Evolution of Metal Phase in the Course of CO Hydrogenation on Potassium Promoted Ni/Al2O3 Catalyst

The hydrogenation of carbon monoxide on Ni/Al₂O₃ catalysts was studied in a flow system by simultaneous following CO conversion and crystallographic state of supported nickel. The examination performed for potassium promoted catalyst revealed that: (1) next to methane, considerable amount of CO₂ is produced, and (2) supported nickel transforms to supersaturated solution of carbon in nickel phase, NiC _x . The analysis of the results has led to formulation of a probable scheme of the carburisation.     

Studies on the promotion of nickel—alumina coprecipitated catalysts: II. Lanthanum oxide

Two series of lanthanum promoted nickel—alumina catalysts have been prepared by coprecipitation of the metal nitrates, using potassium carbonate. The molar ratio between nickel and the sum of aluminium and lanthanum was kept constant at 2.5 or 9.0 within each series. The calcination and reduction of these samples were studied by thermogravimetry and their structures before and after calcination and reduction were examined by X-ray diffraction. The methanation activities of the final catalysts were determined by differential scanning calorimetry. The results showed clearly that the methanation of carbon monoxide over nickel—alumina catalysts is enhanced by the presence of La₂O₃. With low percentages of lanthanum, the promoter is built into the precursor structure during the coprecipitation process. This is a meta-stable situation; phase separation occurs during hydrothermal treatment. In both series there was an optimum amount of lanthanum at which the activity per gram of nickel reached a maximum. The optimum specific activity of a lanthanum promoted nickel—alumina catalyst was twice as large as that of the unpromoted material. Above these optimum values, the activity per gram of nickel decreased because of two effects: an increase in the nickel particle sizes and an increase in the amounts of potassium remaining from the precipitation step. Alumina is needed to stabilize the nickel crystallites against sintering. The promoting action of La₂O₃ is slightly higher after reduction at 400°C than after reduction at 600°C. Lanthanum increased the amount of carbon monoxide which was adsorbed slowly; the amount of carbon monoxide which was rapidly adsorbed, however, was not altered. The increase in activity was accompanied by an increase in the apparent activation energy.     

Studies of carbon monoxide and hydrogen adsorption on nickel and cobalt foils aimed at gaining a better insight into the mechanism of hydrocarbon formation

Systematic studies of adsorption of hydrogen and carbon monoxide on polycrystalline surfaces of nickel and cobalt have been carried out. The aim of these studies was to gain a better insight into the catalyzed formation of hydrocarbons from H₂-CO mixtures. We have studied the adsorption of these gases by means of thermal desorption spectroscopy (TDS) on nickel foils and powders. More recently, we have obtained desorption spectra of hydrogen adsorbed on cobalt foils and powders. In this work we described desorption spectra of carbon monoxide on cobalt foils. Carbon monoxide desorption from cobalt foils was studied in a similar way as prior work, using a mass spectrometric method in an ultra high vacuum system. Two carbon monoxide desorption peaks were observed. These two states correspond to molecular CO and presumably dissociated CO, as it is observed in the case of stepped surfaces of Ni and Co single crystals. An activation energy of around 4.0 kcal/mol is obtained for the molecular state while for the dissociated state the energy is coverage-dependent with a value between 8.0 and 15.0 kcal/mol. The carbon monoxide desorption peaks were fitted with near Gaussian curves which facilitates the analysis of the data to obtain activation energies for desorption. Kinetic parameters for carbon monoxide and hydrogen desorption from nickel and cobalt foils are provided and compared with already published data involving single crystals.     

The influence of carbon monoxide on the voltammetric behaviour of nickel in acid solutions

The voltammetric behaviour of nickel in acid solutions is considerably modified by the presence of CO. As in plain acid the voltammogram also exhibits two main anodic peaks, but in this case, the adsorption of CO on the nickel surface shifts the metal electrodissolution to more positive potentials, and increases the contribution of the second electrooxidation current peak at the expense of the first one. The latter is the main peak in CO-free acids. The presence of CO adsorbates also decreases the charge of the Ni(OH)₂/NiOOH redox couple in alkaline solutions. The potential shift of the nickel electrooxidation reaction in acids follows the trend which is expected from the energy difference between CO and H₂O adsorption on nickel in the gas phase.     

