不同载体Ni基负载型催化剂对甲烷部分氧化制合成气催化行为研究

采用浸渍法制备了单一载体(Al₂O₃、ZrO₂、CeO₂)和ZrO₂、CeO₂改性的Al₂O₃复合载体的Ni催化剂,考察了在甲烷部分氧化制备合成气反应中的催化性能。通过N₂-物理吸附、H₂程序升温还原、X射线衍射、NH₃程序升温脱附和程序升温氧化等技术对催化剂进行了表征。结果表明,在单一载体催化剂中,Ni/Al₂O₃具有较大的比表面积,其初始反应活性较高,但该催化剂表面易形成大量的积炭而快速失活。Ni/ZrO₂和Ni/CeO₂催化剂比表面积较小,活性金属Ni在其表面分散性差,催化剂具有较低的CH₄转化率。而CeO₂和ZrO₂改性的Al₂O₃复合载体催化剂,具有较大的比表面积,反应活性明显高于单一载体催化剂。CeO₂-Al₂O₃复合载体催化剂具有最高的反应活性和较好的反应稳定性。同时表明,含CeO₂催化剂反应后表面积炭较少,CeO₂的储放氧功能增强了催化剂对O₂的活化,提高催化剂活性的同时,可以抑制积炭的生成。     

Ni/Al2O3 catalysts for CO methanation: Effect of Al2O3 supports calcined at different temperatures

The correlation between phase structures and surface acidity of Al₂O₃ supports calcined at different temperatures and the catalytic performance of Ni/Al₂O₃ catalysts in the production of synthetic natural gas (SNG) via CO methanation was systematically investigated. A series of 10 wt% NiO/Al₂O₃ catalysts were prepared by the conventional impregnation method, and the phase structures and surface acidity of Al₂O₃ supports were adjusted by calcining the commercial γ-Al₂O₃ at different temperatures (600–1200 °C). CO methanation reaction was carried out in the temperature range of 300–600 °C at different weight hourly space velocities (WHSV = 30000 and 120000 mL·g^?1·h^?1) and pressures (0.1 and 3.0 MPa). It was found that high calcination temperature not only led to the growth in Ni particle size, but also weakened the interaction between Ni nanoparticles and Al₂O₃ supports due to the rapid decrease of the specific surface area and acidity of Al₂O₃ supports. Interestingly, Ni catalysts supported on Al₂O₃ calcined at 1200 °C (Ni/Al₂O₃-1200) exhibited the best catalytic activity for CO methanation under different reaction conditions. Lifetime reaction tests also indicated that Ni/Al₂O₃-1200 was the most active and stable catalyst compared with the other three catalysts, whose supports were calcined at lower temperatures (600, 800 and 1000 °C). These findings would therefore be helpful to develop Ni/Al₂O₃ methanation catalyst for SNG production.     

Catalytic Activity for Ammonia Synthesis of Iron Supported Catalysts Prepared from an Acid-modified λ-Al2O3 Method

Iron supported catalysts were prepared by impregnation of several acid-modified λ-Al₂O₃ samples with a K₄[Fe(CN)₆] aqueous solution. A concentration range between 0–20 mmole H⁺ added · g^?1λ-Al₂O₃ was used. The quantitative determination of the acid site and iron contents of the modified λ-Al₂O₃ samples was followed by UV spectrometry and F.A.A.S., respectively. An increasing final iron content of the catalysts with increasing acid site content of the support is observed. The catalytic activity for ammonia synthesis was followed at atmospheric pressure and 593 K (N₂/H₂ = 1/3). An increasing ammonia production per gram of catalyst with increasing protonation of the support was observed in the range 0–8 mmole H⁺ added · g^?1λ-Al₂O₃. The catalytic activity of iron supported catalysts prepared by this method was higher (up to twofold) that of a catalyst prepared by the incipient wetness method.     

Influence of support on resistance to carbon-deposition of catalyst for CH4, CO2 with O2 to synthesis gas

In the reaction of catalytic oxidation of CH₄, CO₂ with O₂ to synthesis gas, carbon-deposition is an important factor for deactivation. By adding different oxides to Ni/Al₂O₃ catalyst, its resistance to carbon-deposition was improved. The experimental results indicate that the order of resistance to carbon-deposition is as follows: Ni/CaO-Al₂O₃>Ni/MgO-Al₂O₃>Ni/ TiO₂-Al₂O₃ > Ni/CeO₂-Al₂O₃>Ni/La₂O₃-Al₂O₃>Ni/Y₂O₃-Al₂O₃>Ni/Fe₂O₃-Al₂O₃>Ni/Al₂O₃. The catalysts were characterized by CO₂-TPD, O₂-TPD and XPS methods. Here the relation between the order of resistance to carbon-deposition and performance of catalyst is discussed.     

