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Platinum Metals Rev., 1969, 13, (2), 73

ABSTRACTS: April 1969

of current literature on the platinum metals and their alloys

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PROPERTIES

Fusion Curves for Graphite, Tungsten and Platinum up to 60 kbar

l. f. vereshchagin and n. s. fateeva, Zh. eksper. teor. Fiz., 1968, 55, (4), 1145–1152

Optical measurements on Pt agree well with those obtained by thermal analysis. The temperature of fusion of Pt increases linearly with pressure.

Rheological Properties of Platinum at High Temperatures

v. o. shestopal, Fiz. Metal. Metalloved., 1968, 26, (6), 1127–1130

Measurements of the shear modulus, internal friction and creep of annealed and unannealed samples of Pt were carried out between 1300 and 1980°K and results are depicted graphically.

Coherent and Incoherent Precipitation in the Gold-Platinum System

j. weise and v. gerold, Z. Metallkunde, 1968, 59, (12), 904–909

Resistivity studies of 15, 20, 60 and 65 wt% Au-Pt wires during isothermal ageing and during reheating to the homogenisation temperature showed two rates which can be attributed to coherent and to incoherent precipitation. The metastable coherent miscibility gap in the phase diagram was ∼100–200 deg C below the stable incoherent gap. The temperature dependence of the rate of resistivity change at the start of annealing 65 wt% Au-Pt agreed with spinodal decomposition theory or a nucleation mechanism.

Effect of Deformation on the Physico-mechanical Properties of an Alloy of Platinum with Silver

s. n. pavlova, Fiz.-khim. Mekhan. Mater., 1968, 4, (4), 490–492

Studies of the deformation of 0.1–3 mm Ag-Pt alloy wires after quenching from 1000°C showed that wires of different diameter had different tendencies towards work-hardening. 99% deformation was required to obtain high strength in a 0.1 mm wire but for wires 0.2 mm diameter even 99.8% deformation only produced a UTS of 170 kg/mm2.

Anomalous Low Temperature Susceptibility of Dilute Pt -Co Alloys

j. c. gallop and i. a. campbell, Solid state Commun., 1968, 6, (11), 831–833

Nuclear orientation measurements of the hyper-fine field at 60Co nuclei in Co-Pt as a function of applied field suggest the formation of a spin-compensated state at low temperatures.

Effect of Chemical Composition and Heat Treatment Conditions on the Magnetic Properties of High Coercivity Cobalt-Platinum Alloys

yu. a. gratsianov and a. g. rabin’kin, Sb. Tr. Tsent. Nauch.-Issled. Inst. Chern. Met., 1968, (54), 90–97

Tests on cast and homogenised samples of 24, 25, 26.16, and 29.5 wt% Co-Pt alloys showed that the highest magnetic properties are attained with cast samples, e.g. 24−25% Co-Pt has maximum magnetic energy 40 kJ/m3, Br = 7900 gauss, Hc = 3950 Oe. Hc decreases for >25% Co−Pt, i.e. highest magnetic properties occur for 23−25% Co-Pt, where concentration disordering is less important. Controlled cooling rates lead to more homogeneous and more dispersed structures due to prolonged keeping of samples at 770−830°C, the temperature favourable to nucleation.

Platinum-based Permanent-magnet Alloys

h. c. angus, Proc. Instn Elect. Eng., 1968, 115, (12), 1849–1852

Studies of changes of magnetic properties of PtCo and PtFc when part or all the Pt is replaced by Pd, Rh, Ir, and Ru with various preparations and heat treatments show that the pseudobinary alloys possess no better magnetic properties. Careful heat treatment of sintered and worked or of vacuum-melted PtCo gives energy products of 9.5 and 10.0 × 106 Gs-Oe, and coercive forces of 5.0 and 4.5 × 103Oe respectively.

Study of the Diffusion of Normal Hydrogen and of Hydrogen Enriched with Parahydrogen through a Palladium-Silver Membrane. Determination of the Activation Energies

l. fitoussi, C. r., Sér. C., 1968, 267, (26), 1742–1745

Activation energies measured during diffusion through 23% Ag-Pd were 4.9 kcal/g.atom (±10%) for normal H2 and 3.54 kcal/g.atom (±10%) for H2 enriched with parahydrogen.

