Selectivity control for the catalytic 1,3-butadiene hydrogenation on Pt(111) and Pd(111) surfaces: Radical versus closed-shell intermediates

The hydrogenation of 1,3-butadiene to different C4H8 species on both Pd(111) and Pt(111) surfaces has been studied by means of periodic slabs and DFT. We report the adsorption structures for the various mono- and dihydrogenated butadiene intermediates adsorbed on both metal surfaces. Radical species are more clearly stabilized on Pt than on Pd. The different pathways leading to these radicals have been investigated and compared to those producing 1-butene and 2-butene species. On palladium, the formation of butenes seems to be clearly favored, in agreement with the high selectivity to butenes observed experimentally. In contrast, the formation of dihydrogenated radical species seems to be competitive with that of butenes on platinum, which could explain its poorer selectivity to butenes and the formation of butane as a primary product.     

Chemoselective Hydrogenation of Nitroaromatics at the Nanoscale Iron(III)–OH–Platinum Interface

Catalytic hydrogenation of nitroaromatics is an environment‐benign strategy to produce industrially important aniline intermediates. Herein, we report that Fe(OH)_x deposition on Pt nanocrystals to give Fe(OH)_x/Pt, enables the selective hydrogenation of nitro groups into amino groups without hydrogenating other functional groups on the aromatic ring. The unique catalytic behavior is identified to be associated with the Fe^III‐OH‐Pt interfaces. While H₂ activation occurs on exposed Pt atoms to ensure the high activity, the high selectivity towards the production of substituted aniline originates from the Fe^III‐OH‐Pt interfaces. In situ IR, X‐ray photoelectron spectroscopy (XPS), and isotope effect studies reveal that the Fe³⁺/Fe²⁺ redox couple facilitates the hydrodeoxygenation of the ‐NO₂ group during hydrogenation catalysis. Benefitting from Fe^III‐OH‐Pt interfaces, the Fe(OH)_x/Pt catalysts exhibit high catalytic performance towards a broad range of substituted nitroarenes.     

Thermal chemistry of C4 hydrocarbons on Pt(111): Mechanism for double-bond isomerization

The thermal chemistry of a number of C4 hydrocarbons (1,3-butadiene, 1-bromo-3-butene, 1-bromo-2-butene, trans-2-butene, cis-2-butene, 1-butene, 2-iodobutane, 1-iodobutane, and butane) was investigated on clean and hydrogen- and deuterium-predosed Pt(111) single-crystal surfaces by temperature-programmed desorption and reflection-absorption infrared spectroscopy. A combination of rapid beta-hydride eliminations from alkyls to olefins and the reverse insertions of those olefins into metal-hydrogen bonds explains the hydrogenation, dehydrogenation, and H-D exchange products that desorb from the surface. A preference for hydrogenation at the end carbons and dehydrogenation from the inner carbons also explains the extent of the isotope exchange and the preferential isomerization of 1-butene to 2-butene observed on this Pt(111) surface. The reactions of more dehydrogenated C4 species is also discussed.     

Chemoselective Hydrogenation of Nitroaromatics at the Nanoscale Iron(III)–OH–Platinum Interface

Catalytic hydrogenation of nitroaromatics is an environment-benign strategy to produce industrially important aniline intermediates. Herein, we report that Fe(OH)_x deposition on Pt nanocrystals to give Fe(OH)_x/Pt, enables the selective hydrogenation of nitro groups into amino groups without hydrogenating other functional groups on the aromatic ring. The unique catalytic behavior is identified to be associated with the Fe^III-OH-Pt interfaces. While H₂ activation occurs on exposed Pt atoms to ensure the high activity, the high selectivity towards the production of substituted aniline originates from the Fe^III-OH-Pt interfaces. In situ IR, X-ray photoelectron spectroscopy (XPS), and isotope effect studies reveal that the Fe³⁺/Fe²⁺ redox couple facilitates the hydrodeoxygenation of the -NO₂ group during hydrogenation catalysis. Benefitting from Fe^III-OH-Pt interfaces, the Fe(OH)_x/Pt catalysts exhibit high catalytic performance towards a broad range of substituted nitroarenes.     

