Kinetic dependences foro-xylene oxidation to phthalic anhydride over V?Ti?O catalysts

In accordance with structural data and numerical analysis of relaxation curves, a detailed scheme for the reaction of o-xylene oxidation is suggested.

---

-.

     

A study of Pt–Pd/γ-Al2O3 catalysts for methane oxidation resistant to deactivation by sulfur poisoning

The catalytic oxidation of methane was studied over calcined and reduced Pt–Pd/γ-Al₂O₃ catalysts, in the presence and the absence of SO₂ in the CH₄–O₂ reaction feed. The effect of sulfation (SO₂ + O₂ for 4 h at 500 °C) was also studied on the catalyst resistance to deactivation by sulfur poisoning. Sulfating the calcined Pt–Pd/γ-Al₂O₃ catalysts resulted in a strong deactivation for the CH₄–O₂ reaction. However, the catalytic activity of the reduced-sulfated Pt–Pd/γ-Al₂O₃ catalyst for CH₄–O₂ reaction remained rather unaffected in the presence and in the absence of SO₂ in the reaction feed. XPS analysis revealed, over reduced-sulfated Pt–Pd/γ-Al₂O₃ catalysts, the presence of Pt(0) metallic surface species on which SO₂ interactions may be faster related to Pd surface species. The presence of Pt(0) may be necessary to prevent the interactions between SO₂ and Pd surface species. Long time catalytic tests showed that the activity of a reduced Pt–Pd/γ-Al₂O₃ catalysts for CH₄–O₂ reactions remained rather unaffected despite the presence of SO₂ in the reaction feed.     

High performance CuO-CeO2 catalysts for selective oxidation of CO in excess hydrogen： Effect of hydrothermal preparation conditions

High performance CuO-CeO₂ catalysts for selective oxidation of CO in excess hydrogen were prepared by a hydrothermal method under different preparation conditions and evaluated for catalytic activities and selectivities. By changing the n_CTAB/n_Ce ratio and hydrothermal aging time, the catalytic activity of the CuO-CeO₂ catalysts increased and the operating temperature window, in which the CO conversion was higher than 99%, was widened. XRD results showed no peaks of CuO_x species and Cu-Ce-O solid solution were observed. On the other hand, Cu⁺ species in the CuO-CeO₂ catalysts, which was associated with a strong interaction between copper oxide clusters and cerium oxide and could be favorable for improving the selective oxidation performance of CO in excess H₂, were detected by H₂-TPR and XPS techniques.     

Oxidative dehydrogenation of ethylbenzene over γ-Al2O3 supported ceria-lanthanum oxide catalysts: Influence of Ce/La composition

A series of CeO₂/γ-Al₂O₃ (CA) catalysts with CeO₂ loading of 5, 10, 15 and 20 wt% were prepared by a facile incipient wetness impregnation technique. Another series of La³⁺ doped catalysts (LCA) were prepared, wherein, 1, 3 and 5 wt% of La₂O₃ was doped in 15 wt%CeO₂/γ-Al₂O₃, which were designated as 1LCA, 3LCA and 5LCA catalysts. Both CA and LCA catalysts were characterized by thermogravimetric analysis (TGA), BET surface area, X-ray diffraction (XRD), Infrared (FT-IR) spectroscopy, UV–vis diffuse reflectance spectra (UV–vis DRS), transmission electron microscopy (TEM), temperature programmed desorption of NH₃ (TPD of NH₃) temperature programmed reduction (TPR), CO₂ pulse chemisorption and O₂ pulse chemisorption techniques. All CA and LCA catalysts were evaluated for ethylbenzene (EB) oxidative dehydrogenation to styrene (ST) in vapor phase under atmospheric pressure with CO₂ as an oxidant. Albeit CA and LCA catalysts are active, 15CA and 3LCA catalysts are found to be the best catalysts of the respective series. Apart from compatible acid-base and redox characteristics, sufficient amount of solid solution clusters (Ce_xLa_1-xO_2-δ) are responsible for superior activity of 3LCA catalyst.     

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.     

Syngas production by combined carbon dioxide reforming and partial oxidation of methane over Ni/α-Al2O3 catalysts

Ni/α-Al2O3 catalysts were found to be active in the temperature range 600~900 ℃ for both CO2 reforming and partial oxidation of methane. The effects of Ni loading, reaction temperature and feed gas ratio for the combination of CO2 reforming and partial oxidation of CH4 over Ni/α-Al2O3 were investigated. Catalysts of xwt%Ni/α-Al2O3 (x = 2.5, 5, 8 and 12) were prepared by wet impregnating the calcined support with a solution of nickel nitrate. XRD patterns and activity tests have verified that the 5wt%Ni/α-Al2O3 was the most active catalyst, as compared with the other prepared catalyst samples. An increase of the Ni loading to more than 5 wt% led to a reduction in the Ni dispersion. In addition, by combining the endothermic carbon dioxide reforming reaction with the exothermic partial oxidation reaction, the loss of catalyst activity with time on stream was reduced with the amount of oxygen added to the feed.     

