Source: Kerry M. Dooley and Michael G. Benton, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA

The hydrogenation of ethylene (C₂H₄) to ethane (C₂H₆) has often been studied as a model reduction reaction in characterizing new metal catalysts.^1-2 While supported nickel is not the most active metal catalyst for this reaction, it is active enough that reaction can take place at < 200°C.

The reaction typically involves adsorbed, dissociated hydrogen (H₂) reacting with adsorbed ethylene. In other words, both hydrogen-atoms and ethylene molecules form bonds with a metal site (here denoted "S"). The strong bonding of ethylene with S weakens the double bond sufficiently to allow hydrogen atoms to add to ethylene, forming ethane, which is not adsorbed.

The purpose of this experiment is, first, to convert raw composition measurements to limiting reactant fractional conversions.³ These conversions can then be used in a plug-flow reactor (PFR) to fit the data to a standard power-law kinetics model by the "Integral Method".³ A comparison of the experimental orders of reaction for both ethylene and hydrogen with the theoretical orders reveals in this case that the reaction is kinetically controlled rather than mass-transfer controlled.