Showing papers on "Catalysis published in 1968"
TL;DR: The use of complexes of rhodium of the type trans-RhX(CO)(PR3)2, (X = halogen, R = aryl) as hydroformylation catalysts for alkenes is studied in this paper.
Abstract: The use of complexes of rhodium of the type trans-RhX(CO)(PR3)2, (X = halogen, R = aryl) as hydroformylation catalysts for alkenes is studied. It is shown that an inhibition period is removed by addition of hydrogen halide acceptors and that the halide complex undergoes hydrogenolysis to form a hydrido-species. The hydrido-species is only one of several complexes in equilibrium but it appears that the principal active catalytic species is RhH(CO)2(PPh3)2. This species is formed by addition of carbon monoxide to the monocarbonyl complex RhH(CO)(PPh3)2. The latter is also formed by dissociation when the stable crystalline complex RhH(CO)(PPh3)3 is dissolved in benzene or other solvents. With RhH(CO)(PPh3)3 as catalyst, alkenes undergo rapid hydroformylation even at 25°/1 atm.; with alk-1-enes the ratio of straight- to branched-chain aldehyde formed is considerably higher than the ratios normally found in hydroformylation reactions, being ca. 20 at 25°. Hydrogen atom exchange and isomerisation reactions of alkenes with RhH(CO)(PPh3)3 are described.
483 citations
TL;DR: In this paper, the surface area and hydrogen chemisorption measurements made on palladium-black samples were used to determine surface areas of particles of a size where other techniques, such as electron microscopy, X-ray linebroadening and small-angle scattering, often fail through interference of the support.
228 citations
TL;DR: In this paper, supported platinum consisting of 15-A crystallites has been prepared by reduction of platinum ammine ions adsorbed on the surface of silica gel, which has been carried out by hydrogen chemisorption, X-ray diffraction, and electron microscope techniques.
187 citations
TL;DR: In this paper, the surface state changes in supported chromia catalysts were studied and a method was extended to determine the oxidation state of the surface in situ during reaction, and a tentative explanation was offered for the selectivity for oxygen over nitric oxide in the oxidation-reduction reactions on commonly employed catalysts.
184 citations
TL;DR: Catalytic amounts of o -phenanthroline were found to enhance the rate of air-oxidation of all sulfhydryl groups tested in the presence of copper ions at neutral pH, and the interpretation is discussed that o-phenan Throline necessarily acts as a metal chelator in the inhibitory action of this reagent on any enzyme.
184 citations
TL;DR: In this paper, the reaction of neopentane on supported platinum and platinum powder catalysts has been obtained at 300 °C, 1 atm total pressure, and a hydrogen-to-neopentanes ratio of 10.
180 citations
TL;DR: In this article, carbon dioxide chemisorption studies at 0 °C were used to determine the relative basicities of alkali-promoted reduced magnetite catalysts, showing that a higher surface basicity correlates with a lower methane selectivity in the Fischer-Tropsch synthesis.
175 citations
TL;DR: The most active catalyst for homogeneous hydrogenation of alk-1-enes in benzene or toluene solution is the complex RuClH(PPh3)3.
Abstract: The complex hydridochlorotris(triphenylphosphine)ruthenium(II) as a benzene solvate, RuClH(PPh3)3,C6H6, has been obtained by the interaction of the dichloride, RuCl2(PPh3)3, with molecular hydrogen at ambient temperature pressure in the presence of a base such as triethylamine; other preparative methods are described. The corresponding bromide, RuBrH(PPh3)3,C6H6, has been prepared. From the chloride by interaction with norbornadiene and 2,2′-bipyridyl, the complexes RuClH(C7H8)(PPh3)2 and [RuClH(bipyr)(PPh3)2]2 respectively have been obtained; the complex RuH2(CO)(PPh3)3 has also been prepared.The complex RuClH(PPh3)3 is the most active catalyst yet discovered for the homogeneous hydrogenation of alk-1-enes in benzene or toluene solution. The interaction is highly specific and rates for other types of alkene are slower by a factor of at least 2 × 103. The inherent difficulties of the system however preclude detailed kinetic study and it is shown that slow poisoning of the catalyst occurs under hydrogenation conditions.N.m.r. studies of the hydrido-complex and its deuteride have allowed hydrogen atom exchange studies to be made. Isomerisation of alkenes is studied. The slow exchange between molecular hydrogen and the α-proton of a phenyl group on the phosphine is demonstrated.
