Composition of Pd-La/α-Al2O3 catalysts

The objective of this study is to investigate the structure of the Pd-La/-Al₂O₃ catalyst. X-ray diffraction (XRD) and temperature-programmed reduction (TPRd) were used as characterization techniques. Contrary to the assertions in the literature, XRD studies conducted on La/-Al₂O₃ composite oxides and Pd-La/-Al₂O₃ catalysts show that Pd catalyzes the solid state reaction between A1₂O₃ and Al₂O₃ to form LaAlO₃. TPRd studies conducted on Pd/-Al₂O₃, Pd/La₂O₃, Pd/LaAlO₃, and Pd-La/-Al₂O₃ catalysts suggest that Pd in the Pd-La/-Al₂O₃ catalyst interacts more strongly with LaAlO₃ than with -Al₂O₃. Reaction studies were conducted to investigate the activity of Pd/-Al₂O₃, Pd/La₂O₃, Pd/LaA10₃, and Pd-La/-Al₂O₃ catalysts for nitric oxide (NO) reduction. These studies show that Pd/LaAlO₃ catalysts are most active for NO removal at stoichiometric and under net reducing conditions.     

Effect of Ce addition on Cr/γ-Al2O3 catalysts for methane catalytic combustion

Cerium modified and chromium-based catalysts using nano-γ-Al₂O₃ as the carrier were prepared via incipient wetness impregnation method and investigated for the catalytic combustion of methane (CH₄). The Cr-based catalysts promoted with 3 wt.% Ce displayed the most effective catalytic activity among all catalysts investigated. In addition, Ce significantly improved the catalytic performance of CH₄ combustion by increasing the amount of reaction site [CrO₄]_ads species on the surface of Cr-based catalysts. Introduction of Ce content also restrained the deactivation of catalysts at high calcination temperature. Cr-based catalysts modified with cerium seem to be a promising cheap and low-temperature catalyst for CH₄ combustion.     

An EXAFS study on oxidic and sulfided K-MoO3/γ-Al2O3 catalysts

By analyzing the extended X-ray absorption fine structure (EXAFS) of the Mo K-absorption edge, structural information for both oxidic and sulfided K-MoO₃/-Al₂O₃ catalysts with different potassium content was obtained. The oxidic samples show two backscatterer peaks in the radial distribution function (RDF), which correspond to the Mo-O coordinations in the nearest Mo-O shell. The nearest oxygen atoms are present with large configurational disorder. The RDF for the K/Mo = 0 sample is significantly different from that for crystalline MoO₃ and ammonium heptamolybdate. The RDFs for potassium promoted samples are, in some extent, similar to that for ammonium heptamolybdate. The sample with K/Mo = 0.8 and that with K/Mo=1.5 do not show obvious difference in their local Mo-O structures. The EXAFS results support the earlier conclusions from Raman spectroscopy studies on identical samples [7]. When the samples are sulfided, a rearrangement of the local neighbors around Mo atoms takes place, to form small MoS₂-like crystallites. The Mo-S and Mo-Mo coordination distances on these catalysts are the same as those in crystalline MoS₂, but the coordination numbers are significantly lower than in MoS₂. The EXAFS results indicate that Mo species on the K/Mo=0 catalyst mainly consist of Mo-S-Mo units (the basic building units of MoS₂), which are highly dispersed and show a higher level of disorder than in MoS₂. With the modification by the potassium promoter, Mo species are significantly aggregated and their local neighbors are more similar to those in MoS₂, but the Mo species still exist in a state of high dispersion.     

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.     

Strong improvement on CH4 oxidation over Pt/γ-Al2O3 catalysts

A very strong promotion effect of the presence of 1000 ppmV C₃H₈ in the reaction feed on CH₄–O₂ reaction was found over unsulfated 1%Pt/γ-Al₂O₃ catalyst. This promotion was further increased on pre-sulfated 1%Pt/γ-Al₂O₃. The promoting effect of pre-sulfation on the activity of 1%Pt/γ-Al₂O₃ for propane combustion results in a further improvement on methane combustion due to propane combustion heat which is generated at lower temperatures, activating methane combustion over pre-sulfated 1%Pt/γ-Al₂O₃ at even lower temperatures relative to unsulfated 1%Pt/γ-Al₂O₃. These results suggest that small amounts of propane in the gas feed during CH₄–O₂ reaction over a pre-sulfated Pt/γ-Al₂O₃ catalyst may eliminate methane emissions at low temperatures from lean-burn NGV exhausts without being deactivated by sulfur poisoning as Pd supported catalysts.     

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.     

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.     

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.     

