Thermal Treatment In Hydrogen Research Articles

Asymmetric oxygen vacancy promotes CO-SCR performance on defect-engineered Rh/CeCuOx catalyst

Selective catalytic reduction of NOx with CO (CO-SCR) is a process that purifies both NO and CO pollutants through a catalytic reaction. Specifically, the cleavage of NO on the catalyst surface is crucial for promoting the reaction. During the reaction, the presence of oxygen vacancies can extract oxygen from NO, thereby facilitating the cleavage of NO on the catalyst surface. Thus, the formation of oxygen vacancies is key to accelerating the CO-SCR reaction, with different types of oxygen vacancies being more conducive to their generation. In this study, Rh/CeCuOx catalysts were synthesized using the co-crystallization and impregnation methods, and asymmetric oxygen vacancies were induced through hydrogen thermal treatment. This structural modification was aimed at regulating the behavior of NO on the catalyst surface. The Rh/Ce0.95Cu0.05Ox-H2 catalyst exhibited the best performance in CO-SCR, achieving above 90% NO conversion at 162 °C. Various characterization techniques showed that the H2 treatment effectively reduced some of the CuO and Rh2O3, creating asymmetric oxygen vacancies that accelerated the cleavage of NO on the catalyst surface, rather than forming difficult-to-decompose nitrates. This study offers a novel approach to constructing oxygen vacancies in new CO-SCR catalysts.

Формирование градиентных структур в титановом сплаве при обратимом легировании водородом

The possibility of transforming a large-plate structure and creating a gradient structure in samples of titanium alloy VT23 during thermal hydrogen treatment has been studied. It is shown that by varying the concentration-time parameters of hydrogenation annealing, it is possible to regulate the depth of hydrogen penetration and purposefully form the structure of near-surface layers. Subsequent low-temperature vacuum annealing makes it possible to transform the coarse-plate structure into a finely dispersed one with a hardness of up to 40 HRC. It was established that the thickness of a layer with a finely dispersed structure during unidirectional hydrogenation with a barrier coating is twice as large as during volumetric nonequilibrium hydrogenation in the absence of a coating.

Oxygen Reduction Reaction Activity of Platinum Nanosheets Derived from Layered Platinic Acid

Platinum nanoparticles are mainly utilized as the cathode catalyst for polymer electrolyte fuel cells. However, the utilization of platinum for the oxygen reduction reaction (ORR) is insufficient and one must tackle the trade-off between high surface area and high stability. We have previously shown that metallic nanosheets such as ruthenium nanosheets exhibit high electrocatalytic activity and stability owing to the two-dimensional structure with an atomic scale thickness.1, 2 Platinum nanosheets, if available, should also have the potential to increase the utilization of the atoms and durability. While a few studies have reported the synthesis of platinum nanosheets,3 the thickness of the nanosheets is more than 1 nm, and the utilization of platinum has so far been lower than that of the Pt nanoparticles.In this study, we report double-layered platinum nanosheets derived from layered platinic acid.4 Layered platinic acid was synthesized through a solid-state-reaction and subsequent acid treatment. From the layered platinic acid, platinum oxide nanosheets were obtained as a colloid via chemical exfoliation. The thickness of the platinum oxide nanosheet was ~0.9 nm, consistent with the thickness of a single PtO6 octahedron. The platinum oxide nanosheets on silicon wafer were topotactically reduced to platinum nanosheets by mild thermal treatment in hydrogen. The thickness of the platinum nanosheet was ~0.5 nm, corresponding to a two atomic layer platinum nanosheet.Carbon supported platinum nanosheets were prepared by the reduction of platinum oxide nanosheets supported on carbon. The electrochemically active surface area (ECSA) of the carbon supported platinum nanosheets was 100 to 120 m2 (g-Pt)-1, which was considerably larger than that of 3 nm platinum nanoparticle (80 m2 (g-Pt)-1). In addition, the platinum nanosheet showed 1.7 times higher mass activity towards the oxygen reduction reaction compared to that of 3 nm platinum nanoparticles.Various methods for the topotactic reduction of platinum oxide nanosheets on carbon was studied. In addition to the mild thermal treatment in hydrogen gas, electrochemical reduction was also conducted. The ECSA of the platinum nanosheet prepared by electrochemical reduction at constant potential was 100 to 120 m2 (g-Pt)-1, which was almost same as the platinum nanosheet reduced by the mild thermal treatment in hydrogen. The specific activity was 1.2 to 1.3 times higher than that of the platinum nanosheet reduced by the mild thermal treatment in hydrogen. Therefore, the platinum nanosheet reduced by electrochemical reduction showed high mass activity for ORR.AcknowledgementThis work was supported as part of the “Polymer Electrolyte Fuel Cell Program” and the FC-Platform projects from the New Energy and Industrial Technology Development Organization (NEDO) of Japan (20001201-0, 22101136-0).

