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The exchange reaction between cyclohexane and deuterium gas and the reactions of dehydrogenation and hydrogenolysis in the presence of deuterium have been investigated over a wide range of temperature on platinum and nickel powder catalysts. The results are as follows: 1. i. In the temperature range 30–100 °C only deuterium exchange takes place. The activation energies are the same for both catalysts although the rate of exchange is about one order of magnitude higher on Pt than on Ni. 2. ii. Between 100 and 200 °C poisoning occurs due to extensive decomposition. This effect is characteristic of nickel and causes a decrease of two orders of magnitude in catalytic activity but leaves the activation energy unchanged. 3. iii. Above 200 °C besides exchange other reactions commence and result in the formation of n-hexane, benzene and toluene on Ni and benzene on platinum. In this temperature range the deuterium appears in equilibrium distribution not only in the products but in the parent molecule. It seems very likely that at high temperature the dissociative adsorption is not rate controlling and thus the exchange and the chemical transformation are controlled by the desorption and by the surface reaction, respectively.

Adsorption and hydrogenation of ethylene, 1-hexene, and benzene, and carbon monoxide adsorption on alumina-supported Pt and PtSn catalysts were studied. Gravimetric experiments and infrared (IR) absorption spectroscopy combined with chemisorption measurements were used for this purpose. Additionally fresh and coked catalysts were characterized by the IR spectra of CO and chemisorption data. Added tin causes a slight increase in benzene adsorption and a distinct decrease in ethylene and 1-hexene uptakes, whereas the hydrogenation activity is inhibited. Adsorption and catalytic data with benzene can be explained by a model of flat adsorption on Pt Al 2 O 3 and tilted adsorption on Pt-Sn Al 2 O 3 and are consistent with electronic modification of platinum by tin. Electronic interaction between platinum and tin is also indicated by the IR data. The most active sites for hydrocarbon decomposition on the platinum surface are the same as those on which carbon monoxide is multiply bonded. Deposited coke and tin block the same active sites on the platinum surface.

Pd-Based catalysts are used for the selective hydrogenation of alkynes and alkadienes to the corresponding alkenes on a large scale. Addition of Pb and Zn (Lindlar type catalysts) to Pd, and alloying of Pd with Ag, Cu, Pb improve the selectivity of alkyne hydrogenation. The presence of organic bases organic sulfides, or CO in the reaction mixture is known to inhibit hydrogenation of the alkene formed. Although structure sensitivity in alkene hydrogenation has been systematically investigated, only a few studies have been devoted to the effect of metal dispersion on the selectively of hydrogenation of an alkyne-alkene mixture. The work described in this article aimed to investigate the effect of Pd dispersion on the competitive hydrogenation of a mixture containing 0.3% C/sub 2/H/sub 2/, 0.5% H/sub 2/ balanced by C/sub 2/H/sub 4/ over Pd/alumina as catalyst. In particular, attempts have been made to clarify the extent of ethane formation produced directly from acetylene (intrinsic selectivity of the ethane formation) and that from ethylene in the presence of acetylene with the use of (/sup 14/C)C/sub 2/H/sub 2/. Isotopic labeling techniques have unambiguously demonstrated that ethane is generally formed from both acetylene and ethylene. 30 references.

The effects of pre-irradiation with γ-rays of heat treatment in vacuum on the surface acidity and basicity of TiO 2 , Fe 2 O 3 , V 2 O 5 and Cr 2 O 3 and on the radiocatalytic decomposition of 2-propanol have been studied. Since pre-irradiation and heat treatment have very different effects, the radiocatalytic effects cannot be accounted for by local, radiation-induced, temperature increase. The radiocatalytic effects are attributed to transfer of absorbed radiation energy from the catalysts. This conclusion is supported by comparing the yields of the gas- and of the liquid phase radiolysis with the radiocatalytic transformation of 2-propanol.

70 kGy of γ-irradiation enhances the catalytic transformation of 2-propanol into acetone and propylene on transition metal oxides. Fragment products are formed and for TiO2, V2O5 and Fe2O3 the selectivity of 2-propanol decomposition is shifted towards dehydration by the irradiation. Both catalytic and radiocatalytic transformation of 2-propanol correlate with the adsorption capacity of metal oxides, which suggests, that irradiation acts mainly on the adsorbed 2-propanol. Possible changes in the catalyst's chemical properties due to the irradiation are discussed.

Homologation of pentanes and isohexanes results in the formation of benzene and toluene on Ni black and on supported Ni catalysts.

Formation of carbonaceous deposits from n-hexane, methane and 1, 5-hexadiene has been investigated at 673 K over Pt/SiO2 catalysts of differing dispersion. The measurements with 1, 5-hexadiene, 2, 4-hexadiene and trans-hexatriene over SiO2 have confirmed the monofunctional behaviour of the catalysts. The initial C/Pts value is smaller, the subsequent rate of deposit formation and the fraction of “free” sites are higher on highly dispersed samples than on poorly dispersed ones. On catalysts of high Pt dispersion the C-C bond rupturing activity might impede the transformation of C6 entities into graphitic deposits.

Transformation of n-hexane has been investigated over 0.8 wt% Pt/Al2O3 and 15 wt% Pt/Al2O3 catalysts (metal dispersion is 66 and 6.3%, respectively) at 593 K as a function of the partial pressure of hydrogen. The surface composition of the working surface has been characterized by measuring the fraction of “free” sites, total hydrocarbon coverage, the coverage of the firmly held species. The experimental results confirm that the surface state of the catalysts is affected by the variation of the H2/n-hexane ratio. Under the experimental conditions investigated 10–20% of the surface platinum atoms might participate in forming the reaction sites responsible for the skeletal reactions.