Stereoselective hydrogenation of 2-hexyne on Cu/γ-Al2O3 catalysts

The stereoselective hydrogenation of 2-hexyne in ethanol on Cu/-Al₂O₃ catalysts (1–40 % Cu) at 4–10 atm and 80–120 °C has been studied. The reaction affordscis-2-hexene as the only reaction product in 100 % yield at [Cu] 30 %. For samples with 20 % Cu, hydrogenation proceeds in parallel with absorption of H₂ by the catalyst.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1314–1315, July, 1993.     

RuCl₃·3H₂O catalyzed reactions: facile synthesis of bis(indolyl)methanes under mild conditions

RuCl?·3H?O was found to be an effective catalyst for reactions of indoles, 2-methylthiophene, and 2-methylfuran with aldehydes to afford the corresponding bis(indolyl)methanes, bis(thienyl)methanes, and bis(fur-2-yl)methanes in moderate to excellent yields. Experimental results indicated that mono(indolyl)methanol is not the reaction intermediate under these reaction conditions.     

The remarkable enhancement of CO-pretreated CuO-Mn2O3/γ-Al2O3 supported catalyst for the reduction of NO with CO: the formation of surface synergetic oxygen vacancy

NO reduction by CO was investigated over CuO/γ-Al2O3, Mn2O3/γ-Al2O3, and CuOMn2O3/γ-Al2O3 model catalysts before and after CO pretreatment at 300 °C. The CO-pretreated CuO-Mn2O3/γ-Al2O3 catalyst exhibited higher catalytic activity than did the other catalysts. Based on X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV/Vis diffuse reflectance spectroscopy (DRS), Raman, and H2-temperature-programmed reduction (TPR) results, as well as our previous studies, the possible interaction model between dispersed copper and manganese oxide species as well as γ-Al2O3 surface has been proposed. In this model, Cu and Mn ions occupied the octahedral vacant sites of γ-Al2O3, with the capping oxygen on top of the metal ions to keep the charge conservation. For the fresh CuO/γ-Al2O3 and Mn2O3/γ-Al2O3 catalysts, the -Cu-O-Cu- and -Mn-O-Mn- species were formed on the surface of γ-Al2O3, respectively; but for the fresh CuO-Mn2O3/γ-Al2O3 catalyst, -Cu-O-Mn- species existed on the surface of -Al2O3. After CO pretreatment, -Cu-□-Cu- and -Mn-□-Mn- (□ represents surface oxygen vacancy (SOV)) species would be formed in CO-pretreated CuO/γ-Al2O3 and CO-pretreated Mn2O3/γ-Al2O3 catalysts, respectively; whereas -Cu-□-Mn- species existed in CO-pretreated CuO-Mn2O3/γ-Al2O3. Herein, a new concept, surface synergetic oxygen vacancy (SSOV), which describes the oxygen vacancy formed between the individual Mn and Cu ions, is proposed for CO-pretreated CuO-Mn2O3/γ-Al2O3 catalyst. In addition, the role of SSOV has also been approached by NO temperature-programmed desorption (TPD) and in situ FTIR experiments. The FTIR results of competitive adsorption between NO and CO on all the CO-pretreated CuO/γ-Al2O3, Mn2O3/γ-Al2O3, and CuO-Mn2O3/γ-Al2O3 samples demonstrated that NO molecules mainly were adsorbed on Mn2+ and CO mainly on Cu+ sites. The current study suggests that the properties of the SSOVs in CO-pretreated CuO-Mn2O3/γ-Al2O3 catalyst were significantly different to SOVs formed in CO-pretreated CuO/γ-Al2O3 and Mn2O3/γ-Al2O3 catalysts, and the SSOVs played an important role in NO reduction by CO.     

Formation of the active centers of mixed palladium/γ-Al2O3 catalysts for oxidative purification of gases and their role in the adsorption and activation of carbon monoxide and oxygen

Physicochemical methods (ESR, ESDO, IR spectroscopy, photoluminescence, XRDA, TPD, TPV, etc.) were used to study the status of supported elements in modified Pd/-Al₂O₃ catalysts. The nature of the active centers of adsorption of O₂ and CO was determined. THe laws of the formation of the catalysts and changes of state of supported elements under the effects of environment and temperature wer identified.D. V. Sokolskii Institute of Organic Catalysis and Electrochemistry, Kazakh Academy of Sciences Alma-Ata. Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vo. 27, No. 6, pp. 646–653, November–December, 1991. Original article submitted September 5, 1991.     

