Highly dispersed platinum in metal organic framework NH2-MIL-101(Al) containing phosphotungstic acid – Characterization and catalytic performance

Abstract

The synthesis, characterization (FT-IR, XPS, NMR, UV–Vis), and catalytic performance of Pt supported on phosphotungstic acid (PTA) encapsulated in a metal organic framework (MOF) are reported. The highly dispersed Keggin units of PTA in NH2-MIL-101(Al), synthesized in one step, act as anchoring sites for the Pt precursor species. After different post-treatments, the resulting catalysts have been tested in the oxidation of CO, the preferential oxidation of CO in the presence of H2, and the hydrogenation of toluene. Reduction at 473K results in the formation of small Pt0 clusters and Pt2+ species. Reduction at 573K induces the formation of intermetallic Pt–W5+ species, which exhibit the best CO oxidation activity and a higher selectivity toward CO2 than alumina supported Pt, resembling the combination of a noble metal on a reducible support. In toluene hydrogenation, the MOF catalysts perform worse than Pt on alumina, ascribed to the too small size of the Pt clusters in the MOF catalysts.