NiCe bimetallic nanoparticles embedded in hexagonal mesoporous silica (HMS) for reverse water gas shift reaction

Reverse water gas shift (RWGS) reaction is a crucial process in CO₂ utilization. Herein, Ni- and NiCe-containing hexagonal mesoporous silica (Ni-HMS and NiCe-HMS) catalysts were synthesized using an in-situ one-pot method and applied for RWGS reaction. At certain reaction temperatures 500-750 °C, Ni-HMS samples displayed a higher selectivity to the preferable CO than that of conventionally impregnated Ni/HMS catalyst. This could be originated from the smaller NiO nanoparticles over Ni-HMS catalyst. NiCe-HMS exhibited higher activity compared to Ni-HMS. The catalysts were characterized by means of TEM, XPS, XRD, H₂-TPR, CO₂-TPD, EPR and N₂ adsorption-desortion technology. It was found that introduction of Ce created high concentration of oxygen vacancies, served as the active site for activating CO₂. Also, this work analyzed the effect of the H₂/CO₂ molar ratio on the best NiCe-HMS. When reaction gas H₂/CO₂ molar ratio was 4 significantly decreased the selectivity to CO at low temperature, but triggered a higher CO₂ conversion which is close to the equilibrium.     

Efficient Ni-based catalysts for low-temperature reverse water-gas shift (RWGS) reaction

CO₂ hydrogenation for syngas can alleviate the pressure of un-controlled emissions of CO₂ and bring enormous economic benefits. Advantageous Ni-catalysts have good CO₂ hydrogenation activity and high CO selectivity merely over 700 °C. Herein, we introduced Cu into Ni catalysts, which were evaluated by H₂-TPR, XRD, BET, in-situ XPS and CO₂-TPD, and their CO₂ hydrogenation activity and CO selectivity were significantly affected by the Ni/Cu ratios, which was rationalized by the synergistic effect of bimetallic catalysts. In addition, the reduction temperatures of studied catalysts apparently affected the CO₂ hydrogenation, which were caused by the number and dispersion of the active species. It's found that the Ni₁Cu₁-400 had good stability, high CO selectivity (up to 90%), and fast formation rate (1.81×10⁻⁵ mol/g_cat/s) at 400 °C, which demonstrated a good potential as a superior catalyst for reverse water-gas shift (RWGS) reaction.     

Preparation,Characterization, and Catalytic Behavior of Nanostructured Mesoporous CuO/ZrO2 Catalysts for Low-Temperature CO Oxidation

High-surface area mesoporous 20 mol% CuO/ZrO₂ catalyst was prepared by a surfactant-assisted method of nanocrystalline particle assembly, and characterized by x-ray powder diffraction (XRD), N₂ adsorption, transmission electron microscopy (TEM), H₂-TPR, TG-DTA, and x-ray photoelectron spectra (XPS) techniques. The catalytic properties of the CuO/ZrO₂ nanocatalysts calcined at different temperature were evaluated by low-temperature carbon monoxide oxidation using a CATLAB system. The results showed that these mesoporous nanostructured CuO/ZrO₂ catalysts were very active for low-temperature CO oxidation and the CuO/ZrO₂ catalyst calcined at 400°C exhibited the highest catalytic activity.     

微量Li助剂对Co/AC催化剂合成高碳醇性能的影响

采用等体积浸渍法制备了含微量Li 的15Co_xLi/AC 催化剂,考察了微量Li 助剂对15Co/AC催化剂上CO加氢合成高碳醇性能的影响. 采用X射线衍射、程序升温还原和程序升温表面反应技术对15Co_xLi/AC 催化剂进行了表征,结果表明,微量Li 的添加可以提高催化剂上CO加氢活性、生成C₅₊烃的选择性、合成醇的选择性以及高碳醇的分布. 这主要是由于微量Li 助剂与Co物种形成了弱相互作用,促进了催化剂Co物种的分散,形成较小Co晶粒,促进了Co₂C的形成.     

