Methylcyclopentane Research Articles

Aromatization of methylcyclopentane and cyclohexane over zinc-containing high silica zeolites

High catalytic activity and selectivity of high silica zeolites containing no cations of noble metals, towards aromatization of methylcyclopentane (MCPA) and cyclohexane (CHA) has been revealed.

Ring enlargement and ring opening over mono- and bifunctional catalysts

Ring enlargement and ring opening of methylcyclopentane (MCP) have been studied at atmospheric pressure, 250°C and a H 2/MCP molar ratio of 20 with monofunctional HY, Pt/SiO 2 or Pt/NaY, bifunctional Pt/HY catalysts, and physical mixtures or layered beds of HY and Pt/SiO 2. For ring enlargement the acidic function is found indispensable; only trace amounts of benzene are observed with monofunctional Pt/SiO 2. However, the rate of ring enlargement is higher with bifunctional Pt/HY than with monofunctional HY. A mechanism is proposed in which two paths interconverting (cyclo)paraffins and carbenium ions are operative, one via olefins and one via direct hydride-ion transfer. For rinq opening of MCP the metal function displays highest activity; with highly dispersed Pt/SiO 2 the products 2-methylpentane, 3-methylpentane and n-hexane are formed in nearly statistical distribution (1.0:0.5:1.0, respectively). Acidic sites catalyze the ring opening at a much lower rate, and in the product the branched isomers, 2- and 3-methylpentane and 2,3-dimethylbutane prevail as was observed in liquid superacids. In the bifunctional Pt/HY catalyst, Pt protects acidic sites against deactivation by carbonaceous overlayers, but Pt is deactivated by coke precursors from the acidic sites. Only the (de)hydrogenation activity of Pt, characterized by a very low ensemble requirement, survives considerable de- activation. An almost identical performance of bifunctional Pt/HY and a physical mixture of HY and Pt/SiO 2 with respect to activity, selectivity and deactivation leaves only little room for speculations on significant metal/zeolite interactions such as the model of “electron deficient Pt”.

Upper and lower critical solution temperatures for polystyrene in methyl cyclopentane and in dimethyl cyclohexane

Abstract The demixing of polystyrene in methyl cyclopentane, and in dimethyl cyclohexane has been investigated, and the upper and lower critical solution temperatures established for several polymer molecular weights. In the former solvent both upper and lower θ temperatures can be defined, but not in the latter where cloud point curves for the upper and lower critical temperatures coalesce for high molecular weights. The Patterson theory of polymer solutions has been applied to the data, and the characteristic free volume and exchange energy parameters have been evaluated. The lower critical solution temperatures are nearly the same in cyclopentane and methyl cyclopentane due to a compensation between the free volume and contact interaction terms. Solvent size effects are considered in order to explain the differences in the interaction of solvent with polymer.

Geometric and electronic effects in the conversion of methylcyclopentane on Pt-Sn catalysts

With non-calcined bimetallic Pt—Sn/Al 2O 3 catalysts containing 1% Pt and 0.06 – 4% Sn, previous work has shown a complete reduction of tin for a content <1%. The properties of these catalysts were investigated for the conversions of methylcyclopentane (MCP), methylcyclopentene, hexane, cyclohexene and cyclohexane. A comparison of the product distribution clearly shows that the aromatisation of MCP follows a pure metallic route at temperatures lower than 673 K. Coke and sulphur deposition have effects similar to tin addition. The experimental evidence shows that for C-C bond rupture, the main role of tin is to dilute the platinum surface, as coke and sulphur do. Aromatisation goes through a maximum as a function of tin content. At high tin contents, the main reaction is dehydrogenation to methylcyclopentenes. Sulphur or coke does not affect aromatisation and dehydrogenation markedly. The special behaviour of tin is interpreted in terms of an electronic modification of platinum in the bimetallic catalyst.

The influence of particle size and support on the catalytic properties of rhodium for hydrogenolysis of hexanes and methylcyclopentane

The catalytic properties of rhodium for the hydrogenolysis of C 6 hydrocarbons have been investigated. Rhodium preferentially cleaves bisecondary and primary-secondary carbon-carbon bonds. Primary-tertiary CC bonds react much more slowly. Methylcyclopentane (MCP) is converted to methyl-2-pentane, methyl-3-pentane, and n-hexane at temperatures lower than 503 K. The selectivity to n-hexane is low (10%) but measurable on well-dispersed Rh/Al 2O 3 catalysts and decreases when the dispersion decreases. Rh/SiO 2 catalysts have a low selectivity for the formation of n-hexane whatever the dispersion. The specific activity for MCP conversion changes as a function of the dispersion of rhodium and of the support: small rhodium particles are more active than large particles when the support is silica, but the reverse is true on alumina. These changes of activity are consistent with the results reported for C 2H 6 hydrogenolysis on Rh/SiO 2 and for C 5H 10 conversion on Rh/Al 2O 3. The variations of the catalytic properties for hydrogenolysis may be interpreted as due to the modification of the structure of the small rhodium particles observed on silica.

