Question

Presence of traces of arsenious oxide ($A{s}_2{O}_3$) in the reacting gases $S{O}_2$ and $O_2$ in presence of platinised asbestos in contact process acts as:

• A. catalytic promoter
• B. catalytic poison
• C. dehydrating agent
• D. drying agent.

Answer 1

Answer: (B)

catalytic poison

• Promoters are substances that enhance the activity of a catalyst while poisons decrease the activity of a catalyst.
  
• In the manufacturing of sulfuric acid, a step involves the reaction of $S{O}_2$ and $O_2$ in presence of platinized asbestos to give $S{O}_3$

.i.e. $S{O}_2+O_2\to S{O}_3$

In the above reaction if traces of arsenious oxide ($A{s}_2{O}_3$) is used then it acts as the catalytic poison by reducing the catalytic activity of Platinised asbestos.