Methylcyclopentane conversion

X. L. Bai and W. M. H. Sachtler, Methylcyclopentane conversion catalysis by zeolite encaged palladium clusters and palladium-proton adducts, J. Catal. 129, 121-129 (1991). 

Examples of thermodynamic equilibria are shown in Table IV. The conversion of five- and six-member ring naphthenes to aromatics is quite favorable. Methylcyclopentane conversion is the least favorable. Equilibria for aromatic formation improves with carbon number. For five-member ring naphthenes, the largest improvement occurs between the six-carbon... 

Fig. 17. Methylcyclopentane conversion to 6-membered ring products (benzene + cyclohexane) and hydrogenolysis products, for Pt-component alone, and for mixtures with silica-alumina of two degrees of intimacy, when Pt-component activity is varied.

R. Zaera, D. Goodbey, and G.A. Somoiiai, Methylcyclopentane Conversion Over Platinum Single Crystal Surfaces Evidence for the Cyclic Mechanism of n-Hexane Isomerization, J. Catal., 101 (1986) 73. 

Table 5.3 Methylcyclopentane Conversion over Pt-lr, Pt-Re, and Related Catalysts3 (33)...

The studies of n-heptane and methylcyclopentane conversion provide insight into the advantages of platinum-iridium and platinum-rhenium catalysts over catalysts containing only one of the transition metal components, that is, platinum, iridium, or rhenium. If, for example, we consider an iridium-alumina catalyst for the reforming of a petroleum naphtha fraction, we find that it produces a substantially higher octane number reformate than a platinum on alumina catalyst under normal reforming conditions. The iridium-alumina catalyst will also exhibit a lower rate of formation of carbonaceous residues on the surface, with the result that the maintenance of activity with time will be much superior to that of a platinum-alumina catalyst. 

Zaera F, Godbey D, Somorjai GA (1986) Methylcyclopentane conversion over platinum single crystal surfaces evidence for the cyclic mechanism of n-hexane isomerization. J Catal 101 73-80... 

Figure 3.8 Conversion with time in the hydrogenolysis of cycloalkanes (19Torr, 14.5 equiv.) catalyzed by (=SiO)2TaH (3) at 160°C under hydrogen (470Torr) cycloheptane ( ), methylcyclohexane ( ), cyclohexane ( ), methylcyclopentane (A) and cyclopentane (x).

Fig. 10. Selectivities in hexane conversions versus temperature for benzene formation (Be), hydrogenolysis (Hy), methylcyclopentane formation (MCP), isomerization (ISOM), and dehydrocyclization (Dehy) (9 wt. % Pt on inert Si02).

A modification of this method utilizes the direct conversion of l,2-bis(trimethyl-siloxy)cyclobutene in one step to 2,2-disubstituted cyclopentane-1,3-diones. For example, 2-ethyl-2-methylcyclopentane-l,3-dione (3) was obtained in 91% yield from 1.2-bis(trimethyl-siloxy)cyclobutene and butan-2-one 2,2-dimethylpropane-l,3-diyl acetal.41 Further examples... 

The conversion of cyclohexane to methylcyclopentane is nearly complete at 408°C. Under identical conditions benzene is also converted to methylcyclopentane. This shows that the hydrogenation of benzene to cyclohexane, which can be considered the first step in this reaction, is very rapid. 

Catalytic superactivity of electron-deficient Pd for neopentane conversion was recently verified for Pd/NaHY (157, 170). The reaction rate was positively correlated with the proton content of the catalyst. Samples that contained all the protons generated during H2 reduction of the catalysts were two orders of magnitude more active than silica-supported Pd. Samples prepared by reduction of Pd(NH3)2+NaY displayed on intermediate activity. It was suggested that Pd-proton adducts are highly active sites in neopentane conversion. With methylcyclopentane as a catalytic probe, all Pd/NaY samples deactivated rapidly and coke was deposited. Two types of coke were found (by temperature-programmed oxidation), one of... 

Burch and coworkers (50-53) have reported on the use of Pt-Sn catalysts for hydrocarbon conversions. It was concluded that no proper alloys of Pt and Sn were formed so that this could not account for the changes in the catalytic properties imparted by the presence of Sn (50). Burch and Garla concluded for their catalysts that (i) n-hexane is isomerized by a bifunctional mechanism, (ii) benzene and methylcyclopentane are formed directly from n-hexane at metal sites, and (iii) the conversion of methylcyclopentane requires acidic sites (51). It was also concluded that the Sn (II) ions modified the Pt electronically with the result that self-poisoning by hydrocarbon residues is reduced. However, these later observations were based upon conversions at one bar. 

Dautzenberg et al. (65) tested a number of unsupported PtSn alloys as well as a number of alumina supported PtSn catalysts. n-Hexane conversion was effected at atmospheric pressure for the unsupported alloy catalysts and for some supported catalysts other supported catalyst studies were at 3 bar. These authors reported that the addition of tin decreased the amount of methylcyclopentane and that coke was dramatically reduced during the conversion of n-hexane. 

Sexton et al. (66) also examined the activity for the dehydrogenation of cyclohexane and conversion of methylcyclopentane of a series of PtSn alumina catalysts where the Sn/Pt ratio was varied. They found that the activity decreased as the Sn/Pt ratio increased. Selectivity for benzene formation from methylcyclopentane increased to a maximum at ca. 1.5 to 2.5 wt.% Sn (Sn/Pt = 4.9 to 8.2) and then declined. These conversions were conducted at normal pressures. 

In connection with the research on destructive hydrogenation at the Institute of High Pressures, Maslyanskii (224) passed benzene at 475° under 200 atm. hydrogen over molybdenum oxide (1 mole CeH6 16 moles Ha) to produce 58% methylcyclopentane, 14% cyclohexane, 8% 2-methyl-pentane, 5% n-hexane, and 8% unreacted. Over molybdenum sulfide the product distribution was similar. The preparation of these catalysts was described by him in 1940 (223). Isomerization and other conversions accompanying destructive hydrogenation were also pointed out by Prokopets and by others (257,311,314). 

The benzene selectivity in /i-hexane conversion over Pt/KL catalysts increases with conversion, but the selectivity for methylcyclopentane decreases (21). Lane et al. show that the MCP yield passes through a maximum between 40 and 60% conversion, 2-methylpentane and 3-methylpentane peak around 80% conversion, and hydrogenolysis products and benzene increases with -hexane conversion (29). The same reaction product distribution was found for a variety of supports, e.g., AI2O3, Si02, KL, and KY. On Pt/KY, Pt/NaY, and Pt/ALOj the 2MP/3MP ratios... 

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