Page 212 - Principles of Catalyst Development

CATALYST DEACTIVATION 201
TABLE 8.5. Types of Poisoning Agents

Type of poison Origin Example

Simple ions:
CI and other halide~ Boiler water Low temperature shift
Simple molecules:
S- Petroleum Hydrogenation
N- Petroleum Acid catalysts
P- Petroleum Hydrogenation
As- Petroleum Hydrotreating
CO 2 Synthesis gas Ammonia synthesis
Complex molecules:
Ni, Fe, V porphorins Petroleum Catalytic cracking
Other metals Compressor oil Hydrocracking
Pb compounds Additives Hydrotreating
Automobile exhaust

These are (1) site heterogeneity and (2) diffusion. Adsorption sites may not
have uniform attraction for poison molecules, in which cases curves such
as those in Fig. 8.11 are encountered.
Curve (1) is found with uniform sites. Decay of activity with poison
concentration is linear and follows the form:
R = Ro(l - a) (8.6)
where a is the fraction of surface poisoned. In curve (2), less active, and
in (3), more active, sites are poisoned first. Curve (4) is an extreme case

>-
I-
>
l-
e)
c(

FRACTION OF SURFACE POISONED
Figure 8.11. Loss of activity for different types of poisoning. 1, Uniform; 2, least active sites;
3, most active sites; 4, dual sites.