Gas Hourly Space Velocity Research Articles

Low-silica Cu-CHA Zeolite Enriched with Al Pairs Transcribed from Silicoaluminophosphate Seed: Synthesis and Ammonia Selective Catalytic Reduction Performance.

Cu-exchanged low-silica CHA zeolites (Si/Al ≤ 4) synthesized without organic templates are promising candidate catalysts for ammonia selective catalytic reduction of nitrogen oxides (NH3-SCR), but their practical application is restricted due to the low hydrothermal stability. Here, inspired by the transcription from duplex DNA to RNA, we synthesized Al pairs enriched low-silica CHA zeolite (CHA-SPAEI, Si/Al = 3.7) by using silicoaluminophosphate (SAPO) featured by strict alternation of -Al-O-P(Si)-O-Al-O- tetrahedra as seed. The proportion of Al pairs in CHA-SPAEI is 78%, which is much higher than that in the conventional low-silica CHA (CHA-LS, 52%). After hydrothermal ageing at 800 °C for 6 h, Cu-exchanged CHA-SPAEI shows NO conversion above 90% within 225-500 °C under a gas hourly space velocity of 200,000 h-1, which is much better than that of Cu-exchanged CHA-LS. The spatial close proximity of Al pairs in CHA-SPAEI is confirmed by the 27Al double-quantum single-quantum two-dimensional NMR analyses. The strict -P(Si)-O-Al-O-P(Si)-O- sequence in the fragments from the dissolution of SAPO seed promotes the Al pairs with the -Al-O-Si-O-Al-O- sequence via a transcription process. The utilization of aluminophosphate-based zeolites as seeds opens up a new avenue for the regulation of the Al distribution in zeolites.

Low‐silica Cu‐CHA Zeolite Enriched with Al Pairs Transcribed from Silicoaluminophosphate Seed: Synthesis and Ammonia Selective Catalytic Reduction Performance

AbstractCu‐exchanged low‐silica CHA zeolites (Si/Al≤4) synthesized without organic templates are promising candidate catalysts for ammonia selective catalytic reduction of nitrogen oxides (NH3‐SCR), but their practical application is restricted due to the low hydrothermal stability. Here, inspired by the transcription from duplex DNA to RNA, we synthesized Al pairs enriched low‐silica CHA zeolite (CHA‐SPAEI, Si/Al=3.7) by using silicoaluminophosphate (SAPO) featured by strict alternation of −Al−O−P(Si)−O−Al−O− tetrahedra as seed. The proportion of Al pairs in CHA−SPAEI is 78 %, which is much higher than that in the conventional low‐silica CHA (CHA‐LS, 52 %). After hydrothermal ageing at 800 °C for 6 h, Cu‐exchanged CHA‐SPAEI shows NO conversion above 90 % within 225–500 °C under a gas hourly space velocity of 200,000 h−1, which is much better than that of Cu‐exchanged CHA‐LS. The spatial close proximity of Al pairs in CHA‐SPAEI is confirmed by the 27Al double‐quantum single‐quantum two‐dimensional NMR analyses. The strict −P(Si)−O−Al−O−P(Si)−O‐ sequence in the fragments from the dissolution of SAPO seed promotes the Al pairs with the −Al−O−Si−O−Al−O− sequence via a transcription process. The utilization of aluminophosphate‐based zeolites as seeds opens up a new avenue for the regulation of the Al distribution in zeolites.

Fabrication of the coke-resistant and easily reducible Ni/SiC catalyst for CO2 methanation

