---
title: "Catalytic poisoning"
subject: "Engineering Chemistry"
chapter: 2
key: "semester_2/engineering_chemistry:catalytic-poisoning-def"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/catalytic-poisoning-def
site: BCT Engineering
---

# Catalytic poisoning

Engineering Chemistry · Chapter 2: Catalyst

- Asked in: 2069 Bhadra, 1.5 marks
- Video: [Catalyst ,types, poisoning of catalyst](https://www.youtube.com/watch?v=tyS8dz9pfuk) — Prof. Manohar Ahire
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/catalytic-poisoning-def
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-2

## Question

Explain the term: Catalytic poisoning.

## Short answer

Catalytic poisoning is the loss of catalyst activity caused by a poison strongly adsorbed on active sites, blocking reactants. Examples include As₂O₃ poisoning Pt in the contact process and H₂S poisoning Fe in Haber's process. It can be temporary or permanent.

## Answer

**Catalytic poisoning** is the loss of activity of a catalyst caused by a small amount of a foreign substance (the poison). The poison is strongly adsorbed on the active sites of the catalyst and blocks them, so reactants cannot reach the surface.

Examples: As₂O₃ poisons the Pt catalyst in the contact process; H₂S and CO poison the Fe catalyst in Haber's process. Poisoning may be temporary or permanent.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Catalytic poisoning is:
   A. Increase of catalyst activity by a promoter
   B. Loss of catalyst activity caused by a small amount of a foreign substance
   C. Complete consumption of the catalyst in the reaction
   D. Loss of catalyst by melting only
   Answer: B. A small amount of poison greatly reduces or destroys activity. (Key point: Poisoning definition)

2. How does a poison make a catalyst inactive?
   A. It is strongly adsorbed on the active sites (or forms a stable compound), so reactants cannot be adsorbed
   B. It lowers the activation energy too much
   C. It dissolves the reactants
   D. It increases the surface area of the catalyst
   Answer: A. Blocked active sites mean no reactant adsorption and no catalysis. (Key point: Action of a poison)

3. Which poison-catalyst pair is correct?
   A. As2O3 promotes Pt in the contact process
   B. H2S promotes Fe in Haber's process
   C. CO promotes Pt in a catalytic converter
   D. As2O3 poisons Pt in the contact process
   Answer: D. As2O3 poisons Pt; H2S and CO poison Fe in the Haber process, and CO poisons Pt. (Key point: Poison examples)

## Related in Engineering Chemistry

- [Catalytic poisoning; intermediate compound theory](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Acatalytic-poisoning) — Engineering Chemistry, chapter 2
- [Catalytic poisoning; adsorption theory](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Apoisoning-adsorption) — Engineering Chemistry, chapter 2