High-temperature Hydrogen Treatment Research Articles

Hydrodehalogenation of 4-chlorophenol and 4-bromophenol over Pd–Fe/Al2O3: influence of catalyst reduction conditions

The reduction of monometallic Pd/Al2O3 and bimetallic PdFe/Al2O3 catalysts produced by co-impregnation or sequential impregnation of the support with metal salts was possible not only under high temperature hydrogen treatment but also at 30 °C under the action of aqueous phenol solution and hydrogen. According to the XPS data, both reduction routes provided sufficient degrees of Pd reduction required for fast hydrodehalogenation of 4-chlorophenol and 4-bromophenol to phenol in aqueous solutions. The degree of Pd reduction was higher in the co-impregnated bimetallic PdFe catalyst, which was more efficient in transformation of 4-bromophenol; the bimetallic catalysts were more stable than the monometallic Pd one in the conversion of 4-chlorophenol.

Black hollow TiO2 nanocubes: Advanced nanoarchitectures for efficient visible light photocatalytic applications

Black hollow nanocubic TiO2 (BHC-TiO2) architectures have been synthesized via multi-step approach comprising co-precipitation to prepare hematite nanocubes; titania covering of hematite towards Fe2O3/TiO2 core/shell nanocubes and hydrothermal hematite etching process to yield hollow cubic TiO2 structures with Ti3+ species after high temperature hydrogen treatment. The resultant BHC-TiO2 nanoarchitectures exhibited excelling photocatalytic performance under visible light in the preparation of benzimidazole derivatives. This superior activity can be attributed to the design of BHC-TiO2 with high surface area (⁓206 m2g−1), ultrathin shell (⁓50 nm), hydrogenated visible active structure and void nanoreactor-like space in the cubic structure.

One-step synthesis of Pt-Pd catalyst nanoparticles supported on few-layer graphene for methanol oxidation

In this study, Pt-Pd nanoparticles (NPs) supported on few-layer graphene (FLG) have been firstly prepared by one-step arc discharge evaporation of carbon electrodes containing both Pt and Pd elements. The few-layer graphene and Pt-Pd nanoparticles were achieved simultaneously through the evaporation process. After a high-temperature hydrogen treatment, the Pt-Pd/graphene was applied in the study of methanol oxidation in direct methanol fuel cell. The total weight of electrocatalyst keeps 2 wt% of the electrode. The sample with a mass ratio of Pt:Pd = 3:1 (H-Pt3Pd1/G) exhibits better electrocatalytic activity (198 mA mg-1 pt) and better tolerance to carbon monoxide(CO) poisoning (If/Ib = 1.26). It is noteworthy that the value of If/Ib can reach to 1.55 for the sample with the mass ratio of Pt:Pd = 2:1 (H-Pt2Pd1/G),which implies its excellent ability of CO tolerance. The introduction of Pd element may open a new strategy to improve the CO tolerance by arc discharge evaporation.

Influence of Self-organization of Al2O3 and TiO2/Al2O3 Nanofilaments into Nanotubes Caused by High Temperature Hydrogen Treatment on Propane Cracking

Influence of Self-organization of Al2O3 and TiO2/Al2O3 Nanofilaments into Nanotubes Caused by High Temperature Hydrogen Treatment on Propane Cracking

Influence of the Surface Modification of Mesoporous Activated Carbon on the Removal of Humic Acid From Aqueous Solution

