reactivity of Fe-based OC. In this process, a non-toxic noble-metal-based steam methane reforming (SMR) catalyst is employed for methane conversion, while a Fe-based OC is employed for oxygen transfer between two reactors. Firstly, a commercial Rh-based SMR catalyst is studied in a micro-fixed bed reactor and its intrinsic reaction kinetics are determined. Then, a 1-D CE-aCLR model is developed based on a verified multi-scale aCLR model to facilitate analyzing commercial-scale feasibility. This model accounts for the essentials of the reactor hydrodynamics, mass and heat transfer, detailed reaction kinetics, and the influence of the solids residence time distribution in the fuel reactor. The main dimensions of a commercial CE-aCLR unit are determined and this unit is simulated using the developed model. The results demonstrate the feasibility of the novel, environmentally friendly process that enables high methane conversion using Fe-based OC within realistically sized reactors and an acceptable solid circulation rate. Moreover, sensitivity study shows that the CE-aCLR allows using OCs with low activity (potentially low cost) while maintaining high CH4 conversion.

A facile strategy to prepare ZSM-5-based composites with enhanced light olefin selectivity and stability in the HTO process.

In this study, the influence of different ZSM-5 composite materials (ASA, γ-alumina, η-Al2O3, SiO2, and attapulgite) and their performance in the n-hexane catalytic cracking process in a fixed bed microreactor at 550 °C under atmospheric pressure was studied. XRD, FT-IR spectroscopy, NH3-TPD, BET, FE-SEM, and TG analyses were performed to characterize the catalysts. The result of the n-hexane to olefin process indicated that the A2 catalyst (γ-alumina composition with ZSM-5) showed the highest conversion of 98.89%, highest propylene selectivity of 68.92%, highest yield of light olefins of 83.84%, and highest propylene to ethylene ratio of 4.34. The reason for the significant increase in all these factors and the lowest amount of coke in this catalyst is the use of γ-alumina, which increased the hydrothermal stability and resistance to deactivation, improved the acidic properties with a strong to weak acid ratio of 0.382, and increased the mesoporosity to 0.242. This study indicates the effect of the extrusion process and the composition and the major effect of the properties of this material on the physicochemical properties and distribution of the product.

Controlling the Activity and Selectivity of HZSM-5 Catalysts in the Conversion of Biomass-Derived Oxygenates Using Hierarchical Structures: The Effect of Crystalline Size and Intracrystalline Pore Dimensions on Olefins Selectivity and Catalyst Deactivation

The conversion of biomass-derived oxygenates over zeolite catalysts constitutes a challenge for the efficient production of bio-based chemicals and fuels due to difficulty in controlling the selectivity and high coke formation of such reactions. This is partly attributed to the microstructure of zeolite catalyst which affects the conversion and selectivity of products derived from biomass-derived oxygenates. In this study, the conversion and deactivation characteristics of three different model oxygenates found in biomass bio-oil (namely, acetol, furfural and guaiacol) over ZSM-5 zeolites of varying acidity, pore and crystal size prepared with bottom-up and top-down approaches were evaluated using a fixed bed microreactor at atmospheric pressure and a space velocity of 5 h−1 at a temperature range of 450–650 °C. Analysis of the experimental results indicates that the optimum temperature for such conversions is in the vicinity of 600 °C allowing for complete conversion of the compounds and high resistance to coking. The mechanisms of those conversions are discussed based on the obtained results. In general, crystal size and mesoporosity induce easier access to active sites improving mass transfer but also alter the location type, and strength of acid sites allowing for higher yields of primary and intermediate products such as olefins.