Liquid-Phase Partial Hydrogenation of Phenylacetylene at Ambient Conditions Catalyzed by Pd-Fe-O Nanoparticles Supported on Silica.

Catalysts with no hazardous or toxic components are required for the selective hydrogenation of acetylenic bonds in the synthesis of pharmaceuticals, vitamins, nutraceuticals, and fragrances. The present work demonstrates that a high selectivity to alkene can be reached over a Pd-Fe-O/SiO2 system prepared by the co-impregnation of a silica support with a solution of the metal precursors (NH4)3[Fe(C2O4)3] and [Pd(NH3)4]Cl2 followed by thermal treatment in hydrogen or in air at 400 °C. A DRIFT spectroscopic study of CO adsorption revealed large shifts in the position of the Pdn+-CO bands for this system, indicating the strong effect of Fen+ on the Pd electronic state, resulting in a decreased rate of double C=C bond hydrogenation and an increased selectivity of alkyne hydrogenation to alkene. The prepared catalysts consisted of mono- and bimetallic nanoparticles on an SiO2 carrier and exhibited a selectivity as high as that of the commonly used Lindlar catalyst (which contains such hazardous components as lead and barium), while the activity of the Fe-Pd-O/SiO2 catalyst was an order of magnitude higher. The hydrogenation of a triple bond over the proposed Pd-Fe catalyst opens the way to selective hydrogenation over nontoxic catalysts with a high yield and productivity. Taking into account a simple procedure of catalyst preparation, this direction provides a rationale for the large-scale implementation of these catalysts.

Influence of Gas for Thermal Treatment on Hydrogen Permeation in V-Ni Alloy Membranes.

Hydrogen separation is an important step for the utilization of hydrogen energy. Metallic alloys, such as vanadium-nickel, are potential hydrogen separation materials. Due to the strong propensity of vanadium to form oxides and hydrides, vanadium alloy has a lower hydrogen permeability, and it is difficult to maintain the permeability over time. Therefore, special preparation processes such as Pd coating have been suggested for hydrogen separation vanadium-based membranes. However, aside from the prohibitive price of palladium, the interdiffusion of palladium and vanadium makes the coated membrane inviable to be used at a high temperature. Thermal treatment with inert gas was investigated in this study to assess the applicability of the vanadium alloy without palladium coating for hydrogen separation and clarify the mechanism behind the thermal treatment. Argon is inert with vanadium and displayed permeability recovery after 43 h thermal treatment, but the permeability declined under certain conditions. In contrast, nitrogen is known to interact with vanadium and the hydrogen permeability was maintained at a level lower than the test with argon. Given that nitrogen can compete with hydrogen for the active sites on vanadium, nitrogen might hinder hydrogen adsorption and hydride formation, whereas argon reduced the partial pressure of hydrogen during the thermal treatment, enhancing the driving force of hydrogen desorption. In the X-ray diffraction spectrum, vanadium hydrides and oxides were confirmed after hydrogen permeation and thermal treatment. In the X-ray photoelectron spectroscopy data, oxygen was a dominant element due to vanadium oxides and adsorbed nitrogen was also observed. According to binding energy shifts of nitrogen, nitrogen used for thermal treatment might substitute or compete for active sites with adsorbed nitrogen and hydrogen, existing in vanadium lattice. Although thermal treatment can be used to recover hydrogen permeability, the alloy cannot be recovered as hydrogen-free. However, results demonstrate the potential of thermal treatment to complement an uncoated vanadium alloy for a hydrogen separation membrane.

