双环戊二烯加压连续聚合制备高能量密度燃料

为制备密度大于1 g·ml^-1的高密度燃料母体化合物三环戊二烯（TCPD）,研究了双环戊二烯（DCPD）的加压连续聚合反应。分析了聚合反应产物组成和反应途径,研究了反应条件的影响。与常压间歇反应相比,加压连续反应能极大地提高反应转化率和收率,优化产物组成,TCPD中挂式/桥式（exo/endo）比例大大提高,并生成新的产物exo-DCPD。反应途径分析表明,TCPD中exo/endo比例与exo-DCPD选择性呈线性正相关。研究发现,为维持反应进行压力应不低于1.2 MPa,增加温度能提高反应转化率,而TCPD最高收率出现在160℃,TCPD的exo/endo比例随温度增加而降低,反应转化率和收率随停留时间增加而增加,但转化速率降低,缩短停留时间有利于提高TCPD的exo/endo比例,浓度对反应影响不大。在较优条件下,endo-DCPD转化率达82.2%,TCPD收率达41.7%。     

维生素B6合成中的Diels-Alder反应及重排机理研究

4-甲基-5-乙氧基噁唑与2-正丙基-4,7-二氢-1,3-二氧七环之间的Diels-Alder反应是合成维生素B6传统工艺的关键反应,加成物经过重排即生成维生素B6的前体,经水解脱保护后再成盐即制得维生素B6相关酸加成盐。文章通过分离纯化并鉴定加成反应产物及后续重排反应的中间体,对加成反应的exo/endo选择性及重排反应的机理过程进行了讨论,这些结果将被用于对exo/endo选择性和反应体系收率影响进行研究。     

The effect of Pd/Al2O3 pretreatment on catalytic activity in cyclopentane/deuterium exchange

Big variations in overall activity and product selectivity in the cyclopentane/deuterium exchange reaction were found in effect of various pretreatments of two chlorine‐free Pd/γ‐Al₂O₃ catalysts. The most important changes are observed when severely prereduced (at 600 °C) Pd/Al₂O₃ catalysts have been reoxidised and mildly rereduced: the multiple type of exchange, typical of mildly pretreated Pd catalysts, is replaced by a stepwise mode, and a big increase in catalytic activity occurs. At this state, the Pd/γ‐Al₂O₃ catalysts retain some water (as surface hydroxyls) generated by reoxidation and mild reduction. Deuterium spillover from Pd onto alumina and changes in acidity of alumina are invoked to rationalize the kinetic results. Changes in the state of Pd after various pretreatments, as probed by temperature‐programmed hydride decomposition, can hardly be correlated with changes in the catalytic behaviour in the exchange reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

CO2 corrosion of carbon steel in the presence of acetic acid at higher temperatures

The corrosion behaviour of X 65 carbon steel in the presence of acetic acid in N₂- and CO₂-saturated systems has been investigated using electrochemical techniques. The presence of acetic acid does not influence the anodic reaction but strongly accelerates the cathodic reaction. The cathodic reaction and consequently the corrosion rate of mild steel in the CO₂-saturated system increase with increase in acetic acid concentration and temperature. From the values of the apparent activation energies, the corrosion reaction in the absence of acetic acid was found to be under mixed interfacial reaction/diffusion control while interfacial reaction control dominates in the presence of acetic acid. The reduction of adsorbed undissociated acetic acid on the metal surface is proposed as the key species primarily responsible for accelerated corrosion rate at all temperatures.     

