Many catalysts used in modern steam methane reforming-based hydrogen plants are susceptible to poisons that are present in the hydrocarbon feedstock. There are two main sources of hydrogen in the refinery: the catalytic reformer and on-purpose hydrogen production via hydrocarbon steam reforming. The catalytic reformer is normally the main source of hydrogen for the refinery. The mechanism of carbon deposition on catalysts depends on the nature of the hydrocarbons present and the operating temperature. Heavier hydrocarbons thermally crack at lower temperatures than methane. Less hydrogen is generated per mole of carbon, so the reverse reaction is minimal and alternative reaction paths are available from the various hydrocarbons in a heavier feed. The heart of the plant is a steam methane reformer that extracts hydrogen from a mixture of hydrocarbons and water. The kinetics of the steam methane reforming reaction have been widely studied, and there are several rate equations in the literature.