A review of the use of gold catalysts in selective hydrogenation reactions Lynsey McEwana

The field of gold catalysis has been a lively area of research for the past two decades and gold catalysts are now an established ‘best choice’ for many oxidation reactions. Most well known for its performance in selective and preferential oxidation reactions, gold has more recently found potential in selective hydrogenation reactions. In this work the recent developments using gold and gold-promoted catalysts for selective hydrogenation reactions are reviewed: the use for chemoselective hydrogenation of α,β-unsaturated aldehydes and, in particular, the excellent selectivity exhibited for the selective partial hydrogenation of alkyne, alkadiene and alkene C₂–C₆ hydrocarbon streams.     

Influence of the reactant concentration in selective hydrogenation of 1,3-butadiene over supported gold catalysts under alkene rich conditions: A consideration of reaction mechanism

This article is about the reaction of selective hydrogenation of 1,3-butadiene performed in an excess of alkenes (propene/butadiene ratio = 100) over supported gold catalysts, so as to mimic the conditions of purification of light alkenes (C4 cuts) from the presence of impurities (highly unsaturated compounds, 1–3%). Gold was found highly selective (close to 100%, no propane or butane formation) for the hydrogenation of butadiene to butenes at 100% conversion of butadiene. The influence of the concentrations of the various reactants, i.e. hydrogen, butadiene and propene, on the rates of butadiene and propene hydrogenation was investigated, and the apparent reaction orders were deduced from the dependence of rate on partial pressure in the gas phase. The reason for the high selectivity of gold catalysts is that the reaction of hydrogenation of alkenes occurs at much higher temperature (0.1% conversion at 300°C) than that of selective hydrogenation of butadiene (100% at T <170°C). Moreover, the presence of propene has only a limited influence on the reaction of butadiene hydrogenation, while butadiene has no influence on propene hydrogenation; the two reactions of hydrogenation hardly influence each other. Hydrogen dissociation is the rate limiting step of the reaction (partial order of 0.7 and 1 with respect to H₂ for butadiene and propene hydrogenation, respectively), responsible for the low activity of gold. The catalytic properties of gold were compared to those of palladium-based catalysts, and reasons for their different behaviour were discussed.     

Supported gold catalysts for selective hydrogenation of 1,3-butadiene in the presence of an excess of alkenes

Supported gold catalysts were investigated in the selective gas phase hydrogenation of 1,3-butadiene in an excess of propene (0.3% butadiene, 30% propene and 20% hydrogen), in order to simulate the process required for the purification of industrial alkenes streams to prevent poisoning of the polymerisation catalysts used for polyalkene production. Gold catalysts containing small gold particles (between 2 to 5 nm in average) are less active than commercial palladium catalysts, but they are much more selective. Under our experimental conditions, 100% of butadiene can be converted at ≈170°C into 100% butenes with 1-butene as the main product, and with only very small amount of alkanes formed (≈100 ppm). The absence or presence of propene does not drastically modify the rate of hydrogenation of butadiene.     

Thermodynamic analysis of the gas phase composition over uranium-plutonium carbonitride irradiated with fast neutrons

A thermodynamic analysis of the gas phase composition over uranium-plutonium carbonitride U_0.8Pu_0.2(C_0.5N_0.5)_0.995 irradiated with fast neutrons was carried out with respect to temperature and burnout. In the temperature range of 900–2500 K, accumulation of fission products in fuel resulted in the formation of a multicomponent gas phase containing the following basic elements and compounds: volatile (Cs, Sr, Ba, Se, Te, I, Pd, CsI, Cs₂I₂, BaI, SrI, BaI₂, SrI₂, LaSe, TeSe, and LaTe), nitrogen-containing components (N₂, N, CN, CN₂, C₂N₂, UN, UN₂, PuN₂, CsN, CeN, LaN, YN, MoN, and ZrN), carbon-containing components (C, UC, UC₂, UC₄, PuC, PuC₂, PuC₄, ZrC, ZrC₂, YC₂, CeC₂, LaC₂, and NdC₂), and hardly volatile metals (U, Pu, Ru, Rh, Pd, Y, Ce, La, Nd, Tc, Mo, and Zr). The partial pressures of the said gas phase components over carbonitride fuel were calculated with respect to temperature and burnout (up to 18%).     

