Multiwalled carbon nanotubes synthesis with high yield utilizing Pt/Al-MCM-41 via catalytic chemical vapour deposition technique

Multiwalled carbon nanotubes (MWNTs) were synthesized over Pt impregnated Al-MCM-41 catalyst by decomposition of acetylene and characterized by XRD and nitrogen sorption isotherm to study the mesophase nature of the material. The optimum temperature and flow rate of the carbon source for CNTs synthesis are 800 °C and 60 mL/min, respectively, within a short reaction period, typically 10 min. Moreover, longer reaction time (i.e. 30 min) favours the formation of more amorphous carbon. When the reaction time is reduced to less than 10 min, formation of amorphous carbon is greatly suppressed by the high yield of MWNTs (85%). The products obtained from the decomposition of acetylene over these catalysts were characterized by TGA, SEM, TEM and Raman spectroscopy. The TEM analysis reveals that CNTs are free from amorphous carbon, whereas Raman spectrum shows two prominent peaks at 1,327 and 1,594 cm⁻¹ as the tangential modes of CNTs. As a conclusion, Pt/Al-MCM-41 is an effective template for MWNTs synthesis using acetylene as a carbon source.     

Effect of lanthanum addition on the thiophene hydrodesulfurization activity over Al-MCM-41 supported molybdenum catalysts

A series of Al-MCM-41 modified with 1–7% lanthanum were used as supports to prepare the Mo/La–Al-MCM-41 catalysts containing 10 wt.% molybdenum. The supports and catalysts were characterized with XRD, BET, XPS, TPD, TEM and SEM, and their catalytic activities were tested for thiophene hydrodesulfurization. The La addition did not cause any significant collapse of the structure and morphology of Al-MCM-41 samples, and increased the acidity of Al-MCM-41 samples. The Mo/La–Al-MCM-41 catalysts showed higher thiophene HDS activity than non-modified catalysts. The La-modified catalysts showed an enhanced butene selectivity but a decreased tetrahydrothiophene selectivity, indicating that the La–Al-MCM-41 supports contained a larger amount of acid sites.     

Kinetics of acetone hydrogenation over Pt/Al2O3 catalysts

The hydrogenation of acetone to isopropanol has been studied in the vapour phase over Pt/Al₂O₃ catalysts. The rate law obtained at a total pressure of 1 atm and temperatures between 303 and 363 K is of the form V=kP⁰_aP^1/2_H exp (-44 kJ mol^?1 RT^?1). The kinetic results are consistent with a Langmuir-Hinshelwood hydrogenation mechanism involving a half hydrogenated species and a non-competitive chemisorption of acetone and hydrogen on the platinum surface. The specific activity (calculated per platinum surface atom) has been found to be scarcely dependent on the platinum particle size. It is suggested that the chemisorption sites are made of a very small ensemble of platinum atoms.     

Ring hydrogenation of naphthalene and 1-naphthol over supported metal catalysts in supercritical carbon dioxide solvent

Catalytic ring hydrogenations of naphthalene and 1-naphthol were studied over several supported metal catalysts in supercritical carbon dioxide solvent at low temperature. Higher concentration of hydrogen in supercritical carbon dioxide and lower reaction temperature were responsible for higher catalyst activity and selectivities to the desired partial ring hydrogenated products as compared with those observed in organic solvent for the same catalyst.     

新型Pt/Al2O3苯加氢催化剂研制

在模拟苯加氢制环己烷工业装置建成的催化剂原粒度活性评价装置上，研究气相苯加氢制环己烷的Pt/Al₂O₃催化剂，主要考察催化剂制备方法、Al₂O₃载体物化性能和不同竞争吸附剂对催化剂性能的影响，提出了苯加氢制环己烷最佳的催化剂推荐工艺操作条件。与参比样对比表明，研制的Pt/Al₂O₃苯加氢催化剂性能达到参比催化剂的水平，催化剂侧压强度明显高于参比催化剂。     

Selective catalytic hydrogenation of naphthalene to tetralin over a Ni-Mo/Al2O3 catalyst

