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.     

La-promoted Ni/γ-Al2O3 catalyst for autothermal reforming of methane

Autothermal reforming (ATR) of methane over the synthesized catalysts of 10Ni-2La/γ-Al₂O₃, 10Ni-2Ce/γ-Al₂O₃, 10Ni-2Co/γ-Al₂O₃ was investigated in the temperature range of 600-800 oC for the hydrogen production. The sequence of 2 wt% metal loading on nickel alumina support in relation to their catalytic performance was observed as La>Ce>Co. The excellent activity and selectivity of 10Ni-2La/γ-Al₂O₃ was superior to other catalysts owing to little carbon deposition (~2.23 mg coke/gcath), high surface area and good dispersion and stability in the alumina support. The reforming of methane was inferred to be initiated by the decomposition of hydrocarbon at the inlet zone, preceded by the reforming reactions in the catalyst bed. Our result shows that it can be possible to achieve the H₂/CO ratio optimal to the GTL processes by controlling the O₂/CH₄ ratio of the feed inlet. The addition of oxygen to the feed inlet enhanced conversion efficiency substantially; probably, it favors the re-oxidation of carbonaceous residues formed over the catalyst surfaces, avoiding the catalyst deactivation and hence promoting catalyst stability.     

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.     

Macroporous Monolithic Pt/γ-Al2O3 and K–Pt/γ-Al2O3 Catalysts Used for Preferential Oxidation of CO

Macro-porous monolithic γ-Al₂O₃ was prepared by using macro-porous polystyrene monolith foam as the template and alumina sol as the precursor. Platinum and potassium were loaded on the support by impregnation method. TG, XRD, N₂ adsorption–desorption, SEM, TEM, and TPR techniques were used for catalysts characterization, and the catalytic performance of macro-porous monolithic Pt/γ-Al₂O₃ and K–Pt/γ-Al₂O₃ catalysts were tested in hydrogen-rich stream for CO preferential oxidation (CO-PROX). SEM images show that the macropores in the macro-porous monolithic γ-Al₂O₃ are interconnected with the pore size in the range of 10 to 50 μm, and the monoliths possess hierarchical macro-meso(micro)-porous structure. The macro-porous monolithic catalysts, although they are less active intrinsically than the particle ones, exhibit higher CO conversion and higher O₂ to CO oxidation selectivity than particle catalysts at high reaction temperatures, which is proposed to be owing to its hierarchical macro-meso(micro) -porous structure. Adding potassium lead to marked improvement of the catalytic performance, owing to intrinsic activity and platinum dispersion increase resulted from K-doping. CO in hydrogen-rich gases can be removed to 10 ppm over monolithic K–Pt/γ-Al₂O₃ by CO-PROX.     

Preparation of Pd/γ-Al2O3/nickel foam monolithic catalyst and its performance for selective hydrogenation in a rotating packed bed reactor

Selective hydrogenation plays an important role in chemical industries,yet its selectivity is usually lim-ited by the mass transfer.In this work,the enhanced hydrogenation selectivity was achieved in a rotating packed bed (RPB) reactor with excellent mass transfer efficiency.Aiming to be used under the centrifugal filed,a monolithic catalyst Pd/γ-Al2O3/nickel foam suiting for the shape and size of the rotor of RPB reac-tor was prepared by the electrophoretic deposition method.The mechanical strength of the catalyst can meet the requirement of high centrifugal force in the RPB.The hydrogenation selectivity in the RPB reac-tor using the 3-methyl-1-pentyn-3-ol hydrogenation system was 3-8 times higher than that in a stirred tank reactor under similar conditions.This work proves the feasibility of intensifying the selectivity of hydrogenation process in the RPB reactor.     

Catalytic Oxygen Removal from Synthetic Coke Oven Gas: A Comparison of Sulfided CoMo/γ-Al2O3 and NiMo/γ-Al2O3 Catalysts with Pt/γ-Al2O3 as Benchmark Catalyst

For the oxygen removal from coke oven gas (COG) the catalytic activity of commercial catalysts CoMo/γ-Al₂O₃ and NiMo/γ-Al₂O₃ was evaluated after a sulfidation pretreatment and compared to the Pt/γ-Al₂O₃ reference catalyst. Elemental analysis and temperature-programmed desorption showed that the oxidation reaction and the associated oxidation of active sulfidic centers is the main cause of deactivation despite the presence of other reductants, such as hydrogen. This approach could allow an appropriate sulfide catalyst to be designed for oxygen removal corresponding to the typical COG composition in the presence of H₂S.     