The catalytic methanation of carbon dioxide, which is a promising process for CO2 to fuels, has been extensively investigated using Ni-based catalysts due to their high CH4 selectivity, high CO2 conversion, and affordability. However, owing to its highly exothermic nature, CO2 methanation can cause severe carbon deposition and sintering effects, resulting in catalyst deactivation. This is where high thermal conductivity SiC presents itself as a viable alternative support to enhance the performance of Ni-based catalysts. In this work, Ni catalysts supported on a cheap commercial SiC were prepared by wet impregnation method with different Ni loadings and calcination temperatures. The as-prepared and spent catalysts were characterized using N2 physisorption, X-ray diffraction, H2 temperature-programmed reduction (H2-TPR), temperature-programmed oxidation (TPO) and transmission electron microscopy. H2-TPR analysis revealed that reduction at 400 °C for 15 min is enough to convert most of NiO to active Ni0 to archive the highest activity toward CO2 methanation. The catalytic performance and long-term stability of the as-prepared Ni/SiC catalysts were evaluated for CO2 methanation at stoichiometric CO2/H2 ratio of 1/4, different gas hourly space velocities, reaction temperatures, and reduction conditions. Among the synthesized catalysts, the 10%Ni/SiC-500 exhibited highest CO2 conversion (70%) and CH4 selectivity (98%) as well as stable catalytic performance for 30 h on stream at a GHSV of 20,000 h−1 and reaction temperature of 400 °C.

Fe–Ni–Ce–Zr-modified CuO–ZnO catalyst for methanol steam reforming

Four copper-based catalysts were prepared by co-precipitation method. The catalysts were characterized by scanning electron microscopy, N2 adsorption-desorption, temperature programmed reduction process (H2-TPR), X-ray diffraction (XRD) and in-situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) to explore the effects of different components on catalyst activity. The performance of different catalysts for hydrogen production via methanol steam reforming was evaluated on a fixed-bed reactor. The effects of different components, reaction temperature and gas hourly space velocity (GHSV) on the catalytic performance were investigated. The results exhibited that among the investigated catalysts, 1# and 2# catalysts had the higher catalytic activity and stability. Under the conditions of 280 °C, a molar ratio of methanol to water of 1:1.3, and a GHSV of 13.3 L/(g·h), the methanol conversion rate reached 99.9%, the CO concentration was as low as 0.29%, and the selectivity was only 1.16%. The H2 production flow rate per unit mass of catalyst was 270 mL/(min·g). After 60 h of start-stop experiments, the methanol conversion rate remained above 98.4%, the CO concentration was always lower than 0.5%, and the start-up speed was significantly faster than that of the commercial catalyst M650. This study provided an effective method for the preparation of catalysts for methanol steam reforming.

Multiple-objective optimization on ammonia decomposition using membrane reactor

Ammonia plays a key role in the renewable hydrogen economy nowadays, thus, the efficiency of ammonia decomposition for hydrogen production becomes an important research topic. In this study, a numerical model was built to study the performance of ammonia decomposition using a membrane reactor and Ru/Al2O3 catalyst under various operating conditions such as feed NH3 temperature and volume flow rate as well as retentate side pressure. The reactor performance was characterized by ammonia conversion, hydrogen recovery, and recovered hydrogen flow rate. Pre-exponential factor and activation energy of ammonia reaction rate were obtained by equilibrium conversion and two-step parametric sweeping. It was found that ammonia conversion can be increased by about 33% compared to a conventional fixed-bed reactor under the same operating conditions. H2 recovery can be enhanced when the reactant inlet temperature and the pressure difference between the retentate and permeate sides increase. The increase in feed NH3 flow rate (gas hourly space velocity, GHSV) decreased the ammonia conversion and H2 recovery. An optimum GHSV that results in a maximum recovered H2 flow rate can be found. Finally, optimum operation conditions for maximizing the hydrogen recovery and recovered hydrogen flow rate were analyzed using the multi-objective Non-dominated sorting genetic algorithm-II (NSGA-II). It was found that maximum H2 recovery with a value of 79.7% can be obtained under the conditions of inlet temperature of 336 °C, GHSV of 900 h−1, and retentate side pressure of 9.9875 bar. The maximum recovered hydrogen flow rate with a value of 9.55×10−14(mol·s−1) can be obtained under the conditions of an inlet temperature of 394 °C, GHSV of 1315 h−1, and retentate side pressure of 9.9879 bar.

