Influence of pore size of SBA-15 on activity and selectivity of H3[PMo12O40] supported on tailored SBA-15

• Supporting heteropolyoxo molybdates on SBA-15 resulted in regular Keggin ions.
• PMo12-SBA-15 (10, 14, 19 nm) formed a mixture of mostly [MoO4] and [MoO6] units.
• The resulting [MoxOy] structures depended on the pore size of the SBA-15.
• The stability of the Keggin ions depended mostly on the nature of the support.
• Tailoring the pore radius of SBA-15 permitted to prepare Mo oxide model systems.

Large pore SBA-15 was successfully synthesized and used as support material for molybdenum based oxidation catalysts. H3[PMo12O40] was supported on SBA-15 with modified pore radii (10, 14, 19 nm). All samples were prepared with a similar surface coverage of 1 Keggin ion per 13 nm2 independent of the pore radii. Structural evolution and catalytic activity of H3[PMo12O40] supported on SBA-15 (PMo12-SBA-15) with different pore radii (10, 14, 19 nm) were investigated under selective propene oxidation conditions by in situ X-ray absorption spectroscopy investigations. PMo12-SBA-15 (10, 14, 19 nm) formed a mixture of mostly tetrahedral [MoO4] and octahedral [MoO6] units during thermal treatment in propene oxidation conditions. A higher concentration of octahedral [MoO6] units and higher oligomerized [MoxOy] units were detected for act. PMo12-SBA-15 (10 nm) compared to act. PMo12-SBA-15 (14, 19 nm). The higher concentration of [MoxOy] units present in act. PMo12-SBA-15 (10 nm) resulted in an increased catalytic activity compared to activated PMo12-SBA-15 (14, 19 nm) with a lower concentration of [MoxOy] units. Selectivities towards oxidation products during propene oxidation were comparable and largely independent of the pore radii of act. PMo12-SBA-15 (10, 14, 19 nm). Apparently, tailoring the pore radius of silica SBA-15 permitted to prepare Mo oxide model systems to investigate correlation between activity and structure of characteristic oxide species at similar surface coverage.

Figure optionsDownload as PowerPoint slide