Palladium-catalysed vapour phase aerobic acetoxylation of toluene to benzyl acetate

Supported Pd–Sb acetoxylation catalysts with different Pd and Sb amounts as well as varying supports were prepared by impregnation technique. The contents of Pd and Sb are varied over a wide range, for instance Pd is varied from 0.5 to 20 wt% by keeping Sb content at 8 wt%. In a similar way, Sb content is varied from 4 to 20 wt% by keeping Pd loading constant at 10 wt%. Four different supports such as TiO₂, γ-Al₂O₃, SiO₂ and ZrO₂ are applied at constant Pd (10 wt%) and Sb (8 wt%) contents. Catalytic performance of these solids is evaluated for the gas phase acetoxylation of toluene to benzyl acetate (BA) at T = 210 °C and p = 2 bar. XPS revealed a considerable loss of both Pd and Sb in the near-surface region in the used catalysts. TEM showed that Pd particles exhibit spherical morphology and their size increased dramatically in the spent catalysts compared to their corresponding fresh ones. Monometallic catalysts showed very poor acetoxylation performance but high total oxidation, which results in an increase of the yield of CO_x up to ca. 50%. However, combination of both Pd and Sb was found to suppress total oxidation and thereby enhance the acetoxylation performance with high BA selectivity of ≥85%. Catalytic activity was observed to increase continuously with increase in Pd loading. The catalyst with the highest Pd loading (20 wt% Pd) displayed the best performance (toluene conversion = > 90%, BA yield = > 75%). The activity is however decreasing with time-on-stream due to coke deposits. Nevertheless, the deactivated samples can be regenerated in air to restore their maximum activity. Nature of support, content of co-components showed strong influence on the catalytic performance.     

Characterization and catalytic activity of Pd/V2O5/Al2O3 catalysts on benzene total oxidation

The role of vanadium oxide and palladium on the benzene oxidation reaction over Pd/V₂O₅/Al₂O₃ catalysts was investigated. The Pd/V₂O₅/Al₂O₃ catalysts were more active than V₂O₅/Al₂O₃ and Pd/Al₂O₃ catalysts. The increase of vanadium oxide content decreased the Pd dispersion and increased the benzene conversion. A strong Pd particle size effect on benzene oxidation reaction was observed. Although the catalysts containing high amount of V⁴⁺ species were more active, the Pd particle size effect was responsible for the higher activity.     

不同载体负载Pd双功能催化剂制备及其液相甲醇催化一步合成甲酸甲酯

以γ-Al_2O_3、ZrO_2、Bentonite(膨润土)、MIL-53(Al)和MIL-53(Fe)为载体,采用浸渍法制备负载Pd双功能催化剂,利用XRD、BET和NH3-TPD等表征催化剂结构,在微型高压反应器中评价催化剂的液相甲醇一步催化转化合成甲酸甲酯的反应性能,考察反应条件对催化剂性能的影响。结果表明,不同载体负载Pd催化剂未观察到Pd的XRD特征峰,表明催化剂表面的Pd是高分散状态。不同载体负载Pd催化剂的比表面积、酸强度和酸量差别较大,并且酸强度和酸量对甲醇转化率和产物选择性有较大影响。具有较多中强酸的2%Pd/Bentonite、2%Pd/MIL-53(Al)和2%Pd/MIL-53(Fe)催化剂比中强酸较少的2%Pd/γ-Al_2O_3和2%Pd/ZrO_2催化剂具有更高的甲醇转化率和甲酸甲酯选择性。2%Pd/Bentonite催化剂在每摩尔甲醇Pd用量为0. 030 mmol、反应温度150℃、O_2压力2 MPa和反应时间5 h条件下,液相甲醇一步催化转化合成甲酸甲酯反应中,甲醇转化率56. 08%,甲酸甲酯选择性55. 85%。     

