Performance and deactivation of Ir/γ-Al2O3 catalyst in the hydrogen peroxide monopropellant thruster

The performance of Ir/γ-Al₂O₃ catalyst for the decomposition of high concentration hydrogen peroxide was investigated in a monopropellant thruster. The changes of ignition delay (t₀), chamber pressure (P_c) and catalyst bed temperature (T_c) with the numbers of startup–shutdown cycles were proved to be effective indicators of catalyst bed efficiency. The fresh catalyst and the deactivated catalyst were characterized with H₂-TPR, XRD and XPS. It was found that catalyst oxidation and surface Sn poisoning are the major reasons of catalyst deactivation.     

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。     

Desulfurization of commercial fuels by π-complexation: Monolayer CuCl/γ-Al2O3

Monolayer CuCl/γ-Al₂O₃ sorbent was studied for desulfurization of a commercial jet fuel (364.3 ppmw S) and a commercial diesel (140 ppmw S). The sorbent was prepared by means of spontaneous monolayer dispersion methods. Deep desulfurization (sulfur levels of <1 ppmw) was accomplished with this sorbent using a fixed-bed adsorber. The CuCl/γ-Al₂O₃ sorbent was capable of removing 6.4 and 11.2 mg of sulfur per gram for jet fuel at breakthrough (at <1 ppmw S) and saturation, respectively. The same sorbent was capable of removing 0.94 and 1.8 mg of sulfur per gram for BP diesel at breakthrough and saturation, respectively. The difference in sulfur capacities for jet fuel and diesel was apparently caused by the difference in concentrations of strongly binding compounds, such as nitrogen heterocycles, heavy (polynuclear) aromatics and fuel additives. In comparison with CuCl/γ-Al₂O₃, Cu(I)Y zeolite has higher sulfur capacities but is less stable and can be easily oxidized to Cu(II)Y by fuel additives (such as oxygenates) and moisture and consequently loses π-complexation ability. However, all these cuprous π-complexation sorbents selectively adsorb thiophenic compounds over aromatics and olefins (as predicted by the high separation factors), which resulted in the observed desulfurization capability. A feasibility study is shown for efficient regeneration of CuCl/γ-Al₂O₃ using ultrasound at ambient temperature. Possible problems associated with desulfurization using π-complexation sorbents for commercial fuels are discussed.     

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.     

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.     

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。     

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。     

微波辅助制备Ni-W-P/γ-Al2O3煤焦油加氢催化剂

采用微波辅助浸渍法、微波管式焙烧制备了Ni-W-P/γ-Al₂O₃催化剂,并以中低温煤焦油轻油为原料,在固定床反应器装置上评价了催化剂的加氢活性。通过N₂吸附-脱附、GC-MS等方法对催化剂的物化性能及加氢产物油进行表征,并根据FHH模型,计算出催化剂的表面分形维数。结果表明,添加助剂P可调节催化剂的微观孔结构,改变催化剂的酸性分布与强度,并有助于加氢饱和反应的进行;当助剂P含量为0.9%时,催化剂的加氢脱硫、脱氮活性最高,加氢饱和性能最好;焙烧温度直接影响催化剂物性参数,当温度为500 ℃时,加氢活性最高、加氢产物品质最佳;微波焙烧相比常规制备方法,可增加晶粒烧结程度,形成更多三维孔隙结构,为加氢反应提供更大的表面和空间,且增加中等强度酸的酸量,更有助于表面活性组分的分散及硫化性的增强。     

Modification of catalytic performances due to the co-feeding of hydrogen or carbon dioxide in the partial oxidation of methane over a NiO/γ-Al2O3 catalyst

The influence of the addition of 1–10 vol.% of hydrogen or carbon dioxide to the feed during the partial oxidation of methane was studied over a NiO/γ-Al₂O₃ catalyst. The addition of H₂ decreases the conversion and syngas selectivity. This decrease of performance seems to be related to a higher reduction of the catalyst due to the H₂ co-feeding. The addition of CO₂ also appears unfavorable to the production of hydrogen but increases the CO yield. A combination of the dry reforming and the reverse water gas shift reactions is suggested to explain the observed modifications in the product yields.     

