Gas Hourly Space Velocity Research Articles

ZnO–ZrO2 coupling nitrogen-doped carbon nanotube bifunctional catalyst for co-production of diesel fuel and low carbon alcohol from syngas

Catalytic syngas conversion to liquid fuel is pivotal for biomass utilization, enhancing energy security, reducing carbon emissions and curbing reliance on petroleum imports. Herein, bifunctional catalysts comprising zinc-zirconium dioxide (ZnZrO2) dispersed on nitrogen-doped multi-walled carbon nanotubes (NCNT) (ZnZrO2/NCNT) were successfully designed, enabling the simultaneous production of both diesel fuels (C9–C16 hydrocarbon) and methanol through direct syngas conversion. Operating at 450 °C, 4.5 MPa, a gas hourly space velocity (GHSV) of 4800 mL h−1·gcat−1, the ZnZrO2/NCNT catalyst, featuring 2.6% nitrogen doping, exhibited exceptional performance, achieving a 50.3% selectivity for C9–C16 hydrocarbons and a 26.4% selectivity for methanol, while maintaining a 52.5% single-pass CO conversion rate. The C9+ selectivity significantly surpasses the bottleneck predicted by the ASF distribution theory (C9+ selectivity <36%). This starkly contrasts that of ZnO/NCNT (1.7% C9–C16 and 6.3% methanol) and ZrO2/NCNT (32.5% C9–C16 and 25.4% methanol) catalysts. Moreover, the ZnZrO2/NCNT catalyst still retained C9+ 51.5% selectivity and 25% methanol selectivity after 100 h of continuous operation. The synergistic effects resulting from the amalgamation of highly active nanostructured units with a well-encapsulation structure efficiently hinder active component migration during catalysis. This significantly enhances both the catalyst's activity and stability. Furthermore, nitrogen introduction serves as a key electron donor to ZnZrO2, thereby catalyzing the activation of CO dissociation. This activation step emerges as a pivotal factor crucial for enhancing selectivity in liquid fuel production.

Nano-crystalline NiO-MgO/NiAl2O4 catalyst for coking free low temperature partial oxidation of methane

Here, we report an ultra-small-sized nano-crystalline NiO-MgO/NiAl2O4 catalyst for coking-free partial oxidation of methane reaction at low temperature (450 °C). The catalyst was tested in a packed-bed reactor over a temperature range of 350 to 850 °C. The NiO-MgO/NiAl2O4 catalyst was optimized for calcination temperature and nickel content. The best-optimized sample was then tested for different gas hourly space velocities (GHSVs), resulting in 99 % CH4 conversion and varying H2/CO selectivities from 90 % to 70 % at 450 °C. A stability test was conducted at 500 °C for 100 h for stream on reaction conditions, resulting in 95 % CH4 conversion, 90 % H2 selectivity, and 60 % CO selectivity without any significant deactivation. The excellent catalytic activity and stable performance were attributed to the ultra-small size and nanocrystalline structure of NiO-MgO, as well as the presence of lattice oxygen reservoirs. Additionally, the synergistic interaction between the NiO-MgO solid solution and the support NiAl2O4 contributed to these properties.

Variable frequency microwave induced CO2 Boudouard reaction over biochar

The Boudouard reaction presents promising application prospects as a straightforward and efficient method for CO2 conversion. However, its advancement is hindered primarily by elevated activation energy and a diminished conversion rate. This study employed a microwave reactor with a variable frequency as the initial approach to catalyze the CO2 Boudouard reaction over biochar, with the primary objective of producing renewable CO. The study systematically investigated the influence of various variables, including the heating source, microwave frequency, microwave power, gas hourly space velocity (GHSV), and carrier gas, on the conversion of CO2 and the selectivity towards CO. The experimental findings indicate that under static conditions, with a fixed microwave frequency set at 2450 MHz and 100 W microwave power, the Boudouard reaction did not initiate. Conversely, a CO2 conversion rate of 8.8% was achieved when utilizing a microwave frequency of 4225 MHz. Under this unique frequency, further elevating the microwave power to 275 W leads to the complete conversion of CO2. Furthermore, a comparative analysis between microwave and electrical heating revealed that the CO production rate was 37.7 μmol kJ−1 for microwave heating, in stark contrast to the considerably lower rate of 0.2 μmol kJ−1 observed for electric heating. Following the reaction, the biochar retained its robust 3D skeleton structure and abundant pore configuration. Notably, the dielectric constant increased by a factor of 1.8 compared to its initial state, rendering it a promising microwave-absorbing material.Graphical