Contributions of Surface Oxygen Species and Photoinduced Holes on Photothermocatalytic Toluene Oxidation over CeO2–MgO

To reveal the activity enhancement mechanism of volatile organic compounds (VOC) oxidation reaction, is vital for developing high-efficiency and cost-effective photothermocatalytic materials. Herein, porous and low-cost CeO2–MgO composite oxides were simply constructed via the solution combustion method and applied for toluene photothermocatalytic oxidation. The conversion rate for 1500 ppm of toluene over the optimized sample could reach 90% under the photothermocatalytic process at 330 °C and a gas hourly space velocity of 60,000 mL·g–1·h–1. Both gas phase oxygen and reactive oxygen species (ROS) played the dominant role in the photothermocatalytic activity while the total contribution rate of photoinduced holes and surface lattice oxygen was 25% to the activity. In situ Fourier transform infrared and electron paramagnetic resonance results revealed that the synergistic photothermo activation of molecular oxygen accelerated the low-temperature ROS formation. Under irradiation, photoinduced electrons could benefit the efficient transfer from superoxide radicals to peroxide radicals on material. Hence, it provides not only a comprehensive understanding on the activity enhancement mechanism at the molecular level but also a theoretical reference for designing objective catalysts for VOC abatement.

Fabrication and catalytic evaluation of Ni/CaO–Al2O3 in glycerol steam reforming: Effect of Ni loading

The present study aims to assess the catalytic activity of the Ni/CaO–Al2O3 catalysts with different Ni loadings (2.5, 5, 10, 15, and 20 wt %) for H2 generation via the glycerol steam reforming (GSR). The support was prepared by the mechanochemical method, and then the various contents of nickel were impregnated on the support surface. The synthesized samples were characterized by BET, XRD, H2- TPR, CO2-TPD, TPO, FTIR, and SEM analyses. High stable catalytic activity was reported for the prepared catalysts. Among the investigated catalysts, 15%Ni/CaO–Al2O3 with the highest reducibility, proper BET area (96.6 m2 g−1), and suitable basicity possessed the highest catalytic performance with glycerol conversion of 99.4% at 700 °C. All the samples had high stability after 5 h, and the 15%Ni/CaO–Al2O3 showed 97.5% glycerol conversion at 550 °C without any decline in glycerol conversion durin 15 h time on stream. It was also found that glycerol conversion decreased with the increase in gas hourly space velocity and calcination temperature.

Methane dry reforming on fibrous silica-alumina employing nanocrystals of nickel and cobalt to recognize the most efficient metal

Presently, the production of syngas through the dry reforming of methane is a widely employed approach for reducing vast amounts of greenhouse gas emissions. Several metals, particularly transition metals support have been evaluated as active DRM catalyst systems. In this work, a comparative studies is presented between Cobalt and Nickel metals impregnated over fibrous silica-alumina (FSA) support synthesized by the hydrothermal method for dry methane reforming. The specimens were characterized via FESEM mapping, TEM, XRD, H2-TPR, XRF, N2 physisorption, and KBr-FTIR techniques. Unlike the Co/FSA, Ni/FSA displayed a higher surface area with a fine dispersion of Ni nano-crystalline and less agglomeration, and more active sites which enhanced the metal-support interaction. Approximately 0.2g of each catalyst was evaluated at 650–800 °C with a respective. CH4:CO2:N2 ratio of 1:1:2, gas hourly space velocity 30,000 mL g−1 h−1. The Ni/FSA demonstrated more conversion of CH4 (89%) over (67%) of Co/FSA at 800 °C. After 10 h of long-term reaction, the Ni/FSA exhibited more stability at 800 °C. TGA/DTA, Raman, and TEM results showed that spent Ni/FSA catalysts did not demonstrate signs of considerable nano-graphitic carbon or metal sintering as compared to Co/FSA catalysts, which had bigger crystallites of Co. The finding of this study would add new knowledge on reaction conditions involving and catalytic activities of the metals over the FSA.