Effect of AI content on the phase structure and the hydrogenation characteristic of La（Mg1-xAlx） alloys

La（Mg1-xAlx） （x=0.2, 0.4, 0.6, 0.8） alloys have been prepared using induction melting followed by annealing. It is found that partial substitution of Mg by Al does not lead to a change in crystal structure, and the alloys have a single LaMg phase when x 〈 0.4. The lattice parameter of the LaMg phase decreases obviously after the partial substitution of Mg by Al. However, further substitution of Mg by Al leads to the coexistence of multiple phases when x ≥ 0.6. The alloys consist of the LaMg, LaAl, LaAl2, and La5Al4 phases. The LaMg phase decreases, whereas the La5Al4 phase increases with the increase in x. The Al-substituted La（Mgo.6Al0.4） alloy can be hydrogenated into the tetragonal LaH3, cubic LaH3, MgH2, and LaPd under 5 MPa at 473 K for 5 d.     

Condensation of Cu nanoparticles from the gas phase

In order to determine the most efficient modes of copper-nanoparticle synthesis, a number of experiments on evaporation with the subsequent condensation of the initial material in the argon atmosphere have been carried out. In the course of the experiments, it has been discovered that intensified evaporation significantly increases the average size of the synthesized particles. However, the investigation of the change in the dimensional characteristics of the produced clusters depending on the intensity of the buffer-gas flow faced serious difficulties. The obtained results differ significantly from the earlier experiments on the synthesis of the transition-metal oxides. In order to solve this contradiction, the computer simulation of the condensation of copper atoms from the gas phase with three different cooling rates and two final temperatures T = 373 K and Т = 77 K has been performed. It has been discovered that the cooling rate of the gas mixture and the final temperature directly influence the quantity and size of the produced particles. Thus, at a tenfold lower cooling rate, the average number of particles increases 2.7 times at a final temperature of 77 K and by 3.1 times at T = 373 K.     

The combination effects of trivalent gold ions and gold nanoparticles with different antibiotics against resistant Pseudomonas aeruginosa

Despite much success in drug design and development, Pseudomonas aeruginosa is still considered as one of the most problematic bacteria due to its ability to develop mutational resistance against a variety of antibiotics. In search for new strategies to enhance antibacterial activity of antibiotics, in this work, the combination effect of gold materials including trivalent gold ions (Au³⁺) and gold nanoparticles (Au NPs) with 14 different antibiotics was investigated against the clinical isolates of P. aeruginosa, Staphylococcus aureus and Escherichia coli. Disk diffusion assay was carried out, and test strains were treated with the sub-inhibitory contents of gold nanomaterial. Results showed that Au NPs did not increase the antibacterial effect of antibiotics at tested concentration (40 μg/disc). However, the susceptibility of resistant P. aeruginosa increased in the presence of Au³⁺ and methicillin, erythromycin, vancomycin, penicillin G, clindamycin and nalidixic acid, up to 147 %. As an individual experiment, the same group of antibiotics was tested for their activity against clinical isolates of S. aureus, E. coli and a different resistant strain of P. aeruginosa in the presence of sub-inhibitory contents of Au³⁺, where Au³⁺ increased the susceptibility of test strains to methicillin, erythromycin, vancomycin, penicillin G, clindamycin and nalidixic acid. Our finding suggested that using the combination of sub-inhibitory concentrations of Au³⁺ and methicillin, erythromycin, nalidixic acid or vancomycin may be a promising new strategy for the treatment of highly resistant P. aeruginosa infections.     

Gas sensitiveness of polypyrrole films doped chemically in the gas phase

Electropolymerized polypyrrole films were electrochemically reduced and then chemically doped with one of PCl₃, SO₂, NO₂ or iodine vapour in the gas phase. These chemically-doped polypyrrole films showed a resistance decrease when they were exposed to electron-acceptor gases having electron affinities larger than those used in the chemical doping, except for one case of exposure of iodine-doped polypyrrole films to NO₂, where (although iodine has reportedly a larger electron affinity than NO₂) a resistance increase was seen, which was caused by a partial substitution of the doped iodine with exposed NO₂. The phenomenon is discussed in terms of the stabilization of gaseous species on adsorption. The present study suggests that a selective gas sensitivity may be attached to polypyrrole films if they are doped with an appropriate gas in advance.     