Conversion of 2-propanol over chromium aluminum orthophosphates

The catalytic conversion (dehydration/dehydrogenation) of 2-propanol on a series of CrPO₄-AlPO₄ (CrAlP) catalysts, which were differently prepared and thermally treated at 773–1073 K, has been studied by microcatalytic pulse reactor technique at different temperatures (473–573 K). Kinetic parameters for conversion of 2-propanol to propene have been obtained by analysis of the data through the Bassett-Habgood equation for first-order reaction processes. The influence of the reaction temperature upon alcohol conversion and product selectivities was also investigated. Catalytic performance was affected by the precipitation agent. Catalysts obtained in propylene oxide-aqueous ammonia showed the highest activity towards propene compared to other catalysts. Calcination at increasing temperatures caused a decrease in the activity due to the decrease in surface acid character. The results of dehydration to propene can be well interpreted through the differences in the number and strength of acid sites, which were gas-chromatographically measured using pyridine and 2,6-dimethylpyridine chemisorbed at different temperatures (573 and 673 K). Dehydrogenation to 2-propanone occurred to a small extent at all reaction temperatures and, besides, its conversion changed slightly with reaction temperature. Propene selectivity strongly increased with increasing reaction temperature.     

Pt–Pd bimetallic catalysts for methane emissions abatement

Bimetallic Pd–Pt catalysts with constant 2 wt% metal loading and varying Pt/Pd ratios were prepared, characterized and studied in the catalytic combustion of methane at low temperature under lean conditions in view of their use for CH₄ abatement from lean-burn NGV heavy duty vehicles exhausts. The influence of mild steam ageing featuring long-term use of the catalysts was also addressed together with their tolerance to H₂S. Catalysts were characterised by Transmission Electron Microscopy and Temperature Programmed Oxidation experiments. Experimental data agreed to suggest an interaction between Pd and Pt in Pd-rich catalysts, thus explaining their improved catalytic activity, even after mild ageing, compared to reference Pd/Al₂O₃. This interaction has no effect on the sulfur tolerance.     

Effect of H2S on the hydrogenation of carbon dioxide over supported Rh catalysts

The hydrogenation of CO₂ was studied on supported noble metal catalysts in the presence of H₂S. In the reaction gas mixture containing 22 ppm H₂S the reaction rate increased on TiO₂ and on CeO₂ supported metals (Ru, Rh, Pd), but on all other supported catalysts or when the H₂S content was higher (116 ppm) the reaction was poisoned. FTIR measurements revealed that in the surface interaction of H₂ + CO₂ on Rh/TiO₂ Rh carbonyl hydride, surface formate, carbonates and surface formyl were formed. On the H₂S pretreated catalyst surface formyl species were missing. TPD measurements showed that adsorbed H₂S desorbed as SO₂, both from TiO₂-supported metals and from the support. IR, XP spectroscopy and TPD measurements demonstrated that the metal became apparently more positive when the catalysts were treated with H₂S and when the sulfur was built into the support. The promotion effect of H₂S was explained by the formation of new centers at the metal/support interface.     

Marked Role of Carbon Monoxide in the Formation of Benzene During CH4-CO Reaction Over Rh/SiO2 Catalysts

Temperature-programmed desorption (He-TPD) and temperature-programmed reaction with hydrogen (H₂-TPR), carbon monoxide (CO-TPR) or methane (CH₄-TPR) were carried out to elucidate the benzene formation mechanism as well as the role of CO during CH₄-CO reaction over SiO₂-supported Rh catalysts. The steady-state surface for the CH₄-CO reaction was different from that of the CH₄ decomposition reaction. The existence of benzene-like adsorbed species as building blocks was demonstrated on the CH₄-CO reaction surface, while no such higher hydrocarbon adsorbed species was detected in the case of the CH₄ decomposition surface. On the contrary, in CO-TPR experiments various unsaturated hydrocarbons were released from the steady-state CH₄ decomposition surface, which was not the case from the CH₄-CO reaction surface. It is concluded that adsorbed CO may play an important role to enhance the C-C bond formation of carbonaceous species, which correlates deeply with the novel phenomenon of selective benzene formation in the CH₄-CO reaction.     

