Analysis of electric conductivity of binary solid-state catalysts by computer simulation

Experimental and model studies of concentration dependencies of electric conductivity have been performed for a number of binary mechanical mixtures. The physical origins of various peculiarities are discussed with Fe₃O₄+MgO, Fe₃O₄+NiO, and Ni+ZrO₂ systems considered as examples. The degree of friability of the systems and the degree of homogeneity of the component distribution are estimated. A considerable mutual influence of the phases is observed, which is, however, not a chemical interaction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1874–1877, November, 1993.     

Bimetallic catalysts for hydrogenation in liquid phase

Activity and selectivity of bimetallic catalysts for two model reactions, citral hydrogenation in isopropanol and nitrate reduction in water, are reviewed on the basis of results obtained over bimetallic systems prepared in our laboratory, notably by redox techniques. The parent metal is generally a noble metal (Rh, Pd, Pt), while the additive is most often a non-noble metal (Ge, Sn, Cu…) whose oxidation state plays an important role in hydrogenation. Dramatic improvements of the selectivity to unsaturated alcohols are observed in citral hydrogenation with adequate deposition of the additive and pretreatment of the final catalyst. In nitrate reduction, the second metal essentially affects the first step of the process (conversion of nitrate to nitrite) but the global selectivity (limitation of NH₃ formation) may be significantly improved by tuning the couple parent metal–additive. Other aspects such as the choice of the support and the optimization of reaction conditions (temperature, pressure, pH effects in water) are also discussed.     

Surface acidity of supported vanadia catalysts

The surface acidity of SiO₂, γ-Al₂O₃ and TiO₂ supported vanadia catalysts has been studied by the microcalorimetry and infrared spectroscopy using ammonia as the probe molecule. The acidity in terms of nature, number and strength was correlated with surface structures of vanadia species in the catalysts, characterized by X-ray diffraction and UV-Vis spectroscopy. It was found that the dispersion and surface structure of vanadia species depend on the nature of supports and loading and affect strongly the surface acidity. On SiO₂, vanadium species is usually in the form of polycrystalline V₂O₅ even for the catalyst with low loading (3%) and these V₂O₅ crystallites exhibit similar amount of Brönsted and Lewis acid sites. The 25%V₂O₅/SiO₂ catalyst possesses substantial amount of V₂O₅ crystallites on the surface with the initial heat of 105 kJ mol^-1 and coverage of about 600 mmol g^-1 for ammonia adsorption. Vanadia can be well dispersed on g-Al₂O₃and TiO₂ to form isolated tetrahedral species and polymeric two-dimensional network. Addition of vanadia on γ-Al₂O₃ results in the change of acidity from that associated with g-Al₂O₃ (mainly Lewis sites) to that associated with vanadia (mainly Brönsted sites) and leads to the decreased acid strength. The 3%V₂O₅/TiO₂ catalyst may have the vanadia structure of incomplete polymeric two-dimensional network that possesses the Ti-O-V-OH groups at edges showing strong Brönsted acidity with the initial heat of about 140 kJ mol^-1 for ammonia adsorption. On the other hand, the 10%V₂O₅/TiO₂ catalyst may have well defined polymeric two-dimensional vanadia network, possessing V-O-V-OH groups that exhibit rather weak Brönsted acidity with the heat of 90 kJ mol^-1 for NH₃ adsorption. V₂O₅ crystallites are formed on the 25%V₂O₅/TiO₂ catalyst, which exhibit the acid properties similar to those for 25%V₂O₅ on SiO₂ and γ-Al₂O₃.     

Tungsten-based catalysts for the oxidation of cyclohexanol: The effect of phase transfer catalysts

The oxidation of cyclohexanol with hydrogen peroxide in the presence of tungsten-based catalysts was studied in this paper. The effect of phase transfer catalysts was discussed and clarified. [CTA]₉[SbW₉O₃₃] showed the best activity and good recyclability with a conversion over 95%.     

用于生物质水相加氢多相负载型金属催化剂的稳定策略

生物质是天然的可再生能源和资源,具有来源广泛、储量丰富、价格低廉的优点以及可转化为高附加值化学品的多功能性,因此作为传统化石能源替代材料受到广泛关注和研究.将生物质通过催化转化为平台化合物再进一步利用是生物质利用的重要途径,其中催化加氢是常用的反应之一.由于绝大多数生物质平台化合物分子中都含氧元素,其加氢过程中会不可避...     

