Presence Of Re Research Articles

Effect of Rhenium Loading Sequence on Selectivity of Ag–Cs Catalyst for Ethylene Epoxidation

Rhenium is an important promotor for silver catalyst, and very little work has been focused on the effect of rhenium loading sequence on the selectivity of ethylene oxide. Re was introduced to the Ag–Cs catalyst supported on α-Al2O3 in three different ways: co-impregnation (Ag–Cs–Re), step-impregnation with Re loaded first (Re/Ag–Cs), and step-impregnation with Re loaded last (Ag–Cs/Re). The selectivity of Re/Ag–Cs and Ag–Cs–Re are about 20% higher than that of Ag–Cs/Re, which indicates that the performance of the catalyst is influenced by the synergistic effect of Re and Cs. Rhenium oxides with the valence of + 4 to + 7 are distributed around the Ag particles. The binding energy of Re is increased by about 0.2 eV by the addition of Cs in the Ag–Cs–Re catalyst, and the presence of Re with high valence around Ag will cause the electrons to shift toward the Re atom, facilitating the formation of weakly adsorbed oxygen and improving the selectivity of the Ag–Cs catalyst. On the Ag–Cs/Re catalyst, Re is mostly loaded on the external Ag surface, and the binding energies of Ag 3d5/2 and Cs 3d5/2 increase by 0.2 and 0.4 eV, respectively, from the Ag–Cs/Re catalyst to the Ag–Cs–Re and Re/Ag–Cs catalysts. The higher binding energy of Ag leads to the stronger oxygen adsorption, which contributes to the complete oxidation reaction, thereby resulting in lower selectivity.

Antiviral properties of resveratrol against pseudorabies virus are associated with the inhibition of I\u03baB kinase activation

Pseudorabies virus (PRV) is a pathogen of swine resulting in devastating disease and economic losses worldwide. Resveratrol (Res) exhibits inhibitory activity against a wide range of viruses. Despite these important advances, the molecular mechanism(s) by which Res exerts its broad biological effects have not yet been elucidated. In this paper, the antiviral activity of Res against PRV and its mechanism of action were investigated. The results showed that Res potently inhibited PRV replication in a dose-dependent manner, with a 50% inhibition concentration of 17.17 μM. The inhibition of virus multiplication in the presence of Res was not attributed to direct inactivation or inhibition of viral entry into the host cells but to the inhibition of viral multiplication in host cells. Further studies demonstrated that Res is a potent inhibitor of both NF-κB activation and NF-κB-dependent gene expression through its ability to inhibit IκB kinase activity, which is the key regulator in NF-κB activation. Thus, the inhibitory effect of Res on PRV-induced cell death and gene expression may be due to its ability to inhibit the degradation of IκB kinase. These results provided a new alternative control measure for PRV infection and new insights into the antiviral mechanism of Res.

Cytochrome c and resveratrol preserve platelet function during cold storage

Donated platelets are stored at 22°C and discarded within 5 days because of diminished function and risk of bacterial contamination. Decline of platelet function has been attributed to decreased mitochondrial function and increased oxidative stress. Resveratrol (Res) and cytochrome c (Cyt c), in combination with hypothermic storage, may extend platelet viability. Platelets from 20 donors were pooled into four independent sets and stored at 22°C or 4°C in the absence or presence of Res (50 μM) or Cyt c (100 μM) for up to 10 days. Sequential measurement of platelet counts, coagulation function (thromboelastography), oxygen consumption, lipid peroxidation, glucose-lactate levels, pH, TCO2, and soluble platelet activation markers (CD62P/PF-4) was performed. Platelet function diminished rapidly over time at 22°C versus 4°C (adenosine diphosphate, day 10 [0.6 ± 0.5] vs. [7.8 ± 3.5], arachidonic acid: day 10 [0.5 ± 0.5] vs. [30.1 ± 27.72]). At 4°C, storage treatment with Res or Cyt c limited deterioration in platelet function up to day 10, an effect not observed at 22°C (day 10, 4°C, Con [7.8 ± 3.5] vs. Res [37.3 ± 24.19] vs. Cyt c [45.83 ± 43.06]). Mechanistic analysis revealed oxygen consumption increased in response to Cyt c at 22°C, whereas neither Cyt c or Res affected oxygen consumption at 4°C. Lipid peroxidation was only reduced at 22°C (day 7 and day 10), but remained unchanged at 4°C, or when Res or Cyt c was added. Cytosolic ROS was significantly reduced by pretreatment with Res at 4°C. Total platelet count and soluble activation markers were unchanged during storage and not affected by Res, Cyt c, or temperature. Glucose concentration, pH and TCO2 decreased while lactate levels increased during storage at 22°C but not 4°C. Platelet function is preserved by cold storage for up to 10 days. This function is enhanced by treatment with Res or Cyt c, which supports mitochondrial activity, thus potentially extending platelet shelf life.

