Supported nanometric platinum–nickel catalysts for solvent-free hydrogenation of tetralin

This paper aims to report a method of synthesizing alloyed platinum-nickel nanoclusters on activated carbon to enhance its hydrogenation performance of tetralin without adding solvents. The activated carbon provides a high surface area, while the highly-dispersed platinum acts as the hydrogen adsorption and dissociation site, in addition the Ni can alloy with Pt to induce more electron deficiency. Due to such favorable conditions, the bimetallic Pt–Ni/AC catalysts show good conversion and selectivity for hydrogenation of tetralin within a very short time. Furthermore, after six consecutive cycles, no prominent fluctuations in activity and selectivity are observed. Thus, the supported platinum–nickel nanocatalysts with excellent efficiency and prolonged lifetime for tetralin hydrogenation harbors great significance for future nanocatalyst design.     

Enantioselective hydrogenation of α-ketoesters over Pt/alumina modified with cinchonidine: theoretical investigation of the substrate-modifier interaction

Enantio-differentiation in the asymmetric hydrogenation of -ketoesters to -hydroxyesters over platinum catalysts modified with cinchona-alkaloid modifiers occurs through interaction of the ketoester with the cinchona modifier. The structure of the probable transition complex has been calculated for the system methyl pyruvate (substrate) cinchonidine (modifier) using molecular mechanics and quantum chemistry techniques at both ab initio and semiempirical levels. The calculations suggest that protonated cinchonidine is energetically more likely to interact with the substrate and that the crucial interaction occurs via hydrogen bonding of the quinuclidine nitrogen and the oxygen of the -carbonyl moiety of methyl pyruvate. In this complex the methyl pyruvate is transformed into a half-hydrogenated species which is adsorbed on the platinum surface and on hydrogenation yields the product methyll actate. Theoretical studies indicate that adsorption of the complex leading to (R) -methyl lactate is energetically more favourable than that of the corresponding complex which yields (S) -methyl lactate, which may be the key for the enantio-differentiation.     

Preparation of supported platinum-gold catalysts and alkane reactions on selected platinum and platinum-gold supported “clusters”

A number of methods for the preparation of Aerosil-platinum-gold catalysts was tested using transmission electron microscopy (TEM) and, in some cases, hydrogen chemisorption and X-ray diffraction. With moderate metal loading (5 w/w%) the incipient wetness approach in a number of variations led to poorer metal dispersion than did a cation exchange method. However, at low metal loading (1 w/w%) the incipient wetness method gave excellent dispersion (“clusters”) as also with titania as support.Reaction of n-pentane and of 3,3-dimethylpentane on the cluster catalysts showed the bimetallic clusters to be highly selective hydrogenolysis catalysts. Supporting platinum as dusters on titania gave catalysts which displayed excellent dehydrocyclisation selectivity. These results are interpreted in terms of electronic effects.     

Enantioselective hydrogenation of activated ketones in the presence of Pt–cinchona catalysts. Is the proton transfer concept valid?

Experimental evidences related to the proton transfer in the catalytic system Pt–cinchona alkaloids for enantioselective hydrogenation of activated ketones were collected and analyzed. Both new and earlier results indicate that in aprotic media direct transfer of proton from platinum to the substrate with the involvement of quinuclidine nitrogen as a general rule can be questioned.     

Comparative study of CO and CO2 hydrogenation over supported Rh–Fe catalysts

The hydrogenation of CO, CO + CO₂, and CO₂ over titania-supported Rh, Rh–Fe, and Fe catalysts was carried out in a fixed-bed micro-reactor system nominally operating at 543 K, 20 atm, 20 cm³ min^− 1 gas flow (corresponding to a weight hourly space velocity (WHSV) of 8000 cm³ g_cat^− 1 h^− 1), with a H₂:(CO + CO₂) ratio of 1:1. A comparative study of CO and CO₂ hydrogenation shows that while Rh and Rh–Fe/TiO₂ catalysts exhibited appreciable selectivity to ethanol during CO hydrogenation, they functioned primarily as methanation catalysts during CO₂ hydrogenation. The Fe/TiO₂ sample was primarily a reverse water gas shift catalyst. Higher reaction temperatures favored methane formation over alcohol synthesis and reverse water gas shift. The effect of pressure was not significant over the range of 10 to 20 atm.     

Intramolecular selective hydrogenation of cinnamaldehyde over CeO2–ZrO2-supported Pt catalysts

Selective liquid phase hydrogenation of cinnamaldehyde is reported, for the first time, over CeO₂, ZrO₂, and CeO₂–ZrO₂-supported Pt catalysts. Cinnamyl alcohol is the selective product. These catalysts are highly active and selective even at 25 °C and found to be superior to most of the hitherto known supported Pt catalysts. Alkali addition (NaOH) has enhanced the performance of these catalysts. At an optimized reaction condition, 95.8% conversion of cinnamaldehyde and 93.4% selectivity of cinnamyl alcohol have been obtained. Acidity of the support (due to the presence of ZrO₂ component) and higher electron density at Pt (due to CeO₂ component) are attributed to be responsible for the superior catalytic activity of Pt supported on CeO₂–ZrO₂ composite material.     

