Hydrogen–Water Deuterium Exchange over Unsupported Group VIII Noble Metals

1974 ◽  
Vol 52 (16) ◽  
pp. 2960-2967 ◽  
Author(s):  
Norman H. Sagert ◽  
Rita M. L. Pouteau
Keyword(s):  
Noble Metals ◽  
Chemical Activation ◽  
Activation Energies ◽  
Graphitized Carbon Black ◽  
Hydrogen Chemisorption ◽  
Group Viii ◽  
Hydrogen Atoms ◽  
Hydrogen Water ◽  
Surface Areas ◽  
Specific Activities

Specific activities of unsupported powders of all six Group VIII noble metals have been determined for hydrogen – water deuterium isotope exchange. The metal surface areas, which are required to calculate the specific activities were measured by hydrogen chemisorption and were checked by electron microscopy. Specific activities were measured as a function of temperature in the range 353 to 573 K and also as a function of the partial pressure of hydrogen and water at suitable temperatures and over a tenfold range of partial pressures.The variation in the specific activities was Pd < Ir ≤ Ru < Rh < Os < Pt, and these specific activities varied over a range of about 1000. The observed orders with respect to hydrogen and water are shown to be consistent with a mechanism in which chemisorbed hydrogen atoms exchange with physically adsorbed water.From the orders and the apparent activation energies, the chemical activation energies (E0) were calculated. These varied randomly within the range 61 ± 6 kJ mol−1 for all the metals studied. Previously we showed that there was a correlation of E0 with the work function of the metal when metals were supported on a highly graphitized carbon black, and suggested that electron donation from the carbon to the metal was responsible for the correlation. This suggestion is supported by the present results which show that E0 is relatively constant for all six metals in the absence of a support.

Hydrogen–Water Deuterium Exchange over Graphon Supported Group VIII Noble Metals

1973 ◽  
Vol 51 (24) ◽  
pp. 4031-4037 ◽  
Author(s):  
Norman Henry Sagert ◽  
Rita Mary Louise Pouteau
Keyword(s):  
Activation Energy ◽  
Atomic Number ◽  
Noble Metals ◽  
Activation Energies ◽  
Group Viii ◽  
Surface Exchange ◽  
Hydrogen Water ◽  
Temperature Range ◽  
The Third ◽  
Specific Activities

Specific activities of Group VIII noble metals supported on Graphon have been determined for hydrogen–water deuterium exchange. Metal surface areas, which are required to calculate specific activities, were measured by hydrogen chemisorption, and by reaction of hydrogen with chemisorbed oxygen. For the second triad metals, ruthenium, rhodium, and palladium, and in the temperature range 140 to 225 °C, the variation of activity was Ru < Rh > Pd. For the third triad metals, osmium, iridium, and platinum, the variation of activities was Os < Ir < Pt in the same range of temperature. Apparent activation energies were measured over this temperature range, and orders of reaction with respect to hydrogen and water were measured at 160 °C (200 °C for Pt). From these data, activation energies for the surface exchange reaction were calculated. In the second triad the activation energies decrease slightly with increasing atomic number, but in the third triad they decrease quite markedly with increasing atomic number. A good correlation was obtained between the activation energy for surface exchange and the thermionic work function of the metal. This supports our earlier suggestion that Graphon is able to donate electrons to the metal and thus lower the activation energy for the surface exchange.

Selective adsorption at graphite/hydrocarbon interfaces

1970 ◽  
Vol 314 (1519) ◽  
pp. 473-498 ◽  
Keyword(s):  
Basal Plane ◽  
Plane Surface ◽  
Selective Adsorption ◽  
Carbon Chain ◽  
Butyl Alcohol ◽  
Graphitized Carbon Black ◽  
Adsorptive Capacity ◽  
Hydrogen Atoms ◽  
Surface Areas ◽  
Adsorptive Properties

