Steam reforming of liquid petroleum gas over Mn-promoted Ni/γ-Al2O3 catalysts

Three different Mn-promoted Ni/γ-Al₂O₃ catalysts, Mn/Ni/γ-Al₂O₃, Mn-Ni/γ-Al₂O₃ and Ni/Mn/γ-Al₂O₃, were prepared and applied to the steam reforming of liquid petroleum gas (LPG) mainly composed of propane and butane. For comparison, Ni/γ-Al₂O₃ catalysts containing different amount of Ni were also examined. In the case of the Ni/γ-Al₂O₃ catalysts, 4.1 wt% Ni/γ-Al₂O₃ showed the stable catalytic activity with the least amount of coke formation. Among the various Mn-promoted Ni/γ-Al₂O₃ catalysts, Mn/Ni/γ-Al₂O₃ showed the stable catalytic activity with the least amount of coke formation. It also exhibited a similar H₂ formation rate compared with Ni/γ-Al₂O₃. Several characterization techniques—N₂ adsorption/desorption, X-ray diffraction (XRD), CO chemisorptions, temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and CHNS analysis—were employed to characterize the catalysts. The catalytic activity increased with increasing amount of chemisorbed CO for the Mn-promoted Ni/γ-Al₂O₃ catalysts. The highest proportion of Mn⁴⁺ species was observed for the most stable catalyst.     

SO2 Reactions over γ-Al2O3,Pt/γ-Al2O3,Sn/γ-Al2O3 and Pt–Sn/γ-Al2O3

Platinum and Platinum–tin bimetallic catalysts supported on alumina were prepared by co-impregnation of both metallic precursors on the support and used as catalysts for the oxidation of SO₂. Platinum dispersion was determined by means of H₂–O₂ titration. Tin addition (1 and 2 wt%) only slightly decreased the exposed platinum atoms suggesting that tin is mainly over the support. At temperatures lower than 300 °C, SO₂ did not react with oxygen. Nevertheless, when the temperature was increased, the SO₂ oxidation began. The ignition temperatures for SO₂ oxidation (taken at 50% conversion) were 345 °C for 1% Pt/Al₂O₃ and 520 °C for 1% Pt–2% Sn/Al₂O₃. The strong displacement on activity suggests that tin plays an important role as inhibitor of the SO₂ oxidation reaction.     

Neopentane conversion over Pd/γ-Al2O3

X-ray diffraction showed that during high temperature reduction at 600°C, chlorine-free Pd/-Al₂O₃ undergoes partial transformation to a Pd-Al alloy, which confirms results of other studies [9]. This evolution appears to have a large effect on the catalytic behaviour in the reaction of neopentane with hydrogen: the selectivity towards isomerization increases from <20 up to 80%. At the same time, the activation energy drops from 60 to 22 kcal/mol. These changes can be reversed by oxidation at 500°C followed by reduction at 300°C. The presence of residual chlorine (ex-PdCl₂ precursor) appears to inhibit the Pd induced reduction of Al₂O₃ leading to Pd-Al alloy formation.     

Lean NOxCatalysis over Sn/γ-Al2O3Catalysts

Sn/γ-Al₂O₃were effective and highly stable catalysts for NO reduction with propene under high partial pressures of oxygen and water. The activity depended on the Sn loading. For a 10 wt% Sn/Al₂O₃at 475–500°C, 58% conversion of 1000 ppm NO to N₂was obtained in the presence of 10% water and 15% O₂, at a space velocity of 30,000 h⁻¹, and 77% conversion at 15,000 h⁻¹. The NO conversion increased with O₂partial pressure but was suppressed by water below 500°C. The activity was also suppressed by SO₂but could be restored slowly after the removal of SO₂.     

Gas-phase dehydration of glycerol over commercial Pt/γ-Al2O3 catalysts

Gas-phase dehydration of glycerol to produce acrolein was investigated over commercial catalysts based onγ-Al2O3, viz. A-64, A-56, I-62, AP-10, AP-56, AP-64 and KR-104. To understand the effect of Cl?anions, HCl-impregnated sup-ports have been investigated in the dehydration reaction of glycerol at 375 °C. For comparison, various H-zeolites were also examined. It was found that the glycerol conversion over the solid acid catalysts was strongly dependent on their acidity and surface area. And the relationship between the catalytic activity and the acidity of the catalysts was discussed. The outstanding properties of Pt/γ-Al2O3 catalyst systems for the dehydration of glycerol were revealed. Pt/γ-Al2O3 catalyst (AP-64) showed the highest catalytic activity after 50 h of reaction with an acrolein selectivity of 65%at a conversion of glycerol of 90%. Based on these results, catalysts based onγ-Al2O3 appear to be most promising for gas phase dehydration of glycerol.     

