Influence of Pd-Ce interaction and chlorine ion on hydrodesulfurization reaction: The activity and sulfur tolerance of the Pd-Ceo2/Al2O3 catalyst

CeO₂ promoted palladium catalysts supported on Al₂O₃ were prepared using the impregnation (IM) and the deposition-precipitation (DP) methods. The activities and sulfur tolerance of the catalysts for hydrodesulfurization (HDS) were detected with thiophene HDS as probe reaction. H₂ adsorption, XRD, FTIR, NH₃-TPD, XPS were used to characterize the catalysts. The Pd-CeO₂/Al₂O₃ (IM) catalyst was highly active for the HDS reaction, and it had much stronger sulfur tolerance than the Pd/Al₂O₃ catalyst. Pd-CeO₂/Al₂O₃ (DP) showed excellent sulfur tolerance while its initial activity decreased. It was observed that with the chlorine bridge, the interfacial structure of Pd-Cl⁻¹-Ce³⁺ was responsible for the high activity of the Pd-CeO₂/Al₂O₃ (IM) catalyst, at the same time the interaction of Pd with Ce was weakened by Cl₋₁ ions. The enhanced sulfur tolerance over the Pd-CeO₂/Al₂O₃ (IM) catalyst was attributed to the weakened Pd-S bond caused by the competitive adsorption of H₂S on Ce³⁺ ions. As to the Pd-CeO₂/Al₂O₃ (DP) catalyst, a strong interaction of Pd with Ce put Pd at an electron-deficient state, the creation of sulfided palladium was therefore inhibited.     

Effect of Transition Metals (Cu, Co and Fe) on the Autothermal Reforming of Methane over Ni/Ce0.2Zr0.1Al0.7Oδ Catalyst

The transition metals (Cu, Co, and Fe) were applied to modify Ni/Ce0.2Zr0.1 Al0.7Oδcatalyst. The effects of transition metals on the catalytic properties of Ni/Ce0.2Zr0.1 Al0.7Oδautothermal reforming of methane were investigated. The Ni-supported catalysts were characterized by XRD, TPR and XPS. Tests in autothermal reforming of methane to hydrogen showed that the addition of transition metals (Cu and Co) significantly increased the activity of catalyst under the conditions of lower reaction temperature, and Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδwas found to have the highest conversion of CH4 among all catalysts in the operation temperatures ranging from 923 K to 1023 K. TPR, XRD and XPS measurements indicated that the cubic phases of CexZr1-xO2 solid solution were formed in the preparation process of catalysts. Strong interaction was found to exist between NiO and CexZr1-xO2 solid solution. The addition of Cu improved the dispersion of NiO, inhibited the formation of NiAl2O4, and thus significantly promoted the activity of the catalyst Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδ.     

Effect of metals on the catalytic activity of sulfated zirconia for light naphtha isomerization

We studied on the function of the metal in the sulfated zirconia(SO₄^2–/ZrO₂) catalyst for the isomerization reaction of light paraffins. The addition of Pt to the SO₄^2–/ZrO₂ carrier could keep the high catalytic activity. The improvement in this isomerization activity is because Pt promotes removal of the coke precursor deposited on the catalyst surface. Though this catalytic function was observed in other transition metals, such as Pd, Ru, Ni, Rh and W, Pt exhibited the highest effect among them. It was further found that the Pd/SO₄^2–/ZrO₂–Al₂O₃ catalyst possessed a catalytic function for desulfurization of sulfur-containing light naphtha in addition to the skeletal isomerization. The sulfur tolerance of catalyst depended on the method of adding Pd, and the catalyst prepared by impregnation of the SO₄^2–/ZrO₂–Al₂O₃ with an aqueous solution of Pd exhibited the highest sulfur tolerance.Further, we investigated the improvement in sulfur tolerance of the Pt/SO₄^2–/ZrO₂–Al₂O₃ catalyst by impregnation of Pd. The results of EPMA analysis indicated that this catalyst was a hybrid-type one (Pt/SO₄^2–/ZrO₂–Pd/Al₂O₃) in which Pt/SO₄^2–/ZrO₂ particles and Pd/Al₂O₃ particles adjoined closely. This hybrid catalyst possessed a very high sulfur tolerance to the raw light naphtha that was obtained from the atmospheric distillation apparatus, although this light naphtha contained much sulfur. We assume that such a high sulfur tolerance in the hybrid catalyst is brought about by the isomerization function of Pt/SO₄^2–/ZrO₂ particles and the hydrodesulfurization function of Pd/Al₂O₃ particles. Besides, since the hybrid catalyst also provides high catalytic activity in the isomerization of HDS light naphtha, we suggest that the Pd/Al₂O₃ particles supply atomic hydrogen to the Pt/SO₄^2–/ZrO₂ particles by homolytic dissociation of gaseous hydrogen and also enhance the sulfur tolerance of Pt/SO₄^2–/ZrO₂ particles. Finally, we also propose the most suitable location of Pd and Pt in the metal-supported SO₄^2–/ZrO₂–Al₂O₃ catalyst.     

