Heat Treatment In H2 Research Articles

Hydrogenation of Acetylene over Pd–Ag/Sibunit Catalysts: Effect of the Deposition Sequence of Active Component Precursors

The study investigates interactions between palladium and silver in Pd–Ag bimetallic catalysts supported on a mesoporous carbon material Sibunit and, in particular, the dependence of these interactions on the deposition sequence of the metal precursors. Using XRD and TEM results, it was shown that impregnating the support with an aqueous solution that contained nitrate salts of both metals, followed by hydrogen treatment at 500°C, generates uniformly sized Pd0.6Ag0.4 particles (dav = 5.6 nm). These particles exhibit high selectivity (79%) in the reaction of acetylene hydrogenation to ethylene. The catalysts synthesized by sequential impregnation of the support with solutions of Pd and Ag nitrates interleaved with heat treatment in H2 exhibited a lower selectivity (68–73%) due to the formation of particles non-uniform both in composition and size (about 4 to 60 nm). The IR spectroscopy data suggest this effect is presumably associated with the removal of O-containing functional groups from the carbon surface during the reduction of the supported precursor. Given that O-groups act as anchoring sites for the precursors of active components and suppress the ability of Sibunit to reduce metals from their salt solutions, the subsequent deposition of the second metal salt causes a non-uniform distribution of this metal on the surface and the generation of larger particles.

Fabrication of Large-Sized Invar Alloy Film with Low Thermal Expansion by Pulse Reverse Electrodeposition

Invar alloy film with low thermal expansion is a key substrate for high-resolution organic light-emitting diodes (OLEDs). The preparation of Invar alloy film by electrodeposition has attracted increasing attention due to its low cost and simple process. In this work, a large-sized (8 × 10 cm) uniform Fe-Ni alloy film was fabricated by pulse reverse electrodeposition. The effects of the electrodeposition parameters on the chemical composition and microstructure of Fe-Ni alloy films were investigated. Results showed that greater Ni2+/Fe2+ in the electrolyte, lower pulse frequency (f), smaller reverse pulse coefficient (x), and lower electrodeposition temperature (T) favored the iron content. The Invar alloy film (64 wt% Fe) was electrodeposited at T = 50 °C, x = 0.2, f = 10 Hz, and Ni2+/Fe2+ = 1.9 when the average pulse current density was 30 mA cm−2. The structure of the film was composed of a mixture of fcc and bcc phases, where (110) and (111) preferential orientations were predominant. After heat treatment in H2 at 800 °C for 120 min, the bcc phase transformed into the fcc phase, and the grain size increased (>2 μm). As a result, the coefficient of thermal expansion of the film decreased from 11 × 10−6 to 1.5 × 10−6/°C, which is close to the standard for commercial application.

Hydrogenation of Acetylene over Pd–Ag/Sibunit Catalysts: Effect of the Deposition Sequence of Active Component Precursors

The study investigates interactions between palladium and silver in Pd–Ag bimetallic catalysts supported on a mesoporous carbon material Sibunit and, in particular, the dependence of these interactions on the deposition sequence of the metal precursors. Using XRD and TEM results, it was shown that impregnating the support with an aqueous solution that contained nitrate salts of both metals, followed by hydrogen treatment at 500°C, generates uniformly sized Pd0.6Ag0.4 particles (dav = 5.6 nm). These particles exhibit high selectivity (79%) in the reaction of acetylene hydrogenation to ethylene. The catalysts synthesized by sequential impregnation of the support with solutions of Pd and Ag nitrates interleaved with heat treatment in H2 exhibited a lower selectivity (68–73%) due to the formation of particles non-uniform both in composition and size (about 4 to 60 nm). The IR spectroscopy data suggest this effect is presumably associated with the removal of O-containing functional groups from the carbon surface during the reduction of the supported precursor. Given that O-groups act as anchoring sites for the precursors of active components and suppress the ability of Sibunit to reduce metals from their salt solutions, the subsequent deposition of the second metal salt causes a non-uniform distribution of this metal on the surface and the generation of larger particles.

