Low Reaction Pressure Research Articles

Solvent effects on methane diffusion in gas hydrates: A RxDFT study

Methane hydrate, a promising green energy reservoir located at the seafloor, holds potential for mitigating environmental pollution. The current study uses Reaction Density Functional Theory (RxDFT) to calculate the diffusion energy of methane hydrate in aqueous solution as a function of temperature, pressure, and the confinement provided by graphene channels. Study of changes in activation energy and the fluctuations in solvent water molecule density around the solute molecules suggests that the methane diffusion increases with higher reaction temperatures and lower reaction pressure. Furthermore, the activation energy for methane diffusion peaks at a width of 32 Å in the graphene channel, reaching its maximum value of 40.95 kcal mol−1. This elucidates the intricate interactions between solvent molecules and hydrates, providing insights into the diffusion mechanism.

High-quality Ge1−xSnx (x = 0–0.11) realized by UHV-CVD using Ge2H6 and SnCl4: Materials growth, structural/optical properties, and prototype IR photodetectors

GeSn materials with Sn contents ranging between 0% and 11% have been successfully grown by using Ge2H6 and SnCl4 in a hot-wall UHV-CVD system at low reaction pressures of 0.2–0.4 Torr. Both fully strained and partially relaxed materials have been produced. It was found that the materials were of high crystallinity as evidenced by few threading dislocations from cross-sectional TEM. Photoluminescence studies have shown that the PL spectra shift to longer wavelengths, and the PL intensity increases exponentially as the Sn contents increase. The photoemission cutoff for a 9.5% Sn sample is beyond 2600 nm, and low temperature PL measurements have confirmed that this sample is already in the direct gap material regime. Prototype photoconductor devices were fabricated with a partially strained 5% Sn sample, showing much smaller dark currents and similar spectral coverage as compared to a fully strained 7.8% Sn device reported in the literature. The reported technical route has provided a new path toward high quality, low cost GeSn epitaxy, and will contribute to the development of group IV optoelectronics.

Effects of the outlet contraction ratio on the performance of liquid kerosene/air two-phase rotating detonation combustors

Experiments and numerical simulations were conducted across a range of contraction ratio to investigate the detonation combustion characteristics of liquid aviation kerosene/air rotating detonation combustor. The research indicates that extremely low and high contraction ratio adversely affect the stable operation of the two-phase rotating detonation combustors. At a contraction ratio that is too low (19.03 % in the RDC discussed in this paper), the atomization and mixing properties of the two-phase fuel are poor, with a lower reaction pressure in the fresh mixture, hindering the initiation of detonation waves. On the other hand, a contraction ratio (85.7 % in the RDC discussed in this paper) that is too high enhances the energy of the detonation wave; it triggers oblique shockwave feedback, preventing the fresh mixture from entering the combustor and thus leading to the quenching of detonation waves. With an increase in the contraction ratio of outlet configurations, there is a noticeable rise in both the peak pressure and combustion efficiency of detonation waves. In contrast, the wave height gradually decreases, and the wave velocity shows a pattern of initially increasing and then decreasing. Along the axial position inside the two-phase rotating detonation combustor, the upstream detonation wave is caused by the reflected shockwaves increasing the pressure of the upstream fresh mixture. In contrast, the downstream detonation wave results from increased fresh mixture pressure and enhanced fuel atomization and mixing due to the increased contraction ratio of outlet configurations and wave feedback. So, the detonation wave exhibits a strong-weak-strong distribution characteristic.

