Thermal Activation Conditions Research Articles

Transformation of a Pt–CeO2 Mechanical Mixture of Pulsed‐Laser‐Ablated Nanoparticles to a Highly Active Catalyst for Carbon Monoxide Oxidation

AbstractThe pulsed laser ablation (PLA) in alcohol and water media was employed to prepare Pt and CeO2 PLA‐nanoparticles of different sizes and degrees of defectiveness. Interactions of metallic platinum and ceria particles were studied using the thermal activation of Pt–CeO2 mechanical mixtures in the CO+O2 reaction medium or O2 atmosphere. The thermal activation resulted in oxidized Pt2+/Pt4+ states of platinum in the surface solid solutions PtCeOx and/or PtOx clusters. Catalysts formed after calcination of the PLA‐ablated Pt–CeO2 mixtures in oxygen at 450–600 °C revealed CO conversion at very low temperatures up to 70 % depending on the conditions of PLA particles preparation and thermal activation of Pt–CeO2 mechanical mixture.

Reagent precipitation of copper ions from wastewater of machine-building factories

The article presents the results of reagent removal of copper ions from wastewater of machine-building factories. The urgency of the study is conditioned by the widening of the range of effective reagents through the implementation of industrial waste. The investigation covers mineralogical and fractional composition of chalk enrichment waste. In the work, the conditions of thermal activation of chalk enrichment waste used for reagent removal of copper ions from wastewater were elaborated. It was shown that the thermal activation of waste facilitates the increased treatment efficacy up to the set sanitation, hygiene and technological standards.

The impact of thermal activation conditions on physicochemical properties of nanosheet-derived Mg-Al mixed oxides

Mg-Al mixed oxides with highly accessible basic sites were synthesized from Mg-Al layered double hydroxides bearing interlayer isethionates (Ise). Anion-exchange of interlayer carbonates in synthetic hydrotalcites with Ise induces stacking disorders in layered structure, and subsequent delamination in water followed by drying causes further disordering as characterized by X-ray diffraction technique. However, thermal activation of these materials in air formed Mg-Al mixed oxides with low surface area and low CO2 adsorption capacity. In contrast, thermal activation in N2 or N2 followed by air formed materials exhibiting marked increases in CO2 adsorption capacity up to ∼800% relative to those obtained by thermal activation in air. Thermogravimetric and elemental analyses and IR spectroscopy characterization indicate that thermal activation in N2 enables removal of sulfur species formed from Ise at ∼400 °C, and limits the formation of sulfate species that bridge nanosheets and cause irreversible stacking of them. The proper thermal activation procedure in addition to disordered structure of aggregates of Mg-Al double hydroxide nanosheets enabled the formation of Mg-Al mixed oxides with higher surface area and larger micropore volume than those obtained from the initial hydrotalcites. These results highlight the critical importance of thermal activation steps for such materials, and demonstrate a prospective route to synthesize new porous materials based on Mg-Al mixed oxides.

Surface passivation investigation on ultra-thin atomic layer deposited aluminum oxide layers for their potential application to form tunnel layer passivated contacts

The surface passivation performance of atomic layer deposited ultra-thin aluminium oxide layers with different thickness in the tunnel layer regime, i.e., ranging from one atomic cycle (∼0.13 nm) to 11 atomic cycles (∼1.5 nm) on n-type silicon wafers is studied. The effect of thickness and thermal activation on passivation performance is investigated with corona-voltage metrology to measure the interface defect density Dit(E) and the total interface charge Qtot. Furthermore, the bonding configuration variation of the AlOx films under various post-deposition thermal activation conditions is analyzed by Fourier transform infrared spectroscopy. Additionally, poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) is used as capping layer on ultra-thin AlOx tunneling layers to further reduce the surface recombination current density to values as low as 42 fA/cm2. This work is a useful reference for using ultra-thin ALD AlOx layers as tunnel layers in order to form hole selective passivated contacts for silicon solar cells.

Formation of p-type ZnO thin film through co-implantation

We present a study on the formation of p-type ZnO thin film through ion implantation. Group V dopants (N, P) with different ionic radii are implanted into chemical vapor deposition grown ZnO thin film on GaN/sapphire substrates prior to thermal activation. It is found that mono-doped ZnO by N+ implantation results in n-type conductivity under thermal activation. Dual-doped ZnO film with a N:P ion implantation dose ratio of 4:1 is found to be p-type under certain thermal activation conditions. Higher p-type activation levels (1019 cm−3) under a wider thermal activation range are found for the N/P dual-doped ZnO film co-implanted by additional oxygen ions. From high resolution x-ray diffraction and x-ray photoelectron spectroscopy it is concluded that the observed p-type conductivities are a result of the promoted formation of PZn–4NO complex defects via the concurrent substitution of nitrogen at oxygen sites and phosphorus at zinc sites. The enhanced solubility and stability of acceptor defects in oxygen co-implanted dual-doped ZnO film are related to the reduction of oxygen vacancy defects at the surface. Our study demonstrates the prospect of the formation of stable p-type ZnO film through co-implantation.

