Effects of the nature and composition of the solvent on the thermodynamic characteristics of the individual forms of hydrogen adsorbed on the surface of porous nickel

The effects of the nature and composition of solvents on the thermodynamic characteristics of the adsorption states of hydrogen on nickel were studied. The adsorption can be described in terms of the thermodynamic model of a surface with a discrete nonhomogeneity for three individual forms of adsorbed hydrogen. The thermodynamic characteristics of the individual forms of hydrogen adsorbed on porous nickel from aqueous solutions of sodium hydroxide, dimethylformamide, methanol, and ethanol were determined.     

杂多酸盐在Raney Ni和Raney Co表面上的状态

采用XPS表面分析技术研究了Cu3/2PMo12O40改性Raney Ni和Raney Co的表面状态,结果表明,Raney Ni和Raney Co表面上的Cu3/2PMo12O40分子中的Cu2＋和Mo6＋发生了很大变化,Cu2＋被还原为Cu0,而Mo6＋被部分还原为Mo5＋和Mo4＋.这些变化可归因于Raney Ni和Raney Co在制备过程中表面吸附的活泼氢所致.由于Raney Ni表面吸附的氢比Raney Co表面吸附的氢的活性高,使得Raney Ni表面的Mo6＋被还原到Mo5＋和Mo4＋的量多.混合价态Mo的存在提高了羰基在催化剂表面吸附和活化的能力,同时Cu0的存在有助于羰基的加氢反应.所以,混合价态的Mo和Cu0对羰基加氢起着协同的作用.     

Effect of controlled deactivation on the thermochemical characteristics of hydrogen adsorption on skeletal nickel from sodium hydroxide-water solutions

Differential heats of adsorption in a wide range of surface coverage and maximum amounts of adsorbed hydrogen are determined by adsorption calorimetry on partially deactivated skeletal nickel from aqueous solutions of sodium hydroxide. The effect of the composition of solutions on the values of limiting adsorption and adsorption equilibria of individual forms of hydrogen is shown.     

Acid-base properties of the active sites of the surface of a skeletal nickel and promoted skeletal nickel catalyst

The acid-base and adsorption properties of the active sites of the surface of a skeletal nickel and promoted nickel catalyst in aqueous solutions were studied by the potentiometric and pKspectroscopy methods. Titanium added as a promoter resulted in an increased number of lines in the pK spectra, which may attest to higher chemical activity of the promoted catalyst. An increase in the pH value of the media was shown to cause a shift in the process equilibria toward the formation of atomic strongly-bound forms of adsorbed hydrogen.     

Using solvents to control hydrogen adsorption on skeletal nickel

The results from adsorption-calorimetric studies of hydrogen adsorption on skeletal nickel are generalized. The thermodynamic characteristics of adsorbed hydrogen are calculated according to the model of an ideal surface with discrete heterogeneity. It is shown that the states of surface layers in solutions, formed upon hydrogen adsorption on skeletal and porous nickel, depend on the nature and composition of the solvent. Based on the resulting data, the possibility of using a solvent to control adsorption in a skeletal nickel-hydrogen system is confirmed.     

The heats of hydrogen adsorption on Raney nickel from aqueous-organic solvents with acid and base admixtures

The heats of hydrogen adsorption on porous nickel from aqueous solutions of dimethylformamide containing acetic acid and sodium hydroxide admixtures were measured by adsorption calorimetry. The introduction of acid or alkaline admixtures changed both the amount of hydrogen adsorbed on the surface of porous nickel and the character of the dependences of the heats of adsorption on this amount. The composition of solvents influenced adsorption because of the quantitative redistribution of adsorption values among various hydrogen adsorption forms bound by the active centers of the surface of nickel determined by changes in medium basicity.     

