骨架镍催化剂在腈类加氢中的应用

介绍3种类型骨架镍催化剂在己二腈加氢中的应用,并对加氢结果进行比较。结果表明,3种类型骨架镍催化剂均可以实现己二腈加氢,己二腈转化率和己二胺选择性较高。同时对其他二腈如2-甲基戊二腈和丁二腈进行加氢研究,进一步表明骨架镍在腈类加氢中具有独特优势。     

Hydrogen storage using heterocyclic compounds: The hydrogenation of 2-methylthiophene

Alkyl substituted thiophenes are promising candidates for hydrogen carriers, as their dehydrogenation reactions are known to occur under mild conditions. Four types of catalysts, including supported noble metals, bimetallic noble metals, transition metal phosphides and transition metal sulfides, have been investigated for 2-methylthiophene (2MT) hydrogenation and ring-opening. The major products were tetrahydro-2-methylthiophene (TH2MT), pentenes and pentane, with very little C₅-thiols observed. The selectivity towards the desired product TH2MT follows the order: noble metals > bimetallics > phosphides > sulfides. The best hydrogenation catalyst was 2% Pt/Al₂O₃ which exhibited relatively high reactivity and selectivity towards TH2MT at moderate temperatures. Temperature-programmed reaction (TPR) experiments revealed that pentanethiol became the major product, especially with HDS catalysts like CoMoS/Al₂O₃ and WP/SiO₂.     

Ultra-deep hydrodesulfurization on MoS2 and Co0.1MoS2: Intrinsic vs. environmental factors

A hydrogenation index (HI), measured in the hydrodesulfurization (HDS) of dibenzothiophene (DBT), is used to estimate the intrinsic hydrogenation selectivities of MoS₂, Co_0.1MoS₂, and two supported HDS catalysts. The HI and catalyst activity for desulfurizing 4,6-diethyl-DBT follow the same trend: MoS₂ ? Co_0.1MoS₂ ? supported catalysts. For desulfurizing a petroleum fraction rich in 4,6-alkyl-DBTs and 4-alkyl-DBTs, the activity decreases as follows: Co_0.1MoS₂ > supported catalysts ? MoS₂. These results introduce an apparent conundrum: MoS₂ has such a high hydrogenation power and activity for desulfurizing 4,6-diethyl-DBT, why does it perform poorly in real-feed tests? This conundrum is resolved by showing that an ultra-deep HDS catalyst requires an optimum balance between an intrinsic factor (hydrogenation function) and an environmental factor (tolerance of organonitrogen). Incorporating Co into MoS₂ lowers the hydrogenation function of MoS₂ and hence improves tolerance of organonitrogen. This conclusion corroborates the prediction of an early modeling study.     

Deactivation of supported skeletal Ni catalyst and effect of regeneration temperature on its catalytic performance

Deactivation and regeneration of supported skeletal Ni catalyst applied to hydrogenation of indene and styrene in fixed-bed reactor were investigated. The significant aggregation of skeletal Ni and formation of coke precursors were the main reasons for deactivation of catalyst. Furthermore, TG-DTA, XRD, SEM, BET and H₂-TPR were utilized to characterize the regenerated catalysts and calcining the spent catalysts in air at 550 °C for 3 h and then reducing in H₂ at 450 °C for 3 h under 240 h^− 1 (GHSV) could recover its activity according to hydrogenation evaluation results.     

Microwave-assisted,rapid cycloaddition of allyl glycidyl ether and CO2 by employing pyridinium-based ionic liquid catalysts

This study investigated the use of pyridinium-based ionic liquids (ILs) as an efficient catalyst for the rapid solvent-free microwave-assisted cycloaddition of allyl glycidyl ether (AGE) and CO₂ to yield allyl glycidyl carbonate (AGC) under moderate reaction conditions. The cycloaddition reaction occurred over a short reaction time of 30 s, resulting in a high turnover frequency (TOF) ranging from 200 to 7000 h^− 1. The effects of alkyl chain length and anion of pyridinium-based catalysts on the cycloaddition reactivity were studied. The effects of reaction parameters such as the amount of catalyst, microwave power, CO₂ pressure, and reaction time were also investigated.     

