Catalyst deactivation – primary causes in heterogeneous catalysis A catalyst loses its activity due to which of the following phenomena?

Introduction / Context:
Catalyst activity and selectivity determine reactor performance and economics. Over time, real catalysts deactivate, necessitating regeneration or replacement. Recognizing the major mechanisms of deactivation helps in designing operating windows and protection strategies (e.g., guards, sulfur traps, optimized temperatures).

Given Data / Assumptions:

• Heterogeneous catalysts with active surface sites.
• Thermal and chemical environments typical of industrial reactors.

Concept / Approach:
Deactivation mechanisms include (1) loss of surface area via support collapse or phase changes; (2) agglomeration/sintering where metal nanoparticles grow, reducing dispersion and the number of active sites per mass; and (3) poisoning/fouling in which contaminants (S, Cl, metals, coke) block sites or plug pores, cutting off access to the active phase.

Step-by-Step Solution:

Verification / Alternative check:
Post-run characterizations (BET surface area, TEM particle size, TPO/TPR of spent catalyst) routinely show these deactivation signatures.

Why Other Options Are Wrong:
Each individual mechanism can occur; in practice they often act together. Therefore the comprehensive choice is correct.

Common Pitfalls:
Confusing reversible fouling (e.g., coke burn-off) with irreversible poisoning (e.g., mercury amalgamation on noble metals). Not all deactivation is permanent, but all listed mechanisms reduce activity.

Final Answer:
All (a), (b) and (c).