Solution and diffusion of hydrogen isotopes in tungsten-rhenium alloy

Rhenium is one of the main transmutation elements forming in tungsten under neutron irradiation. Therefore, it is essential to understand the influence of rhenium impurity on hydrogen isotopes retention in tungsten. First-principle calculations were used to study the properties of hydrogen solution and diffusion in perfect tungsten-rhenium lattice. The interstitial hydrogen still prefers the tetrahedral site in presence of rhenium, and rhenium atom cannot act directly as a trapping site of hydrogen. The presence of rhenium in tungsten raises the solution energy and the real normal modes of vibration on the ground state and the transition state, compared to hydrogen in pure tungsten. Without zero point energy corrections, the presence of rhenium decreases slightly the migration barrier. It is found that although the solution energy would tend to increase slightly with the rising of the concentration of rhenium, but which does not influence noticeably the solution energy of hydrogen in tungsten-rhenium alloy. The solubility and diffusion coefficient of hydrogen in perfect tungsten and tungsten-rhenium alloy have been estimated, according to Sievert's law and harmonic transition state theory. The results show the solubility of hydrogen in tungsten agrees well the experimental data, and the presence of Re would decrease the solubility and increase the diffusivity for the perfect crystals.

Geometric and electronic effects of bimetallic Ni–Re catalysts for selective deoxygenation of m-cresol to toluene

Ni–Re/SiO2 bimetallic catalysts were prepared using a co-impregnation method and tested in vapor phase hydrodeoxygenation of m-cresol at 300°C and 1atm H2. In contrast to the use of unselective monometallic Ni/SiO2 for catalyzing deoxygenation, hydrogenation, and CC hydrogenolysis reactions, bimetallic 5%Ni–2.5%Re/SiO2 improved the intrinsic reaction rate of the hydrodeoxygenation reaction by a factor of 6, with the turnover frequency for selective deoxygenation to toluene increased by four times, while that for CC hydrogenolysis to methane was reduced by one-half. Characterization results from X-ray diffraction, Raman, transmission electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy of CO adsorption, H2 temperature-programmed reduction, and CO chemisorption indicate that adding Re increased Ni dispersion and resulted in Ni–Re surface alloy formation after reduction. The presence of Re in the surface alloy breaks the continuous Ni surface into smaller ensembles (geometric effect) and reduces the d-band electron density of Ni (electronic effect). Results from density functional theory calculations indicate that the Ni–Re neighboring site is the active site for breaking the CO bond by adsorbing the O atom on Re and the phenyl ring on the neighboring Ni atoms, which facilitates deoxygenation to toluene. The reduced Ni ensemble size inhibits the hydrogenolysis of the CC bond by destabilizing the transition state, whereas the reduction of the electronic density in d states of Ni weakens the adsorption of the phenyl ring, and both contribute to the greatly reduced methane production from successive CC hydrogenolysis.

Cholesterol-Lowering Effects and Mechanisms in View of Bile Acid Pathway of Resveratrol and Resveratrol Glucuronides.

Resveratrol (Res) was previously reported to be capable of lowering plasma TC and LDL-C. The mechanism behind Res is not clearly understood, although it is presumed to have an effect on bile acid metabolism in the liver: a significant way in eliminating cholesterol from the body. As one of the major metabolites of Res in the liver, resveratrol glucuronides (Gres) is suspected to also contribute to the overall cholestrol-lowering activity of Res, which needs to be studied. In this research, when HepG2 steatosis hepatic cells were treated with Res and Gres at different concentration levels, Res and Gres showed similar activity in lowering cellular TC content. The presence of Res and Gres caused a significant increase in hepatic CYP7A1 and BSEP, indicating the increase in the synthesis and efflux of bile acids, respectively. The reduction of HMG-CoAR tied to a decrease in de novo synthesis of cholesterol and the increase of ABCG5 suggested the increase of direct efflux of cholesterol. All above variations reduced the hepatic cholesterol level, which triggered the significant enhancement of LDLR, illustrating the improvement of clearance of LDL-C from the plasma and prevention of atherosclerosis. Overall, this study demonstrated both Res and Gres might have capabilities in lowering hepatic cholesterol through increasing in the synthesis and efflux of bile acids, and decreasing in synthesis and increasing in the efflux of cholesterol. Gres would have preferred potential than Res because of its lower cytotoxicity, which indicated that the action of the metabolites should also be considered in the future studies.