Catalytic oxidation of methane over Pd/Co3O4

The catalytic activity of Pd/Co₃O₄ toward methane oxidation has been examined in this study as a function of Pd loading, reaction temperature, space velocity and methane concentration in the reaction gas mixture. The bare oxide is quite active achieving a 100% methane conversion at 480°C under the reaction conditions used. The catalyst with the highest Pd loading tested of 10 wt.% yields the best activity curve, but the 5 wt.% Pd/Co₃O₄ catalyst performs nearly as well. Complete conversion for this catalyst is attained at 300°C and the activity remains stable over a 90-min test period.     

Thermal characterization of titania-modified alumina-supported palladium and catalytic properties for methane combustion

Thermal characterization of Pd/TiO₂-Al₂O₃ catalysts under oxygen or hydrogen atmosphere was investigated by means of thermogravimetry (TG), differential scanning calorimetry (DSC), temperature programmed reduction (TPR) and temperature programmed desorption (TPD). Further, the effects of titania on the catalytic property of Pd/Al₂O₃ towards methane combustion were also examined. A TG-DSC studies revealed that the heat evolved during oxygen adsorption at 25 °C depended on the crystallite diameter. TPR and TPD studies of oxidized samples also demonstrated that the coating of Pd/Al₂O₃ catalysts with titania can weaken the strength of the PdO bonds. Apparently the effect of coating Pd/Al₂O₃ catalyst with TiO₂ is the improvement of the methane combustion at lower temperatures. This is probably due to the decrease of the strength of the PdO bonds.     

Ni/Al2O3改性催化剂催化重整生物油模拟物制氢研究

制备了Ni/Al₂O₃、Ni-Cu/Al₂O₃、Ni-Co/Al₂O₃和Ni-Co-Cu/Al₂O₃催化剂,研究了Co和Cu对生物油水蒸气催化重整的影响。实验表明,Co 能促进水汽变换(WGS)反应,提高氢气的产率,Cu能抑制反应中焦炭的形成,提高催化剂的稳定性。对催化剂Ni-Co-Cu/Al₂O₃进行工艺条件考察,当900 ℃、水油比为6 g/g、质量空速(WHSV)为1 h^-1时,碳选择性达到87.5%,氢气产率达到84.2%,潜在氢气产率达到92.4%。     

焙烧温度对 Pd/Al2O3 催化剂上甲烷燃烧反应性能的影响

 考察了载体与催化剂焙烧温度对 Pd/Al2O3 催化剂上低浓度甲烷催化燃烧反应性能的影响. 采用 X 射线衍射、透射电镜、N2 物理吸附、NH3 程序升温脱附和 O2 程序升温氧化等手段对载体和催化剂进行了表征. 结果表明, 焙烧温度对催化剂活性及稳定性的影响显著. 随着载体焙烧温度的升高, Al2O3 的比表面积、物相结构、酸中心的数量及强度明显改变, 相应的 Pd/Al2O3 催化剂中载体与 Pd 的相互作用减弱, Pd 分散度降低. 当载体焙烧温度为 1 100 °C, Pd/Al2O3 焙烧温度为 200 °C 时, 所得催化剂在 260 h 的连续反应中, 甲烷转化率始终维持在 99%以上.     

