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✔ Arsenic, vanadium, and nickel in the feed cause poisoning.✔ Water or oxygen exposure deactivates the catalyst.

The key reactions in the NHT unit are:✔ Hydrodesulfurization (HDS) R−S+H2→R−H+H2SR-S + H₂ → R-H + H₂SR−

Catalyst fouling, carbon deposition (coking), and particulate contamination from feedstock. The solution is to perform catalyst regeneration or replacement and ensure proper filtration of the feed.

🔹 Causes of catalyst deactivation:✔ Coking – Formation of carbon deposits.✔ Metals Deposition – Vanadium & nickel accumulation.✔

✔ Cobalt-Molybdenum (Co-Mo) on Alumina – Used for low-sulfur feeds.✔ Nickel-Molybdenum (Ni-Mo) on Alumina – More active, used for high-sulfur feeds.