Improvement of mechanical properties and microstructural refining of cast titanium alloys by coupling of electropulsing and temporary alloying element hydrogen

The electric pulse treatment and hydrogen as temporary alloying element have been widely used to improve the microstructure and mechanical properties of titanium alloys, respectively. In this study, the microstructure and mechanical properties of as-cast Ti–6Al–4V alloy are improved by electric pulse treatment combined with temporary alloying element hydrogen instead of traditional thermo-mechanical treatment and heat treatment. In comparison to the traditional thermo-mechanical treatment, the microstructure of the as-cast Ti–6Al–4V alloy after solution-aging treatment in pulsed thermal hydrogen treatment is homogeneous and finer, which is due to the lamellar β phase decomposition after thermal hydrogen treatment, accordingly, the ultimate tensile strength and total elongation of the alloy are effectively improved after pulsed thermal hydrogen treatment. It’s the acceleration of atomic diffusion and phase transformation in titanium alloys by hydrogen as temporary alloying element and electric pulse treatment that leads to the decomposition of the lamellar β phase, thereby refining the microstructure and enhancing mechanical properties. Finally, a novel method for improving the microstructure and mechanical properties of titanium alloys using hydrogen as temporary alloying element and electric pulse treatment is presented.

Effect of short-term heat treatment in the hydrogen on magnetic properties of ZnO:Mn nanocrystals

The magnetic properties of ZnO:Mn(2at%) nanocrystals synthesized by ultrasonic aerosol pyrolysis were studied. It has been established that short-term thermal treatment in hydrogen does not affect the magnetization of the synthesized sample, which had ferromagnetic and paramagnetic components. The sample, which underwent heat treatment in air at T = 850°C and acquired paramagnetic properties, after heat treatment in hydrogen again became ferromagnetic without a paramagnetic phase. It has been established by the EPR method that the structure of defects in the synthesized ZnO:Mn(2%) NCs is inhomogeneous. It changes after heat treatment in hydrogen. It is shown that the controlled thermal treatment of the samples, first in air and then in hydrogen, makes it possible to predictably change their magnetic properties. The results obtained are explained using the model of coupled magnetic polarons. During thermal treatment in hydrogen, the ratio of the number of oxygen vacancies Vo and interstitial Mn2+ ions changes in the samples.

Refining the microstructure to strengthen casting titanium alloy by electric pulse

Thermal-hydrogen treatment can effectively refine the microstructure and improve the thermoforming, machining performance and superplasticity of titanium alloy. In this study, pulsed electric current is used to replace the traditional heat treatment in the thermal-hydrogen treatment of cast titanium alloy, and the experimental results and strengthening effect of pulsed thermal hydrogen treatment and traditional thermal hydrogen treatment were compared. After pulsed thermal-hydrogen treatment, the lamellar β phase is broken into spherical shape and uniformly distributed in the matrix, and the cast titanium alloy was significantly strengthened. However, the microstructure refinement and strengthening effect of traditional thermal-hydrogen treatment is not as good as that of thermal-hydrogen treatment under electric pulse. The process of thermal-hydrogen treatment is accompanied by the formation of new phases, and the nucleation and growth of new phases are often controlled by atomic diffusion. In addition to the necessary thermal effects, the pulsed electric current also provides athermal effects, and thermodynamically lowering the energy barrier and promoting nucleation, while kinetically promoting the diffusion of atoms and accelerating the solid solution process. Therefore, based on the experimental results and analyses, thermal-hydrogen treatment under electric pulses provides a novel and effective method for refining the microstructure to strengthen cast titanium alloys.

Influence of Various Production and Processing Methods on the Structure and Properties of Porous Titanium Coatings

A comparison was made of the properties of porous coatings obtained by ion-plasma spraying methods, 3D-coating obtained by direct laser metal deposition (DLMD), as well as a GRIPTION® and POROCOAT® coating. The influence of various methods of obtaining a porous coating on the porosity and structure of the coating, as well as the effect of thermal hydrogen treatment (THT) on the adhesion strength of the titanium coating was determined.

Исследование стойкости пластин из сплава ВТ6 с линейно изменяющейся градиентной структурой к направленному высокоскоростному воздействию

The study results of the protective (barrier) properties of oxide and nitride coatings against the penetration of hydrogen during the thermal hydrogen treatment (THT) are summarized and the formation regularities of the linearly changing gradient structure of the VT6 titanium alloy are established. It has been found out that the finely dispersed (α + β) — structure on the surface formed as a result of THT provides increased strength properties, and the large-lamellar structure in the center provides high impact strength. It is shown that plates made of VT6 alloy of 12.5 mm thick with the linearly varying gradient structure demonstrate good dynamic resistance when fired with 5.45 mm and 7.62 mm jacketed bullets with a steel core.