负载型CuMnO_x/TiO_2催化剂催化燃烧甲苯

采用沉积-沉淀法制备CuMnO_x/TiO_2新型甲苯燃烧催化剂,考察焙烧温度、Cu与Mn物质的量比、Cu和Mn总负载量、空速及水蒸汽含量对催化甲苯燃烧性能的影响。研究表明,焙烧温度500℃和Cu与Mn物质的量比为1∶1时,催化剂活性最好,反应温度250℃时,甲苯去除率为100%;水蒸汽的出现明显降低了甲苯转化率。XRD和H2-TPR表征结果表明,CuMnO_x/TiO_2催化剂的主要活性相为铜锰尖晶石(Cu1.5Mn1.5O4),它的存在降低了CuMnO_x/TiO_2催化剂的还原温度,是催化活性优良的主要原因。     

CO oxidation at low temperature over Pd supported on CeO2-TiO2 composite oxide

Low temperature CO oxidation was carried out over CeO₂-TiO₂ composite oxide and thereon supported Pd catalysts. The effects of Ce/Ti ratio and pre-treatments of calcination and reduction on the catalytic behaviour were investigated. The CO oxidation starts at about 220 °C over CeO₂-TiO₂ and the pre-reduction treatment has little influence on the catalytic activity. Pd supported on CeO₂-TiO₂ (Pd/CeO₂-TiO₂) exhibits high activity for CO oxidation and a complete conversion of CO to CO₂ can be achieved even at ambient temperature, which suggests a synergistic effect between Pd and CeO₂-TiO₂. The activity and stability of Pd/CeO₂-TiO₂ can be further improved by the pre-reduction treatment. Ce/Ti ratio influences the catalytic behaviour significantly; the catalyst Pd/CeO₂-TiO₂ with a Ce/Ti mole ratio of 0.20 (Pd/Ce20Ti) owns the highest activity and stability, which suggests an optimization of the Pd-Ce-Ti interaction in Pd/Ce20Ti. The calcined Pd/CeO₂-TiO₂ with a Ce/Ti mole ratio higher than 0.10 shows a distorted light-off profile with the temperature, which implies an alternation of the reaction mechanism with increasing temperature.     

负载型Mn-Fe/γ-Al2O3低温脱硝催化剂的性能

采用共沉淀法制备了负载型Mn-Fe/γ-Al₂O₃低温SCR催化剂,运用固定床催化反应器,以氨气为还原剂,考察了负载量、活性组分配比、焙烧温度等制备条件和空速、O₂体积分数、NH₃/NO摩尔比等操作条件对Mn-Fe/γ-Al₂O₃催化剂低温脱硝性能的影响,并通过X射线衍射仪(XRD)、比表面积测定仪(BET)等手段对催化剂进行表征.结果表明,负载质量分数为20%、n(Mn):n(Fe)=4:1、焙烧温度为600℃、空速为16000h^-1、O₂体积分数为4%、NH₃/NO摩尔比为1.2、反应温度为200℃的条件下,NO转化率达到了96%以上.     

Studies of the activation process over Pd perovskite-type oxides used for catalytic oxidation of toluene

Calcined and reduced catalysts Pd/LaBO₃ (B = Co, Fe, Mn, Ni) were used for the total oxidation of toluene. Easiness of toluene destruction was found to follow the sequence based on the T₅₀ values (temperature at which 50% of toluene is converted): Pd/LaFeO₃ > Pd/LaMnO_3+δ > Pd/LaCoO₃ > Pd/LaNiO₃. In order to investigate the activation process (calcination and reduction) in detail, the reducibility of the samples was evaluated by H₂-TPR on the calcined catalysts. Additionally, characterization of the Pd/LaBO₃ (B = Co, Fe) surface was carried out by X-ray photoelectron spectroscopy (XPS) at each stage of the global process, namely after calcination, reduction and under catalytic reaction at either 150 or 200 °C for Pd/LaFeO₃ and either 200 or 250 °C for LaCoO₃. The different results showed that palladium oxidized entities were totally reduced after pre-reduction at 200 °C for 2 h (2 L/h, 1 °C/min). As LaFeO₃ was unaffected by such a treatment, for the other perovskites, the cations B are partially reduced as B³⁺ (B = Mn) or B²⁺ even to B⁰ (B = Co, Ni). In the reactive stream (0.1% toluene in air), Pd⁰ reoxidized partially, more rapidly over Co than Fe based catalysts, to give a Pd²⁺/Pd⁴⁺ and Pd⁰/Pd²⁺/Pd⁴⁺ surface redox states, respectively. Noticeably, reduced cobalt species are progressively oxidized on stream into Co³⁺ in a distorted environment. By contrast, only the lines characteristic of the initial perovskite lattice were detected by XRD studies on the used catalysts. The higher activity performance of Pd/LaFeO₃ for the total oxidation of toluene was attributed here to a low temperature of calcination and to a remarkable high stability of the perovskite lattice whatever the nature of the stream which allowed to keep a same palladium dispersion at the different stages of the process and to resist to the oxidizing experimental conditions. On the contrary, phase transformations for the other perovskite lattices along the process were believed to increase the palladium particle size responsible of a lower activity.     

