Effect Of Ammonia Adsorption Research Articles

Characterisation of Basic Sites on Ga2O3, MgO, and ZnO with Preadsorbed Ethanol and Ammonia-IR Study.

The effect of adsorption of ethanol and ammonia on the basicity of Ga2O3, MgO, and ZnO was examined via IR studies of CO2 adsorption. Ethanol reacts with OH groups on Ga2O3, and MgO, forming ethoxyl groups. The substitution of surface hydroxyls by ethoxyls increases the basicity of the neighbouring oxygen. The ethoxyl groups that also form on ZnO do not contain surface OH groups, but the mechanism of their formation is different. On ZnO, ethoxy groups are formed by the reaction of ethanol with surface oxygens. The presence of ethoxyls on ZnO decreases the basicity because some surface oxygens are already engaged in the bonding of ethoxyl groups. The effect of ammonia adsorption on basicity is different for each oxide. For Ga2O3, ammonia adsorption increases the basicity of neighbouring oxygen sites. Ammonia is not adsorbed on MgO; therefore, it does not change the basicity of this oxide. Ammonia adsorbed on ZnO forms coordination bonds with Zn sites; it does not change the number of basic sites but changes how carbonate species are bonded to surface sites.

Ammonia adsorption-induced change in permittivity of zeolite Y in millimeter-wave band

Millimeter wave is a prominent topic for next-generation communication system. To develop functional materials to be used in sensors operated in the millimeter-wave, it is necessary to obtain the variation in the permittivity of the materials. In this study, the effect of ammonia adsorption on the permittivity of zeolite Y in the millimeter-wave of 60–90 GHz is investigated. The results indicate that the ammonia adsorption increases the permittivity of zeolite Y. Specifically, the permittivity change of the gas concentration resulted in 0.025/100 ppm. Based on the characterizations and calculation, ammonia adsorption in zeolite Y stretches the bond between mobile cations and zeolite framework, which results in an increase in the ionic dipole moment of the zeolite. This study provides a fundamental insight on gas sensing materials for millimeter-wave sensors.

Formic acid–ammonium formate mixture: A new system with extremely high dehydrogenation activity and capacity

Formic acid (FA)–ammonium formate (AF) mixture is studied as a possible new system for dehydrogenation over a common Pd/C catalyst synthesized via a modified impregnation-NaBH4 reduction method. The composition and morphology of the Pd/C catalyst are characterized using X-ray diffraction, energy-dispersive X-ray spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and inductively coupled plasma–atomic emission spectrometry. Results show that the initial turn-over frequency of the FA–AF mixtures with total FA and AF concentration of 10 mol dm−3 and FA molar fraction of 0.2 can reach 7959 h−1 at 50 °C, which is the highest value reported for heterogeneous Pd-based catalysts in FA-based systems. FA in this mixture can completely decompose and deliver an electrochemical capacity of 565.87 mAh mL−1. The activity and stability of the Pd/C catalyst in this system are greatly improved in comparison with those of FA–sodium formate system. The excellent dehydrogenation performance of FA–AF mixture can be attributed to the catalytic activity of formate toward the decomposition of FA, the effect of ammonia adsorption on Pd/C catalyst, and the higher solubility of AF in FA solution.

Effects of amination and adsorption of ammonia on the electrical conductivity of the detonation nanodiamond powders

In the present work, the temperature dependence of the static Gdc(T) and dynamic conductivity Gac(T, f) of detonation nanodiamond powders in the frequency range 25-10 6 Hz and 300<T<800 K have been studied. Data on Gdc(T) and Gac(T,f) were obtained for the initial and aminated samples. It has shown that the value of electroconductivity for the intial and amianted nanodiamond powders differs by 2,5 order. A value of activation energy decreases compared to the original and equals 0.46 eV. Data on the effect of ammonia adsorption on Gdc(T), Gac(T, f) and the frequency dependence of dielectric permeability (ε) were obtained for powders of DND at room temperature. The effect of giant dielectric permeability increase at low frequencies was found. After exposure to ammonia within 48 hours, the dielectric permeability changes from 15 to 2,1·105 for initial sample at a 25 Hz, and at 1 kHz from 11 to 1.6·103 for UDD-SP,..

Effect of ammonia adsorption on the electrical characteristics of mesoporous silicon

A detailed study of the current-voltage curves of mesoporous silicon (mesoPS) has been carried out for various dosages of ammonia, employing two different measurement configurations. The gas adsorption strongly modifies the electrical characteristics of the material, both affecting their shape and varying the conductivity values. In particular, it is found that the conductivity gap, arising from a collective Coulomb blockade phenomenon, and the electrical anisotropy of mesoPS can be gradually cancelled by NH3 molecules. Moreover, a nonmonotonic behavior of the conductivity with respect to the gas pressure is observed, in analogy with previous infrared spectroscopy results. From the analysis of such experimental findings, we propose an interaction mechanism between the mesoPS surface and ammonia, involving the screening of trapped positive charges through the dipole moment of NH3 molecules.