Carbon-based catalytic briquettes for the reduction of NO: Effect of H2SO4 and HNO3 carbon support treatment

The influence of treating carbon with sulphuric and nitric acids on the activity of a carbon-based briquette catalyst for NO reduction with NH₃ was examined in a fixed-bed reactor at low temperature (150 °C). The briquette catalysts were prepared from a low-rank coal and a commercial tar pitch. The active phase was impregnated from a suspension of ashes of coke petroleum by means of an equilibrium adsorption method. The catalytic behaviour of NO reduction over acid treated briquettes was found to vary with the surface characteristics of the carbon support. This suggests that the number of oxygen-containing sites as well as vanadium load and dispersion affect the reaction activity. In the presence of oxygen, the SCR activity is enhanced with a nitric acid treatment, activity is promoted by the presence of acidic surface groups such as carboxyl and lactone, which can help not only to create a reservoir of reactants on the catalysts surface but also to improve the dispersion or even increase the amount of vanadium loading. Therefore, the results of this study suggest that the formation of acidic sites on the surface is an important step for NO reduction with NH₃ over carbon-based catalysts. Additional techniques such as XPS and TPD to characterize the oxygen surface and those such as N₂ adsorption to characterize the textural properties were also used in this study.     

Effect of preparation method on the acidities of Al-B-O x mixed oxides

A series of Al-B-O _x metal oxides with various Al/B ratios were prepared with impregnation and coprecipitation methods. The surface acidic properties of these catalysts were examined by temperature-programmed desorption (TPD) of ammonia and the dehydration reaction of isopropanol. The dehydration reaction was carried out in a continuous-flow microreactor at 130–260 °C under atmospheric pressure. The results of TPD of ammonia indicated that the surface acidity of Al-B-O _x material is medium-strong. The acidic strengths are approximately the same for all the Al-B-O _x samples, regardless of its preparation method. In addition, their acid strengths are much stronger than that of pure alumina. However, the acid concentration is increased with decreasing the Al/B atomic ratio of the catalyst. The dehydration activities of these catalysts are increased with decreasing the Al/B atomic ratios of the samples. The results also indicated that the addition of boron on alumina, no matter what preparation method is used, could significantly enhance the acidities of the catalysts. A compensation effect was observed in isopropanol dehydration reaction over these catalysts. The preexponential factor decreases and activation energy increases with increasing Al/B ratio of the catalyst. The results can be interpreted in terms of the acidity of the catalyst.     

Synthesis of Phthalic Anhydride: Catalysts,Kinetics, and Reaction Modeling

Information concerning the oxidation of o-xylene and naphthalene, the two main processes for producing phthalic anhydride, is updated and analyzed. New techniques for the preparation of catalysts, all based in the impregnation method and involving the control of parameters such as pH and ionic strength of solutions, are described; the performance of the resulting catalysts is compared with that of catalysts prepared by other methods. Sulfur-containing substances and promoters such as Ag, P, Nb, and Sb have been shown to enhance catalyst performance; studies of their effect on the surface area, acidic properties, and stabilization of the oxidation state of vanadium in supported V₂O₅ catalysts are described.

The latest attempts to correlate the physicochemical characteristics of the catalysts with their catalytic features are analyzed. FTIR, Raman spectroscopy, adsorption of bases, ⁵¹V-NMR, XRD, XPS, SIMS, and electrical conductivity have been used in the study of V₂O₅/TiO₂ catalysts, allowing further understanding of the effects of the properties such as acidity and the state of oxidation of the surface. Particular emphasis has been given to the presence of V^IV, which is thought to cause lower selectivity to phthalic anhydride.

For o-xylene oxidation, the formation of involatile by-products has been established as a secondary reaction, accounting for the poor carbon balances obtained under some experimental conditions. Involatile by-products, whose formation has been associated with the presence of strong acid sites, can adsorb on the catalyst surface, leading to deactivation, or undergo total combustion, acting as a source of CO₂. Attempts to quantify and characterize those by-products are described.

The modeling of the reaction using both fixed- and fluidized-bed reactors, including the study of parameters such as the inlet temperature and the bath temperature, is analyzed. Models considering catalyst deactivation have been also developed; for o-xylene oxidation, deactivation has been associated with processes both reversible, such as changes in the oxidation state of vanadium, deposition of involatile compounds, and irreversible, such as structural changes, decrease in surface area, sintering, and variation of the promoter concentration at the catalyst surface.