Electrical Resistivity Measurements in Palladium-Hydrogen Alloys

c. t. haywood and l. verdini, Can. J. Phys., 1968, 46, (18), 2065–2071

Studies of Pd and Pd-H at 2−300°K show that at 10°K < T < 60°K the electrical resistivity ρ i ∝Tn, with n = 3.1 for pure Pd but n decreasing to 2.3 when H/Pd = 0.25. ρ i depends on time and rate of cooling at high H concentrations and low temperatures. Residual resistivity is lower for faster cooling. The increase in ρ i due to 1 at.% H2 in Pd is of the same order as that of inter-stitials in other f.c.c. metals but is less than for H2 in b.c.c. Ta and Nb at room temperature.

The Diffusion of Hydrogen in Cu3Pd Alloy

v. b. vykhodets, v. a. gol’tsov and p. v. gel’d, Fiz. Metal Metalloved., 1968, 26, (5), 933–935

Results are plotted and tabulated for studies of the activation energy Q for H2 diffusion in ordered and disordered Cu3Pd by measuring the rate of penetration p, the diffusion coefficient D and the solubility S.

Investigation of Alloys of the Pd2Al-Ag System

l. a. panteleimonov, d. n. gubieva and l. v. azikonda, Vest. moskov. Univ., Ser. II, Khim., 1968, 23, (6), 87–90

The phase diagram and microhardness of these alloys are depicted.

On the Relation of Spontaneous Magnetisation to Composition of the Ordered Alloys Fe(PtαPd1−α)3

s. k. sidorov, v. v. kelarev and a. i, kozlov, Fiz. Metal. Metalloved, 1968, 26, (5), 776–780

A theory is developed for magnetisation of the ordered Fe(PtαPd1−α)3 alloys in which ferro-magnetic-antiferromagnetic exchange reactions occur between the atomic components.

On the Nature of the Coercive Force and Structure of Equiatomic Iron-Palladium Alloys

l. m. magat, a. s. ermolenko, g. v. ivanova, g. m. makarova and ya. s. shur, Ibid., (3), 511–516

The maximum value of the coercive force of equiatomic Fe-Pd occurs in the single phase regulated state. The coercive force of hardened and annealed samples is explained by delay in ordering ferromagnetic domain boundaries at antiphase boundaries. At first the deformed samples after annealing are much more ordered than the hardened and annealed samples but crystallites of the tetragonal phase are so small that they appear to be the main factor determining the size of the coercive force.

Thin Films of Iron-Palladium Alloys with High Coercivity

ya. s. shur, l. m. magat, a. a. glazer, e. v. shcherbakova and n. n. shchegoleva, Ibid., (5), 938–939

Studies of FePd showed that the coercivity Hc is greatest when the crystallites of the alloy are smallest. It follows that a film, consisting of the smallest grain size of all, possesses the highest Hc. Thermal ordering increases the grain size and thereby decreases Hc.

The Surface Tension and Density of the Liquid Alloys Pd-Fe, Pd-Cr, Pd-Si

v. f. ukhov, e. l. dubinin, o. a. esin and n. a. vatolin, Zh. fiz. Khim., 1968, 42, (10), 2631–2634.

Liquid Fe-Pd alloys are nearly ideal. Isotherms of surface tension for molten Cr-Pd are smooth. In molten Si-Pd, molecular groupings in the ratio of the PdSi compound are maintained during isotherms of surface tension.

Alloys with Extra Specific Electrical Resistance and Low Temperature Coefficient of Resistance in a Wide Range of Temperature

m. p. ravdel’ and o. i. evdokimova, Sb. Tr. Tsent. Nauch.-Issled. Inst. Chern. Met., 1968, (54), 26–34

Alloying Ni with Mn-Pd does not alter the resistivity ρ or the temperature coefficient α of resistance of the alloy but annealing Mn-Pd-Ni at 300°C alters both ρ and α. 0.3 mm diameter rods of 65% Mn-15% Pd-15% Ni-5% Cu have: ρ = 2μohm.m, α = 3.10−5 per deg C at −60 to + 120°C, α = (7−8).10−5 per deg C at 120−300°, e.m.f. versus Cu E = 0.7 mV/deg C, σ = 62−68 kg/mm2, δ = 20−28%. Repeated heating and cooling between −60 and +300°C does not change their electrical properties. Protracted annealing at 300°C does not alter their structure or properties but at 500−600°C reduces ρ and leads to brittleness and decomposition.

