Rh promoted and ZrO2/Al2O3 supported Ni/Co based catalysts: High activity for CO2 reforming,steam–CO2 reforming and oxy–CO2 reforming of CH4

Ni (2.5 wt%) and Co (2.5 wt%) supported over ZrO₂/Al₂O₃ were prepared by following a hydrolytic co-precipitation method. The synthesized catalysts were further promoted by Rh incorporation (0.01–1.00 wt%) and tested for their catalytic performance for dry CO₂ reforming, combined steam–CO₂ reforming and oxy–CO₂ reforming of methane for production of syngas. The catalysts were characterized by using N₂ physical adsorption, XRD, H₂–TPR, SEM, CO₂–TPD, NH₃–TPD, TEM and TGA. The results revealed that ZrO₂ phase was in crystalline form in the catalysts along with amorphous Al oxides. Ni and Co were confirmed to be in their respective spinel phases that were reducible to metallic form at 800 °C under H₂. Ni and Co were well dispersed with their nano-crystalline nature. The catalyst with 0.2% loading of Rh showed superior performance in the studied reactions for reforming of methane. This catalyst also showed good coke resistance ability for dry CO₂ reforming reaction with 3.8 wt% of carbon formation during the reaction as compared to 11.6 wt% carbon formation over the catalyst without Rh. The catalyst performance was stable throughout the reaction time for CH₄ conversions, irrespective of carbon formation with slight decline (～1%) in CO₂ conversion. For dry CO₂ reforming reaction, this catalyst showed good conversion for both CH₄ and CO₂ (67.6% and 71.8% respectively) with a H₂/CO ratio of 0.84, while for the Oxy-CO₂ reforming reaction, the activity was superior with CH₄ and CO₂ conversions (73.7% and 83.8% respectively) and H₂/CO ratio of 1.05.     

Pt-Sn/γ-Al2O3 and Pt-Sn-Na/γ-Al2O3 catalysts for hydrogen production by dehydrogenation of Jet A-1 fuel: Characterisation and preliminary activity tests

The partial dehydrogenation of fuels like diesel or kerosene cuts to produce H₂ is an emerging idea of increasing interest. In the present work the study of the partial dehydrogenation of Jet A-1 fuel on Pt-Sn/γ-Al₂O₃ based catalysts to produce H₂ to feed an on-board (aircraft) proton exchange membrane fuel cell is presented. Extensive physico-chemical characterization of 5% wt.Pt-1% wt.Sn/γ-Al₂O₃ and 5%wt.Pt-1%wt.Sn-1%wt.Na/γ-Al₂O₃ pelleted materials has been performed. A gradient of the active metals from the edge to the centre of the pellet has been observed. A higher concentration of Pt⁰ has been detected on the outer part of the pellet than in the inner part, whereas Sn has been detected only on the external part of the pellet. The investigated materials are active as catalysts for the partial dehydrogenation of normal and desulfurised Jet A-1 kerosene fuel. The presence of sulfur compounds and coke deposition strongly affects the H₂ productivity which decreases rapidly with time on stream. The presence of a Na cation addition contributes to give the highest and most sustained H₂ production. The condensed outlet liquid stream retains the fuel properties in the range of the Jet A-1 kerosene fuel. These are encouraging preliminary results, inviting further research; coking and sulfur poisoning as well as identification of appropriate reaction conditions are the main challenges to be overcome in the immediate future.     

Catalytic activity and characterizations of Ni/K2TixOy–Al2O3 catalyst for steam methane reforming

Nickel catalysts supported on the K₂Ti_xO_y–Al₂O₃ were prepared by the wet impregnation method for steam methane reforming to produce hydrogen. X-ray diffraction, N₂ physisorption, scanning electron microscopy with energy dispersive spectroscopy, the H₂ temperature-programed reduction technique, and X-ray photoelectron spectroscopy were employed for the characterization of catalyst samples. The results revealed that the performance of the Ni/K₂Ti_xO_y–Al₂O₃ catalysts was comparable to that of commercial FCR-4 for steam methane reforming under the mild condition. In particular, a catalytic stability test at 800 °C and in the reactant flow with the steam-to-carbon (S/C) feed ratio of 1.0 indicated that the Ni/K₂Ti_xO_y–Al₂O₃ catalysts were more active, thermally stable and resistant to deactivation than the non-promoted Ni/Al₂O₃. It is considered that the appropriate interaction strength between nickel and the modified support and proper K₂Ti_xO_y phases with a surface monolayer coverage achieved at ca. 15 wt.% loading in the support play important roles in promoting the steam methane reforming activity as well as suppressing the sintering of the catalyst.     

