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Computational fluid dynamics (CFD) modeling of a multichannel Fischer–Tropsch reactor with microscale cooling channels was addressed in this study, wherein detailed mass, momentum, and energy balances were solved to retrieve detailed distributions of the conversion and temperature of both catalytic and cooling layers. A comparison between experimental data and simulation results showed relative errors of 6.73% and 1.22% for conversion and C5 + selectivity, respectively, which proves the validity of the proposed model. The novel structure of the reactor composed of mirrored structure cooling layers was suggested to prevent the thermal instability of a large-scale reactor module. The simulation showed that the symmetric distribution of the dense cooling channel area in the early part of the reactor decreased peak temperatures (ΔTmax = 28.6°C), whereas the nonmirrored case resulted in hot spots caused by the limited heat transfer capacity (ΔTmax = 39.2°C). The effects of the feed/coolant temperature, space velocity, and pressure were evaluated, and high temperatures and pressures resulted in a steep temperature increase in the early part of the reactor whereas the high space velocity showed an increase in the area of peak temperature. Further, the analysis showed trade-offs of operating conditions between the conversion and selectivity of desired products.

A series of Zn modified hierarchical ZSM-5 catalysts with Si/Al ratios of 25 and 40, and Zn loading amounts of 0, 0.5, 1, and 2 wt% was designed to pursue a highly efficient catalyst with excellent catalytic activity and stability toward BTEX formation in the aromatization of light hydrocarbons. The Zn modified hierarchical ZSM-5 catalysts with intracrystalline mesopores were prepared by alkali treatment and Zn impregnation. The effects of the alkali treatment and Zn modification on the textural property, acidity, catalytic performance, and coke formation were investigated in detail via various characterization techniques. It was found that the catalytic stability of the alkali-treated catalysts notably improved. This can be mainly attributed to the fact that the alkali treatment of the pre-synthesized ZSM-5 generated a large amount of mesopores, which could alleviate the diffusion limitations. Moreover, the Zn modification remarkably improved the initial BTEX yield, which was due to the improved Lewis/Bronsted (L/B) ratio in the prepared catalysts. However, as the Zn loading amount increased from 0 to 2 wt%, the catalyst stability dramatically decreased, especially for the 2 wt% case. It seems that the balance between the Lewis and Bronsted acid sites (i.e., the suitable L/B ratio) is the key to obtaining both high BTEX yield and catalyst stability, and the optimum Zn loading amount is determined to be 0.5 wt% with an L/B ratio of around 1.

Three HZSM-5 zeolites with initial Si/Al ratios of 15, 25, and 40 were treated using an alkali solution to establish a hierarchical micropore-mesopore interconnected structure in alkali-treated zeolite samples Z15-AT, Z25-AT, and Z40-AT, respectively. The aim of the present work is to improve the catalytic stability in the aromatization of ethylene, a model compound representing the light hydrocarbons produced by the high-temperature Fischer‒Tropsch synthesis. By using characterization techniques, such as XRD, ICP, N2 adsorption/desorption, TEM, 27Al and 29Si MAS/NMR, NH3-TPD, Pyridine-IR, and TGA, we analyzed the textural property and acidity of the fresh catalysts, as well as the coke formation rate of the spent catalysts. The catalytic stability was shown to be successfully enhanced in the light hydrocarbon aromatization and the initial Si/Al ratio is a crucial factor for the mesopore formation and the catalytic performance. Among the prepared zeolite samples, the Z25-AT sample seemed to be the most suitable catalyst owing to its significant enhancement in the catalytic stability. The main reason for the improved stability by alkali treatment seems to be that the hierarchical pore structure facilitates the mass transfer and provides the additional space for carbon deposition as well, thus weakening the pore blocking and prolongs the lifetime of the catalyst.

This study addresses the development of a microchannel-based reactor whereby exothermic oxidative coupling of methane (OCM) and endothermic steam reforming of methane (SRM) reactions were coupled in consecutive catalytic beds to thermally control each bed. A computational fluid dynamics model was developed by combining kinetic rate equations with detailed balance equations, and its effectiveness was corroborated by comparison with experimental data. The temperature of the SRM bed abruptly decreased because the reaction rapidly reached equilibrium, and the large endothermic heat prevented temperature from increasing near the inlet of the OCM bed. Meanwhile, the central region of the bed, which corresponded to the thermodynamically controlled region of the SRM bed, showed a slight temperature increase with a peak temperature observed along the axis. Increasing the linear velocity (by increasing either the amount of N2 in the feed or the space velocity (SV)) enhanced the heat transfer rate, and the increased amount of endothermic heat could further reduce the peak temperature of the OCM bed. By considering the inert materials near the inlet of the SRM bed, the kinetically controlled region was expanded, reducing the peak temperature of the OCM bed. The height of the OCM bed was increased to obtain a high production rate per unit bed, while the increased exothermic heat could be absorbed by increasing the SV of the SRM bed, even after reducing its height to maintain the size of the entire module.