Al-rich Cu-SSZ-13 zeolite synthesized by interconversion from Y: Crystallization process resolution and application in the selective catalytic reduction of NO with NH3

Cu-SSZ-13 zeolite is a promising catalyst in the selective catalytic reduction (SCR) of NOx with NH3 and the interzeolite conversion is considered as a convenient method with relatively low cost to get the Al-rich SSZ-13 zeolite with great hydrothermal stability. However, the crystallization process of interzeolite conversion and its relation to the catalytic performance of Cu-SSZ-13 in the NH3-SCR of NOx are still poorly understood. Herein, the interzeolite conversion process of Y to SSZ-13 was well resolved and the effect of major synthesis factors on the hydrothermal stability and catalytic performance of Cu-SSZ-13 in the NH3-SCR of NOx was investigated. The results indicate that highly crystalline SSZ-13 can be synthesized by the interzeolite conversion from Y, using N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) as the structure-directing agent (SDA) and with a SDA/Si molar ratio of 0.06–0.2. The Y zeolite of FAU framework is first degraded and decomposed into the oligomeric aluminosilicate fragments quickly in the alkaline circumstance; thereafter, the oligomeric fragments develop into the crystal nuclei that arouse the rapid crystallization of the SSZ-13 zeolite of CHA framework with the help of SDA and solid Al(OH)3, during which the Al(OH)3 source is dissolved and restructured to tetrahedral Al species and incorporated into the CHA framework. The synthesized Cu-SSZ-13 zeolite exhibits excellent catalytic performance in the NH3-SCR of NO, achieving an NO conversion of nearly 90% at a rather low temperature of 150 °C and a gaseous hourly space velocity (GHSV) of 100,000 h−1. Moreover, the Cu-SSZ-13 catalyst displays great hydrothermal stability and remains highly active even after aging at 800 °C. These results help to clarify the mechanism of interzeolite conversion and provide an effective method to synthesize highly crystalline Al-rich SSZ-13 zeolite with great potential for application in the NH3-SCR of NOx.

Introducing a novel catalyst for efficient conversion of CO2 into syngas through reverse-water-gas-shift (RWGS) reactions based on highly mesoporous structures MCM-41: Influence of the Fe incorporation

The RWGS is the first step in CO2 hydrogenation. This process converts CO2 into valuable compounds, such as methanol, to address the global issue of CO2 emissions. In this research, the performance of a Cu-Fe bimetallic catalyst mounted onto MCM-41 support in RWGS was investigated. Our results demonstrate that MCM-41′s high specific surface area is advantageous for dispersing active metals and preventing their sintering. The Cu-Fe supported on MCM-41 samples are characterized by Scanning Electron Microscopy (SEM), ex situ X-ray Diffraction (XRD), Brunner–Emmet–Teller (BET), and Temperature Programmed Reduction (TPR). In order to investigate the catalytic activity, key variables including a temperature range of 400–600 °C, different H2/CO2 ratios, and various gas hourly space velocities (GHSV) at atmospheric pressure were assessed. In this study, excellent CO2 conversion was attained at a high GHSV (96,000 ml g-1h−1), which is advantageous for the design of smaller reactor volumes. In comparison to industrial Copper-Zinc catalysts and iron-free copper-supported MCM-41 catalysts, which suffer from a high sintering rate at temperatures above 300 °C, adding Iron (Fe) to the copper could increase the catalyst's activity and stability in terms of CO2 conversion and CO selectivity due to the formation of a Cu-Fe alloy. The novelty of this study lies in the assessment of the benefits afforded by bimetallic Cu-Fe catalysts in conjunction with high surface area MCM-41. Also, three different ratios of Cu-Fe (10-1, 7-1, 4-1) were considered for our experiments. The Cu-Fe = 10-1 ratio reached the highest CO2 conversion and CO selectivity value in 600 °C with amounts of 49 % and 99.7 %, respectively.

Constructing Heterointerfaces in Dual-Phase High-Entropy Oxides to Boost O2 Activation and SO2 Resistance for Mercury Removal in Flue Gas.

