Selective and regular localization of accessible Pt nanoparticles inside the walls of an ordered silica: Application as a highly active and well-defined heterogeneous catalyst for propene and styrene hydrogenation reactions

We describe here an original methodology related to the “build-the-bottle-around-the-ship” approach yielding a highly ordered silica matrix containing regularly distributed Pt nanoparticles (NPs) located inside the silica walls, Pt@{walls}SiO2. The starting colloidal solution of crystalline Pt nanoparticles was obtained from Pt(dba)2 (dba = dibenzylidene acetone) and 3-chloropropylsilane. The resulting nanoparticles (diameter: 2.0 ± 0.4 nm determined by HRTEM) resulted hydrophilic. The NPs present in the THF colloidal solution were incorporated inside the walls of a highly ordered 2D hexagonal mesoporous silica matrix via sol–gel process using a templating route with tetraethylorthosilicate, TEOS, as the silica source, and block copolymer (EthyleneOxide)20(PropyleneOxide)70(EthyleneOxide)20 (Pluronic P123) as the structure-directing agent. Low-temperature calcination of the crude material at 593 K led to the final solid Pt@{walls}SiO2. Characterization by IR, HRTEM, BF-STEM and HAADF-STEM, SAXS, WAXS, XRD, XPS, H2 chemisorption, etc. of Pt@{walls}SiO2 confirmed the 2D hexagonal structuration and high mesoporosity (870 m2/g) of the material as well as the presence of stable 2-nm-sized crystalline Pt(0) NPs embedded inside the walls of the silica matrix. The material displayed no tendency to NPs sintering or leaching (Pt loading 0.3 wt.%) during its preparation.Pt@{walls}SiO2 was found to be a stable, selective and highly active hydrogenation catalyst. The catalytic performances in propene hydrogenation were tested under chemical regime conditions in a tubular flow reactor (278 K, propene/H2/He = 20/16/1.09 cm3/min, Ptot = 1 bar) and were found superior to those of an homologous solid containing Pt NPs along its pore channels Pt@{pores}SiO2 and to those of a classical industrial catalysts Pt/Al2O3, (TOF = 2.3 s−1 vs. TOF = 0.90 and 0.92 s−1, respectively, calculated per surface platinum atoms). Pt@{walls}SiO2 also catalyzes fast and selective styrene hydrogenation. A material containing by design Pt NPs both in its walls and in its pores, Pt@{walls + pores}SiO2, is also described.

Accessible 2 nm crystalline Pt(0) nanoparticles are localized by design in the walls of a highly ordered mesoporous oxide, by the use of novel hydrophilic preformed nanoparticles stabilized by chloroalkylsilane ligands. The embedded nanoparticles show no leaching nor sintering and are highly active in catalytic styrene and propene hydrogenations.Figure optionsDownload high-quality image (133 K)Download as PowerPoint slideHighlights
► Pt0 nanoparticles embedded in the walls of a highly ordered silica matrix by design.
► Original hydrophilic 2-nm-sized Pt nanoparticles stabilized by chloroalkylsilane.
► Hydrophilic/hydrophobic interactions around preformed nanoparticles key to design.
► Material Pt@{walls}SiO2 stable to particle sintering and leaching.
► Highly active catalytic performances in propene and styrene hydrogenations.