Properties of Alloys of Manganese-Palladium, Manganese-Germanium, and Manganese-Gallium Systems

Ibid., 35–42

The search for a high-resistivity alloy showed that when quenching high Mn content alloys from the γ region a f.c. tetragonal lattice appears which upon alloying becomes f.c.c. Resistivity of Mn-Pd quenched from the γ region is higher than that of Mn-Cu or of Mn-Ni. Resistivity ρ of 20−32.7% Pd-Mn varies slightly with temperature at 0−350°C. ρ decreases abruptly above 350°C for all Pd-Mn alloys and dilatometric curves indicate a phase transformation at 350°C.

A Palladium-Magnesium Alloy Phase of Co2Al5 Type

l. westin, Acta. Chem. Scand., 1968, 22, (8), 2574–2580

X-ray studies of hexagonal PdMg∼2·5 give dimensions a = 8.646−8.660 Å and c = 8.175−8.169 Å. The phase has a range of homogeneity.

The Structure of the PuPd Compound

a. v. beznosikova, e. s. smotritskaya and n. t. chebotarev, Atomnaya Energ., 1968, 25, (5), 430–431

Pu5Pd4 has lattice parameters a = 7.028±0.005, b = 4.571±0.001, c = 5.658±0.002 Å. Interatomic distances have been determined and are tabulated and a model is depicted.

Magnetic Susceptibility of Alloys of Plutonium with Palladium

n. t. chebotarev, yu. n. sokurskii, m. a. andrianov and a. a. ivanov, Ibid., 431–433

Magnetic susceptibilities of Pu-Pd alloys are tabulated and shown in graphical form.

Thermomagnetic Measurements on Alloys of the Platinum Metals with Chromium

a. kussman, k. müller and e. raub, Z. Metallkunde, 1968, 59, (11), 859–863

Alloys of Pt metals with Cr which have similar structures have similar magnetic properties. F.c.c. L12 phases of Cr with 25−30 at.% Pt, Pd or Ir have a distinct maximum of magnetisation with typical ferromagnetic behaviour. Saturation magnetisation at −193°C is ∼0.39 Vs/m2 for Pt, ∼0.15 Vs/m2 for Pd, ∼0.06 Vs/m2 for Ir and the respective Curie points are 900, 400 and 170°C. Tetragonal PdCr with L10 structure is weakly ferromagnetic. Rh-Cr, Ru-Cr and Os-Cr possess no L12 structure and are very weakly ferromagnetic. F.c.c. solid solutions rich in Cr are anti-ferromagnetic with high Néel points.

CHEMICAL COMPOUNDS

Mass Spectrometric Determination of the Dissociation Energies of Gaseous RuC, IrC and PtB

n. s. mcintyre, a. vander auwera-mahieu and j. drowart, Trans. Faraday Soc., 1968, 64, (11), 3006–3010

RuC, IrC and PtB molecules have been detected with dissociation energies D0° (RuC) = 151.0±3.0, D0°(IrC) = 148.4±3.0, Do°(PtB) = 113.3±4.0 kcal/mole.

Preparation and Properties of Some Ternary Selenides and Tellurides of Rhodium

r. h. plovnick and a. wold, Inorg. Chem., 1968, 7, (12), 2596–2598

MRh2X4, where M is Cr, Co, Ni and X is Se, Te, and Rh3Te4 have the monoclinic Cr3S4-type structure with space group I2/m, except for CoRh2Te4 and NiRh2Te4, which are trigonal with space group The symmetry of these compounds with defect NiAs structure depends on whether metal ion vacancies are ordered or randomly arranged in alternate metal layers.

Reversible Activation of Covalent Molecules by Transition Metal Complexes. The Role of the Covalent Molecule

l. vaska, Accounts chem. Res., 1968, 1, (11), 335–344

A review of recent work on the mechanism of reactions involving Ir and Rh complexes. Data discussed are from determinations of the role of the reacting gas by studies of a series of reactions of one metal complex MLi with a variety of addenda, and by comparison of kinetic, equilibrium and thermochemical data from these reactions and the electronic and geometric properties of the corresponding adducts ((XY) MLi).

