Direct synthesis of phenol from benzene over hydroxyapatite catalysts

The direct synthesis of phenol from benzene in the gas phase was studied over hydroxyapatite catalysts. The reaction was carried out in a fixed-bed reactor at atmospheric pressure and reaction temperature of 450°C in the presence of ammonia. A high selectivity (about 97%) of phenol formation at about 3.5% conversion of benzene was achieved over catalysts containing Ca and Cu ions in the cation part of hydroxyapatite. Besides phenol as the main reaction product, aniline is also formed. The reaction mechanism involves formation of N₂O from NH₃ in the first step of reaction. Benzene is oxidized by active oxygen species which are formed on the catalyst by decomposition of N₂O.     

Catalytic wet oxidation of phenol over PtxAg1−xMnO2/CeO2 catalysts

Catalytic wet oxidation reactions of aqueous phenol over unpromoted, base- and noble-metal promoted MnO₂/CeO₂ catalysts were carried out under mild conditions (80–130°C, 0.5 MPa O₂) in a batch slurry reactor. Even though the catalyst-mediated oxidation was very effective in destroying phenol, only a moderate selectivity toward complete mineralization into CO₂ and H₂O was attained due to parallel formation of deactivating carbonaceous deposits. Promotion of the mixed-oxide catalysts with platinum and/or silver enhanced the mineralization selectivity and reduced appreciably the amount of deposits.     

铁铝交联黏土催化剂的制备及其苯直接羟基化的催化性能

通过直接向稀释的黏土悬浮液中加入Fe-Al交联剂制备了不同物质的量比的铁铝交联黏土催化剂。研究了该催化剂在苯/H2O2直接羟基化制备苯酚反应中的催化性能。结果表明,铁铝交联黏土催化剂在苯直接羟基化反应中具有良好的催化活性,苯酚收率最高可达4.9%,选择性可高达73.5%。运用XRD、FT-IR、TG-DSC、SEM等手段对铁铝交联黏土催化剂进行了表征。     

苯直接氧化制苯酚反应产物分布测定方法的研究

研究以气相色谱测定苯直接氧化制苯酚反应后产物分布的方法,考察并优化了色谱分析条件。结果表明最佳色谱分析条件为：汽化室温度290℃、检测器温度320℃、升温速率5．0℃／min、载气流速2．0mL／min、分流比120：1、进样量为1μL。采用外标法定量,标准样品的回收率在95％～105％,重复性最大相对标准偏差为1．62％。     

Catalytic and photocatalytic ozonation of phenol on MnO2 supported catalysts

Different series of manganese-supported catalysts containing 10 wt.% of manganese, as oxide, on TiO₂ have been prepared by the sol–gel method and by the traditional method based on the impregnation of the support with the metal precursor on commercial and sol–gel supports. The samples were characterized by measuring the specific area (S_BET), temperature-programmed desorption (TPD), Fourier transform infrared (FTIR) spectroscopy, temperature-programmed reduction (TPR), electrophoretic migration (IP) and X-ray diffraction (XRD). The catalytic and photocatalytic activity was measured in a batch reactor using ozone as the oxidizing agent. The catalytic behavior, expressed as constant rate, in absence of irradiation did not show significant changes for the manganese-supported catalysts. The only exception was the cogelated Mn/TiO₂ catalyst, which showed higher degradation activity, the main product being benzoquinone. On the other hand, all the irradiated systems showed an increase in the phenol degradation, being CO₂ and small organic acids the final product.     

Cerium–terbium mixed oxides as alternative components for three-way catalysts: a comparative study of Pt/CeTbOx and Pt/CeO2 model systems

By using a combination of oxygen buffering capacity (OBC) and oxygen storage capacity (OSC) measurements, the redox behaviour of a Pt/CeTbO_x catalyst is compared to that of a classic model TWC system: Pt/CeO₂. The results reported here show that the redox efficiency of the Pt/CeTbO_x catalyst is much better, especially at low temperature operation conditions such as those occurring during the cold start of engines. The catalyst containing terbium also shows lower ‘light-off’ temperatures for both methane and carbon monoxide oxidation.     