Iminium cations as intermediates in the hydrodenitrogenation of alkylamines over sulfided NiMo/γ-Al2O3

The mechanism of the hydrodenitrogenation of the mixed dialkyl- and trialkylamines C₁NHC₆ and C₁N(C₆)₂ was studied over sulfided NiMo/γ-Al₂O₃ at 280 °C and 3 MPa. C₁NHC₆ reacted by disproportionation to C₁N(C₆)₂ as well as C₆N(C₁)₂ and by substitution by H₂S to methylamine and hexanethiol as well as hexylamine and methanethiol. C₁N(C₆)₂ reacted by substitution with H₂S to C₁NHC₆ and C₆NHC₆ and methane- and hexanethiol. The probability of breaking the C₁N bond was only slightly smaller than of breaking the C₆N bond in C₁N(C₆)₂. In the reaction of an equimolar mixture of C₅NHC₅ and C₁N(C₆)₂ both C₁N(C₅)₂ and C₆N(C₅)₂ were formed. The transfer of the methyl group in these reactions cannot be explained by imine and enamine intermediates, only iminium cation intermediates can explain all the products in the hydrodenitrogenation of monoalkyl-, dialkyl- and trialkylamines.     

Phase diagram of the Al2O3–ZrO2–Nd2O3 system

The phase diagram of the Al₂O₃–ZrO₂–Nd₂O₃ system was constructed in the temperature range 1250–2800 °C. The liquidus surface of the phase diagram reflects the preferentially eutectic interaction in the system. Two new ternary and one new binary eutectics were found. The minimum melting temperature is 1675 °C and it corresponds to the ternary eutectic Nd₂O₃·11Al₂O₃ + F-ZrO₂ + NdAlO₃. The solidus surface projection and the schematic of the alloy crystallization path confirm the preferentially congruent character of phase interaction in the ternary system. The polythermal sections present the complete phase diagram of the Al₂O₃–ZrO₂–Nd₂O₃ system. No ternary compounds or regions of remarkable solid solution were found in the components or binaries in this ternary system.     

The effect of oxygen concentration on the reduction of NO with propylene over CuO/γ-Al2O3

The effect of oxygen concentration on the pulse and steady-state selective catalytic reduction (SCR) of NO with C₃H₆ over CuO/γ-Al₂O₃ has been studied by infrared spectroscopy (IR) coupled with mass spectroscopy studies. IR studies revealed that the pulse SCR occurred via (i) the oxidation of Cu⁰/Cu⁺ to Cu²⁺ by NO and O₂, (ii) the co-adsorption of NO/NO₂/O₂ to produce Cu²⁺(NO₃⁻)₂, and (iii) the reaction of Cu²⁺(NO₃⁻)₂ with C₃H₆ to produce N₂, CO₂, and H₂O. Increasing the O₂/NO ratio from 25.0 to 83.4 promotes the formation of NO₂ from gas phase oxidation of NO, resulting in a reactant mixture of NO/NO₂/O₂. This reactant mixture allows the formation of Cu²⁺(NO₃⁻)₂ and its reaction with the C₃H₆ to occur at a higher rate with a higher selectivity toward N₂ than the low O₂/NO flow. Both the high and low O₂/NO steady-state SCR reactions follow the same pathway, proceeding via adsorbed C₃H₇---NO₂, C₃H₇---ONO, CH₃COO⁻, Cu⁰---CN, and Cu⁺---NCO intermediates toward N₂, CO₂, and H₂O products. High O₂ concentration in the high O₂/NO SCR accelerates both the formation and destruction of adsorbates, resulting in their intensities similar to the low O₂/NO SCR at 523–698 K. High O₂ concentration in the reactant mixture resulted in a higher rate of destruction of the intermediates than low O₂ concentration at temperatures above 723 K.     

浸渍法制备Pt-Sn/γ-Al2O3催化剂及其催化性能

采用等体积共浸渍法和分步浸渍法制备Pt-Sn/γ-Al₂O₃催化剂,并在固定床反应器上进行正丁烷脱氢实验研究。结果表明,与共浸渍法相比,分步浸渍法制备的催化剂表现出更高的催化活性。采用等体积浸渍法制备催化剂时,活性组分与载体之间会发生竞争吸附作用,这会影响活性金属组分在载体表面的分散度,进而影响催化剂活性。     

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.     

Preparation, characterization and deactivation studies of Co–Mo/γ–Al2O3 deoxidizing catalyst

A deoxidizing catalyst was prepared in this paper. Several characterization techniques (XRD, SEM–EDS, TEM, TPD and TPR) were used to study its structure and properties. A normal pressure micro-reactor was built to study its deoxidizing performance. Results show that when inlet O₂ concentration was 0.1%, space velocity was 3000–12 000 h⁻¹ and operation temperature was above 80 °C, the outlet residual O₂ can be as low as 1.0 × 10⁻⁶ (v/v). 300 h continuous operation shows that its deoxidizing activity was stable. Through comparison of the deoxidizing activities for fresh and deactivated catalyst and by simulating the water vapor contents in system, the mechanism of deactivation and reactivation was studied.     

