Kinetic and Thermodynamic Studies on the Non-Isothermal Decomposition of Lanthanum Oxalate Hydrate, Catalysed By Transition Metal Nano Oxides

Abstract

A study on the thermal decomposition of the mixtures of lanthanum oxalate hydrate and transition metal nano oxide compounds(TMNOCs) viz. CuO, Fe 2 O 3 , TiO 2 and Cr 2 O 3 of 5 mole% ratio has been carried out employing Thermogravimetry, Differential Thermal Analysis and chemical analysis. The results reveal that other than CuO the oxides have a retarding effect on the decomposition rate. There is a competition of rate between Fe 2 O 3 and TiO 2 mixture up to 696K after which the trend is reversed and Fe 2 O 3 becomes relatively more catalytic than TiO 2. The best explanation for catalytic activities of the oxides is made by taking the former as a function of electronic configuration of the metal rather than the electronic properties of the oxides. Abnormal behaviour of Cr 2 O 3 may be attributed to an irreversible change in oxidation state of Cr 3+ during which it is oxidised to Cr 6 + prior to decomposition. The kinetic and thermodynamic parameters are evaluated in the light of F 3 mechanism in two different regions of α's and the rate follows the order: S 1 < S 2 > S 3 < S 4 > S 5 (0.1 < α < 0.5) S 1 < S 2 > S 3 > S 4 > S 5 (0.5 < 0.9) Where S 1 , S 2 , S 3 , S 4 and S 5 stand for mixtures of different oxides with lanthanum oxalate.