We study the weakly-guided silicon nitride waveguide to deliver sub picosecond high power laser pulses for dielectric laser accelerators. Damage limited deliverable fluence (0.19 J/cm2) is measured and nonlinear effects are characterized.

We present an OPA with uniform half-wavelength pitch and grating emitters. Aliasing-free beam steering over ∼ 120° field-of-view is measured. Evanescent coupling between closely spaced emitters is suppressed by extreme skin-depth cladding structures.

We propose a multi-layered, 2D optical phased array capable of 180°× 180° beam steering range without wavelength tuning. Evanescent coupling between half-wavelength spaced waveguides is suppressed below –20 dB through index-mismatch and extreme skin-depth metamaterial waveguides.

In a complex reaction system, in which gas, liquid, and solid catalysts work together, understanding the impact of mass transfer that varies with the catalyst pore structure is very challenging but also essential to designing selective catalysts. We investigated the effect of mesopores introduced into bi-functional Co/ZSM-5 catalysts on the direct production of liquid fuel by low-temperature Fischer–Tropsch synthesis (FTS). The influence of mesopores on the textural properties, Co dispersion, zeolite crystallinity, the density of acid sites, and the resulting FTS performance was studied in detail. The presence of mesopores facilitated the dispersion of Co nanoparticles and the regulation of acidity, affording high CO conversion and a moderate degree of isomerization. In addition, close proximity between FTS active sites and acid functionalized sites could be achieved by the introduction of mesopores. However, the relationship between the structural parameter and liquid fuel productivity suggested that the mesopores did not reduce the mass transfer resistance of the reactants and intermediates during the FTS reaction.

A phosphorous-modified γ-Al2O3 (P-Al2O3), where γ-Al2O3 support was prepared by sol-gel method with a high surface area of ∼350 m2/g, has been applied for a preparation of cobalt-supported Co/P-Al2O3 catalysts. The Co/P-Al2O3 catalysts having a different P/Al molar ratio were investigated to elucidate the roles of phosphorous species on the γ-Al2O3 to the catalytic stability and product distribution for CO hydrogenation to hydrocarbons. The γ-Al2O3 surface was partially transformed to aluminum phosphates after phosphorous modification, and the newly formed aluminum phosphate phases simultaneously altered the surface hydrophilicity and cobalt dispersion as well. The partial formation of tridymite aluminum phosphate (AlPO4) phases on the P-Al2O3 support eventually enhanced the dispersion of the supported cobalt crystallites and suppressed the aggregation of cobalt nanoparticles by forming the strongly interacted cobalt crystallites on the P-Al2O3 surfaces. The phosphorous-modified Fischer-Tropsch synthesis (FTS) catalyst also significantly suppressed heavy hydrocarbon depositions due to an increased surface hydrophilicity originated from partially formed SiO2-like tridymite AlPO4 surfaces. A higher stability of the Co/P-Al2O3 catalyst at an optimal phosphorous content in the range of 0.5–1.0 mol% was attributed to homogeneously distributed cobalt crystallites and less deposition of heavy hydrocarbons by forming macro-emulsion droplets with the help of trace amount of alcohols formed during FTS reaction. This was confirmed by in-situ analysis of adsorbed intermediates with surface hydrophilicity and some surface characterizations such as crystallite size, reducibility, and electronic state of the supported cobalt nanoparticles.

