Although catalyst deactivation is inevitable for most processes, how to avoid some direct catalyst premature deactivation as much as possible is of great significance. Catalyst poisoning is an important cause of premature catalyst deactivation. If the feedstock contains impurities such as nickel, vanadium, iron, silicon, arsenic, phosphorus and sodium, even at ppb or even ppm levels in the feedstock, it can have devastating effects on downstream catalysts.
Alfa Chemistry Catalysts offers a wide range of catalyst protectors designed to minimize the potential for premature catalyst deactivation.
Figure 1. Conceptual model of sulfur atom poisoning on metal surfaces 
The following table lists some common poisons for selected catalysts in important representative reactions.
|Silica–alumina, zeolites||Cracking||Organic bases, hydrocarbons, heavy metals|
|Nickel, platinum, palladium||Hydrogenation/dehydrogenation||Compounds of S, P, As, Zn, Hg, halides, Pb, NH3, C2H2|
|Nickel||Steam reforming of methane, naphtha||H2S, As|
|Iron, ruthenium||Ammonia synthesis||O2, H2O, CO, S, C2H2, H2O|
|Cobalt, iron||Fischer–Tropsch synthesis||H2S, COS, As, NH3, metal carbonyls|
|Noble metals on zeolites||Hydrocracking||NH3, S, Se, Te, P|
|Silver||Ethylene oxidation to ethylene oxide||C2H2|
|Vanadium oxide||Oxidation/selective catalytic reduction||As/Fe, K, Na from fly ash|
|Platinum, palladium||Oxidation of CO and hydrocarbons||Pb, P, Zn, SO2, Fe|
|Cobalt and molybdenum sulfides||Hydrotreating of residuum||Asphaltenes, N compounds, Ni, V|
Traps or "getters" are one strategy used to reduce the effects of poisoning, especially sulfur. The researchers investigated the effect of Ce and Yb on the sulfur and water tolerance of Pt/KL aromatization catalysts. The results showed that the addition of Ce and a small amount of Yb significantly suppressed catalyst deactivation in the presence of sulfur. Furthermore, the Ce-promoted Pt/KL catalyst exhibited higher resistance to metal agglomeration and lower coke formation rate.
Figure 2. n-Hexane conversion (a) and benzene selectivity (b) vs. time on stream under 2.5 ppm sulfur-containing feed.