The selective catalytic hydrogenation of naphthalene to high-value tetralin was systematically investigated. A series of Al₂O₃ catalysts containing different active metals (Co, Mo, Ni, W) were prepared by incipient wetness impregnation. The effects of different active metals forms (oxidation, reduction, sulfuration) and reaction conditions on naphthalene hydrogenation were investigated and the catalysts were characterized by XRD, XPS, BET, NH₃-TPD and SEM. Especially, Ni-Mo/Al₂O₃ was first used in this reactive system. The results show that the oxidative 4%NiO-20%MoO₃/Al₂O₃ is the best catalyst for the preparation of tetralin. The conversion of naphthalene and the selectivity of tetralin can reach 95.62% and 99.75% respectively at 200 °C, 8 h and 6 MPa. Compared with reduced and sulfureted 4%NiO-20%MoO₃/Al₂O₃ catalysts, oxidative 4%NiO-20%MoO₃/Al₂O₃ has a well dispersed and uniform monolayer of the active metals, larger pore volume and size, and larger total acidity. NiO-MoO₃/Al₂O₃ has a synergistic effect between NiO activity and MoO₃ selectivity.     

Pt／Al2O3气相苯加氢催化剂的研制

对气相苯加氢制环己烷的Pt／Al2O3苯加氢催化剂进行了研究，考察了催化剂的制备方法、Al2O3载体的物性及竞争吸附剂的种类等对催化剂性能的影响，按优化条件制备了Pt／Al2O3苯加氢催化剂。参考工厂苯加氢制环己烷工艺条件，采用加压原粒度活性评价装置，测试了该催化剂的活性和选择性。评价结果表明，该催化剂的主要性能达到了国外同类型催化剂的水平。     

Enantioselective hydrogenation of pyruvate esters in the mesoporous environment of Pt-MCM-41

Pt-MCM-41 catalysts having loadings of up to 2% Pt have been synthesised using three strategies: (i) direct synthesis from a Pt²⁺-containing gel, (ii) exchange of Na⁺ in Al-MCM-41 (containing 8% aluminium) for Pt²⁺, (iii) exchange of H⁺ in H-MCM-41 (containing 1% aluminium) for Pt²⁺. HRTEM confirmed the retention of the mesoporous structure in the active catalysts and gave information on Pt particle size and location. ²⁷Al NMR provided information on the movement of aluminium within the structure during catalyst preparation. Enantioselective hydrogenation of methyl and ethyl pyruvate was catalysed by cinchonidine-modified Pt-MCM-41 at 293 K and elevated hydrogen pressures; performance was compared to that provided by the standard reference catalyst EUROPT-1. Catalysts prepared by strategies (i) and (ii) performed best, giving values of the enantiomeric excess comparable to those afforded by EUROPT-1 at rates moderated by an order of magnitude by mass transfer effects. Performance was impaired when Pt particle size in the mesopores was so small that conditions favoured racemic reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pt catalysts supported on zeolitized-pumice for the selective hydrogenation of campholenic aldehyde: A characterization and kinetic study

A detailed characterization study of Pt catalysts supported on a novel zeolitized-pumice (Z-PM) support is reported. Two catalysts, named Pt(Cl)/Z-PM and Pt(Ac)/Z-PM, prepared by impregnation from H₂PtCl₆ and Pt(acac)₂ as precursors and subsequent reduction under H₂ at 623 K, were investigated in terms of microstructure, chemical and surface properties by using X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS).Characterization data showed that the microstructural stability of the support was preserved by using Pt(acac)₂ as precursor. It was verified instead that, by using H₂PtCl₆, the microstructure of the support changed during the thermal activation step under hydrogen, favouring a strong interaction between Pt and support as well as the formation of bimetallic Pt–Fe alloys. Moreover, a moderate increase of Pt d-band vacancies with respect to metallic Pt was observed in this catalyst by XPS.The above catalysts were tested in the selective hydrogenation of campholenic aldehydes to the corresponding unsaturated alcohol, naturanol. In comparison to the Pt(Ac)/Z-PM sample, the ex-chloride Pt(Cl)/Z-PM catalyst showed a higher selectivity to naturanol. This behaviour was interpreted on the basis of the different microstructural and electronic properties as evinced by the characterization data.     

