The vanadium oxide-based systems on various carriers are of great interest for the obtaining of catalysts for natural gas processing and organic synthesis. An important stage in the development of sulfuric acid catalysis was obtaining of sulfovanadium catalysts based on diatomite. The catalyst is easy to manufacture, sufficiently durable, and has a relatively long service life. It is necessary to process deactivated vanadium contact masses due to the high hazard of spent vanadium catalysts to humans and the environment, as well as the scarcity and high cost of vanadium compounds. In this regard, there is a need to determine the causes of deactivation of sulfuric acid vanadium catalysts of the SVD brand after their operation. All studied samples have low specific surface area and porosity, indicating the destruction of the support. X-ray spectral analysis indicates a low content of V2O5. This is due to the presence of impurities in the diatomite. Aluminum and iron oxides interact with potassium pyrosulfovanadate. As a result of this reaction, there is a formation of aluminum-potassium and iron-potassium alums. Consequently, is causes the release of V2O5 crystalline phase. This leads to a sharp change in the composition and properties of the active component and decreasing of activity. The results of X-ray diffraction studies show that all studied samples contain crystalline forms of diatomite, predominantly in its high-temperature modification – cristobalite. A significant amount of cristobalite leads to a disruption in the mechanical strength of the granules and a low specific surface area.