Humic acids (HA) constitute the major fraction of natural organic matter in water supplies. HA are very problematic with regard to drinking water treatment and supply since, not being completely removed by conventional treatment processes, they react with chlorine resulting in formation of carcinogenic and regulated disinfection-by products. Adsorption of brown (BHA) and gray (GHA) fractions of humic acid on starting and modified mesoporous activated carbons was investigated. BHA and GHA are fractions of humic acid extracted from young brown coal (Czech Republic) which differ essentially in their characteristics in terms of structure and physicochemical properties. Mesoporous activated carbon was modified by two ways: ammonization (AC/N) and high-temperature hydrogen treatment (AC/H). All activated carbons studied, showed higher adsorption capacity towards BHA comparing to GHA, what is attributed to the smaller molecular weight of BHA molecules, as determined by ultrafiltration method. Comparing to starting AC, nearly 2- and 2.5-fold higher removal degree of both BHA and GHA was observed for AC/N and AC/H, respectively. This observation was found to be a consequence of the increase in aromacity degree of both adsorbents, as shown by increase in the C/H atomic ratio. In the case of AC/H the electrostatic interaction between positively charged surface of AC/H and HA molecules, enhances the extent of adsorption. Adsorption results were discussed in terms of Freundlich adsorption model. The shape of isotherm indicates a strong competition for adsorption centers on AC surface between water and HA molecules, which decreased in the direction AC>AC/N>AC/H. At increased ionic strength of the solution (0.01 M NaCl), no difference in the extent of adsorption between AC/N and AC/H was observed.

Structural transformation of TiO2/Al2O3 nanowires into nanotubes caused by high-temperature hydrogen treatment

It has been shown that the high-temperature hydrogen treatment of aluminum oxide nanowires coated with a monolayer of titanium oxide causes them to curl into nanotubes as a result of self-organization. The physicochemical properties of the nanotubes of a composite aluminum oxide aerogel coated with titanium oxide have been studied using X-ray phase analysis (XRD) and transmission electron microscopy (TEM). As a result of TiO2/Al2O3 nanofibrous aerogel treatment with hydrogen, a conversion of amorphous aluminum oxide fibers into tubes of nanocrystalline η-Al2O3 occurs, but in this case the titanium dioxide monolayer does not form a separate phase. A study of the porous structure by the low-temperature adsorption of nitrogen vapors has shown that the aerogels of TiO2/Al2O3 nanotubes have a developed mesoporous structure with a small amount of micropores and a specific surface of more than 300 m2/g. An increase in the temperature of hydrogen treatment first leads to the growth of an increase in the specific surface to 348 m2/g at 923 K, and then to a gradual decrease to 145 m2/g at 1123 K. In this case, the diameter of mesopores corresponding to a maximum on a curve of the pore size distribution decreases from 35 nm for a freshly prepared sample to 25 nm at 923 K and to 20 nm at 1123 K. The most homogeneous pores of a 25 nm diameter have the samples activated at 923 K. As a result of the high-temperature hydrogen treatment of the samples, the number of primary adsorption centers of water vapor adsorption decreases about two times. The resulting samples of TiO2/Al2O3 aerogels are close in structure to the initial aluminum oxide, whose wires just form nanotubes having a surface coated with titanium dioxide. As a result of the interaction between molecules of titanium dioxide adsorbed on the surface of aluminum oxide tubes, a substantial densification of the composite structure occurs.

PdCuAu ternary alloy membranes: Hydrogen permeation properties in the presence of H2S

PdCuAu ternary alloy membranes with different component compositions were synthesized by sequential electroless deposition of components onto porous stainless steel substrates. The ternary with the highest Au content, Pd69Cu14Au17, exhibited the highest hydrogen permeation flux, comparable to that of a Pd91Au9 membrane. Upon exposure to 100ppm H2S/H2 at 673 K for 24h, all PdCuAu membranes experienced flux reductions of ~55%, followed by recovery to ~80% of the initial hydrogen flux upon reintroduction of pure hydrogen at 400°C. Complete flux recovery after H2S exposure required hydrogen treatment at 500°C. X-ray diffraction (XRD) analysis of the H2S-exposed PdCuAu membranes revealed fcc alloy structure with no evidence of bulk sulfide formation. In agreement with the XRD results, sulfur was not detected in the bulk of H2S-exposed samples by energy dispersive spectroscopy (EDS). However, analysis of H2S-exposed PdCuAu alloys by X-ray photoelectron spectroscopy (XPS) depth profiling revealed low, but measureable, amounts of sulfur in the near-surface region, about 10nm in depth. The depth profiles of samples after hydrogen recovery treatment showed significantly reduced sulfur content. These results indicate that H2S exposure causes flux loss in PdCuAu alloys through a surface-poisoning mechanism, and that the surface sulfide can be removed—and flux recovered—by high temperature treatment in hydrogen.