Improvement of appearance probability of conductance quantization by hydrogen thermal treatment in Pt/NiO/Pt-resistive switching cells

Improvement of appearance probability of conductance quantization by hydrogen thermal treatment in Pt/NiO/Pt-resistive switching cells

V2O5 nanocrystals: Chemical solution synthesis, hydrogen thermal treatment and enhanced rate capability as cathode materials for lithium-ion batteries

Vanadium pentoxide (V2O5) is regarded as a promising cathode material for high-performance lithium-ion batteries (LIBs). In this study, V2O5 nanocrystals with an elongated plate-like morphology are prepared via a chemical solution approach that involves the hydrolyzation of vanadyl sulfate in alkaline solution. Oxygen vacancies are intentionally created by thermal treating the V2O5 samples under hydrogen-containing gases at different temperatures. Although the annealing process does not change the shape, morphology and crystalline structure of V2O5 nanocrystals, it does bring about a small amount of oxygen vacancies, as evidently from the results of XRD patterns and Raman spectra. The presence of oxygen vacancies has positive effects on the electrochemical properties. A higher initial discharge capacity, and excellent rate capability and cycling stability are observed on the oxygen vacancy-containing V2O5 samples. Especially, the sample annealed at 350 °C is found to have an initial capacity of 284 mAh g−1and the capacity still maintains at about 153 mAh g−1 even at 10 C. The combination of nanoscale dimension and oxygen vacancies in V2O5 nanocrystals presents a simple way to improve their rate capability and cycling stability for potential high-performance LIB applications.

Thermal Hydrogen Treatment of Electrodes for Performance and Stability Enhancement of Non-Aqueous Redox Flow Batteries

Vanadium acetylacetonate [(V(acac)3] is being used as model redox species for the study of non-aqueous redox flow battery (NAqRFB). The redox species present reversible redox reactions for both V+2/V+3 (i.e. the negolyte ca. -1.75 V vs Ag/Ag+) and V+3/V+4 (i.e. posolyte ca. 0.45 V vs Ag/Ag+). The same discharge state V+3 of this electrolyte can be used on both sides of the half cell. The latter and the fact it dissolves easily in an organic solvent, besides its commercial availability at a fair price makes it a promising candidate for future commercial versions of non-aqueous redox flow batteries.Nonetheless, merits are usually accompanied by some demerits. Vanadium has four valency states starting from V+2 to V+5; for the V-NAqRFB only three oxidations states are desirable V+2, V3+, and V4+ thus the formation of V5+ is unwanted. To avoid this oxidation state, typically the battery open circuit potential is kept below 2.27 V. Another downside of this electrolyte refers to its sensitivity towards a moisture/oxygen-enriched environment. The presence of moisture/oxygen in the environment triggers a non-reversible reaction which leads to the formation of VO(acac)2 at the positive electrode. VO(acac)2 irreversible formation causes rapid battery capacity loss due to its parasitic and increased concentration on the electrolyte. Therefore, the electrolyte must be kept in an inert atmosphere such as dry nitrogen. Nonetheless, it was observed that even by maintaining a strictly controlled saturation of the electrolyte with inert gas, the stability of the batteries was still rather negligible. Components such as the electrodes (carbon felts, CF) could also represent a major source for the oxygen-enriched surface. Many oxidation pre-treatments such as chemical exfoliation (H2SO4) and thermal oxidation under airflow at 450 °C are commonly performed on CFs to increase their wettability and performance in aqueous all vanadium redox flow cells. Nonetheless, these kind of pre-treatments might not be suitable for the system here in the study due to the beforehand mentioned reasons. The latter served as the main motivation for this study.Initially, cyclic voltammetry (CV) was performed using a three-electrode configuration cell and a glassy carbon as the working electrode. The addition of few DI water drop s (0.005% or 50 ppm) and the electrolyte saturation with O2 caused the immediate disappearance of redox species peaks (V2+/V3+ redox couple) and the appearance of additional peaks which indicated a strong influence for the reaction shift towards the formation of parasitic VO(acac)2. V+3/V+4 redox couple was also degraded significantly after 0.05% (500 ppm). Thus, keeping a dry and oxygen-free atmosphere is of utmost importance for maintaining a stable battery operation. Interestingly, it was found that the reversibility of species on top of the WE depends on the exposure time to oxygen. The effect is negligible up to 20 minutes of oxygen saturation but extremely critical over 4 hours as even upon saturating the electrolyte with an inert gas again, the adsorption of the active species was less effective and non-reversible (much lower anodic current peaks and much wider apart oxidation/reduction peaks).The carbon felt electrodes used for the aqueous vanadium redox flow battery, even with no treatment have already oxygen functional groups which serve as the reaction sites for the vanadium redox reaction in the aqueous electrolyte. Hydrogen is known as a powerful reducing agent and so might be employed to remove these oxygen functionalities. Therefore, the impact of different pre-treatments on the carbon felts morphology and performance for the V-NAqRFB was assessed. Mainly, the effect of solely adding a pre-oxygen heat treatment (referred to as PO) to a pristine carbon felt from SGL (4.6GFD), a hydrogen treatment (PH), and a combination of oxygen followed by a hydrogen treatment (POH) to completely remove all previously formed heteroatoms, were tested, each for 10 hours at 400 °C. For comparison purposes, a pristine electrode (P) was also used. Then upon, the electrochemical surface area of each CF was pre-screened by leading CV measurements and the hydrogen treatment followed by an oxygen heat treatment (POH) appeared to be the best solution to increase the number of active sites on the CF structure. Morphological characterization was performed on all electrodes using SEM and FTIR. Later, these CFs were used in NAqRFB-cell for battery cycling, impedance spectroscopy, and polarization measurements. The co-relation of the results highlighted that POH is performing better in the V(acac)3 based non-aqueous electrolyte. Besides, solely conducting a pre-oxygen heat treatment on the CFs condemns the performance of the battery, as expected. The results are shown in the attached figure. Figure 1