CH4 reforming with CO2 for syngas production over La2O3 promoted Ni catalysts supported on mesoporous nanostructured γ-Al2O3

Nanostructured γ-Al₂O₃ with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, N₂ adsorption-desorption, TPR, TPO, TPH, NH₃-TPD and SEM techniques. The BET analysis showed a high surface area of 204 m²·g⁻¹ and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The BET results revealed that addition of lanthanum oxide to aluminum oxide decreased the specific surface area. In addition, TPR results showed that addition of lanthanum oxide increased the reducibility of nickel catalyst. The catalytic evaluation results showed an increase in methane conversion with increasing lanthanum oxide to 3 mol% and further increase in lanthanum content decreased the catalytic activity. TPO analysis revealed that the coke deposition decreased with increasing lanthanum oxide to 3 mol%. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Addition of steam and O₂ to dry reforming feed increased the methane conversion and led to carbon free operation in combined processes.     

Ni catalysts supported on nano-crystalline aluminum oxide prepared by a microemulsion method for dry reforming reaction

Mesoporous nano-crystalline γ-Al₂O₃ with high surface area prepared by a microemulsion (ME) method was employed as carrier for nickel catalysts in dry reforming of methane for syngas production. The structural properties of the catalysts were characterized by X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, temperature programmed reduction and oxidation and scanning electron microscopy techniques. Microemulsion showed it to be a promising way for the production of nano-crystalline aluminum oxide, and the nickel catalysts prepared with this support have significant features and properties to use in the dry reforming reaction. The results revealed that the prepared γ-Al₂O₃ exhibited a nano-crystalline structure (crystal size: c.4.8 nm) with a high specific surface area (308 m² g^?1). In addition, the catalysts with different nickel contents exhibited high catalytic activity in the dry reforming reaction. The results also showed that an increase in Ni loading from 5 to 15 wt% caused a decrease in the specific surface area and nickel dispersion.     

Catalytic Combustion of Methane over CeO2-MOx (M=La, Ca) Solid Solution Promoted Pd/γ-Al2O3 Catalysts

Solid solution CeO₂-MO_x (M=La³⁺, Ca²⁺) promoted Pd/γ-Al₂O₃ catalysts were prepared by a deposition-precipitation method. The structural properties were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The results showed that Mⁿ⁺ ions incorporated into CeO₂ lattice and solid solutions formed in Pd/γ-Al₂O₃-CeO₂-MO_x catalysts. The formation of solid solution was confirmed by the change in lattice parameters of CeO₂ and the shift of 2θ angles as compared with pure CeO₂. A strain formed in the O²⁻ sub-lattice of CeO₂ was revealed by Raman analyses, which decreased the intensity of the Raman-active band at around 463 cm⁻¹ owing to the F_2g symmetric stretching of Ce−O bond. The appearance of a new band at 615 cm⁻¹ (in the case of Pd/γ-Al₂O₃-CeO₂-CaO) and a shoulder at 320 cm⁻¹ (in the case of Pd/γ-Al₂O₃-CeO₂-La₂O₃) was also confirmed. Ionic Pd^δ+ species were formed in the catalysts, which exhibited higher binding energies (0.5−0.6 eV higher for Pd 3d_5/2) than that of normal PdO. The catalysts showed high activity and stability for low temperature methane combustion. 10% and 100% conversions of methane could be obtained at temperatures of 254 and 340 °C, respectively, over Pd/γ-Al₂O₃-CeO₂-La₂O₃ catalyst under an hourly space velocity of 50000 h⁻¹.     

Effect of Ni loadings on the activity and coke formation of MgO-modified Ni/Al2O3 nanocatalyst in dry reforming of methane

MgO-modified Ni/Al₂O₃ catalysts with different Ni loadings were prepared and employed in dry reforming of methane (DRM). The effect of Ni loadings on the activity and coke formation of Ni/MgO-Al₂O₃ catalysts were investigated. The synthesized catalysts were characterized by XRD, N₂ adsorption-desorption, SEM, TPO and TPR techniques. The obtained results showed that increasing nickel loading decreased the BET surface area and increased the catalytic activity and amount of deposited carbon. In addition, the effect of gas hourly space velocity (GHSV) and feed ratio were studied.     

