Search

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.

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.

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.

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.

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.

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.

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 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

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

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.

The low-temperature rapid transition of cobalt carbide to metal cobalt species in a H 2 environment was studied using in situ analyses, including temperature-programmed decarburization, in situ diffuse reflectance infrared Fourier-transform spectroscopy, X-ray absorption spectroscopy, and time-resolved gas chromatography profiles, during hydrogenation of cobalt carbide. Cobalt carbide was readily prepared by treatment of cobalt metal species in pure CO. By monitoring the evolution of cobalt carbide during hydrogenation, the analysis results give direct evidence for the formation of the cobalt metal hexagonal close packed (hcp) phase and light hydrocarbons (methane, ethane, and propane) as the products of hydrogenation of carbonaceous species on/in the cobalt carbide and clearly demonstrate that hydrogenation was completed at 220 °C in excess H 2 within 2 h. As a result of the low-temperature transition of cobalt carbide, before slurry-phase Fischer–Tropsch (FTS), an activated metal cobalt catalyst was easily obtained in situ by H 2 bubbling at 220 °C, in the slurry phase. Moreover, the cobalt metal hcp phase derived from cobalt carbide exhibited significantly improved catalytic performance in FTS compared with the cobalt metal face-centered cubic phase obtained by cobalt oxide catalyst reduction. These results not only broaden and deepen fundamental understanding of the hydrogenation of cobalt carbide but also provide a potential facile activation route for cobalt catalysts for the synthesis of clean hydrocarbon fuels from syngas.

The influences of cobalt particle size on the Fischer–Tropsch reaction have been studied by using pre-synthesized cobalt oxide nanoparticles. Cobalt oxide nanoparticles in the range of 3–16 nm were synthesized by reacting colloidal solution of Co3O4 at the different reaction temperatures from 150 to 250 °C and stabilized by capping agent. The nanoparticles were impregnated on γ-Al2O3 to prepare 5 wt% Co/Al2O3 catalysts and compared with the catalysts prepared by conventional methods. The reduction degree by TPR and O2-uptake increased with the increase in the cobalt crystal size from 4.8 to 17.5 nm, however H2-uptake decreased. The rapid growth in the catalytic activity was observed when the cobalt crystal size increased from 4.8 to 9.3 nm and then the activity decreased with further increase in crystal size showing volcano shape in catalytic activity. The catalyst with the cobalt particle size of 9.3 nm showed higher CO conversion, better C5+ selectivity and lower methane conversion. These size-defined cobalt catalysts showed considerably higher FTS activity and better TOF (S−1) than conventional catalysts and with the increase in the cobalt particle size, their deactivation rates also decreased as well even after 54 h on stream.

Effects of Ru promoted cobalt oxide nanoparticles on γ-Al 2 O 3 supported catalysts were studied for Fischer–Tropsch reaction. Homogeneously sized cobalt oxide nanoparticles with the different amount of ruthenium promoter were prepared by solvothermal method using oleic acid as capping agent. Pre-synthesized CoRuO x nanoparticles were then impregnated on γ-Al 2 O 3 support to prepare 5CoxRu/100Al 2 O 3 catalysts (5CoxRuAl), with the amount of ruthenium x = 0 to 0.1. The catalysts were characterized by XRD, TEM, TPR, EDX, H 2 chemisorption and O 2 titration methods and compared with the catalyst prepared by conventional impregnation method, i.e. i-5Co0.05RuAl. Interestingly, catalysts prepared by nanoparticle impregnation method showed higher H 2 uptake and better reducibility with the concomitant increase in the activity due to the homogeneous dispersion of the Ru promoter across entire the nanoparticles as compared to the catalyst prepared by conventional impregnation method. The intimate contact between cobalt and ruthenium enhanced the site density of cobalt which was responsible for the promotional results in the case of 5CoxRuAl catalysts.