Effect of loading method on selective hydrogenation of chloronitrobenzenes over amorphous Ni–B/CNTs catalysts

Carbon nanotubes (CNTs)-supported amorphous Ni–B catalysts were prepared by selectively depositing Ni–B particles inside or outside the CNTs (Ni–B-in/CNTs or Ni–B-out/CNTs). Hydrogenation of chloronitrobenzenes was carried out to test how the Ni–B particle-loading method over the CNTs affected the catalytic performance. Compared with the Ni–B-out/CNTs, the Ni–B-in/CNTs, because of the nanospace limitation inside the CNTs, restricted the size and aggregative behavior of the Ni–B particles better, and formed an amorphous Ni–B alloy with high thermal stability. The Ni–B-in/CNTs exhibited a much higher catalytic activity for hydrogenation of chloronitrobenzenes than the Ni–B-out/CNTs.     

Trends for mono‐aromatic compounds hydrogenation over sulfided Ni, Mo and NiMo hydrotreating catalysts

The relative hydrogenation activity in typical hydrotreating conditions of toluene, mxylene, 1,3,5trimethylbenzene and 1,2,4,5tetramethylbenzene was unexpectedly found to decrease over a sulfided NiMo/Al₂O₃ catalyst and to increase over sulfided Ni/Al₂O₃ and Mo/Al₂O₃ catalysts. This change of activity trend is tentatively interpreted by the formation of a mixed NiMoS phase with a different electronic state compared to Ni or Mo sulfide phases. The nature of the aromatic compound influences strongly the magnitude of the promotion effect of Ni on the activity of the Mo in the sulfided NiMo/Al₂O₃ catalyst.     

Acid function of Al‐MCM‐41 supported platinum catalysts in hydrogenation of benzene, toluene o‐xylene

A series of Al‐MCM‐41 mesoporous materials with different Si/Al ratios are synthesized. The acidities of catalysts are measured by the temperature‐programmed desorption of ammonia (NH₃‐TPD) and IR spectra of pyridine. Their catalytic activities for hydrogenation of benzene, toluene and o‐xylene are investigated on a pulse reactor system. NH₃‐TPD and IR results show that only weak and medium acid sites could be observed on the catalysts, and the number of total acid sites decreases obviously with the increase of the Si/Al ratio whereas the medium acid sites are somewhat constant. The introduction of platinum onto Al‐MCM‐41 material decreases the total acid number by a small amount. The hydrogenation activities of the 1% Pt/HAl‐MCM‐41 catalysts are found to correspond well with the ratio of medium acid sites to total acid sites in the employed catalysts. It is proposed that, in addition to metal sites, the acid sites in the metal–acid interfacial regions are also the active sites for hydrogenation and the medium acid sites play important roles in the reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of Mg and Ce addition to ruthenium based catalysts used in the selective hydrogenation of α,β-unsaturated aldehydes

Ce and Mg were used as promoters in two series of Ru based catalysts supported on alumina (Al₂O₃) and activated carbon (AC). The catalysts were characterized by H₂ chemisorption and temperature-programmed reduction (TPR), and studied in the crotonaldehyde (gas phase) and the citral (liquid phase) hydrogenations. Addition of MgO and CeO₂ decreased the catalytic activity in crotonaldehyde and citral hydrogenations. With regard to the selectivity towards unsaturated alcohols, similar trends were observed for the two reactions. MgO did not influence the selectivity, but CeO₂ increased the selectivity to unsaturated alcohols, especially on carbon supported catalyst. Bulk CeO₂ and Ce/AC catalyst showed low activity but very high selectivity (93 and 100%, respectively) to the unsaturated alcohols. Based on these results and the calorimetric experiments of CO adsorption it was suggested that defect sites on the surface of the promoter are the active and highly selective sites for unsaturated aldehydes due to their influence on the CO bond activation.     

AlCl3-promoted MCM-41-supported platinum catalysts with high activity and sulfur-tolerance for tetralin hydrogenation: Effect of Pt–Al interaction

AlCl₃-promoted MCM-41-supported platinum catalysts with different Al–Pt interaction sequences were prepared for tetralin hydrogenation under sulfur-containing condition. Platinum dispersion and acidity of the catalysts were improved by the introduction of aluminum. The aluminum-containing catalysts have similar acidity. Al–Pt interaction leads to the formation of electron-deficient platinum (Pt^δ +). A great improvement in sulfur-tolerance was observed on the catalyst that aluminum is grafted after the supporting of platinum.     

Highly selective hydrogenation of phenol and derivatives over Pd catalysts supported on SiO2 and γ-Al2O3 in aqueous media

Pd/Al₂O₃ and Pd/SiO₂ catalysts containing Pd nanoparticles in the size range of 3–13 nm were prepared and investigated in direct selective hydrogenation of phenol to cyclohexanone. Catalysts with 3 nm Pd nanoparticles present highly active and promoted the selective formation of cyclohexanone under atmospheric pressure of hydrogen in aqueous media without additives. Conversion of 99% and a selectivity higher than 99% were achieved within 3 h at 333 K. The generality of Pd/Al₂O₃ catalyst with 3 nm Pd nanoparticles for this reaction was demonstrated by selective hydrogenation of other hydroxylated aromatic compounds with similar performance.     

