The　grafting　reaction　of　tetraneopentyl　titanium　on　the　surface　of　MCM-41　mesoporous　molecular　sieves　dehydroxylated　preliminary　at　500　degrees　C　leads　to　formation　of　the　well-defined　bigrafted　surface　complex　(　Si-O)(2)Ti(CH2CMe3)(2).　On　reaction　with　water　or　alcohol,　the　neopentyl　ligands　can　be　replaced　selectively　by　alcoxy　or　hydroxy.　On　calcination　at　500　degrees　C,　a　well-dispersed　titanium　oxide　supported　on　MCM-41　is　obtained.　In　situ　FTIR,　DRS,　and　XAFS　characterizations　suggest　that　titanium　is　present　as　isolated　tetrahedral　species　on　the　surface　of　MCM-41.　This　solid　was　used　for　the　photocatalytic　oxidation　of　ethylene　in　oxygen　under　UV　irradiation,　and　its　activity　was　compared　to　that　of　Ti-MCM-41　prepared　by　direct　hydrothermal　synthesis.　The　higher　activity　of　the　samples　prepared　by　reaction　with　the　organometallic　complex　is　attributed　to　the　good　dispersion　of　titanium　on　the　surface　of　MCM-41.　(c)　2005　Elsevier　Inc.　All　rights　reserved.