Self-decoration of Barium Titanate with Rhodium-NP via a facile co-precipitation route for NO sensing in hot gas environment

There is an urgent need to develop real-time gas sensors capable of detection under hot-gas (>400 °C) flow, for applications such as exhaust emission control. In this context, Rh-doped BaTiO3 has been prepared by a co-precipitation route and heat-treated at 900 °C under 2 % hydrogen to obtain in-situ Rh-nanoparticle decoration of submicron BaTiO3 particles. X-ray diffraction, Raman, and X-Ray photoelectron spectrometry analysis confirm the presence of Barium Titanate phases and the substitution of Ti4+ by Rh3+. According to the analytic evidence, thermal hydrogen treatment leads probably to Rhodium diffusion out of titanate lattice, yielding a self-decoration of the nano-sized Barium Titanate particles. Further NO-sensing tests revealed that the sensors produced by deposition of this in-situ Rh-loaded BaTiO3 on the interdigitated electrodes (IDE) yield a significant increase of selectivity and response (∼18 % for 200 ppm NO) towards NO, for the first time, under a hot-gas environment reaching up to 900 °C as synthetic humid air being the carrier gas. The calculated response and recovery times are reasonable, and observed reproducibility confirms suitability to practical applications. Relying on the carried investigations, this good sensing performance can be explained by the creation of excessive oxygen vacancies resulting from Rhodium's surface diffusion. Moreover, it is to claim that excellent catalytic activity of Rhodium plays a key role in enhancing NO-sensing performance.

Study of Hydrogen Thermal Treatment IrxTa1-XOy/Nano-TiO2 Catalyzing Ammonium

With the rapid development of the industrialization process in the world, wastewater's inorganic nitrogen concentration could not be ignored simply. Composite semiconductor materials have been used for many years in electrocatalysis, Titanium dioxide, a semiconductor, is an inactive oxygen evolution electrocatalyst because of its low conductivity and poor reactivity. This study prepared three-electrode configuration, which.represents double-layered nanoparticle titania electrocatalyst (Ti / IrxTa1-xOy / nano-TiO2; denoted as n-TEC) as anode and platinum foil as cathode. The main anodic reactions are the formation of chlorine and decomposition of Ammonia. Through EPMA, SEM, XRD, XPS, EPR, Raman etc., combine with electrochemical test on anode cell (mediate the decomposition of ammonia and electrocatalytic oxidations of chloride), respectively. Hence stability and durability of electrocatalyst materials are major challenges that need to be optimized, hundreds hours of catalytical experiment has been prepared, characterization of the electrodes was compared before and after experiment as well. On the basis of original electrode (raw n-TEC), we did hydrogen thermal treatment. The electrodes show great differences under different retreatment conditions, free chlorine’s faraday efficiency promoted by 6%, which leads to a discussion of the effect of oxygen vacancies on the material. Conductivity should be taken into consideration with electrochemical impedance spectroscopy (EIS) test, after hydrogen thermal treatment charge transfer resistance has been increased 46%. In view of the influence of different constituent materials on electrochemical or electrocatalytic properties, new sights for the engineering and other aspacts of electrochemical are provided.

