Mesoporous Ferromagnetic MPt@Silica/Carbon (M = Fe, Co, Ni) Composites As Advanced Bifunctional Catalysts

Ferromagnetic MPt (Fe, Co, Ni) nanocomposites were obtained by infiltration of aqueous and chloroform precursor solutions into ordered mesoporous SBA-15 and CMK-3. Channel-confined crystallization of the intermetallic phases was achieved under a reductive and inert atmosphere in a temperature range from 673 to 1073 K using conventional and ultrafast IR furnace heating. The proper choice of mesoporous matrix allows one to tailor crystallite size and to affect the phase transformation rate into ordered face-centered tetragonal (fct) MPt alloys. XRD and TEM techniques were used to monitor the structural evolution in the system. Physisorption methods reveal degradation of the mesoporous carbon matrix for MPt@CMK-3 composites while SBA-15 templated structures stay intact. SQUID investigations were carried out, demonstrating a strong dependence of magnetic properties on the intermetallic system, matrix, and treatment conditions. Especially for fct FePt@carbon, very high room-temperature coercivities up to 28.4 kOe were observed. The materials are efficient catalysts for acetylene to ethylene hydrogenation. Structure-sensitive selectivity of FePt is reported for the first time, demonstrating a higher selectivity of fct FePt composites as compared to the disordered face-centered cubic (fcc) phase.