Research of acceptor impurity thermal activation in GaN: Mg epitaxial layers

3rd group element nitride based semiconductor compounds are widely used in various optical and electronic devices. One problem in the fabrication of GaN based device heterostructures is the synthesis of p conductivity epitaxial layers. Magnesium is a typical doping impurity for GaN. The choice of optimum doping and thermal activation conditions is of utmost importance for the synthesis of low-Ohmic p-GaN epitaxial layers.The effect of thermal annealing of GaN:Mg layers on acceptor impurity activation has been investigated. Hole concentration increased and mobility decreased with an increase in thermal annealing temperature. The sample annealed at 1000°C demonstrated the lowest value of resistivity. Rapid thermal annealing (annealing with high heating speed) considerably improved the efficiency of Mg activation in the GaN layers. The optimum time of annealing at 1000°C has been determined. The hole concentration increased by up to 4 times compared to specimens after conventional annealing.

The Influence of Manganese Amount in Oxyhydroxide of Aluminium – Precursor of MnO<sub>x</sub>-Al<sub>2</sub>O<sub>3</sub> Catalysts on Catalytic Activity in Reaction of Oxidation of C<sub>1</sub>-C<sub>3</sub> of Hydrocarbons

The authors have synthesized nanofibrous aluminum oxyhydroxide (AlOOH), modified with different amounts of manganese ions (II), which is the precursor for methane deep oxidation catalysts. It was shown that the catalytic activity of the manganese-based system obtained depends on manganese amount and thermal activation conditions. It is approved that as the catalyst for deep oxidation of hydrocarbons the system with manganese content of 10.5 wt. % is the most perspective despite the fact that the oxidation rate of methane is lower in it than in the catalyst with Mn content of 5.7 wt. %. As opposed to the catalyst with Mn content of 5.7 wt. %., where the aluminium oxide is in metastable form (s-Al2O3), the catalyst with manganese content of 10.5 wt. % contains in its structure a thermodynamically and thermally stable α-Al2O3 phase.

Molecular dynamics study of structural transformations of cylindrical nanopores in gold under thermal activation conditions and under the action of acoustic and shock waves

Structural deformations of cylindrical nanopores in gold under thermal activation conditions and under the action of acoustic and shock waves have been investigated using the molecular dynamics method. It has been shown that, at a temperature above 600 K, dislocation loops arise on the inner surface of a pore and finally form stacking fault tetrahedra. The initial temperature of nanopore collapse decreases under the action of acoustic waves. Under the action of shock waves in the direction perpendicular to the axis of the cylindrical nanopore, it can be separated into two single pores.

Thermosensitive Structural Changes and Adsorption Properties of Zeolitic Imidazolate Framework-8 (ZIF-8)

We compared four types of ZIF-8 with varying sizes and shapes to determine their thermal-structural stability and derive appropriate thermal activation conditions and correlation between structural characteristics and adsorption properties. Under air, the ZIF-8 phase for all the samples was converted completely into the zinc oxide phase above ∼300 °C, though thermalgravimetric analysis (TGA) indicated that the original structure was stable to ∼300–350 °C. Longer exposures (∼30 d) suggested that thermal activation at ∼200 °C was appropriate for the removal of guest and/or solvent molecules under air without structural damage. Despite no noticeable change in X-ray diffraction (XRD) patterns after activation at 250 °C under air, the resulting BET surface areas and CO2 adsorption amounts (at 1 bar and 30 °C) of ZIF-8s were reduced to ∼44–54 and ∼72–87%, respectively, as compared to those of appropriately activated ZIF-8s. It appears that after the activation at 250 °C under air, some Zn and N atoms were dissociated and converted to ZnOH and NOH, respectively, causing the partial structural damage of ZIF-8s.