Synergic effect of palladium-based bimetallic catalysts for the hydrogenation of nitroaromatics

Bimetallic catalysts, PdCl₂-MX_n and PdCl₂(PhCN)₂-Mx_n (MX_n=FeCl₃, Fe(acac)₃, Co(OAc)₂, CoCl₂, Co(acac)₂, NiCl₂, Ni(OAc)₂, RuCl₃, Cu(OAc)₂, CuCl₂), exhibit remarkable synergic effect which can obviously increase the activity of the monometallic Pd catalyst for the hydrogenation of nitroaromatics, whereas MX_n alone is not catalytically active under the same reaction conditions.     

Zinc-containing zeolite catalysts for ethane aromatization prepared by solid-state modification

Solid-state modification was used to prepare zinc-containing zeolite catalysts based on pentasils with different framework SiO₂/Al₂O₃ ratios. The catalysts were studied by X-ray diffraction analysis and IR spectroscopy. The activity and selectivity of the Zn—pentasil systems prepared by the solid-state modification and impregnation methods were compared in the aromatization of ethane. The active and stable zeolite catalysts modified by transition metal ions can be obtained by the topochemical method.     

Temperature dependence of benzene hydrogenation over sulfide catalysts

Non-Arrhenius temperature dependence of benzene hydrogenation was found for sulfide alumina-supported (Ni,Mo) and (Ni,W) catalysts under unsteady-state reaction conditions. It was shown that THE observed decrease in the catalyst activity at high temperature cannot be explained by the increasing role of the reverse reaction. The activity decrease was supposed to result from the catalyst reduction with the reaction mixture.     

Preparation and characterization of ultrafine Fe-Cu-based catalysts for CO hydrogenation

The ultrafine particles of a new style Fe-Cu-based catalysts for CO hydrogenation were prepared by impregnating the organic sol of Fe（OH）3 and Cu（OH）2 onto the activated Al2O3, in which the organic sol of Fe（OH）3 and Cu（OH）2 were prepared in the microemulsion of dodecylbenzenesulfonic acid sodium（S）/n-butanol（A）/toluene（O）/water with V（A）/V（O） = 0.25 and W（A）/W（S） = 1.50. This catalyst was characterized by particle size analysis, XRD and TG. The results of particle size analysis showed that Fe（OH）3 particles with a mean size of 17.1 nm and Cu（OH）2 particles with an average size of 6.65 um were obtained. TG analysis and XRD patterns suggested that 673 K is the optimal calcination temperature. CO hydrogenation produced C＋OH with a high selectivity above 58 wt% by using the ultrafine particles as catalyst, and the total alcohol yield of 0.250 g·ml^-1 ·h^-1 was obtained when the contents of Al2O3 and K were 88.61 wt% and 1.60 wt%, respectively.     

Membrane catalysts for hydrogenation with cryochemically synthesized palladium clusters

New type of membrane catalysts has been prepared through blinding of 2–3 µm pores of cermet membranes with Pd clusters from its cryochemically synthesized sol in toluene. Those catalysts display 30 times superior activity with respect to Pd weight than the membrane catalysts in the form of foil from Pd alloys.     

Applications of thermal analysis in some solid-state reactions

TG-DTG-DTA has been used to characterize various isomers of CoCl₂·2(CH₃C₆H₄NH₂). Thermal analysis is further used to analyse the binary mixtures of these isomers. DTA recorded after different elapsed times follows the progress of reaction between cobalt chloride and benzocaine where progressively small endotherms are associated with starting materials. The application of thermal analysis to following the solid-solid reactions between metal acetates and 8-hydroxyquinoline was highlighted. The stoichiometry of such reactions was confirmed from the decrease in intensity of an endotherm as one increases the stoichiometry.Thanks are due to Drs. Keshav Chander, K. Kaur, Rajinder Singh and G. S. Chopra for helpful discussions and experimental work.     

Role of single-site catalysts in the hydrogenation of thiophenes: from models systems to effective HDS catalysts

The hydrogenation of thiophenes, leading to cyclic thioethers, thiols or hydrocarbons and H₂S, can be achieved by single-site metal catalysts in both homogeneous and heterogeneous phase. An overview of the processes that have provided useful mechanistic information on hydrodesulfurization catalysis, is presented and commented.     