Adsorption,oxidation and effect of CO on hydrogen adsorption at smooth rhodium electrodes in acid solution

The adsorption of carbon monoxide was studied under steady state conditions on smooth rhodium electrodes in 0.5 M H₂SO₄ at room temperature. The coverage with carbon monoxide is equal to saturation coverage between 0.1 and 0.5 V vs a hydrogen electrode in the same solution. Above 0.5 V it decrease to 0 within 0.2 V. The oxidation of chemisorbed carbon monoxide at constant current is accompanied by the formation of the oxygen layer above 0.6 V. A correction for the contribution of the oxygen layer formation to the anodic charge has to be applied in the determination of the CO_ad coverage even at small current densities.The coverage with H_ad was determined as a function of potential at constant coverage with preadsorbed carbon monoxide from anodic charging curves. These curves were taken at a sufficiently small current density so that the equilibrium of the Volmer reaction remained practically established. The coverage of CO_ad, computed from the charge for the oxidation of CO_ad, agreed well with that obtained from the decrease of the length of the hydrogen branch of the charging curves. The isotherms of hydrogen adsorption are of the Temkin type at CO_ad coverages above 0.4. The characteristic parameters of the Temkin isotherm were determined as a function of the coverage with CO_ad.     

Selective electrodeposition of metals from simulated waste solutions

Most industrial waste streams contain a number of different heavy metals. The feasibility of selective electrodeposition of cadmium, cobalt and nickel as their pure metals (99%) from binary mixtures has been investigated. Single cation linear sweep voltamograms and nucleation potential measurements have been made and used to predict the optimum potentials and conditions for selective electro-deposition from the mixed-cation solutions. The anions used in this work are SO₄ ^2–, Cl^– and BF₄ . The optimum potential for removal by electrodeposition of Cd from a solution containing Cd(ii) and Co(ii) or Ni(ii) without codepositing Co or Ni has been evaluated from a simple diagram constructed from nucleation potential measurements. It is shown that the [Cd(ii)] remaining in the solution after exhaustive electrolysis at a fixed potential is determined by the Nernst equation, and not by the electrolysis time provided that a critical minimum time has been exceeded.     

High-pressure synthesis of ethyl benzoate from chloro- and bromobenzene

When chlorobenzene was reacted with ethyl alcohol and carbon monoxide under pressure, the conversions of chlorobenzene to ethyl benzoate and benzoic acid under optimum reaction conditions were 31.3% and 30.1% respectively, with nickel naphthenate supported on silica gel (Ni:SiO₂ = 50:50) as the best catalyst. When bromobenzene was used instead of chlorobenzene, the best catalyst was found to be nickel iodide supported on silica gel (Ni:SiO₂ = 50:50), and the above conversions were 74.7% and 25.1% respectively under optimum reaction conditions.     

Mechanistic approach to electrochemical processes in the passive and pitting corrosion regions of carbon steel in dilute NaOH solutions containing Na2SO4

Passive film growth, electrodissolution and pitting corrosion of prepassivated carbon steel in dilute NaOH solutions containing Na₂SO₄ are studied by using potentiostatic and potentiodynamic techniques. Two kinetic reaction models implying different passive film growth mechanisms are proposed to describe the passive film growth, the electrodissolution process through the passive film and pitting corrosion. Current transients at constant potential recorded in the passive and pitting region can be satisfactorily reproduced by assuming the occurrence of simultaneous processes. The physical interpretation of adjusting parameters derived from the two models is consistent with a duplex structure for the passive film and with the nucleation and growth of pits when the applied potential exceeds the breakdown potential although both mechanisms for the passive layer growth seem to be equally probable.     

Thermal degradation of cinnamoylated poly(vinyl alcohol)

Thermogravimetry and pyrolysis in combination with gas chromatography and infrared spectroscopy were the experimental techniques applied to the thermal degradation of cinnamoylated poly(vinyl alcohol) samples, constituted from vinyl alcohol-vinyl cinnamate photocrosslinkable copolymers. The thermal decomposition products include gases, liquids and solids. The gases are formed from saturated and unsaturated volatile hydrocarbons C₁? C₄, carbon monoxide and carbon dioxide. The liquid fraction includes aromatic hydrocarbons and some oxygenated organic compounds. The solid product identified in the greatest amount was cinnamic acid. The content in the thermal decomposition products varies considerably both with copolymer composition and temperature.     

High-pressure synthesis of ethyl benzoate from chloro- and bromobenzene

When chlorobenzene was reacted with ethyl alcohol and carbon monoxide under pressure, the conversions of chlorobenzene to ethyl benzoate and benzoic acid under optimum reaction conditions were 31.3% and 30.1% respectively, with nickel naphthenate supported on silica gel (Ni:SiO₂= 50:50) as the best catalyst. When bromobenzene was used instead of chlorobenzene, the best catalyst was found to be nickel iodide supported on silica gel (Ni:SiO₂ = 50:50), and the above conversions were 74.7% and 25.1% respectively under optimum reaction conditions.     

