Abstract: The co-hydrogenation of silicon tetrachloride and silicon with CuCl as catalyst was studied in a fixed bed reactor for the purpose of studying mechanism of activity changes of solid active species.Heating strategy was designed to ensure Cu3Si formed completely before co-hydrogenation.Typical activity curves including induction period，steady period，and deactivation period were observed after reaction started.The causes of induction period were discussed and the chlorination of Cu3Si sites was indicated to be a necessary step to form catalytic active site.The particle samples were prepared by utilizing inert gas sweeping cooling technology to discontinue the reaction.Changes in particle surface morphology，crystalline structure，and elemental composition of the particles were measured by SEM-EDS，XRD，and XRF，respectively，in reaction process.A deactivation model was proposed and the decrease of diffusion rate due to the changes of surface morphology and composition was indicated to be the main reason of deactivation.

Key words: hydrogenation, activity, diffusion, SiCl4, CuCl