Different deactivation behaviors of the prototype Co/γ-Al2O3 (CoAl) and Co/SiO2 (CoSi) catalysts under an excess CO2 environment were investigated in terms of the surface oxidation and aggregation of cobalt crystallites for the Fischer–Tropsch synthesis (FTS) reaction. The presence of excess CO2 in the syngas feed largely altered the catalytic activity and product distribution, especially on the CoAl catalyst. A relatively faster deactivation and lower C5+ selectivity under an excess CO2 environment were observed on CoAl compared with the CoSi, which also were fairly stable under the same reaction conditions. From measurements of the reduction–oxidation behaviors of the cobalt crystallites, it could be seen that CO2 molecules acted as a mild oxidant by partially oxidizing the exposed metallic cobalt surfaces. The dramatic decrease in CO conversion and an increase in CH4 selectivity under the CO2 environment over CoAl were mainly attributed to the irreducible oxidation of the metallic cobalt surfaces through strong interactions with the Al2O3 support. Meanwhile, the marginal deactivation rate and lower changes of selectivity on CoSi were mainly attributed to the reversible oxidation–reduction property of the metallic cobalt crystallites by forming larger cobalt crystallites with relatively weak interactions with the SiO2 support. An excess exposure to the mild oxidant of CO2 on the FTS catalysts generally decreased the catalytic activity irreversibly by forming strongly interacted large cobalt crystallites, which was more predominantly seen on the acidic Co/Al2O3 than on the Co/SiO2 catalyst. The easy reversibility of the oxidation–reduction of the surface metallic cobalt crystallites on SiO2 even in the presence of excess CO2 could prevent catalyst deactivation during the FTS reaction.

Two process models for a carbon-dioxide-utilized gas-to-methanol (GTM) process (CGTM) that primarily produces methanol were developed using the process simulation software Aspen Plus. Both models comprised a reforming unit, a methanol synthesis unit and a recycling unit, with the feeding point of the fresh feed CO2 as the principal configurational difference. In the reforming unit, CO2/Steam–mixed reforming was performed to generate the targeted syngas in flexible compositions. Meanwhile, CO2 hydrogenation was conducted over a Cu-based catalysts in the methanol synthesis unit to directly produce the targeted product, methanol. After methanol synthesis, the unreacted syngas was recycled to the methanol synthesis and reforming units to enhance energy efficiency. The simulation results revealed that both CGTM options can favorably improve the energy efficiency and significantly reduce the total CO2 emissions, compared to a conventional GTM process. The energy efficiency was shown to be highly affected by the recycle ratio and a higher recycle ratio seemed to favorably improve CO2 conversion, enhance energy efficiency, and reduce CO2 emissions. However, the split ratio (recycle-to-reforming unit/total recycle) seems to have little effect on the energy efficiency, and the optimum recycle to the reforming unit was determined to be none.

We study the weakly guided silicon nitride waveguide as an on-chip power delivery solution for dielectric laser accelerators (DLAs). We focus on the two main limiting factors on the waveguide network for DLAs: the optical damage and nonlinear characteristics. The typical delivered fluence at the onset of optical damage is measured to be ∼0.19 J/cm2 at a 2 μm central wavelength and 250 fs pulse width. This damage fluence is lower than that of the bulk Si3N4 (∼0.65 J/cm2), but higher than that of bulk silicon (∼0.17 J/cm2). We also report the nonlinearity-induced spectrum and phase variance of the output pulse at this pulse duration. We find that a total waveguide length within 3 mm is sufficient to avoid significant self-phase modulation effects when operating slightly below the damage threshold. We also estimate that one SiNx waveguide can power 70 μm silicon dual pillar DLAs from a single side, based on the results from the recent free-space DLA experiment.

A TE 0 block TE 1 pass filter is proposed and experimentally demonstrated on SOI platform over C band. The filter suffers negligible reflection and is theoretically immune to phase dependent spectral fluctuation under dual-modes concurrent input.

We propose a fiber-to-chip edge coupler based on trident-shaped dielectric metamaterial. Experiment shows < 2 dB/facet coupling loss with high NA fiber and near 0.5 dB/facet coupling loss using lensed fiber at the best polarization.

Aiming at achieving the large-scale CO2-equivalent reduction in the landfill industry, conceptual design of two sustainable landfill gas-to-methanol process options without the pre-treatment and methanol upgrading sections were implemented via using Aspen Plus simulator. In both proposed options, the optimum syngas ratio (H2/(2CO + 3CO2) = 1) is fulfilled by either supplying additional H2 (option 1) or pre-separating the surplus CO2 in LFG using membrane (option 2). A comparative techno-economic analysis was carried out to determine the energy efficiency and the CO2-equivalent reduction rate, as well as the net present value (NPV), the internal rate of return (IRR), and the discounted payback period (DPBP) of both proposed options. It is shown that both options 1 and 2 can be regarded as alternative processes for converting landfill gas to methanol, and option 1 is more energy efficient and eco-friendly, while, option 2 is more economically competitive. Moreover, a sensitivity analysis indicates that the CAPEX, the prices of methanol, CO2 allowance, and H2 are the most sensitive factors, and option 1 can be economically comparable with option 2 given that the H2 price can be lowered down to around 1000 $/Mt. This work provides two candidate process routes for efficient conversion of landfill gas to value-added methanol, which makes the landfill industry become more sustainable and profitable, especially in the event of a future high carbon tax and low H2 price.