Tuning product selectivity of CO2 hydrogenation by OH groups on Pt/γ-AlOOH and Pt/γ-Al2O3 catalysts

Herein, we explore how OH groups on Pt/γ-AlOOH and Pt/γ-Al₂O₃ catalysts affect CO₂ hydrogenation with H₂ at temperatures from 250°C to 400°C. OH groups are abundant on γ-AlOOH, but rare at Pt-(γ-AlOOH) interface which is the most favorable site for CO₂ conversion on Pt/γ-AlOOH. This makes CO₂ hydrogenation on Pt/γ-AlOOH form CO weakly bonding to γ-AlOOH, which prefers to desorption from Pt/γ-AlOOH rather than further conversion, thus enhancing CO production on Pt/γ-AlOOH. Different from Pt/γ-AlOOH, OH groups are abundant at Pt-(γ-Al₂O₃) interface which is the most favorable site for CO₂ conversion on Pt/γ-Al₂O₃. This promotes CO₂ hydrogenation on Pt/γ-Al₂O₃ to form CO strongly bonding to Pt, which prefers to further hydrogenation to CH₄, and thereby increases CH₄ selectivity on Pt/γ-Al₂O₃. Therefore, the OH groups at metal-support interface are crucial factor influencing product distribution, and must be considered seriously when fabricating catalysts.     

The effect of the Ce content on the oxidative dehydrogenation of propane over CrOy-CeO2/γ-Al2O3 catalysts

A series of CrO_y (17.5 wt%)-CeO₂ (X wt%)/γ-Al₂O₃ catalysts (X = 0, 0.5, 2, 5, 8) with various Ce contents were prepared by a wetness impregnation method and were applied to the dehydrogenation of propane to propylene at 550 °C and 0.1 MPa. The prepared catalysts were characterized by BET, H₂-TPR, O₂-TPD, XPS, XRD, SEM-EDS and Raman spectroscopy. Among the prepared catalysts, the 17.5Cr-2Ce/Al catalyst with the largest amount of lattice oxygen exhibited the best catalytic performance for the dehydrogenation of propane to propylene with lattice oxygen. The decreased presence of oxygen defects and reducibility were the factors responsible for the improved dehydrogenation activity of the catalysts. The CeO₂ layer could inhibit the evolution of lattice oxygen (O²⁻) to electrophilic oxygen species (O₂⁻), and the oxygen defects on the catalyst surface were reduced. The inhibited lattice oxygen evolution prevented the deep oxidation of propane or propylene, the average CO_x selectivity decreased from 24.41% (17.5Cr/Al) to 5.71% (17.5Cr-2Ce/Al), and the average propylene selectivity increased from 60.15% (17.5Cr/Al) to 85.05% (17.5Cr-2Ce/Al).     

The effect of the Ce content on the oxidative dehydrogenation of propane over CrOy-CeO2/γ-Al2O3 catalysts

A series of CrO_y (17.5 wt%)-CeO₂ (X wt%)/γ-Al₂O₃ catalysts (X=0, 0.5, 2, 5, 8) with various Ce contents were prepared by a wetness impregnation method and were applied to the dehydrogenation of propane to propylene at 550℃ and 0.1 MPa. The prepared catalysts were characterized by BET, H₂-TPR, O₂-TPD, XPS, XRD, SEM-EDS and Raman spectroscopy. Among the prepared catalysts, the 17.5Cr-2Ce/Al catalyst with the largest amount of lattice oxygen exhibited the best catalytic performance for the dehydrogenation of propane to propylene with lattice oxygen. The decreased presence of oxygen defects and reducibility were the factors responsible for the improved dehydrogenation activity of the catalysts. The CeO₂ layer could inhibit the evolution of lattice oxygen (O^2-) to electrophilic oxygen species (O₂^-), and the oxygen defects on the catalyst surface were reduced. The inhibited lattice oxygen evolution prevented the deep oxidation of propane or propylene, the average CO_x selectivity decreased from 24.41% (17.5Cr/Al) to 5.71% (17.5Cr-2Ce/Al), and the average propylene selectivity increased from 60.15% (17.5Cr/Al) to 85.05% (17.5Cr-2Ce/Al).     

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.     

Improving the dispersion of CeO2 on γ-Al2O3 to enhance the catalytic performances of CuO/CeO2/γ-Al2O3 catalysts for NO removal by CO

Acetic acid (HAc) aqueous was used as solvent in wetness impregnation to prepare CeO₂-modified γ-Al₂O₃ support. With the help of HAc, the dispersion of CeO₂ on γ-Al₂O₃ is significantly improved and the size of CeO₂ nanoparticles can be controlled through tuning the concentration of HAc aqueous. XPS analysis shows that the percentages of Ce^3 + in CeO₂ nanoparticles will vary with the size. Then we load CuO on the as-prepared CeO₂-modified γ-Al₂O₃ support and choose NO reduction with CO as a probe reaction to investigate the influences of impregnation solvent on the catalytic properties. The results demonstrate that the CuO/CeO₂/γ-Al₂O₃ prepared in the solvent with volume ratio of 20:1 (H₂O:HAc) has the highest activity in NO + CO reaction. Combing the structural characterizations and catalytic performances, we think that the size of the CeO₂ nanoparticles should be a key factor that affects the activities of CuO/CeO₂/γ-Al₂O₃. Furthermore, CuO dispersed on CeO₂ nanoparticles with an average size of ca. 5 nm should be the highest active sites for NO + CO reaction.     