Fischer–Tropsch synthesis (FTS) for the co-production of C2–C4 olefins and clean fuels such as gasoline and middle distillate from syngas was investigated on four different iron-based catalysts in a fixed-bed and a bubbling fluidized-bed reactor. The catalysts were prepared by wet-impregnation using the Al2O3, SiO2 and iron ore (FeOx) supports with the active components of Fe, K and (or) Cu, and each K/FeCuAlOx catalyst was prepared by a co-precipitation method. Except for the catalyst impregnated on SiO2, CO conversion of the other catalysts is similar regardless of the type of reactor. However, the yield of light olefins in the range of C2–C4 hydrocarbons and clean fuels is closely related to the formation of active iron carbide species and to surface acidity. The impregnated K/FeOx catalyst is found to be one of the promising catalysts to be applied in a bubbling fluidized-bed reactor for middle temperature FTS reaction due to its high resistance to catalyst attrition with a high catalytic performance.

Kinetics of the methanol (MeOH) dehydration has been investigated using two kinds of alkali metal-modified ZSM-5 (mZSM-5) catalysts, which were developed for the purpose of preparing dimethyl ether (DME) from water-containing MeOH. Two intrinsic kinetic mechanisms have been suggested and rigorous reaction rate equations were derived based on a series of reaction experiments in the presence and in the absence of water. In addition to the kinetic parameters, the heats of adsorption of MeOH and water were successfully estimated. The values are in good agreement with those obtained from the previously reported experimental results. According to the reaction pathways of our concern, two adsorbed MeOH molecules on the mZSM-5 simultaneously react with acidic sites to produce the intermediate molecule, which then undergoes the rate-determining step that the intermediate molecule rearranges itself to split into the smaller intermediates for the next step with or without the abstraction of water. In addition, the existence of the crucial intermediate closely related to the rate-determining step was also confirmed through FT-IR spectroscopy.

The catalytic stability of cobalt-based catalyst using phosphorous-modified alumina support (P-Al2O3), promoted with Pt or Ru, during Fischer–Tropsch synthesis (FTS) has been investigated for 1000 h on stream using a slurry-phase continuous-stirred tank reactor. Although catalytic properties such as surface area and particle size of metallic cobalt are similar for both the catalysts, the different deactivation behaviors were observed with respect to the kind of noble metal addition. The slower catalyst deactivation was observed on Pt promoted Co/P-Al2O3 catalyst than Ru promoted one, which seems to be owing to small deposition of polymeric carbons on the surface, confirmed by hydrogenation of surface carbons, and suppressed formation of aggregated catalyst lump at the beginning of FTS reaction.

The Fischer–Tropsch synthesis of unpromoted and nano-sized iron oxide supported on δ-Al2O3 was investigated using a fixed-bed reactor. The catalysts prepared from pre-synthesized iron oxide with varying particle size (2–12 nm) showed much higher catalytic activities than the one prepared by using conventional impregnation method. The best results for CO conversion were obtained when the catalyst had Fe particle size of 6.1 nm. With an increase in particle size, the reduction degree and C5+ selectivity was increased, whereas CH4 selectivity and the uptake of adsorbed CO were decreased. Turnover frequency (TOF) at 300 °C was increased from 0.02 to 0.16 s−1 when d(Fe0) was increased from 2.4 to 6.2 nm, and then it remains almost constant up to a particle size of 11.5 nm. Particle sizes of prepared iron oxide were analyzed by XRD and TEM, and the reduction behaviors of Fe/Al2O3 catalysts were studied by H2-TPR. The effective iron size, metal dispersion and reduction degree of Fe/Al2O3 catalysts were measured by CO chemisorption and O2 titration.

A novel doubly promoted Ru/Co/ZrP/SiO 2 catalyst with zirconium–phosphorous species (ZrP) reveals high activity and stability on Fischer–Tropsch synthesis (FTS). The surface modification of SiO 2 with ZrP species containing appropriate amount of phosphorous component, has an effect on the suppression of cobalt particle aggregation during FTS reaction. The spatial confinement of cobalt particles in ZrP matrix could be significantly enhanced when P /(Zr + P) molar ratio is around 0.13 (CoZrP(0.5)).