A study was made of adsorption of n -dotriacontane and n -butanol dissolved in n -heptane onto graphitized carbon black and various ground graphites having surface areas ranging from 5 to 700 m 2 g -1 . It was established that the adsorption of n -dotriacontane by the graphites is confined entirely to the basal planes of graphite crystals. This is attributed to a remarkable fit between the hydrogen atoms attached to one side of the zig-zag carbon chain in the normal paraffins and the centres of hexagons formed by the carbon atoms in the basal planes of the substrate. The longer the chain the more contacts it can form with the graphite surface and the more strongly it is adsorbed. More detailed studies of the adsorption of n -paraffins on ground graphites have shown that they form close-packed monolayers of horizontally disposed molecules on the basal planes. There is little further adsorption after the monolayers are complete. The heat of adsorption per molecule increases uniformly with the chain length reaching very high values for the normal paraffins having more than 30 carbon atoms. The formation of the close-packed layers has been used for the measurement of the proportion of basal plane surface in different types of graphites. n -Butyl alcohol also forms closely packed monolayers, but on the polar sites of graphites, which can be used for the estimation of their area. The basal plane and polar sites act independently in adsorption and their relative proportions characterize the adsorptive properties of graphites. Examination of graphite ground in n -heptane, which consists of plates of average area of several square micrometres and average thickness of 5 nm, shows that its surface consists predominantly of basal planes having a high adsorptive capacity for n -paraffins.

The Specific Activity of Silica Supported Platinum for the Catalysis of Hydrogen – Water Deuterium Exchange

1971 ◽  
Vol 49 (21) ◽  
pp. 3411-3417 ◽  
Author(s):  
N. H. Sagert ◽  
R. M. L. Pouteau
Keyword(s):  
Particle Size ◽  
Specific Activity ◽  
Deuterium Exchange ◽  
Hydrogen Chemisorption ◽  
Unit Surface Area ◽  
Particle Sizes ◽  
X Ray Diffraction ◽  
Hydrogen Water ◽  
Surface Areas ◽  
Platinum Particles

Some rate data are reported for deuterium exchange between water and hydrogen using series of platinum–silica catalysts. Three different methods of preparing catalysts were used to give different series of metal particle sizes. Within each series, the particle size was increased by sintering batches in air, at temperatures up to 700 °C. These methods produced platinum particles ranging from 5 to 250 Å in diameter. Metal surface areas and particle sizes were measured by hydrogen chemisorption, X-ray diffraction, and electron microscopy.The specific rates, i.e., rates per unit surface area of platinum varied by a factor of three within each series, reaching a maximum for sintering temperatures of about 500 °C. These maximum rates, measured at 127 °C with a water-to-hydrogen ratio of 0.31, varied from 1.9 × 10−8 to 5 × 10−8 mol D2 cm−2 s−1. Thus no effect of particle size on rate was observed, and the differences noted are ascribed to other effects of the methods of preparing the catalysts.

Hydrogen–Water Deuterium Exchange Over Metal Oxide Promoted Nickel Catalysts

1975 ◽  
Vol 53 (21) ◽  
pp. 3257-3262 ◽  
Author(s):  
Norman H. Sagert ◽  
Paul E. Shaw-Wood ◽  
Rita M. L. Pouteau
Keyword(s):  
Nickel Oxide ◽  
Chromium Oxide ◽  
Adsorbed Water ◽  
Nickel Catalysts ◽  
Metallic Nickel ◽  
Hydrogen Chemisorption ◽  
Nickel Surface ◽  
Hydrogen Atoms ◽  
Hydrogen Water ◽  
And Tungsten

Specific rates have been measured for hydrogen–water deuterium isotope exchange over unsupported nickel promoted with about 20% of various metal oxides. The oxides used were Cr2O3, MoO2, MnO, WO2−WO3, and UO2. Nickel surface areas, which are required to measure the specific rates, were determined by hydrogen chemisorption. Specific rates were measured as a function of temperature in the range 353 to 573 K and as a function of the partial pressure of hydrogen and water over a 10-fold range of partial pressure.The molybdenum and tungsten oxides gave the highest specific rates, and manganese and uranium oxides the lowest. Chromium oxide was intermediate, although it gave the highest rate per gram of catalyst. The orders with respect to hydrogen and water over molybdenum oxide and tungsten oxide promoted nickel were consistent with a mechanism in which nickel oxide is formed from the reaction of water with the catalyst, and then is reduced by hydrogen. Over manganese and uranium oxide promoted catalysts, these orders are consistent with a mechanism in which adsorbed water exchanges with chemisorbed hydrogen atoms on the nickel surface. Chromium oxide is intermediate. It was noted that those oxides which favored the nickel oxide route had electronic work functions closest to those of metallic nickel and nickel oxide.

