Surface properties and reactivity of Cu/γ-Al2O3 catalysts for NO reduction by C3H6: Influences of calcination temperatures and additives

The influences of calcination temperatures and additives for 10 wt.% Cu/γ-Al₂O₃ catalysts on the surface properties and reactivity for NO reduction by C₃H₆ in the presence of excess oxygen were investigated. The results of XRD and XPS show that the 10 wt.% Cu/γ-Al₂O₃ catalysts calcined below 973 K possess highly dispersed surface and bulk CuO phases. The 10 wt.% Cu/γ-Al₂O₃ and 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalysts calcined at 1073 K possess a CuAl₂O₄ phase with a spinel-type structure. In addition, the 10 wt.% La–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K possesses a bulk CuO phase. The result of NO reduction by C₃H₆ shows that the CuAl₂O₄ is a more active phase than the highly dispersed and bulk CuO phase. However, the 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K possesses significantly lower reactivity for NO reduction than the 10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K, although these catalysts possess the same CuAl₂O₄ phase. The low reactivity for NO reduction for 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K is attributed to the formation of less active CuAl₂O₄ phase with high aggregation and preferential promotion of C₃H₆ combustion to CO_x by MnO₂. The engine dynamometer test for NO reduction shows that the C₃H₆ is a more effective reducing agent for NO reduction than the C₂H₅OH. The maximum reactivity for NO reduction by C₃H₆ is reached when the NO/C₃H₆ ratio is one.     

Highly dispersed NiW/γ-Al2O3 catalyst prepared by hydrothermal deposition method

This article describes a novel hydrothermal deposition method for preparing highly dispersed NiW/γ-Al₂O₃ catalysts and demonstrates its advantages over the conventional impregnation method. Via the hydrothermal precipitation reactions between sodium tungstate and hydrochloric acid and between nickel nitrate and urea, respectively, the active species W and Ni were deposited on γ-Al₂O₃. In the hydrothermal deposition of WO₃, a surfactant hexadecyltrimethyl ammonium bromide (CTAB) was used to prevent the aggregation of WO₃. The characterization results obtained by means of X-ray photoelectron spectroscopy (XPS), N₂ adsorption and high-resolution transmission electron microscopy (HRTEM) measurements showed that compared with the catalyst prepared by the conventional impregnation method, the catalyst with the same metal contents prepared by the hydrothermal deposition had much higher W and Ni dispersion, higher specific surface area, larger pore volume, the significantly decreased slab length and slightly increased stacking degree of sulfided W species, leading to the significantly enhanced dibenzothiophene (DBT) hydrodesulfurization (HDS) activity. The DBT HDS assessment results also revealed that the catalyst containing 17.7 wt% WO₃ and 2.4 wt% NiO prepared by the hydrothermal deposition method had the similar DBT HDS activity as a commercial NiW/γ-Al₂O₃ catalyst containing 23 wt% WO₃ and 2.6 wt% NiO, resulting in the greatly decreased amount of active metals for achieving the same HDS activity.     

Desulfurization of Transportation Fuels by Adsorption

This paper is a review on sorbents for desulfurization of transportation fuels (gasoline, diesel, and jet fuel). Since the π-complexation sorbents are the most promising, they are the focus of the discussion. During π-complexation, the thiophenic compounds can bind selectively to the sorbents, especially the substituted ones. The later remain highly unreacted in hydrodesulfurization (HDS) (i.e., “refractory” sulfur). Molecular orbital (MO) calculations and experiments have shown that these refractory compounds [(e.g., 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene (DMDBT)] bind strongly with the π-complexation sorbents because of a better electron donation/back-donation ability. The sorbents reviewed include Ag-Y, Cu(I)-Y, Ni(II)-Y, and Ni(II)-X zeolites prepared using various ion-exchange techniques. The techniques included vapor and solid-state ion exchanges, which are suitable for obtaining high loadings of transition metals. The best sorbent, Cu(I)-Y [vapor-phase ion-exchanged (VPIE)], is capable of producing almost 38 cm³ of desulfurized fuel per g of sorbent with a sulfur concentration of less than 0.2 ppmw. Using these π-complexation sorbents in layered bed matrices further increases the desulfurization capacity.     