Resveratrol inhibits high glucose induced collagen upregulation in cardiac fibroblasts through regulating TGF-β1–Smad3 signaling pathway

Cardiac fibrosis is a common pathological process presented in a variety of diseases, including hypertension and diabetes. Cardiac fibroblasts (CFs) have been identified as the most important participants in the development of cardiac fibrosis. Exposure of cultured CFs to high glucose (HG) or angiotensin II (Ang II) resulted in increased collagen synthesis. Resveratrol (Res) is a natural polyphenol exhibiting anti-fibrosis effects in a number of different organs fibrosis process, whether Res can prevent HG and Ang II induced fibrosis response in CFs remains unclear. The aim of this work was to evaluate the effects of Res in HG and Ang II induced fibrosis response in CFs. We cultured rat CFs in either normal glucose (5.6mM) or HG (25mM) media in the presence of Res or not and the changes in collagens synthesis and TGF-β1 production were assessed by Real-time PCR, Western blotting, and enzyme linked immunosorbent assay (ELISA). Furthermore, normal and diabetic mice (induced by single dose of streptozotocin (100mg/kg) via tail vein) receiving Res (10mg/kg) were used to explore the effects of Res on cardiac fibrosis in vivo. Masson staining and immunohistochemistry were performed to visualize cardiac collagen deposition. Results indicate that CFs exposed to HG condition shows enhanced proliferation rate. Furthermore, in the presence of HG or Ang II, CFs exhibited increased collagens synthesis and TGF-β1 production. And these effects were abolished by Res intervention. In vivo results show that diabetic mice exhibit increased collagen deposition in the cardiac compared with the normal mice. And this change was prevented by the treatment of Res. These results suggest that Res possesses a potential antifibrogenic effect in hypertension and diabetes-related cardiac fibrosis. Moreover, the action mechanism is probably associated with its ability to reduce TGF-β1 content in CFs.

Selective hydrogenative cleavage of C–C bonds in sorbitol using Ni–Re/C catalyst under nitrogen atmosphere

The use of high pressure fossil derived hydrogen limits the commercial prospects of transforming sorbitol to glycols. Ni–Re/C catalyst which was developed in this study demonstrated high selectivity toward hydrogenative cleavage of C2–C3 and C3–C4 bonds of sorbitol to produce glycols under 1MPa nitrogen. Acetol which is proposed as important intermediate to explain the reaction mechanism was first detected in the sorbitol conversion reactions. Detailed investigations showed that the presence of Re could prevent the sintering of Ni particles during the reduction process and make the catalyst efficiently generate hydrogen on the active sites to selectively cleave C–C bonds in sorbitol under nitrogen atmosphere.

Effect of microalloying with rare-earth on recrystallization behaviour and damping properties of Mg sheets

The effect of a small amount of rare earth elements (RE: Nd and Dy, 0.5wt.%) on recrystallization behaviour, microstructural evolution and damping properties of deformed Mg sheets have been investigated. The recrystallization behaviour was analyzed in terms of the Johnson–Mehl–Avrami–Kolmogorov model via the variation of microhardness. The Avrami exponent of pure Mg sheet ranged from 1.02 to 1.16, and it was reduced by adding REs. The acceleration of recovery and retardation of recrystallization were detected by the presence of REs. Three point bending was carried out to assess damping properties. At the temperature of ∼150°C, the damping peak corresponds to grain boundary relaxation, which was affected by grain size, basal texture and the variation of dislocation density on basal plane. At elevated temperatures, a non-thermal activated peak was mainly dependent upon annealing condition, where its height and temperature were increased by adding REs, assigning to be a recrystallization peak.