Enhanced low-temperature activity for CO2 methanation over Ru doped the Ni/CexZr(1−x)O2 catalysts prepared by one-pot hydrolysis method

A series of 30 wt%Ni/Ce_xZr_1?xO₂ catalysts doped with Ru ranging from 0 to 5 wt% were prepared by one-pot hydrolysis of metal nitrates with ammonium carbonate for carbon dioxide methanation at low temperature range of 150–310 °C. The influences of Ce/Zr molar ratios and Ru contents on the physicochemical properties and catalytic activities of prepared catalysts were systematically investigated. The addition Ru can improve the Ni dispersion and the basicity of the yRu-30Ni/Ce_0.9Zr_0.1O₂ catalysts surface. As a result, their low-temperature catalytic activity had been enhanced over these doped Ru promoted catalysts. The optimal catalyst was 3Ru-30Ni/Ce_0.9Zr_0.1O₂ on which the CO₂ conversion reached theoretical equilibrium value as high as 98.2% with the methane selectivity of 100% at a reaction temperature as low as 230 °C. Moreover, there was almost no deactivation for the 3Ru-30Ni/Ce_0.9Zr_0.1O₂ catalyst during 300 h at 230 °C indicating excellent catalytic stability and coke resistence ability. It was also found that the low-temperature activity of 3Ru-30Ni/Ce_0.9Z_r0.1O₂ catalyst prepared by one-pot hydrolysis method was much higher than the one prepared by impregnation method.     

Characterization and activity test of commercial Ni/Al2O3, Cu/ZnO/Al2O3 and prepared Ni–Cu/Al2O3 catalysts for hydrogen production from methane and methanol fuels

In this study, methane and methanol steam reforming reactions over commercial Ni/Al₂O₃, commercial Cu/ZnO/Al₂O₃ and prepared Ni–Cu/Al₂O₃ catalysts were investigated. Methane and methanol steam reforming reactions catalysts were characterized using various techniques. The results of characterization showed that Cu particles increase the active particle size of Ni (19.3 nm) in Ni–Cu/Al₂O₃ catalyst with respect to the commercial Ni/Al₂O₃ (17.9). On the other hand, Ni improves Cu dispersion in the same catalyst (1.74%) in comparison with commercial Cu/ZnO/Al₂O₃ (0.21%). A comprehensive comparison between these two fuels is established in terms of reaction conditions, fuel conversion, H₂ selectivity, CO₂ and CO selectivity. The prepared catalyst showed low selectivity for CO in both fuels and it was more selective to H₂, with H₂ selectivities of 99% in methane and 89% in methanol reforming reactions. A significant objective is to develop catalysts which can operate at lower temperatures and resist deactivation. Methanol steam reforming is carried out at a much lower temperature than methane steam reforming in prepared and commercial catalyst (275–325 °C). However, methane steam reforming can be carried out at a relatively low temperature on Ni–Cu catalyst (600–650 °C) and at higher temperature in commercial methane reforming catalyst (700–800 °C). Commercial Ni/Al₂O₃ catalyst resulted in high coke formation (28.3% loss in mass) compared to prepared Ni–Cu/Al₂O₃ (8.9%) and commercial Cu/ZnO/Al₂O₃ catalysts (3.5%).     

Al–Li3AlH6: A novel composite with high activity for hydrogen generation

A novel material for hydrogen generation with high capacity of H₂ generation has been successfully prepared by ball milling the mixture of Al and home-made fresh Li₃AlH₆ powder. Its theoretical capacity of hydrogen released is higher than that of pure Al. Results obtained have shown conversion efficiency of Al–Li₃AlH₆ composite can be close to 100% by increasing the content of Li₃AlH₆. When the content of Li₃AlH₆ is 20 wt%, the maximum hydrogen generation rate and hydrogen yield are 2737.6 mL g⁻¹ min⁻¹ and 1513.1 mL g⁻¹, respectively, at room temperature. By XRD, SEM analyses and reaction heat measurements, it demonstrates that the additive Li₃AlH₆ can provide an additional source of H₂ and an alkaline environment (LiOH) as well as additional heat to promote the Al/H₂O reaction. Therefore, the Al–Li₃AlH₆ composite has a very high activity and high capacity of hydrogen released.     

