Synthesis of Al–Fe/SiO2 and Al–Co/SiO2 Catalysts by Solid-Phase Method

Powders of catalysts are obtained from Fe and Co aluminides on a SiO₂ support (33.3 wt %) by thermomechanical synthesis. The formation of coarse powder fractions (>100 μm) is experimentally found, the parts of which are ~43% and ~55% for Fe–Al–SiO₂ and Co–Al–SiO₂, respectively, which is a positive result for further catalytic studies. After calcination of the powders at 700 and 900°C in vacuum, the SiO₂ support and a compound Co₂₇Al₇₃ (similar in composition to intermetallic compounds of the CoAl₃ and Co₄Al₁₃ type) and intermetallic Fe₃Al with the presence of iron silicide of the Fe_0.9Si_0.1 type and a compound Al_0.3Fe₃Si_0.7 in small volumes are identified in the composition of the obtained catalysts by X-ray diffraction. Concerning the synthesis of cobalt aluminides, a conclusion is made about more efficient calcination at 900°C than at 700°C. For Fe–Al–SiO₂ powders, it is reasonable to carry out calcination in a temperature range of 700–750°C with an assumption about the effect of the SiO₂ support on the thermosynthesis of iron aluminides. An experimental analysis of the morphology and elemental composition of the surface of the obtained samples is presented. It is found that the catalyst powders have medium sphericity and angularity. Fe–Al–SiO₂ powders have a more developed surface than Co–Al–SiO₂. Lower intermetallic compounds are predominantly formed on the surface of the Co–Al–SiO₂ sample. Correction of the modes of mechanical alloying by means of fragmentation of the process, variation of the intensity of its parameters, and different conditions of calcination for Co–Al–SiO₂ and Fe–Al–SiO₂ are proposed.