Effect of phosphorus addition on the hydrotreating activity of NiMo/Al2O3 carbide catalyst

A series of phosphorus promoted γ-Al₂O₃ supported NiMo carbide catalysts with 0–4.5 wt.% P, 13 wt.% Mo and 2.5 wt.% Ni were synthesized and characterized by elemental analysis, pulsed CO chemisorption, BET surface area measurement, X-ray diffraction, near-edge X-ray absorption fine structure, DRIFT spectroscopy of CO adsorption and H₂ temperature programmed reduction. X-ray diffraction patterns and CO uptake showed the P addition to NiMo/γ-Al₂O₃ carbide, increased the dispersion of β-Mo₂C particles. DRIFT spectra of adsorbed CO revealed that P addition to NiMo/γ-Al₂O₃ carbide catalyst not only increases the dispersion of Ni-Mo carbide phase, but also changes the nature of surface active sites. The hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) activities of these P promoted NiMo/γ-Al₂O₃ carbide catalysts were performed in trickle bed reactor using light gas oil (LGO) derived from Athabasca bitumen and model feed containing quinoline and dibenzothiophene at industrial conditions. The P added NiMo/γ-Al₂O₃ carbide catalysts showed enhanced HDN activity compared to the NiMo/γ-Al₂O₃ catalysts with both the feed stocks. The P had almost no influence on the HDS activity of NiMo/γ-Al₂O₃ carbide with LGO and dibenzothiophene. P addition to NiMo/γ-Al₂O₃ carbide accelerated CN bond breaking and thus increased the HDN activity.     

Performance and characterization of Ru/Al2O3 and Ru/SiO2 catalysts modified with Mn for Fischer–Tropsch synthesis

Mn effect and characterization on γ-Al₂O₃-, -Al₂O₃- and SiO₂-supported Ru catalysts were investigated for Fischer–Tropsch synthesis under pressurized conditions. In the slurry phase Fischer–Tropsch reaction, γ-Al₂O₃ catalysts showed higher performance on CO conversion and C₅⁺ selectivity than -Al₂O₃ and SiO₂ catalysts. Moreover, Ru/Mn/γ-Al₂O₃ exhibited high resistance to catalyst deactivation and other catalysts were deactivated during the reaction. From characterization results on XRD, TPR, TEM, XPS and pore distribution, Ru particles were clearly observed over the catalysts, and γ-Al₂O₃ catalysts showed a moderate pore and particle size such as 8 nm, where -Al₂O₃ and SiO₂ showed highly dispersed ruthenium particles. The addition of Mn to γ-Al₂O₃ enhanced the removal of chloride from RuCl₃, which can lead to the formation of metallic Ru with moderate particle size, which would be an active site for Fischer–Tropsch reaction. Concomitantly, manganese chloride is formed. These schemes can be assigned to the stable nature of Ru/Mn/γ-Al₂O₃ catalyst.     

η-Al2O3与γ-Al2O3在CS2催化水解反应中的性能比较

通过制备高纯度的前驱体湃铝石获得了η-Al₂O₃材料,采用XRD验证了η-Al₂O₃与γ-Al₂O₃在晶相结构上的差异,比较了两者的表面形貌、织构及酸碱性能,结果显示,η-Al₂O₃与γ-Al₂O₃的比表面积相当,但η-Al₂O₃具有更弱的弱碱位和较少的强碱位,并拥有丰富的中等强度酸性位。将η-Al₂O₃与γ-Al₂O₃作为催化剂应用于CS₂水解反应,结果表明,在(200~450) ℃测试温度范围内,η-Al₂O₃催化剂对CS₂的水解活性始终优于γ-Al₂O₃,两种催化剂上CS₂反应的浓度效应也明显不同,推测与它们的酸碱性质影响了对CS₂的吸附能力有关,导致两者催化CS₂水解反应遵循了不同的机制。     