Investigation of CO and formaldehyde oxidation over mesoporous Ag/Co3O4 catalysts

CO and formaldehyde(HCHO)oxidation reactions were investigated over mesoporous Ag/Co3O4 catalysts prepared by one-pot(OP)and impregnation(IM)methods.It was found that the one-pot method was superior to the impregnation method for synthesizing Ag/Co3O4 catalysts with high activity for both reactions.It was also found that the catalytic behavior of mesoporous Co3O4 and Ag/Co3O4 catalysts for the both reactions was different.And the addition of silver on mesoporous Co3O4 did not always enhance the catalytic activity of final catalyst for CO oxidation at room temperature(20 C),but could significantly improve the catalytic activity of final catalyst for HCHO oxidation at low temperature(90 C).The high surface area,uniform pore structure and the pretty good dispersion degree of the silver particle should be responsible for the excellent low-temperature CO oxidation activity.However,for HCHO oxidation,the addition of silver played an important role in the activity enhancement.And the silver particle size and the reducibility of Co3O4 should be indispensable for the high activity of HCHO oxidation at low temperature.     

富氧条件下Au/γ-Al2O3催化剂上的CO氧化反应

用脉冲反应研究了Au／γ-Al2O3催化剂上的CO氧化反应，结果表明在催化剂的表面首先发生CO和O2的吸附，然后吸附态的CO和O2之问反应生成CO2；在催化剂的表面CO的吸附强度大于O2的吸附强度，O2单独存在时不能在催化剂表面发生吸附．升高反应温度和提高含氧量都能提高CO的转化活性．     

CH4 reforming with CO2 for syngas production over La2O3 promoted Ni catalysts supported on mesoporous nanostructured γ-Al2O3

Nanostructured γ-Al₂O₃ with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, N₂ adsorption-desorption, TPR, TPO, TPH, NH₃-TPD and SEM techniques. The BET analysis showed a high surface area of 204 m²·g⁻¹ and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The BET results revealed that addition of lanthanum oxide to aluminum oxide decreased the specific surface area. In addition, TPR results showed that addition of lanthanum oxide increased the reducibility of nickel catalyst. The catalytic evaluation results showed an increase in methane conversion with increasing lanthanum oxide to 3 mol% and further increase in lanthanum content decreased the catalytic activity. TPO analysis revealed that the coke deposition decreased with increasing lanthanum oxide to 3 mol%. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Addition of steam and O₂ to dry reforming feed increased the methane conversion and led to carbon free operation in combined processes.     

Unique influence of rare earth (Pr,Nd, and Er) oxide surface acidic texture over CeO2/γ-Al2O3 catalysts for selective production of styrene using CO2 flow

Research on Chemical Intermediates - Variety of rare earth oxide-doped CeO2/γ-Al2O3 catalysts were prepared by a wet impregnation method and evaluated for oxidative dehydrogenation of...     

用辛烷基硫醇单层保护Au纳米粒子制备CO氧化催化剂Au/γ-Al2O3

采用两相法合成出含活性组分Au的辛烷基硫醇单层保护Au纳米粒子(C8AuNPs)的正己烷溶胶, 用“逐次浸润”法将C8AuNPs负载在γ-Al2O3上, 经真空干燥及活化处理制得Au/γ-Al2O3催化剂. 所制得的Au催化剂前体C8AuNPs/γ-Al2O3表面Au粒子平均粒径可控制在2-3 nm范围内, 且分布比较单一; 催化剂活性评价600 h后, 其表面Au的粒径仍主要分布在2-4 nm范围内; 真空干燥温度影响Au催化剂的粒子尺寸和催化活性, 随着真空干燥温度的提高, Au纳米粒子的粒径增大. 将所制备的催化剂用于低温CO氧化反应, 催化活性评价结果表明, 经25 ℃真空干燥制得的2.5%(质量分数, w)Au/γ-Al2O3具有较高的活性和长期稳定性, 其催化CO完全转化的最低温度为-19 ℃, 在15 ℃下CO完全转化时Au/γ-Al2O3的单程寿命至少900 h; 4.0%(w) Au/γ-Al2O3在15 ℃和进料中含水条件下对CO完全氧化的单程寿命不低于2000 h, 可见催化剂具有强的抗潮湿中毒特性. 综合上述实验结果, 讨论了影响Au/γ-Al2O3催化剂活性的可能因素.     