The possibility of supercritical fluid regeneration for Pt-Re/γ-Al2O3 industrial reforming catalyst in O3/CO2 mixtures

This work continues a cycle of studies aimed at developing new approaches to the regeneration of coked bimetallic heterogeneous catalysts. The activities of three Ru-125 (Pt-Re/γ-Al₂O₃) industrial reforming catalyst samples (fresh catalyst (A), catalyst removed from an industrial reactor (B), and sample B after treating it with ozone in supercritical carbon dioxide (SC-CO₂) (C)) are been compared in the reforming of n-heptane. It is established that sample B is deactivated appreciably: the conversion of n-heptane and the yield of reforming products are generally much lower than on the fresh catalyst. After treating it with an O₃/SC-CO₂ mixture, the conversion of n-heptane not only returns to the level of fresh sample A, but also exceeds it by a factor of 1.2. The qualitative composition of the products obtained on samples A, B, and C is nearly the same, but there are some changes in the quantitative ratio of certain products. Regeneration with ozone is found to be promising for further development and scaling.     

Milliseconds steam reforming of methane using Rh/MgO/γ-Al2O3 catalyst

采用负载型Rh/MgO/γ-Al₂O₃催化剂研究了毫秒级甲烷蒸汽重整过程,在水碳比为1和3的条件下,详细考察了反应温度、空速和催化剂Rh含量对反应转化率和选择性的影响。研究结果表明,Rh/MgO/γ-Al₂O₃催化剂在毫秒级操作条件下具有良好的催化性能,使用5%（质量分数）Rh催化剂,在水碳比3、反应温度1150 K、空速641.11 L•（g cat）^-1•h^-1时,CH₄转化率约90%,CO₂选择性约20%,毫秒级接触时间反应行为即可接近热力学平衡。高温有利于毫秒级甲烷蒸汽重整过程。     

Preparation of solid acid catalyst SO42−/TiO2/γ-Al2O3 for esterification: A study on catalytic reaction mechanism and kinetics

In this work, a series of SO₄^2-/TiO₂/γ-Al₂O₃ solid acid catalysts were synthesized by impregnation method, in which nano-TiO₂ was prepared by sol-gel method, and then the nano-TiO₂ sol was loaded on porous γ-Al₂O₃ supporter through impregnation. The structure and property of catalyst were characterized by XRD, N₂-BET, SEM, TEM, XPS, NH₃-TPD, Pyridine-IR and FT-IR. In addition, the catalyst of chelate bidentate coordination acid center model was established. The catalytic performance test was carried out in the esterification of n-butyl alcohol with lauric acid and the catalyst showed excellent activity. The experimental results showed that the medium strength acid sites were more dominant active sites than the strong and weak acid sites for the rapid esterification reaction. Its kinetic behaviors and activation energy were studied for the esterification under the catalytic reaction condition.     

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.     

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.     

Catalytic activity and characterization of V2O5/γ-Al2O3 for ammoxidation of m-xylene system

An ammoxidation of m-xylene was evaluated in a fixed-bed reactor using V₂O₅ on various oxides. Catalysts were prepared by wet impregnation method. At first, the loading of V₂O₅ was varied from 5 wt% to 20 wt% on γ-Al₂O₃ support to estimate the most effective amount of V₂O₅. Second, the effect of catalyst supports was examined at 10 wt% loading of V₂O₅. V₂O₅/TiO₂ and V₂O₅/SiO₂ catalysts were employed to compare the ammoxidation reaction with V₂O₅/γ-Al₂O₃. Most catalytic activity was observed when γ-Al₂O₃ was used as a support. Careful characterization was followed by physicochemical techniques, such as BET measurement, X-ray diffraction (XRD), Raman spectroscopy and temperature-programmed reduction (TPR). The results provided the clue that monolayer V₂O₅ was favorably dispersed on the surface of γ-Al₂O₃ up to 10 wt%, which led to the highest yield of isophthalonitrile (IPN).     