Role of support in CO2 reforming of CH4 over a Ni/γ-Al2O3 catalyst

A catalyst of 10% Ni/γ-Al₂O₃ for CO₂/CH₄ reforming was prepared and characterized by TPR, TPD, XPS, XRD and activity measurements. XPS and TPR showed that Ni mainly exists in the form of NiAl₂O₄ in the calcined catalyst and is hard to reduce below 650°C, indicating a strong interaction between metal and support. Reduction of the calcined catalyst results in fine particles of Ni⁰, with an average diameter of about 20 nm as determined by XRD. The uptake of H on the reduced catalyst measured by H₂-TPD is 4.2–4.6 mole per mole of Ni species and does not depend on the reduction degree of Ni species. This provides a convincing piece of evidence for the occurrence of hydrogen spillover in the reduced catalyst. Only reduced catalysts present good activity, but the degree of nickel reduction has almost no effect on the reforming activity. This seems to suggest that Ni⁰ is vital for the reforming activity, but γ-Al₂O₃ is also involved in CO₂/CH₄ reforming and contributes even more. Based on the mechanism proposed by Bradford et al. and on our observations, a mechanistic model has been proposed to elucidate the role of γ-Al₂O₃ in CO₂/CH₄ reforming.     

Mechanism of the hydrodenitrogenation of o-toluidine and methylcyclohexylamine over NiMo/γ-Al2O3

The hydrodenitrogenation (HDN) of o-toluidine and its reaction intermediates was studied over a NiMo/γ-Al₂O₃ catalyst. The kinetics of the HDN of methylcyclohexylamine and of the hydrogenation of cyclohexene were also studied. Hydrogenation of o-toluidine alone produces methylcyclohexene and methylcyclohexane. When a sufficient quantity of cyclohexene is added during the HDN of toluidine, methylcyclohexylamine, the first intermediate in the hydrogenation of toluidine, becomes detectable. Because of its strong adsorption constant and high rate constant for reacting further to methylcyclohexene and methylcyclohexane, methylcyclohexylamine is not observed in the HDN of toluidine. Adding cyclohexene decreases the adsorption of methylcyclohexylamine, thus enabling its detection. The rate and adsorption constants of methylcyclohexylamine and cyclohexene in the HDN of methylcyclohexylamine were calculated by fitting the kinetic data to a Langmuir–Hinshelwood equation. A two-site model was used to describe the surface reactions, with one site for the methylcyclohexylamine reactions and the other for the cyclohexene reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Onset of perovskite formation in the catalytic system La2O3/γ-Al2O3

Molecular dynamics simulations of model systems for the surface interaction of lanthanum oxide supported on -alumina have been carried out at 1500 K. The onset of formation of perovskite-like phases has been analysed in samples containing four different concentrations of lanthanum oxide. A mechanism of the formation of perovskite-like polyhedra is proposed. This mechanism essentially involves a displacement of an oxide ion associated to an octahedral aluminum by a lanthanum ion and appears to be independent of La₂O₃ loadings.     

Plasma-driven CO2 hydrogenation to CH3OH over Fe2O3/γ-Al2O3 catalyst

We report a plasma-assisted CO₂ hydrogenation to CH₃OH over Fe₂O₃/γ-Al₂O₃ catalysts, achieving 12% CO₂ conversion and 58% CH₃OH selectivity at a temperature of nearly 80°C atm pressure. We investigated the effect of various supports and loadings of the Fe-based catalysts, as well as optimized reaction conditions. We characterized catalysts by X-ray powder diffraction (XRD), hydrogen temperature programmed reduction (H₂-TPR), CO₂ and CO temperature programmed desorption (CO₂/CO-TPD), high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), x-ray photoelectron spectroscopy (XPS), Mössbauer, and Fourier transform infrared ( FTIR). The XPS results show that the enhanced CO₂ conversion and CH₃OH selectivity are attributed to the chemisorbed oxygen species on Fe₂O₃/γ-Al₂O₃. Furthermore, the diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) and TPD results illustrate that the catalysts with stronger CO₂ adsorption capacity exhibit a higher reaction performance. In situ DRIFTS gain insight into the specific reaction pathways in the CO₂/H₂ plasma. This study reveals the role of chemisorbed oxygen species as a key intermediate, and inspires to design highly efficient catalysts and expand the catalytic systems for CO₂ hydrogenation to CH₃OH.     