Effect of Heat Treatment Schedules on Creep Performance of Ni-Based Superalloy Mar-M247 at 871 °C and 250 Mpa

The effects of heat treatment (H1 and H2) on the creep behavior and microstructures of Mar-M247 at 871 °C/250 MPa are studied. The results show that the as-cast microstructure is composed of eutectics, γ phase, γ’ phase, MC and M23C6 carbides, while new M6C appears in heat-treated microstructures, indicating the transformation of carbides after heat treatments. The Mar-M247 is excellent, with over 1500 h of creep life, and H1 is 48% higher than H2. The addition of post-brazing and diffusion heat treatment in H2 is detrimental to creep resistance; the two steps promoted the transformation of MC into M23C6 in advance. The increase and coarsening of M23C6 would consume more γ-phase-forming elements, weakening the solution strengthening at grain boundaries. As a result, the resistance of the grain boundary and γ/γ’ interface to dislocation motion is significantly reduced, leading to the cracks’ initiation and propagation along the grain boundaries.

Study on the effect of high temperature heat treatment of H2 on the pore structure of activated carbon

As a high-quality adsorbent, activated carbon is widely used in air purification, natural gas storage, sewage treatment, gas enrichment, and separation, etc. The pore microstructure of activated carbon directly affects the adsorption capacity. In this paper, the altered in the microstructure of activated charcoal before and after high-temperature treatment were investigated by high-temperature thermal treatment of activated charcoal at 600°C and 700°C under an H2 atmosphere. The results of low-temperature (77 K) nitrogen adsorption showed that after high-temperature H2 heat treatment, the pores of activated carbon would be ablated and the pore structure would be significantly changed. The specific surface area, micropore specific surface area, total pore volume, and micropore pore volume all increased, and the degree of enhancement was proportional to the temperature of the heat treatment. The pore size distribution of activated charcoal before and after heat treatment was analyzed by density functional theory, and it was concluded that the pore volume of activated carbon mesopores (2-4 nm) increased significantly after high-temperature heat treatment, which could effectively improve the adsorption and separation capacity of activated carbon in larger molecular systems.

Efficient photocatalytic reduction of CO2 by improving adsorption activation and carrier utilization rate through N-vacancy g-C3N4 hollow microtubule

The g-C3N4 is considered to be a promising non-metallic semiconductor photocatalyst for converting CO2 into value-added products. However, g-C3N4 undergoes recombination of photogenerated electrons and holes and its low CO2 adsorption capacity. Here, g-C3N4 hollow microtube (TCN) structure with tunable N-vacancy concentrations (TCN-1) was controllably fabricated by hydrothermal self-assembly followed by H2 heat treatment. The resultant N-vacancy with one-dimensional structure g-C3N4 exhibits excellent activity for photocatalytic CO2 reduction, giving the CO generation rate of 7.06 μmol/g/h (TCN-1) under visible-light illumination without any co-catalyst or a sacrificial agent, which is 2.2- and 8.8- times that of TCN (3.12 μmol/g/h) and pristine g-C3N4 (0.75 μmol/g/h). It is well evidenced with experiments and DFT calculations that N-vacancy mainly originates from the selective cleavage of C=N–C sites on the surface of g-C3N4. The N-vacancy can act as electron trap, extending the lifetime of charge carriers. Moreover, the changes in the electron distribution around the vacancies thereby provide the driving force for the dissociation of excitons, which in turn promotes the activation of CO2 adsorption. The bifunctional of g-C3N4 with structural optimization and defect design is a very promising candidate for enhancing the adsorption-activation of reactants and the carrier utilization of photocatalysts in the photocatalytic process.

Effect of Hydrogen Treatment on Photoluminescence and Morphology of InGaN Multiple Quantum Wells.