New phenomenon in competitive hydrogenation of binary mixtures of activated ketones over unmodified and cinchonidine-modified Pt/alumina catalyst

Competitive hydrogenations of eight binary mixtures of ethyl pyruvate (EP), methyl benzoylformate (MBF), ketopantolactone (KPL), pyruvic aldehyde dimethyl acetal (PA) and trifluoroacetophenone (TFAP) on platinum/alumina catalysts unmodified (racemic hydrogenation) and modified by cinchonidine (chiral hydrogenation) were studied under the experimental conditions of the Orito reaction. Reaction rates of chiral and racemic hydrogenations were determined and relative adsorption coefficients were calculated. In the competitive chiral hydrogenation of EP + MBF, EP + TFAP and KPL + MBF binary mixtures a new phenomenon was observed: namely the EP and KPL are hydrogenated faster than MBF and TFAP, whereas in racemic one the MBF and TFAP are hydrogenated faster than EP or KPL. Effects of the activated ketones structure on their reactivity and the stability of the surface complexes are discussed. It was found that differences in rate enhancement are caused by the differences both in the adsorptivity and in the reactivity of adsorbed substrates and adsorbed intermediate complexes.     

Higher alcohol synthesis from syngas over KCoMoP catalysts

Carbon modified K_xCo_0.75MoP (0 ≤ x ≤ 1.5) catalysts were prepared from a sol–gel method using citric acid as a complexant. The catalysts were evaluated with CO hydrogenation and characterized by XRD, XPS and CO₂-TPD techniques. Results show that the addition of cobalt accelerates the dispersion of catalytic components in phosphide catalysts while the participation of potassium in phosphide catalysts enhances the interaction between MoP and CoMoP and facilitates the rearrangement of electron density in different Mo species. In K₁Co_0.75MoP, a large number of Mo^4 + species resulted in high selectivity to C_2 + higher alcohol.     

Synthesis and characterization of new Mg–O–F system and its application as catalytic support

The Mg–O–F system (MgF₂–MgO) with different contents of MgF₂ (100–0%) and MgO is tested as support of iridium catalysts in the hydrogenation of toluene as a function of the MgF₂/MgO ratio. Mg–O–F samples have been prepared by the reaction of magnesium carbonate with hydrofluoric acid. The MgF₂–MgO supports, after calcination at 500 °C, are classified as mesoporous of surface area (34–135 m²·g^− 1) depending on the amount of MgO introduced. The Ir/Mg–O–F catalysts have been tested in the hydrogenation of toluene. The highest activity, expressed as TOF, min^− 1, was obtained for the catalyst supported on Mg–O–F containing 75 mol%MgF₂.     

Vapour phase hydrogenation of phenol over Pd/C catalysts: A relationship between dispersion,metal area and hydrogenation activity

A series of palladium supported on activated carbon catalysts, with Pd varying from 0.5 to 6.0 wt%, were prepared via wet impregnation method using PdCl₂ · xH₂O as a precursor salt. The dried samples were further reduced at 573 K in hydrogen and characterized by CO adsorption at room temperature in order to determine the dispersion, metal area and particle size. The catalysts were tested for vapour phase phenol hydrogenation in a fixed-bed all glass micro-reactor at a reaction temperature of 453 K under normal atmospheric pressure. The decrease in metal surface area as well as dispersion with corresponding increase in turn-over frequency (TOF) against palladium loadings suggest the unusual inverse relationship that exist between Pd dispersion and phenol hydrogenation activity over Pd/carbon catalysts. The stability of TOF at larger crystallite size indicates that phenol hydrogenation is less sensitive reaction especially beyond 3 wt% of Pd content. It is evident from the results that structural properties of the catalysts strongly influence the availability of Pd atoms on the surface for CO chemisorption and hence for phenol hydrogenation. A comparison between selectivity and product yield of the reaction against overall phenol conversion indicates that changes in reaction selectivity for cyclohexanone or cyclohexanol is independent of phenol conversion level and either of the product is not formed at the cost of another. The stability of the catalysts with reaction time suggests that coke formation on the surface of the catalyst is less significant and the formation of cyclohexanone remains almost total even at higher reaction temperatures.     

