Anchoring Platinum Nanoparticles onto Oxygen Vacancy-Modified Mixed Metal Oxides for Selective Oxidation Reaction of Aromatic Alcohols

Directed transformation of organic compounds under mild conditions, especially alcohol oxidation, presents great challenges in green chemistry. Herein, we report a platinum nanoparticle catalyst supported on zinc-gallium mixed metal oxides (denoted as Pt/ZnGa-MMOs), which displays superior catalytic activity for the selective oxidation reaction of benzyl alcohol to benzaldehyde (conversion: >99%; selectivity: >99%; reaction rate: 125 mmolbenzyl alcohol gPt-1 h-1). Both experimental studies [X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS)] and DFT calculations reveal the formation of an interfacial structure (Zn2+δ-Ov-Ga3-δ) on the ZnGa-MMOs support. Moreover, in situ Fourier transform infrared (FT-IR) spectroscopic analysis demonstrates that the Pt species acts as an intrinsic active center to promote the oxidation of the carbon-oxygen bond in the benzyl alcohol molecule, with the formation of the benzaldehyde. This work provides an effective strategy for the preparation of heterogeneous catalysts via constructing the support oxygen vacancy to anchor metal sites toward selective oxidation reactions.

Reusable Magnetite Nanoparticle (Fe3O4 NP) Catalyst for Selective Oxidation of Alcohols under Microwave Irradiation

Iron oxide nanoparticles (NPs) are nontoxic and abundant materials which have long been investigated as reusable catalysts in oxidation reactions, but their use so far has been hampered by a low selectivity. Here, unsupported iron oxide NPs have been found to successfully catalyze the microwave-assisted oxidation of primary and secondary alcohols to their respective aldehydes and ketones with a high selectivity when N-methylmorpholine N-oxide was used as the terminal oxidant. The crystalline phase and size of the iron-based catalyst have a drastic effect on its activity, with small magnetite (Fe3O4) NPs being the optimal catalyst for this reaction. The nanocatalyst could be easily recovered by magnetoseparation and successfully recycled four times without any need for special pretreatment or reactivation step and with a minimal loss of activity. The subsequent loss of activity was attributed to the transition from magnetite (Fe3O4) to maghemite (γ-Fe2O3), as confirmed by X-ray diffraction, Fourier transform infrared, and X-ray absorption near-edge spectroscopy. The nanocatalyst could then be reactivated by the high-temperature microwave treatment and used again for the microwave-assisted oxidation reaction.

Construction of N-Rich Aminal-Linked Porous Organic Polymers for Outstanding Precombustion CO2 Capture and H2 Purification: A Combined Experimental and Theoretical Study

A large number of scientific investigations are needed for developing a sustainable solid sorbent material for precombustion CO2 capture in the integrated gasification combined cycle (IGCC) that is accountable for the industrial coproduction of hydrogen and electricity. Keeping in mind the industrially relevant conditions (high pressure, high temperature, and humidity) as well as good CO2/H2 selectivity, we explored a series of sorbent materials. An all-rounder player in this game is the porous organic polymers (POPs) that are thermally and chemically stable, easily scalable, and precisely tunable. In the present investigation, we successfully synthesized two nitrogen-rich POPs by extended Schiff-base condensation reactions. Among these two porous polymers, TBAL-POP-2 exhibits high CO2 uptake capacity at 30 bar pressure (57.2, 18.7, and 15.9 mmol g-1 at 273, 298, and 313 K temperatures, respectively). CO2/H2 selectivities of TBAL-POP-1 and 2 at 25 °C are 434.35 and 477.93, respectively. On the other hand, at 313 K the CO2/H2 selectivities of TBAL-POP-1 and 2 are 296.92 and 421.58, respectively. Another important feature to win the race in the search of good sorbents is CO2 capture capacity at room temperature, which is very high for TBAL-POP-2 (15.61 mmol g-1 at 298 K for 30 to 1 bar pressure swing). High BET surface area and good mesopore volume along with a large nitrogen content in the framework make TBAL-POP-2 an excellent sorbent material for precombustion CO2 capture and H2 purification.