Design of Sodium Titanate Nanowires as Anodes for Dual Li,Na Ion Batteries

The bottleneck in the implementation of hybrid lithium-sodium-ion batteries is the lack of anode materials with a desired rate capability. Herein, we provide an in-depth examination of the Li-storage performance of sodium titanate nanowires as negative electrodes in hybrid Li,Na-ion batteries. Titanate nanowires were prepared by a simple and reproducible hydrothermal method. At a low reaction pressure, the well-isolated nanowires are formed, while by increasing the reaction pressure from 2 to 30 bar, the isolated nanowires tend to bundle. In nanowires, the local coordinations of Na and Ti atoms deviate from those in Na2Ti3O7 and Na2Ti6O13 and slightly depend on the reaction pressure. During the annealing at 350 °C, both Na and Ti coordinations undergo further changes. The nanowires are highly defective, and they easily crystallize into Na2Ti6O13 and Na2Ti3O7 phases. The lithium storage properties are evaluated in lithium-ion cells vs. lithium metal anode and titanate electrodes fabricated with PVDF and carboxymethyl cellulose (CMC) binders. The Li-storage by nanowires proceeds by a hybrid capacitive-diffusive mechanism between 0.1 and 2.5 V, which enables to achieve a high specific capacity. Sodium titanates accommodate Li+ by formation of mixed lithium-sodium-phase Na2−xLixTi6O13, which is decomposed to the distinct lithium phases Li0.54Ti2.86O6 and Li0.5TiO2. Contrary to lithium, the sodium storage is accomplished mainly by the capacitive reactions, and thus the phase composition is preserved during cycling in sodium ion cells. The isolated nanowires outperform bundled nanowires with respect to rate capability.

Supported mesoporous Pt catalysts with excellent performance for toluene hydrogenation under low reaction pressure

Aromatic hydrogenation is a matter of great importance because of its multiple applications and meaningfulness in environmental protection. However, lowering the reaction pressure for toluene hydrogenation with suitable catalyst is a primary challenge. Hence, in this work, we report good catalytic performance of toluene hydrogenation using supported mesoporous Pt (MP) under low reaction pressure. The MP has porous morphology and particle diameter is around 50 nm. The whole structure is constituted by mutual-connected Pt nanoparticles with size of 3-5 nm. Owing to the abundant highly exposed Pt atoms of MP and electron transfer between MP and support, MP catalyst shows a superior catalytic performance than traditional Pt nanoparticle catalysts under lower reaction pressure.

Thermodynamic analysis of hydrogen production from carbide slag used as oxygen carrier, hydrogen carrier and in-situ carbon capture agent during the gasification of lignite

Coal-based chemical looping gasification (CCLG) has attracted much attention for hydrogen production. The hydrogen and oxygen carriers are the vital part of this process. Additionally, the CO2 coming out from the CCLG process for hydrogen generation is not conducive to the environment and direct use of hydrogen. It is significant to explore industrial solid waste, which can simultaneously be used as oxygen carrier, hydrogen carrier and in-situ carbon capture agent. In the current work, the feasibility of using industrial waste-carbide slag as the oxygen carrier, hydrogen carrier and for in-situ carbon capture in a CCLG with lignite for hydrogen production was investigated by the thermodynamic software FactSage and experiments. The results show that carbide slag could be used as an in-situ carbon capture agent, and as hydrogen and oxygen carriers in the CCLG process. The suitable reaction conditions were found to be as follows. The reaction temperature lied within the range of 623–900 K, whereas 1:4 of the molar ratio of C:Ca(OH)2 was worth recommend. Moreover, the lower reaction pressure was more favorable for the performance of the CCLG process, the pressure of 0.1 atm achieved better performance of CCLG. As for the mechanism of the process, C of lignite was partly transformed into CH4 through C reacted with Ca(OH)2. After which, it was converted into hydrogen and realized carbon capture through CH4 reacted with Ca(OH)2. The other part of C in lignite directly reacted with Ca(OH)2 of carbide slag to produce hydrogen and in-situ capture carbon. The current work opens up a novel way for integrating efficient utilization of low-quality coal with carbide slag.