Robust nickel silicate catalysts with high Ni loading for CO2 methanation

CO₂ is the main component of greenhouse gases and also an important carbon source. The hydrogenation of CO₂ to methane using Ni-based catalysts can not only alleviate CO₂ emissions but also obtain useful fuels. However, Ni-based catalysts face one major problem of the sintering of Ni nanoparticles in the process of CO₂ methanation. Thus, this work has synthesized a series of efficient and robust nickel silicate catalysts (NiPS−X) with different nickel content derived from nickel phyllosilicate by the hydrothermal method. It was found that the Ni loading plays a critical role in the structure and catalytic performance of the NiPS−X catalysts. The catalytic performance gradually increases with the increase of Ni loading. In particular, the highly dispersed NiPS-1.6 catalyst with a high Ni loading of 34.3 wt% could obtain the CO₂ conversion greater than 80%, and the methane selectivity was close to 100% for 48 h at 330 °C and the GHSV of 40,000 mL g⁻¹ h⁻¹. The excellent catalytic property can be assigned to the high dispersion of Ni nanoparticles and the strong interaction between the active component and the carrier, which is derived from a unique layered silicate structure with lots of nickel phyllosilicate and a large number of Lewis acid sites.     

Ni_2P/TiO_2-Al_2O_3催化剂的制备及其加氢脱硫、脱氮性能

采用溶胶-凝胶法制备了TiO2-Al2O3复合载体,采用浸渍法制备了Ni2P/TiO2-Al2O3催化剂,并用X射线衍射(XRD)、N2吸附比表面积(BET)测定、热重-差热分析(TG-DTA)、X射线光电子能谱(XPS)等技术对催化剂的结构和性质进行了表征.催化剂加氢脱硫(HDS)和脱氮(HDN)活性评价在实验室固定床连续反应装置上,以噻吩和吡啶为模型反应物进行.考察了不同载体、Ni2P负载量、标称Ni/P摩尔比、催化剂焙烧温度对Ni2P/TiO2-Al2O3催化剂上同时进行的噻吩加氢脱硫和吡啶加氢脱氮性能的影响.结果表明,TiO2含量为80%(w)的TiO2-Al2O3复合氧化物为载体,Ni2P负载量为30.0%(w),标称Ni/P摩尔比为1/2,催化剂焙烧温度为500℃时,Ni2P/TiO2-Al2O3催化剂加氢脱硫脱氮活性最高.在360℃,3.0MPa,氢油比800(V/V),液时体积空速1.5h-1的条件下,噻吩HDS和吡啶HDN转化率分别为61.32%和64.43%.     

Study of CuZnMOx oxides (M = Al,Zr, Ce,CeZr) for the catalytic hydrogenation of CO2 into methanol

CuO–ZnO–Al₂O₃ catalysts were synthesized by two methods, sol–gel and co-precipitation syntheses. Al₂O₃ was then substituted with other supports, such as ZrO₂, CeO₂ and CeO₂–ZrO₂ in order to have a better understanding of the support's effect. These catalysts containing 30 wt% of Cu were then tested for CO₂ hydrogenation into methanol. The effect of reaction temperature and GHSV on the catalytic behaviour was also investigated. The best results were obtained with a 30 CuO–ZnO–ZrO₂ catalyst synthesized by co-precipitation and calcined at 400 °C. This catalyst presents a good CO₂ conversion rate (23%) with 33% of methanol selectivity, leading to a methanol productivity of 331 g_MeOH.kg_cata⁻¹·h⁻¹ at 280 °C under 50 bar and a GHSV of 10,000 h⁻¹.     