The influence of ammonia poisoning on the selectivity of the hydrogenolysis of methylcyclopentane on Platinum

The hydrogenolysis of methylcyclopentane (MCP) on platinum is known to proceed via two different pathways: (i) a selective one occurring at large metal particles and (ii) a nonselective one occurring at small particles. In this paper results are presented on the effect of ammonia poisoning of supported platinum catalysts on the nature of the product distribution obtained in hydrogenolysis of MCP. With supported platinum catalysts of high dispersion the poisoning causes a shift from a nearly nonselective pathway to a more selective pathway typical of lower metal dispersion. Hence it is concluded, that ammonia is preferably adsorbed at platinum sites, which are responsible for the nonselective hydrogenolysis. These sites have been identified earlier [1] to be platinum sites situated at the metal-support phase boundary.

Particle size effect on catalysis caused by adlining metal-support sites

Platinum model catalysts of low metal dispersion were prepared by high vacuum evaporation of platinum (mass thickness 1–2 nm) onto either alumina or silica films. After annealing at 800 K in air and reduction at 520 K in hydrogen the size of the Pt particles was found to be ∼10 nm. In these catalysts the hydrogenolysis of methylcyclopentane (MCP) at 520 K and 1 bar pressure of H2 was studied. The main products were 2-methylpentane, 3-methylpentane and n-hexane. The n-hexane portion of these products was low (10–12%), a result which is to be expected from the effect of the large particle size on the product distribution of the MCP hydrogenolysis. This particle size effect is discussed.

Catalytic reactions of hydrocarbons over Pt-Pd alloys: IV. Hydrogen effects in the conversion of saturated C 6 hydrocarbons over PtPd/SiO 2 catalysts

The activities and selectivities of a series of PtPd/SiO 2 catalysts have been determined for the conversion of n-hexane ( nH), 3-methylpentane (3MP), and methylcyclopentane (MCP). Saturated C 6 products predominate under high hydrogen pressures whereas benzene and olefin formation prevails under hydrogen-deficient conditions. The overall activity has a minimum for alloys; at the same time, isomerization selectivity (at the expense of C 5-cyclization and hydrogenolysis) had a maximum at similar compositions. On the basis of the hydrogen dependence of yields as well as of the isomer ratios obtained from alkanes and methylcyclopentane, the possible reaction mechanisms are discussed. These are in agreement with data published earlier for both pure metals and alloys. The contribution of the bond shift mechanism is important especially for 3MP isomerization. This is supported also by the formation of 2,2-dimethylbutane over each catalyst. This bond shift as well as the C 5-cyclic mechanism of isomerization requires less dissociated surface species as distinct from dehydroisomerization producing benzene from 3MP and MCP. Possible ensemble and hydrogen effects are discussed.

Fouling of a platinum-rhenium reforming catalyst using model reforming reactions

It is well known that rhenium stabilizes a commercial platinum reforming catalyst; however, the exact role of Re is still in doubt. The function of Re was investigated by determining and then comparing the fouling characteristics of two model reforming reactions catalyzed by bifunctional Pt and PtRe catalysts. The methylcyclohexane (MCH) dehydrogenation reaction was used to probe for changes in the metallic function and the methylcyclopentane (MCP) dehydroisomerization reaction was used to determine variations in the acidic function. Both sulfided and unsulfided catalysts were investigated. Presulfiding either a Pt or PtRe catalyst altered significantly the observed reaction rates and deactivation characteristics of the metallic function. The addition of Re to a Pt reforming catalyst greatly reduced the rate of those structure-sensitive secondary reactions catalyzed by the metallic function: toluene dealkylation, MCP ring opening, and long-term MCH fouling. The addition of Re, however, did not affect the structure-insensitive MCH reaction or the initial MCP fouling rate; also, little or no affect was noted in the MCP fouling characteristics. The results presented suggest that there is a metal-metal interaction between Pt and Re.