Effect of simultaneous dealumination and metal incorporation of zeolite ZSM-5 on the catalytic performance in HTO process

The hierarchical Metal Fluorinate ZSM-5 zeolites, known as M-F-Z (M: Ga, Fe, Zr, La, Ce), were modified and dealuminated through the post-synthesis method, using an NH4HF2 + metal salt mixture. The zeolites were utilized in the catalytic cracking of normal hexane to produce light olefins in high yield and propylene to ethylene ratio. A unique post-synthesis method was used in this study without any structural collapse in which a significant amount of the metal was incorporated into the zeolite framework to provide effective interactions with the acidic sites. The catalytic cracking and investigation of the performance of the prepared catalyst were carried out in a fixed-bed microreactor system. The effect of zeolite modification during the dealumination process; especially acidity changes and hierarchical factors, on the performance of the modified ZSM-5 zeolite was studied. The modified catalysts showed superior acidic properties and higher mesoporosity volume compared with the parent zeolite. XRD, ATR-FTIR, FESEM, AAS, UV–visible (DRS), BET, EDX Dot-Mapping, H2-TPR, NH3-TPD, and TGA analyses were used to determine the physicochemical properties of the modified zeolites. Based on the results, the modified Ga-F-Z zeolite, with the minimum strong to weak acidic site ratio (0.1) and the highest hierarchical factor (0.192), had the maximum light olefin production yield and propylene to ethylene ratio of 63.26% and 3.13, respectively, which is a significant improvement compared to the parent zeolite.

A high activity mesoporous Pt@KIT-6 nanocomposite for selective hydrogenation of halogenated nitroarenes in a continuous-flow microreactor.

In this study, we designed a Pt@KIT-6 nanocomposite prepared by impregnating platinum nanoparticles on the nanopores of the KIT-6 mesoporous material. This Pt@KIT-6 nanocomposite was used as a catalyst in a micro fixed bed reactor (MFBR) for the continuous-flow hydrogenation of halogenated nitroarenes, which demonstrates three advantages. First, the Pt@KIT-6 nanocomposite has a stable mesoporous nanostructure, which effectively enhances the active site and hydrogen adsorption capacity. The uniformly distributed pore structure and large specific surface area were confirmed by electron microscopy and N2 physisorption, respectively. In addition, the aggregation of the loaded metal was avoided, which facilitated the maintenance of high activity and selectivity. The conversion and selectivity reached 99% within 5.0 minutes at room temperature (20 °C). Furthermore, the continuous-flow microreactor allows precise control and timely transfer of the reaction system, reducing the impact of haloid acids. The activity and selectivity of the Pt@KIT-6 nanocomposite showed virtually no degradation after 24 hours of continuous operation of the entire continuous-flow system. Overall, the Pt@KIT-6 nanocomposite showed good catalysis for the hydrogenation of halogenated nitroarenes in the continuous-flow microreactor. This work provides insights into the rational design of a highly active and selective catalyst for selective hydrogenation systems.

Synthesis, Characterization, and Application of Pt/PtO2-TiO2/SiO2 Materials on a Continuous Flow Packed Bed Microreactor for Enhanced Photocatalytic Activity under Sunlight

The present work aimed at the development of Pt-TiO2/SiO2 materials applied to the degradation of a pharmaceutical pollutant in a fixed-bed microreactor in continuous mode. First, a wide investigation of the optimal platinum content in TiO2/SiO2 was carried out based on extensive characterization through XRD, DRS, SEM, TEM, and XPS techniques. For the content range studied, no significant changes were observed in the crystallinity of the material, with peaks related to the anatase phase and PtO2 in the diffractograms. SEM images combined with EDS spectra indicated the presence of platinum and a large heterogeneity in the particles. MET analyses showed PtO2 nanoparticles in close contact with TiO2, allowing the formation of a type II heterojunction. XPS showed platinum in the 0 and +4 oxidation states, suggesting that platinum metal and PtO2 are both present. Regarding the degradation experiments, the optimal catalyst achieved 81% degradation of acetaminophen for a residence time of 1 h, while the catalyst without platinum reached only 27% degradation. The catalyst activity dropped from 81 to 57% in 2 h and remained stable for six reuse cycles. Increasing the inlet flow rate and concentration reduced the pollutant degradation although there was an increase in the reaction rate. Finally, a photocatalytic mechanism was proposed in which a type II heterojunction was developed, with generation of hydroxyl radicals by the positive holes in the VB of TiO2 as well as superoxide radicals by the electrons in the CB of PtO2.