Facile and Large-Scale Fabrication of Sub-3 nm PtNi Nanoparticles Supported on Porous Carbon Sheet: A Bifunctional Material for the Hydrogen Evolution Reaction and Hydrogenation

Facile and large-scale preparation of materials with uniform distributions of ultrafine particles for catalysis is a challenging task, and it is even more difficult to obtain catalysts that excel in both the hydrogen evolution reaction (HER) and hydrogenation, which are the corresponding merging and splitting procedures of hydrogen, respectively. Herein, the fabrication of ultrafine bimetallic PtNi nanoparticles embedded in carbon nanosheets (CNS) by means of in situ self-polymerization and annealing is reported. This bifunctional catalyst shows excellent performance in the hydrogen evolution reaction (HER) and the hydrogenation of p-nitrophenol. Remarkably PtNi bimetallic catalyst with low metal loading (PtNi₂@CNS-600, 0.074 wt % Pt) exhibited outstanding HER activity with an overpotential as low as 68 mV at a current density of 10 mA cm⁻² with a platinum loading of only 0.612 μg_Pt cm⁻² and Tafel slope of 35.27 mV dec⁻¹ in a 0.5 m aqueous solution of H₂SO₄, which is comparable to that of the 20 % Pt/C catalyst (31 mV dec⁻¹). Moreover, it also shows superior long-term electrochemical durability for at least 30 h with negligible degradation compared with 20 % Pt/C. In addition, the material with increased loading (mPtNi₂@CNS-600, 2.88 % Pt) showed robust catalytic activity for hydrogenation of p-nitrophenol at ambient pressure and temperature. The catalytic activity towards hydrogen splitting is a circumstantial evidence that agrees with the Volmer–Tafel reaction path in the HER.     

Highly Active Supported Pt Nanocatalysts Synthesized by Alcohol Reduction towards Hydrogenation of Cinnamaldehyde: Synergy of Metal Valence and Hydroxyl Groups

The hydrogenation of α,β‐unsaturated aldehydes to allylic alcohols or saturated aldehydes provides a typical example to study the catalytic effect on structure‐sensitive reactions. In this work, supported platinum nanocatalysts over hydrotalcite were synthesized by an alcohol reduction method. The Pt catalyst prepared by the reduction with a polyol (ethylene glycol) outperforms those prepared with ethanol and methanol in the hydrogenation of cinnamaldehyde. The selectivity towards the C=O bond is the highest over the former, although its mean size of Pt particles is the smallest. The hydroxyl groups on hydrotalcite could act as an internally accessible promoter to enhance the selectivity towards the C=O bond. The optimal Pt catalyst showed a high activity with an initial turnover frequency (TOF) of 2.314 s^?1. This work unveils the synergic effect of metal valence and in situ promoter on the chemoselective hydrogenation, which could open up a new direction in designing hydrogenation catalysts.     

Mo(CO)3(NCMe)(PPh3)2: Synthesis, X-ray structure and evaluation of its catalytic activity for the homogeneous hydrogenation of olefins and their mixtures

The complex Mo(CO)₃(NCMe)(PPh₃)₂, was synthesized by the reaction of Mo(NCMe)₃(CO)₃ with two equivalents of PPh₃ and characterized by UV–Vis, IR, NMR and X-ray diffraction. This complex was used as a catalyst precursor for the hydrogenation of 1-hexene, styrene, cyclohexene and 2,3-dimethyl-1-butene and their mixtures under moderate conditions in homogeneous media. Under mild reaction conditions (T = 373 K, P = 60 atm), the substrates showed the following reactivity order: styrene > 1-hexene > cyclohexene > 2,3-dimethyl-1-butene. A quaternary equimolar mixture showed a different hydrogenation order: 1-hexene > cyclohexene > styrene > 2,3-dimethyl-1-butene; the presence of dibenzothiophene or mercury does not interfere with the activity of the catalyst.     

Mechanisms of Methylenecyclobutane Hydrogenation over Supported Metal Catalysts Studied by Parahydrogen-Induced Polarization Technique

In this work the mechanism of methylenecyclobutane hydrogenation over titania-supported Rh, Pt and Pd catalysts was investigated using parahydrogen-induced polarization (PHIP) technique. It was found that methylenecyclobutane hydrogenation leads to formation of a mixture of reaction products including cyclic (1-methylcyclobutene, methylcyclobutane), linear (1-pentene, cis-2-pentene, trans-2-pentene, pentane) and branched (isoprene, 2-methyl-1-butene, 2-methyl-2-butene, isopentane) compounds. Generally, at lower temperatures (150–350 °C) the major reaction product was methylcyclobutane while higher temperature of 450 °C favors the formation of branched products isoprene, 2-methyl-1-butene and 2-methyl-2-butene. PHIP effects were detected for all reaction products except methylenecyclobutane isomers 1-methylcyclobutene and isoprene implying that the corresponding compounds can incorporate two atoms from the same parahydrogen molecule in a pairwise manner in the course of the reaction in particular positions. The mechanisms were proposed for the formation of these products based on PHIP results.     