Insights into catalytic oxidation mechanism of CO over Cu catalyst: Experimental and modeling study

Cu thin films have been synthesized using a chemical vapor deposition technique for catalytic kinetic study of CO oxidation. The obtained samples are morphologically uniform and homogeneous with porous textures. Structure analysis by X-ray diffraction indicated the formation of pure Cu metal. X-ray photoelectron spectroscopy exhibited the existence of Cu in a metallic state at the surface, in addition to a minor quantity of Cu1+ that could be formed during the deposition process. The catalytic performance was evaluated through CO oxidation at gas hourly space velocity (GHSV) of ∼300,000 mL·g−1·h−1. The results showed that the Cu catalyst is very active in CO oxidation. The CO2 effect on the CO conversion during the catalytic reaction was investigated by using different amounts of CO2 in the inlet gas mixtures. Moreover, density functional theory (DFT) calculations were performed to determine the adsorption and reaction energies, revealing the best results on Cu hollow active sites. The surface reaction mechanism of the catalytic oxidation of CO over Cu catalyst was developed with reasonable prediction against the measured results. The simulated results revealed a good correlation with the experimental data when Langmuir-Hinshelwood (LH) mechanism is followed. CO2 exhibits an inhibiting effect on the catalytic oxidation of CO. Accordingly, the findings revealed that combining experimental data and theoretical calculations could allow a better understanding of the catalytic reaction mechanism, which can pave the way to investigate other catalytic reactions.

Dry reforming of methane using bimetallic Pt–Ni/Ti-SBA-15: Effect of Si/Ti ratio on catalytic activity and stability

A one-pot hydrothermal technique was used to make a series of Ti-incorporated mesoporous SBA-15 with varying Si/Ti ratios. The synthesized mesoporous materials were modified by introducing Ni (9%) as active metal and Pt (0.5%) as promoter using nickel nitrate and chloroplatinic acid, respectively, as metal precursors through incipient wetness impregnation method. All the catalysts and supports were characterized by X-ray diffraction, BET surface area, Fourier Transform–Infrared spectroscopy, UV–Visible diffuse reflectance spectroscopy, H2–temperature-programmed reduction, NH3–temperature-programmed desorption, transmission electron microscopy, and thermogravimetric analysis. The catalysts were subjected to dry reforming of methane using CH4/CO2 (molar feed ratio of 1:1) with a gas hourly space velocity (GHSV) of 36,000 mL. g−1. h−1 at a temperature range of 400–800 °C. The characterization results confirmed the incorporation of titanium ions in the SBA-15 matrix. However, Si/Ti loadings of 10 and 20 exhibited low extra-framework anatase phase titania levels, and high surface acidity. Among the subjected catalysts, Pt–Ni/Ti-SBA-15 (Si/Ti = 10) showed higher catalytic activity (CH4 = 84% and CO2 = 91%) with a H2/CO ratio of 3.6 after an 8 h reaction, and exhibited higher stability and coke tolerance than the bare catalysts and other modified Pt–Ni/Ti-SBA-15 catalysts. The characterization results of spent catalysts also confirmed low coke deposition on titanium-incorporated catalysts. The remarkable performance of the Pt–Ni/Ti-SBA-15 towards CH4 conversion and CO2 conversion may be related to strong metal–support interaction, presence of strong and weak acid sites, well-dispersed active metals and bi-metallic interaction.

Modeling and comprehensive analysis of hydrogen production in a newly designed steam methane reformer with membrane system

The use of a hydrogen perm-selective membrane in the conventional steam methane reformer (SMR) is a promising technology for producing ultra-pure hydrogen under moderate operating conditions. A detailed computational fluid dynamics (CFD) analysis is performed on a membrane SMR unit for an on-site hydrogen refueling station (HRS) to get the optimum operating conditions. The developed model was validated with experimental results. The obtained results predicted that the high temperature of the process gas inlet, the high operating pressure, and the low gas hourly space velocity (GHSV) were advantageous. However, these factors must be carefully adjusted to achieve optimal efficiency. Furthermore, the simulation with a counter-current sweep gas flow configuration gave better results than a co-current operation. The estimated optimal conditions for improved CH4 conversion and H2 recovery were 4500 h−1 GHSV, 500 K inlet temperature, and the 8.5 bar operating pressure, representing CH4 conversion and H2 recovery of approximately 94.7% and 95.8%, respectively.