Clean production of chloroanilines by selective gas phase hydrogenation over supported Ni catalysts

We have established for the first time 100% selectivity in the continuous gas phase hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline for reaction over a series of oxide and carbon supported Ni catalysts (6 ± 2%, w/w) under mild reaction conditions (T = 393 K, P = 1 atm). Catalyst activation by temperature programmed reduction (TPR) is addressed, BET area and H₂ uptake measurements provided and mean metal particle sizes evaluated by transmission electron micrographic (TEM) analysis. The following activity sequence has been determined: Ni/Al₂O₃ > Ni/SiO₂ > Ni/Activated Carbon > Ni/graphite. Pd/Al₂O₃, as an alternative catalyst, delivered an appreciably higher activity but with the production of nitrobenzene (principal product) and aniline (secondary product), i.e. hydrodechlorination with subsequent –NO₂ reduction prevailed. Exclusive formation of the corresponding haloaniline is also demonstrated for the hydrogenation of o-chloronitrobenzene, m-chloronitrobenzene and p-bromonitrobenzene over Ni/Al₂O₃. A lower hydrogenation rate is established for p-CNB relative to nitrobenzene, consistent with a halogen substituent deactivation effect. While the Ni catalysts suffered a loss of activity with time-on-stream, exclusive selectivity to the haloamine product was maintained. These preliminary results can serve as a basis for the development of a cleaner, high throughput production of commercially important haloamines.     

Influence of the support nature and morphology on the performance of ruthenium catalysts for partial hydrogenation of benzene in liquid phase

This paper is aimed at studying the influence of the support nature and morphology on the performance of ruthenium catalysts for partial hydrogenation of benzene in liquid phase. Therefore, Al₂O₃ and Nb₂O₅ supports were employed with different values of particle diameter and superficial specific area. The catalysts were prepared through incipient impregnation from an aqueous solution of the RuCl₃·xH₂O precursor. After impregnation, the solids underwent a reduction treatment under H₂ flow at the temperature of 573 K. The solids were characterized through the techniques of particle size distribution, XRD, BET, SEM + EDX and TPR. The catalytic performances were evaluated within the hydrogenation of benzene in liquid phase, conducted at 373 K under constant pressure of 5.0 MPa of H₂. For the conditions employed, the results show that the support nature practically exerts no influence upon the selectivity of the intermediate product to the benzene → cyclohexene → cyclohexane reaction. However, the increase in the particle diameter or in the superficial specific area of the support decreases the yield of cyclohexene.     

The effect of TiO2 particle size on the characteristics of Au–Pd/TiO2 catalysts

The nanocrystalline TiO₂ materials with average crystallite sizes of 9 and 15 nm were synthesized by the solvothermal method and employed as the supports for preparation of bimetallic Au/Pd/TiO₂ catalysts. The average size of Au–Pd alloy particles increased slightly from sub-nano (< 1 nm) to 2–3 nm with increasing TiO₂ crystallite size from 9 to 15 nm. The catalyst performances were evaluated in the liquid-phase selective hydrogenation of 1-heptyne under mild reaction conditions (H₂ 1 bar, 30 °C). The exertion of electronic modification of Pd by Au–Pd alloy formation depended on the TiO₂ crystallite size in which it was more pronounced for Au/Pd on the larger TiO₂ (15 nm) than on the smaller one (9 nm), resulting in higher hydrogenation activity and lower selectivity to 1-heptene on the former catalyst.     

Effect of component interaction on the activity of Co/CuZnO for CO hydrogenation

Co/CuZnO is known as a base metal catalyst active for C₂₊ oxygenate synthesis. This study probed the interactions of the different components of Co/CuZnO catalysts on CO hydrogenation using Fischer–Tropsch synthesis (250 °C, H₂/CO = 2) and SSITKA. Only combination of all three metal components produced a catalyst with relatively high C₂₊ oxygenate selectivity, but with much lower activity compared to that for Co/Al₂O₃. In situ reaction characterizations, albeit at somewhat different conditions than alcohol synthesis, helped explain interaction of the components. SSITKA, under methanation conditions, indicated that the most striking feature for the combination of Co with ZnO and/or Cu was a much decreased amount of reaction intermediates. Ethane hydrogenolysis results suggested that the different components for these catalysts were in close contact and few or no large ensembles (n ? 12) of Co atoms existed, confirming that ZnO and/or Cu covered/blocked a substantial number of active sites on Co for CO hydrogenation.     