In this paper, the photoluminescence (PL) properties and surface morphology of InGaN/GaN multiple quantum well (MQW) structures with the hydrogen (H2) heat treatment of InGaN are investigated to elucidate the effect of hydrogen on the structure and surface of the MQWs. The experimental results show that the H2 heat treatment on the as-grown MQWs may lead to the decomposition of InGaN and the formation of inhomogeneous In clusters. The atomic force microscope (AFM) study indicates that although the surface roughness of the uncapped samples increases after H2 treatment, the V-defects are suppressed. Moreover, the luminescence efficiency of the MQWs can be effectively improved by growing a GaN cap layer with an appropriate thickness on the top of the MQWs, which can reduce the effects of the H2 atmosphere and high temperature on the MQWs. In addition, a morphologic transformation from step bunching to shallow steps occurs and a much smoother surface can be obtained when a thicker cap layer is adopted.

Insights into the heat contributions and mechanism of CO2 adsorption on metal–organic framework MIL-100 (Cr, Fe): Experiments and molecular simulations

Metal–organic frameworks (MOFs) MIL-100 (Cr, Fe) synthesized by the hydrothermal method were subjected to heat treatment under an H2 flow. The MIL-100 (Cr) samples had specific surface areas and pore volumes approximately-two times higher than those of the MIL-100 (Fe) samples. The H2 heat treatment enhanced the crystallinity, especially for MIL-100 (Fe). The resulting adsorbents exhibited a superior CO2 adsorption capacity. Furthermore, the grand canonical Monte Carlo method was used to examine the adsorption mechanism at a molecular level. The heat contribution of each atom type of MOFs was demonstrated. The highest heat was found at low loadings (Henry’s law region) among other regions owing to CO2 adsorption inside the supertetrahedron. The most active atoms were C atoms (CO > CC > CH), followed by the O atom (COunsaturated metal), the unsaturated metal site, the other O atom (COsaturated metal), the saturated metal site, the H atom of the ligands, and the O atom of the metal cluster, respectively. This study can provide insights into the determination of the atomic heat contributions of other adsorbents for a better understanding of material design and the mechanism of adsorption.

Deactivation and Regeneration Method for Ni Catalysts by H2S Poisoning in CO2 Methanation Reaction

The carbon dioxide (CO2) methanation reaction is a process that produces methane (CH4) by reacting CO2 and H2. Many studies have been conducted on this process because it enables a reduction of greenhouse gases and the production of energy with carbon neutrality. Moreover, it also exhibits a higher efficiency at low temperatures due to its thermodynamic characteristics; thus, there have been many studies, particularly on the catalysts that are driven at low temperatures and have high durability. However, with regards to employing this process in actual industrial processes, studies on both toxic substances that can influence catalyst performance and regeneration are still insufficient. Therefore, in this paper, the activity of a Ni catalyst before and after hydrogen sulfide (H2S) exposure was compared and an in-depth analysis was conducted to reveal the activity performance through the regeneration treatment of the poisoned catalyst. This study observed the reaction activity changes when injecting H2S during the CO2 + H2 reaction to evaluate the toxic effect of H2S on the Ni-Ce-Zr catalyst, in which the results indicate that the reaction activity decreases rapidly at 220 °C. Next, this study also successfully conducted a regeneration of the Ni-Ce-Zr catalyst that was poisoned with H2S by applying H2 heat treatment. It is expected that the results of this study can be used as fundamental data in an alternative approach to performance recovery when a small amount of H2S is included in the reaction gas of industrial processes (landfill gas, fire extinguishing tank gas, etc.) that can be linked to CO2 methanation.

Interfacial heterogeneous precipitation of Ag nanoparticles in soda-lime silicate glass for improved toughness and conductivity

The fracture toughness and thermal conductivity of soda-lime glass were enhanced by an interfacial precipitation of Ag. Large quantities of silver nanoparticles (AgNPs) are formed on the surface and subsurface layers of the Ag–Na ion exchanged glass powders during the heat-treatment in H2 for various times, and are fully densified by subsequent spark plasma sintering (SPS). The AgNPs with particle sizes above 50 nm are mainly located near the interfaces with the original glass particles, whereas smaller AgNPs are observed inside the glass particles. Moreover, the thickness of the precipitated Ag layer is seen to increase with increasing heat-treatment time. The incorporation of AgNPs is shown to enhance the fracture toughness of the soda-lime glass due to ductile deformation, crack deflection, and crack bridging. Finally, a maximum fracture toughness of 1.14 MPa m1/2, and a maximum thermal conductivity of 1.20 W m−1K−1, are obtained for the glass powders that were subjected to the entire process of ion-exchange, heat-treatment, and SPS densification.