Design and evaluation of a novel system for the flue gas compression and purification from the oxy-fuel combustion process

The process of flue gas compression and purification is essential for oxy-fuel combustion, because of its significance in determining the quality of the CO2 product. Based on the difference of dew points between CO2 and acid contaminants, a novel system, which integrated the partial CO2 recirculation with the flue gas purification, was proposed and evaluated in this study. The simulation results confirmed that a CO2 stream with a purity of 99.9% could be achieved, and the distillate after treatment in SO2 and NO absorbers could be directly recycled back to the boiler. The performance of CO2 recovery was enhanced by elevating the condensing pressure to 3.0–4.0 MPa. Besides, there was a critical ratio between the recycled CO2 liquid and the raw flue gas for the abatement of contaminants, which was 11.0 L/m3. Furthermore, the performances of SO2 and NO removal were investigated. The efficiencies of SO2 and NO abatement could be more than 99% when the reaction pressures were 0.5 MPa and 1.5 MPa separately. Besides, a critical molar ratio of SO2 to NO in the raw feeding flue gas was determined, and the removal of SO2 was restrained when the SO2/NO molar ratio increased over the critical point. As for the NO abatement, the continuous re-oxidation of NO released from the dissociation of HNO2 was dominant in the NO absorber, and the performance of NO removal was dramatically enhanced with the presence of NO pre-oxidation at low reaction pressures.

Optimizing Ni−Fe−Ga alloys into Ni2FeGa for the Hydrogenation of CO2 into Methanol

AbstractA screening study of the catalytic performance of ternary alloy nanoparticles containing nickel, iron and gallium supported on silica for methanol synthesis from CO2 and H2 was performed. Catalysts were prepared by incipient wetness impregnation and subsequently reduced in H2 before catalytic testing. Ni2FeGa showed the best performance of the tested catalysts in terms of methanol yield. An optimization of the preparation was done to improve activity and selectivity, reaching a performance close to that of commercially available Cu/ZnO/Al2O3/MgO at low reaction temperatures and pressure. Extensive in situ characterisation using environmental TEM, in situ XRD and in situ EXAFS of the formation of the Ni2FeGa catalyst explains an optimal reduction temperature of 550 °C: warm enough that the three atomic species will form an alloy while cold enough to prevent the catalyst from sintering during the formation.

Effect of calcination temperature on steam reforming activity of Ni-based pyrochlore catalysts

This work served as the second part of a study evaluating the effect of calcination temperature (700–1000 °C) on Ni-based lanthanum zirconate pyrochlore catalysts for methane steam reforming. A previous study (Haynes et al. Ceram. Int. 2017 (43) 16744) provided a thorough characterization of the material properties for the catalysts used here, and this study focuses on the evaluation of catalytic activity. The activity was assessed by two different experimental studies: the effect of reaction temperature using a temperature programmed surface reaction (TPSR), and the effect of reaction pressure. The results demonstrate a complex interaction between the Ni particles and surface LaOx species under the methane steam reforming conditions. Specifically, the material calcined at the lowest temperature (700 °C) possesses the highest activity and selectivity, which is attributed to smaller and more well-dispersed Ni particles on the surface, and, more importantly, a lesser degree La enrichment at the surface. All catalysts were deactivated by steam to NiO under all conditions tested, but at certain low reaction pressure (p = 0.23 MPa) conditions the materials calcined at 700–900 °C are able to completely recover equilibrium activity in-situ that is then robust and stable under both low and high reaction pressures (p = 1.8 MPa) suggesting the formation of a synergistic relationship between Ni and La for syngas production. However, exposure of a fresh material to high reaction pressures leads to a rapid and irreversible loss in both CH4 conversion and syngas selectivity whether in the fresh (no pretreatment), or pretreated (steam, H2 or Ar only at 800 °C) form for any catalyst. The mechanism for deactivation appears to be due to the presence of LaOx species that become mobile, possibly by the formation of La–OH, and covers the active Ni particles and inhibits sites responsible for the CH4 decomposition.

Catalytic Dehydrogenation of para-Diethyl Benzene to para-Divinyl Benzene over Iron Oxide Supported Catalyst

The vapor-phase catalytic dehydrogenation of para-diethyl benzene (PDEB) to para-divinyl benzene (PDVB) with super-heated steam as a diluent was investigated using alumina supported iron oxide catalyst system. During the catalytic dehydrogenation reaction, ethyl styrene (EST) and thermal cracking products were observed as side products. It was found that various reaction parameters influence the rate of dehydrogenation reaction. However, the reaction is favored by high temperature and low reaction pressure. Moreover, addition of potassium into iron-oxide catalyst acts as a promoter and thereby increases the efficiency of the catalyst. The conversion of PDEB and yield of PDVB also increases as the Water/PDEB flow ratio increases.