Ammonia Adsorption on Bamboo Charcoal with Acid Treatment

The effect of ammonia adsorption in aqueous solutions was examined for bamboo charcoal carbonized at 400, 700 and 1000°C, and activated carbon. Furthermore, the change of the ammonia adsorption in aqueous solutions was also examined by treatment of each sample with diluted sulfuric acid. Bamboo charcoal carbonized at 400°C and treated with diluted sulfuric acid was the most effective for removing ammonia from aqueous solutions. Although the ammonia adsorption of the bamboo charcoal carbonized at 400°C in gas phase hardly changed by the treatment with diluted sulfuric acid, that in aqueous solutions significantly increased by the treatment.

Effect of the Initial Doping Level on Changes in the Free-Carrier Concentration in Porous Silicon during Ammonia Adsorption

Infrared spectroscopy is used to investigate the effect of ammonia adsorption on the concentration of equilibrium charge carriers in porous-silicon layers with various initial types of dopants at different concentrations. It is found that ammonia adsorption results in an increase in the number of free electrons in n-type samples up to a level exceeding 1018 cm−3. In p-type samples, a nonmonotonic dependence of the charge-carrier concentration on ammonia pressure is observed. The obtained results are accounted for by the appearance of adsorption-induced shallow donor states that, along with the initial-dopant and surface-defect states, specify the charge-carrier type and concentration in the silicon nanocrystals of the porous layer after ammonia adsorption.

Flexible Aluminum Coordination in Alumino−Silicates. Structure of Zeolite H−USY and Amorphous Silica−Alumina

The aluminum coordination in amorphous silica−alumina with different aluminum concentrations as well as in pure γ-Al2O3 has been studied by means of 27Al (MQ) MAS NMR spectroscopy. The effect of ammonia adsorption at 120 °C has been studied and compared with that on zeolite H−USY, as well as with zeolites with different topologies. As for protonic zeolites, part of the octahedral aluminum reversibly changed to tetrahedrally coordinated upon ammonia adsorption on amorphous silica−alumina. The distinction between flexible aluminum coordination in zeolites and silica−alumina was possibly based on the quadrupolar parameters. Ammonia adsorption on pure γ-Al2O3 did not influence the aluminum coordination. A parallel between the structure of zeolite USY and that of amorphous silica−alumina was made on the basis of the results of 27Al MQ MAS NMR spectroscopy. A partial conversion from octahedral to tetrahedral coordination upon ammonia adsorption was observed for zeolite H−USY. Most of the flexible aluminum speci...

Effect of Si to Al substitution at next-nearest-neighbor sites on the acid strength 2. Low Si/Al ratio or high ammonia loading

The acidity variations upon Si/Al substitution at next-nearest-neighbor (NNN) sites were studied by ab initio molecular orbital calculations. Our previous study on the Si/Al substitution occurring at only one NNN site (1NNN models) revealed that the effect of the substitution on the acid strength is not unique but is site-dependent [Microporous Mater. 5 (1995) 233]. In the present report, a lower Si/Al ratio was investigated using the models where two NNN sites were substituted from Si to Al (2NNN models). Even among 2NNNs, there were some cases which exhibited higher acidity than isolated Al site (0NNN). Also it was found that the Si/Al substitution at a particular site always had a similar effect on the acidity regardless of the Al occupations at other NNN sites. Furthermore, in order to examine the variation of acidity as the ammonia loading is increased, the effect of ammonia adsorption at NNN site was studied. Acidity variation was again found to be dependent upon the substitution site. The traditional explanations for the acid strength variations upon the change of Si/Al ratio from the number of Als occupying NNN sites are thus strongly doubted.

The effect of ammonia adsorption on the acidity of silica-alumina and alumina catalysts: The nature of the acid sites

Acidic catalysts employed in a number of petroleum refining processes are known to be readily poisoned by basic nitrogen compounds. To throw light on the poisoning process and the nature of the acid sites, the effect of basic nitrogen compounds on the acid strength distribution of silica-alumina and alumina catalysts was determined using H R as well as 0 indicators. Adsorption of NH 3 on M-46 silica-alumina has a pronounced effect on the acid strength distribution with a minor change in the number of sites; on alumina, the situation is reversed. Desorption of NH 3 from silica-alumina at elevated temperatures is accompanied by the loss of a considerable amount of bound water; this should modify the number and strength of the catalyst acid sites. Acid strength distributions derived from high temperature NH 3 desorption data are therefore believed incorrect. The oxidation of triphenylmethane to the trityl ion in the presence of light and of perylene to the cation radical by silica-alumina are not readily poisoned by nitrogen bases, in contrast to the catalytic activity. This suggests the sites involved are weakly electrophilic and of little catalytic importance. The results favor the view that oxygen under the catalytic influence of Bronsted acids leads to oxidation of these hydrocarbons rather than strong Lewis acids as proposed by several investigators. Some suggestions relating to the nature of the acid sites on silica-alumina are made based on these experimental data.