Deactivation phenomena during catalytic wet air oxidation (CWAO) of phenol over platinum catalysts supported on ceria and ceria–zirconia mixed oxides

Catalytic wet air oxidation (CWAO) of aqueous solution of phenol was carried out with pure oxygen at 160 °C in a stirred batch reactor on platinum supported oxide catalysts (Pt/CeO₂^c calcined at 650 and 800 °C and Pt/Ce_xZr_1 − xO₂ with x = 0.90, 0.75 and 0.50). The catalysts were characterized before (BET, FT-IR spectroscopy, hydrogen chemisorptions, oxygen storage capacity (OSC)) and after reaction (TPO, elementary analysis, GC–MS and DTA–TGA). The results demonstrate a poisoning of the catalysts during CWAO reaction due to the formation of different forms of carbon deposit on the materials: carbonates and polymeric carbon species. This poisoning phenomenon is limited by the introduction of 50% of zirconium into ceria lattice for the catalysts presenting the lowest surface area. Polymeric deposits play a major role in the catalyst deactivation.     

一种苯氧化直接制备苯酚的方法

苯酚是一种广泛使用的基础工业原料,对其合成方法的研究具有重要意义。使用非均相催化剂（SAC-16）对苯直接氧化制备苯酚的工艺过程进行了研究,并得到最佳工艺条件：反应温度为400℃,H2/CH3OH=4,HLSV=1,系统压力为3.0 MPa。     

TS-1分子筛在过氧化氢氧化苯制苯酚反应中的催化性能研究

以TS-1分子筛为催化剂,在淤浆反应器中对过氧化氢氧化苯制苯酚反应的催化性能进行了研究,考察了不同溶剂、过氧化氢进料方式、原料配比和反应条件等对催化性能的影响,优化了反应工艺条件,苯的转化率约达12.5%,苯酚的选择性约达92%,为进一步开展研究奠定了基础。     

Electrochemical oxidation of CO in sulfuric acid solution over Pt and PtRu catalysts modified with TaOx and NbOx

In order to survey new CO-tolerant anode for the PEFC application, the addition of TaO_x and NbO_x to the Pt catalyst was examined in the electrochemical oxidation of CO in a sulfuric acid solution. Voltammetric peak potentials for the oxidation of CO pre-adsorbed on the Pt surface shifted to lower potentials by these additives, indicating an enhancement of electro-catalysis of Pt for the CO oxidation. Both oxides of Ta or Nb also bring about an inhibition of the CO adsorption rate onto the Pt surface. Concerted effect of these oxides with Ru is discussed for the CO oxidation over the PtRu-TaO_x and the PtRu-NbO_x anodes.     

The effect of mass transfer on the catalytic combustion of benzene and methane over palladium catalysts supported on porous materials

Catalytic combustion of benzene and methane over palladium catalysts supported on FAU and MOR zeolites and MCM-41 and KIT-1 mesoporous materials were studied to illustrate the effect of pore size and shape of supports on their catalytic activities. The palladium catalysts supported on mesoporous materials showed high activity and a steep increase in the conversion of benzene with rising temperature. The low activity of palladium catalysts supported on FAU zeolite was ascribed to mass transfer limitation. However, conversion profiles of methane on palladium catalysts were similar, although their supports were different as zeolites and mesoporous materials. The catalytic behavior of palladium catalysts in the combustion of benzene and methane was explained by the diffusion properties of fuels in the pores of zeolites and mesoporous materials.     

Complete oxidation of benzene on Co---Cr and Co---Cr oxide catalysts

Supported mixture metal oxide systems, Cu---Cr and Co---Cr on γ-A1₂O₃ and γ-A1₂O₃+ SiO₂ were prepared and studied. They exhibited catalytic activity in the complete oxidation of benzene.     