The Effect of Y Zeolites with Different Pores on Tetralin Hydrocracking for the Production of High-Value Benzene, Toluene, Ethylbenzene and Xylene Products

A series of Y zeolites with different pore properties was prepared as a support for hydrocracking catalysts for the production of BTEX (benzene, toluene, ethyl-benzene, and xylene) from tetralin. Some important characterizations, including N2 adsorption–desorption, NH3-TPD, Py-IR, and HRTEM, were applied to obtain the properties of different catalysts. Meanwhile, the tetralin hydrocracking performances of those catalysts were investigated on a high-pressure fixed-bed microreactor. The results showed that Si/Al ratio is the core property of zeolites and that the increase in the Vmicro/Vmeso of zeolites could facilitate the formation of BTEX products by hydrocracking tetralin. The method of hydrocracking tetralin was proposed. It was also found that the hydrogenation–cracking path was controlled by aromatic saturation thermodynamics, and strong acidity aided the backward shift of equilibrium temperature.

Effect of O2 on Selective Catalytic Reduction of NO by C3H6 over Fe Catalysts Supported on Porous Clay Heterostructures (Fe-PCH)

K10 montmorillonite was used as the raw clay to prepare porous clay heterostructures (PCH) by organic template intercalation and tetraethylorthosilicate (TEOS) was used as silicone source. Fe was load on the PCH support by impregnation method to prepare Fe-PCH catalysts. The catalytic activity tests were carried out in a fixed bed micro-reactor in the atmosphere of 0.1% C3 H6 , 0.1%NO, 0~10%O2 in N2 balance. The total flow rate was 100ml/min and corresponding gas hourly space velocity (GHSV) was 15000h-1. The mircro-reaction pathways were studied by Diffuse Reflection Infrared Fourier Transform Spectrometer (DRIFTS). The influence of O2 on the SCR-C3 H6 reactivity over Fe-PCH was analyzed. The results showed that FePCH catalyst exhibited the best catalytic performance without oxygen, which reached the maximum NO conversion of 100% at 4000 C. When the concentration of O2 is below a critical value, [O2 ]crit, the catalytic activity gradually decreased with the increasing concentration of O2 . When the concentration of O2 is above [O2 ]crit, the NO conversion was only 20%~30%. Fe-PCH catalysts were characterized by transmission electron microscope (TEM), N2 adsorption/desorption and X-ray photoelectron spectroscopy (XPS) techniques. The results showed that Fe-PCH had supermicroporous and mesoporous structures. The active components on Fe-PCH catalyst were mainly α-Fe2 O3 nanorods, exposing (024) and (104) planes. The in situ DRIFTS technique was used to detect the reactive intermediates over the surface of Fe-PCH catalyst, which could help analyze the mechanism of the influence of oxygen on catalytic activity. The results presented that oxygen could inhibit the formation of isocyanate species over Fe-PCH catalyst during C3 H6 -SCR, which might be the reason for the decrease of NO conversion. Finally, a reasonable reaction path of C3 H6 -SCR over Fe-PCH catalyst was proposed.

Oxidation of Toluene by Ozone over Surface-Modified γ-Al2O3: Effect of Ag Addition

In this study, the ability of ozone to oxidise toluene present in low levels into CO and CO2 was studied. The catalytic ozonation of toluene was carried out in a micro-fixed bed reactor. The oxidation was done in two steps: toluene adsorption on the catalyst followed by sequential ozone desorption. Toluene breakdown by ozone at low temperature and atmospheric pressure was achieved using γ-Al2O3 supported transition metal oxides impregnated with a reduced noble metal. The catalyst Ag–CoOx/γ-Al2O3 efficiently oxidised and transformed toluene into products (52.4% COx yield). This catalyst has a high surface area, more acidic sites, and lattice oxygens for better toluene oxidation. The addition of Ag to the CoOx/γ-Al2O3 catalyst surface improved toluene adsorption on the catalyst surface, resulting in improved product yield, selectivity, and carbon balance.