Silicon Nanohole Arrays Fabricated by Electron Beam Lithography and Reactive Ion Etching

The fabrication of silicon nanohole (SiNH) using a combination of electron beam lithography (EBL) and reactive ion etching (RIE) processes is reported. The optimum exposure dose of EBL process was found to be in the range of 210-240 µC/cm2 due to small enlargement of hole diameter after pattern development process. The anisotropic etching and isotropic etching was achieved at low and high reaction pressures, respectively. As expected, the etching rate increase with time and RF power. A relatively smooth and well-defined NH has been obtained at RF power of 100 W and reaction pressure of 0.08 Torr, which is suitable to be applied for optical waveguide.

Promoting CO2 hydrogenation to methanol by incorporating adsorbents into catalysts: Effects of hydrotalcite

CO2 hydrogenation, in which CO2 conversion to methanol plays a key role, is of increasing importance in mitigating the climate crisis. However, high reaction pressures are required to conduct methanol synthesis because of poor catalytic performance of conventional catalysts, leading to high energy consumption. In this study, a novel strategy was applied to promote methanol synthesis by adsorption-enhanced CO2 hydrogenation. Catalysts made from Cu-ZnO-Al2O3 mixed with different hydrotalcite contents (named CZA-HT) were prepared by physically mixing a commercial copper-based catalyst for methanol synthesis with hydrotalcite for high temperature CO2 adsorption. In these catalysts, only the commercial copper-based component contains the active part for CO2 hydrogenation and its copper surface area is 48.1 m2 g−1 with an optimal reaction temperature of 523 K. Hydrotalcite exhibits no catalytic activity, yet the catalytic performance of the CZA-HT catalysts were clearly facilitated by CO2 adsorption on HT. The sample containing 40 wt% hydrotalcite and 60 wt% CZA showed the highest methanol selectivity of 73.4% and a methanol yield of 4.4% among all samples. The reaction was conducted at a low reaction pressure of 30 bar (much lower than conventional pressure), so that the methanol yield was not high. However, it is observed that the methanol formation rate based on a unit mass of active CZA always increases as the hydrotalcite content in CZA-HT increases, confirming the promotion effects of CO2 adsorption on HT on catalytic performance. The mechanism of adsorption enhanced catalytic reaction was also analysed and discussed, in which the well mixed finer particles of CZA and HT perform better than CZA alone with a 73.9% higher methanol yield.

Effect of Reaction Pressures on Structure–Performance of Co2C-Based Catalyst for Syngas Conversion

The effect of reaction pressures on structure–performance of Co2C-based catalyst for syngas conversion was studied in detail. Co2C nanoprisms with exposed facets of (101) and (020) used for the dissociation adsorption of CO molecules were stable at low reaction pressure, and promising FTO (Fischer–Tropsch to olefins) performance with low CH4 selectivity and high C2–4= selectivity simultaneously was achieved. With the increase of reaction pressure, the oxygenates selectivity significantly increased at the expense of decreasing C2–4= selectivity. The characterization results indicated that the morphology of Co2C nanostructures changed from nanoprisms to nanospheres and that the metallic Co0 was observed with the increase of reaction pressures. The appearance of Co2C(111) benefited CO insertion, and the formation of Co/Co2C(111) as dual active sites contributed to the enhancement of oxygenates selectivity at elevated pressure. This study suggested that reaction pressures had a strong effect on structure–perf...

Selective hydrogenolysis of glycerol to 1,3-propanediol over Pt-WOx/SAPO-34 catalysts