Effect of A-site element on the performance of three-dimensionally ordered macroporous manganese-based perovskite catalyst

Three-dimensionally ordered macroporous manganese-based perovskite catalyst (3DOM AMnO₃, A = Ce, La, Ni) were synthesized by PMMA hard-templating and impregnation method. Physicochemical properties of the samples were characterized by means of various techniques including XRD, BET, SEM, TEM, XPS and H₂-TPR, and their catalytic activities were evaluated by toluene combustion. It was found that the 3DOM AMnO₃ in each of the samples was perovskite in crystal structure, and only the samples possessed a good quality 3DOM architecture with a surface area of 48.8 m²/g. Due to the highest adsorbed oxygen species concentration (O_ads/O_latt = 2.330), the best low-temperature reducibility (The low-temperature reduction peaks of 3DOM CeMnO₃ catalysts occur at 425 °C) and the strong interaction between CeO₂ and MnO_x formed during calcination. The 3DOM CeMnO₃ sample showed lower apparent activation energy (34.51 kJ·mol⁻¹, SV = 15,000 h⁻¹) and the best catalytic activity for toluene combustion, with the reaction temperatures (T50%, and T90%) required for achieving toluene conversions of 50%, and 90% being 100 °C, 172 °C at SV = 15,000 h⁻¹, respectively.     

Oscillations during partial oxidation of methane to synthesis gas over Ru/Al2O3 catalyst (Special column of methane transformation, Article)

Oscillations in temperatures of catalyst bed as well as concentrations of gas phase species at the exit of reactor were observed during the partial oxidation of methane to synthesis gas over Ru/Al₂O₃ in the temperature range of 600 to 850 °C. XRD, H₂-TPR and in situ Raman techniques was used to characterize the catalyst. Two types of ruthenium species, i.e. the ruthenium species weakly interacted with Al₂O₃ and that strongly interacted with the support, were identified by H₂-TPR experiment. These species are responsible for two types of oscillation profiles observed during the reaction. The oscillations were the result of these ruthenium species switching cyclically between the oxidized state and the reduced state under the reaction condition. These cyclic transformations, in turn, were the result of temperature variations caused by the varying levels of the strongly exothermic CH₄ combustion and the highly endothermic CH₄ reforming (with H₂O and CO₂) reactions (or the less exothermic direct partial oxidation of methane to CO and H₂), which were favored by the oxidized and the metallic sites, respectively. The major pathway of synthesis gas formation over the catalyst was via the combustion-reforming mechanism.     

Regeneration of C4H10 dry reforming catalyst by nonthermal plasma

Carbon deposition via coke formation is one of the critical problems causing catalyst deactivation during the reforming of hydrocarbons. An effort was made to regenerate the catalyst (Ni/γ-alumina) by oxidation methods. Two approaches were carried out for the regeneration of the deactivated catalyst. The first one involves the plasma treatment of the deactivated catalyst in the presence of dry air over a temperature range of 300～500 °C, while the second one only the thermal treatment in the same temperature range. The performance of the regenerated catalyst was evaluated in terms of C₄H₁₀ and CO₂ conversions and the physicochemical characteristics were examined using a surface area analyzer, an elemental analyzer, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was observed that the carbon deposit (coke) on the catalyst was about 9.89 wt% after reforming C₄H₁₀ for 5 h at 540 °C. The simple thermal treatment at 400 °C reduced carbon content to 6.59 wt% whereas it was decreased to 3.25 wt% by the plasma and heat combination. The specific surface area was fully restored to the original state by the plasma-assisted regeneration at 500 °C. As far as the catalytic activity is concerned, the fresh and regenerated catalysts exhibited similar C₄H₁₀ and CO₂ conversion efficiencies.     

Fe/Al-PILC催化C_3H_6选择性还原NO的实验研究

采用浸渍法制备了负载于铝柱撑黏土的铁基催化剂(Fe/Al-PILC),在固定床反应器上测试其催化C3H6选择性还原NO的性能。通过N2吸附-脱附、X射线衍射(XRD)、H2的程序升温还原(H2-TPR)、紫外可见光谱(Uv-vis)、吡啶吸附红外光谱(Py-FTIR)等手段对催化剂的物理化学性质进行表征。结果表明,9Fe/Al-PILC在400-550℃能够还原98%以上的NO,而且SO2和水蒸气对其催化性能的影响很小。XRD、N2吸附-脱附表征结果表明,Fe/Al-PILC催化剂中铁氧化物高度分散在载体表面,催化剂有较大的比表面积和孔容。H2-TPR结果表明,催化剂的活性主要由Fe_2O_3物相的还原性能决定。Uv-vis结果表明,催化剂的活性与铁氧低聚物种FexOy呈正相关性。Py-FTIR结果表明,催化剂表面同时存在Lewis酸和Brnsted酸,L酸性位是NO和C3H6反应的主要催化活性中心。     

