Influence of Metal Dispersion on n-Hexane Reactions over Platinum-Alumina Catalysts

Abstract

The n-hexane transformations over alumina-supported platinum have been investigated in order to understand the influence of metal dispersion on the catalytic processes. To obtain reproducible behavior of the catalysts a set of pretreatments was necessary. Hydrogenolysis and dehydrocyclization rates increase with dispersion while the isomerization rate does not change. The ratios among the isomerization products (2-methylpentane and 3methylpentane) remain constant for the examined catalysts. This finding suggests the preeminence of a mechanism which occurs through a cyclic intermediate.

Ligand-Promoted Alumina Dissolution in the Preparation of MoOX/γ-Al2O3 Catalysts: Evidence for the Formation and Deposition of an Anderson-type Alumino Heteropolymolybdate

“…The phenomenon of support dissolution is taken into account (for alumina supported catalysts) when the solution containing the metallic precurssor is strongly acidic. This is the case, for example, for the preparation of Pt/γ-Al 2 O 3 catalyst from hexachloroplatinate (H 2 PtCl 6 ) solution. , However, support dissolution is thought to have negligible effects on the final catalyst in this case.…”

“…In many studies on supported catalyst preparation, dissolution of the oxide support (Al 2 O 3 , SiO 2 ...) is neglected because of the low reported solubility product of these oxides. , Yet, in the already mentioned Ni 2+ ,Co 2+ /γ-Al 2 O 3 systems, extensive support dissolution occurred even at “nonaggressive” pH values between 7 and 8. − …”

A kinetic modeling approach to the design of catalysts: formulation of a catalyst design advisory program

“…They found that on a Pt(lll) surface (T = 573 K, H2/HC = 10), the reaction products contained 35% methylcyclopentane (MCP), 26% hydrogenolysis products, 24% isomerization products (2-and 5-methylpentane), and 15% benzene. A well-dispersed Pt/Si02 catalyst also favored methylcyclopentane over isomerization products (Santacessaria et al 1978). In contrast, van Schaik et al (1975) found that on larger Pt particles supported on Si02, the products contained 48% isomerization products, 43% hydrogenolysis products, 7% methylcyclopentane, and 2% benzene.…”

Cracking

“…It enables metal-catalyzed side reactions and adds a few complications to the mechanistic description: 1) Some metals, such as Ni [28][29][30][31] and Pt [28,29,32,33], are prone to hydrogenolysis, which is an analogous reaction to protolysis, but it is the result of C-C bond cleavage by hydrogen. It enables metal-catalyzed side reactions and adds a few complications to the mechanistic description: 1) Some metals, such as Ni [28][29][30][31] and Pt [28,29,32,33], are prone to hydrogenolysis, which is an analogous reaction to protolysis, but it is the result of C-C bond cleavage by hydrogen.…”

“…Cracking products 2) Metals, such as Pt, can also catalyze skeletal isomerization, which is believed to occur mainly through a cyclic intermediate [32][33][34]. This also implies that the metal is able to effect ring closure and hydrogenolysis of the ring to cause ring opening.…”