Thermal Decomposition of Rhodium, Iridium, and Ruthenium Chlorides

a. e. newkirk and d. w. mckee, J. Catalysis, 1968, 11, (4), 370–377

Decomposition studies of RhCl3, IrCl3 and RuCl3 hydrates in air and in H2 were studied by thermo-gravimetric analysis and reduction studies were made for dispersions on low- and high-area substrates. Reduction to the respective metals was complete at 105, 190, and ∼350°C. In air, dechlorination and oxidation was complete at 890, 680 and ∼440°C respectively. B4C, which has low area, has little effect on the reduction temperature of the Rh salt but Al2O3, which has high area, is associated with desorption of decomposition products.

The Metallic Nature of Osmium Dioxide

j. e. greedan, d. b. willson and t. e. haas, Inorg. Chem., 1968, 7, (11), 2461–2463

Single crystals of OsO2 were prepared and electrical conductivity and Hall effect measurements were made. The data can be rationalised on the basis of a wholly collective electron approach involving the concepts of narrow bands and high density of states which are often encountered in the transition metals and their compounds.

ELECTROCHEMISTRY

Hydrogen Adsorption Equilibrium on Platinum Electrodes

i. telcs and m. jáky, Acta Chim. Acad. Sci. Hung., 1968, 58, (3), 275–285

A review of experimental evidence and theory of H2 adsorption equilibrium on Pt electrodes shows that most probably the observed effects are due to the several states of H2 adsorption on Pt, all of which obey the Langmuir adsorption isotherm to a good approximation. There are probably such states.

Diffusion Coefficient of Hydrogen in Palladium Alloy Electrodes

j. bersier and a. küssner, U.S. Rept N68–33984, 1968, 9pp

Diffusion coefficient of H2 in 23% Ag-Pd alloy and in this alloy with 0.5, 0.9, 2.0 and 3.0 at.% B additions was determined as a function of H2 concentration and temperature at 30−300°C and varies with H2 concentration as D(C) = 12B [RT + C(1−C)d/dC(∆μH(C))].

On the Behaviour of a Ruthenium Electrode-catalyst in Solutions of Sulphuric and Oxalic Acid at Various Temperatures

r. b. taran and g. p. khomchenko, Vest, moskov. Univ., Ser. II, Khim., 1968, 23, (6), 83–86

The rate of catalytic hydrogenation of CH3NO2 on Ru was ∼ twice that of electrochemical reduction but the difference decreased as the temperature rose.

Catalytic and Electrochemical Reduction of Nitromethane on Ruthenium Electrode-catalyst

l. p. mashkova, a. i. pletyushkina and g. p. khomchenko, Ibid., 104–106

Further studies of these reactions in 0.1 N H2SO4.

LABORATORY APPARATUS AND TECHNIQUE

Correction for Temperature Loading and High Gas Pressure Effects for the Constant-temperature Hot-wire Anemometer

h. hassan and j. c. dent, Br. J. appl. Phys., J. Phys. D., 1969, 2, (1), 85–92

Tests on Pt and 30% Ir-Pt wires enabled a calibration curve to be plotted for a constant-temperature hot-wire anemometer using the alloy at high temperature in a high-temperature and high-density gas flow. The temperature coefficient of resistance for 30% Ir-Pt was determined and also its thermal conductivity.

Electrolytic Cell with a Rotating Double Ring Electrode for High Frequencies in the Measurement of Fast Reactions

g. trimborn, a. heindrichs and w. vielstich, Messtechnik, 1968, 76, (9), 224–229

The construction of a double ring Pt electrode system is described together with requirements for its use at high speeds of rotation.

BRAZING AND WELDING

Bits for Soldering Irons

h. c. angus, r. d. berry and b. jones, Engng Mater. Design, 1968, 11, (12), 1965–1968

The suitability of Ru for the bits of soldering irons is limited by its cost and so methods have been developed to localise it on bit surfaces and also to protect the non-functional shank surfaces. The most promising tipped bit has an Al shank to which is welded Ru facing.