Data on chemisorption, exchange, hydrogenolysis of c-pentane(cP) and n-pentane(nP) have been compared on Pt and Ni blacks. Product distribution pattern, and reaction order with respect to hydrogen have been presented as a function of dispersion. (change-para-here) Experimental results permit the suggestion that ring opening and hydrogenolysis proceed by 1,2 interaction on two or more adjacent Ni sites independent of dispersion (H/Ni=6.4×10 −2 −0.59). Measurements on Pt black reveal large difference with respect to the reactivity of cP and nP. Results are discussed in terms of likely contributing surface species.

The chemisorption and transformation of n-hexane have been investigated over Pt black in the presence of hydrogen between 450 and 600 K. Direct gravimetric measurements have confirmed that only 3–8% of the total hydrocarbon coverage can be removed by evacuation or by purging the system with an inert gas. Hydrogenation experiments have been used to separate reactive and irreversibly bound hydrocarbons; their coverages have been measured as a function of temperature and partial pressure of hydrogen. The variation of the product selectivity with the partial pressure of hydrogen has been interpreted considering the effect of the irreversibly bound hydrocarbons on ensemble size and on availability of hydrogen.

Hydrogen sensitivity of MCP ring opening on Ir/Al2O3 and that of n-hexane transformation on Pt black have been investigated. Comparison of the results on O2–H2-treated and ‘carbon’-precovered catalysts confirms that in the interpretation of the hydrogen effect on product distribution one has to regard the steric/electronic effect of trapped hydrocarbons on the surface metal atoms.

The adsorption and deuterium exchange of methane and ethane and the hydrogenolysis and isomerization of ethane, butanes and some C5 hydrocarbons have been investigated on Ru, Rh and Ir blacks. Product distribution patterns, together with data on chemisorption and deuterium exchange, suggest that surface transformations of hydrocarbons into strongly/multiply bonded species easily take place. The initial multiple rupture of hydrocarbons is a result of the slow product desorption, that seems to be the rate limiting step of the hydrogenolysis on these metals.

Hydrogen–deuterium exchange in methane, ethane and propane, hydrogenolysis of ethane, n-butane and isobutane and chemisorption of methane and ethane have been studied on rhenium powder catalysts.The kinetic isotope effect and the rate sequences of the exchange reactions mentioned above show that the rate limiting step is C—H bond dissociation.Ethane hydrogenolysis overlaps ethane exchange at 523 K. The hydrogenolysis reaction order with respect to hydrogen is slightly positive for ethane and greater than unity for butane. Methane is the main product of butane hydrogenolysis. Hydrogen assisted thermal desorption of methane produced from chemisorbed ethane evolves a peak with a maximum at 560–570 K, similar to the thermal desorption peak of methane. Therefore a strong, multiple metal–carbon bond is involved in rhenium–saturated hydrocarbon interaction, C—C bond breaking takes place easily but desorption of the reaction products is hindered.

Transformation of n-pentane, 2-methylbutane and 2,2-dimethylbutane has been investigated as a function of the H2/hydrocarbon ratio over a 10 wt % Ir/Al2O3 catalyst of 14 % dispersion. The selectivity of isomer formation has been observed to decrease with the increase of the H2/hydrocarbon ratio and follow the sequence n-pentane > 2-methylbutane 2,2-dimethylbutane. The effect of the experimental conditions on the product selectivity has been interpreted considering the actual surface state of the working catalyst.

The chemisorption and transformation of n-hexane have been investigated over Pt black in the presence of hydrogen between 450 and 600 K. Direct gravimetric measurements have confirmed that only 3–8% of the total hydrocarbon coverage can be removed by evacuation or by purging the system with an inert gas. Hydrogenation experiments have been used to separate reactive and irreversibly bound hydrocarbons; their coverages have been measured as a function of temperature and partial pressure of hydrogen. The variation of the product selectivity with the partial pressure of hydrogen has been interpreted considering the effect of the irreversibly bound hydrocarbons on ensemble size and on availability of hydrogen.

Chain lengthening homologation of propane,n-butane,2-methylpropane,2-methylbutane and 2,2-dimethylpropane has been investigated over Pt, Pd and Ni catalysts. With both Pd and Ni the chain lengthening selectivity was observed to be commensurable to the isomerisation one. Addition of CHx onto the β-carbon atom in n-butane and propane as well as chain lengthening of 2-methylpropane and 2-methylbutane were observed. The mechanism of the skeletal rearrangement is discussed in terms of CHx addition.

Deuterium exchange reactions of methane, ethane, propane and neopentane, and the hydrogenolysis and isomerization of ethane, propane, n-butane and isobutane on platinum black have been studied in the temperature range 363–743 K. There is a gap of 150 K between the temperature of deuterium exchange and that of hydrogenolysis and isomerization. Only at high hydrogen pressure (about 50 kN m–2) and at low catalytic activity is the hydrogenolysis characterized by selective loss of a terminal methyl group, except for n-butane in which there is an equal chance of any of the C—C bond rupturing. The selectivity for isomerization has a maximum at high hydrogen pressure. These values together with kinetic data suggest that the ability of platinum in an exchange reaction to convert weakly bonded intermediates into strongly bonded ones is much less than that of nickel. The phenomenon of π-olefin and π-allyl bond conversion is applied in part to explain the results obtained. Brief comparison is given between the catalytic properties of platinum and those of nickel for the reactions investigated.