噻吩在γ-Mo2N(100)表面上加氢脱硫反应的密度泛函理论研究

利用密度泛函理论研究了γ-Mo₂N(100)表面上的噻吩加氢脱硫(HDS)过程. 噻吩在γ-Mo₂N(100)表面上不同作用形式的结构优化结果显示, η5-Mo₂N吸附构型最稳定, 具有最大的吸附能(-0.56 eV), 此时噻吩通过S原子与Mo2原子相连平行表面吸附在四重空位(hcp 位). H原子和噻吩在hcp位发生稳定共吸附, hcp位是噻吩HDS的活性位点. 噻吩在γ-Mo₂N(100)表面进行直接脱硫反应, HDS过程分为S原子脱除和C₄产物加氢饱和两部分. 过渡态搜索确定了HDS最可能的反应机理及中间产物, 首个H原子的反应需要最大的活化能(1.69 eV),是噻吩加氢脱硫的控速步骤. 伴随H原子的不断加入, 噻吩在γ-Mo₂N(100)表面上优先生成―SH和丁二烯, 随后―SH加氢生成H₂S, 丁二烯加氢饱和生成2-丁烯和丁烷. 由于较弱的吸附, H₂S、2-丁烯和丁烷很容易在γ-Mo₂N(100)表面脱附成为产物.     

Herstellung und Umsetzungen von β-Lactamen

The cycloaddition of N-chlorosulfonyl-isocyanate with isoprene, butadiene and a polyolefin as well as the reaction of ketenes with some bis-azomethines were investigated. Suitably substituted bis-azomethines could be separated in the rac. and the meso-form. The reactivity of the azetidinones towards hydrolysis and hydrogenation was tested. Attempts to polymerise 4-vinyl-azetidin-2-one, polyazetidinone and N-substituted bis-azetidinones to give cross-linked poly-β-amides were not successful.     

Synthesis of Novel Thioethers and Sulfoxide Compounds

Abstract

Thiosubstituted butadiene and butenyne compounds were synthesized from the reactions of 1,1,3,3,4,4-hexachloro-1-butene or 1,1,2,4,4-pentachlorobuta-1,3-diene with different thiols in EtOH/H₂O solution of NaOH. Tris(thio)substituted butadiene compound was treated with potassium tert-butoxide to obtain tris(thio)substituted butatrienyl halide compound. The novel sulfoxide compounds were synthesized from the reactions of polyhalobutadiene compounds with aliphatic thiols in CHCl₃ with m-CPBA at 0°C. The structures of the novel compounds were characterized by micro analysis, FT-IR, ¹H-NMR, ¹³C-NMR, and MS.     

Structure Evolution and Associated Catalytic Properties of PtSn Bimetallic Nanoparticles

Bimetallic nanoparticles (NPs) often show new catalytic properties that are different from those of the parent metals. Carefully exploring the structures of bimetallic NPs is a prerequisite for understanding the structure‐associated properties. Herein, binary Pt?Sn NPs with tunable composition are prepared in a controllable manner. X‐ray characterizations reveal that their structures evolve from SnO_2?x‐patched PtSn alloys to SnO_2?x‐patched Pt clusters when more tin is incorporated. An obvious composition‐dependent catalytic performance is observed for the hydrogenation of α,β‐unsaturated aldehydes: the selectivity to unsaturated alcohol increases substantially at high tin content, whereas the reaction rate follows a volcano shape. Furthermore, Pt sites are responsible for hydrogen dissociation, whereas oxygen vacancy (O_vac) sites, provided by SnO_2?x, drastically enhance the adsorption of carbonyl group.     

The homogeneous pyrolysis of 2-butenes

The homogeneous pyrolysis of 2-butene subjected to shock heating was studied in the limit of high pressures by a relative rate technique. Over the temperature range of 1150–1325°K nearly equal amounts of methane, propylene, and butadiene were formed starting with either the cis- or trans-2-butene, while isomerization remained far from equilibrium. The results are consistent with a simple free radical mechanism for which we find as the initial rate-limiting step.     