Selective catalytic hydrogenolysis of glycerol to 1,3-PDO is cost-effective for both production of the 1,3-PDO with an increasing industrial demand and valorization of the glycerol derived from biodiesel production, and both acid and metal are thought necessary for the catalysts for the reaction that proceeds by a dehydration-hydrogenation mode. Acidic mesoporous SAPO-34 was synthesized by a hydrothermal method and used to load Pt and WOx. The prepared Pt/SAPO-34 catalyst was active for glycerol hydrogenolysis due to its surface acidity and textural properties except for a low selectivity to 1,3-PDO. The WOx introduced on Pt/SAPO-34 markedly promoted glycerol conversion and the selectivity to 1,3-PDO. The content of WOx was found vital for the reaction, and the optimized catalytic performances were realized on the Pt-WOx/SAPO-34 catalyst with 20% WOx. The optimized content of WOx in the Pt-WOx/SAPO-34 catalyst was confirmed as non-stoichiometric and highly dispersed polymerized tungsten oxide species, and strongly interacted with the metallic platinum loaded. Accordingly, the metallic platinum was well dispersed on the WOx/SAPO-34. Moreover, the decoration of WOx enhanced the strength of surface acidity of the Pt/SAPO-34 catalysts in term of weak and moderate acid. Moreover, long reaction time, low reaction temperature and high reaction pressure facilitated the selective production of the desired 1,3-PDO from glycerol.

Insights into the reaction pathway of hydrodeoxygenation of dibenzofuran over MgO supported noble-metals catalysts

Conversion of oxygen-containing compounds derived from lignin arises wide interest due to fossil-derived resources consumption and growing environmental concerns. In this work, hydrodeoxygenation (HDO) of dibenzofuran (DBF) was studied over high-surface-area MgO supported Pt, Pd and Ru catalysts at 370 °C and 1.0 MPa. It was determined that the active metals not only affect the catalytic activity, but also change the reaction pathway of HDO of DBF. The intrinsic activity (TOF) of MgO supported catalysts follows the trend: Pt/MgO (0.36 s−1) > Ru/MgO (0.29 s−1) > Pd/MgO (0.09 s−1), companied by the increasing activate barrier. Pt has a high activity in the hydrogenation of DBF, and exhibits a perfect deoxygenation activity followed by hydrogenation (HYD) pathway. Ru shows better cleavage ability of CaromaticO bond and the removal of oxygen from DBF mainly occurs via direct deoxygenation (DDO) pathway. The increased Pt loadings largely promote the conversion of DBF by enhancing both HYD and DDO pathways. In addition, more direct cleavage of CaromaticO bond occurs at higher temperature and the production of aromatics by the DDO pathway prefers the relatively low reaction pressure. Based on the pseudo-first-order kinetics, the analysis of the fitted reaction rate constant shows that the DDO selectivity follows the order: Ru/MgO > Pd/MgO > Pt/MgO, which depends on the capacity of active metals to the cleavage of CaromaticO bond and the hydrogenation of aromatic ring.

Study on the thermal liquefaction of Xilinguole lignite in solvent at high temperature

In this paper, thermal liquefaction (TL) of Xilinguole lignite (XL) in the range of 400–540 °C have been carried out in toluene, tetralin (THN) and their mixed solvent, respectively. Results indicated that the conversion of XL primarily depends on the hydrogen donor ability of solvent. The highest conversions of XL in toluene and THN were obtained at 480 °C, which are 25.8% and 98.6%, respectively. The condensation of pyrolytic free radicals dominates the TL in toluene solvent but there is hardly obvious coking occurred in THN at below 510 °C. In toluene and THN mixed solvent, the conversion of XL increases with the THN content. The products of TL in toluene mainly consist of oil and gas (O + G) fraction, but the asphaltene (AS) and preasphaltene (PA) factions prevail in the products of TL in THN. Hydrogen donor solvent has obvious improvement on the deoxygenation in the TL process. Therefore, TL in hydrogen donor solvent is a potential conversion technology of XL due to low reaction pressure and without H2 and catalyst used.

Hydrogen Utilization in Green Fuel Synthesis via CO2 Conversion to Methanol over New Cu-Based Catalysts

The use of hydrogen as an energy vector and raw material for “very clean liquid fuels” manufacturing has been assessed by the catalytic conversion of CO2 to methanol over copper based catalysts. A systematic evaluation of copper based catalysts, prepared varying the chemical composition, has been carried out at 0.1–5.0 MPa of total pressure and in the range of 453–513 K by using a semi-automated LAB-microplant, under CO2/H2 reactant mixture (1/3), fed at GHSV of 8.8 NL∙kgcat−1∙h−1. Material’s properties have been investigated by the means of chemical-physical studies. The findings disclose that the addition of structure promoters (i.e., ZrO2/CeO2) strongly improves the textural properties of catalysts, in term of total surface area and exposure of metal surface area (MSA), also reducing the sintering phenomena. The results of the catalytic study clearly prove a structure-activity relationship at low reaction pressure (0.1 MPa), while at higher pressure (3.0–5.0 MPa) the reaction path is insensitive to structure and chemical composition.