HETEROGENEOUS CATALYSIS

UOP Catalyst Improves Yield of Aromatics

Eur. chem. News, 1969, 15, (361, Jan. 3), 34

Reduced operating pressures are claimed at high severity conditions without loss of stability for U.O.P.’s new R-16 Platforming catalyst. Improved product distribution selectivity at lower pressures permits dehydrocyclisation of paraffins and dehydrogenation of naphthenes to create aromatics with a minimum of hydrocracking to light hydrocarbons, i.e. yield of motor fuel reformate of a given octane number is higher at lower operating pressures. The aromatics-creating reactions are favoured by lower pressures. Plants which have switched to this catalyst have not yet taken full advantage of R-16 because of their different operating pressures. See also Chem. W., 1969, 104, (2), 60–61.

Results of Testing of Platinum on Alumina Catalysts by Hydrogenating Benzene to Cyclohexane

yu. i. kozorezov and n. m. pikalo, Khim. Promyshlennost’, 1968, (11), 821–822

C6H6 hydrogenation tests using a modified Pt/Al2O3 catalyst showed that the latter is extremely active, selective and stable, and is suitable for industrial use.

Investigation of the Conversion of Cyclo-hexene on Pt-Zeolite Catalyst under Pressure of Hydrogen

v. i. garanin, u. m. kurkchi and kh. m. minachev, Kinet. Kataliz, 1968, 9, (5), 1080–1085

Studies of cyclohexene and cyclohexane isomerisations on decationised zeolite, on CaY and on 0.5% Pt/CaY show that on Pt/CaY the isomerisation of cyclohexane proceeds via formation of cyclohexene on Pt with subsequent isomerisation on the acid centres of the zeolite. The isomerisation of cyclohexene depends on temperature.

The Effect of Heat Treatment on the Catalytic Activity of Platinum Catalysts

s. a. khassan, s. g. fedorkina, g. i. emelyanova and v. p. lebedev, Zh. fiz.Khim., 1968, 42, (10), 2507–2512

Sintering studies on Pt black in vacuum at 300, 400, 500, 600 and 700°C indicate a second order relation between changes in the activity and surface area. Sintering produces a fixed activity and surface area for each temperature. The relation between activity and roasting temperature is exponential. Given the activity at two temperatures, an equation relating activity to temperature can be derived. Kinetics of decomposition of H2O2 and of hydrogenation of cyclohexene on sintered black are similar. Specific activity is unrelated to the duration and temperature of sintering but change of surface area and size of crystals are.

Hydroisomerisation of Normal Pentane over a Zeolite Catalyst

a. voorhies and p. a. bryant, A.I.Ch.E.J., 1968, 14, (6), 852–856

A series of screening tests on zeolite hydroisomerisation catalysts showed that the most active is Pd/hydrogen mordenite. Typical test conditions were 550°F, 450 lb/in2, H2:C5H12 = 3.4, 8 g n- C5H12/h.g. catalyst. Neither gas to particle mass transfer, nor macropore diffusion nor chemical reactions at Pd sites are rate-limiting.

Hydrogenation and Hydrogenolysis. X. The Hydrogenation of Methoxy- and Ethoxy-anilines with Rhodium Catalyst

s. nishimura, h. uchino and h. yoshino, Bull. Chem. Soc. Japan, 1968, 41, (9), 2194–2195

Hydrogenation of alkoxyanilines with alkali-promoted Rh catalysts showed that Rh oxide prepared by fusion of RhCl3 with LiNO3 gives high yields of methoxy- and ethoxycyclohexylamines from methoxy- and ethoxyanilines respectively. <6% hydrogenolysis occurred and secondary amine formation was negligible. Studies with LiNO3 replaced by NaNO3, LiOH and NaOH are reported and less satisfactory yields were obtained. Best conditions appear to be 90°C, high , and use of LiNO3 with RhCl3 when ∼2% catalyst: substrate is required.