Impact of nitrogen doping of carbon nanospheres on the nickel-catalyzed hydrogenation of butyronitrile

Three nickel catalysts supported on carbon and nitrogen-doped carbon nanospheres have been prepared by deposition-precipitation (DP) with urea (ca. 2% w/w). The nanospheres were prepared by thermal pyrolysis of benzene (CNS_B), aniline (CNS_A) and nitrobenzene (CNS_N) and characterized by transmission electron microscopy (TEM), N₂ adsorption–desorption, temperature-programmed oxidation (TPO), X-ray diffraction (XRD), elemental (CHN) analysis, X-ray photoelectron spectroscopy (XPS), temperature-programmed decomposition (TPD) and acid/base titrations, revealing different graphitic characteristics and different distribution of nitrogen (when present) functionalities. Upon Ni introduction, the catalysts were characterized by temperature-programmed reduction (TPR), XRD and TEM. Surface area weighted mean Ni particle diameters (post activation at 603 K) were in the range 10.5–18.2 nm. Ni particle size exhibited a big dependence on CNS nitrogen doping, where nitrogen introduction, essentially in the quaternary form, enhanced metal sintering by enriching the surface electron density of the support. The catalysts were tested in the gas phase hydrogenation of butyronitrile (T = 493 K). Extracted specific reaction rates in the steady state followed the sequence: Ni/CNS_B < Ni/CNS_A < Ni/CNS_N. When the active metal was physically mixed with the support, the following sequence was obtained: Ni + CNS_B < Ni + CNS_A < Ni + CNS_N. Our results demonstrate that doping carbon nanospheres with nitrogen strongly impacts on reactant adsorption and metal sintering, both critical aspects in the hydrogenation of nitriles. Selectivity was not sensitive to the support (or the physical mixture) employed and was in all cases close to 100% to the primary amine.     

Selection of ionic liquids for the extraction of aromatic hydrocarbons from aromatic/aliphatic mixtures

The separation of aromatic hydrocarbons (benzene, toluene, ethyl benzene and xylenes) from C₄ to C₁₀ aliphatic hydrocarbon mixtures is challenging since these hydrocarbons have boiling points in a close range and several combinations form azeotropes. In this work, we investigated the separation of toluene from heptane by extraction with ionic liquids.Several ionic liquids are suitable for extraction of toluene from toluene/heptane mixtures. The toluene/heptane selectivities at 40 °C and 75 °C with several ionic liquids, [mebupy]BF₄, [mebupy]CH₃SO₄, [bmim]BF₄ (40 °C) and [emim] tosylate (75 °C), are a factor of 1.5–2.5 higher compared to those obtained with sulfolane (S_tol/hept = 30.9, D_tol = 0.31 at 40 °C), which is the most industrially used solvent for the extraction of aromatic hydrocarbons from a mixed aromatic/aliphatic hydrocarbon stream. From these five ionic liquids, [mebupy]BF₄ appeared to be the most suitable, because of a combination of a high toluene distribution coefficient (D_tol = 0.44) and a high toluene/heptane selectivity (S_tol/hept = 53.6). Therefore, with [mebupy]BF₄ also extraction experiments with other aromatic/aliphatic combinations (benzene/n-hexane, ethylbenzene/n-octane and m-xylene/n-octane) were carried out. The aromatic/aliphatic selectivities were all in the same range, from which it can be concluded that the toluene/heptane mixture is a representative model system for the aromatic/aliphatic separation.     

Effect of mixed γ- and χ-crystalline phases in nanocrystalline Al2O3 on the dispersion of cobalt on Al2O3

This paper reports the results of a study into the effect of mixed γ and crystalline phases in Al₂O₃ on the characteristics and catalytic activities for CO hydrogenation of Co/Al₂O₃ catalysts. The catalysts were characterized by X-ray diffraction, N₂ physisorption, transmission electron microscopy, and H₂ chemisorption. Increasing Co loading from 5 to 20 wt% for the mixed phase Al₂O₃-supported Co catalysts resulted in a constant increase in both the number of cobalt metal active sites and the hydrogenation activities. However, for those supported on γ-Al₂O₃, Co dispersion increased up to 15 wt%Co and declined at 20 wt%Co loading. It is suggested that the spherical-shape like morphology of the χ-phase Al₂O₃ prevented agglomeration of Co particles, especially at high Co loadings.     