Influence of concentration-time parameters on nitride coatings formation on VT6 titanium alloy and their stability during subsequent treatment

The possibility of using a titanium nitride coating as a «protective» layer against the penetration of hydrogen into VT6 titanium alloy semi-finished or finished products was shown in this article. It was found that the titanium nitride coating does not dissolve during high-temperature vacuum annealing and «isolates» sample sides from hydrogen penetration, which allows to form a linear gradient structure during subsequent thermal hydrogen treatment.

Oxide films resistance to hydrogen penetration in VT6 titanium alloy

The ability of hydrogen to penetrate through the oxide film formed during air-atmosphere annealing at elevated temperatures on VT6 titanium alloy samples was studied in this paper. It was investigated that oxide film prevents the penetration of up to 0.4 wt.% hydrogen. It was shown that it is possible to change the depth of hydrogen penetration and the surface layer structure by varying the amount of added hydrogen. It was determined that the formation of a finely dispersed surface structure after the thermal hydrogen treatment allows to increase the surface hardness by 8-10 HRC, compared to the center of material.

Au-Ir alloy nanofibers synthesized from Au-Ir/IrO2 composites via thermal hydrogen treatment: Application for glucose oxidation

This paper reports the facile formation of the alloy nanofibers of highly immiscible Au and Ir with diverse composition ratios (denoted as TH2_AuxIr1−x, x = 0.05, 0.10 or 0.33, relative molar content of Au precursor) and the application for direct glucose oxidation. First, the composite nanofibers consisting of Ir/IrO2 fibrous main frames decorated with Au nanoparticles (denoted as Pre_AuxIr1−xOy) were synthesized via electrospinning and calcination. Then, these composites were annealed under H2 gas flowing and successfully transformed to Au-Ir alloy nanofibers along with IrO2 reduction to Ir metal in the Ir/IrO2 fibrous frames. Thermal H2-treatments with varying temperatures and duration times confirmed that Au-Ir alloy production required an unusually low temperature ≥ 90 °C at which Au and Ir were completely alloyed within 1 min. This study suggests that the Au-Ir alloying and IrO2 reduction occur simultaneously and promote each other. TH2_Au0.33Ir0.67, with ∼50.4 % Au atomic %, was found to still have segregated Au phase, indicating the limited solubility (molar ratio of Au/Ir < 1). Alloyed TH2_Au0.10Ir0.90 exhibited high electroactivity for glucose oxidation: a surprisingly low onset potential (<< −0.4 V vs SCE) and greatly enhanced oxidation current levels compared with Pre_Au0.10Ir0.90Oy and pure Au nanoparticles. The high activity of TH2_Au0.10Ir0.90 was attributed to the higher surface area of Au and more favorable formation of catalytically active OHads in the Au-Ir alloy. Current study presents that Au-Ir alloys can be formed under moderate condition via thermal H2-treatment and possess a feasibility for nonenzymatic glucose oxidation.

Study on the active phase formation of Pd-Zn/Sibunit catalysts during the thermal treatment in hydrogen

In the present research, the process of the formation of the active components of Pd-Zn catalysts supported on carbonaceous material Sibunit prepared by the joint impregnation (Pd:Zn = 1) is studied. It was shown by means of TPR and EXAFS techniques that the interaction between palladium and zinc begins already at T > 200 °C. During the reduction in hydrogen at temperatures of 200–300 °C the surface of particles being formed is enriched with oxidized zinc. In the temperature range of 400–500 °C zinc is completely reduced, and the crystal lattice of a substitutional solid solution based on fcc lattice of palladium is restructured in tetragonal lattice of PdZn. However, an increase of the calcination temperature in H2 atmosphere (500 °C) significantly rises up the probability of partial destruction of bimetallic phase due to the partial migration of zinc atoms from the surface into the bulk of particles.

The effects of sodium content and hydrogenation of TiO2 nanotubes on photocatalytic activity

The effects of sodium content and hydrogenation of TiO2 nanotubes on their photocatalytic activity were investigated. TiO2 nanotubes with different contents of sodium were prepared by an alkaline reflux method, followed by washing with different concentrations of acid. When a hydrogen thermal treatment was applied to the nanotubes, the white nanotubes with and without sodium would transform into blue polyhedral and light yellow chain-like structures, respectively. UV–vis absorption spectra indicated that a higher absorption in the visible light range was obtained for the blue polyhedral structure. Interestingly, an amorphous surface layer and Ti3+ species appeared and became more pronounced when the sodium was removed completely. This led to the formation of a defect energy band belt, which not only narrowed the band gap but lowered the rate of recombination of photo electrons and holes. As a consequence, a higher rate of photocatalytic decomposition of methanol for hydrogen evolution under visible light illumination were obtained.