Kinetics of methane combustion over Pt and Pt–Pd catalysts

A kinetic study was performed over thermally aged and steam-aged Pt and Pt–Pd catalysts to investigate the effect of temperature, and methane and water concentrations on the performance of catalysts in the range of interest for environmental applications. It was found that both catalysts permanently lose a large portion of their initial activity as result of exposure to 5 vol.% water in the reactor feed. Empirical power-law and LHHW type of rate equations were proposed for methane combustion over Pt and Pt–Pd catalysts respectively. Optimization was used to determine the parameters of the proposed rate equations using the experimental results. The overall reaction orders of one and zero in methane and water concentration was found for stabilized steam-aged Pt catalyst in the presence and absence of water. The apparent self-inhibition effect caused by methane over Pt–Pd catalyst in the absence of water was associated with the inhibiting effect of water produced during the combustion of methane. A significant reversible inhibition effect was also observed over steam-aged Pt–Pd catalyst when 5 vol.% water vapor was added to the reactor feed stream. A significant reduction in both activity and activation energy was observed above temperatures of approximately 550 °C for steam-aged Pt–Pd catalyst in the presence of water (the activation energy dropped from a value of 72.6 kJ/mol to 35.7 kJ/mol when temperature exceeded 550 °C).     

Copolymerization of ethylene with α-olefins over supported titanium–magnesium catalysts. II. Comonomer as a chain transfer agent

The data on the effect of comonomer (propylene and 1-hexene) on molecular weight (M_w), molecular weight distribution (MWD), and content of terminal double bonds were obtained for ethylene/α-olefin copolymers produced over a supported titanium–magnesium catalyst (TMC) upon polymerization in the absence of hydrogen. The experimental data on the effect of comonomer concentration on M_w of polymers were used to calculate the ratios between the effective rate constants of chain transfer with monomer and the propagation rate constant. It was shown that the effective rate constant of chain transfer with monomers increases in the row of monomers: ethylene < 1-hexene < propylene. Meanwhile, the data on the effect of copolymers on content of terminal double bonds of various types demonstrate that different reactions of chain transfer with comonomer may simultaneously occur during copolymerization. It results in simultaneous formation of terminal vinylidene and trans-vinylene bonds. Therefore, the calculated rate constants of chain transfer with comonomer are complex values, which include the rate constants of chain transfer with comonomer occurring via different mechanisms. The data on MWD, short chain branching (SCB) and terminal double bonds content of different types were obtained by molecular weight fractionation of copolymers followed by the analysis of narrow fractions. The analysis of the data on MWDs of SCB and terminal double bonds shows that active sites of the TMC are considerably heterogeneous with respect to the rates of different chain transfer reactions with monomers. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A preliminary study of the n‐heptane conversion over supported platinum acid–base ZrPON catalysts

The catalytic behaviour of zirconium phosphate oxynitrides ZrPON and Pt supported ZrPON catalysts in n‐heptane conversion is examined. The results show that the distribution of the products depends on the reaction temperature. In addition, it has been established that the acid–base properties of ZrPON supports greatly influence the n‐heptane reforming reactions since the increase of ZrPON basicity enhances both n‐heptane conversion and aromatics selectivity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enhancement of pyrolysis gasoline hydrogenation over Zn- and Mo-promoted Ni/γ-Al2O3 catalysts

Alumina-supported nickel catalysts modified by Zn and/or Mo were prepared and characterized using several techniques (XRF, BET, XRD, XPS, and TPR). The effect of Zn and Mo on catalytic hydrogenation activity was evaluated in hydrogenation of pyrolysis gasoline (PyGas) using styrene conversion for monitoring the activity trend in a fixed-bed reactor under the following conditions: temperature of 70–120 °C, H₂:PyGas volume ratio of 200:1, pressure of 2.8 MPa, and volume space velocity of 3.0 h^− 1. The promoted Ni-based catalysts exhibited excellent catalytic activity for the hydrogenation of PyGas. The styrene conversion doubled after the introduction of Zn and Mo.     

Shape-selective synthesis of 4,4′-dimethylbiphenyl. 1. Methylation of 4-methylbiphenyl over modified zeolite catalysts

Methylation of 4-methylbiphenyl with methanol was carried out using zeolites HY, HM, and HZSM-5 as catalysts under fixed-bed down-flow conditions. HY and HM display no shape selectivity, but HZSM-5 shows moderate selectivity to the target product, 4,4-dimethylbiphenyl (4,4-DMBP) under proper reaction conditions. Modification of the surface of HZSM-5 zeolite can improve the selectivity to 4,4-DMBP, especially the simultaneous modification of external and internal surface with inorganic P compound. The selectivity to 4,4-DMBP can be increased to as high as 65% over the HZSM-5 modified with a small amount of ammonium hydrogen phosphate.