Studies on the promotion of nickel—alumina coprecipitated catalysts: I. Titanium oxide

A series of TiO₂-promoted nickel—alumina catalysts has been prepared and characterized. The promoter was added in various proportions to a calcined coprecipitated nickel—alumina material by adsorption of the acetylacetonate complex of titanium, followed by further calcination and reduction. The structure of the resultant materials was similar to that of the unpromoted coprecipitated nickel—alumina. The chemisorption properties of the catalyst and its behaviour in the CO/H₂ reaction were characteristic of a strong metal-support interaction (SMSI) reported in the literature for Ni/TiO₂. The strong adsorption of both carbon monoxide and hydrogen were suppressed while the activity for carbon monoxide hydrogenation was increased, the activation energy being lowered. The higher activity, however, was relatively unstable under reaction conditions.     

Corrosion inhibition of carbon steel in acid chloride solution using ethoxylated fatty alkyl amine surfactants

Four novel non-ionic ethoxylated fatty alkyl amine surfactants (I–IV) were synthesised and investigated as corrosion inhibitors of carbon steel in 1 M hydrochloric acid solution using gravimetric, open circuit potential and potentiostatic polarisation techniques. The percentage inhibition efficiency (η%) for each inhibitor increased with increasing concentration until the critical micelle concentration (cmc) was reached. The maximum inhibition efficiency approached 95.1% in the presence of 400 ppm of the inhibitor (IV). It was found that the adsorption of the surfactants on carbon steel followed the Langmuir adsorption isotherm. Potentiostatic polarisation data indicated that these surfactants act as mixed type inhibitors. The values of activation energy (E _a*) of carbon steel dissolution in 1 M HCl were calculated in the absence and presence of 400 ppm of each inhibitor. Finally, scanning electron microscopy (SEM) was used to examine the surface morphology of polished carbon steel surfaces and those immersed in 1 M HCl in the absence and presence of 400 ppm of inhibitor (IV).     

Effect of Catalyst Preparation on Catalytic Activity: VI. Chemical Structures on Nickel/Alumina Catalysts: their Impact on the Rate-Determining Step in the Hydrogenation of Carbon Monoxide

Titration of the carbon pool subsequent to steady-state reaction of hydrogen and carbon monoxide over Ni/Al₂O₃ catalysts in conjunction with temperature-programmed surface reaction studies has been performed to assess the impact of nickel speciation on the rate-determining step in the methanation reaction. Mass balances for the desorption products reveal significant differences that depend on the weight loading of the catalyst. Low-weight loading catalysts prepared by incipient wetness consist of NiAl₂O₄ reactive centers as revealed by electron spectroscopy for chemical analysis and carbon monoxide temperature-programmed reaction experiments. Data are presented which support the hypothesis the rate of methanation is controlled by the rate of surface-bound carbon monoxide dissociation over the catalysts. On the other hand, high-weight loading catalysts prepared by this method consist of “particle-like” nickel. Over these catalysts, the rate of methanation is found to be controlled by the rate of hydrogenation of CH_x. It is proposed that variation in catalyst preparation procedures can account for the wide-spread controversy in the determination of rate-determining step for methanation over Ni/Al₂O₃ catalysts.     

MONOLITHIC-SUPPORTED NICKEL CATALYSTS: I. METHANATION ACTIVITY RELATIVE TO PELLET CATALYSTS

The catalytic activity and selectivity of pellet and monolithic supported Ni/A1₂O₃ for methanation of carbon monoxide were investigated to determine the role of support geometry in catalyst performance. Turnover numbers, CO conversion versus temperature data, and product distributions were measured at space velocities from 15,000 to 50,000 hr^-1 and pressures of 140 to 2500 kPa. The data show that monolithic supported nickel is significantly more active and selective for methane production at both low and high CO conversions compared to nickel catalysts beads and pellets. Monolithic supported methanation catalysts apparently operate with a higher effectiveness and rate of mass transfer than do catalyst beads or pellets. Because of its superior activity, selectivity and tow pressure drop at high space velocities, monolithic nickel may be the ideal catalyst for use in a high throughput recycle methanator     

In situ photoelectrochemistry and Raman spectroscopic characterization on the surface oxide film of nickel electrode in 30 wt.% KOH solution