过氧化氢氧化苯制苯酚的催化剂研究进展

综述了过氧化氢直接氧化苯制苯酚过程中相关催化剂的研究进展,重点介绍了含钛、钒、铁、铜的催化剂,同时给出了各种催化剂所达到的收率和选择性及其工业化前景。     

Lean-DeNOx titania based monolithic catalysts

The activity of titania based copper and platinum monolithic catalysts in the reduction of nitrogen oxides was studied with exhaust gases from a Diesel engine injecting fuel as reductant. Combining both catalysts, a two-stage system was designed, studying the influence of the copper catalysts composition on its performance with synthetic gas mixtures. The influence of reactants concentration and operating conditions was also investigated. Taking into account these results, a double-bed system with a cell density of 33 cell cm⁻² (210 c.p.s.i.) was prepared. Linear velocity had a strong influence on the performance of the Pt catalyst and of the double-bed. Two NO_x conversion maxima were observed with Pt/TiO₂ at 225°C and 350°C operating at 6.6 m s⁻¹. Promising NO_x conversions were achieved in the temperature range 200–450°C.     

Kinetics analysis of phenol and benzene decomposition in supercritical water

Decomposition of phenol and benzene was studied in supercritical water (SCW) at 370–450 °C and 25 MPa over very short residence times (0.5–100 s). The study of simple model compounds such as phenol and benzene is an essential preliminary step to elucidate the primary mechanism of char and gas formation from lignin compounds. A quantitative detailed chemical kinetics model for the primary pathways of phenol and benzene decomposition in SCW was determined using the reaction pathways for its decomposition under supercritical conditions. The activation energy of benzene decomposition (91.16 kJ mol⁻¹) in SCW is much higher than that of phenol (54.17 kJ mol⁻¹) under similar experimental conditions. This emphasized the importance of the substituent group (hydroxyl group) in the benzene ring to enhance its decomposition rate. In addition, the reaction rate parameters, which are deduced for the overall reaction network of its decomposition under similar conditions, show good agreement with each another. Hence, the reaction rates of these reaction pathways are successfully described in this study.     

Sulphur dioxide interaction with NOx storage catalysts

The effect of SO₂ on the NO_x storage capacity and oxidation and reduction activities of a model Pt/Rh/BaO/Al₂O₃ NO_x storage catalyst was investigated. Addition of 2.5, 7.5 or 25 vol. ppm SO₂ to a synthetic lean exhaust gas caused deactivation of the NO_x storage function, the oxidation activity and the reduction activity of the catalyst. The degree of deactivation of the NO_x storage capacity was found to be proportional to the total SO₂ dose that the catalyst had been exposed to. SO₂ was found to be accumulated in the catalyst as sulphate.     

A comparative study of the water-gas shift activity of Pt catalysts supported on single (MOx) and composite (MOx/Al2O3, MOx/TiO2) metal oxide carriers

The water-gas shift (WGS) activity of platinum catalysts dispersed on a variety of single metal oxides as well as on composite MO_x/Al₂O₃ and MO_x/TiO₂ supports (M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, La, Ce, Nd, Sm, Eu, Gd, Ho, Er, Tm) has been investigated in the temperature range of 150–500 °C, using a feed composition consisting of 3% CO an 10% H₂O. For Pt catalysts supported on single metal oxides, it has been found that both the apparent activation energy of the reaction and the intrinsic rate depend strongly on the nature of the support. In particular, specific activity of Pt at 250 °C is 1–2 orders of magnitude higher when supported on “reducible” compared to “irreducible” metal oxides. For composite Pt/MO_x/Al₂O₃ and Pt/MO_x/TiO₂ catalysts, it is shown that the presence of MO_x results in a shift of the CO conversion curve toward lower reaction temperatures, compared to that obtained for Pt/Al₂O₃ or Pt/TiO₂, respectively. The specific reaction rate is in most cases higher for composite catalysts and varies in a manner which depends on the nature, loading, and primary crystallite size of dispersed MO_x. Results are explained by considering that reducibility of small oxide particles increases with decreasing crystallite size, thereby resulting in enhanced WGS activity. Therefore, evidence is provided that the metal oxide support is directly involved in the WGS reaction mechanism and determines to a significant extent the catalytic performance of supported noble metal catalysts. Results of catalytic performance tests obtained under realistic feed composition, consisting of 3% CO, 10% H₂O, 20% H₂ and 6% CO₂, showed that certain composite Pt/MO_x/Al₂O₃ and Pt/MO_x/TiO₂ catalysts are promising candidates for the development of active WGS catalysts suitable for fuel cell applications.     