Novel aluminophosphate (AlPO) binders consisting of dense phases of alpha-cristobalite and tridymite were prepared by the treatment of pseudo-boehmite (AlO(OH)) with phosphoric acid. The ZSM-5 extrudates prepared by using AlPO binders have been characterized by XRD, N 2 sorption, NH 3 -TPD, 27 Al and 31 P NMR techniques to elucidate the changes that occurred in the textural properties of the catalyst and their implications on the catalytic activity of the resultant ZSM-5-based extrudates towards methanol to propylene (MTP) reaction. XRD indicated the chemical interaction of P with the alumina binder to form a highly dense crystalline phase of aluminophosphate, alpha-cristobalite. N 2 adsorption, while NH 3 -TPD studies revealed the changes in pore morphology of AlO(OH) binder and acidity of ZSM-5 in phosphorus containing extrudates. The drastic decrease in mesoporosity of the AlO(OH) observed after phosphorus addition indeed envisions the disappearance of inter-crystalline voids in the AlO(OH), probably due to a change in its morphology from the crystalline phase to amorphous AlPO phase. 27 Al and 31 P NMR studies further confirmed the formation of AlPO in these samples. The resultant ZSM-5-based extrudates exhibited enhanced properties of hydrothermal stability, mechanical strength, propylene yield and coke resistance in methanol to propylene (MTP) reaction. The positive aspect of P addition was continuously increased with P amount; at optimum P/Al (binder) ratio of ∼0.8, the catalyst exhibited about 80% yield to C 2 –C 4 olefins with the major component being propylene (∼50%) at near 100% methanol conversion. The catalyst also exhibited the stable performance in the studied period of 150 h.

Cobalt supported on amorphous aluminum phosphate (Co/AlPO4) catalysts were prepared by the impregnation method using three different cobalt precursors such as cobalt nitrate, acetate and chloride to elucidate the activity of Fischer–Tropsch synthesis. The use of AlPO4 as a support for cobalt-based catalysts exhibits better catalytic performance during FTS reaction than the corresponding Co/Al2O3 catalyst. TPR results also suggest that the reducibility of the catalysts varies with the nature of cobalt precursors employed during the impregnation on AlPO4 support. The Co/AlPO4 catalyst prepared from cobalt nitrate shows higher CO conversion and C8+ selectivity than the others due to the facile formation of homogeneous cobalt particles with proper electronic characters and high reducibility. Interestingly, all Co/AlPO4 showed a growth of filamentous carbon initiated from the large mobile cobalt particles during the reaction. The differences in catalytic properties of Co/AlPO4 are mainly attributed to the cobalt particle size, reducibility with different electronic states of metallic cobalt, pore diameter of AlPO4 and formation of filamentous carbon.

The catalytic activity on the coprecipitated Cu–ZnO–Al2O3/Zr-ferrierite (CZA–ZrFER) with different Zr content from 0 to 5 wt.% was investigated for the direct synthesis of dimethylether (DME) from H2-deficient and biomass-derived model syngas (H2/CO molar ratio = 0.93). The catalytic functionalities, such as CO conversion and DME selectivity, showed their maxima on the bifunctional catalyst with 3 wt.% Zr-modified ferrierite. Detailed characterization studies were conducted on the catalysts to measure their properties such as surface area, acidity by temperature-programmed desorption of ammonia (NH3-TPD), reducibility of Cu oxide by temperature-programmed reduction (TPR), copper surface area measurements by N2O titration method, electronic states of copper by IR analysis and particle size measurement by XRD and TEM analysis. The number of acid sites measured by NH3-TPD on the bifunctional catalysts decreased monotonously with the increase of Zr content, meanwhile, the acidic strength is found to be minimal on the catalyst showing best performance. The reducibility of copper oxide and the surface area of metallic copper also exhibited their maximum values at the same Zr composition indicating that these are responsible for the optimum functionality of the bifunctional CZA–ZrFER catalyst. The role of easily reducible copper species with small particle size and the suppressed strong acidic sites is also emphasized in the consecutive reaction from syngas to DME on the bifunctional catalyst. The different behavior of intrinsic rate of the bifunctional catalysts is also well correlated with the metallic surface area of copper and the amount of acidic sites with their acidic strength.