169 citations
TL;DR: Cobalt carbonyl complexes containing a complementary tertiary phosphine, arsine or phosphite ligand, e.g., [Co(CO)3PBu3]2, have catalytic properties for the hydroformylation of olefins which are considerably different from those of dicobalt octacarbonyl.
168 citations
145 citations
TL;DR: In this article, a new method to prepare Bi 2 O 3 -MoO 3 catalysts consisting in boiling slurries of mixtures of freshly prepared and thoroughly washed bismuth hydroxide and molybdic acid has been developed.
TL;DR: In this paper, the effects of acid, PbIV and catalysts on the rates of decarboxylation and conversions of acids are examined and a convenient preparation of ω-alkenoic acids from dibasic acids such as 6-heptenoic acid from suberic acid is described.
TL;DR: In this article, the specific catalytic activity of rhenium and technetium was investigated for hydrogenation of benzene to cyclohexane. But the performance of the catalysts was not analyzed.
TL;DR: In this article, the authors studied the chemisorption of hydrogen sulfide on some nickel catalysts in the temperature range 550-645 °C and showed that a saturation layer was formed at ratios above 5 × 10−6, approximately, and at ratios at 10−3 bulk sulfide (Ni2S3) was formed.
TL;DR: In this article, the intrinsic kinetics of the hydrogenolysis of thiophene on a cobalt molybdate catalyst were studied in a differential reactor with recirculation, at a total pressure of about 1 atm. and temperatures of 235° to 265°C.
Abstract: The intrinsic kinetics of the hydrogenolysis of thiophene on a cobalt molybdate catalyst were studied in a differential reactor with recirculation, at a total pressure of about 1 atm. and temperatures of 235° to 265°C. Retardation of the reaction by both thiophene and hydrogen sulfide was significant and the rate of thiophene disappearance was correlated by a Langmuir-Hinshelwood type of kinetic equation. Hydrogenation of the butene intermediate was inhibited by both butene and hydrogen sulfide and the rate of this reaction was also described with a Langmuir-Hinshelwood rate equation. The forms of the kinetic expressions obtained imply that the butene is not hydrogenated at the original desulfurization site.
TL;DR: In this article, it is shown that the substrate which reduces slowest as a single substrate can be hydrogenated preferentially in a mixture of unsaturated substances, and the degree of selectivity achieved can be enhanced by the addition of polar solvents.
Abstract: When mixtures of unsaturated substances, or compounds containing multiple sites of unsaturation are hydrogenated using RhCl(PPh3)3 as catalyst, it is possible that the substrate which reduces slowest as a single substrate can be hydrogenated preferentially in the mixture. The degree of selectivity achieved can be enhanced by the addition of polar solvents, the effects of which are discussed. The degree of participation of the two kinetically indistinguishable forward routes, i.e., via substrate attack on a hydrido intermediate, or hydrogen attack on a substrate intermediate, may also be of importance in determining the degree of selectivity achieved.
TL;DR: The effect of adding 20-50% H2 to active nitrogen has been studied at both 196 and 320° K in this paper, where the consumption of both nitrogen atoms and oxygen atoms was followed photometrically and the results yields a ration k8/k9-1.4± 0.1 at 320° k.
Abstract: The effect of adding 20–50 % H2 to active nitrogen has been studied at 196 and 320° K. At neither temperature is there a primary reaction but when the nitrogen atoms are partially titrated with nitric oxide at 320° K, a catalytic removal of atoms is induced involving the reactions : O + H2= OH + H (5), N + OH = NO + H (8), N + NO = N2+ O (1), O + OH = O2+ H (9), with (5) rate controlling. The consumption of both nitrogen atoms and oxygen atoms was followed photometrically and the results yields a ration k8/k9– 1.4±0.1 at 320° K. The rate constant k5 was (1.2 × 0.1)× 107cm3 mole –1 sec–1at 320° K in separate experiments. The role of H2 as a third body in the recombination reactions of nitrogen and oxygen atoms has been examined at 196° K where reaction (5) is unimportant.