Ti元素改性ZrCo合金在CO杂质气氛中吸氢行为及影响机制

采用EDS和XRD表征了Ti改性ZrCo合金的相结构及表面元素分布,采用飞行时间二次离子质谱(TOF-SIMS)以及程控升温热解脱附(TPD)方法研究少量CO(1.05%CO+98.95%H_2气氛,体积分数,)对Zr_(0.8)Ti_(0.2)Co合金氢化行为的影响及作用机制。结果表明:在纯氢环境下ZrCo合金和Zr_(0.8)Ti_(0.2)Co合金饱和吸氢时间分别少于2和4 min,饱和吸氢容量分别为1.8%和1.9%(质量分数)。而在含1.05%CO的氢中ZrCo合金和Zr_(0.8)Ti_(0.2)Co合金在2500 min内均未能达到吸氢饱和,吸氢容量分别下降到0.91%和0.48%,Ti改性导致ZrCo合金在CO杂质气氛中的吸氢动力学性能下降。实验表明,通过773 K、0.5 h热抽空处理可恢复至毒化前吸氢性能。     

Hyperfine interactions on iron nuclei in the BCC and fractally decomposed BCC/FCC mixed phase iron–gold alloys

Iron–gold alloys for the gold concentration ranging from 1 at.% till 70 at.% were investigated by means of the ⁵⁷Fe-14.4 keV Mössbauer spectroscopy, X-ray diffraction and scanning electron microscopy. Samples were prepared by arc melting of the elements, and investigated as cast and after annealing. A single BCC phase is obtained for the gold concentration up to about 3 at.%, while for the higher gold concentration one obtains mixed phase samples containing BCC and FCC phases both. The BCC phase is ferromagnetically ordered at room temperature. Contributions to the charge and spin density on iron atoms in the BCC phase due to the gold impurities were determined up to the second neighbors. The FCC phase is either magnetically ordered at room temperature or it is paramagnetic at the above temperature depending upon iron concentration, as the magnetic transition temperature is increasing with the increasing iron concentration. BCC/FCC mixed phase samples are characterized by very small crystallites (nanoparticles) of both phases. These nanoparticles form hierarchical fractal structures on the scale ranging from more than 1 mm till less than 30 nm.     

Surface electrical properties of tungsten oxides in equilibrium with the gas phase

The work function of the tungsten-oxygen system has been investigated at temperatures of 750, 800 and 850°C vs. oxygen partial pressure within the stability range of various oxide phases. The reproducibility of both reduction and oxidation runs indicates that the investigated system achieves the thermodynamic equilibrium state. Sharp changes of the work function are observed at oxygen partial pressures corresponding to the phase transformations. This effect allows a determination the oxide phases WO₃, WO_2.90, WO_2.72, and WO₂ as the most stable and well-defined. Good agreement between the work function and the electrical conductivity data has been shown. This indicates that the work function method is sensitive to the crystalline structure of semiconducting oxides. Good agreement with the literature data is also observed.The work has been carried out in the Institute of Catalysis and Surface Chemistry, Kraków, Poland, in conjunction with the Polish-French Collaboration Research Project.     

Surface impregnation of steel with boron from the gas phase

Summary The possibility of gas phase boronizing or boron vapor plating with a mixture of diborane and hydrogen has been established. The best results were obtained at 800–850°C (1470–1560°F) in 4–5 hours, with diborane/ hydrogen=1/75, flowing at 75–100 liters per hour. Under these conditions, a very hard boronized case, 200 microns (0.008 in) thick, was obtained on [carbon] steel 45; the surface microhardness was 3000.     

The role of nanosized gold particles in adsorption and oxidation of carbon monoxide over Au/Fe2O3 Catalyst

The presence of gold is found to promote the development of weakly bonded (CO)_ad species over the surface of Au/Fe₂O₃ catalyst during interaction with carbon monoxide (CO) or a mixture of carbon monoxide and oxygen. The concentration of these species and the nature of the bonding depend on the gold particle size. No such species are formed for gold particles larger than ∼11 nm or over gold-free iron oxide. The bulk carbonate-like species, formed in the process with the involvement of the hydroxy groups of the support, are merely side products not responsible for the low temperature activity of this catalyst.     

Structure/processing relationships in the fabrication of nanoporous gold

Nanoporous gold made by dealloying silver/gold alloys is a relatively new material finding application in catalysis, sensing, and other areas. Here we discuss the metallurgical processing required to make patterned foils of nanoporous gold with large, flat grains, with which we are exploring an application as substrates for the heterogeneous nucleation of protein crystals.     