Pt–Fe catalyst nanoparticles supported on single-wall carbon nanotubes: Direct synthesis and electrochemical performance for methanol oxidation

Single-wall carbon nanotubes (SWCNTs) supported Pt–Fe nanoparticles have been prepared by one-step hydrogen arc discharge evaporation of carbon electrode containing both Pt and Fe metal elements. The formation of SWCNTs and Pt–Fe nanoparticles occur simultaneously during the evaporation process. High-temperature hydrogen treatment and hydrochloric acid soaking have been carried out to purify and activate those materials in order to obtain a new type of Pt–Fe/SWCNTs catalyst for methanol oxidation. The Pt–Fe/SWCNTs catalyst performs much higher electrocatalytic activity for methanol oxidation, better stability and better durability than a commercial Pt/C catalyst according to the electrochemical measurements, indicating that it has a great potential for applications in direct methanol fuel cells.

Transformations of Phases in Titanium Alloy after High Temperature Hydrogen Treatment

Positive nature of the effects of hydrogen on the properties of titanium alloys is manifested in the high temperature hydrogen treatment (HTM - Hydrogen Treatment of Materials), where hydrogen is temporary alloying component. The paper presents the results of the possibilities of hydrogen using as a temporary alloying element in Ti-6Al-4V alloy and titanium Grade 3. Treatment of hydrogen alloy consisted of three stages: hydrogenation in hydrogen gas atmosphere at 650°C, a cyclic hydrogen-treatment (3 cycles 850 °C to 250 °C) and a dehydrogenation in vacuum (550°C). It was shown that hydrogen affects appreciably changes the microstructure of surface layer of the tested titanium alloy. The aim of this work is to determine the effect of hydrogen on the two-phase microstructure in Ti-6Al-4V alloy and Grade 3 titanium and hardness after high temperature hydrogen treatment.

Effect of a High-Temperature Hydrogen Treatment on a Microstructure and Surface Fracture in Titanium Ti-6Al-4V Alloy

Influence of hydrogen on the structure of titanium alloys is a complex phenomenon, depending on the circumstances, may be negative or positive [1,2]. The presence of hydrogen in titanium alloys usually results in degradation of their microstructure and properties, as well promote some undesirable effects such as hydrogen corrosion and hydrogen embrittlement [3]. Positive nature of the effects of hydrogen on the properties of titanium alloys is manifested in the high temperature hydrogen treatment (HTM - Hydrogen Treatment of Materials), where hydrogen is temporary alloying component [4-9]. This is possible because of the high values of diffusion coefficients can be easily introduced into the titanium and it just as easily removed. Titanium and its alloys show the absorbability of almost 60 at. % of hydrogen at 600°C. The limit hydrogen of solubility in Tiα is very low and does not exceed 0.05 at. % at room temperature. The limit hydrogen of solubility in Tiβ is much higher and its maximum value is 48 at. %. Since the beginning of the titanium industry, a great deal of attention has been paid to control the hydrogen content at titanium products – above 0.2 ppm. The paper presents the results of the possibilities of hydrogen using as a temporary alloying element in Ti-6Al-4V alloy. Treatment of hydrogen alloy consisted of three stages: hydrogenation in hydrogen gas atmosphere at 650 °C, a cyclic hydrogen-treatment (3 cycles 650 °C to 250 °C) and a dehydrogenation in vacuum (550 °C). It was shown that hydrogen affects appreciably changes the microstructure of surface layer of the tested titanium alloy. The aim of this study is thus to determine the effect of hydrogen on the two-phase microstructure, hardness, and surface fracture of the titanium alloy Ti-6Al-4V due to high-temperature hydrogen treatment.