Selective methanation of CO in the presence of CO<Subscript>2</Subscript> in hydrogen-containing mixtures on nickel catalysts

The screening of commercial nickel catalysts for methanation and a series of nickel catalysts supported on CeO₂, γ-Al₂O₃, and ZrO₂ in the reaction of selective CO methanation in the presence of CO₂ in hydrogen-containing mixtures (1.5 vol % CO, 20 vol % CO₂, 10 vol % H₂O, and the balance H₂) was performed at the flow rate WHSV = 26000 cm³ (g Cat)⁻¹ h⁻¹. It was found that commercial catalytic systems like NKM-2A and NKM-4A (NIAP-07-02) were insufficiently effective for the selective removal of CO to a level of <100 ppm. The most promising catalyst is 2 wt % Ni/CeO₂. This catalyst decreased the concentration of CO from 1.5 vol % to 100 ppm in the presence of 20 vol % CO₂ in the temperature range of 280–360°C at a selectivity of >40%, and it retained its activity even after contact with air. The minimum outlet CO concentration of 10 ppm at 80% selectivity on a 2 wt % Ni/CeO₂ catalyst was reached at a temperature of 300°C.     

CeO2-ZrO2-La2O3-Al2O3 composite oxide and its supported palladium catalyst for the treatment of exhaust of natural gas engined vehicles

Composite supports CeO2-ZrO2-Al2O3 (CZA) and CeO2-ZrO2-Al2O3-La2O3 (CZALa) were prepared by co-precipitation method. Palladium catalysts were prepared by impregnation and their purification ability for CH4, CO and NOx in the mixture gas simulated the exhaust from natural gas vehicles (NGVs) operated under stoichiometric condition was investigated. The effect of La2O3 on the physicochemical properties of supports and catalysts was characterized by various techniques. The characterizations with X-ray diffraction (XRD) and Raman spectroscopy revealed that the doping of La2O3 restrained effectively the sintering of crystallite particles, maintained the crystallite particles in nanoscale and stabilized the crystal phase after calcination at 1000 ℃. The results of N2-adsorption, H2-temperature-programmed reduction (H2-TPR) and oxygen storage capacity (OSC) measurements indicated that La2O3 improved the textural properties, reducibility and OSC of composite supports. Catalytic activity testing results showed that the catalysts exhibit excellent activities for the simultaneous removal of methane, CO and NOx in the simulated exhaust gas. The catalysts supported on CZALa showed remarkable thermal stability and catalytic activity for the three pollutants, especially for NOx. The prepared palladium catalysts have high ability to remove NOx, CH4 and CO, and they can be used as excellent catalysts for the purification of exhaust from NGVs operated under stoichiometric condition. They also have significant potential in industrial application because of their high performance and low cost.     

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.     

The effect of the nature of the support on catalytic properties of ruthenium supported catalysts in partial oxidation of methane to syn-gas

The effect of the carrier on catalytic properties of ruthenium supported catalysts in partial oxidation of methane (POM) was investigated. A variety of supports differed in texture and reducibility (Al₂O₃, SiO₂, TiO₂, Cr₂O₃, CeO₂ and Fe₂O₃) were used. The catalyst activity is governed by ruthenium phase formation (RuO₂ → Ru⁰), and it depends on redox properties of the support as well as support-ruthenium phase interaction. The activity of Ru supported catalysts decreases in the order Al₂O₃ ≈ SiO₂ > Cr₂O₃ > TiO₂ > CeO₂ > Fe₂O₃. No significant effects of the specific surface area and porosity of catalysts on the methane conversion and selectivity of CO formation were found. The selectivity of CO₂ formation (total oxidation of CH₄) under conditions of POM (a ratio of CH₄/O₂ = 2) is associated with the contribution of reducible support oxides into the catalytic performance.     

Methane-fueled SOFC with traditional nickel-based anode by applying Ni/Al2O3 as a dual-functional layer

Novel γ-Al₂O₃ supported nickel (Ni/Al₂O₃) catalyst was developed as a functional layer for Ni–ScSZ cermet anode operating on methane fuel. Catalytic tests demonstrated Ni/Al₂O₃ had high and comparable activity to Ru–CeO₂ and much higher activity than the Ni–ScSZ cermet anode for partial oxidation, steam and CO₂ reforming of methane to syngas between 750 and 850 °C. By adopting Ni/Al₂O₃ as a catalyst layer, the fuel cell demonstrated a peak power density of 382 mW cm^?2 at 850 °C, more than two times that without the catalyst layer. The Ni/Al₂O₃ also functioned as a diffusion barrier layer to reduce the methane concentration within the anode; consequently, the operation stability was also greatly improved without coke deposition.     