A modular multichannel reaction module with microchannel-based coolant channels was considered, and a computational fluid dynamics (CFD) model was developed to describe the hydrodynamic behavior of the module. Reaction rates for the lumped chain length distribution of hydrocarbon products generated by the Fischer–Tropsch synthesis reaction were proposed, and the developed kinetic and CFD models were shown to satisfactorily fit the experimental data under different production rates. High heat transfer rates resulting from the use of microchannel-based cooling channel maintained the temperature peak below 10 °C, and simulation results with increased size of the catalytic bed and absence of inert materials showed that the high heat of reactions could be efficiently removed over entire catalytic beds, preventing the creation of local hot spots, which are usually observed in conventional fixed bed reactors. In addition, the efficient use of thermal energy could guarantee that methane selectivity, which needs t...

In Fischer–Tropsch synthesis (FTS), cobalt carbide (Co2C) is not a catalytically active material, but rather an undesired cobalt phase associated with low catalytic performance. It is known that Co2C can be easily transformed back to metal cobalt in a H2 environment at 220 °C. The transformed metal cobalt (hcp phase) even shows higher catalytic activity in low-temperature FTS, compared with the reduced cobalt metal from the cobalt oxide species. In this study, to obtain Co2C with high catalytic activity in FTS, we determined the optimum conditions for effective metal cobalt carburization and Co2C hydrogenation by monitoring the phase transformation of cobalt using X-ray absorption spectroscopy (XAS) and temperature-programmed hydrogenation (TPH). We also verified that the transitions effectively occur under the same conditions as those for FTS (2.0 MPa, 220 °C). Based on the conditions determined for the transitions, the deactivated cobalt catalyst can be completely regenerated in the FT reactor by simply altering the injected gases from syngas to CO and then H2. Moreover, the regenerated catalyst shows enhanced catalytic performance compared with the fresh catalyst. The selective formation of hcp cobalt metal via carburization and hydrogenation of the spent catalyst was found to be the key for both the improved catalytic activity and the effective regeneration in situ. As a result, the formation of Co2C, which is mainly considered a nuisance, could provide valuable applications in investigations into catalyst activation and regeneration in FTS.

This publisher’s note reports corrections to Optica 7, 881 (2020)OPTIC82334-253610.1364/OPTICA.394987.

The design of efficient zeolite-supported Co catalysts is essential for the further development of the one-step production of liquid fuels via the low-temperature Fischer–Tropsch synthesis (FTS). Herein, Co/zeolite catalysts were prepared from zeolites SSZ-13, ZSM-22, ZSM-11, ZSM-5, Mordenite, and Y. Their textural and acidic properties, Co dispersion, and internal diffusion behaviors were comprehensively analyzed, along with their FTS product mixtures. Counterintuitively, the degree of isomerization and hydrocarbon decomposition did not correlate with the acidic properties of the zeolite support. Instead, catalysts with high characteristic diffusivity delivered product mixtures with high degree of isomerization and decomposition, suggesting that the access of paraffinic hydrocarbons to the internal acid sites of the zeolite determines the upgrading performance of the bifunctional Co/zeolite catalyst in the low-temperature FTS reaction. Hence, the present findings support upcoming efforts on the design of new and effective FTS catalysts.

Electromagnetic coupling is ubiquitous in photonic systems and transfers optical signals from one device to the other, creating crosstalk between devices. While this allows the functionality of some photonic components such as couplers, it limits the integration density of photonic chips, and many approaches have been proposed to reduce the crosstalk. However, due to the wave nature of light, complete elimination of crosstalk between closely spaced, identical waveguides is believed to be impossible and has not been observed experimentally. Here we show an exceptional coupling that can completely suppresses the crosstalk utilizing highly anisotropic photonic metamaterials. The anisotropic dielectric perturbations in the metamaterial mutually cancel the couplings from different field components, resulting in an infinitely long coupling length. We demonstrate the extreme suppression of crosstalk via exceptional coupling on a silicon-on-insulator platform, which is compatible with a complementary metal-oxide-semiconductor process. The idea of exceptional coupling with anisotropic metamaterials can be applied to many other electromagnetic devices, and it could drastically increase the integration density of photonic chips.

