Decomposition of methane with various precious metal catalysts for the tokamak exhaust processing

Abstract

The Tokamak exhaust processing system (TEP) in the deuterium-tritium fuel cycle for DEMO is the key system where hydrogen isotopes and impurity gases are separated. Then the impurity gases are decomposed into hydrogen isotopes and other chemical species. The major impurity gas to be processed in TEP is tritiated hydrocarbons. Among tritiated hydrocarbons, tritiated methane is hard to be decomposed directly since the temperature of catalyst for thermal decomposition is 500 °C or above with conventional precious metal supported catalysts such as Pt, Pd, and Rh. The effect of constitutive elements of catalysts on methane decomposition was investigated for a catalyst that could decompose methane efficiently at low temperatures. The investigation showed that the activity of the catalyst for methane decomposition depends on some constitutive elements such as precious metal species, particle sizes of metals, pore sizes of catalyst supports. The experimental results indicated that methane could be decomposed effectively by optimizing precious metal species and the particle sizes of precious metals. Especially the particle size of precious metals had a great influence on methane decomposition efficiency. It was notable that the decomposition efficiency rose 5 times by enlarging a particle size from 12 nm to 23 nm.