In accordance with the present invention, there is provided a process for producing hydrogen and graphitic carbon from a hydrocarbon gas comprising: contacting at a temperature between 600 C. and 1000 C. the catalyst with the hydrocarbon gas to catalytically convert at least a portion of the hydrocarbon gas to hydrogen and graphitic carbon, wherein the catalyst is a low grade iron oxide.

The present disclosure discloses a high-temperature and high-pressure preparation method for hexagonal diamond, which belongs to the field of superhard material synthesis technology. The method comprises making high-purity graphite into a precursor, assembling the synthesis block, and then subjecting it to heating, pressurizing, temperature holding, and pressure holding processes to obtain hexagonal diamond. The preparation method for hexagonal diamond according to the present disclosure allows high-purity graphite to achieve higher pressure along the c-axis direction, further promoting the phase transition of graphite. In addition, the temperature field where the precursor is located has a certain temperature gradient, which facilitates the transformation of high-purity graphite into hexagonal diamond and achieves a better conversion rate of hexagonal diamond.