Aiming at achieving large-scale CO2 mitigation in the iron & steel industries via efficient utilization of the by-product gases such as the coke oven gas (COG) and Linz-Donawitz converter gas (LDG) in the iron & steel works, conceptual design of a LDG-to-methanol process (option 1) and two LDG/COG-to-methanol processes (options 2 and 3 without or with H2 purification, respectively) was implemented using the process simulator Aspen Plus. Both the process development and economic analysis for all the three proposed options were conducted to determine the technical performance via indicators such as the energy efficiency and CO2 reduction rate, and the profitability via indicators such as the total capital investment and the net methanol production cost. Meanwhile, six case studies under different recycle ratios (0.5–0.95) were conducted for each proposed option to investigate the effects of recycle ratio on the technical and economic performance. The techno-economic analysis results clearly show that all the three proposed options are highly efficient for CO2 mitigation via methanol production using the by-product gases LDG and COG. More specifically, options 1 and 3 seem to be more energy efficient and eco-friendly than option 2, in terms of energy efficiency and CO2 reduction rate. Whereas, options 2 and 3 seem to be more economically feasible than option 1, considering the net methanol production cost. From the aspects of both technical and economic performance, option 3 is considered as the most competitive process. This work provides candidate process routes for the iron & steel industries to become more sustainable and profitable, especially in the event of a high carbon tax and a low H2 price in the future.

A kinetic model for methanol synthesis was validated for a conventional fixed-bed reactor at the mini-pilot scale by determining a heat transfer coefficient to fit the experimental data satisfactorily. To enhance the thermal controllability of the reaction system, a compact reactor, which utilizes heat transfer with both cooling media and cool feed gas, was introduced. The analysis of detailed profiles of mass, momentum, and heat was conducted by applying the developed kinetic model to the computational fluid dynamics modeling approach. While the accumulation of heat was observed in a conventional reactor because of its limited heat transfer capability, a compact reactor could efficiently remove the generated heat. The space velocity and feed temperature were manipulated to increase the production rate while unstable thermal behavior was prevented, and it was clearly shown that the proposed reactor could produce twice the methanol, with its peak temperature maintained below the conventional one. When the diameter of the catalytic bed in the compact reactor was increased, the reaction remained in the kinetic regime, resulting in high methanol productivity as well as maximum utilization of the bed.

We propose a 3-micron-radius, TE 0 /TE 1 multiplexed 90-degree bend that numerically exhibits 0.8 dB bending loss and 20 dB crosstalk suppression over 30nm bandwidth on an silicon-on-insulator platform. An S-bend shows >37 dB colorless crosstalk suppression.

The merits of increasing the width of the catalytic bed in the channel-type Fischer–Tropsch synthesis reactor module were considered in the present study. Computational fluid dynamics (CFD) modeling was applied to evaluate the effect of different numbers of layers in the gas distributor on the distribution of inlet flows; the use of more than four layers could guarantee that the fraction of dead volume was less than 3%. To obviate the use of the distributor in the cooling channel and successfully dissipate the heat released in the highly exothermic Fischer–Tropsch synthesis, a cross-current flow pattern was considered. In addition, the CFD model including the kinetic reaction rate was validated by comparison of the experimental and simulated results. The cooling performance of the cross-current channel was found to be as good as that of the counter-current case. Further analysis also showed that even when the height of the catalytic bed was increased, the temperature of the bed was maintained below the allowable limit.

Conceptual design of two options of carbon dioxide utilized gas-to-liquids process (CUGP), which mainly produces light olefins and Fischer–Tropsch (F–T) synthetic oils, has been implemented with the aid of Aspen Plus software. The mass and energy stream results as well as the process efficiencies and CO2 emissions of the proposed options were obtained from the developed models. The capital investment and the product cost estimations were conducted before the following economic analysis. Several indicators such as net present value (NPV), discounted payback period (DPBP) and internal rate of return (IRR) were calculated to evaluate the profitability of the two proposed options. In the economic analysis, sensitivity analysis as well as break-even analysis was carried out. In addition, effects of several sensitive factors such as the prices of synthetic oil, olefin and natural gas, capital investment, carbon tax and plant scale on the IRR of each option were analyzed in detail. It was found that the CUGP, regardless of option, was economically feasible at the plant scale of 40,000 BPD and was more competitive compared with conventional GTL processes, in case of high carbon tax.