Effect and behavior of cerium oxide in Ni/γ-Al2O3 catalysts on autothermal reforming of methane: CeAlO3 formation and its role on activity

Nickel supported γ-alumina (Ni/γ-Al₂O₃) catalysts are well-known to be highly active on the autothermal reforming of methane, but to be unstable due to coke deposition. Cerium oxide (CeO₂) is one of promising promoter to overcome the fast deactivation of nickel-based catalysts by coke formation. Herein, catalytic behavior of CeO₂ over Ni/γ-Al₂O₃ catalysts on the autothermal reforming of methane was investigated. The catalytic activity was maintained for 100 h with H₂/CO molar ratio of 1.9. The formation of CeAlO₃ is observed at the reduction and reaction conditions. In this work, it was found that the formation of CeAlO₃ promoted the catalytic oxidation toward CO₂ and prevented the formation of α-Al₂O₃ and nickel-aluminate, resulting in stable activity for autothermal reforming of methane.     

Catalytic activity and sulfur tolerance for Mn-substituted La0.75Sr0.25CrO3±δ in gas containing H2S

Lanthanum chromites substituted by transition metal are potentially applied as anode catalysts in solid oxide fuel cell fed with fuel gas containing H₂S. In order to understand the effect of composition on catalytic activity and sulfur tolerance of anode catalysts, La_0.75Sr_0.25Cr_1−xMn_xO_3±δ (noted as LSCM, x = 0.2, 0.5, 0.8) series were synthesized and characterized by XRD, XPS and H₂-TPR. The results demonstrate that LSCM55 with moderate Mn-substitution content has the highest activity for H₂S, which is attributed to considerable reducibility of Mn⁴⁺ determined by H₂-TPR. XRD patterns reveal that as-synthesized samples with different Mn-substitution contents have different sulfur tolerance. Sr 3d_5/2, Cr 2p_3/2, Mn 2p_3/2 regions of XPS for samples with different Mn-substitution contents imply that dominance of Mn⁴⁺, responsible for the catalytic activity, is the consequence of the interactions between cations at A-site and B-site. On the other hand, evolution of Mn in H₂S atmosphere indicates Mn³⁺ in Mn⁴⁺-O-Mn³⁺ clusters contributes greatly to the sulfur tolerance of LSCM. By analyzing consistency in the contents of lattice oxygen, S species (mainly sulfate) and Mn³⁺, a hypothetical mechanism of LSCM catalysts involving catalysis and sulfur tolerance was proposed.     

Adiabatic burning velocity of H2–O2 mixtures diluted with CO2/N2/Ar

Global warming due to CO₂ emissions has led to the projection of hydrogen as an important fuel for future. A lot of research has been going on to design combustion appliances for hydrogen as fuel. This has necessitated fundamental research on combustion characteristics of hydrogen fuel. In this work, a combination of experiments and computational simulations was employed to study the effects of diluents (CO₂, N₂, and Ar) on the laminar burning velocity of premixed hydrogen/oxygen flames using the heat flux method. The experiments were conducted to measure laminar burning velocity for a range of equivalence ratios at atmospheric pressure and temperature (300 K) with reactant mixtures containing varying concentrations of CO₂, N₂, and Ar as diluents. Measured burning velocities were compared with computed results obtained from one-dimensional laminar premixed flame code PREMIX with detailed chemical kinetics and good agreement was obtained. The effectiveness of diluents in reduction of laminar burning velocity for a given diluent concentration is in the increasing order of argon, nitrogen, carbon dioxide. This may be due to increased capabilities either to quench the reaction zone by increased specific heat or due to reduced transport rates. The lean and stoichiometric H₂/O₂/CO₂ flames with 65% CO₂ dilution exhibited cellular flame structures. Detailed three-dimensional simulation was performed to understand lean H₂/O₂/CO₂ cellular flame structure and cell count from computed flame matched well with the experimental cellular flame.     