非负载镍催化剂的2-乙基蒽醌加氢活性及其氢吸脱附性质

 分别制备了金属镍粉、兰尼镍、Ni-B非晶态合金及镧掺杂的Ni-B非晶态合金(Ni-B-La)催化剂,研究了催化剂的氢吸附和脱附性质以及对2-乙基蒽醌加氢反应的催化性能. 结果表明,金属镍粉、兰尼镍和Ni-B催化剂表面均具有两种氢吸附位: 弱吸附位和强吸附位. Ni-B-La催化剂表面只有氢的强吸附位,其强吸附氢量与兰尼镍相当. 推测只有氢的强吸附位是2-乙基蒽醌加氢反应的活性中心,并且Ni-B-La催化剂上的强吸附氢较兰尼镍上的更活泼,因而Ni-B-La非晶态合金催化剂对加氢反应的催化活性高于兰尼镍.     

The thermodynamic characteristics of acetone adsorption on Raney nickel under liquid phase hydrogenation conditions

An adsorption-calorimetric study was performed to determine the thermodynamic characteristics of adsorption of acetone on Raney nickel from aqueous solutions of 2-propanol of various compositions directly during liquid-phase hydrogenation. At adsorbate concentrations below 3 × 10⁻³ M, adsorption occurred by the mechanism of the filling of the pore volume of the catalyst with saturated solutions of complex compositions. At higher concentrations, the process followed the mechanism of condensation interactions. Two-dimensional phase diagrams were obtained for Raney nickel surface layers involved in the adsorption of acetone. These diagrams substantiated the possibility of two-dimensional phase transitions in adsorption solutions.     

Dependence of the thermodynamic characteristics of forms of hydrogen adsorbed on a porous nickel surface on the degree of deactivation

Thermodynamic characteristics of the adsorption equilibria of individual forms of adsorbed hydrogen are calculated using data from adsorption-calorimetric studies of liquid-phase hydrogenation in a model of a surface with discrete nonuniformity in the ideal adsorption layer approximation under conditions of liquid-phase hydrogenation. It is shown that partial deactivation raises the fraction of the molecular α form via the atomic β form of adsorbed hydrogen and increases the adsorbate-adsorbent binding energy.     

Azorhodanine derivatives as inhibitors for acidic corrosion of nickel

Azorhodanine derivatives (HL1-HL5) were tested as corrosion inhibitors for nickel in 2M HNO3 solution using weight loss and galvanostatic polarization techniques. The results showed that these derivatives act as inhibitors for nickel in this medium. The inhibition was assumed to occur via adsorption of the inhibitor molecule on the metal surface. Polarization measurements indicated that these compounds act as mixed-type inhibitors, but the cathode is more polarized when an external current was applied. This means that these compounds retard the rate of hydrogen evolution and the rate of dissolution of the metal. Results showed that azorhodanine derivatives are adsorbed on the nickel surface following Temkin's adsorption isotherm. The activation energy and thermodynamic parameters were calculated and discussed at different temperatures (30-45 degrees C).     

Vibrational spectroscopy of adsorbed species on nickel by neutron inelastic scattering

In a test of the utility of neutron inelastic spectroscopy (NIS) for studying molecular vibrations in surface reactions, we have examined the adsorption, co-adsorption, and reaction of hydrogen and carbon monoxide on Raney nickel catalysts.     

Influence of the Oxide Content in the Catalytic Power of Raney Nickel in Hydrogen Generation

The influence of oxides in the hydrogen evolution on Raney nickel electrocatalysts was characterized by electrochemical impedance measurements. In addition, these materials show competitive overpotentials for hydrogen evolution with a modified Watts bath as a binder for the Raney nickel. The optimum result was ?190?mV of overpotential at 100?mA?cm^?2. Oxygen in the Raney Ni catalyst affects its electroactivity toward hydrogen evolution. The source of oxygen is related to the presence of chloride ions in the modified Watts bath. A Watts bath binds Raney Ni particles to the surface of the catalysts and chloride regulates the oxygen content in the nickel binder during electrodeposition. High oxygen content increases the hydrogen evolution overpotential of the electrode. The electroactivity of the synthesized porous coatings was evaluated by polarization curves and impedance plots. In addition, surface characterization by X-ray diffraction, field emission–scanning electron microscopy equipped with energy-dispersive analysis, and X-ray photoelectron spectroscopy is reported.     

