Transformation of n-hexane over EUROPT-1: fragments and C₆products on fresh and partially deactivated catalyst

Abstract

The reactions of n-hexane have been studied on 6.3% Pt/SiO, (EUROPT-1) at different hydrogen and n-hexane pressures, and at 543-633 K, over fresh catalyst and over catalysts deactivated by long runs. Turnover numbers are compared with literature data: the differences are attributed to hydrogen pressure effects. Deactivation influences first of all, selectivity. In addition, the 'depth' and ' pattern' of hydrogenolysis have been determined.At low temperature multiple splitting s e e m s to be favoured. lsomerization gives predominantly 3-methylpentane.At medium temperatures, isomerization, C,cyclization and internal splitting prevail ; their ratio is controlled by the hydrogen pressure. The ratio of 2-methylpentane to 3-methylpentane is related to the ratio of internal to terminal rupture. Terminal splitting prevails at highest temperature. Aromatization increases with temperature but s e e m s to be independent of the other reactions. The results are interpreted in terms of three different surface states. These correspond to Pt-H, Pt-C-H and Pt-C under increasing severity of conditions.

Carbon accumulation, deactivation and reactivation of Pt catalysts upon exposure to hydrocarbons

“…The results obtained with another Pt black (Pt-HCHO, BET surface, 2.64 m 2 g −1 , dispersion D = 1.6% [6]) were very similar, thus they will not be tackled in detail here. The supported catalysts were: 6% Pt/SiO 2 , known as EUROPT-1 [23], D = 60%; 2%; Pt/CeO 2 calcined at 773 K, corresponding to 2Pt-Ce HTR in Ref. [26], D = 35%.…”

“…The differences are conspicuous. The main products were MCP and isomers with much less fragments [20] and [23]. Deactivation slightly increased the MCP selectivity at the expense of isomerization.…”

“…The present study will report on the effect of two deactivating hydrocarbons: hexane (nH) and trans-transhexa-2,4-diene (2,4HD ) alone or with a six-fold excess of H 2 in a wide temperature range (483-663 K). The effect(s) of the unsaturated and saturated deactivated agents in the presence (and also in the absence) of hydrogen will be compared using Pt black as well as three monofunctional supported Pt catalysts: Pt/SiO 2 (the well-known and much used EUROPT-1 [23] and [24]) Pt on a graphitenanofiber (GNF) support [25] and Pt/CeO 2 [26]. The latter supports exhibited opposite behavior towards spilt over hydrogen: GNF stored it whereas ceria reacted with hydrogen to give Ce III .…”

Synthesis and characterization of carbon black supported Pt–Ru alloy as a model catalyst for fuel cells

“…The bond-shift mechanism in addition to isomerization gives also the hydrogenolysis reaction being this latter the preferred one. On platinum catalysts the cyclic mechanism prevails over the bond-shift producing isomerization, dehydrogenative C 5 -cyclation and aromatization (via C 5 -cycle enlargement) [32] and it seems that the selectivity pattern of our monometallic Pt catalysts support this route of reaction. It has been showed that the cyclic intermediate is flatly chemisorbed on the platinum surface requiring ensembles of platinum atoms of certain size and disposition [33,34].…”

n-Hexane Hydrogenolysis Behavior of Alumina-Supported Palladium–Platinum Alloys

“…Considering similar reaction conditions, the M f values for different forms of Pd catalysts were reported as close to 2 [22,23] whereas M f for Pt catalysts was usually much higher, often approaching a level of ca. fivefold higher [22,24]. Figure 3 shows results obtained for n-hexane hydrogenolysis over Pd-Pt/Al 2 O 3 catalysts prereduced at different conditions.…”