Pd-Cu/γ-Al_2O_3双金属催化剂脱除水中硝酸盐

采用分步浸渍法和共浸渍法制备系列Pd负载质量分数为1%的Pd-Cu/γ-Al2O3双金属催化剂,以氢气为还原剂研究其对水中硝酸盐催化脱除的性能。结果表明,催化剂中Cu与Pd物质的量比以及Cu、Pd的浸渍顺序对催化剂性能有重要影响,硝酸根转化率随着Cu与Pd物质的量比的增大而增大;硝酸根转化活性以Cu与Pd物质的量比为5∶1、先浸渍Pd再浸渍Cu所得催化剂较优;从氨氮选择性方面看,以先浸渍Cu后浸渍Pd制备的催化剂选择性较低,在Cu与Pd物质的量比为1∶1、先浸渍Cu再浸渍Pd所得催化剂较优。     

CuO含量对Pd/Al2O3催化剂乙醇氧化性能的影响

采用浸渍法制备了一系列具有不同CuO含量的Pd-CuO/Al₂O₃催化剂，并将其用于乙醇氧化反应，其结构与性质通过XRD、H₂-TPR和NH₃-TPD等手段进行分析。结果发现，催化剂的活性并不是随着CuO含量的增加而增强，Pd-1.0%CuO/Al₂O₃催化剂表现出最佳的活性，其点火温度和完全转化温度比Pd/Al₂O₃催化剂至少降低了50℃。与Pd/Al₂O₃催化剂相比，含CuO催化剂增强的衍射峰强度以及氢化钯分解峰的消失，说明Pd-Cu合金结构的形成有利于Pd、Cu物种之间的协同作用。对于Pd-1.0%CuO/Al₂O₃催化剂来说，还原峰向低温的移动以及还原峰面积的增大说明该催化剂上氧化性物质更易被还原且数量在增加，这对于氧化反应是十分有利的，新出现的还原峰表示Pd、Cu的相互作用生成了新物种。NH₃-TPD结果中更高含量的低温酸有利于高活性，而且新出现的脱附峰说明形成了新的酸性位点。     

Conversion of CCl2F2 (CFC-12) in the presence and absence of H2 on sol–gel derived Pd/Al2O3 catalysts

Conversion of CCl₂F₂ in the presence (hydrogenolysis) and absence of hydrogen was investigated on Al₂O₃, AlF₃ and Pd/Al₂O₃ xerogel and aerogel catalysts. CCl₂F₂ was found to form CClF₃ and CCl₃F on Al₂O₃ and AlF₃ in the presence and absence of hydrogen as well as on the Pd/Al₂O₃ catalysts in the absence of hydrogen. Overall activity increased during the hydrogenolysis reactions at 230°C as a function of time which was paralleled by a significant increase in the yield of CClF₃ formed through a Cl/F-exchange reaction. X-ray diffraction patterns of the spent catalyst recovered after 3 h of hydrogenolysis confirmed the presence of Pd(C) (Pd–carbon solid solution) and AlF₃ phases on Pd/Al₂O₃ catalysts indicated that the carbon incorporation into the Pd lattice and the transformation of Al₂O₃ to AlF₃ starts at the initial stage of the reaction. It was concluded that AlF₃ is responsible for the Cl/F-exchange reactions. CH₄, a complete hydrogenation product, is formed during hydrogenolysis. Another route for its formation is the reaction between hydrogen in the gas phase and the interstitial carbon.     