The Fischer-Tropsch synthesis (FTS) reaction was investigated for the direct production of gasoline range hydrocarbons (C5-C9) from syngas on Ru-, Pt- and La-promoted Co-Al2O3/ZSM-5 (Si/Al=25) hybrid catalysts prepared by co-precipitation method in a slurry. The hybrid catalysts were characterized by BET surface area, XRD, H2-TPR and NH3-TPD analyses. Their physicochemical properties were correlated with the activity and selectivity of the catalysts. The promoted Co-Al2O3-(promoter)/ZSM-5 hybrid catalysts were superior to the unpromoted Co-Al2O3/ ZSM-5 catalyst in terms of better C5-C9 yield. In particular, the Co-Al2O3-Pt/ ZSM-5 hybrid catalyst exhibited the highest catalytic activity with a low C1 and olefin selectivity and a high C5-C9 selectivity. It could be due to not only a higher value for the reduction degree by H2-TPR, but also assigned to weak acidic sites of a low temperature desorption peak by NH3-TPD.

Carbon dioxide reforming of methane on Ni–MgO–Al 2 O 3 catalysts has been investigated systematically at various Mg/Al ratios, focusing on catalytic activity and coke resistance. Ni catalysts supported on MgO–Al 2 O 3 were prepared by sol–gel method using citric acid as a gelling agent. The characterization of the catalyst was carried out by XRD, TEM, TPR, N 2 adsorption, H 2 chemisorption, O 2 titration, CO 2 -TPD and TGA. In the comparison with a catalyst prepared by coprecipitation method, it was found that the catalyst prepared by the sol–gel method showed higher coke resistance. In the variation of Mg/Al ratios, high coke resistance was obtained with increasing MgO loading, while high catalytic activity was observed with the catalysts of medium MgO/(MgO + Al 2 O 3 ) ratio (0.44–0.86), of which the superior catalytic activity is likely attributed to high specific surface area and well dispersed Ni particles.

A phosphorous-modified Al2O3 support was prepared by the impregnation method and applied for the preparation of cobalt-based Fischer–Tropsch synthesis (FTS) catalysts (Co/P–Al2O3), which were calcined at different temperatures. The Co/P–Al2O3 showed a significant increase of thermal stability with a higher catalytic performance without severe deactivation even above a calcination temperature of 600 °C compared with the unmodified Co/Al2O3. These findings are explained by the suppressed cobalt aluminate formation and less pronounced aggregation of cobalt particles. The suppressed aggregation of cobalt particles is attributed to the localized presence of aluminum phosphate by forming a thermally stable metal–phosphorous oxo-species on Al2O3 surfaces thus suppressing the migration of cobalt particles to the outer pore mouths of the support. These effects significantly enhance the catalytic activity with a higher thermal stability of the catalysts.

Metal/ordered mesoporous aluminosilicates (OMAS) have received great attention as bifunctional Fischer–Tropsch (FT) catalysts that directly convert syngas into liquid fuels. However, both synthesis of OMAS with large pores and efficient pore confinement of metal nanoparticles still remain challenging. Here, we report a simple method to synthesize Ru nanoparticles confined in the nanochannels of OMAS (Ru@OMAS). This method eliminates laborious multi-processes that are typically required for pore confinement of metal nanoparticles. We prepare three types of Ru@OMAS with different Si/Al molar ratios (denoted as Si/Al-x, x = 10, 30, and 50) having the same large pore size (∼30 nm) and Ru NP loading (3 wt%). Changing the Si/Al ratio strongly affects the number/strength of acid sites and the metal–support interaction, thereby mediating the catalytic activity and product selectivity. With increasing Al content (decreasing Si/Al ratio), support's acidity and metal–support interactions increase, whereas the reducibility of Ru decreases significantly. As a consequence, among the Si/Al-x catalysts, the Si/Al-50 shows the highest selectivity (63.6%) for liquid fuels (C5–C20) and excellent FT activity (CO conversion of 47.8%) due to its mild acidity and relatively good reducibility.

We propose an on-chip optical power delivery system for dielectric laser accelerators based on a fractal 'tree-branch' dielectric waveguide network. This system replaces experimentally demanding free-space manipulations of the driving laser beam with chip-integrated techniques based on precise nano-fabrication, enabling access to orders of magnitude increases in the interaction length and total energy gain for these miniature accelerators. Based on computational modeling, in the relativistic regime, our laser delivery system is estimated to provide 21 keV of energy gain over an acceleration length of 192 um with a single laser input, corresponding to a 108 MV/m acceleration gradient. The system may achieve 1 MeV of energy gain over a distance less than 1 cm by sequentially illuminating 49 identical structures. These findings are verified by detailed numerical simulation and modeling of the subcomponents and we provide a discussion of the main constraints, challenges, and relevant parameters in regards to on-chip laser coupling for dielectric laser accelerators., Comment: 14 pages