Effect of cobalt precursors on the dispersion, reduction, and CO oxidation of CoO(x)/γ-Al2O3 catalysts calcined in N2

The present work tentatively investigated the effect of cobalt precursors (cobalt acetate and cobalt nitrate) on the physicochemical properties of CoO(x)/γ-Al(2)O(3) catalysts calcined in N(2). XRD, Raman, XPS, FTIR, and UV-vis DRS results suggested that CoO/γ-Al(2)O(3) was obtained from cobalt acetate precursors and CoO was dispersed on γ-Al(2)O(3) below its dispersion capacity of 1.50 mmol/(100 m(2) γ-Al(2)O(3)), whereas Co(3)O(4)/γ-Al(2)O(3) was obtained from cobalt nitrate precursors and Co(3)O(4) preferred to agglomerate above the dispersion capacity of 0.15 mmol/(100m(2) γ-Al(2)O(3)). Compared with Co(3)O(4)/γ-Al(2)O(3), CoO/γ-Al(2)O(3) catalysts were difficult to be reduced and easy to desorb oxygen species at low temperatures and presented high activities for CO oxidation as proved by H(2)-TPR, O(2)-TPD, and CO oxidation model reaction results. A surface incorporation model was proposed to explain the dispersion and reduction properties of CoO/γ-Al(2)O(3) catalysts.     

Low-temperature CO oxidation over CuO-CeO2/SiO2 catalysts：Effect of CeO2 content and carrier porosity

The effects of CeO2 contents and silica carder porosity with their pore diameters ranging from 5.2 nm to 12.5 nm of CuO-CeO2/SiO2 catalysts in CO oxidation were investigated. The catalysts were characterized by N2 adsorption/desorption at low temperature, X-ray diffraction (XRD), temperature-programmed reduction by H2 (H2-TPR), oxygen temperature programmed desorption (O2-TPD) and X-ray photoelectron spectroscopy (XPS). The results suggested that, the ceria content and the porosity of SiO2 carder possessed great impacts on the structures and catalytic performances of CuO-CeO2/SiO2 catalysts. When appropriate content of CeO2(Ce content ≤8 wt%) was added, the catalytic activity was greatly enhanced. In the catalyst supported on silica carrier with larger pore diameter, higher dispersion of CuO was observed, better agglomeration-resistant capacity was displayed and more lattice oxygen could be found, thus the CuO-CeO2 supported on Si-1 showed higher catalytic activity for low-temperature CO oxidation.     

In situ FTIR study of surface site transformations in Pd3In/α-Al2O3 and Pd3Ag/α-Al2O3 induced by CO adsorption

In the course of the treatment of Pd3Ag/α-Al2O3 in 0.5%CO + He at 200 °C, intense transformation of single atom Pd1 surface sites isolated from each other by Ag atoms to multiatomic Pdn (n ≥ 2) ensembles occurs, as revealed by a rapid increase in the intensity of multibonded CO bands in FTIR spectra. The structure of intermetallic Pd3In nanoparticles is significantly more stable, and the formation of new multiatomic adsorption centers was not observed even after extended CO exposures.     

Deep oxidation in propane oxidative dehydrogenation to propene over V2O5/γ-Al2O3 studied by in-situ DRIFTS

In-situ DRIFTS was used to study the deep oxidation of propane, a side reaction during propane oxidative dehydrogenation to propene. Strong adsorption of propene was supposed to be the main reason for the deep oxidation. It was found that gaseous oxygen in the feed and the reaction temperature had great influence on the reaction. To obtain a relative high selectivity to propene, the reaction temperature should be maintained at 150250 °C with a proper content of gaseous oxygen in the feed for a certain catalyst and some modifiers which could weaken the adsorption of propene on the catalyst surface would be favorable.     

Application of in-plasma catalysis and post-plasma catalysis for methane partial oxidation to methanol over a Fe2O3-CuO/γ-Al2O3 catalyst

Methane partial oxidation to methanol (MPOM) using dielectric barrier discharge over a Fe2O3-CuO/γ-Al2O3 catalyst was performed. The multicomponent catalyst was combined with plasma in two different configurations, i.e., in-plasma catalysis (IPC) and post-plasma catalysis (PPC). It was found that the catalytic performance of the catalysts for MPOM was strongly dependent on the hybrid configuration. A better synergistic performance of plasma and catalysis was achieved in the IPC configuration, but the catalysts packed in the discharge zone showed lower stability than those connected to the discharge zone in sequence. Active species, such as ozone, atomic oxygen and methyl radicals, were produced from the plasma-catalysis process, and made a major contribution to methanol synthesis. These active species were identified by the means of in situ optical emission spectra, ozone measurement and FT-IR spectra. It was confirmed that the amount of active species in the IPC system was greater than that in the PPC system. The results of TG, XRD, and N2 adsorption-desorption revealed that carbon deposition on the spent catalyst surface was responsible for the catalyst deactivation in the IPC configuration.