Sorption properties of polymers based onN-substituted maleimides

Physicochemical and functional properties of 2,2-diallyl-1,1,3,3-tetraethylguanidinium chloride copolymers with N-(n-carboxyphenyl)maleimide, of N-vinylpyrrolidone with N-(n-carboxyphenyl)maleimide, and of N-vinylpyrrolidone with N-phenylmaleimide have been investigated. Specific surface area and porosity of the copolymers under investigation have been determined by using the low-temperature adsorption method. Electron microscope investigations in surfaces of the polymers have evinced that all of them have a spongy microstructure, the N-vinylpyrrolidone copolymer with N-(n-carboxyphenyl)maleimide being the most homogeneous of these. Sorption capacity of the copolymers toward Re(VII) ions has been investigated. The process is described by the Langmuir isotherm. The pH is the most important parameter for sorption process of Re(VII). In the conjoint presence of Re(VII) and Mo(VI) in a solution of acid and ammoniac mediums, rhenium can be separated from molybdenum by using the sorbents under investigation at pH > 4.5 or at hydrochloric acid concentrations 0.1 mol L−1 and more. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Solvent-Free Friedel-Crafts Acylation of Fluorobenzene Catalyzed by Trifluoromethanesulfonic Acid and Rare Earth Triflates

Solvent-free Friedel-Crafts acylation of fluorobenzene with benzoyl chloride was investigated over the trifluoro- methanesulfonic acid (TfOH) and rare earth triflate (Re(OTf)3) composite catalyst. The results showed that the presence of Re(OTf)3 leads to the decrease in a half amount of TfOH catalyst, and there is a synergistic effect between TfOH and Re(OTf)3 in this composite catalyst. For the solvent-free acylation of fluorobenzene with benzoyl chloride, the catalytic activities of 11 kinds of rare earth elements Re(OTf)3 were tested, and it was found that among all Re(OTf)3 compounds La(OTf)3 exhibits the best catalytic performance and it can be repeatedly used. After the acylation of fluorobenzene with benzoyl chloride over the La(OTf)3 and TfOH catalyst at 140 ℃ for 4 h, the selectivity and yield to para-product fluorobenzophenone reach up to 99% and 87%, respectively. For the acylation of different benzene derivatives with benzoyl chloride over the TfOH and Re(OTf)3 catalyst, the promoting catalysis of different elements Re(OTf)3 is different, for instance, for the acylation of dimethylbenzene, Ce(OTf)3 exhibits the best catalytic performance among the tested Re(OTf)3 promoters. Keywords Trifluoromethanesulfonic acid and rare earth triflate; Fuorobenzene; Benzoyl chloride; Friedel-Crafts acylation; Composite catalyst system.

Dinuclear triple-stranded complexes of ReV with bis(benzene-o-dithiolato) ligands

The reaction of K2ReCl6 with 1,2-bis(2,3-dimercaptobenzamido)ethane (H4-1), and 1,2-bis(2,3-dimercaptobenzamido)benzene (H4-2) in the presence of Na2CO3 in methanol affords dinuclear complexes of ReV. Experimental evidence supports the presence of self-assembled complexes with two {Re(S2C6H3)3} units connected in a triple-stranded fashion. Density Functional Theory (DFT) studies on geometry and electronic properties were conducted employing the hybrid B3LYP and PBE1PBE functionals. The helical (ΔΔ and ΛΛ) and meso-helical (ΔΛ) isomers were considered. For the helicate complexes included in this study, differences in the stability of the isomers were observed originating in different steric and strain interactions between the three ligand strands. The geometries at the minimum exhibit a distorted trigonal-prismatic coordination environment at the metal centers. Natural bond orbitals (NBO) analysis indicates the presence of Re–S bonds which are strongly polarized toward the non-metal. Time-Dependent DFT (TD-DFT) calculations were performed for a further understanding of the optical spectra. The calculations show the occupied 5d orbitals of the rhenium lying beneath occupied sulfur-based MOs. The general features of the electronic spectra in the visible region are reasonably reproduced by the calculations. The analysis of molecular orbitals also allows the assignment of the origin for all experimentally detected absorption bands. In the high-energy region of the spectrum the absorptions are attributed to ligand-to-metal–ligand charge transfer (LMLCT), in which sulfur-based orbitals and unoccupied orbitals at the rhenium atom and the benzene-o-dithiolato groups are involved. Also in the blue region, shoulders originating from LMLCT are observed.

Effects of rhenium alloying on adhesion of Mo/HfC and Mo/ZrC interfaces: A first-principles study

Adhesion and electronic structure of Mo/HfC and Mo/ZrC interfaces with and without Re impurity are investigated using first-principles density functional calculations. For Re free interface, results show that Mo atoms bind preferentially on top of C atoms, forming covalent bonds. The presence of Re alloying at the interface improves the adhesion, but does not affect the nature of interfacial Mo-C bonds.