The phosphorous-modified γ-Al2O3 support is used to prepare cobalt-based Fischer–Tropsch (FT) catalysts (Co/P–Al2O3) by slurry impregnation method. Since alumina surface is partially transformed to aluminum phosphate by phosphorous modification, it alters the cobalt cluster size resulting in the changes of FT activity. The appropriate amount of phosphorous loading on alumina surface is around 1–2 wt.% based on the alumina support. The enhanced activity is mainly attributed to the formation of a homogeneously distributed small cobalt clusters and redispersion of cobalt species during the FT reaction.

A simple sol–gel method was adopted to synthesize boehmites with high surface area using aluminum iso-propoxide (AIP), acetic acid (AA) and 2-propanol, and the effects of surface area and methanol dehydration on activity were investigated. The hydrolysis conditions of AIP in the presence of AA in 2-propanol solvent were systematically varied to observe their effect on phase formation, crystallinity, surface area and pore size distribution of the alumina. The surface area and the number of acidic sites varied considerably with the variation in the molar ratio of AA/AIP. This study revealed that a high surface area boehmite (in the range of 628–717 m2/g) could be obtained by keeping the molar ratio of AA/AIP as 0.5 and that of H2O/AIP at ∼3. Rod shaped, porous γ-Al2O3 powder with a high surface area of 438 m2/g was obtained after calcination of the boehmite at 500 °C for 5 h in air. The temperature programmed desorption of ammonia (NH3-TPD) of the γ-Al2O3 samples demonstrated higher concentration of acidic sites when acetic acid was used during preparation than when it was not used. The vapor phase dehydration of methanol (containing 20 mol% H2O) to dimethyl ether (DME) was conducted on the prepared aluminas. With increasing surface area of γ-Al2O3, the temperature required to reach 50% conversion of methanol decreased due to the increased number of acidic sites which are favorable for methanol dehydration with low byproduct formation. The catalytic activity for methanol dehydration to DME correlated well with the total number of acidic sites of γ-Al2O3, which was controlled by changing the AA/AIP and H2O/AIP molar ratios.

The influence of CO 2 on the deactivation of Co/γ-Al 2 O 3 Fischer–Tropsch (FT) catalyst in CO hydrogenation has been investigated. The presence of CO 2 in the feed stream reveals a negative effect on catalyst stability and in the formation of heavy hydrocarbons. The CO 2 acts as a mild oxidizing agent on cobalt metal during Fischer–Tropsch synthesis. During FT synthesis on Co/γ-Al 2 O 3 of 70 h, the CO conversion and C 5+ selectivity in the presence of CO 2 decreased more significantly than in the absence of CO 2 . CO 2 is found to be responsible for the partial oxidation of surface cobalt metal at FT synthesis environment with the co-existence of generated water.

Effects of templating on the catalytic performance of SAPO-34 catalyst have been investigated in conversion of methanol to olefins (MTO). SAPO-34 catalysts were synthesized using a single agent or a mixture of morpholine or tetraethyl ammonium hydroxide of (TEAOH) as the template during synthesis of gel with nominal composition as 1Al2O3:1P2O5:0.6SiO2:x morpholine:(2 − x)TEAOH:52H2O. Compared with using single template, using a mixed template leads to the particle size reduction and the morphology change to spherical type formed by the aggregation of nano-sized crystals. Although all the catalysts showed similar activity and product distribution in the MTO reaction, the catalyst obtained using the mixture of 75% morpholine and 25% TEAOH gave the longest lifetime.

Pitch-based porous carbons having –SO 3 H groups on their surfaces were synthesized by carbonization of mesophase pitch and then sulfonation of the resulting compounds. As-synthesized carbons were characterized by BET surface area analysis, pore volume analysis and XRD. The concentration of –SO 3 H groups present on the carbons was measured by neutralization titration. PtRu nano-clusters were supported on the pitch-based porous carbons, and these electrocatalysts were used as anodic materials in a DMFC. Membrane–electrode assemblies prepared using these electrode materials showed an improved power density compared with a commercial 60% PtRu/Vulcan XC-72. This performance is ascribed to the higher ionic conductivity of the anode layer and the well exposed catalytic active sites.