Preparation of Ag–Fe-decorated single-walled carbon nanotubes by arc discharge and their antibacterial effect

A simple one-step approach for the preparation of Ag–Fe-decorated single-walled carbon nanotubes (Ag–Fe/SWCNTs) by DC hydrogen arc discharge is presented in this article. The growth of SWCNTs and the attachment of Ag and Fe nanoparticles to the SWCNTs occur simultaneously during the arc discharge evaporation process. It has been confirmed that the Ag and Fe nanoparticles in the diameter range of 1–10 nm are well dispersed and tightly attached to the outer surfaces of SWCNTs. The as-grown Ag–Fe/SWCNTs have been purified by high-temperature hydrogen treatment to remove amorphous carbon and carbon shells. Antibacterial tests show that the antibacterial activity of the purified Ag–Fe/SWCNT hybrid nanoparticles is excellent against Escherichia coli. The percentage of the E. coli killed by 100 μg/ml Ag–Fe/SWCNTs can reach up to 85.1 % at a short residence time of 2 h, suggesting that the purified Ag–Fe/SWCNTs may have potential antibacterial applications.

Changes of microstructure in titanium alloy during high temperature hydrogen treatment

The paper regarding the HTM - Hydrogen Treatment of Materials as an attractive method for controlling microstructure and improving final mechanical properties of titanium alloys. A new variant of high-temperature hydrogen treatment that includes cyclic heat treatment is proposed. This paper present the qualitative description of the microstructure in Ti-6Al-4V alloy after high-temperature hydrogen treatment with cyclic heat treatment operation. Hydrogen treatment consists of the three stages: hydrogenation in hydrogen gas atmosphere (600°C), cyclic heat hydrogen treatment (580°C), dehydrogenation in vacuum (550°C). The possibilities of hydrogen treatment for controlling microstructure layer of titanium alloy was presented.

Positive Effect of Hydrogen Treatment in Titanium Ti-6Al-4V Alloy

Positive nature of the effects of hydrogen on the properties of titanium alloys is manifested in the high temperature hydrogen treatment (HTM - Hydrogen Treatment of Materials), where hydrogen is temporary alloying component. This is possible because of the high values ​​of diffusion coefficients can be easily introduced into the titanium and it just as easily removed. Titanium and its alloys exhibit a high affinity for hydrogen absorption capacity, about 60% at. hydrogen at 600 °C. The hydrogen in titanium alloy is present in the form – an interstitial solution or titanium hydride. Since the specific volume of titanium hydride is about 13 ÷ 17% higher compared to α phase, it is high stress in the crystal lattice of this phase leads to local plastic deformation and large deformation phase. The paper presents the results of the possibilities of hydrogen using as a temporary alloying element in Ti-6Al-4V alloy. Treatment of hydrogen alloy consisted of three stages: hydrogenation in hydrogen gas atmosphere at 650 °C, a cyclic hydrogen-treatment (3 cycles 650 °C or 950 °C to 250 °C) and a dehydrogenation in vacuum (550 °C). It was shown that hydrogen affects appreciably changes the microstructure of surface layer of the tested titanium alloy. The aim of this study is thus to determine the effect of hydrogen on the two-phase microstructure, hardness, and corrosion resistance of the titanium alloy Ti-6Al-4V due to high-temperature hydrogen treatment.

Effect of high-temperature hydrogen treatment on the microstructure and properties of titanium alloy Ti-6Al-4V