ChemInform Abstract: HYDROGEN-WATER DEUTERIUM EXCHANGE OVER UNSUPPORTED GROUP VIII NOBLE METALS

1974 ◽  
Vol 5 (45) ◽  
pp. no-no
Author(s):  
NORMAN H. SAGERT ◽  
RITA M. L. POUTEAU
Keyword(s):  
Noble Metals ◽  
Deuterium Exchange ◽  
Group Viii ◽  
Hydrogen Water

scholarly journals The Effects of Methane Storage Capacity Using Upgraded Activated Carbon by KOH

2018 ◽  
Vol 8 (9) ◽  
pp. 1596 ◽  
Author(s):  
Jung Park ◽  
Gi Lee ◽  
Sang Hwang ◽  
Ji Kim ◽  
Bum Hong ◽  
...  
Keyword(s):  
Surface Area ◽  
Storage Capacity ◽  
Activated Carbons ◽  
Chemical Activation ◽  
High Surface ◽  
Heat Of Adsorption ◽  
Low Grade ◽  
Surface Areas ◽  
Ch4 Adsorption ◽  
Ch4 Storage

In this study, a feasible experiment on adsorbed natural gas (ANG) was performed using activated carbons (ACs) with high surface areas. Upgraded ACs were prepared using chemical activation with potassium hydroxide, and were then applied as adsorbents for methane (CH4) storage. This study had three principal objectives: (i) upgrade ACs with high surface areas; (ii) evaluate the factors regulating CH4 adsorption capacity; and (iii) assess discharge conditions for the delivery of CH4. The results showed that upgraded ACs with surface areas of 3052 m2/g had the highest CH4 storage capacity (0.32 g-CH4/g-ACs at 3.5 MPa), which was over two times higher than the surface area and storage capacity of low-grade ACs (surface area = 1152 m2/g, 0.10 g-CH4/g-ACs). Among the factors such as surface area, packing density, and heat of adsorption in the ANG system, the heat of adsorption played an important role in controlling CH4 adsorption. The released heat also affected the CH4 storage and enhanced available applications. During the discharge of gas from the ANG system, the residual amount of CH4 increased as the temperature decreased. The amount of delivered gas was confirmed using different evacuation flow rates at 0.4 MPa, and the highest efficiency of delivery was 98% at 0.1 L/min. The results of this research strongly suggested that the heat of adsorption should be controlled by both recharging and discharging processes to prevent rapid temperature change in the adsorbent bed.

scholarly journals On the catalytic dehydrogenation of naphthenes II. Competition experiments and energies of C-H bonds

1947 ◽  
Vol 190 (1022) ◽  
pp. 309-328 ◽  
Keyword(s):  
Activation Energy ◽  
Active Sites ◽  
Catalyst Surface ◽  
Resonance Energy ◽  
Activation Energies ◽  
Theoretical Treatment ◽  
Catalytic Dehydrogenation ◽  
Simple Relationship ◽  
Hydrogen Atoms ◽  
Methyl Cyclohexane