Monomer-Isomerization Oligomerization of Methylenecyclohexane and Methylenecyclopentane by Acidic Catalysts

On treatment with an oxo acid (CF3SO3H) or an oxo-acid derivative (CH3COClO4) in benzene, methylenecyclohexane (MCH) and methylenecyclopentane (MCP) isomerized quantitatively to 1-methylcyclohexene and 1-methylcyclopentene, respectively. These isomerized monomers subsequently reacted to give their oily oligomers (mainly dimers). On the other hand, in the presence of a metal halide (AlEtCl2), MCH and MCP scarcely isomerized and oligomers (dimers to pentamers) of MCH and MCP were produced. The catalytic behavior of BF3OEt2 and SnCl4 was intermediate between that of CF3SO3H and of AlEtCl2; that is, a portion of the monomers was isomerized before oligomerization. The structure of the dimers obtained with CF3SO3H and AlEtCl2 was determined by 1H NMR spectroscopy, which confirmed the “monomer-isomerization” oligomerization induced specifically by oxo-acid catalysts. It was concluded that quantitative monomer isomerization precedes propagation, since a nucleophilic counterion derived from an oxo acid promotes proton elimination from protonated MCH or MCP.

Isomerization of 13C labeled hexanes on Pt/Al 2O 3 and on “organometallic cluster derived” catalysts; effect of the metal particle size

Skeletal isomerization of 2-methylpentane (2-MP) and hydrogenolysis of methylcyclopentane (MCP) have been studied over a series of Pt/Al 2O 3 and “cluster derived” (CD) catalysts of high dispersions. 13C labeling allowed estimation of the relative contributions of cyclic mechanisms in isomerization. High resolution electron microscopy was used jointly to determine the metal particle size distributions. In the isomerization of 2-MP to 3-MP the relative amount of selective cyclic mechanisms increases with the percentage of surface or length particles ( d ⩽ 10 Å) whatever the catalyst used. In the isomerization of 2-MP to n-hexane for catalysts having the same mean size of particles, the CD catalysts show differences in selectivity compared to the classical Pt/Al 2O 3 catalysts. The observed particle size effect could be explained by changes in electronic or geometrical factors, especially it is proposed that the electronic rather than the geometrical one should be considered in the case of the “organometallic cluster derived” catalysts.

Selectivity in mechanistic studies of alkanes on “classical” and “inorganic cluster-derived” platinum catalysts

Skeletal isomerization of 2-methylpentane (2MP) and hydrogenolysis of methylcyclopentane (MCP) have been studied over a series of Pt/Al2O3 catalysts, mono- or bi-metallic “cluster-derived” catalysts and well-characterized single-crystal faces of platinum. 13C labelling allowed an estimation of the relative contributions of cyclic or bond-shift mechanisms in isomerization. The bond-shift mechanisms predominate on large crystallites and on single-crystal faces of platinum. The highly dispersed catalysts can be easily simulated by “inorganic cluster-derived catalysts”. “Chini's cluster-derived catalysts” showed differences in selectivity due to the number of active sites. “Parshall and Wilkinson cluster-derived catalysts” have the same catalytic behaviour as industrial bimetallic Pt–Sn catalysts. New platinum catalysts derived from Chatt clusters led to a very selective demethylation and to a total disappearance of the cyclic mechanisms in spite of the very high dispersion of these catalysts (ds≈ 20 Å). Geometric and electronic factors are taken into account to explain the differences in the selectivities obtained on “classical” and “inorganic cluster-derived” catalysts.

The isomerization of 3,3-dimethylbut-1-ene, 3-methylcyclopent-1-ene, and methylenecyclopentane over γ-alumina

Skeletal isomerization of 3,3-dimethylbut-1-ene (33DMB1) and double-bond migration of 3-methylcyclopent-1-ene (3MCP =) and methylenecyclopentane (MCP) have been studied over γ-alumina. The activity for the isomerization of all three alkenes increases with increasing catalyst activation temperature. Addition of fluoride to the catalyst greatly increases its activity. Treatment of the γ-Al 2O 3 catalysts with H 2S results in some enhancement of activity for 33DMB1 and MCP isomerization but reduces activity for 3MCP = isomerization by ~90%. The importance of initial water content of the alumina on subsequent activity is discussed. It is concluded that skeletal isomerization of 33DMB1 and double-bond migration in MCP occur via carbonium ion intermediates on Brønsted acid centers whereas double-bond migration in 3MCP = occurs predominantly via π-allylic intermediates on Lewis acid sites.

Rhodium-catalysed synthesis of substituted methylene cyclopentanes

4,4-Disubstituted 1,6-dienes are cyclised in good yield by Wilkinson's catalyst [RhCl(PPh3)3], in boiling chloroform, to methylene cyclopentanes.

