N-Butane, hydrogenolysis

Figure A3.10.22 Relationship between seleetivity and surfaee stnieture forn-butane hydrogenolysis on iridium, (a) Illustrations of the Ir(l 10)-(1 x 2) and Ir(l 11) surfaees. The z-axis is perpendieular to the plane of the surfaee. (b) Seleetivity for C2Hg produetion (inol% total produets) for n-butane hydrogenolysis on both Ni single erystals and supported eatalysts at 475 K. The eflfeetive partiele size for the single erystal surfaees is based on the speeified geometrie shapes [43]. A Ir/Al203 nir/Si02.

Fig. 11. Arrhenius plots for n-butane hydrogenolysis on (a) Ir(lll) and (b) Ir(l 10)-(1 X 2). From Refs, /f/,/72.) The pressure of n-butane was 1 torr and that of hydrogen was 100 torr. The dashed line in (a) represents data for n-butane hydrogenolysis on a supported Ir/SiOj catalyst . ...

By using ratio the number of edge (C7) atoms to the number of (111) face (Cg) atoms (Fig. 12) to define an effective particle size , the selectivity of n-butane hydrogenolysis as a function of particle size for the two surfaces could be plotted and compared to selectivities measured on supported Ir catalysts This comparison is shown in Fig. 13. Clearly, the results on single... 

Fig. ii. Selectivity for ethane production from n-butane hydrogenolysis on iridium as a function of effective particle size. (From R s. HI. 112.) Also shown are data for n-butane hydrogenolysis on supported Ir catalysts The temperature is 47S K in all cases. 

It has been reported that the size of the metal cluster frame of Ru6Pt3(CO)2i( X3-H) ( X-H)3 remains on Y-AI2O3 and MgO after its impregnation and decarbonylation under He at 300 °C [65, 66]. The metallic clusters were rather strongly bound to both supports, Y-AI2O3 and MgO. The catalytic behavior of these materials in n-butane hydrogenolysis shows the suppression of the isomerization reaction according with an intimate association of Pt with Ru atoms. 

Figure 15.22 Barcharts of (a) butane conversion (%) and (b) product selectivity in n-butane hydrogenolysis on RhPt catalysts supported on Si02, FSM-16 and HMM-1 with and without scCO, treatment.

Scheme 15.1 Proposed mechanism of n-butane hydrogenolysis via 1,3-adsorbed and 1,2-adsorbed species on Rh and RhPt sites on a nanoscale area of SCCO2 RhPt catalysts.

This can in pan be answered because Pt/alumina, e,g. EUROPT-3 (and Pt/Re/alumina) has also been studied [7]. In n-butane hydrogenolysis on Pt/alumina the accumulation of carbonaceous deposits on the catalyst surface suppressed ethane formation (i.e. relative to that of propane formation (i.e. S3), Thus for Pt/alutnina sites responsible for central C-C bond scission in n-butane may be selectively deactivated, e.g. at 603K sample S2 S3... 

Figure 6 Arrhenius plot of the rate of n-butane hydrogenolysis over Sample 1 (ion-exchanged Ni catalyst) and Sample 3 (precipitated Ni catalyst).

Early higher pressure reaction smdies over Pt-Sn model catalysts by Paffett [62,63] and Somorjai [64, 65] and their coworkers revealed new insights into hydrocarbon catalysis in such systems. Szanyi et al. [62] showed that n-butane hydrogenolysis under moderate pressures (1-200 Torr H3/butane=20) and temperatures (up to 650 K) could be carried out without disruption of the ordered Sn/Pt(lll) surface alloys. This established that such catalytic reactions could be studied while maintaining the composition and geometric structure of these alloys under reducing reaction conditions (but not catalytic oxidation due to the aggressive interaction of O3 with Sn). These ordered Sn/Pt surfaces are qualitatively different from those in many studies of promoters and poisons, or disordered alloys, e.g., Au-Pt, in which the quantitative information on ensemble sizes available for reactions is difficult to determine. 

Szanyi J, Anderson S, Paffet MT (1994) n-Butane hydrogenolysis at Sn/Pt (111) surface alloys. J Catal 149 438... 

Bond et al [25] found that Ru/ZrOz is ten times less active than Ru/SiOz in propane and n-butane hydrogenolysis. 

Namizek (109) has studied the rate of n-butane hydrogenolysis over Ni/ A1203 for Ni crystallites of d varying between 1.0 and 10 nm. A maximum rate is found at about 2.5 nm, so that those results resemble closely those for C3H8 and for C2H6. The maximum in the rate curve occurs at a d that corresponds roughly to the maximum surface concentration of Bs sites, as measured by the method of van Hardeveld and van Montfoort (106). 

In later work, Namizek and Ryczkowski (110) measured rates of propane and n-butane hydrogenolysis over Ni/Al203 catalysts of various FE. They found maximum values of TOF for propane at d = 3-4 nm and for butane at 2-3.5 nm. Masson et al. (Ill) have studied n-butane hydrogenolysis on well-characterized Ni vapodeposited on silica, prepared as already discussed (78, 79). The TOF rises as d is decreased, reaches a maximum at about 2 nm, and then tends toward zero as d goes toward zero (FE = 1.0). 

Hydrogen Chemisorption and n-Butane Hydrogenolysis Activity after Reduction by H Atoms ... 

Fig. 21. Evolution of conversion for n-butane hydrogenolysis at 623 K as a function of reaction time. Circles represent Rh/Ti02 catalysts squares, Rh/V203. Full symbols represent tank purity reactants open symbols, high-purity reactants. (After Ref. 87.)...

Propane, ethane, isobutane and n-butane hydrogenolysis Quantitative scheme of reactions 8 - 8 [81... 

The heterogeneous catalysts prepared from [MoIr3Cp(CO)n] (12) and [Mo2lr2Cp2(CO)io] (13) on alumina were studied for n-butane hydrogenolysis, a structure-sensitive reaction. From comparisons made with catalysts derived from homometallic clusters or their mixtures, it was deduced that the properties of the MMCD catalysts originated from bimetallic interactions maintained in the activated materials. 

Somewhat different conclusions have been reached in a study of n-butane hydrogenolysis on a series of PtRe/a-AhOs catalyst covering the whole composition range. There was an astronomic factor (x 10 ) between the rates shown by platinum and the Pt25Re7s catalyst (Figure 13.25), and as little as 12.5% rhenium was sufficient to increase methane selectivity and to move the Arrhenius... 

Figure 13.26. Activity of PtRe/a-Al203 catalysts for n-butane hydrogenolysis as a function of rhenium content at 513 K (In (rate/molecules cm s )). ° ...

Softie recent publications focus the attention on the performance of titania modified metal/silica catalysts in an attempt to get a better understanding of the metal-promoter-support interactions [11,16]. We include some data on the preparation of Rh and Pt dispersed on TiOj-SiOj reporting information on the catalytic behavior for the n-butane hydrogenolysis reaction. 

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