Synergistic oxidation of NH3 and Hg0 over Cu-ATP catalyst: Influence of SO2 and reaction mechanisms

NH3 and Hg0 could be synergistically oxidized by copper modified attapulgite (Cu3-ATP) catalyst at the gas hourly space velocity (GHSV) below 5 × 104 h−1 despite competition exist between these two reactions. Its Hg0 oxidation showed good sulfur resistance when HCl was present, but the NH3 oxidation was partially inhibited after SO2 was added. In order to explain this phenomenon, the composition and physical characteristics of Cu3-ATP before and after sulfurization were characterized by XRF, BET, XRD and FTIR. And H2-TPR, NH3-TPD, in situ DRIFT and XPS of the catalysts were adopted to reveal the influence of SO2 on NH3/Hg0 oxidation and the reaction mechanisms. The results showed that SO2 would adsorb and oxidize on the catalyst surface to form very small amount of sulfite and sulfate species, and partially change the composition and structure of Cu3-ATP. This reduced the reducibility of Cu3-ATP and increased the weak and moderate acid sites on its surface. The presence of SO2 was beneficial to NH3 adsorption, but inhibited NH2 → NOx conversion in iSCR mechanism for NH3 oxidation. Cl2 formation were also inhibited by SO2, while the generated surface active Cl and O species could ensure high Hg0 oxidation efficiency.

From CO2 to DME: Enhancement through Heteropoly Acids from a Catalyst Screening and Stability Study.

The direct synthesis of dimethyl ether (DME) via CO2 hydrogenation in a single step was studied using an improved class of bifunctional catalysts in a fixed bed reactor (T R: 210-270 °C; 40 bar; gas hourly space velocity (GHSV) 19,800 NL kgcat -1 h-1; ratio CO2/H2/N2 3:9:2). The competitive bifunctional catalysts tested in here consist of a surface-basic copper/zinc oxide/zirconia (CZZ) methanol-producing part and a variable surface-acidic methanol dehydration part and were tested in overall 45 combinations. As dehydration catalysts, zeolites (ferrierite and β-zeolite), alumina, or zirconia were tested alone as well as with a coating of Keggin-type heteropoly acids (HPAs), i.e., silicotungstic or phosphotungstic acid. Two different mixing methods to generate bifunctional catalysts were tested: (i) a single-grain method with intensive intra-particular contact between CZZ and the dehydration catalyst generated by mixing in an agate mortar and (ii) a dual-grain approach relying on physical mixing with low contact. The influence of the catalyst mixing method and HPA loading on catalyst activity and stability was investigated. From these results, a selection of best-performing bifunctional catalysts was investigated in extended measurements (time on stream: 160 h/7 days, T R: 250 and 270 °C; 40 bar; GHSV 19,800 NL kgcat -1 h-1; ratio CO2/H2/N2 3:9:2). Silicotungstic acid-coated bifunctional catalysts showed the highest resilience toward deactivation caused by single-grain preparation and during catalysis. Overall, HPA-coated catalysts showed higher activity and resilience toward deactivation than uncoated counterparts. Dual-grain preparation showed superior performance over single grain. Furthermore, silicotungstic acid coatings with 1 KU nm-2 (Keggin unit per surface area of carrier) on Al2O3 and ZrO2 as carrier materials showed competitive high activity and stability in extended 7-day measurements compared to pure CZZ. Therefore, HPA coating is found to be a well-suited addition to the CO2-to-DME catalyst toolbox.

Unlocking efficient and robust ozone decomposition with CNT-confined manganese oxide via synergistic electronic modulation

Manganese oxides (MnO2)-based catalysts are prominent candidates for ozone elimination, which always bear the accumulation of the intermediate oxygen species and water, resulting in unsatisfactory catalytic efficiency. To overcome this critical defect, we propose carbon nanotubes confined MnO2 catalysts (MnO2-in-CNT) for efficient and stable ozone decomposition over a wide relative humidity range (RH, 15–90%). Strikingly, the catalyst exhibits an efficient and sustainable ozone conversion (98%) over 100 h under a gas hourly space velocity (GHSV) of 600,000 mL g−1 h−1 and RH of 15%, and durability under high RH (77% over 50 h, RH 70%), well beyond its unconfined analog and most reported works. This excellent catalytic performance can be attributed to the facilitated intermediate desorption on active sites and the confined structure alleviated the effect of water on inner MnO2. This discovery is expected to drive great progress in the applications of confined-structure catalysts for air purification.