稀土掺杂改性对Cu/ZnAl水滑石衍生催化剂甲醇水蒸气重整制氢性能的影响

采用原位合成法在γ-Al₂O₃表面合成了锌铝水滑石,再通过顺次浸渍法制备了一系列掺杂稀土改性的M（M=Y、La、Ce、Sm、Gd）/Cu/ZnAl催化材料,并将其应用于甲醇水蒸气重整制氢反应。探讨了稀土掺杂改性对Cu/ZnAl催化剂催化性能的影响,并采用XRD、SEM-EDS、BET、H₂-TPR、XPS和N₂O滴定等手段对催化剂进行了表征。结果表明,催化剂的活性与Cu比表面积和催化剂的还原性质密切相关,Cu比表面积越大,还原温度越低,催化活性越高。稀土Ce、Sm、Gd的引入能改善活性组分Cu的分散度、Cu比表面积以及催化剂的还原性质,进而提高催化剂的催化活性。其中,Ce/Cu/ZnAl催化剂表现出最佳的催化活性,在反应温度为250 ℃时,甲醇转化率达到100%,CO含量为0.39%,相比Cu/ZnAl催化剂,甲醇转化率提高了近40%。     

Hydrotalcite-derived Co-containing mixed metal oxide catalysts for methanol incineration

The Co–Mg–Al mixed metal oxides were prepared by calcination of co-precipitated hydrotalcite-like precursors at various temperatures (600–800 °C), characterised with respect to chemical (AAS) and phase (XRD) composition, textural parameters (BET), form and aggregation of cobalt species (UV–vis-DRS) and their redox properties (H₂-TPR, cyclic voltammetry). Moreover, the process of thermal decomposition of hydrotalcite-like materials to mixed metal oxide systems was studied by thermogravimetric method combined with the analysis of gaseous decomposition products by mass spectrometry. Calcined hydrotalcite-like materials were tested as catalysts for methanol incineration. Catalytic performance of the oxides depended on cobalt content, Mg/Al ratio and calcination temperature. The catalysts with lower cobalt content, higher Mg/Al ratio and calcined at lower temperatures (600 or 700 °C) were less effective in the process of methanol incineration. In a series of the studied catalysts, the best results, with respect to high catalytic activity and selectivity to CO₂, were obtained for the mixed oxide with Co:Mg:Al molar ratio of 10:57:33 calcined at 800 °C. High activity of this catalyst was likely connected with the presence of a Co–Mg–Al spinel-type phases, containing easy reducible Co³⁺ cations, formed during high-temperature treatment of the hydrotalcite-like precursor.     

Hydroformylation of vinylsilanes with Rh(acac)(CO)2/tris(N-pyrrolyl)phosphine catalytic system

Rh(acac)(CO)₂ as catalyst precursor with a small excess of free N-pyrrolylphosphine ([P(NC₄H₄)₃]:[Rh] = 3–10) was found to be very active in hydroformylation of vinyltrisubstituted silanes at 80 °C and 10 atm CO/H₂ = 1. After 2 h the yields of aldehydes were 80 % (n/iso = 8) for vinyltrimethylsilane, 100 % (only n-isomer) for vinyldimethylphenylsilane and 95 % (n/iso = 5.5) for vinyltrimethoxysilane. The rate of hydroformylation of vinyltrimethylsilane is ca. three times higher than that of other vinylsilanes. 3,3-Dimethyl-1-butene undergoes hydroformylation much slower than vinyltrimethylsilane probably because of its high steric hindrance and the reaction produces 4,4-dimethylpentanal as the only product.     

Syngas production from ethanol dry reforming over Rh/CeO2 catalyst

Carbon dioxide reforming of ethanol over Rh/CeO₂ catalyst was deeply investigated at different reaction temperatures of 450–700 °C and reactant ratios (CO₂/ethanol from 1 to 3) under atmospheric pressure. The obtained results indicated that Rh/CeO₂ catalyst presented a promising activity and stability for syngas production from renewable bio-ethanol instead of conventional methane. Typically, CO₂-rich conditions (CO₂/ethanol = 3) were favorable for reaction process and dynamic coke cleaning, which led to remarkably stable performance over 65 h on stream. The strong redox capacity of CeO₂ support might also accelerate CO₂ activation and prevent the carbon accumulation over the catalyst surface. Additionally, tunable H₂/CO ratios were available by changing the CO₂/ethanol ratios. The results from characterization of samples before and after catalytic tests allowed to establish the relationship between textural properties and catalytic performance.     