Hydrogenation of Olefins. Part 4. Reaction of n -Butenes with Hydrogen Catalysed by Alumina-supported Ruthenium and Osmium

g. c. bond, g. webb and p. b. wells, Trans. Faraday Soc., 1968, 64, (11), 3077–3085

Studies in a static system of product distributions, orders of reaction and activation energies for hydrogenation and isomerisation of but-1-ene, cis- and trans -but-2-ene at 0−70°C using 1 mol.% Ru/α-Al2O3 and at 60−140°C using 1 mol.% Os/α-Al2O3 show that Ru gives more isomerisation than Os. The suggested mechanism is isomerisation by loss of one H atom from adsorbed C4H9 to yield adsorbed C4H8 and H, and hydrogenation where the rate is determined by H addition to adsorbed C4H9 for each C4H8. Rate-determining steps for cis-trans isomerisation and double-bond migration are discussed.

The Hydrogenation of Alkadienes. Part II. The Hydrogenation of Buta-1,3-diene Catalysed by Rhodium, Palladium, Iridium, and Platinum Wires

p. b. wells and a. j. bates, J. Chem. Soc., A, inorg. phys. theor., 1968, (12), 3064–3069

Studies of buta-1,3-diene hydrogenation over Rh, Pd, Ir, and Pt wires showed that C4H8 compositions depended on temperature but not on activity, initial or conversion up to 50%. C4H10 yield was zero on Pd and 1−15% on the other wires. But-1-ene was the main product; trans-cis ratios for but-2-ene were determined. Chemisorption of buta-1,3-diene by interaction of only one double bond became more important as the temperature rose. Hydrogenation activity of clean Ir was replaced by hydrogenolysis as C residues accumulated on it. CH4 was the sole product of hydrogenolysis at 245°C on Ir of C4H8-1, C5H10-1, etc. Comparing wires with Al2O3-supported catalysts, reactions seem characteristic of the metal rather than of the type of catalyst.

HOMOGENEOUS CATALYSIS

Homogeneous Catalysis in the Reactions of Olefinic Substances. XI. Homogeneous Catalytic Hydrogenation of Short-chain Olefins with Dichlorobis-(triphenylphosphine)platinum(II)-Tin(II) Chloride Catalyst

r. w. adams, g. e. batley and j. c. bailar, J. Am. Chem. Soc., 1968, 90, (22), 6051–6056

Studies of homogeneous hydrogenation of short-chain olefins with PtCl2(PPh3)2 and SnCl2. 2H2O catalyst mixtures showed that mono-olefins hydrogenate rapidly only when the double bond is terminal. Reduction of hexadiene and pentadiene isomers does not stop necessarily at the monoene stage. Dienes react most when both double bonds are terminal. Conjugation is not a necessary step before hydrogenation; short-chain conjugated diene isomers inhibited further reaction. Long-chain conjugated dienes are reduced since their larger size prevents formation of stable catalyst-diene complexes. Unsaturated nitriles are hydrogenated when the double bond is terminal; substituent groups on the β-C atom do not hinder this and the CN group remains intact.

A Palladium-catalysed Synthesis of Benzyl Esters from Methylbenzenes

d. r. bryant, j. e. mckeon and b. c. ream, J. org. Chem., 1968, 33, (11), 4123–4127

Liquid phase production of benzyl esters from methylbenzenes takes place at moderate temperatures using Pd(OAc)2-Sn(OAc)2 catalyst and 1 atm air, e.g. toluene in CH3COOH gives benzyl acetate. The secondary oxidation product benzylidine diacetate is formed at high conversions. Other methylbenzenes behave similarly. Xylenes undergo selective diacetoxylation in CH3COOH to give α,α′-diacetates rather than α,α-di-acetates.

Palladium-catalysed Reactions of Unsaturated Compounds in Non-aqueous Solvents. Synthesis of Vinyl Acetate via Palladium Salt/Ethylene Complexes

r. van helden, c. f. kohll, d. medema, g. verberg and t. jonkhoff, Rec. Trav. chim. Pays-bas, 1968, 87, (10), 961–991

The rate of the reaction of C2H4 with Pd(OAc)2 in CH3COOH to produce vinyl acetate increases considerably on addition of small amounts of NaOAc, LiCl or LiCl, Fe(OAc)3 to the system. The reaction is first order with respect to both Pd(OAc)2 and the additions. When using PdCl2 and NaOAc the rate is proportional to them.