Preparation of cobalt-ruthenium nanocatalysts supported on nitrogen-doped graphene aerogel and carbon nanotubes in Fischer-Tropsch synthesis

In this study, cobalt-ruthenium nanocatalysts supported on nitrogen-doped graphene aerogel (NGA) and carbon nanotubes (CNT) were synthesized using the wet impregnation method for Fischer-Tropsch process with a cobalt to ruthenium ratio of 1:50. The synthesized catalysts underwent various characterizations such as FTIR, ICP, BET, XRD, EDX, TPR and TEM. The performance of the synthesized catalysts was compared to that of a cobalt-ruthenium nanostructured catalyst supported on NGA and CNTs. The catalysts were evaluated in a fixed-bed reactor at 25 bar, with a gas ratio H2/CO: 2 and Gas Hourly Space Velocity (GHSV) 10,000 mlg-1h-1, at temperatures of 260 °C and 280 °C. The use of NGA as a cobalt catalyst support led to a 70.5% conversion of carbon monoxide and higher methane selectivity. Conversely, the use of CNTs led to 63.7% conversion of carbon monoxide and higher selectivity towards C5+ production.

Performance optimization of a cavity type concentrated solar reactor for methane dry reforming reaction with coupled optics-CFD modeling

High performance solar reactor is critical for getting high yield of solar-driven chemical conversion process. In this paper, the performance of a cavity type concentrated solar reactor for methane dry reforming reaction was investigated and optimized with coupled optics-computational fluid dynamics modeling method. The impact of critical parameters, including gas hourly space velocity, feed gases composition, catalyst loading amount, as well as heat recovery treatment, on the reaction performance of the concentrated solar reactor were discussed. It was found that: (1) Higher gas hourly space velocity would lead to lower reaction extent since the residence time of reactant is shorter and the chemical reaction locates in the limit region of intrinsic kinetics. (2) Both formation rates of H2/CO and energy storage efficiency exhibited volcanic type curves with the ratio of CH4/CO2. In addition, lowering down the ratio of CH4/CO2 might also promote RWGS reaction, leading to the decrease of H2/CO ratio. (3) Increasing catalyst loading as well as the utilization of heat recovery could both improve the performance of solar reactor. However, more expensive operation costs should be considered in practical applications. It is believed that the conclusions obtained in this paper would provide sufficient support for the design and optimization of concentrated solar reactors.

Synergistic Catalysis at the Ni/ZrO2–x Interface toward Low-Temperature CO2 Methanation

The CO2 methanation reaction, which achieves the carbon cycle and gains value-added chemicals, has attracted much attention, but the design and exploitation of highly active catalysts remain a big challenge. Herein, zirconium dioxide-supported Ni catalysts toward low-temperature CO2 methanation are obtained via structural topological transformation of NiZrAl-layered double hydroxide (LDH) precursors, which have the feature of an interfacial structure (Ni-O-Zr3+-Vö) between Ni nanoparticles and ZrO2-x support (0 < x < 1). The optimized catalyst (Ni/ZrO2-x-S2) exhibits exceptional CO2 conversion (∼72%) at a temperature as low as 230 °C with a ∼100% selectivity to CH4, without obvious catalyst deactivation within a 110 h reaction at a high gas hourly space velocity of 30,000 mL·g-1·h-1. Markedly, the space-time yield of CH4 reaches up to ∼0.17 ·gcat-1·h-1, which is superior to previously reported Ni catalysts evaluated under similar reaction conditions. Both in situ/operando investigations (diffuse reflectance infrared Fourier transform spectroscopy and X-ray absorption fine structure) and catalytic evaluations substantiate the interfacial synergistic catalysis at the Ni/ZrO2-x interface: the Zr3+-Vö facilitates the activation adsorption of CO2, while the H2 molecule experiences dissociation at the metallic Ni sites. This work demonstrates that the metal-support interface effect plays a key role in improving the catalytic behavior toward CO2 methanation, which can be extended to other high-performance heterogeneous catalysts toward structure-sensitive systems.