The low O2 activation ability at low temperatures and SO2 poisoning are challenges for metal oxide catalysts in the application of Hg0 removal in flue gas. A novel high-entropy fluorite oxide (MgAlMnCo)CeO2 (Co-HEO) with the second phase of spinel is synthesized by the microwave hydrothermal method for the first time. A high efficiency of Hg0 removal (close to 100%) is achieved by Co-HEO catalytic oxidation at temperatures as low as 100 °C and in the atmosphere of 145 μg m-3 Hg0 at a high GHSV (gas hourly space velocity) of 95,000 h-1. According to O2-TPD and in situ FT-IR, this extremely superior catalytic oxidation performance at low temperatures originates from the activation ability of Co-HEO to transform O2 into superoxide and peroxide, which is promoted by point defects induced from the spinel/fluorite heterointerfaces. Meanwhile, SO2 resistance of Co-HEO for Hg0 removal is also improved up to 2000 ppm due to the high-entropy-stabilized structure, construction of heterointerfaces, and synergistic effect of the multicomponents for inhibiting the oxidation of SO2 to surface sulfate. The design strategy of the dual-phase high-entropy material launches a new route for metal oxides in the application of catalytic oxidation and SO2 resistance.

Puffy hierarchical nanonet structured multifunctional membranes for NO degradation and ultrafine dust filtration

Multifunctional nanofibrous catalytic membranes are used for comprehensive treatment of fine particulate matter (PM) and toxic gaseous contaminants. However, the need for high purification efficiency with low resistance presents a unique challenge. Herein, a method of optimizing the morphology of manganese oxide (MnOx) on Zr-TiO2 (TZ) nanofiber membranes was developed to remove ultrafine PM and nitric oxide (NO) efficiently with relatively low pressure drops. After tailoring the hydrothermal solution properties, the MnO2 ultrafine nanowires (≈22 nm) and Mn3O4 nano-octahedra assembled with scaffold nanofibers formed dual-network structures with high gas permeabilities, superior redox properties, and abundant surface acidities. The resultant M2TZ (2-MnOx/Zr-TiO2) catalytic membranes exhibited exceptional NH3 selective catalytic reduction (NH3-SCR) activity (T90 = 215 °C) with a gas hourly space velocity of 75,000 h−1, as well as outstanding SO2 and H2O tolerance and long-term stability. Meanwhile, owing to the puffy hierarchical nanonet structure, the M2TZ catalytic membranes also show a high filtration efficiency of 99.99% for PM0.3 removal with a low air resistance of 125 Pa, high air permeability of 1259 m3 m−2 h−1 kPa−1, and satisfactory PM capture at 300 °C. This work may shed light on the design of advanced multifunctional membranes for air pollutant purification.

Enhancing Bio-Ethanol conversion to renewable H2 via Ethanol Steam Reforming over a highly porous “one-pot” nickel and molybdenum carbide-based catalyst

The pursuit of an economical, active, and stable catalyst for Bio-Ethanol Steam Reforming (ESR) to facilitate renewable H2 production continues. Especially considering that traditional-noble-metal-based catalysts, are too expensive for large scale applications. In this paper, a sol-gel Ni–Mo2C–Al2O3 catalyst was employed for the first time in the ESR reaction. Synthesized by an innovative “one-pot” sol-gel method, this highly porous catalyst (670 m2. gcat−1) promises to deliver, in a single material, the nickel's ability on cleaving C–C bonds with the known catalytic stability of Mo2C in reforming reactions. Catalytic stability and activity were tested over a wide range of temperatures (450 °C-700 °C) and at a high Gas-Hourly-Space-Velocity (GHSV), 200,000 mmol h−1. gcat−1. The high temperature tests (T > 650 °C) exhibited elevated stability (over 12 h) and activity (ethanol conversion and H2-Production-Rate of 100 % and 1700 mmol h−1. gcat−1, respectively). Besides, TPO-O2 and TEM micrographs have shown the presence of both graphitic and aromatic coke on tests E and H spent catalysts, 2.08 mgcarbon. gcat− 1h−1 and 541 mgcarbon. gcat− 1h−1, respectively. Nevertheless, given its more graphitic nature and lower formation rate, H2 yield, and conversion remained constant throughout the entirety of the high-temperature tests, confirming that the coke did not block the catalytic sites.

