Thermal analysis of ammonium trioxalatometallate complexes supported on titania and reducibility of their decomposition products

Thermal decomposition of the bulk and supported ammonium trioxalatometallate complexes (NH4)3[M(C2O4)3]·xH2O, where M = Cr, Fe, Ru in air has been studied using TG-DTA, TPR, and XRD. The decomposition temperatures and behavior depend on the metal nature. The decomposition of the supported Cr complex occurs below 340 °C, whereas it lasts up to 380 °C for the bulk phase, and results in the formation of CrO1.92 at 400 °C. First synthesized Ru trioxalato complex decomposed to RuO1.8 in three stages before 315 °C, the decomposition being completed around 280 °C if the complex is supported on titania. Both bulk and supported Fe complex decomposed rapidly at the same temperatures to FeOx with x = 1.37 for the supported system. The supported CrOx and FeOx phases are finely dispersed and X-ray amorphous. Their reduction with hydrogen below 500 °C resulted in Cr(III) and Fe(II) oxide species respectively. Only partial reduction to Fe0 occurred at as high temperature as 850 °C. The RuO1.8/TiO2 system was reduced with hydrogen completely to Ru0 below 300 °C.