The oxide films of nickel electrode formed in 30 wt.% KOH solution under potentiodynamic conditions were characterized by means of electrochemical, in situ PhotoElectrochemistry Measurement (PEM) and Confocal Microprobe Raman spectroscopic techniques. The results showed that a composite oxide film was produced on nickel electrode, in which aroused cathodic or anodic photocurrent depending upon polarization potentials. The cathodic photocurrent at −0.8 V was raised from the amorphous film containing nickel hydroxide and nickel monoxide, and mainly attributed to the formation of NiO through the separation of the cavity and electron when laser light irradiates nickel electrode. With the potential increasing to more positive values, Ni₃O₄ and high-valence nickel oxides with the structure of NiO₂ were formed successively. The composite film formed in positive potential aroused anodic photocurrent from 0.33 V. The anodic photocurrent was attributed the formation of oxygen through the cavity reaction with hydroxyl on solution interface. In addition, it is demonstrated that the reduction resultants of high-valence nickel oxides were amorphous, and the oxide film could not be reduced completely. A stable oxide film could be gradually formed on the surface of nickel electrode with the cycling and aging in 30 wt.% KOH solution.     

Electrooxidation of benzyl alcohol at high surface area nickel (NiS x ) electrodes in alkaline solution

The heterogeneous catalytic redox behaviour of NiS _x deposited electrodes was investigated with and without benzyl alcohol in KOH solution using cyclic voltammetry and linear sweep voltammetry. The limiting current density for benzyl alcohol oxidation on a NiS _x electrode was 22 times larger than that on a polished nickel electrode. The experimental results in galvanostatic electrolysis using fractional factorial design showed that the main and interaction effects of benzyl alcohol concentration, temperature, and OH^– concentration are the key variables influencing the selectivity of benzaldehyde formation during electrolysis.     

Catalytic syntheses of methyl and ethyl lactates under pressure

Methyl and ethyl lactates have been synthesised under pressure from acetaldehyde, carbon monoxide and methyl or ethyl alcohol with various supported nickel, cobalt and iron catalysts. Under the optimum conditions, in the presence of nickel iodide supported on silica gel (Ni:SiO₂ = 50:50), the maximum yields of methyl lactate and by-product lactic acid were 20.7% and 15.2% respectively, whereas the maximum yields of ethyl lactate and lactic acid were 12.6% and 12.3% respectively (all on the input acetaldehyde basis).     

Chrysocolla as a Methanation Catalyst Support

The kinetic properties of nickel supported on chrysocolla (CHR) and nickel—copper mixtures supported on silica were measured by steady-state kinetics (carbon monoxide hydrogenation), temperature-programmed desorption (carbon monoxide, hydrogen), and temperature-programmed reaction (carbon monoxide and carbon hydrogenation). Leached chrysocolla, a silica-like material containing 7.1% copper, is shown to be an effective catalyst support; NI/CHR has methanation activity and adsorption properties (hydrogen, carbon monoxide) that are similar to Ni/SiO₂. The Ni/CHR catalyst has a much higher selectivity to methane formation, however, and a lower activation energy. The copper in the CHR support does not appear to affect the catalyst properties and thus apparently does not interact with the nickel. Copper in CuNi catalysts decreases the turnover number for methanation, the amount of hydrogen adsorption, the strength of hydrogen binding to the surface, and the rate of carbon monoxide disproportionation. Copper also increases higher hydrocarbon selectivity at higher temperature, though the temperature at which this occurs depends significantly on the support. The rate of carbon hydrogenation, however, is relatively independent of the presence of copper. Good agreement was obtained between carbon monoxide hydrogenation kinetics measured by steady-state reaction and by temperature-programmed reaction.     

Neo acids chemistry and applications

Four commercial neo acids (synthetic trialkylacetic acids) C₅, C₇, C₁₀, and C₁₃ are synthesized employing an olefin, carbon monoxide, and acidic catalyst and possess the hindered neo configuration around the alpha carbon. Esterification using simple alcohols and polyols, and preparation of peroxyesters and metal salts using neo acids as well as toxicity,LD ₅₀ values of the acids, are discussed. Hydrolytic stability of the esters, and possible end use applications are described. Presented in part at AOCS Meeting, Los Angeles, April 1966.     

Relation between the presence of inhibitors and deposit morphology in nickel deposition

Nickel deposition on vitreous carbon from concentrated nickel chloride solutions has been studied. The formation of inhibitors such as H_ads and nickel hydroxides has been related to both the shape of thei-t transient and the morphology of the deposit. The experimental parameters (pH, nickel (ii) and chloride concentration) were varied in order to study the conditions leading to a compact, homogeneous metallic deposit.