Conversions of Methane to Synthesis Gas over Co/γ-Al2O3 by CO2 and/or O2

The goal of the paper was to investigate the effect of the catalyst precursor on the catalytic activity. For this reason, the structure, the reducibility and the reaction behavior of -Al₂O₃-supported Co (24 wt%) catalysts as a function of calcination temperature (T _c) were investigated using X-ray diffraction, temperature-programmed reduction, CO chemisorption, pulse reaction with pure CH₄, and the catalytic reactions of methane conversion to synthesis gas. Depending on T _c, one, two, or three of the following Co-containing compounds, Co₃O₄, Co₂AlO₄, and CoAl₂O₄, were identified. Their reducibility decreased in the sequence: Co₃O₄>Co₂AlO₄>CoAl₂O₄. Co₃O₄ was generated as a major phase at a T _c of 500°C and Co₂AlO₄ and CoAl₂O₄ at a T _c of 1000°C. The reduced Co/-Al₂O₃ catalysts, obtained via the reduction of the 500 and 1000°C calcined catalysts, provided high and stable activities for the partial oxidation of methane and the combined partial oxidation and CO₂ reforming of methane. They deactivated, however, rapidly in the CO₂ reforming of methane. Possible explanations for the stability are provided.     

Stability of Pt/γ-Al2O3 Catalysts in Model Biomass Solutions

The stability of a Pt/??-Al₂O₃ catalyst in liquid water and aqueous solutions of 5?wt% glycerol or sorbitol at 225?°C is examined using a variety of physicochemical methods. It is demonstrated that the presence of glycerol and sorbitol significantly reduces the hydration of ??-Al₂O₃ to form boehmite as compared to treatment in pure water. The stability against hydration increases with increasing carbon chain length. Treatment with polyol solutions also results in reduced agglomeration of supported metal particles. The prevention of boehmite formation and agglomeration of metal particles are attributed to the formation of carbonaceous species on the surface. In addition to these effects, the deposits block a considerable portion of active metal surface area. IR spectroscopic analysis indicates that dehydration reactions play an important role in the formation of the carbonaceous deposits. The present results illustrate that water and dissolved biomass compounds can strongly affect the stability of heterogeneous catalysts under reaction conditions.     

O3/TiO2/γ-Al2O3/UV降解草酸

采用臭氧与TiO2/γ-Al2O2/UV联用技术对降解草酸进行研究.考察了进气流量、草酸初始浓度、催化剂投加量,pH值及温度等因素对草酸降解的影响.研究表明,在一定范围内,随着进气流量的增加、温度的升高都会促使草酸的降解速率加快;溶液pH值对催化臭氧化有比较重要的影响,pH值2时,草酸的去除率最高.     

Reductive dehydration of butanone to butane over Pt/γ-Al2O3 and HZSM-5

We show that butanone can be reacted to form n-butane in an isothermal reactor containing a 1 wt.% Pt/γ-Al₂O₃ and an HZSM-5 catalyst (total mass of 12–400 mg, Si/Al = 11.5) below 160 °C with up to 99% selectivity and 67% yield. The catalyst loading (12–400 mg) and temperature (100–250 °C) were varied to obtain primary products whose selectivities decreased with conversion and secondary/tertiary products whose selectivities increased with conversion. As conversion increased, the selectivities of butanol and butene decreased, showing the formation of butane from butanone through a series reaction pathway: butanone → 2-butanol → butene → butane. Butane selectivity increased as the temperature was increased from 100 to 200 °C when compared at similar conversions due to higher dehydration rates over the zeolite. Processing ketones at low temperatures over bifunctional catalysts may be an efficient means of obtaining high yields of stable paraffins from reactive oxygenates.     

CO hydrogenation on Co/γ-Al2O3 and CoRe/γ-Al2O3 studied by SSITKA

Co/γ-Al₂O₃ and CoRe/γ-Al₂O₃ catalysts have been studied by the steady-state isotopic transient kinetic analysis (SSITKA) technique. It was found that neither the CO partial pressure, the temperature nor the space velocity influences the in situ CO adsorption. The space velocity, H₂/CO ratio and temperature was found to affect the intrinsic activity ( ) slightly, while the total pressure and syngas partial pressure had only a negligible effect. The surface concentrations and coverages were, however, unaffected by the space velocity, temperature, total pressure, syngas partial pressure and H₂/CO ratio. All changes, however, affected the methane selectivity, indicating that the methane selectivity was not a function of the surface inventory of methane precursors.     

