Shell Chemicals operates the styrene monomer propylene oxide (SMPO) process in four world-scale plants and is currently building a fifth plant in China. The heart of this process comprises the epoxidation reaction of propylene with ethyl benzene hydro peroxide to propylene oxide and methyl phenyl carbinol (a styrene monomer precursor) over a proprietary titanium-on-silica epoxidation catalyst. One of the key performance aspects of the SMPO process is the high atom efficiency, partly resulting from the high selectivities in the epoxidation step. The efficiency of the process can be further improved through intimate knowledge of suitable supports for titanium-on-silica catalysts and by gaining increased understanding of the chemistry of catalytic epoxidation. Research in these areas has provided leads to longer-lived, more selective titanium-on-silica catalysts. This is an example of how improvements of the SMPO process support our initiatives in sustainable development. (C) 2004 Published by Elsevier B.V.