The rates of dehydrogenation in competition experiments using mixtures of two naphthenes, or a naphthene and a cyclic mono-olefine or two cyclic mono-olefines, have been examined theoretically and experimentally for the stationary state conditions. Provided the two reactants can occupy the same sites on the catalyst surface, then the ratio of the rates should be directly proportional to the ratio of the partial pressures at any instant. Theory suggests that a constant which can be derived from these competition experiments should be independent of the overall pressures, or of the initial ratio of concentrations or of the overall extent of dehydrogenation. Further, the ratio of the rates in competition should bear no simple relationship to the ratio of the individual rates alone, but should be related to the slopes of the 1/rate against 1/pressure plot for the two components considered separately. Moreover, the constant should be a ratio of two functions each of which is characteristic of one of the naphthenes. The theoretical conclusions have been confirmed experimentally which proves either that the groups of active sites on the catalyst surface are widely separated or that any set of sites is available for the reaction of any molecular species, and no interference takes place between naphthene molecules adsorbed on adjacent sites. Proof that a naphthene and cyclohexene are dehydrogenated on the same sites is supplied by the observation that a constant is obtained when different mixtures of cyclohexene and trans -1:4-dimethyl cyclohexane are allowed to compete for the surface. The ratios for methyl, ethyl, the three dimethyl and the three trimethyl cyclohexanes in competition with cyclohexane have been accurately determined at temperatures of 400 and 450° C. From the constants so derived the activation energy differences for the removal of the first pair of hydrogen atoms has been obtained. These values are discussed in terms of the possible transition complexes, and it is shown that the reaction proceeds by the loss of a pair of hydrogen atoms simultaneously and not by a half-hydrogenated state mechanism. Using these activation energies and the experimentally found overall activation energy of 36 kcal./g. mol., the resonance energy per resonating structure was determined as 1-73 kcal. This is in good agreement with the energies of C-H bonds in alkyl radicals (2-2 kcal./g.mol./ resonating structure). The theoretical treatment suggests that the weakest C-H link in methyl cyclohexane should be in the three position to the methyl group. A study of the activation energies involved shows that the methyl cyclohexene produced from methyl cyclohexane is not 1-methyl-1-cyclohexene, thus confirming the theoretical deduction.

INTENSIFICATION OF DISPERSED AND FINE-GRAINED SILVER EXTRACTION IN CYANIDE HEAP LEACHING OF GOLD

2020 ◽  
Vol 26 (8) ◽  
pp. 40-48
Author(s):  
Yu. Rubtsov ◽  
◽  
А. Trubachev ◽  
E. Voronov ◽  
A. Lavrov ◽  
...  
Keyword(s):  
Noble Metals ◽  
Ph Value ◽  
Chemical Activation ◽  
Precious Metals ◽  
Federal District ◽  
Heap Leaching ◽  
Sodium Cyanide ◽  
Cycle Duration ◽  
Mining Equipment ◽  
Gold Bearing

Since the cost of gold has increased by an order of magnitude over the past 20 years, gold mining began to be carried out from ores that are not previously acceptable for heap leaching (HL) technology – these are refractory ores with thin and ultrafine inclusions of precious metals, ore with an increased silver content. In the Russian Federation, classical representations in the field of gold and silver HL prevail in design solutions. At the same time, the problem of silver leaching is considered in terms of the associated extraction of the main component. This approach is determined by a limited set of technological measures that have become an integral part of the classic technological regulation: ore crushing to the class –200–40 mm, sodium cyanide consumption at the level of 0,5 kg/t; pH value – 10,5; cycle duration 65 days or more; gold concentration in production solutions – fractions, mg/l; using activated carbon for sorption of noble metals. Processing ores with silver contents of 30 g/t and a more classical approach to gold HL does not allow to increase the degree of extraction. There is a need to modernize the circuit or change the parameters of the technological regulations. The object of the study was a sample of poor quartz ore provided by the customer developing one of the gold and silver deposits of the Far Eastern Federal District, the object was to increase the degree of leaching of silver from poor gold-bearing ores without changing the technological scheme and without attracting additional mining equipment. Critical analysis of literary data was carried out and the main directions of gold production from poor gold-bearing ores were identified. Chemical and mineralogical compositions of silver-containing minerals and ore rocks were investigated. Forms of association of silver with ore minerals and rocks have been established. The option of physical and chemical activation of increase of reactivity of cyanide solutions during heap leaching of silver from poor gold-bearing ores is chosen. In laboratory conditions, it was found that an increase in the concentration of sodium cyanide by 6 times or more contributes to a satisfactory extraction of gold both in agitation and percolation leaching of silver. However, in the latter case, the positive result was obtained only with the use of solutions with increased reactivity

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