The study of V₂O₅/TiO₂ EUROCAT catalysts, involving a number of European laboratories, is reviewed, and their performance is compared with that of other V₂O₅/TiO₂ catalysts.     

Liquid phase selective hydrogenation of phthalic anhydride to phthalide over titania supported gold catalysts

Au/TiO₂ catalysts with different gold loadings were prepared by deposition–precipitation method and used for the liquid phase hydrogenation of phthalic anhydride. All the studied Au/TiO₂ catalysts exhibited excellent activity with high selectivity (>92%) to phthalide under mild reaction conditions (180 °C and 3.0 MPa H₂). Specially, catalysts with 2–3 wt.% gold loading were highly active and selective for the formation of phthalide. When reused, the catalyst showed a certain deactivation, but still was highly selective to phthalide. The deactivation was attributed to the leaching of gold, collapse of the pore structure and accumulation of organic species on the surface.     

Novel preparation method of highly active Co/SiO2 catalyst for Fischer-Tropsch synthesis with chelating agents

Co/SiO₂ catalysts were prepared by the incipient wetness method using the aqueous Co nitrate solution modified with various organic acids and/or chelating agents followed by drying and calcination. After H₂ reduction at 773 K, the catalyst prepared with nitrilotriacetic acid (NTA) showed Fischer-Tropsch synthesis (FTS) activity ca. 3 times higher than the catalyst without additives under mild reaction conditions (503 K, 1.1 MPa).     

Heterogeneous catalysts for hydrogenation of CO2 and bicarbonates to formic acid and formates

Formic acid and formates are often produced by hydrogenation of CO₂ with hydrogen over homogeneous catalysts. The present review reports recent achievements in utilization of heterogeneous catalysts. It shows that highly dispersed supported metal catalysts are able to carry out this reaction by providing activation of hydrogen on the metal sites and activation of CO₂ or bicarbonate on the support sites. Important advances have recently been achieved through utilization of catalysts using C_xN_y materials as supports. The high activity of these catalysts could be assigned to their ability to stabilize the active metal in a state of single-metal atoms or heterogenized metal complexes, which may demonstrate a higher activity than metal atoms on the surface of metal nanoparticles.     

Hydrogen Lean-DeNOx as an Alternative to the Ammonia and Hydrocarbon Selective Catalytic Reduction (SCR)

The present article consists a critical up-to-date review of the research conducted so far on the selective catalytic reduction of NO_x with hydrogen under lean-burn conditions as an alternative technology to the existing NH₃- and HC-SCR. Noble Metal based catalysts are described in detail with emphasis on the analysis of the various reaction mechanisms that have been put forward in the literature. The influence of the nature of the support chemical composition and the preparation method and structure of the catalysts on the reaction mechanism is also discussed. Finally, the effects of various reaction parameters on the catalysts activity, selectivity and stability with reaction time are discussed in detail.     

Characterization of bimetallic surface structures of highly active Rh-Sn/SiO2 catalysts for NO-H2 reaction by EXAFS

Rh-Sn/SiO₂ catalysts prepared by the reaction of (CH₃)₄Sn with Rh metal particles supported on SiO₂ have remarkably high activities for NO-H₂ reaction and NO dissociation. The bimetallic surface structure of Rh-Sn/SiO₂ composed of an isolated Rh atom surrounded by six Sn atoms, is presented by Rh K-edge and Sn K-edge EXAFS, FT-IR, TEM and CO adsorption.     