The effect of γ-alumina as a binder on the catalytic performance of Na-modified ZSM-5 was investigated by using the dehydration of methanol to dimethyl ether (DME). A series of modified ZSM-5 catalysts were prepared with/without γ-alumina and the activity of each catalyst was examined in the dehydration of crude methanol to DME using a fixed-bed reactor at the reaction pressure of 10 atm and LHSV of 10 h −1 . The surface and pore characteristics were investigated by Ar adsorption and the acid properties were studied by TPD of ammonia and FT-IR of adsorbed pyridine. Though the addition of γ-alumina lowered the activity of NaHZSM-5, it broadened the operative temperature range (OTR), thereby resulting in more stable catalysts. The ZSM-5 containing 70% of γ-alumina was found to be an efficient catalyst, exhibiting quite high activity as well as wide OTR. This beneficial effect is ascribed to the adequate dilution of the strong acid sites of ZSM-5 in the γ-alumina matrix.

Zeolites are crystalline nanoporous aluminosilicates widely used in industry. In order for zeolites to find applications as innovative materials, they need to be organized into large two- and three-dimensional (2D and 3D) arrays. We report that uniformly aligned polyurethane films can serve as templates for the synthesis of uniformly aligned 2D and possibly 3D arrays of silicalite-1 crystals, in which the orientations of the crystals are controlled by the nature of the polymers. We propose that the supramolecularly organized organic-inorganic composites that consist of the hydrolyzed organic products and the seed crystals are responsible for this phenomenon.

Optical resonators with high quality factors (Qs) are promising for a variety of applications due to the enhanced nonlinearity and increased photonic density of states at resonances. In particular, frequency combs (FCs) can be generated through four-wave mixing in high-Q microresonators made from Kerr nonlinear materials such as silica, silicon nitride, magnesium fluoride, and calcium fluoride. These devices have potential for on-chip frequency metrology and high-resolution spectroscopy, high-bandwidth radiofrequency information processing, and high-data-rate telecommunications. Silicon nitride microresonators are attractive due to their compatibility with integrated circuit manufacturing; they can be cladded with silica for long-term stable yet tunable operation, and allow multiple resonators to be coupled together to achieve novel functionalities. Despite previous demonstrations of high-Q silicon nitride resonators, FC generation using silicon nitride microresonator chips still requires pump power significantly higher than those in whispering gallery mode resonators made from silica, magnesium, and calcium fluorides, which all have shown resonator Qs between 0.1 and 100 billion. Here, we report on a fabrication procedure that leads to the demonstration of “finger-shaped” Si3N4 microresonators with intrinsic Qs up to 17 million at a free spectrum range (FSR) of 24.7 GHz that are suitable for telecommunication and microwave photonics applications. The frequency comb onset power can be as low as 2.36 mW and broad, single FSR combs can be generated at a low pump power of 24 mW, both within reach of on-chip semiconductor lasers. Our demonstration is an important step toward a fully integrated on-chip FC source.

In this work, an attempt has been made to modify the shape and nanostructure of core-shell materials, which have been usually generated on the basis of amorphous spherical cores. Novel core-shell silicate particles, each of which consists of a silicalite-1 zeolite crystal core and mesoporous shell (ZCMS), were synthesized for the first time. The ZCMS core-shell particles are unique because they are of pseudohexagonal prismatic shape and have hierarchical porosity of both a uniform microporous core and a mesoporous shell coexisting in a particle framework. The nonspherical bimodal porous core-shell particles were then utilized as templates to fabricate a new carbon replica structure. Interestingly, the pore replication process was carried out only through the mesopores in the shell, and not through the micropores due to the narrower micropore size in the core, resulting in nonspherical carbon nanocases with a hollow core and mesoporous shell (HCMS) structure. Nonspherical silica nanocases with HCMS structure were also generated by replication using the carbon nanocases as templates, which are not possible to synthesize through other synthetic methods. Interestingly, the pseudohexagonal prismatic shape of the zeolite crystals was transferred onto the carbon and silica nanocases.