Abstract: The invention concerns a continuous reaction method by solid/gas catalysis in unconventional medium, using different substrates to obtain predetermined products, substrates and products forming compounds, which consists in controlling: the reaction in temperature to determine the saturation pressure of each pure compound taking part in determining the compound thermodynamic activity; the total pressure at a level lower than atmospheric pressure; the molar flow rates of the compounds and the vector gas, to adjust the gas mixture molar composition on the basis of the predetermined values of the thermodynamic activity of said compounds.