Catalytic steam reforming of biomass-derived tar for hydrogen production with K2CO3/NiO/γ-Al2O3 catalyst

A major problem of using Ni-based catalysts is deactivation during catalytic cracking and reforming, lowering catalytic performance of the catalysts. Modification of catalyst with alkali-loading was expected to help reduce coke formation, which is a cause of the deactivation. This paper investigated the effects of alkali-loading to aluminasupported Ni catalyst on catalytic performance in steam reforming of biomass-derived tar. Rice husk and K₂CO₃ were employed as the biomass feedstock and the alkali, respectively. The catalysts were prepared by a wet impregnation method with γ-Al₂O₃ as a support. A drop-tube fixed bed reactor was used to produce tar from biomass in a pyrolysis zone incorporated with a steam reforming zone. The result indicated that K₂CO₃/NiO/γ-Al₂O₃ is more efficient for steam reforming of tar released from rice husk than NiO/γ-Al₂O₃ in terms of carbon conversion and particularly hydrogen production. Effects of reaction temperature and steam concentration were examined. The optimum temperature was found to be approximately 1,073 K. An increase in steam concentration contributed to more tar reduction. In addition, the K₂CO₃-promoted NiO/γ-Al₂O₃ was found to have superior stability due to lower catalyst deactivation.     

Effects of pretreatment atmospheres on the catalytic performance of Pd/γ-Al2O3 catalyst in benzene degradation

In the current paper, a strategy for catalytic degradation of benzene over Pd/γ-Al₂O₃ catalysts via different atmospheres (H₂, N₂, He and air) pretreatment was carried out in a fixed bed reactor. The experimental results indicated that H₂, N₂, and He pretreatments have a significant positive effect on the initial activity of the catalyst compared to air. We have also investigated the effects of pretreatment atmospheres on the catalytic performance for benzene degradation through the information on the chemical state and crystal structure of the catalysts using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and CO chemisorption measurements techniques. The chemical state of Pd species decreased via H₂ pretreatment, leading to the increase of the initial catalytic activity, while chemical state increased accompanying with a decrease in degradation benzene via air pretreatment. There is no change in the chemical state of Pd species using inert atmosphere (N₂ and/or He) pretreatment, but the initial activity of the catalyst improved significantly due to the modified crystal structure of Pd species in the catalysts, with the crystalline PdO being transformed to amorphous state.     

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.     

Hydrodesulfurization and hydrogenation of aromatic compounds catalyzed by Ni-Mo/γ-Al2O3: effects of nickel sulfide and vanadium sulfide deposits

A standard Ni-Mo/-Al₂O₃ catalyst containing 4 wt% Ni was modified by addition of nickel (2 wt%) and, alternatively, of vanadium (4 wt%) by contacting with a solution of the respective metal naphthenate. The catalysts were sulfided and tested in a batch reactor at 350°C and 165 bar for hydrogenation of naphthalene and for hydroprocessing of dibenzothiophene. Reaction networks were determined for each reactant, and the dependence of the pseudo firs-torder rate constants on the amount of nickel and of vanadium in the catalyst was used to determine the effects of nickel sulfide and of vanadium sulfide deposits on catalyst performance. For example, the nickel sulfide deposits only slightly affected the rate constants for hydrogenation in either network, but the vanadium sulfide deposits led to a decrease of at most 50% in the rate constants for hydrogenation reactions in the naphthalene network and to a doubling of the rate constants for hydrogenation reactions in the dibenzothiophene network. The nickel sulfide deposits led to almost no change in the rate constant for hydrogenolysis of dibenzothiophene (to give biphenyl), but the vanadium sulfide deposits led to a threefold decrease in the rate constant for this reaction. The nickel sulfide deposits have little activity for reactions giving lower-molecular-weight (cracking) products, but the vanadium sulfide deposits have a relatively high activity for cracking, which suggests that they are acidic. The effects of the deposits are complex, as they both block catalytic sites and form new ones. The results indicate a need for representing the nickel and sulfide deposits separately in process models for heavy oil hydroprocessing.     