桥联茂金属催化1-癸烯聚合及其产物结构与性能

采用桥联茂金属催化体系rac-Et(1-Ind)₂ZrCl₂/Al(ⁱBu)₃/[Me₂NHPh]⁺[B(C₆F₅)₄]^-催化1-癸烯聚合,考察了茂金属浓度、Al/Zr摩尔比、B/Zr摩尔比、温度、反应时间对反应转化率、黏度和摩尔质量的影响.当反应条件为1-癸烯20mL、甲苯20mL、Zr/烯摩尔比8×10^-5、Al/Zr摩尔比80、B/Zr摩尔比1.5、温度80℃、反应时间1h时,转化率达到96.2%.采用¹³C NMR和¹H NMR表征了产物的结构,优化条件下所得的聚合产物具有高黏度指数(259)和低分子量分布(2.088),可作为理想的润滑油基础油的原料.     

低负载Pd/Al2O3催化剂的制备及其对CO室温催化性能研究

采用等体积浸渍法和还原法结合制备了Pd/Al_2O_3催化剂,通过N_2吸附-脱附、SEM、TEM、X射线衍射、X射线光电子能谱和CO原位漫反射傅里叶变换红外光谱等表征手段对制备的样品微观结构进行了系统分析,考察了不同Pd负载量和测试条件下CO催化氧化性能。实验结果表明,水合肼还原法实现了Pd在Al_2O_3载体上的均匀分散,Pd颗粒的直径在9 nm左右,且为Pd单质;负载后的催化剂呈现明显的中孔结构特征,有利于气体分子的扩散。在0.2%～0.5%的低负载质量分数下,CO的催化性能随着Pd负载量的增加而增加,随着CO进口浓度和空速的升高而逐渐降低,在进口浓度为0.05%,空速为4 017 h~(-1)时,不同负载量的催化剂均能使CO完全催化;温度对催化剂的催化效果影响显著,从常温到50℃催化剂的性能变化显著;湿度增加对催化有一定的促进作用。Pd负载质量分数0.5%的催化剂稳定性测试表明,催化剂能够在100 h内保持92%以上的稳定转化率。     

高效稳定的铜镍催化剂在草酸二甲酯加氢中的应用

为了探索高效、稳定的草酸二甲酯（DMO）加氢制乙醇酸甲酯（MG）催化剂,采用水热合成法制备Cu-Ni/SiO₂催化剂,探索了不同Cu：Ni摩尔比对于催化剂活性的影响。通过XRD、TEM和XPS等表征,结果表明：利用二氧化硅微球作载体,铜镍物种的分散更加均匀。并且调变不同的Cu：Ni摩尔比,对Cu⁺在催化剂中的比例有一定的影响,从而影响乙醇酸甲酯的收率。在氢酯比为150、反应压力2 MPa、反应温度200℃和液时空速为0.5 h^-1的反应条件下,Cu：Ni摩尔比为1：1时的催化剂Cu₁Ni₁/SiO₂表现出了最好的催化性能,草酸二甲酯的转化率达到90%,乙醇酸甲酯的选择性达到了80%,催化剂能稳定运行100 h。上述结果可为研制催化活性高、选择性强、寿命长、易于生产乙醇酸甲酯的催化剂提供一定的参考。     

Comparison of supports for the direct synthesis of hydrogen peroxide from H2 and O2 using Au–Pd catalysts

The direct synthesis of hydrogen peroxide from H₂ and O₂ using a range of supported Au–Pd alloy catalysts is compared for different supports using conditions previously identified as being optimal for hydrogen peroxide synthesis, i.e. low temperature (2 °C) using a water–methanol solvent mixture and short reaction time. Five supports are compared and contrasted, namely Al₂O₃, -Fe₂O₃, TiO₂, SiO₂ and carbon. For all catalysts the addition of Pd to the Au only catalyst increases the rate of hydrogen peroxide synthesis as well as the concentration of hydrogen peroxide formed. Of the materials evaluated, the carbon-supported Au–Pd alloy catalysts give the highest reactivity. The results show that the support can have an important influence on the synthesis of hydrogen peroxide from the direct reaction. The effect of the methanol–water solvent is studied in detail for the 2.5 wt% Au–2.5 wt% Pd/TiO₂ catalyst and the ratio of methanol to water is found to have a major effect on the rate of hydrogen peroxide synthesis. The optimum mixture for this solvent system is 80 vol.% methanol with 20 vol.% water. However, the use of water alone is still effective albeit at a decreased rate. The effect of catalyst mass was therefore also investigated for the water and water–methanol solvents and the observed effect on the hydrogen peroxide productivity using water as a solvent is not considered to be due to mass transfer limitations. These results are of importance with respect to the industrial application of these Au–Pd catalysts.     