A series of core–shell cobalt oxide catalysts were prepared by tuning the pore diameter of mesoporous silica shell and the influence of pore dimensions on Fischer–Tropsch synthesis was studied. TEM images of core–shell 20Co3O4@MSN-x catalysts showed an increase in the silica shell porosity with increasing molar ratio of the swelling agent to tetraethyl orthosilicate used during catalyst preparation. As a result of this porosity increase, the dispersion of congregated core Co oxide particles within the shell increased, resulting in multiple core centers. Reference catalysts were synthesized using conventional supports, and the effects of pore dimensions on the activity and hydrocarbon selectivity of the reference and the prepared core–shell catalysts were compared. In the experiments performed, 20Co3O4@MSN-x catalysts showed an increase in their CO conversion and C5+ selectivity with increasing silica shell porosity. Moreover, the prepared core–shell catalysts demonstrated higher selectivity toward C5–C18 ...

A kinetic model for the synthesis of methanol over commercial catalysts was developed based on the adsorption of CO and CO2 onto various active sites of Cu, while the kinetic parameters were estimated by fitting 118 experimental sets of data under a variety of conditions. When both CO and CO2 hydrogenations take place, CO conversion was influenced by the change in temperature as well as in space velocity and pressure, while CO2 conversion was minimally influenced as a result of its correlation to the water–gas shift reaction. However, the CO and H2 fractions significantly influenced both conversions. The analysis based on the model developed in this investigation clearly confirmed that the contribution of each reaction and the maximum methanol concentration was expressed as a function of temperature and the CO fraction. Additionally, catalysts with varying particle sizes were used to evaluate the effect of the internal diffusion limitation on catalytic performance and the effectiveness factors were subsequently calculated and regressed with respect to the particle size.

In this study, kinetic models were developed for the mixed reforming and synthesis of methanol (MeOH). The effectiveness of the reforming model in our previous work was proven in an experimental study using a bench-scale reactor, while the intrinsic rate model and effectiveness factors were developed to represent the MeOH synthesis. For a 10-ton-per-day production of MeOH, the rate model was used to determine the size of a reforming reactor so that the supplied heat could be used exclusively to engage the reaction (not for the heat-up of the reactant), while the MeOH reactor was specified using the reported values. The process model was then used to evaluate various effects of the following factors on the MeOH production rate: (1) reaction temperature, (2) CO2 fraction in the feed, and (3) the recycle route of the unreacted gas either to the feed or to the MeOH reactor. Additionally, an analysis was conducted with respect to both the overall and local CO2 conversions in each reactor, and it was shown that a trade-off existed between the maximum MeOH production rate and the maximum CO2 utilization, regardless of the existence of a recycle stream.

in toluene. Alkyne group was introduced into amino SBA-15 (4) by imine-linkage or substitutionwith propargyl bromide to afford iminoalkyne 5a and aminoalkyne 5b, respectively. Meanwhile, alkyne 5c wasprepared in one-step by reacting triethoxysilyl hexyne with SBA-15. Dicobalt-complexes 6a-c werecharacterized by means of FT-IR, solid-state NMR and elemental analysis. Key Words : Alkyne, Cobalt complex, Mesoporous SBA-15, ImmobilizationIntroductionDiverse physicochemical properties of cobalt complexesrelied on the oxidation state or the ligands on-bound have ledtheir applications into the catalytic Fisher-Tropsche

Two process models for carbon dioxide utilized gas-to-liquids (GTL) process (CUGP) mainly producing light olefins and Fischer-Tropsch (F-T) synthetic oils were developed by Aspen Plus software. Both models are mainly composed of a reforming unit, an F-T synthesis unit and a recycle unit, while the main difference is the feeding point of fresh CO2. In the reforming unit, CO2 reforming and steam reforming of methane are combined together to produce syngas in flexible composition. Meanwhile, CO2 hydrogenation is conducted via reverse water gas shift on the Fe-based catalysts in the F-T synthesis unit to produce hydrocarbons. After F-T synthesis, the unreacted syngas is recycled to F-T synthesis and reforming units to enhance process efficiency. From the simulation results, it was found that the carbon efficiencies of both CUGP options were successfully improved, and total CO2 emissions were significantly reduced, compared with the conventional GTL processes. The process efficiency was sensitive to recycle ratio and more recycle seemed to be beneficial for improving process efficiency and reducing CO2 emission. However, the process efficiency was rather insensitive to split ratio (recycle to reforming unit/total recycle), and the optimum split ratio was determined to be zero.

