The utility of a hierarchically ordered nanoporous SBA-15 architecture, comprising 270 nm macropores and 5 nm mesopores (MM-SBA-15), for the catalytic aerobic selective oxidation of sterically challenging allylic alcohols is shown. Detailed bulk and surface characterization reveals that incorporation of complementary macropores into mesoporous SBA-15 enhances the dispersion of sub 2 nm Pd nanoparticles and thus their degree of surface oxidation. Kinetic profiling reveals a relationship between nanoparticle dispersion and oxidation rate, identifying surface PdO as the catalytically active phase. Hierarchical nanoporous Pd/MM-SBA-15 outperforms mesoporous analogues in allylic alcohol selective oxidation by (i) stabilizing PdO nanoparticles and (ii) dramatically improving in-pore diffusion and access to active sites by sesquiterpenoid substrates such as farnesol and phytol. © 2013 American Chemical Society.
Bibliographical noteWe thank the EPSRC (EP/F009488/1, EP/G007594/2 and EP/E046754/1) for a Leadership Fellowship (A.F.L.) and studentship support (C.M.A.P. and S.G.W.), and the Royal Society for an Industry Fellowship (K.W.). TEM was provided through the Leeds EPSRC Nanoscience and Nanotechnology Research Equipment Facility (LENNF) (EP/F056311/1).
Additional support and catalyst characterization, and selox reaction data. This material is available free of charge via the Internet at http://pubs.acs.org.
- selective oxidation