Protein loop compaction and the origin of the effect of arginine and glutamic acid mixtures on solubility, stability and transient oligomerization of proteins

Addition of a 50mM mixture of L: -arginine and L: -glutamic acid (RE) is extensively used to improve protein solubility and stability, although the origin of the effect is not well understood. We present Small Angle X-ray Scattering (SAXS) and Nuclear Magnetic Resonance (NMR) results showing that RE induces protein compaction by collapsing flexible loops on the protein core. This is suggested to be a general mechanism preventing aggregation and improving resistance to proteases and to originate from the polyelectrolyte nature of RE. Molecular polyelectrolyte mixtures are expected to display long range correlation effects according to dressed interaction site theory. We hypothesize that perturbation of the RE solution by dissolved proteins is proportional to the volume occupied by the protein. As a consequence, loop collapse, minimizing the effective protein volume, is favored in the presence of RE.

Photoreduction of CO2 on p-type Silicon Using Re(bipy-But)(CO)3Cl: Photovoltages Exceeding 600 mV for the Selective Reduction of CO2 to CO

Hydrogen-terminated p-type silicon was used as a photocathode for the selective photoreduction of CO2 to CO in the presence of Re(bipy-But)(CO)3Cl (bipy-But = 4,4′-di-tert-butyl-2,2′-bipyridine) as an electrocatalyst. The reduction of CO2 to CO on p-type silicon was achieved at a potential more than 600 mV lower than that required with a Pt electrode. A Faradaic efficiency of 97 ± 3% and an overall efficiency of 9.3% and 10% for the conversion of monochromatic and polychromatic light, respectively, to electricity were observed for the CO2 photoreduction process. A short-circuit quantum efficiency of 61% for light-to-chemical energy conversion was observed for the conversion of CO2 to CO.

Catalytic Performance of Re/Ga2O3/WO3/ZrO2 Catalyst for n-Hexane Isomerization

Abstract A series of Re/Ga 2 O 3 /WO 3 /ZrO 2 catalysts were prepared by the impregnation method. The crystalline structure, redox, and acid site distribution of the catalysts were characterized by X-ray powder diffraction, temperature-programmed reduction of H 2 , and temperature-programmed desorption of NH 3 . Their catalytic performance for n -hexane isomerization was studied. The results showed that the addition of Re greatly affected the redox properties and the acid site distribution of the catalysts. Owing to the presence of Re, n -hexane isomerization was catalyzed by metal and acid sites, and thus the conversion of n -hexane and the selectivity for 2,2-dimethylbutane were significantly increased. Under the conditions of 195 °C, 1.0 MPa, LHSV = 1.0 h −1 , and n (H 2 )/ n (C 6 ) = 2.0, the conversion of n -hexane over 1.0%Re/1.0%Ga 2 O 3 /WO 3 /ZrO 2 is 84.8%, and the selectivities for 2,2-dimethylbutane, i -hexane, and cracking products (C 5- ) are 20%, 97.7%, and 2.1%, respectively. The catalyst is stable during 150 h operation.

Fischer–Tropsch synthesis over un-promoted and Re-promoted γ-Al 2O 3 supported cobalt catalysts with different pore sizes

The effect of rhenium on the Fischer–Tropsch synthesis activity and selectivity of γ-Al 2O 3 supported cobalt catalysts was investigated in fixed-bed reactors at T = 483 K, P = 20 bar, and H 2/CO = 2.0. Catalysts containing 20 wt.% cobalt and 0 or 0.5 wt.% rhenium were prepared by incipient wetness impregnation of different γ-Al 2O 3 supports with aqueous solutions of cobalt nitrate hexahydrate and for the Re-promoted catalysts, also perrhenic acid. The γ-Al 2O 3 supports had very different pore characteristics. The post-calcination Co 3O 4 crystallite size was predominantly controlled by the γ-Al 2O 3 support pore diameter. Presence of Re had only a minor effect on the crystallite size. For all catalysts, supported Co 3O 4 was reduced in two steps to Co 0 with CoO as intermediate species. However, while reduction of Co 3O 4 to CoO took place in the same temperature range for all catalysts, the reduction temperature of CoO to Co 0 was dependent on the catalyst properties. Large particles present in wide pores were easier to reduce than small particles located in narrow pores. In addition, Re promoted the reduction of CoO. The effect of rhenium as a reduction promoter was less pronounced at increasing pore size and particle size. Re also had a similar positive impact on the cobalt dispersion of the catalysts. Although Re significantly increased the Fischer–Tropsch synthesis cobalt-time yield, it did not modify the site-time yield. The deactivation rates of all the catalysts were also similar up to 100 h on stream. Positive correlations were found between the catalyst pore diameter and the C 5+ selectivity and between the cobalt particle size and the C 5+ selectivity. Re had a consistent positive, albeit small, effect on the C 5+ selectivity.

