(57b) Reduction of Iron(III) Oxide Deposited On Silica Aerogel by ALD

One form to store and/or purify hydrogen is through the steam-iron process, based on the oxidation and reduction of iron to split water obtaining hydrogen as a product. This process can be limited by the fact that iron sinters when reduced from iron(III) oxide, reducing its surface area and with so, limiting its reactivity. Instead, it is proposed to use silica aerogel coated with iron(III) oxide by atomic layer deposition as a reactant. In this project the isothermal reduction of iron(III) oxide coating silica aerogel was studied by using a Thermogravimetrical Analyzer to study mass changes and compare them to the isothermal reduction of bulk iron(III) oxide. A model of three steps proposed for the reduction of bulk iron(III) oxide was followed to study both cases at two different temperatures. It appears that bulk iron(III) oxide as well as the coating iron(III) oxide follow such model, with a nuclei-growth mechanism for the first two steps followed by a diffusion mechanism. Differences between the models were the index of reaction, which explains geometry of nuclei growth, being a mixture of a one-dimensional and a two-dimensional model for the bulk iron(III) oxide, and one-dimensional for the coating iron(III) oxide; and the diffusion model exponent, being larger for the coating iron(III) oxide. Physical differences between the products of the reductions were the sintering of bulk iron, while the coated particles remained without sintering.