Characterizations and performances of Ni/diatomite catalysts for dry reforming of methane

Monometallic 5wt% Ni containing catalysts were prepared by a two-solvent (cyclohexane/water) deposition method using cheap and widely available natural diatomites (Ni/AW2 and Ni/MN3) as supports. The fresh samples were characterized by SEM, EDX microanalysis, N2 adsorption–desorption isotherms, XRD and tested after reduction (in hydrogen) in dry reforming of methane. Spent catalysts were further characterized by TPH coupled with mass spectrometry. Although slightly less active than a reference Ni/Aerosil (Ni/SiO2) catalyst prepared in similar conditions, the Ni/diatomites catalysts showed good activity with 90% methane conversion reached on Ni/MN3 at 800°C and a high selectivity towards dry reforming reaction (H2:CO molar ratio around unity over the entire temperature range). The catalysts were also relatively stable during catalytic measurements conducted at 650°C for 12h. In addition, depending on the nature of the diatomite and on the conditions of thermal activation, carbon deposits with lower toxicity (easier to remove by reactivation) than those formed on the Ni/Aerosil were obtained.

Study of Three-Component Reactions Between 5-Amino-3-Methylisoxazole, N-Arylamides of Acetoacetic Acid, and Aromatic Aldehydes

A three-component cyclocondensation between 5-amino-3-methylisoxazole, N-arylamides of aceto-acetic acid, and aromatic aldehydes was studied under the conditions of thermal activation and ultrasonication. Upon heating in n-butanol, depending on the substituent in aldehyde, the reaction produced either N,4-diaryl-3,6-dimethylisoxazolо[5,4-b]pyridine-5-carboxamides, or their 4,7-dihydro derivatives. Ultrasonication unexpectedly produced N1,N3,2-triaryl-4-hydroxy-4-methyl-6-oxocyclo-hexane-1,3-dicarboxamides.

STUDY OF THREE-COMPONENT REACTIONS BETWEEN 5-AMINO-3-METHYLISOXAZOLE, N -ARYLAMIDES OF ACETOACETIC ACID, AND AROMATIC ALDEHYDES

A three-component cyclocondensation between 5-amino-3-methylisoxazole, N‑arylamides of aceto-acetic acid, and aromatic aldehydes was studied under the conditions of thermal activation and ultrasonication. Upon heating in n -butanol, depending on the substituent in aldehyde, the reaction produced either N ,4‑diaryl-3,6-dimethylisoxazolо[5,4- b ]pyridine-5-carboxamides, or their 4,7‑dihydro derivatives. Ultrasonication unexpectedly produced N 1 , N 3 ,2-triaryl-4-hydroxy-4-methyl-6-oxocyclo-hexane-1,3-dicarboxamides. How to Cite Tkachenko, V. V.; Muravyova, E. A.; Shishkina, S. V.; Shishkin, O. V.; Desenko, S. M.; Chebanov, V. A. Chem. Heterocycl. Compd. 2014 , 50 , 1166. [ Khim. Geterotsikl. Soedin. 2014 , 1263.] For this article in the English edition see DOI 10.1007/s10593-014-1578-0

Effects of thermal activation conditions on the microstructure regulation of corncob-derived activated carbon for hydrogen storage

Activated carbons derived from corncob (CACs) were prepared by pyrolysis carbonization and KOH activation. Through modifying activation conditions, samples with large pore volume and ultrahigh BET specific surface area could be obtained. The sample achieved the highest hydrogen uptake capacity of 5.80 wt% at 40 bar and −196 °C. The as-obtained samples were characterized by N2-sorption, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Besides, thermogravimetric analysis was also employed to investigate the activation behavior of CACs. Detailed investigation on the activation parameters reveals that moderate activation temperature and heating rate are favorable for preparing CACs with high surface area, large pore volume and optimal pore size distribution. Meanwhile, the micropore volume between 0.65 nm and 0.85 nm along with BET surface area and total pore volume has great effects on hydrogen uptake capacities. The present results indicate that CACs are the most promising materials for hydrogen storage application.

Te/Cu bi-layer: A low-resistance back contact buffer for thin film CdS/CdTe solar cells

A buffer layer based on a Te/Cu bi-layer useful for forming ohmic contact to p-CdTe has been developed for application in CdS/CdTe solar cells. The bi-layer buffer was prepared by vapor deposition and a thermal annealing (~200°C) was required for activation. Enhanced efficiency and stability were obtained by optimizing the Cu/Te compositions and the thermal activation conditions. Characterization by XRD, XPS, and PL indicates that under the thermal activation conditions Cu diffuses rapidly in the Te without forming CuxTe compounds. The enhanced stability can be attributed to the mediation of Cu diffusion into CdTe by the Te layer. The Te/Cu buffers are particularly useful for the fabrication of ultra-thin CdS/CdTe solar cells.