Catalytic Asymmetric Hydrogenation Employing a Soluble, Optically Active, Rhodium Complex

w. s. knowles and m. j. sabacky, Chem. Commun., 1968, (22), 1445–1446

A catalyst precursor which contains optically active tertiary phosphine ligands is prepared by dissolving RhL3Cl3 complexes with L = tertiary phosphine in 1 : 1 v/v C6H6 : C2H5OH containing triethylamine and pressurising with H2. Examples of its use are described.

Catalysis of Hydrogen Transfer by a Method Hypothetically Similar to Fermentation. VI. High-activity Hydrogenation Catalysts on the Basis of π-Complexes of Rhodium(I) with Amino Acids

o. n. efimov, m. l. khidekel’, v. a. avilov, p. s. chekrii, o. n. eremenko and a. g. ovcharenko, Zh. obshch.Khim., 1969, 38, (12), 2668–2677

Studies of Rh complex catalysts with N-phenyl-anthranilic acid and L-tyrosine showed that low-valent compounds are stabilised at the expense of reactions with aromatic rings and carboxyl groups. Both in solid and solution states the complex is supposedly the dimer H[Rh2(phen)2Cl] but H decomposes it to the monomer. The Rh complexes catalyse D exchange with H2O. A hydrogenation mechanism for trans -stilbene is suggested. H2 is derived during hydrogenations of fumaric acid and acetylene derivatives by the cis -scheme.

Selective Homogeneous Hydrogenation of Alk-l-enes Using Hydridocarbonyltris-(tri-phenylphosphine)rhodium(I) as Catalyst

c. o’connor and g. wilkinson, J. Chem. Soc., A, inorg. phys. theor., 1968, (11), 2665–2671

RhH(CO)(PPh3)3 efficiently catalyses homogeneous hydrogenation of unsaturated RCH = CH2 compounds. For hex-1-ene and dec-1-ene in C6H6 solution the rate law is rate = k1 K1 c [S][A]/(1 + K1[S]), where [S] and [A] are respective concentrations of alk-1-ene and catalyst, C is H2 concentration in solution, K1 is the formation constant for an alkene intermediate complex, and k1 is the rate constant for the rate-determining H2 activation step. High selectivity for reduction of alk-1-ene is due to steric factors caused by the bulky triphenylphosphine groups.

Hydroformylation of Alkenes by Use of Rhodium Complex Catalysts

d. evans, j. a. osborn and g. wilkinson, Ibid., (12), 3133–3142

The inhibition period of trans -RhX(CO)(PR3)2 catalysts, where X = halogen and R = aryl, is removed by addition of hydrogen halide acceptors and the halide complex forms a hydrido-species by hydrogenolysis. The principal catalytic species seems to be RhH(CO)2(PPh3)2 formed by CO addition to RhH(CO)(PPh3)2, which is also formed by dissociation when RhH(CO)(PPh3)3 is dissolved in C6H6 or other solvents. Rapid hydroformylation of alkenes occurs at 250°C, 1 atm with RhH(CO)(PPh3)3 catalyst, giving a ratio of ∼20 for the formation of straight- and branched-chain aldehydes from alk-1-enes. H exchange and isomerisation of alkenes with RhH(CO)(PPh3)3 are described.

The Preparation and Reactions of Hydrido-chlorotris(triphenylphosphine)ruthenium(II) Including Homogeneous Catalytic Hydrogenation of Alk-1-enes

p. s. hallman, b. r. mcgarvey and g. wilkinson, Ibid., 3143–3150

RuClH(PPh3)3.C6H6 was prepared from RuCl2 (PPh3)3 and H2 in ambient conditions in the presence of a base such as triethylamine. RuBrH (PPh3)3.C6H6, RuClH(C7H8)(PPh3)2, [RuClH (bipyr)(PPh3)2]2, and RuH3(CO)(PPh3)3 were also prepared. RuClH(PPh3)3 is the most active catalyst yet discovered for homogeneous hydrogenation of alk-1-enes in C6H6 or C6H5.CH3. It is highly specific but kinetic study is difficult and slow poisoning occurs.

Carbonylation of Acetylene with [Ru(CO)4]3 as Catalyst

p. pino, g. braca, g. sbrana and a. cuccuru, Chem. & Ind., 1968, (49, Dec. 7), 1732–1733

Hydroquinone was prepared by carbonylation of C2H2 under anhydrous conditions, in either tetra-hydrofuran or dioxan as solvent, in the presence of [Ru(CO)4]3. Highest yields occurred at Yields up to 65% hydroquinone were obtained by reacting C2H2 with CO and H2O or alcohols in the presence of [Ru(CO)4]3 at 150−250°C and relatively low pco.