助剂对Pd/γ-Al2O3催化剂一步法合成二甲醚反应稳定性的影响

采用浸渍法制备了一系列不同助剂下的负载型Pd/γ-Al₂O₃催化剂,考察了助剂类型对Pd/γ-Al₂O₃催化剂一步法合成二甲醚（STD）反应稳定性的影响规律;采用氮吸附、XRD、H₂-TPR及TG等多种表征手段考察了稳定性试验前后以及烧炭再生后催化剂的表面物化性质及结构变化。结果表明,助剂成分对Pd/γ-Al₂O₃催化剂的STD反应稳定性影响显著。相比Pd/γ-Al₂O₃催化剂,添加CeO₂可以提高Pd在γ-Al₂O₃表面的分散度,但会覆盖表面的部分酸性位,一定程度上提高了催化剂的活性和稳定性,但仍存在Pd烧结和积炭现象;添加复合助剂CeO₂-ZrO₂后形成的Ce-O-Zr固熔晶面能显著促进Pd均匀分散,提高催化剂的抗积炭能力和抗烧结能力,催化剂的活性和稳定性更高;经SO₄^2-改性后Pd/γ-Al₂O₃催化剂会因为表面积炭加剧和表面硫流失严重,中强酸酸性位减少而快速失活。CeO₂-ZrO₂-Pd/γ-Al₂O₃催化剂经历20h的稳定性试验后CO转化率仍保持59%以上,二甲醚选择性65%以上,烧炭再生后催化活性恢复至新鲜催化剂的91.83%。     

Enantioselective hydrogenation of N-acetyl dehydrophenylalanine methyl ester using cinchonine-modified Pd/TiO2 catalysts

The enantioselective hydrogenation of N-acetyl dehydrophenylalanine methyl ester (NADPME) to N-acetyl phenylalanine methyl ester is investigated using cinchonine-modified Pd/TiO₂ catalysts. The catalysts were prepared using deposition–reduction and wet impregnation methods and were evaluated for reaction using methanol as solvent with various cinchonine/NADPME molar ratios. Enantioselectivity was sensitive to this ratio and comparison with Pd/γ-Al₂O₃ showed that the Pd/TiO₂ gave marginally higher enantioselectivity when tested under comparable conditions. The effect of Pd loading and dispersion was investigated and the maximum enantiomeric excess observed was dependent on the dispersion; the role of the Pd particle size is discussed in the context of cinchonine adsorption. The reactions were carried out in solvents (methanol and dimethyl formamide) and mixed solvents (methanol–water and dimethyl formamide–water); the enantiomeric excess was significantly enhanced using dimethyl formamide. The addition of water does not have a significant effect for the Pd/TiO₂ catalysts. In this paper we report the highest enantiomeric excess for the hydrogenation of a prochiral ester using an immobilised catalyst.     

Effect of Pd precursor salt on the activity and stability of Pd-doped hexaaluminate catalysts for the CH4 catalytic combustion

This study reports the influence of palladium salt precursor on the catalytic activity of palladium-doped hexaaluminate catalysts for the combustion of 1 vol% CH₄ in the presence of CO₂ and H₂O as inhibitors. Thermal stability of the catalysts is evaluated in long-term catalytic test at 700 °C. The hexaaluminate supports were synthesized using two different procedures: conventional coprecipitation and solid/solid diffusion procedure. Palladium impregnation was carried out by two different routes using Pd(NO₃)₂ in water or Pd(acac)₂ in toluene as impregnation solution. It was observed that using Pd(acac)₂ as precursor allows to attain higher dispersion of the active phase (Pd particles size <3 nm). Compared to the catalysts obtained by impregnation of Pd(NO₃)₂, higher catalytic activities are then obtained. Nevertheless, a deactivation of the samples obtained using Pd(acac)₂ is observed. At the end of the stability test, almost similar catalytic activity is obtained whatever the palladium precursor. Reduction–reoxidation experiment showed that this deactivation is irreversible, and TEM analysis suggest that this deactivation is related to the sintering of Pd particles under reaction over samples synthesized using Pd(acac)₂ as precursor.     