PdCl2-CuCl2/Al2O3催化剂低温催化CO氧化的失活机理

采用X射线衍射、N₂吸-脱附、X射线光电子能谱分析、氢气-程序升温还原和原位红外漫反射等方法对新鲜和失活的PdCl₂-CuCl₂/Al₂O₃低温催化CO氧化催化剂进行表征,研究了高相对湿度(100%)下催化剂的失活机理.结果表明,催化剂表面沉积的水使得活性铜物种容易从催化剂表面向载体孔道内部迁移,由于Pd、Cu相互作用弱化从而减弱了Pd与Cu物种间的相互作用,使得催化剂的氧化还原性能受到影响,抑制了Pd⁰再氧化为Pd²⁺的过程,从而因CO氧化反应中催化剂氧化还原循环受阻而导致失活.     

Study of CO2 Hydrogenation to Methanol over Cu-V/γ-Al2O3 Catalyst

The effect of vanadium addition to CU/γ-Al2O3 catalyst used in the hydrogenation of CO2 to produce methanol was studied. It was found that the catalytic performance of the Cu-based catalyst improved after V addition. The influence of reaction temperature, space velocity and the molar ratio of H2 to CO2 on the performance of 12%Cu-6%V/γ-Al2O3 catalyst were also studied. The results indicated that the best conditions for reaction were as follows: 240℃, 3600 h-1 and a molar ratio of H2 to CO2 of 3:1. The results of XRD and TPR characterization demonstrated that the addition of V enhanced the dispersion of the supported CuO species, which resulted in the enhanced catalytic performance of CU-V/γ-Al2O3 binary catalyst.     

Catalytically Promoted NOx Sorption by ZrO2-Based Oxides

Metal promoted zirconia-based oxide sorbents, such as Pt–ZrO₂/Al₂O₃ for NO _x have been investigated. To clarify the role of the catalyst component, sorption of NO and NO₂ was compared using the samples with and without Pt. The catalytic oxidation of NO to NO₂ and successively to nitrate ions is an important role for the Pt catalyst. The experimental results indicate that a high-temperature calcination is essential to remove residual Cl from Pt–ZrO₂–Al₂O₃ prepared from H₂PtCl₆ in order to provide more active NO _x sorption sites. Of M–ZrO₂–Al₂O₃ samples investigated, ruthenium as well as Pt demonstrated relatively good performance as a catalyst component in the sorbent. The FT-IR spectra after sorption of NO and NO₂ demonstrated a strong band attributed to stored nitrate ions. The Pt catalyst was more resistant to sulfur poisoning than a base metal catalyst. However, the NO _x sorptive capacities of the Pt–ZrO₂/Al₂O₃ sorbents were expected to be deteriorated in dilute SO₂ as far as observed from FT-IR spectra.     

Promoting effect of Mg in supported Mo/HBeta–Al2O3 catalyst for cross-metathesis of ethene and butene-2 to propene

Promoting effects of Mg in heterogeneous Mo/HBeta–Al₂O₃ catalyst have been carefully studied for cross-metathesis of ethene and butene-2 to propene. The catalyst shows good stability with Mg content in the range of 1–2 wt%. Such effect may be attributed to the elimination of weak acid sites through introduction of Mg which suppresses the side olefin oligomerization reaction, as evidenced from NH₃-TPD and ¹H MAS NMR results. Addition of more Mg content to 3 wt% may change the state and reducibility of Mo species, as indicated from the UV–vis, UV-Raman and H₂-TPR measurements. The increasing difficulty for the reduction of Mo(VI) species is closely related with the poor performance of 3 wt% Mg–4Mo/HBeta–30% Al₂O₃ catalyst in the metathesis reaction.     

