Hydrogenolysis ethane

Alkane hydrogenolysis, or crackmg, involves the dissociation of a larger alkane molecule to a smaller alkane molecule. For example, ethane hydrogenolysis in tire presence of FI2 yields methane ... 

Figure A3.10.20 Arrhenius plot of ethane hydrogenolysis aetivity for Ni(lOO) and Ni(l 11) at 100 Torr and H2/C2Hg = 100. Also ineluded is the hydrogenolysis aetivity on supported Ni eatalysts at 175 Torr and H2/C2H6 = 6.6 [43].

Figure 13. Dependence of ethane hydrogenolysis TOF and apparent activation energy on Pt particle size. TOFs decrease by two orders of magnitude over the size range, while the apparent activation energy increases. Coordinatively unsaturated surface atoms in small particles have a higher reactivity and subsequently a smaller barrier for hydrogenolysis than highly coordinated surface atoms of larger particles. TOFs were measured at 20 Torr C2H6, 200 Torr H2, and 658 K [16]. (Reprinted from Ref [16], 2006, with permission from American Chemical Society.)...

Table 5. Ethane hydrogenolysis reaction rates and kinetic parameters for both series of Pt/SBA-15 catalysts [13,16].

Figure 12. TEM images of the Pt(X)/SBA-15 catalysts X = (a) 1.7 nm, (b) 2.6 nm, (c) 2.9 nm, (d) 3.6 nm, and (e) 7.1 nm (the scale bars represent 20 nm) (1) structure sensitivity of ethane hydrogenolysis on 1% Pt(X)/SBA-15 with Pt particle sizes ranging from X= 1.7 to 7.1 nm. Rates corrected to 20Torr C2H6, 200Torr H2, and 643 K. (Reprinted from Reference [143], 2005, with permission from American Chemical Society).

The main issue of the book is application of nanosized particles in both homogeneous and heterogeneous catalysis. A variety of reactions catalyzed by metal colloids or supported nanosized metals is discussed. The most intriguing reaction seems to be ethane hydrogenolysis catalyzed by Pt clusters on porous carrier and studied by G. A. Somorjai and his group. Another challenging observation by this group is shape isomerization of Pt metal particles affected by the addition of silver ions. 

IV. Contrast between Ethane Hydrogenolysis and Other Reactions. 106... 

A further consideration in the mechanism of hydrogenolysis of hydrocarbons is the structure of the chemisorbed species that undergoes scission of the carbon-carbon bond. In the case of ethane hydrogenolysis, one readily visualizes bonding of the two carbon atoms in the species C2H to adjacent metal surface atoms. It is convenient to refer to the adsorbed C2H as a... 

The first reported work on the kinetics of hydrogenolysis reactions of simple hydrocarbons appears to be that of Taylor and associates at Princeton (2-4, 14, 15), primarily on the hydrogenolysis of ethane to methane. The studies were conducted on nickel, cobalt, and iron catalysts. More recently, extensive studies on ethane hydrogenolysis kinetics have been conducted on all the group VIII metals and on certain other metals as well (16,28-83). 

Kinetic Parameters for Ethane Hydrogenolysis on Silica-Supported Metals (16)... 

Fig. 1. Catalytic activities of metals for ethane hydrogenolysis in relation to the percentage d character of the metallic bond. The closed points represent activities compared at a temperature of 205°C and ethane and hydrogen pressures of 0.030 and 0.20 atm, respectively, and the open points represent percentage d character. Three separate fields are shown in the figure to distinguish the metals in the different long periods of the periodic table.

Fig. 4. Comparison of activity patterns of the group VIII noble metals for cyclopropane hydrogenation and ethane hydrogenolysis. The activities were all determined at hydrogen and hydrocarbon partial pressures of 0.20 and 0.030 atm, respectively (63).

Fig. 6. Activities of copper-nickel alloy catalysts for the hydrogenolysis of ethane to methane and the dehydrogenation of cyclohexane to benzene. The activities refer to reaction rates at 316° C. Ethane hydrogenolysis activities were obtained at ethane and hydrogen pressures of 0.030 and 0.20 atm., respectively. Cyclohexane dehydrogenation activities were obtained at cyclohexane and hydrogen pressures of 0.17 and 0.83 atm, respectively (74).

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