PdO/Pd system equilibrium phase diagram under a gas mixture of oxygen and nitrogen

The thermal equilibrium decomposition properties of the PdO-Pd system under oxygen partial pressures ranging from 0.1 to 1.0 atm in a total combined pressure of oxygen and nitrogen of 1.0 atm were investigated by means of thermal-gravimetric analyses. The phase diagram of Pd-PdO over the range of oxygen/nitrogen gas concentration was established. The decomposition temperature of PdO to Pd was found to increase with the partial pressure of oxygen.     

PdO/Pd system equilibrium phase diagram under a gas mixture of oxygen and nitrogen

The thermal equilibrium decomposition properties of the PdO-Pd system under oxygen partial pressures ranging from 0.1 to 1.0 atm in a total combined pressure of oxygen and nitrogen of 1.0 atm were investigated by means of thermal-gravimetric analyses. The phase diagram of Pd-PdO over the range of oxygen/nitrogen gas concentration was established. The decomposition temperature of PdO to Pd was found to increase with the partial pressure of oxygen.     

Kinetics of stripping of gold loaded in DBC organic phase by sodium sulfite

The kinetics of stripping of gold loaded in dibutyl carbito (DBC) organic phase by sodium sulfite was investigated in a Lewis cell. After the stirring speed reached 400 r·min-1, the reaction of gold stripping conformed with the pseudo-first-order reaction. The stripping rate of gold was in direct proportion to interfacial area, concentration of sodium sulfite and reaction temperature. The experimental results showed that the process of stripping gold was controlled by inter-facial chemical reaction, and its activation energy was 36.06 kJ·mol-1. The kinetics equation was put forward for gold stripping by sodium sulfite.     

Enhanced catalytic performance for selective oxidation of propene with O_2 over bimetallic Au-Cu/SiO_2 catalysts

Au-Cu bimetallic nanoparticles with uniform size,shape,and compositions were synthesized by wet chemistry method,and then the Au-Cu/SiO_2 catalyst supported on SiO_2 was prepared.Meanwhile,their catalytic activity for the selective oxidation of propene to acrolein using O_2 as an oxidant was evaluated.The bimetallic catalyst shows a significantly enhanced catalytic performance comparing with Au and Cu monometallic catalysts.Characterization of the materials and kinetic study was conducted to explore the cooperating mechanism of Au and Cu for improving the catalytic activity of the bimetallic catalyst.Cu component can segregate to the alloy surface and the Au-Cu alloy transferred to Au-CuO core/shell structure after annealing during the preparation process.Based on the Mars-van Krevelen mechanism for the selective oxidation of propene over the prepared catalysts,the coexistence of CuO can promote the adsorption and activation of O_2.Meanwhile,the electrons transfer from Au to Cu in the catalyst can facilitate the adsorptions of both oxygen on CuO sites and propene on Au sites.The combined effects of the above two aspects result in the high catalytic activity of the Au-Cu/SiO_2 catalyst for selective oxidation of propene to acrolein,compared to the Au/SiO_2 and CuO/SiO_2 catalysts.     

Influence of the C14 Ti35.4V32.3Fe32.3 Laves phase on the hydrogenation properties of the body-centered cubic compound Ti24.5V59.3Fe16.2

Bcc Ti_24.5V_59.3Fe_16.2 alloys containing 10 and 30% of C14 Laves phase inclusions were prepared by induction melting followed by annealing at 1000 °C. X-ray powder diffraction and BSE microscopy confirmed the presence of the C14 Laves phase (average composition Ti_35.4V_32.3Fe_32.3) embedded in the bcc matrix. The two end members of the series, the C14 Laves phase and the bcc Ti_24.5V_59.3Fe_16.2 alloy, have very different hydrogenation behaviors. The C14 Laves phase does not absorb as much hydrogen as does the bcc phase. No equilibrium plateau and little hysteresis between absorption and desorption were observed at 25 °C for the C14 Laves on the PCI curves whereas those of the bcc sample present one equilibrium plateau and significant hysteresis between absorption and desorption. As a result, the absorption capacity and the length of the equilibrium plateau of the multiphase alloys decrease with the C14 Laves phase content. The hydrogenation properties of an as-cast bcc Ti_24.5V_59.3Fe_16.2 sample were also investigated: the kinetics of the first hydrogenation is found to be slower and the plateau pressures higher for the as-cast alloy than for the annealed sample.