Reactions of small negative ions with O2(a Δg) and O2(X Σg)

The rate constants and product ion branching ratios were measured for the reactions of various small negative ions with O₂(X ³Σ_g⁻) and O₂(a ¹Δ_g) in a selected ion flow tube (SIFT). Only NH₂⁻ and CH₃O⁻ were found to react with O₂(X) and both reactions were slow. CH₃O⁻ reacted by hydride transfer, both with and without electron detachment. NH₂⁻ formed both OH⁻, as observed previously, and O₂⁻, the latter via endothermic charge transfer. A temperature study revealed a negative temperature dependence for the former channel and Arrhenius behavior for the endothermic channel, resulting in an overall rate constant with a minimum at 500 K. SF₆⁻, SF₄⁻, SO₃⁻ and CO₃⁻ were found to react with O₂(a ¹Δ_g) with rate constants less than 10⁻¹¹ cm³ s⁻¹. NH₂⁻ reacted rapidly with O₂(a ¹Δ_g) by charge transfer. The reactions of HO₂⁻ and SO₂⁻ proceeded moderately with competition between Penning detachment and charge transfer. SO₂⁻ produced a SO₄⁻ cluster product in 2% of reactions and HO₂⁻ produced O₃⁻ in 13% of the reactions. CH₃O⁻ proceeded essentially at the collision rate by hydride transfer, again both with and without electron detachment. These results show that charge transfer to O₂(a ¹Δ_g) occurs readily if the there are no restrictions on the ion beyond the reaction thermodynamics. The SO₂⁻ and HO₂⁻ reactions with O₂(a) are the only known reactions involving Penning detachment besides the reaction with O₂⁻ studied previously [R.S. Berry, Phys. Chem. Chem. Phys., 7 (2005) 289–290].     

Development of a Ni–Pd/CeZrO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst for the effective conversion of methane into hydrogen-containing gas

The effects of the Pd content (0–1 wt %) and the synthesis method (joint impregnation with Ni + Pd and Pd/Ni or Ni/Pd sequential impregnation) on the physicochemical and catalytic properties of Ni–Pd/CeZrO₂/Al₂O₃ were studied in order to develop an efficient catalyst for the conversion of methane into hydrogen-containing gas. It was shown that variation in the palladium content and a change in the method used for the introduction of an active constituent into the support matrix make it possible to regulate the redox properties of nickel cations but do not affect the size of NiO particles (14.0 ± 0.5 nm) and the phase composition of the catalyst ((γ + δ)-Al₂O₃, CeZrO₂ solid solution, and NiO). It was established that the activity of Ni–Pd catalysts in the reaction of autothermal methane reforming depends on the method of synthesis and increases in the following order: Ni + Pd < Ni/Pd < Pd/Ni. It was found that, as the Pd content of the Ni–Pd/CeZrO₂/Al₂O₃ catalyst was decreased from 1 to 0.05 wt %, the ability for self-activation, high activity, and operational stability of the catalyst under the conditions of autothermal methane reforming remained unaffected: at 850°C, the yield of hydrogen was ~70% at a methane conversion of ~100% during a 24-h reaction.     

超声改性的CuO/Al2O3-MgO催化剂结构 及其超低浓度甲烷催化燃烧性能

采用普通浸渍和超声改性的方法分别制备了CuO/Al₂O₃-MgO催化剂,用于超低浓度甲烷的催化燃烧,并利用SEM、XRD、XPS、H₂-TPR等技术对催化剂进行表征,研究了超声改性作用对催化剂的结构和性能的影响.结果表明,与普通浸渍法制备的催化剂相比,在超声改性的CuO/Al₂O₃-MgO催化剂上,甲烷的转化率得到提高,燃烧特征温度降低.随着超声时间的延长和超声功率的增加,催化剂的催化活性均呈现先增大后减小的趋势;催化剂制备的最佳超声工况为功率150 W、时间20 min.超声改性可使催化剂的比表面积和孔容积增大,表面催化活性较高的Cu⁺浓度增加,活性组分CuO由晶相向非晶相转变、分散度增大,晶粒粒径变小、分布更均匀;这使得甲烷催化燃烧的表观活化能下降、催化剂活性得到增强.     

