Carbon is not only a major product of the methane decomposition but also a catalyst for the heterogeneous methane decomposition reaction. It is highly desirable that the morphology and surface properties of the product carbon be controlled to maximize their catalytic effects. In this paper, we characterize the physical properties of two activated carbon samples by sizes, and crystallographic structures using scanning electron microscope, x-ray diffraction, particle size analyzer, and surface area measurement. The paper also includes high temperature thermogravimetric experiment results on the carbon–hydrogen reaction to show if the injected carbon particles reacts with the formed hydrogen, which has not been studied in solar thermal hydrocarbon decomposition before. Results show that carbon does not react with hydrogen to form methane or any other intermediate compounds up until 900°C, which explains the favorable effect of carbon laden flow experiments for catalytic methane decomposition at lower temperatures. These results will be used to identify the optimal operating conditions for our solar reactor.