Shape and Size Controlled Pt Nanocrystals as Novel Model Catalysts

A tremendous development of nanotechnology enabled us to prepare precisely structure-controlled nanocrystals (NCs). Recently, such structure controlled NCs have been applied as model catalysts with controlled active sites to evaluate reaction mechanisms. Here, we review our recent works on preparation of shape controlled Pt NCs, such as cube and wire, and on application as model catalysts for olefin hydrogenation to assess active Pt sites. A hydrogen reduction method of Pt(II) ion was adopted in an aqueous phase to prepare Pt cube in the presence of shape forming agent (NaI) and organic protective agent (sodium polyacrylate or sodium succinate). We succeed to prepare Pt cube with high size and shape selectivity, followed by very small Pt cube of less than 3 nm. Such simultaneous control of both size and shape of Pt NCs has been successfully achieved by the sophisticated tuning of multiple conditions for the growth kinetics of Pt nuclei during hydrogen reduction of PtCl₄ ²⁻ in aq. N-, N-dimethylformamide (DMF) solution. The key strategy is to produce small Pt nuclei and to avoid the excessive growth of Pt nuclei, in conjunction with face selective adsorption of anionic protective and shape-forming agents by the control of solvent system. For the preparation of Pt nanowires with high anisotropy, template-assisted methods have been usually used. We have developed facile liquid phase preparation method at room temperature in air without any template. The key factors of the method are: firstly, to use aqueous organic solvent system to control solvent polarity; secondly, to use co-solvent DMF as shape forming agent; thirdly, to use excess NaBH₄ as a stabilizer of Pt nuclei to prevent formation of conventional particles. Single-crystalline Pt nanowires of 2 nm diameter and more than micron length were easily obtained by the reduction of Pt(IV) with excess NaBH₄ in water–DMF–toluene solution (1:8:5 volume ratio) in a short reaction period of 3 h. Then, we have applied shape-controlled Pt NCs protected with PAA prepared by our original methods, such as cube, tetrahedron and wire, as model catalysts for olefin (cis- and trans-stilbenes) hydrogenation in ethanol to evaluate the active facet of Pt catalysts; e.g., Pt(111) or Pt(100). The estimated TOF values for the hydrogenation of cis- and trans-stilbene decreased in the order: cube > cuboctahedron > tetrahedron ~ nanowire. This tendency indicates that Pt(100) show high activity compared with Pt(111). The result is compatible with measurement of XPS and Raman spectra, suggesting strong adsorption of reactant on Pt(100). Hydrogenation of olefins (1-hexene and cyclohexene) has been carried out over Pt cubes with different sizes (8.2–10.1 nm) as catalysts to get information about active sites of Pt catalysts, e.g., flat facet or edge/corner atoms. The results of similar TOF values among Pt cubes with different sizes imply that the active sites are flat facets.     

Characterization of monomer sequence structure distribution of poly(1-butene)/poly(propylene-co-butene) in-reactor alloys through 13C-NMR

In situ FTIR testing demonstrated that crystallization of novel poly(1-butene)/poly(propylene-co-butene) in-reactor alloys from melt shows thermodynamic stable Form I directly rather than general reported unstable crystal Form II. In order to make clear this phenomenon, the microstructure and monomer sequence distribution of the as-obtained poly(1-butene)/poly(propylene-co-butene) in-reactor alloys was determined by ¹³C-NMR. The raw alloy was separated by fractional dissolution to five grades. The characterization of raw alloys and different grades demonstrates that propylene monomer unit distributes in a form of isolated or segmented along poly(1-butene) molecular chains. The fractional dissolution of the selected alloy indicates that chain structure changes gradually with fractional solvent. The number average sequence length of propylene and 1-butene unit has been calculated. The number average sequence length and distribution could help us to study the crystallization and transformation clearly. From the results of in situ FTIR and NMR, the random distribution of the propylene unit with certain content in the as-obtained alloys play role to accelerate the crystallization transformation.     

An improved method for the diimide hydrogenation of butadiene and isoprene containing polymers

The hydrogenation of unsaturated polymers with diimide generated in-situ by thermolysis of p-toluenesulfonyl hydrazide (TSH) is a commonly used method for preparing laboratory scale quantities of saturated diene based polymers. The by-products from TSH, particularly p-toluenesulfinic acid, can attack at olefinic sites, adding p-tolylsulfone functionality and degrading polymer molecular weight. The addition of tri-n-propyl amine has been found to eliminate these side reactions in butadiene containing polymers and copolymers, enabling the preparation of polymers devoid of backbone unsaturation. No detectable sulfur-containing impurities were indicated by IR, NMR, or elemental analysis, and no chain degradation was observed via GPC analysis of the hydrogenated polymers. cis-Polybutadiene and butadiene containing random and block copolymers with styrene were hydrogenated cleanly using this technique. A ratio of 2 mol TSH and 2 mol amine/mol of olefin was necessary to assure > 99% hydrogenation, and a w/v ratio of 2 parts butadiene/100 parts o-xylene gave the most efficient hydrogenation. Polymers prepared from isoprene were only partially hydrogenated when treated with TSH in the presence of tri-n-propyl amine, and gave evidence of slight degradation of the polymer structure.     