Pt/C催化剂的制备及其在对氯苯胺合成中的应用

采用浸渍法制备Pt/C催化剂，考查了催化剂中Pt含量，催化剂还原温度以及第二金属的加入对由对氯硝基苯合成对氯苯胺的影响。结果表明，Pt/C催化剂中Pt含量为2％，还原温度500 ℃效果最佳，加入第二金属后氯苯胺的选择性高达99%以上。通过XRD、SEM和BET等方法对催化剂的失活进行初步探讨，分析发现，失活催化剂的Pt晶粒明显长大、载体形貌发生变化和比表面积变小等是导致催化剂失活的重要因素。     

Ethanol electrooxidation on novel carbon supported Pt/SnOx/C catalysts with varied Pt:Sn ratio

Novel carbon supported Pt/SnO_x/C catalysts with Pt:Sn atomic ratios of 5:5, 6:4, 7:3 and 8:2 were prepared by a modified polyol method and characterized with respect to their structural properties (X-ray diffraction (XRD) and transmission electron microscopy (TEM)), chemical composition (XPS), their electrochemical properties (base voltammetry, CO_ad stripping) and their electrocatalytic activity and selectivity for ethanol oxidation (ethanol oxidation reaction (EOR)). The data show that the Pt/SnO_x/C catalysts are composed of Pt and tin oxide nanoparticles with an average Pt particle diameter of about 2 nm. The steady-state activity of the Pt/SnO_x/C catalysts towards the EOR decreases with tin content at room temperature, but increases at 80 °C. On all Pt/SnO_x/C catalysts, acetic acid and acetaldehyde represent dominant products, CO₂ formation contributes 1-3% for both potentiostatic and potentiodynamic reaction conditions. With increasing potential, the acetaldehyde yield decreases and the acetic acid yield increases. The apparent activation energies of the EOR increase with tin content (19-29 kJ mol⁻¹), but are lower than on Pt/C (32 kJ mol⁻¹). The somewhat better performance of the Pt/SnO_x/C catalysts compared to alloyed PtSn_x/C catalysts is attributed to the presence of both sufficiently large Pt ensembles for ethanol dehydrogenation and C-C bond splitting and of tin oxide for OH generation. Fuel cell measurements performed for comparison largely confirm the results obtained in model studies.     

不同硅铝比ZSM-5负载铁基催化剂二氧化碳加氢性能

CO₂加氢在铁基催化剂上直接制取高附加值化学品是实现其资源化利用的重要途径。通过等体积浸渍法制备了不同硅铝比（25,70,150）的ZSM-5负载的铁基催化剂,考察硅铝比对铁基催化剂上CO₂加氢性能的影响。结果表明,随着硅铝比的升高,催化剂活性先升高后降低,最优化硅铝比为70。CO₂-DRIFTS和CO₂-TPD结果显示,硅铝比为70的ZSM-5载体制备的催化剂具有较多且较强的表面碱性位,促进CO₂分子的活化解离。通过H₂-TPR、XRD、Raman等表征揭示了催化剂结构的演变过程。还原后催化剂的活性金属以单质Fe形式存在,反应过程中单质Fe向Fe₃O₄和FeC_x物种转化。不同硅铝比配位环境影响Fe与C的相互作用,影响FeC_x的生成,从而影响CO₂加氢的活性和选择性。     

中孔碳负载铂催化剂制备及其催化3,4-二氯硝基苯加氢反应

以糠醇为碳源,在酸性中孔模板剂MSU-S上缩合,合成具有中孔结构碳材料(MC),通过浸渍法合成Pt/MC催化剂。采用XRD、BET、SEM和TEM等手段对MC和Pt/MC进行表征,MC富含中孔,有效分散Pt纳米粒子并在反应过程中稳定Pt。研究Pt/MC对3,4-二氯硝基苯催化加氢反应的催化性能,在3,4-二氯硝基苯 1 mmol、催化剂用量100 mg、乙醇5 mL、反应温度30 ℃、常压氢气和反应时间6 h条件下,3,4-二氯硝基苯转化率达100%,3,4-二氯苯胺选择性达99.7%,Pt/MC重复使用5次,催化性能保持不变。     

The promoting effect of Pb on carbon supported Pt and Pt/Ru catalysts for electro-oxidation of ethanol

Carbon supported Pt/Pb and Pt/Ru/Pb catalysts were prepared by deposition of Pb on commercial Pt and Pt/Ru catalysts, respectively. It was found that after addition of Pb, the catalytic activity of Pt and Pt/Ru for ethanol oxidation increased greatly, especially at high potentials. It has been shown that decorating commercial Pt and Pt/Ru catalysts with Pb is a simple and effective way to prepare carbon supported Pt/Pb and Pt/Ru/Pb catalysts for ethanol oxidation. The physical properties of the catalysts were characterized by XRD, EDX and TEM, and it was found that no Pt/Pb and Pt/Ru/Pb alloys were formed.     