Dry reforming of methane over Ni/fibrous Zeolite-Y: optimization and regeneration studies

This study optimized the catalytic performance of Ni/Fibrous Zeolite-Y (Ni/FHY) toward dry reforming of methane (DRM). The optimization study was conducted under three independent variables employing the response surface methodology (RSM), trailed by a regeneration and stability studies. The study focused on the independent parameters of reaction temperature (A) (700 °C–900 °C), gas hourly space velocity (GHSV) (B) (15,000 mL/gcat −1.h−1 – 35,000 mL/gcat −1.h−1), and CH4/CO2 ratio (C) (1.0–3.0). The catalyst exhibited excellent activity (CH4 conversion = 94.5%, CO2 conversion = 88.3%, and H2/CO = 1.05) when all the parameters were under these optimum conditions (A = 833 °C, B = 24,962 mL/gcat −1.h−1, and C = 2.08). The catalytic stability study revealed an excellent performance of Ni/FHY where there was no indication of catalyst deactivation up to 30 h of time-on-stream (TOS). The outcome of the excellent catalytic activity can be explained by Ni-metal inclusion that enabled a substantial increase in the interaction between FHY and Ni, hence, subdued carbon formation. The regeneration study showed a good performance of regeneration owing to the capability of air to regenerate the catalyst completely, thus resulting in an excellent performance with 90 h TOS.

Kinetic Modeling of the Direct Dimethyl Ether (DME) Synthesis over Hybrid Multi-Site Catalysts

This paper deals with the proposition of a kinetic model for the direct synthesis of DME via CO2 hydrogenation in view of the necessary optimization of the catalytic system, reactor design, and process strategy. Despite the fact that DME synthesis is typically treated as a mere combination of two separated catalytic steps (i.e., methanol synthesis and methanol dehydration), the model analysis is now proposed by taking into account the improvements related to the process running over a hybrid catalyst in a rational integration of the two catalytic steps, with boundary conditions properly assumed from the thermodynamics of direct DME synthesis. Specifically, the CO2 activation step at the metal–oxide interface in the presence of ZrO2 has been described for the first time through the introduction of an ad hoc mechanism based on solid assumptions from inherent studies in the literature. The kinetic modeling was investigated in a tubular fixed-bed reactor operating from 200 to 260 °C between 1 and 50 bar as a function of a gas hourly space velocity ranging from 2500 to 60,000 NL/kgcat/h, in a stoichiometric CO2/H2 feed mixture of 1:3 v/v. A well-detailed elementary mechanism was used to predict the CO2 conversion rate and identify the key reaction pathways, starting with the analysis of the implicated reactions and corresponding kinetic mechanisms and expressions, and finally estimating the main parameters based on an appropriate modeling of test conditions.

New insights into the effect of polyvinyl alcohol on Co3O4 spinel oxide catalyst for N2O decomposition

Polyvinyl alcohol (PVA)-assisted precipitation method offered surface modification Co3O4 spinel oxides which were applied to catalytic N2O decomposition. PVA was added in the preparation process and endowed catalysts with changes in surface metal ions valance state properties, i.e. Co2+ ions which served as active centers. Co3O4 adding PVA (Co3O4-P) showed superior performance for catalytic N2O decomposition with a high gas hourly space velocity of 400,000 h−1. Co2+ ion quantities were positively correlated to catalytic performance which was inseparable from PVA superhydrophobicity and reducibility during the preparation process. Moreover, density functional theory (DFT) calculation revealed N2O preferable adsorption on Co2+ sites whether near oxygen vacancies or not, which indirectly affirmed the reason Co3O4-P with superior catalytic N2O decomposition property. Our research gave more evidence to N2O decomposition active sites from atom-scale for Co3O4 spinel oxides and provided a novel pathway for high-performance catalyst preparation.