MIL‐100(Fe) Supported Pt−Co Nanoparticles as Active and Selective Heterogeneous Catalysts for Hydrogenation of 1,3‐Butadiene

Superior catalytic performance for selective 1,3‐butadiene (1,3‐BD) hydrogenation can usually be achieved with supported bimetallic catalysts. In this work, Pt−Co nanoparticles and Pt nanoparticles supported on metal–organic framework MIL‐100(Fe) catalysts (MIL=Materials of Institut Lavoisier, PtCo/MIL‐100(Fe) and Pt/MIL‐100(Fe)) were synthesized via a simple impregnation reduction method, and their catalytic performance was investigated for the hydrogenation of 1,3‐BD. Pt1Co1/MIL‐100(Fe) presented better catalytic performance than Pt/MIL‐100(Fe), with significantly enhanced total butene selectivity. Moreover, the secondary hydrogenation of butenes was effectively inhibited after doping with Co. The Pt1Co1/MIL‐100(Fe) catalyst displayed good stability in the 1,3‐BD hydrogenation reaction. No significant catalyst deactivation was observed during 9 h of hydrogenation, but its catalytic activity gradually reduces for the next 17 h. Carbon deposition on Pt1Co1/MIL‐100(Fe) is the reason for its deactivation in 1,3‐BD hydrogenation reaction. The spent Pt1Co1/MIL‐100(Fe) catalyst could be regenerated at 200 °C, and regenerated catalysts displayed the similar 1,3‐BD conversion and butene selectivity with fresh catalysts. Moreover, the rate‐determining step of this reaction was hydrogen dissociation. The outstanding activity and total butene selectivity of the Pt1Co1/MIL‐100(Fe) catalyst illustrate that Pt−Co bimetallic catalysts are an ideal alternative for replacing mono‐noble‐metal‐based catalysts in selective 1,3‐BD hydrogenation reactions.     

Stereoselective Synthesis of the Urinary Metabolite N-Acetyl-S-(3,4-dihydroxybutyl)cysteine

On exposure to the potential carcinogen 1,3-butadiene, the major urinary metabolite in humans is N-acetyl-S-(3,4-dihydroxybutyl)cysteine. A novel, stereoselective synthesis of this cysteine–butadiene metabolite has been developed that is suitable for the production of either diastereomer for use in occupational exposure analysis. L-Cysteine and 4-bromo-1-butene are coupled via an S_N2 reaction to give the core structure. A Sharpless asymmetric dihydroxylation using the dihydroquinidine (DHQD) ligand provided the terminal 1,2-diol with the 3-hydroxyl group in the R configuration.

Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental resource.     

Temperature hysteresis phenomena in heterogeneous catalysis

Temperature hysteresis is observed only in exothermic heterogeneous catalytic reactions (viz., oxidation and methanation of CO or propene hydrogenation) and is absent in the case of endothermic reactions (dehydrogenation of isobutane) or reactions with heat close to zero (viz., 2-butene isomerization). Temperature hysteresis in hydrogenation reactions was discovered for the first time. The concept of local overheating of catalyst active sites caused by poor removal of the reaction heat is proposed to provide a noncontradictory interpretation of the appearance of hysteresis loops. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1379–1385, August, 2000.     

Synergism of Pt nanoparticles and iron oxide support for chemoselective hydrogenation of nitroarenes under mild conditions

An efficient and low-cost supported Pt catalyst for hydrogenation of niroarenes was prepared with colloid Pt precursors and α-Fe₂O₃ as a support. The catalyst with Pt content as low as 0.2 wt% exhibits high activities, chemoselectivities and stability in the hydrogenation of nitrobenzene and a variety of niroarenes. The conversion of nitrobenzene can reach 3170 mol_conv h^?1 mol_Pt^?1 under mild conditions (30 °C, 5 bar), which is much higher than that of commercial Pt/C catalyst and many reported catalysts under similar reaction conditions. The spatial separation of the active sites for H₂ dissociation and hydrogenation should be responsible for the high chemoselectivity, which decreases the contact possibility between the reducible groups of nitroarenes and Pt nanoparticles. The unique surface properties of α-Fe₂O₃ play an important role in the reaction process. It provides active sites for hydrogen spillover and reactant adsorption, and ultimately completes the hydrogenation of the nitro group on the catalyst surface.