The role of cationic Au and nonionic Au species in the low-temperature water–gas shift reaction on Au/CeO2 catalysts

The roles of cationic and nonionic Au species in the water–gas shift (WGS) reaction on Au/CeO₂ catalysts were studied by comparing the reaction behavior of a cyanide leached catalyst, after removal of the Au nanoparticles by cyanide leaching, with that of non-leached catalysts, following the technique introduced by Q. Fu et al. [Science 301 (2003) 935]. Using rate measurements as well as in situ spectroscopic and structure-sensitive techniques, we found that based on the Au mass balance, cyanide leaching removed all Au except for ionic Au³⁺ species, and that leaching resulted in a pronounced decay of the catalyst mass normalized activity to 1–25% of that of a non-leached catalyst. The extent of the activity loss strongly depended on the post-treatment of the leached catalyst. Both the catalyst treatment after leaching and, in particular, the WGS reaction resulted in considerable reformation of Au⁰ species by thermal decomposition of Au oxides (Au³⁺) and subsequent nucleation and growth of very small Au⁰ aggregates and metallic Au⁰ nanoparticles, as indicated by Au(4f) signals at 85.9 eV (Au³⁺), 84.0–84.6 eV (up-shifted signal of small Au⁰ aggregates), and 84.0 eV (metallic Au⁰). In this work, correlations between ionic and nonionic Au species and between total WGS activity and activity for the formation/decomposition of bidentate formate species are evaluated, and the role of the respective Au species in the WGS reaction on Au/CeO₂ catalysts is discussed.     

Influence of the catalyst surface area on the activity and stability of Au/CeO2 catalysts for the low-temperature water gas shift reaction

The influence of the support surface area on the activity and stability/deactivation of Au/CeO₂ catalysts (2.7 wt% Au) in the water gas shift reaction in dilute water gas were investigated by kinetic measurements and in situ Diffuse Reflectance IR spectroscopy. For ceria support surface areas between 24 and 284 m² g⁻¹, the gold particle size is independent on the catalyst surface area (about 2.1 nm) up to 188 m² g⁻¹, and we found increased amounts of (i) Auⁿ⁺, (ii) Ce³⁺, (iii) OH groups, and (iv) carbon containing adsorbed side products such as formates and carbonates for increasing surface area supports. Consequences of these results on the mechanistic understanding of the reaction are discussed.     

CuO and CuO-ZnO catalysts supported on CeO2 and CeO2-LaO3 for low temperature water-gas shift reaction

This paper describes an investigation on CuO and CuO-ZnO catalysts supported on CeO₂ and CeO₂-La₂O₃ oxides, which were designed for the low temperature water-gas shift reaction (WGSR). Bulk catalysts were prepared by co-precipitation of metal nitrates and characterized by energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), surface area (by the BET method), X-ray photoelectron spectroscopy (XPS), and in situ X-ray absorption near edge structure (XANES). The catalysts' activities were tested in the forward WGSR, and the CuO/CeO₂ catalyst presented the best catalytic performance. The reasons for this are twofold: (1) the presence of Zn inhibits the interaction between Cu and Ce ions, and (2) lanthanum oxide forms a solid solution with cerium oxide, which will cause a decrease in the surface area of the catalysts. Also the CuO/CeO₂ catalyst presented the highest Cu content on the surface, which could influence its catalytic behavior. Additionally, the Cu⁰ and Cu¹⁺ species could influence the catalytic activity via a reduction-oxidation mechanism, corroborating to the best catalytic performance of the Cu/Ce catalyst.     

Cu–ZrO2 Catalysts for Water-gas-shift Reaction at Low Temperatures

A series of Cu–ZrO₂ catalysts with Cu content in the range of 10–70 at.% Cu (=100×Cu/(Cu+Zr)) were prepared by coprecipitation, and their performances were tested for the water-gas-shift (WGS) reaction. The activity of the catalyst increased with Cu loading and, depending on the loading, the activity was comparable to or better than the activity of a conventional Cu–ZnO–Al₂O₃ catalyst at low temperatures below 473 K. Characterization of the catalysts revealed that the amount of Cu⁺ present on the catalyst surface, after being reduced by a H₂ mixture at 573 K, was well correlated with the activity of the catalyst, indicating that the Cu⁺ species were the active sites of the WGS reaction. The easy redox between Cu²⁺ and Cu⁺ during the WGS reaction was considered to be responsible for the high activity of Cu–ZrO₂ at low temperatures. A reaction mechanism based on the redox was proposed.