Novel Ni/CeO2-Al2O3 composite catalysts synthesized by one-step citric acid complex and their performance in catalytic partial oxidation of methane

A series of novel Ni/CeO2-Al2O3composite catalysts were synthesized by one-step citric acid complex method. The as-synthesized catalysts were characterized by N2physical adsorption/desorption, X-ray diffraction(XRD), Fourier transform infrared(FT-IR) spectroscopy, hydrogen temperature-programmed reduction(H2-TPR), X-ray photoelectron spectroscopy(XPS) and thermogravimetry analysis(TGA). The effects of nickel content, calcination and reaction temperatures, gas hourly space velocity(GHSV) and inert gas dilution of N2on their performance of catalytic partial oxidation of methane(CPOM) were investigated. Catalytic activity test results show that the highest methane conversion(85%), the best selectivities to carbon monoxide(87%) and to hydrogen(95%), the excellent stability and perfect H2/CO ratio(2.0) can be obtained over Ni/CeO2-Al2O3with 8 wt% Ni content calcined at 700 ℃ under the reaction condition of 750 ℃, CH4/O2ratio of 2 : 1 and gas hourly space velocity of 12000 mL h-1 g-1. Characterization results show that the good catalytic performance of this composite catalyst can be contributed to its large specific surface area(～108 m2 g-1), small crystallite size, easy reducibility and low coking rate.     

Biodiesel Preparation from Jatropha curcas Oil Catalyzed by Hydrotalcite Loaded With K2CO3

This paper discusses the synthesis of biodiesel catalyzed by solid base of K₂CO₃/HT using Jatropha curcas oil as feedstock. Mg–Al hydrotalcite was prepared using co-precipitation methods, in which the molar ratio of Mg to Al was 3:1. After calcined at 600 °C for 3 h, the Mg–Al hydrotalcite and K₂CO₃ were grinded and mixed according to certain mass ratios, in which some water was added. The mixture was dried at 65 °C, and after that it was calcined at 600 °C for 3 h. Then, this Mg–Al hydrotalcite loaded with potassium carbonate was obtained and used as catalyst in the experiments. Analyses of XRD and SEM characterizations for catalyst showed the metal oxides formed in the process of calcination brought about excellent catalysis effect. In order to achieve the optimal technical reaction condition, five impact factors were also investigated in the experiments, which were mass ratio, molar ratio, reaction temperature, catalyst amount and reaction time. Under the best condition, the biodiesel yield could reach up to 96%.     

Effect of Nano‐support and Type of Active Metal on Reforming of CH4 with CO2

Two series of Co and Ni based catalysts supported over commercial (ZrO₂, CeO₂, and Al₂O₃) nano supports were investigated for dry reforming of methane. The catalytic activity of both Co and Ni based catalysts were assessed at different reaction temperatures ranging from 500—800 °C; however, for stability the time on stream experiments were conducted at 700 °C for 6 h. Various techniques such as N₂ adsorption‐desorption isotherm, temperature‐programmed reduction (H₂‐TPR), temperature‐programmed desorption (CO₂‐TPD), temperature‐programmed oxidation (TPO), X‐ray diffraction (XRD), thermogravimetric analysis (TGA) were applied for characterization of fresh and spent catalysts. The catalytic activity and stability tests clearly showed that the performance of catalyst is strongly dependent on type of active metal and support. Furthermore, active metal particle size and Lewis basicity are key factors which have significant influence on catalytic performance. The results indicated that Ni supported over nano ZrO₂ exhibited highest activity among all tested catalysts due to its unique properties including thermal stability and reducibility. The minimum carbon deposition and thus relatively stable performance was observed in case of Co‐Al catalyst, since this catalyst has shown highest Lewis basicity.     

Catalytic oxidation of benzene at low temperature over novel combination of metal oxide based catalysts: CuO,MnO2, NiO with Ce0.75Zr0.25O2 as support

Mesoporous Ce_0.75Zr_0.25O₂ solid solution powders were successfully synthesized by a co-precipitation method. A combination of 10 wt% copper oxide, manganese oxide, and nickel oxide was added to the Ce_0.75Zr_0.25O₂ support by impregnation method and calcined in the air with a flow rate of 2 ml s^?1 at 400 °C for 4 h. All catalysts were characterized using Hydrogen Temperature Programmed Reduction (H₂-TPR), X-ray Diffraction (XRD), and Brunauer-Emmet-Teller (BET) isotherm methods to find the interaction between metals, the crystallinity of the catalyst, surface area and pore volume of the catalyst, respectively. The 3.3% CuO-3.3% MnO₂-3.3% NiO/Ce_0.75Zr_0.25O₂ catalyst showed higher catalytic activity for benzene oxidation with benzene conversion of 90% at 250 °C and weight hourly space velocity (72,000 mL g^?1 h^?1) when compared to one metal oxide only. This finding presents a high activity and low-cost catalysts for removing a very lean concentration of benzene containing in the industrial flue gas at low temperatures.     