In the present study, a reactor model for mixed reforming over Ni-based catalyst was developed to investigate non-equilibrium behavior and reactions. Kinetic parameters were estimated by fitting experimental data for CH4 and CO2 conversions and H2/CO ratios under a variety of conditions, and the CO2 consumption rate was shown to be significantly affected by operating conditions due to the different characteristics of each reaction: dry reforming (DRM), steam reforming for the production of CO (SRM1) and CO2 (SRM2), and the water–gas shift (WGS) reaction. For optimization study, a reactor composed of three sections with different inert fractions and wall temperatures was considered, and optimization was conducted using various weighting factors on the CO productivity and the CO2 consumption per unit CO productivity; when maximum CO2 consumption per CO productivity was achieved, inert fraction of the first part of the reactor was lowered and wall temperature for the third part of the reactor was decreased, compared to maximum CO productivity case. Further analysis of instantaneous reaction rates showed that, in the case of maximum CO2 consumption, one third of the later part of the reactor could be obviated, resulting in an increase in CO productivity per unit volume, that is, the efficiency of the reactor. As a result, the strategy in the present study was successfully applied in the design of a mixed reforming reaction process providing maximum CO2 conversion as well as minimum CO2 emissions while reducing energy costs.

Fischer-Tropsch synthesis (FTS) reaction for the direct production of gasoline range hydrocarbons (C5-C9) from syngas was investigated on Ru, Pt, and La promoted Co/ZSM-5 (Si/Al = 25) catalysts. The hybrid catalysts were characterized by BET surface area, XRD, H2-TPR, NH3-TPD and XPS analyses. These physico-chemical properties were correlated with activity and selectivity of the catalysts. The promoted Co/ZSM-5 hybrid catalysts were found to be superior to the unpromoted Co/ZSM-5 catalyst in terms of better C5-C9 selectivity. Pt-Co/ZSM-5 exhibited the highest catalytic activity because of the small cobalt particle size.

To improve metal proximity of Co-Cu-Al2O3 catalyst, xerogel-derived mesoporous Co-Cu-Al2O3 catalysts (CoCuAl-Xe) with various Co:Cu molar ratios (3:1, 2:1, 1:1, 1:2, and 1:3) were prepared by an epoxide-driven sol-gel method and applied to higher alcohol synthesis from syngas. The CoCuAl-Xe catalyst induced the formation of a composite spinel structure containing Co, Cu, and Al. At the optimal Co/Cu ratio, the Cu atoms efficiently substituted the Co2+ ions in Co3O4 to form the CuCo2O4 spinel structure. However, an excess amount of Cu induced segregation of CuO, leading to decreasing Co-Cu proximity. In higher alcohol synthesis from syngas, all the catalysts showed the linear quasi-Anderson Schulz Flory plot of carbon-containing products, which was attributed to the CO insertion mechanism in higher alcohol synthesis. Among the xerogel catalysts, 2Co1CuAl-Xe exhibited the highest CO conversion and higher alcohol yield. The Co-rich CoCuAl-Xe catalyst was disadvantageous in terms of alcohol selectivity because of a lack of CO insertion sites, and the Cu-rich one was disadvantageous in CO dissociation and led to methanol formation. The computational study suggests that high Co-Cu proximity favors CHOH* mechanism for CH* formation and promotes CO insertion reaction. Consequently, it was found that the optimal Co/Cu ratio and high Co-Cu proximity is required for high catalytic activity in higher alcohol synthesis.

The catalytic behavior of a K/Fe–Cu–Al catalyst has been investigated together with carbon deposition by variation of the CO2/(CO + CO2) ratios in H2-sufficient feed gas during the Fischer–Tropsch synthesis (FTS). Both fresh and used catalysts were characterized by means of X-ray diffraction, temperature-programmed decarburization, thermogravimetric analysis, and elemental analysis. Under H2-sufficient and CO2-abundant conditions [H2/(2CO + 3CO2) = 1, and CO2/(CO + CO2) ≥ 0.5], CO2 in the feed gas was consumed for hydrocarbon production. The COx conversion to hydrocarbons increased with the temperature, pressure, and CO content in the feed gas. Under high-pressure reaction conditions, carbon deposition was significantly reduced, as compared to that at low pressures. Overall, conditions involving a high CO2/(CO + CO2) ratio, temperature, and pressure are beneficial for both CO2 utilization and prevention of carbon deposition in the FTS using Fe catalysts.