Reduction of NO by H2 on PdO-MoO3/γ-Al2O3 of low molybdena loading

The catalytic activity and selectivity of three PdO-MoO₃/-Al₂O₃ catalysts containing about 2% Pd and 2% Mo were studied for the reduction of NO by h₂ in the presence of varying amounts of oxygen at temperatures from 50 to 550 °C. The results are compared with those for PdO/-Al₂O₃, PdO-MoO₃/-Al₂O₃ containing 2% Pd and 20% Mo, and a commercial Pt-Rh catalyst. In the absence of oxygen, the conversion of NO to N₂ and N₂O is higher on the three catalysts than it is on PdO/-Al₂O₃ at 500 and 550 °C. In the presence of oxygen, the yields of N₂ and N₂O are generally lower on two of the PdO-MoO₃/-Al₂O₃ catalysts than on PdO/-Al₂O₃.     

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.     

Influence of Catalyst Pretreatments on Propane Oxidation Over Ru/γ-Al2O3

The influence of different treatments (in H₂ or in O₂ at 250 or 600 °C) of alumina supported Ru catalysts on the total oxidation of propane was investigated. Ruthenium catalysts were prepared using RuCl₃ as metal precursor and characterized by H₂ chemisorption, O₂ uptake, BET, XRD and TEM. The presence of chloride on the catalyst surface was found to exert an inhibiting effect on the activity of Ru. The reduced Ru/γ-Al₂O₃ catalysts after partial removing chlorine ions were more active than the same samples oxidized at 250 °C. The higher activity of the reduced Ru/γ-Al₂O₃ catalysts was attributed to the presence of a large amount of active sites on small Ru _x O _y clusters without well defined stoichiometry or on a poorly ordered layer of a ruthenium oxide on the larger Ru particles. The formation of highly dispersed, but in some extent crystallized RuO₂ phase in catalysts oxidized at 250 °C, leads to slightly lower activity of the Ru phase. Strong decline of the activity was found for catalysts oxidized at 600 °C. At this temperature, the Ru particles were completely oxidized to well-crystallized RuO₂ oxide, and the mean crystallite size of the Ru oxide phase was much higher (9–25 nm) than that of after oxidation at 250 °C (~4 nm). The effect of the regeneration treatment in H₂ on the activity of the Ru/γ-Al₂O₃ catalysts was also studied. The active ruthenium species for propane oxidation were discussed based on the catalytic and characterization data both before and after activity tests.     

The effect of the addition of Y2O3 to Ni/α-Al2O3 catalysts on the autothermal reforming of methane

The addition of Y₂O₃ to Ni/α-Al₂O₃ catalysts was investigated by BET surface area measurements, hydrogen chemisorption, X-ray diffraction, UV–vis diffuse reflectance spectroscopy, X-ray fluorescence, temperature programmed reduction, temperature programmed oxidation and cyclohexane dehydrogenation. Autothermal reforming experiments were performed in order to evaluate the methane conversion and proceeded through an indirect mechanism consisting of total combustion of methane followed by CO₂ and steam reforming generating the synthesis gas. The Y₂O₃·Al₂O₃ supported catalysts presented better activity and stability in autothermal reforming reaction. Temperature programmed oxidation analysis demonstrated that the addition of Y₂O₃ resulted in a change of the type or the location of coke formed during reaction. None of the prepared catalyst presented deactivation by sintering under the tested conditions. The improved stability of supported catalysts Y₂O₃·Al₂O₃ was the result of minimizing the formation of coke on the surface of nickel particles.     

Reduction of NO by CO on PdO-MoO3/γ-Al2O3 of low molybdena loading

The catalytic activity for the reduction of NO by CO of five PdO-MoO₃/-Al₂O₃ catalysts is compared in the presence of varying amounts of oxygen at reaction temperatures from 25 to 550 °C. The samples were prepared by different methods and contain about 2% of Mo and 2% Pd. Results are compared with the activities and selectivities of PdO/ -A1₂O₃ and PdO-MoO₃/-Al₂O₃ containing 2% Pd and 2% Pd + 20% Mo, respectively. All catalysts showed appreciable activity at temperatures between 300 and 550 °C and at stoichiometric ratios,R, of the oxidizing to reducing gases of 0.1 <R < 1.1. The activity of three PdO-MoO₃/ -A1₂O₃ catalysts with low concentrations of Mo and Pd was found to be significantly higher than the activity of PdO/-Al₂O₃ at 1.1 <R < 1.3 and at temperatures between 300 and 500 °C. The improved activity is ascribed to the interaction of the active metals.     

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。     

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.