Unusual reactivity of N-tert-butylimines under FVT conditions

Thermal reactions of N-tert-butyl-(E)-crotonaldimine (1a) and 1,4-di-(tert-butyl)-1,4-diazabuta-1,3-dien (glyoxal-bis-N-tert-butylimine) (1b) under FVT conditions have been studied. It has been found that at 800 °C compound 1a yielded pyrrole and crotononitrile, presumably via homolytic t-Bu–N bond cleavage and formation of the iminyl radical. In the reaction of 1b at 800 °C, 2-methylimidazole (4b) has been obtained unexpectedly as the major product. The mechanism of these reactions has been proposed. Furthermore, combined FVT and UV-photoelectron spectroscopy have been applied for direct generation and in situ characterization of compounds 1a and 1b under thermal activation conditions.

In-situ X-ray diffraction study of phase crystallization from an amorphous MoVTeNb oxide catalyst precursor

Abstract The formation of the crystalline phases M2, M1, orthorhombic MoO 3 , and a tetragonal M 5 O 14 (M = Mo,V,Nb) type phase during heat treatment of an amorphous Mo-V-Te-Nb oxide precursor in helium is investigated applying in - situ X-ray diffraction. The precursor was synthesized by precipitation, spray-drying and subsequent calcination of the dried orange powder in air at 275 °C. Crystallization of M2 starts at 450 °C, and it occurs simultaneously with the initial liberation of tellurium. Concurrent formation of M1, M 5 O 14 , and MoO 3 at temperatures higher than 550 °C suggests that structural building blocks consumed during crystallization are competitively supplied from a common amorphous precursor. The results indicate that the availability of tellurium could play a decisive role with respect to phase distribution in the final catalyst providing one possible explanation for the susceptible response of the phase composition of Mo-V-Te-Nb oxide catalysts for selective oxidation of propane to acrylic acid on the experimental conditions of thermal activation.

Hydrogen reactivity toward carbon monoxide under mechanochemical processing

The study focuses on the hydrogenation of carbon monoxide over Co–Fe-based catalysts. The catalytic reactions were performed under both isothermal and mechanical activation conditions and their rates estimated by monitoring the gradual consumption of carbon monoxide. Aimed at carrying out a sound comparison, the rate of mechanically activated processes was referred to individual collisions by normalizing its value to the amount of powder involved in individual collisions and to the time interval of ongoing deformation. This allowed to point out that the amount of carbon monoxide converted per unit of catalyst mass and unit of time under mechanical activation conditions is at least four orders of magnitude larger than the one reacted under thermal activation conditions. This result is tentatively connected with the generation of local excited states at the catalyst surface.

Weakness of the “hot spots” approach to the kinetics of mechanically induced phase transformations

A systematic investigation on different systems has been performed in order to ascertain the possible role of local temperature rise at impacts in the mechanism of mechanically induced phase transformation processes. High-purity commercial powders have been mechanically treated under different milling conditions to study their kinetic behavior. Phase transformations have been correlated to the minimum temperatures needed to trigger the transformation processes under thermal activation conditions. Deep contradictions have arisen in connection with the so-called “hot spots” theory.

Mechanistic inferences on the synthesis of Co 50Fe 50 solid solution by mechanical alloying

An equiatomic Co–Fe solid solution was synthesized by mechanical processing. A dissolution process of Co in Fe was observed. Its kinetic characterization permitted a reliable estimate of the number of Co atoms dissolved in collision events. This number was then compared with the corresponding quantity observed in Co–Fe diffusion couples under thermal activation conditions. The data support a mechanistic hypothesis for mechanochemical transformations alternative to the ones based on thermal diffusion.

CO substitution in H 4Ru 4(CO) 12 by the diphosphine ligands 1,2-bis(diphenylphosphino)benzene (dppbz) and 1,8-bis(diphenylphosphino)naphthalene (dppn): X-ray diffraction structures of the diphosphine-chelated clusters 1,1-H 4Ru 4(CO) 10(dppbz) and 1,1-H 4Ru 4(CO) 10(dppn)

The reaction of the diphosphine ligands 1,2-bis(diphenylphosphino)benzene (dppbz) and 1,8-bis(diphenylphosphino)naphthalene (dppn) with the hydride-bridged cluster H 4Ru 4(CO) 12 ( 1) has been investigated under thermal and Me 3NO activation conditions. Both activation methods furnish the diphosphine-substituted clusters 1,1-H 4Ru 4(CO) 10(P–P) (where P–P = dppbz, dppn) as the sole isolable products. The chelating coordination mode adopted by the ancillary diphosphine ligands has been confirmed by NMR spectroscopies and X-ray crystallography. The stability of the new clusters 1,1-H 4Ru 4(CO) 10(dppbz) and 1,1-H 4Ru 4(CO) 10(dppn) has been examined, and both clusters have been found to be stable at elevated temperatures in toluene and extended near-UV photolysis.