PREPARATION OF (Ni/W)-γ-Al2O3 MICROSPHERES AND THEIR APPLICATION IN ADSORPTION DESULFURIZATION FOR MODEL GASOLINE

A kind of desulfurization adsorbent, (Ni/W)-γ-Al₂O₃ microsphere, was prepared by a new method of in situ chemical reduction. The adsorbent consists of active components (transition metals Ni and W) and a carrier (γ-Al₂O₃). Ni and W in γ-Al₂O₃ microspheres are fine in size and can be distributed homogeneously on the surface and inside of the γ-Al₂O₃ carrier. The desulfurization of the adsorbent made by the in situ chemical reduction method was carried out in model gasoline. Its desulfurization capacity increases 23% in comparison with that made by the conventional impregnation method. The composition and configuration of adsorbents were analyzed by scanning electron microscopy (SEM), electron energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The in situ chemical reduction method offers a new and promising method for preparation of desulfurization adsorbents containing active components.     

低成本大比表面积γ-Al2O3的制备

以廉价无机铝盐硫酸铝为原料,氨水为沉淀剂,十二烷基硫酸钠为添加剂,采用简单沉淀法制备得到较大比表面积γ-Al₂O₃。通过N₂低温物理吸附-脱附、X射线衍射、红外光谱、热重、元素分析、扫描及透射电镜等,研究制备过程中沉淀温度、溶液pH值和添加剂用量对产物γ-Al₂O₃及其前驱体的晶相结构、形貌织构等性质的影响。结果表明,在沉淀温度75 ℃、硫酸铝浓度0.25 mol·L^-1、溶液pH=9.0、老化时间12 h和n(十二烷基硫酸钠)∶n[Al₂(SO₄)₃]=0.375∶1条件下,所得前驱体(拟薄水铝石)经600 ℃焙烧后,可获得大比表面积(416.65 m²·g^-1)γ-Al₂O₃,并且样品中因十二烷基硫酸钠添加,引入的S及Na等杂质含量极少。     

K2CO3/γ-A12O3催化剂在棉籽油制备生物柴油中的应用

利用等体积浸渍法制备K₂CO₃/γ-A1₂O₃负载型固体碱催化剂,应用于棉籽油和甲醇酯交换反应制备生物柴油。对催化剂使用前的保存条件、水分、重复使用性能、游离脂肪酸影响以及失活和再生进行了分析。结果表明,固体催化剂K₂CO₃/γ-Al₂O₃具有较好的抗水性,酸度对催化剂影响明显,重复使用4次未经活化的催化剂,催化活性明显降低,催化剂应密封保存。K₂CO₃/γ-A1₂O₃负载型固体碱催化剂经济实惠且催化效果良好。     

Study of Ag/La0.6Sr0.4MnO3 catalysts for complete oxidation of methanol and ethanol at low concentrations