TL;DR: In this paper, the influence of chemical structure of the hydrocarbon molecule on the catalytic process is discussed, and the conditions required for heterogeneous thermal ignition are studied. But the results of the analysis are limited.
DSM1
TL;DR: In this article, it was found that SnO 2, contacted around 450 °C with a gas saturated with MoO 2 (OH) 2, sorbs MoO 3 (or a hydrated form) to its surface.
TL;DR: The decomposition of rhodium, indium, and ruthenium chloride hydrates in air and in hydrogen has been studied by means of thermogravimetric analysis; additional studies have been made of their reduction when dispersed on low and high-area substrates as discussed by the authors.
DSM1
TL;DR: In this article, it was shown that the reaction rate of SO2 on a sodium-potassium-vanadium catalyst also proceeds via rapid establishment of the equilibrium, SO2 + 2V5+ + O2− SO3+ 2V4+ (equilibrium constant K) and the reaction of oxygen with V4+ is the rate determining step.
TL;DR: In this article, the stereochemistry and mechanism of hydrogenation of naphthalenes on transition metal catalysts is discussed, as a stepwise process of two-by-two additions of hydrogen.
Abstract: Publisher Summary This chapter discusses the stereochemistry and mechanism of hydrogenation of naphthalenes on transition metal catalysts. The chapter discusses the mechanism of saturation of naphthalene, as a stepwise process of two-by-two additions of hydrogen. The reaction scheme gives no hint of the mechanisms of adsorption and desorption, the extent and manner of the hydrogen exchange that always accompanies saturation, and whether each pair of hydrogen is added simultaneously or in separate steps. The hydrogenation of naphthalene to decalins has been known to proceed by way of tetralin as an intermediate. Two kinds of mechanisms have been proposed for formation of trans-decalin. One suggestion is that trans isomers may be formed by direct trans addition of hydrogen at the two bridgehead positions. The other mechanism involves cis addition in a more complicated process that involves turning over of some sort of intermediate, with or without intervening desorption.
TL;DR: In this article, the spectroscopic and magnetic properties of a fresh (i.e., unsulphided) cobalt-molybdenum-alumina hydrodesulphurization catalyst are reported and compared with the properties of the above compounds in order to determine the chemical and structural environment of cobalt and moly bdenum in the catalyst.
Abstract: The u.v., visible, and i.r. spectra of the following compounds containing cobalt, molybdenum, and aluminium in tetrahedral and octahedral co-ordination in oxide lattices, and the magnetic susceptibilities over the temperature range 80–380°K of the first four compounds are reported: hydrated cobalt molybdate, calcined cobalt molybdate (CoMoO4), cobalt(II) molybdenum(IV) oxide (Co2Mo3O8), cobalt aluminate, cobalt(II) oxide, cobalt(II,III) oxide (Co3O4), sodium molybdate, ammonium paramolybdate, molybdenum trioxide, and γ-alumina. The spectroscopic and magnetic properties of a fresh (i.e., unsulphided) cobalt–molybdenum–alumina hydrodesulphurisation catalyst are reported and compared with the properties of the above compounds in order to determine the chemical and structural environment of cobalt and molybdenum in the catalyst. Cobalt is present as cobalt(II), approximately 50% in octahedral co-ordination and 50% in tetrahedral co-ordination by oxide. There is very little magnetic interaction between the cobalt ions which are well dispersed in the catalyst. Molybdenum is present as molybdenum(VI) in tetrahedral co-ordination by oxide. There is no evidence for the presence in the catalyst of Co3O4 or any well defined compound of cobalt, molybdenum, or aluminium. The relevance of the results to the preparation of the catalyst is discussed.