Interaction of hydrogen with unsupported and supported nickel

The adsorption of molecular hydrogen on Ni powder and on Ni/Al(2)O(3) and Ni/SiO(2) catalysts was studied by the temperature-programmed desorption (TPD) method. The examinations were performed in the flow system, starting the TP measurements at low temperatures of 100 or 78 K, which resulted in the formation of complete characteristics of the interaction of hydrogen with nickel. Generally, three forms of chemisorbed hydrogen were distinguished: alpha, adsorbed on Ni surface, beta, adsorbed in the "second layer", and gamma, located in the subsurface region of nickel. The comparison of the results of this work with those obtained in vacuum systems for various Ni surfaces has led to the conclusion that the same form of hydrogen desorbs from nickel above 200 K in vacuum systems but above 300 K in flow systems. The examinations performed for Ni/Al(2)O(3) and Ni/SiO(2) samples show that alumina suppresses but silica enhances the formation of the beta-form of hydrogen.     

An adsorption calorimetry study of the adsorption of acetone on raney nickel under conditions of liquid-phase hydrogenation

Adsorption calorimetry was used to study the characteristics of the adsorption of acetone on Raney nickel from 2-propanol-water solutions under conditions of liquid-phase hydrogenation. The isotherms of adsorption of acetone on Raney nickel and the dependences of integral and differential heats of adsorption on the adsorption value were obtained. It was established that the adsorption of acetone on Raney nickel occurs by the mechanism of volume filling of micropores in the pore space of the catalyst with adsorbate solution, which consists of partially or completely desolvated acetone molecules irrespective of the concentration of 2-propanol in the solvent.     

Raney镍催化松香加氢反应的机理

催化加氢;反应机理;氢化松香;Raney镍催化松香加氢反应的机理     

原位红外光谱研究Ni/Al2O3催化剂上CO的吸附态:Ⅰ.CO的倒式吸附态

CO在过渡金属上的吸附方式一般认为可分成三类:线式吸附态,桥式吸附态和多重键吸附态.这些吸附态的C—O伸缩振动具有红外活性,共振动频率分别位于～2050,～1950和～1700cm~(-1).但也有人认为CO在过渡金属表面上可能会形成倒式吸附态,即C—O键向表面倾斜,甚至平行于表面.例如,Dijk等曾推测在Ni/SiO_2催化剂上CO可能形成倒式双点吸附态(即C,O原子同时与表面成键).Krasser等用喇曼光谱研究CO在Ni/SiO_2上的吸附态时发现在330cm~(-1)处有一喇曼峰,认为这个峰可能来自倒式     

The influence of 1,4-phenylenediamine admixtures on liquid-phase hydrogenation of 4-nitroaniline

The influence of the composition of aqueous solvents containing 1,4-phenylenediamine on the rate and selectivity of the liquid-phase hydrogenation of 4-nitroaniline was studied. The observed reaction rates decreased by a factor of from 2 to 8 and the activation energies on the equiaccessible surface of Raney nickel remained virtually unchanged as the concentration of 1,4-phenylenediamine in solution increased. The rate constants for the hydrogenation of 4-nitroaniline and its adsorption values and the heats of solvation in aqueous solutions of 1,4-phenylenediamine were found to be interrelated. The data obtained are discussed in terms of the influence of specific solvation interactions on adsorption and reaction rate constants on the surface of Raney nickel.     

The influence of the nature of substituents on adsorbability and the rate of liquid-phase hydrogenation of nitrobenzenes

The influence of the nature of substituents on the rate of liquid-phase hydrogenation of nitrobenzenes on Raney nickel was studied in an aqueous solution of 2-propanol. Interrelation between the rate of the reaction on the equiaccessible surface of the catalyst and solvation parameters, reactivity indices, and adsorption values of hydrogenated compounds containing electron acceptor (4-nitrobenzoic acid) and electron donor (4-nitroaniline) substituents was considered.     

The states of hydrogen adsorbed on the surface of skeleton nickel

The experimental data on hydrogen adsorption on skeleton nickel were used to construct the pK spectrum of atomic hydrogen on this surface. The pK spectrum obtained corresponded to the presence of three adsorption centers on the surface of skeleton nickel. A chemical model of hydrogen adsorption on the surface of skeleton nickel was suggested.