Ag-modified La_0.6Sr_0.4MnO₃-based catalysts with the perovskite-type structure were prepared by using a citric acid sol–gel method, and their catalytic performance for complete oxidation of methanol and ethanol was evaluated and compared with that of the γ-Al₂O₃-supported catalysts, Ag/γ-Al₂O₃, Pt/γ-Al₂O₃, and Pd/γ-Al₂O₃. The results showed that the Ag-modified La_0.6Sr_0.4MnO₃-based catalysts with the perovskite-type structure displayed the activity significantly higher than that of the supported precious metal catalysts, 0.1%Pd/γ-Al₂O₃ and 0.1%Pt/γ-Al₂O₃ in the temperature range of 370–573 K. Over a 6%Ag/20%La_0.6Sr_0.4MnO₃/γ-Al₂O₃ catalyst, the T₉₅ temperature for methanol oxidation can be as low as 413 K. Even at such low reaction temperature, there were little HCHO and CO detected in the reaction exit-gas. However, for the 0.1%Pd/γ-Al₂O₃ and 0.1%Pt/γ-Al₂O₃ catalysts, the HCHO content in the reaction exit-gas reached 200 and 630 ppm at their T₉₅ temperatures. Over a 6%Ag/La_0.6Sr_0.4MnO₃ catalyst, the T₉₅ temperature for ethanol oxidation can be as low as 453 K, with a corresponding content of CH₃CHO in the exit-gas at 782 ppm; when ethanol oxidation is performed at 493 K, the content of acetaldehyde in the exit-gas can be below 1 ppm. Characterization of the catalysts by X-ray diffraction (XRD), TEM, XPS, laser Raman spectra (LRS), hydrogen temperature-programmed reduction (H₂-TPR) and oxygen temperature-programmed desorption (O₂-TPD) methods revealed that both the surface and the bulk phase of the perovskite La_0.6Sr_0.4MnO₃ played important roles in the catalytic oxidation of the alcohols, and that γ-Al₂O₃ as the bottom carrier could be beneficial in creating a large surface area of catalyst. Moreover, a small amount of Ag⁺ doped onto the surface of La_0.6Sr_0.4MnO₃ was able to partially occupy the positions of La³⁺ and Sr²⁺ due to their similar ionic radii, and thus, became stabilized by the perovskite lattice, which would be in favor of preventing the aggregation of the Ag species on the surface and enhancing the stability of the catalyst. On the other hand, modification of the Ag⁺ to the surface of La_0.6Sr_0.4MnO₃ resulted in an increase in relative content of the surface O₂²⁻/O⁻ species highly reactive toward the alcohols and aldehydes as well as CO. Besides, solution of low-valence metal oxides SrO and Ag₂O with proper amounts in the lattice of the trivalent metal perovskite-type oxide LaMnO₃ would also lead to an increase in the content of the reducible Mnⁿ⁺ and the formation of anionic vacancies, which would be favorable for the adsorption-activation of oxygen on the functioning catalyst and the transport of the lattice and surface oxygen species. All these factors would contribute to the pronounced improvement of the catalyst performance.     

Synthesis of bulk and alumina-supported γ-Mo2N catalysts by a single-step complex decomposition method

A single-step complex decomposition method for the synthesis of bulk and alumina-supported γ-Mo₂N catalysts is described. The complex precursor (HMT)₂(NH₄)₄Mo₇O₂₄·2H₂O (HMT: hexamethylenetetramine) is converted to γ-Mo₂N under a flow of Ar in a temperature range of 823–1023 K. Furthermore, decomposition of the precursor in a NH₃ flow forms γ-Mo₂N in a temperature range of 723–923 K. Compared with direct decomposition of the precursor in Ar, the reaction in NH₃ shows obvious advantages that the nitride forms at a lower temperature. In addition, alumina-supported γ-Mo₂N catalysts with different nitride loadings can be prepared from the alumina-supported complex precursor in the Ar or NH₃ flow. The resultant catalysts exhibit good dibenzothiophene HDS activities, which are similar to the γ-Mo₂N/γ-Al₂O₃ prepared by traditional TPR method. The catalyst prepared by decomposition in an Ar flow exhibits highest activity. It proves that such a single-step complex decomposition method possesses the potential to be a general route for the preparation of molybdenum nitride catalysts.     

