Daniel L. Baptista

Hybrid tantalum oxide nanoparticles from the hydrolysis of imidazolium tantalate ionic liquids: efficient catalysts for hydrogen generation from ethanol/water solutions

The reaction of equimolar amounts of 1-n-butyl-3-methylimidazolium chloride (BMI·Cl) or 1-n-decyl-3-methylimidazolium chloride (DMI·Cl) with TaCl5 affords imidazolium tantalate ionic liquids (ILs) BMI·TaCl61 and DMI·TaCl62. The hydrolysis of ILs 1 and 2 yields hybrid-like tantalum oxide nanoparticles (NPs) with size distribution dependent on the nature of the IL used (3.8–22 nm from IL 1 and 1.5–6 nm from 2). A significant aggregation/agglomeration of the particles was observed after the removal of the IL content of the hybrid material by calcination, forming predominantly large particles (mainly bulk tantalum oxides). These new hybrid-like Ta2O5/IL NPs are highly active photocatalyst nanomaterials for hydrogen production by reforming of ethanol at ambient temperature. Hydrogen evolution rates up to 7.2 mmol H2 g−1 h−1 and high apparent quantum yields up to 17% were measured. The hybrid-like Ta2O5/IL NPs sputtered-decorated with ultra-small Pt NPs (1.0 ± 0.3 nm) as co-catalysts reached activities leading to even higher hydrogen production (9.2 H2 mmol g−1 h−1; apparent quantum yield of 22%). The calcined materials (with or without Pt NPs) showed much lower photocatalytic activity under the same reaction conditions (up to 2.8 mmol g−1 of H2). The remarkable activity of the hybrid-like Ta2O5/IL NPs may be related to the presence of the remaining IL that provides hydrophilic regions, facilitating the approach of polar molecules (water and alcohol) to the semiconductor active photocatalytic sites.

Challenging thermodynamics: hydrogenation of benzene to 1,3- cyclohexadiene by Ru@Pt nanoparticles

Since the earliest reports on catalytic benzene hydrogenation, 1,3‐cyclohexadiene and cyclohexene have been proposed as key intermediates. However, the former has never been obtained with remarkable selectivity. Herein, we report the first partial hydrogenation of benzene towards 1,3‐cyclohexadiene under mild conditions in a catalytic biphasic system consisting of Ru@Pt nanoparticles (NPs) in ionic liquid (IL). The tandem reduction of [Ru(COD)(2‐methylallyl)2] (COD=1,5‐cyclooctadiene) followed by decomposition of [Pt2(dba)3] (dba=dibenzylideneacetone) in 1‐n‐butyl‐3‐methylimidazolium hexafluorophosphate (BMI⋅PF6) IL under hydrogen affords core–shell Ru@Pt NPs of 2.9±0.2 nm. The hydrogenation of benzene (60 °C, 6 bar of H2) dissolved in n‐heptane by these bimetallic NPs in BMI⋅PF6 affords 1,3‐cyclohexadiene with an unprecedented 21 % selectivity at 5 % benzene conversion. Conversely, almost no 1,3‐cyclohexadiene was observed when using monometallic Pt0 or Ru0 NPs under the same reaction conditions and benzene conversions. This study reveals that the selectivity is related to synergetic effects of the bimetallic composition of the catalyst material as well as to the performance under biphasic reaction conditions. It is proposed that colloidal metal catalysts in ILs and under multiphase conditions (“dynamic asymmetric mixtures”) can operate far from the thermodynamic equilibrium akin to chemically active membranes.