High organic sulfur coal derived carbon-based sorbent for Hg0 capture from coal-fired flue gas

To develop the high value utilization of high organic sulfur coal instead of combustion as well as save the cost of mercury pollution control, we attempted to transmute the inherent sulfur of high organic sulfur coal, in the case of LF coal (which is from Linfen city, China), to active sulfur species for mercury capture by doping metal oxides, and CuO performed best among various metal oxides. The sorbent (or activated sample) prepared from LF coal with doping CuO is labelled LF+Cu-A, around which a series of experiments were conducted. Firstly, the effects of operational conditions, including GHSV (gas hourly space velocity), temperature and flue components, on the mercury capture performance of LF+Cu-A were thoroughly investigated, and results showed that LF+Cu-A had an excellent mercury capture performance. The average mercury capture efficiency is 97.8 % during a two-hour test under N2+O2+H2O+SO2+NO atmosphere with GHSV of 240000 h−1 and temperature of 120 °C. Secondly, the experimental data were fitted by four kinetic models, and it is found that the mercury adsorption process under low temperatures (60, 90, 120 °C) and high temperature (150 °C) are in the best agreement with the pseudo-first-order model and the intra-particle diffusion model respectively. Last, the mercury capture mechanisms of LF+Cu-A were revealed by Hg-TPD (Hg-temperature programed desorption) experiment, Raman analysis and XPS (X-ray photoelectron spectrometer) spectra, and it is indicated that the multiple sulfur species and Cu2+ play roles in the mercury capture process, during which elemental mercury are oxidized to HgS and fixed on the surface of LF+Cu-A.

Adsorbed oxygen atoms for improving the oxidative dehydrogenation of ethane over B-site-doped layered perovskite La2Ti2O7

In this study, Nd, Ga, and Sm were used to partially replace Ti in layered perovskite La2Ti2O7 (A2B2O7 type) with the aim of developing a highly efficient low-temperature catalyst for the oxidative dehydrogenation of ethane (ODHE). Ethylene was successfully produced by the ODHE over the modified catalysts at temperatures of as low as 600 °C, and the Ga-doped catalyst exhibited the highest ethylene yield of 16.9 % at 625 °C with a high gas hourly space velocity of 35,273 h−1 and short reactant–catalyst contact time of 0.1 s. Thermal activation improved the ethylene yield to 33.6–39.4 % at 650–700 °C with a short contact time (<0.1 s) and productivity of approximately 10 gethylene·gcatalyst−1·h−1, which exceeds reported values. However, the pure catalytic activity could not be depicted at higher temperatures (>700 °C) because the reaction became more complex owing to thermally activated processes such as thermal dehydrogenation, thermal–oxidative dehydrogenation, and reforming reactions. The effects of B-site doping were explored through in situ characterization and density functional theory calculations, and a mechanism for the ODHE was proposed based on the results. Adsorbed oxygen atoms, which form by the dissociation of molecular oxygen at high temperatures, are responsible for the selective dehydrogenation of ethane to ethylene. Overall, the electronic modification of the B-site doped La2Ti2O7 catalysts improved the catalytic activity at 525–575 °C, and the experimental and calculation results confirmed that dissociatively adsorbed oxygen atoms were responsible for the improved ODHE.

A CFD model of natural gas steam reforming in a catalytic membrane reactor: Effect of various operating parameters on the performance of CMR

The use of hydrogen as an energy carrier has increased for reasons related to its environmentally friendly characteristics. The most common and low-cost method of producing hydrogen from natural gas (or CH4) is the steam reforming process. The 2-D axisymmetric catalytic membrane reactor (CMR) model is developed for pure hydrogen production from real natural gas (NG) using a Pd–Ru membrane with a Ni/Al2O3 catalyst. In this paper, a CFD model is prepared to investigate the performance of a catalytic membrane reactor through natural gas conversion and hydrogen production under various operation parameters, i.e., temperature of reaction in the range of 600, 700, 800, 900, and 1000 K, gas hourly space velocity GHSV with a range of 500, 700, 1000, 2000, and 3000 h−1, and sweep gas flow rate (Re No.) 1, 50, 100, 150, and 250. The results of the simulation show that the CMR exhibits a high permeation rate of hydrogen on the permeate side (tube side) and achieves a high methane conversion rate of approximately 99.9 % at 1000 K on the retentate side. The hydrogen flux exhibits a decline as the temperature increases from 900 to 1000 K, despite the achievement of complete (NG) conversion. Hence, it can be concluded that the performance of the catalytic membrane reactor (CMR) process exhibits a pattern of increase when the other parameters, such as (GHSV) and (Re.No.), are increased.