CO气相偶联合成草酸二甲酯Pd/α-Al2O3催化剂失活与再利用

作为合成气制乙二醇关键步骤之一,CO与亚硝酸甲酯合成草酸二甲酯备受关注。综述了近年来CO气相偶联合成草酸二甲酯Pd/α-Al₂O₃催化剂失活与再利用研究进展,探讨催化剂再利用工艺存在的问题,指出应根据在工业应用中出现的问题对Pd/α-Al₂O₃催化剂进行失活研究,在此基础上开发针对性的再生工艺;钯催化剂回收方面萃取法和吸附法逐渐成为研究重点,高效、低耗、短流程绿色工艺的开发是失活钯催化剂再利用的发展方向。     

Origin of transient species present on the surface of a PdO/γ-Al2O3 catalyst during the methane combustion reaction

Operando DRIFTS was applied to the study of the evolution of surface species formed on a Pd (2 wt.%)/γ-Al₂O₃ catalyst in various conditions. No differences were observed as a function of the initial oxidation state of palladium. Formates/carbonates species were identified at low temperature (<400 °C) and disappeared when CO₂ production started. These species come from the Pd-catalyzed interaction of CO with the alumina support, while CO₂ induces hydrogenocarbonates formation at low temperature (<300 °C). Their presence does not explain the inhibiting effect of CO₂ observed in CCM on Pd/γ-Al₂O₃ catalysts.     

Effect of La on the thermal stability of Pd/γ-Al2O3 catalytic membranes

Lanthanum-doped Pd/γ-Al₂O₃ and Pd/γ-Al₂O₃ membranes were prepared by sol-gel methods. The thermal stability of the unsupported Pd/γ-Al₂O₃ and La/Pd/γ-Al₂O₃ membranes was investigated with BET (including average pore size, pore volume and BET surface area), XRD, and DTA techniques. The average pore size of the Pd/γ-Al₂O₃ membranes increased sharply after sintering at temperatures higher than 1000°C. Addition of 3 mol% lanthanum can raise the temperature of the γ-Al₂O₃ to-Al₂O₃ phase transformation significantly. This improves the thermal stability of the Pd/γ-Al₂O₃ catalytic membranes.     

Deactivation studies over NiO/γ-Al2O3 catalysts for partial oxidation of methane to syngas

Two types of NiO/γ-Al₂O₃ catalysts prepared by the impregnation and the sol–gel method were used for the partial oxidation of methane to syngas at 850°C (GHSV1.8×10⁵ lkg⁻¹ h⁻¹). The effects of the carbon deposition, the loss and sintering of nickel and the phase transformation of γ-Al₂O₃ support on the catalytic performance during 80 h POM reaction were investigated with a series of characterization such as XRD, BET, AAS, TG, and XPS. The results indicated that the carbon deposition and the loss and sintering of nickel could not cause the serious decrease of catalytic performance over NiO/γ-Al₂O₃ catalyst during the short-time reaction. However, the slow process of the support γ-Al₂O₃ phase transforming into -Al₂O₃ could slowly decrease the performance of NiO/γ-Al₂O₃ catalysts. Aimed at the reasons of the deactivation, an improved catalyst was obtained by the complexing agent-assisted sol–gel method.     

Nanosized γ-Al2O3 protective film for fluorescent lamps

Nanosized γ-Al₂O₃ particles were prepared by the sol–gel method with aluminum ion hydrolysis control performed by nitric acid. The as-prepared particles were mixed with deionized-water and stabilizer, and cycled in a high speed sand mill to form a stable γ-Al₂O₃ suspended slurry, which was then coated on the surface of the glass substrate to form a γ-Al₂O₃ protective film. Observations of SEM and visible transmission spectra show that a well-dispersed γ-Al₂O₃ slurry could be obtained after three-cycle grinding suitable to coat fluorescent lamp glass with a dense and uniform film of visible light transmission up to 95%.     