A polymolecular mechanism of conversion of cyclohexene on Pd-Al 2O 3 catalyst

The kinetics of conversion of cyclohexene on Pd-Al 2O 3 in a flow system at temperatures from 70 to 300 °C and under various partial pressures of reactive substance in the range 760 - 20 mmHg were studied. The presence of methyl groups in the structure of condensation products on the catalyst surface was established. The effect of pretreatment with different gases on the activity and selectivity of the catalyst was observed using an impulse technique. The main product and the composition of the condensation products were analysed. The condensation products were intermediate substances in the main process. During the process the labile part of the condensation products was able to decompose giving benzene, cyclohexane, cyclohexadiene and methyl cyclopentane at elevated temperatures. The labile condensation products contained more dehydrogenated substances than were present in the reaction product. The net content of benzene in these condensation products was greater than the absorption capacity of the catalyst by a factor of 2.4. The relative amount of labile condensation products decreased with increase in working time of the catalyst. The results obtained provide evidence of the effective contribution of the labile condensation products in the conversion of cyclohexene via a polymolecular mechanism.

Comparative study of various platinum catalysts in skeletal reactions of C 6-hydrocarbons

Four platinum catalysts, Pt-black, Pt C , Pt SiO 2 , and Pt Al 2O 3 , have been compared in skeletal reactions of 3-methylpentane (3MP) and methylcyclopentane (MCP), in the presence of various partial pressures of hydrogen. Analogous hydrogen effects (defined as primary and secondary) have been observed for each catalyst. The selectivities could be explained almost exclusively by the influence of hydrogen. The selectivity of isomerization plus C 5-cyclization vs fragmentation increased with increasing hydrogen pressure as did the ratio of saturated vs unsaturated C 6 products. The 2-methylpentane vs n-hexane ratio (2MP/ n-H) from both 3MP and MCP exhibited a strong hydrogen dependence (permitting separation of bond shift and C 5-cyclic isomerization as a function of the hydrogen pressure), and significant crystallite size effects were also observed here.

ChemInform Abstract: A NEW CLASSIFICATION OF METAL CATALYSTS IN SKELETAL REACTIONS OF HYDROCARBONS

GENERAL knowledge about the factors governing the catalytic activity of various metals in different skeletal reactions of hydrocarbons is rather limited. Comparative studies are reported here on the depth of hydrogenolysis and the formation of saturated products of 3-methylpentane (3MP) and methylcyclopentane (MCP) for eleven different metals. We have found that isomerisation, C5 ring closure and opening activity of Rh, Pd, Ir and Pt can be correlated with their f.c.c. structure, and their atomic dimensions being in a narrow range. These four metals promote single hydrogenolysis whereas multiple fragmentation is the only reaction observed over Co, Ni, Cu, Ru, Ag, Re, Os. Hydrogenolysis activity and pattern are less characteristic for each group.

The selectivity in ring opening of cyclohexane and methylcyclopentane over a nickel-alumina catalyst

Ring opening of cyclohexane and methylcyclopentane (MCP) catalyzed by a nickel-alumina catalyst was investigated at a hydrogen pressure of 10 atm, in the temperature range from 230 to 320 °C. MCP can react at a temperature some 50 °C lower than cyclohexane. At lower temperatures, the major products of either reaction are hexane isomers which consist of n-hexane (HEX), 2-methylpentane (2MP), and 3-methylpentane (3MP). The composition of hexane isomers obtained from cyclohexane depends on the reaction temperature, and the relative molar proportions can be expressed as HEX:2MP:3MP = 2–6:1:1. The composition of hexane isomers obtained from MCP is almost unchanged over the temperature range and expressed as HEX:2MP:3MP = 1:5:5. It is found that ring opening of cyclohexane proceeds along two different paths: (a) isomerization to MCP with subsequent conversion to hexane isomers, (b) direct opening of the cyclohexane ring to form n-hexane. The difference in reactivities between cyclohexane and MCP is discussed in terms of the specific modes of their adsorption on the catalyst.

A new classification of metal catalysts in skeletal reactions of hydrocarbons

GENERAL knowledge about the factors governing the catalytic activity of various metals in different skeletal reactions of hydrocarbons is rather limited. Comparative studies are reported here on the depth of hydrogenolysis and the formation of saturated products of 3-methylpentane (3MP) and methylcyclopentane (MCP) for eleven different metals. We have found that isomerisation, C5 ring closure and opening activity of Rh, Pd, Ir and Pt can be correlated with their f.c.c. structure, and their atomic dimensions being in a narrow range. These four metals promote single hydrogenolysis whereas multiple fragmentation is the only reaction observed over Co, Ni, Cu, Ru, Ag, Re, Os. Hydrogenolysis activity and pattern are less characteristic for each group.

Platinum/Alumina Catalysts in Reforming Methylcyclopentane

Platinum/Alumina Catalysts in Reforming Methylcyclopentane