Influence de certains ions inorganiques, de l'éthanol et du peroxyde d'hydrogène sur la photominéralisation du β-naphtol en présence de TiO2

TiO₂ photocatalytic mineralization of β-naphthol: influence of some inorganic ions, ethanol, and hydrogen peroxide. In this work, the photocatalytic oxidation of β-naphthol in aqueous suspensions of TiO₂ was investigated at room temperature, by following the formation of CO₂. The disappearance of β-naphthol fits a Langmuir-Hinshelwood kinetic model. The activation energy for the degradation reaction of β-naphthol is estimated at 10.2 kJ/mol. The effects of some additives such as ethanol, H₂O₂, and inorganic ions (Cl⁻, SO₄²⁻, HCO₃⁻, NO₃⁻, Fe³⁺, Cu^2+, and Cr³⁺) on the photomineralization of β-naphthol were examined. The inhibition of the anions for this reaction was in the order : NO₃⁻ < HCO₃⁻ < SO₄²⁻ < Cl⁻. This can be due to a partial blockage of catalyst active sites by these ions or their reaction with an oxidizing radical such as OH. The most photoactive systems for β-naphthol degradation were found in the presence of ferric ions, while the addition of Cr³⁺ strongly inhibited the photocatalytic decomposition of β-naphthol.     

Synthesis of dimethyl ether from methane mediated by HBr (Special column of methane transformation, Article)

Dimethyl ether (DME) was synthesized from methane through a two-step process, in which CH₃Br was prepared from the oxidative bromination reaction of methane in the presence of HBr and oxygen over a Rh-SiO₂ catalyst and then, in the second step, CH₃Br was hydrolyzed to DME over a silica supported metal chloride catalyst. 12 mol%ZnCl₂/SiO₂ catalyst was found to be the most active, but it deactivated because of Cl⁻ losing.     

组合型Pt3Sn/Al2O3催化剂用于芳香硝基化合物一锅法合成N-烷基芳胺

采用吸附法制备了组合型Pt₃Sn/Al₂O₃双金属催化剂, 将该催化剂用于芳香硝基化合物原位液相加氢一锅法合成N-烷基芳胺. 研究表明, 在503 K, 空速为7.5 h^-1, 水体积分数为5%时, 1%(质量分数)Pt₃Sn/Al₂O₃催化剂具有较高的催化性能, 硝基苯的转化率为100%, N-乙基苯胺和N,N-二乙基苯胺的总选择性为98.2%. 同时,该催化剂对原位液相加氢烷基化反应具有一定普适性, 本文研究的14 种芳香硝基化合物与低级脂肪醇反应,均具有较高的N-烷基化产率.     

The support and characterization of C60 and MoO3 on Al2O3

A new type of catalyst from supporting C₆₀ on MoO₃ and Al₂O₃ has been prepared. The effect of different order of impregnation and calcination atmosphere on catalyst are investigated by the solution test in toluene, UV-VIS spectroscopy and temperature programmed reduction (TPR). The results show that when the catalyst was prepared by supporting MoO₃ on C₆₀/Al₂O₃ and calcined in N₂, there is a stronger interaction between C₆₀, MoO₃ and Al₂O₃, but when supporting C₆₀ on MoO₃/Al₂O₃, the interaction is relatively weak. We consider that in the former method a new complex, Mo–C₆₀–O–Al, is formed.     

Catalytic properties of Pd supported on hexaaluminate coated alumina in low temperature combustion of coal mine ventilation air methane

Palladium supported on γ-Al₂O₃ has been demonstrated as most active catalyst for catalytic combustion of methane. However, the sintering of support and PdO seriously affects its activity. We prepared a composite Pd/hexaaluminate/Al₂O₃ catalyst and compared its catalytic activity as well as sintering behavior with Pd/Al₂O₃. This composite catalyst exhibits higher activity and better resistance to sintering. The effect of water vapor presented in feed has also been investigated.     

Effect of sol-gel derived Al2O3-ZrO2 and Al2O3-TiO2 oxides on the selectivity of NO reduction by CO under oxidizing conditions

The role of Al₂O₃-ZrO₂ and Al₂O₃-TiO₂ sol-gel prepared supports in the activity of platinum for the NO reduction by CO under oxidizing conditions has been studied. ²⁷Al MAS-NMR spectra have shown the formation of pentacoordinate Al^V in alumina-zirconia support. ZrO₂ or TiO₂ crystalline phases cannot be identified by XRD diffraction, suggesting the formation of nanosized structures supported on alumina. When the reaction was carried out in presence of oxygen, large amounts of NO₂ were observed on Pt/Al₂O₃-ZrO₂catalyst, while the formation of N₂O is more prononced on Pt/Al₂O₃-TiO₂ catalyst. The effect of water during NO reduction is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.