Lattice-parameter misfits between the γ and γ′ phases in single crystals of nickel superalloys

X-ray diffractometry has been used to study the transformation of the profiles of X-ray diffraction lines (222), (004), (003) and to determine the values of the lattice misfit between the γ and γ′ phases (γ/γ′ misfit) for single crystals of nickel superalloys ZhS6U, ZhS30, ZhS32, VZhM1, and VZhM4 in the as-cast state and after heat treatment. It has been established that with an increase in the γ/γ′ misfit there increase tetragonal distortions of the fcc lattice of the γ solid solution. For the single crystals of VZhM4 alloyed with rhenium and ruthenium, splitting of the superlattice reflection of the strengthening γ′ phase has been revealed. The structural regularities revealed testify to qualitative changes in the factors that govern the redistribution of refractory alloying elements between the lattices of the γ and γ′ phases, for example, of Mo in the presence of Re and Ru.

The role of rhenium in the conversion of glycerol to synthesis gas over carbon supported platinum–rhenium catalysts

Reaction kinetics measurements were carried out to study the conversion of aqueous solutions of glycerol (30 and 80 wt%) over carbon-supported Pt and Pt–Re catalysts at temperatures from 483 to 523 K. The results of these studies show that the turnover frequencies for production of H2, CO, CO2, and light alkanes (primarily methane) all increase upon the addition of Re to Pt/C catalysts. The molar ratio of H2/CO increases, while the CO/CO2 ratio decreases with Re addition, indicating increased rate of water–gas shift. For glycerol conversion over a Pt–Re/C catalyst with an atomic Pt:Re ratio of 1:1, increasing pressure or decreasing temperature leads to an increase in the production of alkanes and light oxygenated hydrocarbons (ethanol, methanol, propanediols, and acetone) at the expense of CO and CO2. Temperature-programmed desorption studies and microcalorimetric measurements indicate that addition of Re to Pt modifies the interaction of CO with surface sites. X-ray absorption spectroscopy and transmission electron microscopy studies provide evidence indicating that Pt–Re/C catalysts consist primarily of bimetallic nanoparticles with sizes below 2 nm, and Re inhibits the sintering of these nanoparticles during reaction conditions for glycerol conversion. The results of these reaction kinetic studies and characterization studies indicate that the performance of Pt–Re/C catalysts for glycerol conversion is related to the formation of Pt–Re nanoparticles, for which Re promotes the overall rate of glycerol reforming by reducing the binding energy of CO to Pt, thereby leading to less extensive blocking of surface sites by reaction intermediates and/or products. In addition, the presence of Re facilitates water–gas shift and CO bond cleavage reactions.

Adsorption and flotation of hydrophilic and hydrophobic materials in the presence of hydrocarbon polyethylene glycol ethers

Polyoxyethylated alkanols (C n E m ) and nonylphenols (C 9PhE m ), or generally hydrocarbon polyethylene glycol ethers (RE m ), are preferentially adsorbed on solids with pH pzc lower than 4. This is due to basic character of OH groups of RE m and acidic properties of the OH groups of the solids. The saturation adsorption of RE m increases with the number of carbon atoms in the hydrocarbon part of the molecule and decreases with the increasing number of oxyethylenic groups. This pattern is not always reflected in flotation because of interplay of different parameters including surface tension of RE m solution and original hydrophobicity of the solid. The adsorption of RE m surfactants renders hydrophilic surfaces slightly hydrophobic. For instance, the induced hydrophobicity of hydrophilic materials such as quartz in the presence of C 16E 23, expressed as contact angle, is less than 20°. The flotation with RE m usually occurs for solids with pH pzc < 4. The flotation of naturally hydrophobic solids such as coal is better than that of hydrophilic materials due to enhanced adsorption of the hydrocarbon part of RE m on hydrophobic surfaces. There is no correlation between CMC and flotation of solids. The flotation above CMC is a result of penetration and reorganization of the adsorbed layers of C n E m when the bubbles approach the solid. Cease of flotation at high C n E m concentrations mostly results from a decreasing surface tension of the solution. The separation of different mineral particles in the presence of RE m surfactants is possible only in gently agitated flotation cells due to low hydrophobicity caused by the surfactant.