Efficient Imine Formation by Oxidative Coupling at Low Temperature Catalyzed by High-Surface-Area Mesoporous CeO2 with Exceptional Redox Property

High-surface-area mesoporous CeO₂ (hsmCeO₂) was prepared by a facile organic-template-induced homogeneous precipitation process and showed excellent catalytic activity in imine synthesis in the absence of base from primary alcohols and amines in air atmosphere at low temperature. For comparison, ordinary CeO₂ and hsmCeO₂ after different thermal treatments were also investigated. XRD, N₂ physisorption, UV-Raman, H₂ temperature-programmed reduction, O₂ temperature-programmed desorption, EPR spectroscopy, and X-ray photoelectron spectroscopy were used to unravel the structural and redox properties. The hsmCeO₂ calcined at 400 °C shows the highest specific surface area (158 m² g⁻¹), the highest fraction of surface coordinatively unsaturated Ce³⁺ ions (18.2 %), and the highest concentration of reactive oxygen vacancies (2.4×10¹⁵ spins g⁻¹). In the model reaction of oxidative coupling of benzyl alcohol and aniline, such an exceptional redox property of the hsmCeO₂ catalyst can boost benzylideneaniline formation (2.75 and 5.55 mmol h⁻¹ based on >99 % yield at 60 and 80 °C, respectively) in air with no base additives. It can also work effectively at a temperature of 30 °C and in gram-scale synthesis. These are among the best results for all benchmark ceria catalysts in the literature. Moreover, the hsmCeO₂ catalyst shows a wide scope towards primary alcohols and amines with good to excellent yield of imines. The influence of reaction parameters, the reusability of the catalyst, and the reaction mechanism were investigated.     

Disclosing Support-Size-Dependent Effect on Ambient Light-Driven Photothermal CO2 Hydrogenation over Nickel/Titanium Dioxide

The size of support in heterogeneous catalysts can strongly affect the catalytic property but is rarely explored in light-driven catalysis. Herein, we demonstrate the size of TiO₂ support governs the selectivity in photothermal CO₂ hydrogenation by tuning the metal-support interactions (MSI). Small-size TiO₂ loading nickel (Ni/TiO₂-25) with enhanced MSI promotes photo-induced electrons of TiO₂ migrating to Ni nanoparticles, thus favoring the H₂ cleavage and accelerating the CH₄ formation (227.7 mmol g⁻¹ h⁻¹) under xenon light-induced temperature of 360 °C. Conversely, Ni/TiO₂-100 with large TiO₂ prefers yielding CO (94.2 mmol g⁻¹ h⁻¹) due to weak MSI, inefficient charge separation, and inadequate supply of activated hydrogen. Under ambient solar irradiation, Ni/TiO₂-25 achieves the optimized CH₄ rate (63.0 mmol g⁻¹ h⁻¹) with selectivity of 99.8 %, while Ni/TiO₂-100 exhibits the CO selectivity of 90.0 % with rate of 30.0 mmol g⁻¹ h⁻¹. This work offers a novel approach to tailoring light-driven catalytic properties by support size effect.     

Promoted porous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for ammonia decomposition

Transition metal catalysts have been considerably used for NH₃ decomposition because of the potential application in CO_x-free H₂ generation for fuel cells. However, most transition metal catalysts prepared via traditional synthetic approaches performed the inferior stability due to the agglomeration of active components. Here, we adopted an efficient method, aerosol-assisted self-assembly approach (AASA), to prepare the optimized cobalt-alumina (Co₃O₄-Al₂O₃) catalysts. The Co₃O₄-Al₂O₃ catalysts exhibited excellent catalytic performance in the NH3 decomposition reaction, which can reach 100% conversion at 600 °C and maintain stable for 72 h at a gaseous hourly space velocity (GHSV) of 18000 cm³ g_cat^?1 h^?1. The catalysts were characterized by various techniques including transmission electron microscope (TEM), scanning electron microscope (SEM), nitrogen sorption, temperature-programmed reduction by hydrogen (H₂-TPR), ex-situ/in-situ Raman and ex-situ/in-situ X-ray diffraction (XRD) to obtain the information about the structure and property of the catalysts. H₂-TPR and in-situ XRD results show that there is strong interaction between the cobalt and alumina species, which influences the redox properties of the catalysts. It is found that even a low content of alumina (10 at%) is able to stabilize the catalysts due to the adequate dispersion and rational interaction between different components, which ensures the high activity and superior stability of the cobalt-alumina catalysts.     

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.