Depleted Fullerene Soot As Support Materials of Pt-Base Catalysts for Oxygen Reduction Reaction

The carbon materials containing metal nanoparticles were filtrated from two kinds of depleted fullerene soot including C60 (denoted as DFS) and GdC82(GDFS), respectively. The structure of depleted carbon materials was investigated by XRD, Raman, SEM and TEM. The DFS and GDFS show onion like morphology with Fe and Fe, Gd nanoparticles, respectively. The obtained carbon materials were used as support materials of Pt-based alloy catalysts (Pt-DFS and Pt-GDFS) synthesized from H2 heat treatment for oxygen reduction reaction. The half-wave and onset potentials of Pt-DFS and Pt-GDFS were 1.1, 0.89 V and 1.1 V, 0.93 V (vs. RHE), respectively, in 0.5 mol L-1 H2SO4solutions. The ECSA of Pt-GDFS has no obvious decrease during 8000 CV cycles in acid solutions indicating good stability on oxygen reduction reaction.

Simple one-step ion exchange enhanced Faraday rotation in heavy metal oxide diamagnetic glasses

Ion exchanges (IE) on silicate, tellurite, borate and phosphate glass have been extensively studied for different objectives such as changing glass refractive index, strengthening glass structure or realizing nanometal-glass systems, however, ion exchange on lead-bismuth-borate diamagnetic glass for Faraday rotation improvement is interesting and attractive for magneto optical glass and magneto optical waveguide devices. In this study, for the first time, we studied the one-step Ag+-Na+ ion exchange on diamagnetic Bi2O3-PbO-B2O3-Na2O (PBBN) glass for the aim of improving diamagnetic properties and providing an efficient route for magneto-optical waveguide. The Ag+-Na+ ions has been sucessfully exchanged at 270 °C for 20 min condition. And without any further heat or H2 treatment after IE, the Ag+ ions and Ag0 nanoparticles co-existed in glass. Heat treatment in H2 after IE not only greatly increased the Ag0 NPs size, but also produced the Bi0 crystals which were not helpful for glass properties. Ag nanoparticles showed characteristic surface plasmon resonance peak at 500–550 nm range. Raman spectra displayed the evolutions of Ag+ and Ag0 in functions of different ion exchange conditions. The UV–Visible and Faraday rotation measurements suggested that high polarizability and diamagnetic susceptibility properties of diamagnetic Ag+ ions and Ag0 nanoparticle induced surface plasmonic effects improved the optical refractive index and magneto optical Verdet constant. A simple linear optical waveguide also were obtained on PBBN glass surface using the optimized IE parameters. The proposed one-step ion exchange technique on diamagnetic glass will be an efficient method for glass properties enhancement and magneto optical waveguide fabrication.

Potentiometric CO sensors using anion-conducting polymer electrolyte: Effects of the kinds of noble metal-loaded metal oxides as sensing-electrode materials on CO-sensing properties

Potentiometric CO-sensing properties of electrochemical gas sensors using an anion-conducting polymer as an electrolyte and a metal oxide (MO; Bi2O3, CeO2, In2O3, SnO2, or V2O5) loaded with or without 2.0 wt% noble metal (N; Ag, Au, Ir, Ru, Rh, Pd, or Pt) as an electrode material (EC(N/MO) or (EC(MO) sensor; N/MO: N-loaded MO) were investigated in wet synthetic air (57%RH) at 30 °C. Among all the EC(MO) sensors, the EC(CeO2) sensor showed the largest CO response and excellent CO selectivity against H2 and the EC(Bi2O3) sensor showed relatively large CO and H2 responses (no CO selectivity against H2). Other EC(MO) sensors hardly showed both CO and H2 responses. However, the Au loading just onto In2O3 and SnO2 was effective in improving the magnitude of CO and H2 responses of the EC(In2O3) and EC(SnO2) sensors, respectively, which resulted in relatively poor CO selectivity against H2. On the other hand, the Pt loading only onto SnO2 extremely enhanced only the magnitude of CO response of the EC(SnO2) sensor, and thus the EC(Pt/SnO2) sensor showed the most excellent CO selectivity against H2, among all the sensors in this study. The heat treatment of N/MO powders in H2 at 250 °C reduced only the H2 response of the EC(Au/SnO2) sensor, leading to an improvement of the CO selectivity of only the EC(Au/SnO2) sensor against H2. On the other hand, the heat treatment drastically enhanced both CO and H2 responses of the EC(Pt/SnO2) sensor, resulting in a decrease in its CO selectivity against H2. The CO and H2 responses of other EC(N/SnO2) sensors before and after the heat treatment in H2 at 250 °C were also examined, and the effectiveness of the noble metal loading and the heat treatment on the CO-sensing properties was discussed in this study. In addition, gas-sensing mechanism was also proposed on the basis of chemical surface states of representative N/MO.

