The Chemisorption and Catalytic Decomposition of Ethylene on Nickel

Abstract

1109small K . When X is a chloro group interaction between the donor chlorine atom and the iodineappears to occur in addition to interaction with the carbonyl. This interaction is probably best described as London dispersion and dipole-induced dipole interactions. Since the interaction is weak, it has a x ' G\H N (~W I I1 H0 Fig. 4.-Possible isomers in XCH,C-N( CHI), compounds.negligible effect on A H , but ring formation leads to a favorable entropy term enhancing the stability of the complex. The favorable entropy term is in part cancelled by the entropy of rearrangement. Coordination can also occur to a lesser extent with isomer 11. As a result of all of these effects, C1-0 // CH&-N(CH& falls on the u* plot. In the case of DMTCA, a chloro group most probably is always cis to the carbonyl. Fischer-Hirschfelder models indicate a pronounced steric effect between the C1 and -N(CH& groups when they are both in the same plane. This steric effect requires the chloro group to be cis to the carbonyl. This chloro group interacts with the iodine and the equilibrium constant for the iodine complex of DMTCA is larger than that expected from the u* number. Since all molecules have a chloro-group cis to the carbonyl, rearrangement is not necessary aad the absence of the unfavorable entropy term for complexation produces a large deviation from the u*-log K line. The interaction of the chloro group with the iodine is not manifested in the heats of association for this effect is smaller than the experimental error in the AH.The chemisorption and dissociation of ethylene on unsupported nickel catalysts has been studied by a volumetric technique over the temperature range -78 to 200'. The formation of ethane by self-hydrogenation was measureable even at the lowest temperature and the kinetics of the reaction were studied between -78' and 0'. The rate of ethane evolution was found to be proportional to the initial concentration of chemisorbed ethylene and the apparent activation energy for the self-hydrogenation reaction was 3 kcal./mole. Above 60°, methane began to appear in the gas phase and at 200' was the sole gaseous product. The mechanism of catalytic dissociation of ethylene and the nature of the adsorbed residiies on the metal surface are discussed.

Galvanostatic and Volumetric Studies of Hydrocarbons Adsorbed on Fuel Cell Anodes

“…In addition to the saturated hydrocarbons from selfhydrogenation, lower molecular weight materials are also found in the gas phase. This parallels the methane production that has been observed from ethylene and ethane adsorbed on rhodium (23), nickel (24), and other metals (31) and the methane and ethane from propane in gas phase studies at low pressures with nickel (25) and platinum (26). It also parallels the observations of Grubb on related fuel cell systems (27).…”

Infrared spectra of hydrocarbons chemisorbed on silica-supported metals. II. Ethylene on nickel and platinum over a range of temperatures

“…From magnetic measurements Selwood (1962) has concluded th a t ethylene is associatively adsorbed a t 0 °C, whereas dissociative adsorption has set in by 28 °C. The results of this present investigation, and of th a t conducted by McKee (1962), indicate instead th a t dissociative adsorption can occur to some extent even a t -78 °C, although a t this low tem perature associatively adsorbed ethylene may represent a significant proportion of the chemisorbed species after short periods of adsorption. Our conclusions concerning the production of a surface carbide on adsorption at 150 °C, and the evolution of methane on hydrogenation a t this temperature, agree with Selwood's general conclusions.…”

“…According to our results retention on the surface is correlated more with the presence of surface dimerization. McKee (1962) reports th a t the self hydrogenation reaction to form ethane on unsupported nickel occurs even a t -78 °C, but th a t a t 0 °C the surface is rapidly covered with non-volatile residues which inhibit the self hydrogenation. Our spectroscopic conclusions show th a t these non-volatile residues are partly n-butyl in type and th a t they are formed by surface self hydrogenation reactions.…”

Artificially Metals-Poisoned Fluid Catalysts. Performance in Pilot Plant Cracking of Hydrotreated Resid

“…Aromatics have been formed from Ce and C7 naphthenes (Germain, 1969), and small amounts of olefins and aromatics have been reported from paraffin reaction over NiX zeolite (Galich, 1964). Adsorbed carbon residue was also reported by McKee (1962) in a study of ethylene decomposition on clean, unsupported nickel powder at low temperatures (392 °F). Nickel-catalyzed reactions such as these probably account for most of the "contaminant" coke and hydrogen formation observed in our study.…”