Methane dry reforming on Ni/Ce0.75Zr0.25O2–MgAl2O4 and Ni/Ce0.75Zr0.25O2–γ-alumina: Effects of support composition and water addition

Nickel catalysts (10wt.%) supported on MgAl₂O₄ and γ-Al₂O₃ were prepared by the wet impregnation method and promoted with various contents of Ce_0.75Zr_0.25O₂. X-ray diffraction (XRD), BET surface area, scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), H₂-temperature programmed reduction (TPR) and CO₂-temperature programmed desorption (TPD) were employed to observe the characteristics of the prepared catalysts. Ni/γ-Al₂O₃ and Ni/Ce_0.75Zr_0.25O₂ (5wt.%)–MgAl₂O₄ showed better activity in CO₂ methane reforming with 75.7(0.93) and 75.4(0.82) CH₄ conversions (and H₂/CO ratio). H₂O was added to feed in the range of H₂O/(CH₄ + CO₂): 0.1–0.5 to suppress reverse water gas shift (RWGS) effect and adjusting H₂/CO ratio. The CH₄ conversions (and H₂/CO) increased to 81(1.1) with 0.5 water/carbon mole ratio in Ni/γ-Al₂O₃ and 85(1.2) with 0.2 water/carbon mole ratio in Ni/Ce_0.75Zr_0.25O₂ (5wt.%)–MgAl₂O₄. The stability of Ni/Ce_0.75Zr_0.25O₂ (5wt.%)–MgAl₂O₄ in the presence and absence of water was investigated. Coke formation and amount in used catalysts were examined by SEM and TGA, respectively. The results showed that the amount of carbon was suppressed and negligible coke formation (less than 3%) was observed in the presence of 0.2 water/carbon mole ratio over Ni/Ce_0.75Zr_0.25O₂ (5wt.%)–MgAl₂O₄ catalyst.     

O2/CO2和O2/N2氛围下煤粉富氧燃烧数值模拟

在目前煤炭依然作为能源主体的背景下，控制燃煤污染物排放有着重要意义。基于CFD数值模拟，建立伴流燃烧器模型，控制燃料、氧化剂入口流量恒定，设计了O₂/CO₂、O₂/N₂氧化剂氛围中O₂浓度在21%～40%内的多种工况，对煤粉燃烧特性及燃烧产生的污染物进行了研究。分析了不同工况下煤粉燃烧的温度分布、燃烧速率、碳烟、NO_x的生成情况。结果显示，在O₂/CO₂、O₂/N₂两种氧化剂氛围中，随着O₂浓度的上升，煤粉燃烧温度升高、燃烧速率增大，碳烟生成量均增加，同等O2浓度条件下，O₂/CO₂氛围的煤粉燃烧温度和燃烧速率均高于O₂/N₂氛围，碳烟生成量小于O₂/N₂氛围，且O₂/CO₂...     

Oxidative steam reforming of ethanol over Ni/Al2O3 catalysts promoted by CeO2, ZrO2 and CeO2–ZrO2

Oxidative steam reforming of ethanol at low oxygen to ethanol ratios was investigated over nickel catalysts on Al₂O₃ supports that were either unpromoted or promoted with CeO₂, ZrO₂ and CeO₂–ZrO₂. The promoted catalysts showed greater activity and a higher hydrogen yield than the unpromoted catalyst. The characterization of the Ni-based catalysts promoted with CeO₂ and/or ZrO₂ showed that the variations induced in the Al₂O₃ by the addition of CeO₂ and/or ZrO₂ alter the catalyst's properties by enhancing Ni dispersion and reducing Ni particle size. The promoters, especially CeO₂–ZrO₂, improved catalytic activity by increasing the H₂ yield and the CO₂/CO and the H₂/CO values while decreasing coke formation. This results from the addition of ZrO₂ into CeO₂. This promoter highlights the advantages of oxygen storage capacity and of mobile oxygen vacancies that increase the number of surface oxygen species. The addition of oxygen facilitates the reaction by regenerating the surface oxygenation of the promoters and by oxidizing surface carbon species and carbon-containing products.     

