What is the impact of sulfur compounds on the performance of Ni-based SMR catalysts, and how is this mitigated?

Sulfur compounds have a detrimental impact on the performance of Ni-based catalysts used in Steam Methane Reforming (SMR) because they cause catalyst poisoning, which reduces the catalyst's activity and shortens its lifespan. Nickel (Ni) is the active metal in SMR catalysts, responsible for adsorbing and activating methane and steam. Sulfur compounds, such as hydrogen sulfide (H2S) and mercaptans, strongly adsorb onto the nickel surface, blocking the active sites and preventing the reactant molecules from accessing them. This reduces the rate of the reforming reactions and lowers the hydrogen production rate. Even small concentrations of sulfur compounds can significantly deactivate the catalyst. To mitigate this, a desulfurization unit is installed upstream of the reformer to remove sulfur compounds from the natural gas feed. This typically involves passing the natural gas through a bed of adsorbent material, such as zinc oxide (ZnO), which reacts with the sulfur compounds to form solid zinc sulfide (ZnS). The desulfurization unit ensures that the sulfur concentration in the feed gas is reduced to very low levels (typically below 1 ppm) before it enters the reformer. Therefore, sulfur removal is crucial for maintaining catalyst activity and preventing catalyst poisoning.