Hydrogen–deuterium isotope effects in the reactions of chlorobenzene and benzene on a Pt/γ-Al2O3 catalyst

The kinetic isotope effect for combustion of a C₆H₅Cl/C₆D₅Cl mixture on Pt/-Al₂O₃ was found to be close to unity between 520 and 580 K. However, in the presence of an excess of heptane, an isotope effect of 1.5 was found between 460 and 490 K. For the combustion of a C₆H₆/C₆D₆ mixture the k_H/k_D value was around 2 between 404 and 439 K. The results show that in the combustion of chlorobenzene per se, C–H bond activation is not a rate-determining step. On Pt sites, C–Cl bond scission probably occurs already at low temperatures. The chlorine and the phenyl group cannot easily react further. Chlorine on the surface is active in chlorination, which is shown by the formation of C₆D₅Cl in an experiment with C₆H₅Cl and C₆D₆. Only at a certain temperature is the chlorine removed, partly as polychlorinated benzenes. The removal of chlorine from the catalyst allows oxygen to take part in the reaction, which determines the rate of the combustion of chlorobenzene. When heptane is present, Cl is removed from the surface and C–H bond scission can become rate determining, as is also the case in the combustion of C₆H₆/C₆D₆. Upon (partial) combustion of C₆H₅Cl/C₆D₅Cl and C₆H₆/C₆D₆ mixtures on a Pt/-Al₂O₃ catalyst, hydrogen–deuterium exchange occurs on the -Al₂O₃ support.     

Improved activity of Pt/γ-Al2O3 catalysts for CH4O2 reaction under lean conditions due to sulfation and catalyst loading

The catalytic oxidation of low concentration of methane (2000 ppmV) in excess oxygen was investigated over unsulfated and pre-sulfated Pt/γ-Al₂O₃ catalysts. Over unsulfated samples, catalyst activity increased slightly with Pt concentration and with catalyst loading in the reactor. This enhancement was stronger over pre-sulfated catalyst relative to unsulfated samples. The results suggest that the new catalytic sites generated during sulfation (formed by the interaction between surface support sulfates and highly oxidized Pt atom at the edge of the platinum particle) may activate the almost non-polar C–H bonds of methane through a dissociate adsorption of CH₄, thus the increase in the sulfated catalyst loading results in the increase in the number of the catalytic sites generated during sulfation. The probability of the initial C–H activation of CH₄ increases and may lead to the observed increase in the oxidation rate for CH₄O₂ reaction.     

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.     

Active Sites of a NiSO4/γ-Al2O3 Catalyst for the Oligomerization of Isobutene

Structural characterization, the mechanism of catalytic activity generation and the nature of active sites of a NiSO₄/γ-Al₂O₃ catalyst for isobutene oligomerization were studied by temperature programmed reduction (TPR), X-ray diffraction (XRD), diffuse reflectance infrared fourier transformed (DRIFTS) and X-ray photoelectron spectroscopy (XPS) techniques. The TPR measurements together with the XRD data indicated that calcination of the catalyst at 500 °C did not form either nickel oxide or nickel aluminate. The presence of only one type of surface nickel species formed by the incorporation of nickel ions into the surface vacant sites of γ-alumina lattice was indicated by XPS with Ar⁺ ions sputtering and TPR measurements. XPS analysis of the calcined catalyst suggested that the oxidation state of nickel ions in the calcined catalyst was (+2) and after calcination the nickel ions were coordinated to relatively more basic ligands. The surface acid centers of the catalyst were found to be only Lewis type. SO₄ ^2? ions were found to be present as a chelating bidentate ligand and enhanced the acidity of metal ( $ {\text{Al}}^{3 + } $ and/or $ {\text{Ni}}^{2 + } $ ) Lewis acid centers. The results suggested that the combined effects of the presence of the bidentate SO₄ ^2? ligand and dehydroxylation generate coordinatively unsaturated $ {\text{Ni}}^{2 + } $ that interact with isobutene during the oligomerization reaction. The formation of lower-valent nickel ions ( $ {\text{Ni}}^{x + } ,x\; \le\; 1 $ ) was demonstrated by in situ DRIFTS using CO as a probe molecule and by XPS measurements. Formation of a binuclear bridging carbonyl complex, $ [{\text{Ni}}({\text{CO}})^{ + } ]_{2} $ suggested that some lower-valent nickel species were formed via in situ reduction by isobutene. Analysis of Ni 2p photolines indicated the appearance of a new lower-valent nickel species ( $ {\text{Ni}}^{x + } ,x \;\le\; 1 $ ) during the course of isobutene oligomerization. Hence it is plausible that lower-valent nickel species might act as the active center for the oligomerization reaction, while the SO₄ ^2? ions enhance the acidity of the Lewis acid sites on the surface and assist in the adsorption of reactant molecules on the surface.