Abstract
Energy-saving and cost-efficient reaction routes to prepare highly active catalysts for CO(2) hydrogenation or solid oxide fuel cells (SOFCs) are enormously important. In this paper, we report a detailed study of a dichromate salt of [Fe(urea)(6)](3+), a member of the [M(urea)(6)](3+) complex family (M = Fe, Al, Mn, Cr, V, or Ti) with oxidizing anions, which is a promising precursor of a Cr-rich mixed chromium iron oxide catalyst prepared at a low temperature in the solid phase. The single-crystal X-ray structure, various (infrared, ultraviolet-visible, and Raman) spectroscopic studies, and thermal analysis (differential scanning calorimetry and thermogravimetric analysis/mass spectrometry) of [hexakis(urea-O)iron(III)] dichromate {[Fe(urea-O)(6)](2)(Cr(2)O(7))(3)} and its decomposition products confirmed the presence of a quasi-intramolecular redox reaction between the urea ligands and dichromate anions. The redox reactions result in various mixed Cr-Fe oxides with amorphous structure, whereas above 550 °C, the crystal structure and composition of the final products depend on the atmosphere during the thermal decomposition. The iron-chromium mixed oxides are potential catalysts in CO(2) hydrogenation that afford CO, CH(4), C(2)H(6), and C(3)H(8). Furthermore, our Mössbauer spectroscopy studies show a possible electron hopping between the Fe(II) and Fe(III) ions at the tetrahedral sites of the spinel structure, which suggests that the formed chromite is also a potential SOFC material. Our study also demonstrates that hexaureairon(III) dichromate is a selective oxidation agent of sulfur-containing organic compounds.