Synergistic effect between In2O3 and ZrO2 in the reverse water gas shift reaction.

Efficient activation of CO2 at low temperature was achieved through the interface effect between In2O3 and ZrO2 by their geometric and electronic effects. The results show that 75In2O3-25ZrO2 (In2O3 : ZrO2 molar ratio of 3 : 1), as a catalyst for the reverse water gas shift reaction, can achieve 28% CO2 conversion with 96% CO selectivity at 400 °C, 0.1 MPa, a H2 : CO2 molar ratio of 3 : 1 and a gas hourly space velocity of 10 000 mL g-1 h-1. In situ FTIR experiments provide a basis for clarifying the pivotal role of formate (facilitated at In2O3-ZrO2 interface) in this reaction.

Heat transfer intensification in compact tubular reactors with cellular internals: A pilot-scale assessment of highly conductive packed-POCS with skin applied to the Fischer-Tropsch synthesis

Heat management poses severe constraints when designing non-adiabatic multi-tubular packed-bed reactors for strongly exothermic or endothermic catalytic processes. The exploitation of conduction in the solid matrix of engineered continuous internals (e.g., honeycomb monoliths, open-cell foams, periodic open-cell structures) as a heat transfer mechanism alternative, or possibly additional, to fluid-phase convection, is a promising strategy to relax some of these constraints, offering new opportunities for the intensification of catalytic reactors. Preliminary experimental data and modelling studies show that this is particularly true for compact-scale applications, when conductive internals are packed with catalyst micro-pellets. In this work, through pilot-scale testing, we show that overall heat transfer coefficients as high as 1300 W/m2/K can be achieved in periodic open-cell structures (POCS) made of a highly conductive aluminium alloy, 3D printed with an external continuous skin and packed with 300–400 μm catalyst micro-pellets. To this aim, a Fischer-Tropsch experimental campaign has been carried out in a pilot-scale rig, using an established 20 wt% Co/Al2O3 catalyst formulation and a tubular reactor (28.80 mm I.D., 20 cm catalyst bed length) externally cooled with an isothermal diathermic oil. Thanks to the outstanding heat transfer properties of the packed-POCS reactor, by progressively increasing the oil temperature from 180 °C to 225 °C, once-through CO conversions as high as 70 % have been measured at gas hourly space velocities exceeding 4000 cm3(STP)/h/gcat, resulting in C5+ yields in excess of 0.35 g/h/gcat, with a CH4 selectivity always below 15 %. Such performances, made possible by the intensified heat management granted by the adopted reactor internals, are among the best ever reported for a compact-scale Fischer-Tropsch tubular reactor.

Catalytic Hydrogenation Property of Methyl Benzoate to Benzyl Aldehyde over Manganese-Based Catalysts with Appropriate Oxygen Vacancies

The synthesis of benzaldehyde, a compound widely utilized in food, medicine, and cosmetics, was achieved through a one-step catalytic hydrogenation using the cost-effective raw material, methyl benzoate. This process aligns with the principles of atom economy and green production. Despite the development of numerous high-performance catalysts by scholars, the challenge remains in achieving lower reaction temperatures, ideally below 400 °C. In this study, a series of MnOx/γ-Al2O3 catalysts were meticulously prepared using the precipitation-impregnation method. These catalysts featured supports calcined at various temperatures and distinct manganese active components. Characterization techniques such as X-ray diffraction (XRD), N2 physical adsorption, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), H2 temperature programmed reduction (H2-TPR), and NH3 temperature-programmed desorption (NH3-TPD) were employed to analyze the structure and surface properties of the catalysts. Notably, the optimized reaction temperature was found to be 360 °C. The catalyst exhibited the most favorable performance when the calcination temperature of the support was 500 °C and the Mn/Al molar ratio reached 0.18. Under these conditions, the catalyst demonstrated the most suitable oxygen vacancy concentration, yielding impressive results: a conversion rate of 87.90% and a benzaldehyde selectivity of 86.1%. These achievements were attained at 360 °C, atmospheric pressure, a hydrogen to methyl benzoate molar ratio of 40:1, and a Gas Hourly Space Velocity (GHSV) of 800 h−1. This research underscores the potential for optimizing catalysts to enhance the efficiency and sustainability of benzaldehyde synthesis.