O3/TiO2/γ-Al2O/UV降解草酸

采用臭氧与TiO2/γ-Al2O/UVV联用技术对降解草酸进行研究。考察了进气流量、草酸初始浓度、催化剂投加量、pH值及温度等因素对草酸降解的影响。研究表明,在一定范围内,随着进气流量的增加、温度的升高都会促使草酸的降解速率加快;溶液pH值对催化臭氧化有比较重要的影响,pH值2时,草酸的去除率最高。     

Complete oxidation of formaldehyde at ambient temperature over γ-Al2O3 supported Au catalyst

Au supported on γ-Al₂O₃ prepared by deposition–precipitation (DP) using urea is found to be a highly active catalyst for the total oxidation of HCHO at room temperature under humid air, without the need for a reducible oxide as support. In-situ DRIFTS studies suggested that the surface hydroxyl groups played a key role in the partial oxidation of HCHO into the formate intermediates, which can be further oxidized into CO₂ and H₂O with participation of nano-Au. This study challenges the traditional idea of supporting noble metals on reducible oxides for HCHO oxidation at room temperature.     

NiMoNx/γ-Al2O3 catalyst for HDN of pyridine

A series of NiMoN_x/γ-Al₂O₃ catalysts with various Ni contents were prepared by a topotactic reaction between their corresponding precursors NiO·MoO₃/γ-Al₂O₃ and NH₃. The catalysts were characterized using BET, XRD, and H₂-TPR techniques, and the HDN activity of pyridine over these catalysts was tested. XRD patterns show that metallic Ni, Mo₂N and a new phase of Ni₃Mo₃N exist in NiMoN_x/γ-Al₂O₃ catalyst. H₂-TPR studies indicate that the presence of Ni lowers the reduction temperature of the passivated surface layer of nitrided Mo/γ-Al₂O₃. The HDN activity for NiMoN_x/γ-Al₂O₃ is much higher than that for NiMoS_x/γ-Al₂O₃. The nitride catalyst with about 5.0 wt% NiO and 15.0 wt% MoO₃ in its precursor has the highest specific denitrogenation activity. The appearance of Ni₃Mo₃N and the synergy between metallic Ni and nitrided Mo are probably responsible for the high activity of NiMoN_x/γ-Al₂O₃ catalyst. The role of Ni in HDN reaction was also investigated. The activities decrease in the order: reduced Ni/γ-Al₂O₃≥nitrided Ni/γ-Al₂O₃>partially reduced Ni/γ-Al₂O₃ and sulfided Ni/γ-Al₂O₃.     

肉桂醛在γ-Al2O3、La2O3和La2O3/γ-Al2O3表面吸附的红外光谱分析

利用傅立叶变换红外光谱,研究真空条件(87.78 kPa,353 K)下肉桂醛在γ-Al2O3、La2O3和La2O3/γ-Al2O3样品表面的吸附情况,并根据文献归属了肉桂醛吸附在这些氧化物表面的红外吸收峰.结果表明,肉桂醛在氧化物表面产生多部位吸附.吸附在La2O3/γ-Al2O3样品的肉桂醛分子的1 496 cm...     

VOCs催化燃烧催化剂Mn/γ-Al2O3和CuMn/γ-Al2O3的性能研究

用浸渍法制备了两种负载型的Mn/g -Al2O3和Cu-Mn/g-Al2O3复合氧化物催化剂,同时用共沉淀法制备了Cu-Mn-O复合氧化物催化剂。以气相色谱为检测手段,用常压气体流动评价装置考察了这三种催化剂对苯、甲苯、二甲苯等挥发性有机化合物VOCs的催化燃烧性能。发现负载型的催化剂转化率达到99%时的反应温度比非负载型的降低30~40C,其中Cu-Mn/g-Al2O3催化剂具有更好的低温活性,催化燃烧反应的速率明显提高。负载型催化剂表面的活性组分以高度分散状态存在和催化剂高的比表面积是性能好的主要原因。     

Catalytic formation of carbonyl sulfide during warm gas clean-up of simulated coal-derived fuel gas with Pd/γ-Al2O3 sorbents

Coal gasification processes, such as the Integrated Gasification Combined Cycle (IGCC), will increase in importance due to the expanding concern over CO₂ emissions and global climate change. During the development of a Pd/γ-Al₂O₃ sorbent for warm (200 °C) fuel gas cleanup, the catalytic formation of carbonyl sulfide (COS), was observed. This is attributed to a heterogeneous reaction involving fuel gas components (CO/CO₂/H₂/H₂S/H₂O) and Pd/γ-Al₂O₃. The concentration of COS increases 200-fold when exposed to the Pd/γ-Al₂O₃ sorbent. A Langmuir–Hinshelwood reaction mechanism is proposed and a kinetic model is developed based on experimental results. The effect of γ-Al₂O₃, a common catalyst for hydrolysis of COS, and H₂O on the COS concentration is discussed.