用于丙烷催化燃烧的PdxPty-ZSM-5/Cordierite整体式催化剂

以ZSM-5分子筛、铝溶胶、硝酸钯、硝酸铂和水为原料制备分子筛浆料，采用真空抽提-一次涂覆法在堇青石蜂窝陶瓷载体表面制备出Pd_xPt_y-ZSM-5/Cordierite整体式催化剂，考察了Pd负载量、ZSM-5分子筛的硅铝比和Pd/Pt质量比对整体式催化剂的丙烷催化燃烧性能的影响，并用超声波振荡、SEM、XRD、H₂-TPR和C₃H₈-TPD等手段对整体式催化剂进行了表征。当球磨时间为60 min，分子筛浆料固含量为38%时，整体式催化剂的涂层上载量可达到178 g?L^-1，涂层脱落率低于0.5%。Pd₂Pt₃-ZSM-5/Cordierite整体式催化剂（贵金属总负载量为1.2 g?L^-1）对于丙烷的催化燃烧具有较好的催化活性（T₅₀=259℃，T₉₀=323℃）和稳定性，具有良好的工业应用前景，其中较低的ZSM-5分子筛硅铝比以及Pd和Pt之间的相互作用增加了对丙烷的吸附能力和表面活性氧物种的数量，从而提高了整体式催化剂的催化活性。     

Performance of alumina-supported noble metal catalysts for the combustion of trichloroethene at dry and wet conditions

The performance of four different alumina-supported noble metal catalysts (0.5% of Pd, Pt, Rh and Ru, respectively) for the deep oxidation of trichloroethene (1000–2500 ppmV, WHSV = 55 h⁻¹) in air was studied in this work. Experiments were carried out at both dry and wet (20,000 ppm of H₂O) conditions. Catalysts were compared in terms of activity, selectivity for the different reaction products (CO₂, HCl, Cl₂, C₂Cl₄, CCl₄ and CHCl₃), and stability at reaction conditions.

As general trend, the activity of the catalysts decreases in the order Ru  Pd > Rh > Pt. Concerning to the effect of the water addition, no important effect on the catalyst activity was observed, except in the case of Pt, for which an increase of the catalytic activity was observed. Reaction mechanism (and hence product distribution) is very similar for Rh, Pd and Pt, being in these cases C₂Cl₄ the only organochlorinated by-product detected. In the case of Ru, the reaction mechanism seems to be quite different, CCl₄ and CHCl₃ being the main organic by-products.

Simple power-law kinetic expressions (first order on trichloroethene concentration for Pd, Rh and Ru, and zeroth order for Pt) provide fairly good fits for catalytic performance of the studied catalysts.

Finally, deactivation studies show that both formation of active metal chlorides (especially in the case of Rh) and fouling (especially for Pd and Pt) are the main deactivation causes.     

Pd catalysts supported on silicon nitride for the combustion of methane: Influence of the crystalline and amorphous phases of the support and of the preparation method on the catalytic performances

Non-oxide refractory materials, such as silicon nitride having high thermal stability and thermal conductivity can be used as catalytic supports. The influence of the Si₃N₄ support nature and of the chemical compounds used for preparations on the physical-chemistry and catalytic properties of the palladium systems in the total oxidation of methane was investigated. A strong influence of the phase composition and the crystalline state of supports on the catalytic properties in the total oxidation of methane of the Pd catalysts was found. The activity of Pd catalysts increases with the -Si₃N₄ content and crystallization state of the support. The catalytic activity of Pd/-Si₃N₄ is also strongly affected by the preparation procedure. The Pd/-Si₃N₄ catalyst obtained by aqueous impregnation is less active and less stable. It was proposed that if water is used as an impregnation solvent, the surface acid-based properties of Si₃N₄ support and/or of the Pd active phase are irreversibly damaged. Pd supported on -Si₃N₄, prepared by impregnation of the Pd precursors in toluene solutions are found to be the most active and stable under reaction conditions.