Preparation of Cs/Cu-LDO@X catalysts and reaction mechanism of the side-chain alkylation of toluene to styrene

The Cu-LDH@X composite materials were synthesized using the in-situ self-sacrificial template method, and the acid-base bifunctional Cs/Cu-LDO@X catalysts were prepared by impregnation-calcination. The as-synthesized catalysts were characterized by XRD, N2 adsorption-desorption, SEM, HRTEM (EDS), FTIR, XPS, NH3-TPD, CO2-TPD techniques. The catalytic performance of the catalysts was evaluated in one step by implying a fixed-bed microreactor for the side-chain alkylation of toluene with methanol to styrene. The reaction mechanisms of the side-chain alkylation on the catalysts surface were deeply investigated. The Cs/Cu-LDO@X catalysts with adjustable acid-base sites and nanolayered structures demonstrated good catalytic performance for the side-chain alkylation of toluene. The Cs/Cu-LDO@X-3 catalyst exhibited the best catalytic performance with toluene conversion is up to 6.58%, while the selectivity of side-chain alkylated products and styrene is 91.64% and 54.16% respectively. The reaction mechanism investigation indicates that methanol dehydrogenated firstly to form formaldehyde under the action of the base sites on the catalyst surface, later, the adsorbed toluene on the acid sites underwent side-chain alkylation with formaldehyde. High selectivity of produced styrene owing to the synergistic interactions of acid-base sites and layered space-confined effects of the catalytic system.

Performance of catalytic cycloaddition of CO2 to styrene oxide in three-phase co-current (micro)fixed-bed and monolith reactors

Synthesis of cyclic carbonates via catalytic cycloaddition of CO2 to epoxides represents one of the most promising green routes for CO2 utilization. The present work investigates, from a multiphase reactor engineering perspective, the design of three-phase catalytic reactors for cycloaddition of CO2 to styrene oxide in the presence of non-deactivating silica-supported pyrrolidinopyridinium iodide catalyst via an exhaustive modeling framework containing a series of isothermal unsteady-state two-dimensional models. A comparative analysis is made for fixed-bed reactors/microreactors and three-phase monolith reactors. The results show a remarkable performance of fixed-bed microreactor which significantly outperforms both fixed-bed and monolith reactors and hold great promise for efficient implementation of CO2 cycloaddition process under relatively mild reaction conditions. At equal liquid space velocity, upflow monolithic reactor outperforms downflow/upflow fixed-bed reactors due to reduced resistance to external and internal diffusion in catalyst pore network, but it would require a higher reactor volume for the same amount of catalyst. A confinement-induced amplification of concentration of CO2 adsorbed on the surface of catalyst generates an enhanced performance of styrene carbonate synthesis process due to increased sorption of CO2. Fixed-bed microreactor generates the smallest confinement-induced performance improvement, possibly because catalytic process is controlled by the considerable improvement in mass transfer.

Influence of adding a modified zeolite-Y onto the NiMo/Al2O3 catalyst utilized to produce a diesel fuel with highly reduced sulfur content

In order to make a Na–Y zeolite with Si/Al ratio of 2.27 more acidic with a higher volume of mesopores, a combination of different and consecutive methods including; chemical (i.e.; utilizing different compounds, such as NH4F and EDTA) and thermal/hydrothermal (i.e.; implementing calcination/steaming) methods, were employed for modification and dealumination. The combination of acidic-hydrothermal dealumination method led to a further structural collapse compared to that of the acidic calcination. In comparison with the other dealumination methods, the fluorination strategy (i.e.; utilizing NH4F) resulted in a zeolite with higher crystallinity, acidity, and specific surface area. The modified and dealuminated zeolites were employed to prepare the catalyst support of FAU + Al2O3 for the HDS process. The sulfidation and performance evaluation of the prepared catalysts were carried out in a fixed bed microreactor. Then after, the effects of zeolite modification during the dealumination process, especially acidity and Si/Al ratio variations, upon the activity of NiMo/FAU + Al2O3 catalyst were understudied. Results indicated that, the enhanced performance of the catalysts containing the modified zeolites in removing of the sulfur containing aromatic compounds, as well as their longer observed lifetime in terms of lower coke deposition levels were obtained. The removal of the sulfur containing compounds increased with acidity so that the maximum removal (i.e.; of conversion = 93%) was determined using Cat-F-AT-Cal catalyst containing the zeolite modified by acid treatment-calcination together with fluorination. In addition, the highest performances in terms of removal of aromatic compounds and catalyst lifetime (i.e.; due to lower coke deposition) were shown by the Cat-AT-St and Cat-AT-Cal catalysts, respectively. These species contained the zeolite modified through the acid treatment-steaming and acid treatment-calcination methods, respectively.