Effects of Preparation Method on the Performance of Ni/Al2O3 Catalysts for Hydrogen Production by Bio-Oil Steam Reforming

Steam reforming of bio-oil derived from the fast pyrolysis of biomass is an economic and renewable process for hydrogen production. The main objective of the present work has been to investigate the effects of the preparation method of Ni/Al₂O₃ catalysts on their performance in hydrogen production by bio-oil steam reforming. The Ni/Al₂O₃ catalysts were prepared by impregnation, co-precipitation, and sol?Cgel methods. XRD, XPS, H₂-TPR, SEM, TEM, TG, and N₂ physisorption measurements were performed to characterize the texture and structure of the catalysts obtained after calcination and after their subsequent use. Ethanol and bio-oil model compound were selected for steam reforming to evaluate the catalyst performance. The catalyst prepared by the co-precipitation method was found to display better performance than the other two. Under the optimized reaction conditions, an ethanol conversion of 99% and a H₂ yield of 88% were obtained.     

Effect of Calcination Temperature on the Catalytic Oxidation of Formaldehyde Over Co<Subscript>3</Subscript>O<Subscript>4</Subscript>–CeO<Subscript>2</Subscript> Catalysts

The effect of calcination temperature (350–650?°C) on the structure and catalytic activity of Co₃O₄–CeO₂ mixed oxides prepared by sol–gel method was investigated by XRD, H₂-TPR, O₂-TPD and formaldehyde (HCHO) oxidation. The Co₃O₄–CeO₂ calcined at 450?°C (Co₃O₄–CeO₂-450) exhibited the best performance, showing that the complete oxidation of HCHO was achieved at temperature as low as 80?°C. The results of characterizations revealed that the Co₃O₄–CeO₂-450 had excellent catalytic activity due to the larger specific surface area, the best reducibility and more abundant surface active oxygen species.     

Effect of the support calcination temperature on selective hydrodesulfurization of TiO2 nanotubes supported CoMo catalysts

TiO₂ nanotubes (TiO₂-NTs) were synthesized by the hydrothermal method. Co and Mo active components were supported on a series of the as-prepared TiO₂-NTs samples which were calcined at different temperatures. The effects of support calcination temperature of CoMo/TiO₂-NTs catalysts on their catalytic performance were investigated for selective hydrodesulfurization (HDS). The samples were characterized by means of the scanning electron microscopy (SEM), the transmission electron microscopy (TEM), N₂ adsorption-desorption, X-ray diffraction (XRD), Raman spectroscopy and H₂ temperature-programmed reduction (H₂-TPR). The experimental results revealed that TiO₂-NTs support calcined under 500 °C can maintain the nanotubular structure with higher surface area and pore volume. Meanwhile, the obtained supported CoMo/TiO₂-NTs catalysts exhibited weak metal-support interaction, more octahedral Mo⁶⁺ species and high catalytic performance in selective HDS.     

The effect of copper content on the reactivity of Cu/Co6Al2 solids in the catalytic steam reforming of methane reaction

The steam reforming of methane over Cu/Co₆Al₂ mixed oxides with different copper contents was studied. The Co₆Al₂ support was prepared via the hydrotalcite route. It was thermally stabilized at 500 °C, impregnated with 5 wt.%, 15 wt.% or 25 wt.% copper using copper (II) nitrate Cu(NO₃)₂·3H₂O precursor and then calcined again at 500 °C under an air flow. The impregnation of copper enhanced significantly the reactivity of the solids in the considered reaction. The 5Cu/Co₆Al₂ solid was the most reactive one, with a methane conversion of 96% at 650 °C. The selectivities of H₂ and CO₂ were also better for the catalyst containing 5 wt.% copper compared to higher copper loadings. The decrease in the catalytic reactivity with increasing the copper content was attributed to the formation of agglomerated and less reactive CuO species, which were detected by XRD and TPR analyses.