Catalytic oxidation of naphthalene using a Pt/Al2O3 catalyst

Polycylic aromatic hydrocarbons (PAHs) are listed as carcinogenic and mutagenic priority pollutants, belonging to the environmental endocrine disrupters. Most PAHs in the environment stem from the atmospheric deposition and diesel emission. Consequently, the elimination of PAHs in the off-gases is one of the priority and emerging challenges. Catalytic oxidation has been widely used in the destruction of organic compounds due to its high efficiency (or conversion of reactants), its economic benefits and good applicability.

This study investigates the application of the catalytic oxidation using Pt/γ-Al₂O₃ catalysts to decompose PAHs and taking naphthalene (the simplest and least toxic PAH) as a target compound. It studies the relationships between conversion, operating parameters and relevant factors such as treatment temperatures, catalyst sizes and space velocities. Also, a related reaction kinetic expression is proposed to provide a simplified expression of the relevant kinetic parameters.

The results indicate that the Pt/γ-Al₂O₃ catalyst used accelerates the reaction rate of the decomposition of naphthalene and decreases the reaction temperature. A high conversion (over 95%) can be achieved at a moderate reaction temperature of 480 K and space velocity below 35,000 h⁻¹. Non-catalytic (thermal) oxidation achieves the same conversion at a temperature beyond 1000 K. The results also indicate that Rideal–Eley mechanism and Arrhenius equation can be reasonably applied to describe the data by using the pseudo-first-order reaction kinetic equation with activation energy of 149.97 kJ/mol and frequency factor equal to 3.26 × 10¹⁷ s⁻¹.     

Direct atomic scale analysis of the distribution of Cu valence states in Cu/γ-Al2O3 catalysts

In this paper, the microstructure of a 1 wt.% Cu/γ-Al₂O₃ catalyst that was reduced in a 4% hydrogen/argon atmosphere at temperatures of 523, 773 and 1073 K, is studied by Z-contrast imaging and electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). Results show that the copper species are well dispersed when the catalyst is reduced below 523 K. At 773 K, separated Cu(I) and Cu(0) species are found existing as ring-like and bulk-like particles. This appears to indicate that the copper has not been reduced to its metallic form due to the interaction between the copper oxide and the support. Large spherical particles having core-shell structures with Cu(I) in the shells and Cu(0) in the cores are generated when the catalyst is reduced at 1073 K. The formation of partially oxidized copper species upon reduction at 1073 K is attributed to the metallic copper interaction with the alumina support. This study also demonstrates that high-spatial resolution Z-contrast imaging and EELS performed simultaneously can provide unique information on the morphology and chemistry of metal species in supported metal catalysts.     

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.     

柠檬醛在La2O3/γ-Al2O3催化剂上的等温吸附

对柠檬醛-乙酸乙酯溶液中柠檬醛在La₂O₃/γ-Al₂O₃催化剂上等温吸附行为进行了研究。结果表明,30 ℃柠檬醛在La₂O₃/γ-Al₂O₃催化剂上的吸附动力学符合准二阶吸附动力学模型,吸附动力学方程为：1/q_t=2.350/t+0.063 3(R²=0.998 5)。（30~65） ℃柠檬醛在La₂O₃/γ-Al₂O₃催化剂上的等温吸附符合Langmuir方程,温度升高使柠檬醛的饱和吸附量增加,吸附热为32.19 kJ·mol^-1。     

An investigation of the thermal stability and sulphur tolerance of Ag/γ-Al2O3 catalysts for the SCR of NOx with hydrocarbons and hydrogen

The sulphur tolerance and thermal stability of a 2 wt% Ag/γ-Al₂O₃ catalyst was investigated for the H₂-promoted SCR of NO_x with octane and toluene. The aged catalyst was characterised by XRD and EXAFS analysis. It was found that the effect of ageing was a function of the gas mix and temperature of ageing. At high temperatures (800 °C) the catalyst deactivated regardless of the reaction mix. EXAFS analysis showed that this was associated with the Ag particles on the surface of the catalyst becoming more ordered. At 600 and 700 °C, the deactivating effect of ageing was much less pronounced for the catalyst in the H₂-promoted octane-SCR reaction and ageing at 600 °C resulted in an enhancement in activity for the reaction in the absence of H₂. For the toluene + H₂-SCR reaction the catalyst deactivated at each ageing temperature. The effect of addition of low levels of sulphur (1 ppm SO₂) to the feed was very much dependent on the reaction temperature. There was little deactivation of the catalyst at low temperatures (≤235 °C), severe deactivation at intermediate temperatures (305 and 400 °C) and activation of the catalyst at high temperatures (>500 °C). The results can be explained by the activity of the catalyst for the oxidation of SO₂ to SO₃ and the relative stability of silver and aluminium sulphates. The catalyst could be almost fully regenerated by a combination of heating and the presence of hydrogen in the regeneration mix. The catalyst could not be regenerated in the absence of hydrogen.