The construction and the way of working of an improved X-ray reactor chamber (XRK) are described, designed for studies of solid state-gas reactions; a particular area of application is heterogeneous catalysis. By means of the XRK the structural and catalytic properties of Cu-SiO2, Ni-SiO2, Cu-ZnO-Al2O3 and Si-Cu catalysts were investigated in situ during the stages of reduction, reaction and ageing. The structure of the detected amorphous phase (Cu,Zn)-hydrotalcite was studied by the calculation of the radial atomic distribution function (RDF).