Ce1−xCuxO2−x/Al2O3/FeCrAl catalysts for catalytic combustion of methane

A series of the Ce_1−xCu_xO_2−x/Al₂O₃/FeCrAl catalysts (x = 0–1) were prepared. The structure of the catalysts was characterized using XRD, SEM and H₂-TPR. The catalytic activity of the catalysts for the combustion of methane was evaluated. The results indicated that in the Ce_1−xCu_xO_2−x/Al₂O₃/FeCrAl catalysts the surface phase structure were the Ce_1−xCu_xO_2−x solid solution, -Al₂O₃ and γ-Al₂O₃. The surface particle shape and size were different with the variety of the molar ratio of Ce to Cu in the Ce_1−xCu_xO_2−x solid solution. The Cu component of the Ce_1−xCu_xO_2−x/Al₂O₃/FeCrAl catalysts played an important role to the catalytic activity for the methane combustion. There were the stronger interaction among the Ce_1−xCu_xO_2−x solid solution and the Al₂O₃ washcoats and the FeCrAl support.     

M/γ-Al2O3催化剂对煤油水重整制氢的影响

以γ-Al₂O₃为载体,采用等体积分步浸渍法制备了以Ni为活性组分,La、Ce、Fe、Cr、Co为助剂的催化剂M/γ-Al₂O₃,在固定床管式反应器中研究了M/γ-Al₂O₃催化剂的性能,考察了反应温度、水碳比和空速对氢产率的影响,并对催化剂进行XRD、SEM和BET表征。结果表明,NiLaCeFeCrCo/γ-Al₂O₃催化剂具有较好的催化性能,在反应温度700 ℃、水碳物质的量比10和空速6 min^-1的条件下,氢产率达到27.335 mol·mol^-1,并在300 min内表现出较好的活性,平均氢产率为21.966 mol·mol^-1。     

Kinetic studies of CH4 oxidation over Pt–NiO/δ-Al2O3 in a fluidised bed reactor

The oxidation of CH₄ over Pt–NiO/δ-Al₂O₃ has been studied in a fluidised bed reactor as part of a major project on an autothermal (combined oxidation–steam reforming) system for CH₄ conversion. The kinetic data were collected between 773 and 893 K and 101 kPa total pressure using CH₄ and O₂ compositions of 10–35% and 8–30%, respectively. Rate–temperature data were also obtained over alumina-supported monometallic catalysts, Pt and NiO. The bimetallic Pt–NiO system has a lower activation energy (80.8 kJ mol⁻¹) than either Pt (86.45 kJ mol⁻¹) and NiO (103.73 kJ mol⁻¹). The superior performance of the bimetallic catalyst was attributed to chemical synergy. The reaction rate over the Pt–NiO catalyst increased monotonically with CH₄ partial pressure but was inhibited by O₂. At low partial pressures (<30 kPa), H₂O has a detrimental effect on CH₄ conversion, whilst above 30 kPa, the rate increased dramatically with water content.     

Quantification of the in situ DRIFT spectra of Pt/K/γ-A12O3 NOx adsorber catalysts

A method to quantify DRIFT spectral features associated with the in situ adsorption of gases on a NO_x adsorber catalyst, Pt/K/Al₂O₃, is described. To implement this method, the multicomponent catalyst is analysed with DRIFT and chemisorption to determine that under operating conditions the surface comprised a Pt phase, a pure γ-Al₂O₃ phase with associated hydroxyl groups at the surface, and an alkalized-Al₂O₃ phase where the surface –OH groups are replaced by –OK groups. Both DRIFTS and chemisorption experiments show that 93–97% of the potassium exists in this form. The phases have a fractional surface area of 1.1% for the 1.7 nm-sized Pt, 34% for pure Al₂O₃ and 65% for the alkalized-Al₂O₃. NO₂ and CO₂ chemisorption at 250 °C is implemented to determine the saturation uptake value, which is observed with DRIFTS at 250 °C. Pt/Al₂O₃ adsorbs 0.087 μmol CO₂/m²and 2.0 μmol NO₂/m², and Pt/K/Al₂O₃ adsorbs 2.0 μmol CO₂/m²and 6.4 μmol NO₂/m². This method can be implemented to quantitatively monitor the formation of carboxylates and nitrates on Pt/K/Al₂O₃ during both lean and rich periods of the NO_x adsorber catalyst cycle.