Impact of operation parameters and lambda input signal during lambda-dithering of three-way catalysts for low-temperature performance enhancement

A synthetic exhaust gas bench was dynamically operated to investigate the impact of temperature, amplitude, split cycle, mean lambda, gas hourly space velocity, and oxygen storage capacity on average pollutant conversion and product selectivity of three-way catalysts in periodic operation. As temperature and amplitude increase and oxygen storage capacity decreases, the optimal frequency for maximum pollutant conversion increases. This is consistent with faster desorption of CO and O2 from the catalyst, yielding free surface sites. Regarding the formation of secondary products, the optimal frequency for maximum pollutant conversion does not always correspond to minimal N2O and NH3 emissions. The split cycle variation reveals the enhancement of C3H8 and NO conversion after both lean-rich and rich-lean switches and C3H6 and CO conversion after rich-lean switches at the optimal frequency. As periodic operation does not affect existing engine settings or operating conditions, it is a cost-effective control strategy for meeting future emission limits.

Effects of molybdenum addition to activated carbon supported Ni‐based catalysts for CO2 methanation

AbstractRecently, CO2 methanation has become a technique that aims to reduce anthropogenic CO2 emissions by converting CO2 captured from stationary and mobile sources and H2 produced from renewable sources into CH4. Due to their excellent performance‐to‐cost ratio, Ni‐based catalysts were frequently used in such conversions. The main drawbacks, however, are that Ni has the propensity to aggregate and deposit carbon during the high‐temperature reaction. These issues can be partially resolved by including a support (e.g., MOF, zeolite, activated carbon, etc.) and a second transition metal (e.g., Mo, Co, or Fe) in Ni‐based catalysts. Therefore, the activity of Ni‐based catalysts at low temperatures needs to be improved. In this study, a series of mesoporous activated carbon (AC) supported bimetallic Ni–Mo catalysts (Ni–xMo/AC, Ni = 13 wt.%, x = 5, 7, 9, 11 wt.%) were synthesized using the incipient wetness impregnation method. The effect of Mo content on the catalyst's activity was examined in a fixed‐bed reactor. At 250–650°C, 1‐atmosphere pressure, gas hourly space velocity (GHSV): 1200 mL h−1 g−1, and H2/CO2 ratio: 4:1, the catalytic efficiency of these catalysts was examined. The catalysts were analyzed using transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), X‐ray powder diffraction (XRD), N2‐physisorption, and scanning electron microscopy/energy dispersive X‐ray spectroscopy (SEM‐EDX). Ni–7%Mo/AC catalyst showed the lowest carbon deposition rate, superior stability, and the best activity. The addition of Mo can improve the heat resistance of the Ni/AC catalyst and the interaction between the metal nickel and the support, which prevents the sintering of the catalyst. © 2023 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

A novel multi-objective optimization model of solar-driven methanol steam reforming system combining response surface methodology and three-dimensional numerical simulation

Solar-driven methanol steam reforming (MSR) to produce hydrogen is a pivotal thermochemical process for enhancing green energy utilization with low-carbon emissions. While this process has been explored in the thermochemical reforming literature, with valuable studies on fuel to hydrogen, this study marks the first comprehensive examination and multi-objective optimization of the MSR process within a solar-driven catalyst-filled reactor. The study begins by modeling and validating the MSR’s reaction kinetic. Subsequently, the effects of the reactor surface energy flux density and key operating characteristics, such as steam-to-methanol ratio (SMR) and space velocity, on the gas composition and conversion efficiency as well as H2 yield are comprehensively analyzed. In order to effectively optimize the operating parameters, the interactions between the various factors were elucidated and an optimization procedure was established to scrutinize the impact of these factors on hydrogen production. The model accuracy is assessed using Analysis of Variance (ANOVA), which also identifies optimal operating parameters under varying conditions. Predictions from the Response surface methodology (RSM) indicate optimal conditions with a SMR of 1.13, a gas hourly space velocity of 45.24, and an inlet temperature of 507.4 K. Numerical calculations confirm the practicality of these conditions, yielding an actual methanol conversion of 0.9998, deviating only by 0.17 % from the predicted value. This work underscores the feasibility and efficacy of studying MSR performance based on response surface method. The analysis of factor significance and interactions provides valuable guidance for practical operations.