The influence of hydrogen on the structure of titanium alloys is a complex phenomenon, which, depending on the circumstances, may be negative or positive. Negative effects of hydrogen on the properties of titanium alloys primarily manifest themselves in a decrease in plastic properties and impact resistance and the formation of cracks in the structure. The positive effect of hydrogen on the titanium alloy properties is manifested in the high-temperature hydrogen treatment (HTM—Hydrogen Treatment of Materials), where hydrogen is a temporary alloying component. Because of the high values of its diffusion coefficient, hydrogen can be easily introduced into the titanium and just as easily removed from it. The HTM plays an important role in the forming and fragmentation of titanium hydride. Because the diameter of a hydrogen atom is very small, the hydrogen atoms occupy the interstitial sites. Titanium and its alloys exhibit a high affinity for hydrogen absorption, about 60 at.% hydrogen at 600 °C. Because the specific volume of titanium hydride is about 13-17% higher compared to that of the α phase, high stresses in the crystal lattice of the titanium hydride phase leads to local plastic deformation and a highly deformed phase. These developments lead to changes in the structure of titanium alloys and their mechanical properties. This paper presents characterization studies of the structure of two-phase titanium alloy Ti-6Al-4V after hydrogen treatment. This hydrogen treatment consisted of three stages: hydrogenation in a hydrogen gas atmosphere at 850 °C, a cyclic hydrogen treatment (1 or 3 cycles at 250 °C) and dehydrogenation in a vacuum (550 °C). It was shown that hydrogen appreciably changed the microstructure of the surface layer of the tested titanium alloy. Qualitative analyses of the structure using secondary electrons in a scanning electron microscope (SEM) were carried out. Image analysis helped to determine a quantitative description of the alloy structure after the hydrogen treatments.

Effects of hydrogen treatment on ohmic contacts to p-type GaN films

This study investigated the effects of hydrogen (H 2) treatment on metal contacts to Mg-doped p-GaN films by Hall-effect measurement, current–voltage ( I– V) analyzer and X-ray photoemission spectra (XPS). The interfacial oxide layer on the p-GaN surface was found to be the main reason for causing the nonlinear I– V behavior of the untreated p-GaN films. The increased nitrogen vacancy (V N) density due to increased GaN decomposition rate at high-temperature hydrogen treatment is believed to form high density surface states on the surface of p-GaN films. Compared to untreated p-GaN films, the surface Fermi level determined by the Ga 2p core-level peak on 1000 °C H 2-treated p-GaN films lies about ∼2.1 eV closer to the conduction band edge (i.e., the surface inverted to n-type behavior). The reduction in barrier height due to the high surface state density pinned the surface Fermi level close to the conduction band edge, and allowed the electrons to easily flow over the barrier from the metal into the p-GaN films. Thus, a good ohmic contact was achieved on the p-GaN films by the surface inversion method.

Water Vapor Absorption on Nanostructured Carbide Derived Carbon (CDC)

In this work, carbide derived carbon (CDC) layers were synthesized on SiC and kept isolated from the environment until exposed to controlled water vapor atmospheres, so that the effects of water vapor pressure on the absorption could be quantified. The effects of high temperature hydrogen treatment are also described. CDC samples after chlorination are very hygroscopic, absorbing up to 35% of their weight in water in low humidity environments.

Structured catalyst of Pd/ZnO on sintered metal fibers for 2-methyl-3-butyn-2-ol selective hydrogenation

An innovative structured catalyst based on sintered metal fibers (SMFs) coated by a grain-structured ZnO layer was developed for the selective 3-phase hydrogenation of functionalized alkynes. The catalyst was synthesized by the deposition of Pd 0-sol with 7-nm nanoparticles stabilized by molybdate anions on ZnO/SMF after reduction in hydrogen at 773 K. The crystallites of PdZn alloy (24 nm) were formed by high-temperature treatment in hydrogen and contained partly Pd(0) nanoparticles. Pd/ZnO/SMF (0.2 wt% Pd, 6 wt% ZnO) allowed > 95 % yield of 2-methyl-3-buten-2-ol (MBE) during 2-methyl-3-butyn-2-ol hydrogenation at 308 K and 5 bar pressure using water as the solvent and adding a small amount of quinoline. The consecutive reaction of MBE hydrogenation was suppressed due to the presence of PdZn in the active phase. The catalyst activity of the catalyst was an order of magnitude higher compared with that of commercial Lindlar catalyst (Pd, Pb/CaCO 3), which quickly deactivated in aqueous media due to irreversible chemical transformations of the CaCO 3 support. The structured catalyst developed in this study could be reused after ultrasonic regeneration, retaining the original selectivity and most of its initial activity. The catalyst showed high mechanical stability, precluding leaching of its components during the reaction. Due to easy shaping, high permeability, and low pressure drop during the fluid passage, the structured Pd/ZnO/SMF catalyst is suitable for a continuously operated staged bubble column reactor.

