It has been shown experimentally that nano-sized titania (TiO2) particles enhance the burn rate of a composite propellant by an average of 30%. It has been assumed that it may occur through catalyzing the decomposition of ammonium perchlorate (AP). Moreover, the anatase polymorph exhibited the greatest degree of enhancement. In order to gain a better understanding of TiO2-based catalysts, it is important to obtain atomistic-scale information on well-characterized catalytic surfaces. Anatase and rutile show inherent particle size differences and this might cause some of the observed differences in chemical properties and it is necessary to find the most stable nano-cluster configurations and evaluate their activity toward AP decomposition. The AP adsorption on both TiO2 surfaces and clusters has been studied using the density functional theory (DFT) approach. The calculated binding energy indicates that the most energetically stable cluster with diameter of 1 nm has brookite polymorph and for the larger diameters, the most stable clusters have anatase polymorph. The values of adsorption energy of AP on the TiO2 clusters are larger as compared with AP adsorption on TiO2 surface that can be associated both with the structural reconstruction due to interaction with AP and the large ratio of (001) face in anatase TiO2 clusters. The effects of transition metals doping and oxygen vacancy defects on the catalytic activity of TiO2 clusters were also studied. It has been found that the Fe and Co doping stabilize the small cluster of TiO2 anatase with size of 1 nm. The changes in adsorption energy are due to involving the transition metal atoms in adsorption process by charge transfer. For the large cluster sizes, it has been found that the formation of metal cluster on cluster surface is not energetically preferable since the configuration of transition metal doped cluster with uniform distribution of metal atoms is more stable. The lower vacancy formation energy was found in the case of anatase TiO2 clusters and the formation energy decreases with increasing of cluster size. The oxygen vacancy defects significantly increases the adsorption energy of AP molecule on small TiO2 clusters and it can be concluded that the anatase TiO2 clusters with oxygen vacancy show higher catalytic activity toward AP adsorption.

Role of nano-sized TiO2 particles in catalytic decomposition of ammonium perchlorate

254th National Meeting (2017)

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