Ethylene is hydrogenated to form ethane in the presence of a finely divided nickel catalyst according to
C₂H₄(g) + H₂(g) → C₂H₆(g) (Reaction 3)
During extended plant operation, trace amounts of CO enter the feed stream and are suspected of poisoning the catalyst. Kinetic measurements at 500 K provide the following data for otherwise identical reaction conditions:
P_CO (kPa) k_obs (mol L⁻¹ s⁻¹)
0.00 4.5 × 10⁻³
1.00 2.7 × 10⁻³
2.50 1.5 × 10⁻³
4.00 0.80 × 10⁻³
(a) Describe, without drawing a graph, the quantitative relationship between k_obs and P_CO illustrated by the data.
(b) Using the first and last data points, calculate the percentage decrease in k_obs that results from increasing P_CO from 0.00 kPa to 4.00 kPa.
(c) Propose a kinetic explanation for how CO acts as a catalyst poison in this system, referencing surface site occupancy and effective activation energy.
(d) Suggest two operational changes that could mitigate the negative impact of CO on the hydrogenation rate, and justify each suggestion based on kinetic principles.