Inroad to modification of detonation nanodiamond

Our research is directed towards finding inroad(s) for conversion of detonation nanodiamond to more standard nanopowder with, first of all, enhancement of chemical and phase purity and, secondly, establish monofunctional surface termination. We have designed and tested a novel approach to detonation nanodiamond purification and surface functionalization, using a high temperature treatment in hydrogen-(H 2, NH 3) and chlorine-containing (Cl 2, CCl 4) gaseous media. A serious reduction in Al, Cr, Si and Fe content in nanodiamond was achieved by Cl 2 treatment at 850 °C. Moreover a drastic decrease in the hydrophility (by a factor of 20) from annealing in a CCl 4 / Ar mixture is demonstrated. Other remarkable features after high temperature treatment in H 2 and NH 3 are being studied by independent characterization techniques (chemical analyses; pH-measurements, FTIR-, Raman-, and ESR spectroscopy), indicating profound nanodiamond modification and prescribed functionalization are possible.

Promoting effect of zinc on the vapor-phase hydrogenation of crotonaldehyde over copper-based catalysts

The promoting effect of zinc for the vapor-phase hydrogenation of crotonaldehyde was studied on impregnated Cu/SiO 2 and Cu–ZnO/SiO 2, and on coprecipitated Cu–Al 2O 3 and Cu x –Zn y O 2 y –ZnAl 2O 4 catalysts. The reaction was carried out in a tubular reactor at 120 °C and atmospheric pressure. Samples were characterized by temperature-programmed reduction, X-ray diffraction, transmission electronic microscopy, diffuse reflectance FTIR spectroscopy of adsorbed CO, and X-ray photoelectron spectroscopy. Cu/SiO 2 and Cu–Al 2O 3 catalysts reduced in hydrogen either at 300 or 500 °C hydrogenated preferentially the C C bond of crotonaldehyde and gave more than 90% of selectivity to butyraldehyde. In contrast, the initial butyraldehyde selectivity on Cu–ZnO/SiO 2 reduced at 500 °C was only about 55%, essentially because the selectivity to crotyl alcohol significantly increased on this zinc-containing sample as compared to Cu/SiO 2. This selectivity enhancement for hydrogenating the C O bond on Cu–ZnO/SiO 2 reduced at 500 °C was explained by considering that the high-temperature hydrogen treatment forms mobile ZnO x reduced species that strongly interact with Cu 0 crystallites. The resulting Cu 0–ZnO x species preferentially catalyze the crotyl alcohol formation from crotonaldehyde via a dual-site reaction pathway. A similar explanation was proposed to interpret the observed enhancement of the C O hydrogenation rate on ternary Cu–Zn–Al catalysts reduced at 500 °C as compared to Cu–Al 2O 3. Nevertheless, the Cu 0–ZnO x species were unstable on stream and the selectivity to crotyl alcohol continuously decreased with reaction time on zinc-containing samples reduced at high temperatures.

High Catalytic Activity for CO Oxidation of Gold Nanoparticles Confined in Acidic Support Al-SBA-15 at Low Temperatures

While there is a large number of recent studies of Au nanocatalysts supported on metal oxides, low-temperature CO oxidation under an acidic environment has not yet been accomplished. Over a novel acidic Al-SBA-15 support, uniformly distributed gold nanoparticles with sizes approximately 2.7 nm were obtained by a successive procedure of aminosilane grafting, gold adsorption-reduction, and then high-temperature hydrogen treatment. The catalyst system, Au@Al-SBA-15, exhibits extraordinarily high activity for CO oxidation at 80 degrees C. By varying the Si/Al ratio of the support, the dependence of the catalytic activity on the support Si/Al ratio was found in the CO oxidation reaction.