FUEL CELLS

Electrocatalysts for the Direct Electrochemical Oxidation of n -Octane in Fuel Cells

e. j. cairns and j. paynter, J. Electrochem. Soc., 1968, 115, (12), 1218–1224

Activity of supported and unsupported Pt prepared in various ways was compared with that of commercial Pt black. An increase in the specific area of a C substrate gave a corresponding increase in electrocatalytic activity up to at least 200 m2/g. Some types of Pt/C had 6–18 times the activity of Pt black. No current or voltage cycling occured with 36 mol.% HF electrolyte at 105°C in contrast to other acid electrolytes.

Structure and Performance of Hydrophobic Gas Electrodes

a. d. d. tantram and a. c. c. tseung, Nature, 1969, 221, (5176, Jan. 11), 167–168

Electron micrography showed that a catalyst prepared by mixing Pt black with a dispersion of PTFE and applying it to a metal screen before drying and curing at 300°C consists of porous aggregates of Pt intermingled with PTFE. Performance is very dependent on microstructure. Whereas hydrophilic electrodes become flooded with electrolyte hydrophobic electrodes become full of gas and the whole thickness of the electrode is effective. The effect of catalyst surface area was studied using graphite powder as the catalyst.

CHEMICAL TECHNOLOGY

The Separation of Hydrogen from Ammonia Synthesis Exhaust Gases by the Method of Diffusion through Palladium

yu. k. baichtok, m. b. aizenbud, v. a. kurkovskii, a. s. furmanov, i. ya. azbel’ and z. v. korbutova, Khim. Promyshlennost’, 1968, (10), 744–746

NH3 synthesis is more economic when H2 in the exhaust gas is purified and when Ar is recovered. Tests on such gas and on pure N2-H2 mixtures compared pure Pd and 5% Ni-10% Ag-Pd foils for H2 purification by diffusion at 400 and 500°C. Both gas mixtures gave similar results. Ag dusted on Pd foil activated the latter for H2 diffusion.

TEMPERATURE MEASUREMENT

The Effect of Stress on the Thermal EMF of Platinum-Platinum/13% Rhodium Thermocouples

e. s. morgan, Br. J. appl. Phys., J. Phys. D, 1968, 1, (11), 1421–1429

Variations in thermal e.m.f. with stress of Pt and 13% Rh-Pt wires with junctions at 20 and 550°C are −47 and −12 pV deg C−1kg−1cm−2 respectively. The thermal e.m.f. hysteresis loop of some metal-sheathed mineral-insulated thermocouples is explained; the maximum discrepancy from this loop is 23μV at 550°C by calculation, 14μV by experiment on a single thermocouple. Mechanical hysteresis of the loop may cause fracture. A reliable thermocouple of this type needs matching expansion coefficients of sheath and thermocouple.

Comparison of Platinum Resistance Thermometers between 63K and 373.15K. Part I. Part II

m. r. m. moussa, h. van dijk and m. durieux, Physica, 1968, 40, (1), 33–48, 49–60

Twelve Pt resistance thermometers were compared with a reference one at 63–273.15°K and at 373.15°K using a constant temperature bath with the thermometers inserted in a Cu block immersed in liquid iso -C5H12, C3H8, O2, or N2 and the differences of the reduced resistances W = R(t)/R(O°C) of them were determined. The number of calibration points to determine the W-T relation was studied and discussed.

A Direct-reading Bridge for a Platinum Resistance Thermometer

c. w. van der wal and l. c. e. struik, J. sci. Instrum., J. Phys. E, 1969, 2, (2), 143–145

A Wheatstone bridge for a Pt resistance thermometer was modified so that the angle of rotation of a linear potentiometer is proportional to the temperature with bridge sensitivity fairly independent of temperature. Although not intended for high precision thermometry, irrespective of the inaccuracy of the thermometer itself the reading accuracy is to better than ±0.1 deg C at 0−500°C and the bridge can be used for both temperature control and temperature measurement.

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