Synthesis and characterization of composite visible light active photocatalysts MoS2–g-C3N4 with enhanced hydrogen evolution activity

Molybdenum disulfide (MoS₂) and graphitic carbon nitride (g-C₃N₄) composite photocatalysts were prepared via a facile impregnation method. The physical and photophysical properties of the MoS₂–g-C₃N₄ composite photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microcopy (HRTEM), ultraviolet–visible diffuse reflection spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. The photoelectrochemical (PEC) measurements were tested via several on–off cycles under visible light irradiation. The photocatalytic hydrogen evolution experiments indicate that the MoS₂ co-catalysts can efficiently promote the separation of photogenerated charge carriers in g-C₃N₄, and consequently enhance the H₂ evolution activity. The 0.5wt% MoS₂–g-C₃N₄ sample shows the highest catalytic activity, and the corresponding H₂ evolution rate is 23.10 μmol h⁻¹, which is enhanced by 11.3 times compared to the unmodified g-C₃N₄. A possible photocatalytic mechanism of MoS₂ co-catalysts on the improvement of visible light photocatalytic performance of g-C₃N₄ is proposed and supported by PL and PEC results.     

Li2CO3/Na2CO3/K2CO3及其混合熔融盐储热材料热物性分子动力学研究

对Li₂CO₃/Na₂CO₃/K₂CO₃及其二元和三元混合熔融盐的密度、比热容、黏度、热导率进行分子动力学模拟(MD),对比得出模拟结果与现有的实验数据和模拟值相近。结果表明：随着温度的升高,密度逐渐减小,离子之间的距离增加,导致对剪切应力的抵抗力变小,这说明单组分、二元和三元熔融盐黏度的负温度依赖性。对于熔融盐的热导率,单组分和二元熔融盐也呈现出负温度依赖性,而三元熔融盐趋势是随温度的升高呈上升状态。     

Syngas production from CH4 dry reforming over Co–Ni/Al2O3 catalyst: Coupled reaction-deactivation kinetic analysis and the effect of O2 co-feeding on H2:CO ratio

The dry and oxidative dry reforming of CH₄ over alumina-supported Co–Ni catalysts were investigated over 72-h longevity experiments. The deactivation behaviour at low CO₂:CH₄ ratio (≤2) suggests that carbon deposition proceeds via a rapid dehydropolymerisation step resulting in the blockage of active sites and loss in CO₂ consumption. In particular, at high temperatures of 923 K and 973 K, a ‘breakthrough’ point was observed in which deactivation that was previously slow suddenly accelerated, indicating rapid polymerisation of deposited carbon. Only with feed CO₂:CH₄ > 2 or with O₂ co-feeding was coke-induced deactivation eliminated. In particular, O₂ co-feeding gave improved carbon removal, product H₂:CO ratios more suitable for downstream GTL processing and stable catalytic performance. Conversion-time data were adequately fitted to the generalised Levenspiel reaction-deactivation model. Activation energy estimate (66–129 kJ mol⁻¹) was dependent on the CO₂:CH₄ ratio but representative of other hydrocarbon reforming reactions on Ni-based catalysts.     

Hydrogen production through methanol steam reforming: Effect of synthesis parameters on Ni–Cu/CaO–SiO2 catalysts activity

The objectives of this study were to prepare Ni–Cu/CaO–SiO₂ catalysts by a modified polyol process with different preparation conditions and evaluate the feasibility of hydrogen production from methanol steam reforming. CaO–SiO₂ materials possess high specific surface areas and CO₂ absorption capacities which were synthesized through the sol–gel method to serve as supports. The experimental results of the methanol steam reforming indicated that the highest catalytic activity was achieved when the Ni–Cu/CaO–SiO₂ catalyst was prepared under Ar atmosphere at a reduction temperature of 160 °C (160-Ar). The 160-Ar catalyst synthesized by this method has a large pore volume and a high mesoporosity. These physical properties contribute to the effective dispersion of metal particles in the 160-Ar catalyst. Increasing the MeOH/H₂O ratio was found to promote the water–gas shift reaction and direct methanol decomposition to produce more H₂.     

O2/CO2/H2O气氛下CO燃烧机理的分子动力学模拟研究

采用反应分子动力学(ReaxFF MD)模拟方法研究了O₂/CO₂/H₂O气氛下CO的燃烧。结果表明：根据化学平衡原理,高浓度CO₂抑制CO的氧化,同时CO₂在高温下参与反应CO₂+H—→CO+OH,进一步抑制CO氧化。在较低温度条件下,较高浓度H₂O的三体效应显著,抑制了CO氧化。另一方面,在较高温度条件下,H₂O参与的H₂O+H—→H₂+OH和H₂O+O—→OH+OH反应占据其化学作用的主导地位,进而促进CO氧化。随着O₂浓度的增加,CO的氧化速度加快。