Preparation of percycloalkylphosphines by catalytic hydrogenation using a Rh/Pt catalyst of the adams type

By smooth catalytic hydrogenation phenylated phosphine oxides are reduced to the corresponding cyclohexyl derivatives using a Rh/Pt catalyst. In chiral phosphines the optical activity is restored.     

添加Ni对Cu基催化剂乙炔选择性加氢性能的影响

采用等体积浸渍法制备了Cu/Al_2O_3及Cu-Ni/Al_2O_3催化剂,将其应用于乙炔选择性加氢反应。结果表明,与Cu/Al_2O_3催化剂相比,Cu-Ni/Al_2O_3催化剂的加氢活性及乙烯选择性(当反应出口尾气中乙炔物质的量分数减少到0.003%时)明显提高。通过对Cu与Ni的浸渍顺序考察发现,先浸渍Ni制得的Cu-Ni/Al_2O_3催化剂活性有所下降,但乙烯选择性提高;通过对Ni含量的考察发现,当Ni质量分数为2%时,催化剂性能最佳。     

Pd/Ni-MCM-41制备及其对苯甲醛加氢的催化性能

以十六烷基三甲基溴化铵为模板剂,正硅酸乙酯为硅源,MCM-41为载体,碱性条件下,合成Pd/Ni-MCM-41。通过XRD、HR-TEM、FT-IR和BET等对Pd/Ni-MCM-41进行表征。Pd/Ni-MCM-41的比表面积为(444.32～621.69) m^2·g(-1),孔容为(0.54～0.69) cm^3·g^(-1),孔径分布均匀,主要集中在(2～4) nm。将Pd/Ni-MCM-41用于苯甲醛加氢制备苯甲醇反应中,Ni质量分数6%时,在反应温度100℃和反应压力0.20 MPa条件下反应2 h,苯甲醛转化率65.1%,苯甲醇选择性为100%。     

高温下工业NiW/Al2O3催化剂上萘的加氢饱和反应

在中压固定床中,高温条件下研究了工业NiW/Al2O3催化剂上硫化氢气氛中反应温度、反应压力和空速对萘加氢饱和反应过程的影响。实验结果表明,在液时空速为10—30 h-1,氢油体积比为800,高反应温度区320—380℃的实验条件下,萘加氢主要生成四氢萘和十氢萘,而进一步加氢裂化产物较少;提高反应温度,萘转化率和四氢萘的收率下降,加氢裂化产物略有升高,表明高温不利于芳环的加氢饱和;提高加氢反应压力,萘的转化率和四氢萘的芳环加氢程度提高;综合反应结果,提出了高温条件下萘加氢的简化可逆连串反应途径。     

Coupled hydrogenation and ring opening of tetralin on potassium modified Pt/USY catalysts

Coupled hydrogenation and ring opening of tetralin (THN) on Pt/USY catalyst were performed on a high-pressure fixed-bed reactor. The effect of reaction temperature in range of 100–300 °C and the nature of the catalyst (metal and acid sites) on the catalytic performance were studied. The results indicated that the extent of hydrocracking, a sequential reaction of ring opening, should be reduced in order to maintain high yields of the ring opening products (ROP). Introduction of the Pt component accelerated the hydrogenation and ring opening of the THN significantly. It was also found to be an effective way to optimize the acid properties of the catalysts by introducing an appropriate amount of potassium to the catalyst, such that the strong acid sites of the catalysts were diminished, and a higher ROP yield could be obtained as a result of the inhibiting of the hydrocracking activity of the catalyst. When the yield of the C10 fractions could be maintained at 90 wt.%, then a maximal ROP yield of 35.6 wt.% could be obtained on a 0.5 wt.% Pt/USY catalyst loaded with 2.0 wt.% of K.     

Modeling of the enantioselective hydrogenation of 1-phenyl-1,2-propanedione over Pt/Al2O3 catalyst

A kinetic model was developed for the enantioselective hydrogenation of 1-phenyl-1,2-propanedione based on parallel racemic and enantioselective routes in the presence of cinchonidine. The Langmuir–Hinshelwood type of competitive adsorption approach was used in the model, which was combined with a batch reactor model. The proposed model could sufficiently describe the observed kinetic results.