Hydrodeoxygenation and hydroisomerization of palmitic acid over bi-functional Co/H-ZSM-22 catalysts

Hydrodeoxygenation and hydroisomerization of palmitic acid were achieved over bi-functional Co/H-ZSM-22 catalysts (about 4wt% Co loading), and the maximum of isoproducts reached up to 73.4% selectivity at 260°C for 4h in presence of 2MPa H2. Compared to parent H-ZSM-22, the impregnation of Co species for bi-functional catalysts could catalyze completely palmitic acid conversion into 100% selectivity of alkanes in spite of low pressure (1MPa H2). Furthermore, bi-functional Co/H-ZSM-22 catalysts tailored the deoxygenation route via hydrodeoxygenation leading to more C16 formation. With decreasing of reaction pressure, mole ratio of C16/C15 decreased during complete conversion of palmitic acid, indicating that low reaction pressure favored hydrodecarbonylation to produce more C15. Bi-functional Co/H-ZSM-22 catalysts also exhibited great stability after five runs without any deactivation.

Reductive carbonylation of methanol for ethanol production in Rh-Ru-dppp-methyl iodide catalytic system under mild conditions – The effect of lithium salts and catalyst composition

Reductive carbonylation of methanol is a potential process for ethanol production, but the reaction temperature is always higher than 190°C and reaction pressure higher than 19MPa. Due to the corrosions of the catalytic system, the reaction conditions, especially the pressure limited commercial applications of this process. The catalytic system consists of rhodium, ruthenium, dppp and methyl iodide, and was investigated for reductive carbonylation of methanol to ethanol under 6.0MPa at 120°C, and it exhibited an attractive catalytic activity. By comparing the products selectivity and the turnover frequency (TOF) of the catalytic systems, the role of each component in the catalytic system has been investigated. Rhodium catalyst was found to catalyze methanol reductive carbonylation for acetaldehyde formation, and ruthenium catalyst was responsible to catalyze hydrogenation of acetaldehyde to ethanol. The dppp can coordinate to rhodium and form a molecule rhodium active species, which enhanced the stability and solubility of the rhodium catalyst under the relatively low reaction pressure. The methyl iodide can promote the split of a carbon‑oxygen bond of methanol, thus accelerate the reaction process even at 120°C. The synergy effects of these catalyst compositions give rise to the ethanol formation under the relatively mild condition. Additionally, reaction conditions, catalytic system proportional and presence of lithium salts were combined to tune the TOF and ethanol production. Properly increasing initial methyl iodide addition, dppp/Rh mole ratio, H2/CO mole ratio, reaction temperature and pressure can accelerate the TOF. Raising Ru/Rh ratio and reaction temperature were in favor of acetaldehyde hydrogenation to ethanol. High H2/CO and dppp/Rh ratio can suppress the acetic acid formation. This work could provide a deeper understanding for further optimization to enhanced ethanol production.

Soldering of Iron Catalysts for Direct Synthesis of Light Olefins from Syngas under Mild Reaction Conditions

High-temperature Fischer–Tropsch synthesis represents a sustainable alternative for direct light olefin synthesis from syngas derived from fossil and renewable feedstocks. It is found that the promotion of iron catalysts with metals used for soldering (Bi and Pb) results in a remarkable increase in the light olefin production rate with a possibility to conduct Fischer–Tropsch synthesis at low reaction pressure. A combination of characterization techniques uncovered notable migration of the promoting elements during the reaction and decoration of iron carbide nanoparticles with the promoters. The promoters seem to facilitate CO dissociation by removing O atoms from iron carbide.