Facile synthesis of urchin-like Cs x WO3 particles with improved transparent thermal insulation using bacterial cellulose as a template.

Urchin-like CsxWO3 particles were synthesized using bacterial cellulose (BC) as a template by the hydrothermal method. The effects of the BC addition amount on the morphology, W5+ content and transparent thermal insulation of CsxWO3 were studied. It has been confirmed that abnormal growth of CsxWO3 rods was greatly reduced after introduction of BC into the precursor solution. Moreover, introduction of BC into the precursor solution could significantly improve the transparent thermal insulation properties of the CsxWO3 film. In particular, when the BC amount was appropriate, the prepared CsxWO3 film exhibited better visible transparency, with the visible light transmittance (TVis) more than 60%. In addition, the urchin-like particles could be transformed into small size nanorods after H2 heat-treatment, exhibiting excellent visible light transparency and thermal insulation performance. In particular, it has been proved that the 20BC-HT-CsxWO3 film exhibits excellent thermal insulation performance, and shows broad application prospects in the field of solar heat filters and energy-saving window glass.

Carbon Fiber Supported Pt-Co Electrocatalyst for Coal Electrolysis for Hydrogen Production

Carbon fibers (CFs) supported platinum-cobalt (Pt-Co) electrocatalysts are prepared with H2 heat-treatment and used for hydrogen production by coal electrooxidation. Pt-Co alloy was formed and characterized by X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results show that the electrocatalystic activity and long-time stability of Pt-Co/CFs for coal electrolysis are enhanced with the introduction of cobalt. The PtCo/CFs (1:1) catalyst exhibits better catalytic activity than PtCo/CFs (7:3) and PtCo/CFs (3:7). The strong catalytic activities of the catalysts are attributed to synergistic effect between metallic alloying and modification of surface electrons of the bimetallic Pt-Co electrocatalysts.

Electrochemical characterization of Raney nickel electrodes prepared by atmospheric plasma spraying for alkaline water electrolysis

A Raney Ni electrode was prepared by the simple and economical atmospheric plasma spraying method. It showed excellent performance for hydrogen evolution reaction (HER), as indicated by a Tafel slope of 54mV/dec and overvoltage of 108mV at 300mA/cm2. The Ni–Al alloy coating contained a NiAl phase, which has a very slow Al leaching rate in alkaline solution. H2 heat treatment of the electrode enhanced the uniformity of Al distribution in the coating and adhesion of the coating to the substrate. However, the HER performance did not improve and the electrode was rendered more structurally vulnerable to deactivation.

Experimental cation redistribution in the tourmaline lucchesiite, CaFe2 + 3Al6(Si6O18)(BO3)3(OH)3O