Structured Catalysts for Non-Thermal Plasma-Assisted Ammonia Synthesis

Ammonia has been intensively studied as a clean, sustainable fuel source and an efficient energy storage medium due to its effectiveness as a hydrogen carrier molecule. However, the currently used Haber–Bosch process requires a large fossil fuel input, high temperatures and pressures, as well as a significant capital investment. These constraints prevent decentralized and small-scale ammonia production at the level of small farms and local communities. Non-thermal plasma (NTP) can promote ammonia synthesis in operating conditions in which, in a conventional process, a catalyst is generally not active. In this study, the production of NTP-assisted catalytic ammonia at milder temperatures and ambient pressure was investigated. Four different structured catalysts were prepared and tested using an experimental plant based on a dielectric barrier discharge (DBD) reactor. The effect of the gas hourly space velocity (GHSV) was investigated, as well as the effect of the N2/H2 ratio on catalyst performance. The results evidenced that the best catalytic activity (about 4 mmol h−1 of produced NH3) was obtained using the 10Ni/zeolite 13X sample with the lowest energy consumption, thus highlighting the feasibility of this innovative technology in this field.

Revealing the Excellent Low-Temperature Activity of the Fe1–xCexOδ-S Catalyst for NH3-SCR: Improvement of the Lattice Oxygen Mobility

The development of selective catalytic reduction catalysts by NH3(NH3-SCR) with excellent low-temperature activity and a wide temperature window is highly demanded but is still very challenging for the elimination of NOx emission from vehicle exhaust. Herein, a series of sulfated modified iron-cerium composite oxide Fe1-xCexOδ-S catalysts were synthesized. Among them, the Fe0.79Ce0.21Oδ-S catalyst achieved the highest NOx conversion of more than 80% at temperatures of 175-375 °C under a gas hourly space velocity of 100000 h-1. Sulfation formed a large amount of sulfate on the surface of the catalyst and provided rich Brønsted acid sites, thus enhancing its NH3 adsorption capacity and improving the overall NOx conversion efficiency. The introduction of Ce is the main determining factor in regulating the low-temperature activity of the catalyst by modulating its redox ability. Further investigation found that there is a strong interaction between Fe and Ce, which changed the electron density around the Fe ions in the Fe0.79Ce0.21Oδ-S catalyst. This weakened the strength of the Fe-O bond and improved the lattice oxygen mobility of the catalyst. During the reaction, the iron-cerium composite oxide catalyst showed higher surface lattice oxygen activity and a faster replenishment rate of bulk lattice oxygen. This significantly improved the adsorption and activation of NOx species and the activation of NH3 species on the catalyst surface, thus leading to the superior low-temperature activity of the catalyst.

Baffled-type thermochemical reactor for high-efficient hydrogen production by methanol steam reforming

A baffled-type thermochemical reactor (BTR) for high-efficient hydrogen production by methanol steam reforming (MSR) based on the novel concept of methanol-based solar-driven hydrogen station is proposed and numerically investigated in terms of geometric and operating conditions with a multi-physics coupled model. It is found that the radius of heat-exchanging tube shows a significant impact on hydrogen yield (YH2) whereas the radius of heat-exchanging tube array shows little effect. Both the inlet velocity (Vin,HTF) and temperature (Tin,HTF) of heat transfer fluid (HTF) affect the reactor performance by influencing the heat transfer inside BTR. Excessively higher Vin,HTF and higher Tin,HTF would promote the side reaction of methanol decomposition (MD) against the main reaction of MSR, which finally decreases YH2. Moreover, it is also found that for each gas hourly space velocity (GHSV) there is a corresponding optimal value of Vin, HTF to maximize YH2. Based on this, an optimal operating curve has been obtained via data-fitting, where YH2 decreases while the hydrogen production rate (RH2) increases nonlinearly against GHSV, and the corresponding maximal values of 97.84% and 1.66 mol h−1 have been achieved separately. The results suggest that the practical operating conditions should follow the optimal operating curve with the compromise between YH2 and RH2. Finally, based on the performance evaluation against the traditional tubular reactor, the hydrogen yield of BTR is up to 1.79% higher than that of the tubular reactor due to (30.44%) more uniform temperature distribution, (15.30%) longer contact time and (7.46%) higher thermal-to-hydrogen energy conversion efficiency.