Effects of preparation conditions in hydrothermal synthesis of highly active unsupported NiMo sulfide catalysts for simultaneous hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene

Unsupported NiMo sulfide catalysts were prepared from ammonium tetrathiomolybdate (ATTM) and nickel nitrate by using a hydrothermal synthesis method involving water, organic solvent and hydrogen. The activity of these catalysts in the simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was much higher than that of the commercial NiMo/Al₂O₃ sulfide catalysts. Interestingly, the unsupported NiMo sulfide catalysts showed higher activity for hydrogenation (HYD) pathway than the direct desulfurization (DDS) pathway in the HDS of DBT. The same trends were observed for the HDS of 4,6-DMDBT. Morphology, surface area, pore volume and the HDS activity of unsupported NiMo sulfide catalyst depended on the catalyst preparation conditions. Higher temperature and higher H₂ pressure and addition of an organic solvent were found to increase the HDS activity of unsupported NiMo sulfide catalysts for both DBT and 4,6-DMDBT HDS. Higher preparation temperature increased HYD selectivity but decreased DDS selectivity. High-resolution TEM images revealed that unsupported NiMo sulfide prepared at 375 °C shows lower number of layers in the stacks of catalyst with more curvature and shorter length of slabs compared to that prepared at 300 °C. On the other hand, higher preparation pressure increased DDS selectivity but decreased HYD selectivity for HDS of 4,6-DMDBT. HRTEM images showed higher number of layers in the stack for the NiMo sulfide prepared under an initial H₂ pressure of 3.4 MPa compared to that under 2.1 MPa. The optimal Ni/(Mo + Ni) ratio for the NiMo sulfide catalyst was 0.5, higher than that for the conventional Al₂O₃-supported NiMo sulfide catalysts. This was attributed to the high dispersion of the active species and more active NiMoS generated. The present study also provides new insight for controlling the catalyst selectivity as well as activity by tailoring the hydrothermal preparation conditions.     

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.     

Selection of ionic liquids for the extraction of aromatic hydrocarbons from aromatic/aliphatic mixtures

The separation of aromatic hydrocarbons (benzene, toluene, ethyl benzene and xylenes) from C₄ to C₁₀ aliphatic hydrocarbon mixtures is challenging since these hydrocarbons have boiling points in a close range and several combinations form azeotropes. In this work, we investigated the separation of toluene from heptane by extraction with ionic liquids.Several ionic liquids are suitable for extraction of toluene from toluene/heptane mixtures. The toluene/heptane selectivities at 40 °C and 75 °C with several ionic liquids, [mebupy]BF₄, [mebupy]CH₃SO₄, [bmim]BF₄ (40 °C) and [emim] tosylate (75 °C), are a factor of 1.5–2.5 higher compared to those obtained with sulfolane (S_tol/hept = 30.9, D_tol = 0.31 at 40 °C), which is the most industrially used solvent for the extraction of aromatic hydrocarbons from a mixed aromatic/aliphatic hydrocarbon stream. From these five ionic liquids, [mebupy]BF₄ appeared to be the most suitable, because of a combination of a high toluene distribution coefficient (D_tol = 0.44) and a high toluene/heptane selectivity (S_tol/hept = 53.6). Therefore, with [mebupy]BF₄ also extraction experiments with other aromatic/aliphatic combinations (benzene/n-hexane, ethylbenzene/n-octane and m-xylene/n-octane) were carried out. The aromatic/aliphatic selectivities were all in the same range, from which it can be concluded that the toluene/heptane mixture is a representative model system for the aromatic/aliphatic separation.     

Aqueous-phase hydrogenation of biomass-derived itaconic acid to methyl-γ-butyrolactone over Pd/C catalysts: Effect of pretreatments of active carbon

The effect of active carbon pretreatment on the catalytic performance of Pd/C catalysts in the hydrogenation of itaconic acid was studied. The catalysts were prepared by deposition–precipitation and characterized by XRD, BET, NH₃-TPD, TEM and FT-IR. Due to the modification of the surface functional groups, surface structure and surface acidities of active carbon via pretreatment, the Pd/C catalysts showed varied catalytic performances. High dispersion and uniform particles were conducive to the excellent activity of Pd/C catalyst with support copretreated with HNO₃ and NaClO, which exhibited 89.5% selectivity towards methyl-γ-butyrolactone at 180 °C, 4 MPa H₂ for 20 h.