Natural Mg-rich lucchesiite was thermally treated in air and hydrogen atmosphere up to 800 °C to study potential changes in Fe-, Mg- and Al ordering over the octahedrally coordinated Y- and Z-sites, and to explore possible applications to intracrystalline geothermometry based on tourmaline. Overall, the experimental data (structural refinement, Mossbauer, infrared and optical absorption spectroscopy) show that thermal treatment of lucchesiite results in an increase of Fetot contents at Z balanced by an increase of Mg and Al at Y. This process is accompanied by a significant deprotonation of the O3 anion site. The Fe order–disorder reaction depends more on temperature, than on redox conditions. During heat treatment in H2, reduction of Fe3+ to Fe2+ was not observed despite strongly reducing conditions, indicating that the fO2 conditions do not exclusively control the Fe oxidation state at the present experimental conditions. On the basis of this and previous studies, the intersite order–disorder process induced by thermal treatment indicates that Fe redistribution is an important factor for Fe–Mg–Al-exchange and is significant at temperatures around 800 °C. As a result, Fe–Mg–Al intersite order–disorder is sensitive to temperature variations, whereas geothermometers based solely on Mg–Al order–disorder appear insensitive and involve large uncertainties. The presented findings are important for interpretation of the post-crystallization history of both tourmaline and tourmaline host rocks, and indicate that successful tourmaline geothermometers may be developed by thermal calibration of the Fe–Mg–Al order–disorder reaction.

Activity and Stability of Carbon Supported PtxY Alloys for the ORR Determined by RDE and Single-Cell PEMFC Measurements

Bimetallic alloys based on Pt and Y are potential cathode catalysts for proton exchange membrane fuel cells (PEMFCs) due to their high oxygen reduction reaction (ORR) activity. Nevertheless, the synthesis of carbon supported PtxY catalysts is challenging due to the low standard reduction potential of yttrium compared to platinum. Hence, extended electrochemical testing in actual PEMFCs remains elusive, especially with respect to catalyst degradation upon voltage-cycling. In this publication, we present the synthesis of a bimetallic PtxY/C catalyst via impregnation of commercial Pt/C with an yttrium halide precursor and subsequent heat-treatment in H2 at 1200°C. This catalyst showed a high specific ORR activity, at a mass activity similar to Pt/C due to its comparably low electrochemical surface area (ECSA). On the other hand, the large particle size of the here synthesized PtxY/C catalyst (≈10 nm) resulted in a significantly enhanced stability versus degradation in an accelerated stress test (AST) based on voltage-cycling between 0.6 and 1.0 VRHE at 50 mV s−1, showing a superior ECSA, ORR activity and H2/air performance after 30000 cycles compared to a standard Pt/C catalyst.

Synthesis of spherical nanocrystalline titanium hydride powder via calciothermic low temperature reduction

Spherical nanocrystalline TiH2 powder was synthesized by calciothermic reduction of TiO2 with CaH2 at low temperature. Reduction was performed in solid state either by reactive milling in H2 or via pre-milling in Ar with subsequent heat treatment in H2. Reactively milled powders are pyrophoric on exposure to air. Leaching of the side product CaO was only successful from the pre-milled and heat treated powders. As synthesized TiH2 is stable in air and desorbs H2 below 600°C forming nanocrystalline Ti. Therefore it is suitable to prepare ultra finegrained cp-Ti.

Potentiometric Carbon Monoxide Sensors Using an Anion-Conducting Polymer Electrolyte and Au-Loaded SnO2 Electrodes

Potentiometric gas sensors using an anion-conducting polymer as an electrolyte and SnO2 loaded with or without 2.0 wt% Au as an electrode material were fabricated and the CO-sensing properties were investigated mainly in wet synthetic air (57%RH) at 30°C. Loading of Au onto SnO2 powders by precipitation-deposition technique was quite effective in improving the sensing properties to CO and H2, and the magnitude of CO response was larger than that of H2 response. In addition, the CO response was largely dependent on concentration of O2 in the gaseous atmosphere. These results indicate that electromotive force of the sensor is probably determined by mixed potential resulting from CO oxidation and O2 reduction. Heat treatment of the Au-loaded SnO2 powder under reducing atmosphere decreased the H2-sensing properties, and thus largely enhanced the CO selectivity against H2. Especially, the sensor using Au-loaded SnO2 which was heat-treated in H2 at 250°C showed large CO response, the largest CO selectivity against H2, and the fastest response and recovery speeds among all the sensors tested, while storage of the sensor under normal atmosphere weakened the effect of the heat-treatment in H2 at 250°C on the CO-sensing properties.