Synthesis and reactivity of gold nanoparticles supported on transition metal doped mesoporous silica

Mixed mesoporous silica samples with Co, Al and Fe as heteroelements were synthesized. Two classes of mesoporous silica were studied: MCM-41 prepared under basic conditions to yield one dimensional (1-D) pores; and aerosol-derived silica prepared under acidic conditions to yield 1-D pores arranged within spherical particles. The silica surface was subsequently functionalized with amine groups to allow deposition–precipitation of gold nanoparticles. These gold catalysts supported on amine functionalized mixed mesoporous silica were tested for CO oxidation and were found to become active at T > 250 °C. The Au particles grew in size after reactivity measurements to sizes larger than the pore diameter; however, the majority of Au particles remained within the pores. Our results indicate that the silica walls (1 nm thick) are not able to restrain the growth of Au particle size. The addition of the heteroelement did not lead to a significant improvement in the thermal stability of these catalysts; the major effect was an increase in CO oxidation activity compared to the pure silica. The highest reactivity was seen in cobalt-silica mixed mesoporous oxide prepared by the aerosol method, with a reactivity of 2.3 × 10−5 mol CO2/s/gcat at 250 °C and activation energy of 40 kJ/mol.