Combustion of non-halogenated volatile organic compounds over group VIII metal catalysts

Catalytic combustion of volatile organic compounds (VOCs), present in low concentrations (10–1000 ppm) in industrial effluent streams, is a promising air abatement technology. The oxidation of benzene, butanol and ethyl acetate over group VII metal catalysts supported on alumina carriers has been investigated. Pt, Pd and Co were found to be the most active among group VIII metals, while ethyl acetate was found to be the most-difficult-to-oxidize compound. Benzene and ethyl acetate oxidations over Pt/Al₂O₃ were found to be structure sensitive reactions with the turnover frequency (TOF) increasing with increasing mean metal particle size. The presence of chloride on the catalyst surface, originating from chloride-containing metal precursor compounds was found to exert an inhibiting effect on the activity of Pt. Apparent activation energies of the reactions over Pt and Pd catalysts were found to be in the 70–120 kJ/mol range while the reaction order with respect to the VOC was positive in all cases. During oxidation of benzene-butanol mixtures, benzene oxidation was completely suppressed as long as butanol was present in the reaction mixture.     

Lean NOx reduction with CO + H2 mixtures over Pt/Al2O3 and Pd/Al2O3 catalysts

The reduction of NO_x by hydrogen under lean burn conditions over Pt/Al₂O₃ is strongly poisoned by carbon monoxide. This is due to the strong adsorption and subsequent high coverage of CO, which significantly increases the temperature required to initiate the reaction. Even relatively small concentrations of CO dramatically reduce the maximum NO_x conversions achievable. In contrast, the presence of CO has a pronounced promoting influence in the case of Pd/Al₂O₃. In this case, although pure H₂ and pure CO are ineffective for NO_x reduction under lean burn conditions, H₂/CO mixtures are very effective. With a realistic (1:3) H₂:CO ratio, typical of actual exhaust gas, Pd/Al₂O₃ is significantly more active than Pt/Al₂O₃, delivering 45% NO_x conversion at 160 °C, compared to >15% for Pt/Al₂O₃ under identical conditions. The nature of the support is also critically important, with Pd/Al₂O₃ being much more active than Pd/SiO₂. Possible mechanisms for the improved performance of Pd/Al₂O₃ in the presence of H₂+CO are discussed.     

Selective reduction of NOx by liquid hydrocarbons with supported HPW–metal catalysts

The catalytic multifunctional system based on H₃PW₁₂O₄₀·6H₂O (HPW), Pt and support (Zr–Ce or Zr–Ti mixed oxides) has been investigated for lean NO_x storage and reduction. It was applied in the NO_x storage and reduction (NSR) concept by including a cyclic operation of short NO_x storage (oxygen rich phase) and reduction (hydrocarbon rich phase: hexane). For NO_x reduction, the assistance of hydrogen is one of the key parameters possibly as a result of the regeneration of metallic sites active for mild oxidation of the hydrocarbon (by forming C_xH_yO_z). The difference in oxygen mobility of supports (higher in the case of Zr–Ce than for Zr–Ti) became another strategic parameter for catalyst selection since the possibility of total hydrocarbon oxidation. The influence of temperature was also considered for optimizing NO_x storage and reduction.