Mechanism of the Catalytic Gasification and Reactivity of Graphite

Abstract

Graphite is being used as a carbon source for gasification to insure that hydrogen or hydrogen in hydrocarbons is derived from water. Relatively low temperatures (500–800K) are used to favor the equilibrium C+2H₂O →CH₄ +CO₂ which is almost thermally neutral. In the presence of alkali hydroxide C₂-C₆ hydrocarbons are formed in addition to H₂, CH₄ and CO₂. Formation of hydrocarbons is a stoichiometric reaction proceeding on the crystal edges to form a phenolate and hydrocarbons, e.g. 5C+4KOH 4COK+CH₄. Surface spectroscopy has confirmed the presence of phenolate, which can be decomposed over metal oxide to make the reaction truly catalytic: $44C0K\xrightarrow{{Me0x}}2{K_2}0 + 2C + 2C0$; 2K₂O+2H₂O→4KOH. In the presence of both KOH and metal oxide the major products are CO₂ and H₂ with traces of CH₄ and CO. The 2:1 ratio of H₂/CO₂ appears due to either or both watergas shift and Boudouart reaction. The mechanisms will be illustrated by electron microscopy and XPS measurements.