Several tetravalent metals (Cc, Zr, Sn, Ti) phosphates were synthesized, characterized and evaluated for the oxidative dehydrogenation of n-butane in the temperature range of 683-843 K, at atmospheric pressure. Zirconium and cerium phosphates appeared to be the most active catalysts but titanium phosphate led to the best yields in butenes and butadiene with a maximum of 14% at 803 K. The study of TiP2O7 showed that conversion increased continuously when the air to n-butane ratio increased from 2 to 5. In the same time, over the ratio equal to 4 the butenes and butadiene selectivities remained high and constant. The addition of water to the gas feed was shown to have a negative effect on both the conversion and selectivity to butenes and butadiene with a significant decrease of the yield in butadiene compared to that of butenes. The results obtained clearly showed that two reaction mechanisms took place on pyrophosphates but for TiP2O7 each mechanism depending upon the reaction temperature. The low temperature one was also common to the other pyrophosphates whereas the high temperature one was only specific to TiP2O7 and involved the Ti4+/Ti3+ redox couple.