Design of molecular catalysts for achievement of high turnover number in homogeneous hydrogenation

Development of highly active catalysts has been an important research area in synthetic chemistry, especially from a practical point of view. Herein, we focus on the homogeneous catalytic hydrogenation using well‐defined molecular catalysts and discuss recent advances in the field with regard to the turnover number for these catalysts. DOI 10.1002/tcr.201100019     

Surface modification to control protein/surface interactions

Protein/surface interactions are well known to play an important role in various biological phenomena and to determine the ultimate biofunctionality of a given material once it is in contact with a biological environment. Control over the interactions between proteins and material surfaces are not only of great theoretical interest but also of crucial importance for many biomedical applications. In this Feature Article, we summarize various successful approaches used in our laboratory and other groups for controlling protein adsorption through chemical modification of the surface and/or the introduction of specific topographic features. Some perspectives on future research in these areas are also presented.     

焙烧温度对CuMgAl催化剂催化糠醛气相加氢制糠醇性能的影响

采用分步沉淀过程制得质量比m(CuO)∶m(MgO)∶m(Al_2O_3)为25∶26∶49的CuMgAl类水滑石前驱体,经过不同温度焙烧制得CuMgAl-t催化剂。通过BET、热重、XRD、H_2-TPR和CO_2-TPD对催化剂进行表征,在固定床中考察CuMgAl-t催化剂催化糠醛气相加氢制糠醇的性能。结果表明,焙烧温度影响催化剂活性、稳定性及对产物的选择性,低温焙烧的催化剂经还原后可获得较多活性中心,高温焙烧的催化剂表面具有更多的碱性位,CuMgAl催化剂经450℃焙烧表面存在适宜的活性中心和碱性位。在常压、反应温度180℃、氢醛物质的量比5∶1、糠醛体积空速0.3h~(-1)的条件下,CuMgAl-450催化剂上糠醛的转化率和糠醇的选择性分别达到98.64%和97.66%。     

Surface species and gas phase products in the preferential oxidation of CO on TiO2-supported Au-Rh bimetallic catalysts

The oxidation of CO in the presence of hydrogen (PROX process) was investigated on bimetallic Au-Rh catalysts at 300–373 K by Fourier transform infrared spectroscopy and mass spectroscopy. The effects of catalyst composition, reaction temperature and composition of the reacting gas mixtures have been studied. The IR studies revealed the formation of bi- and monodentate carbonates, bicarbonates and hydrocarbonates on the catalysts surfaces; these surface species proved to be not involved in the surface reactions. The formation of adsorbed formaldehyde was observed on all surfaces, except 1% (0.25Au+0.75Rh)/TiO₂. Adsorbed CO₂ (as the surface product of CO oxidation) was not detected on any surface. The presence of both O₂ and H₂ reduced the surface concentration of CO adsorbed on the metallic sites. Mass spectroscopic analysis of the gas phase showed that gaseous CO₂ was formed in the highest amount in the CO+O₂ mixture, the presence of H₂ suppressed the amount of CO₂ produced. This negative effect of H₂ was the lowest on the 1% Rh/TiO₂ and 1% (0.25Au+0.75Rh)/TiO₂ catalysts.     

Phase composition of manganese-alumina catalysts for the reactions of deep oxidation

X-ray powder diffraction, transmission electron microscopy and differential dissolution were used for investigation of the phase transformation peculiarities of biphasic manganese-alumina catalysts during their thermal treatment. An effect of interaction between aluminium and manganese oxides depending on the sample preparation procedure was found.     

Effect of acid-base properties on copper catalysts for hydrogenation of carbon dioxide

Acidic or basic components as co-catalysts were added to the Cu-based catalysts for hydrogenation of CO₂. Effects of acid-base properties on the catalytic activity and methanol selectivity are discussed.     

Pd/TiN nanocomposite catalysts for selective hydrogenation of phenol and its derivatives

Pd/TiN nanocomposite catalysts were fabricated for one-step selective hydrogenation of phenol to cyclohexanone successfully. High conversion of phenol (99%) and selectivity of cyclohexanone (98%) were obtained at 30℃ and 0.2 MPa H₂ for 12 h in the mixed solvents of H₂O and CH₂Cl₂. The Pd nanoparticles were stable in the reaction, and no aggregation was detected after four successive runs. The catalytic activity and selectivity depended on slightly the Pd particle sizes. The generality of the catalysts for this reaction was demonstrated by the selective hydrogenation of phenol derivatives, which showed that the catalyst was selective for the formation of cyclohexanone.