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[Display omitted] • Thermosensitive pseudohomogeneous catalysts (Pt, Pd, and Au) are synthesized. • Thermoresponsive PNIPAM polymer serves as the capping agent. • These catalysts show superior catalytic activity for reduction of nitroarenes. • PNIPAM-Pd can realize the homogenous reaction and heterogeneous separation. The reduction of nitroarenes is usually catalyzed by heterogeneous catalysts. In this work, highly stable aqueous dispersions of monodisperse Pt, Pd, and Au nanoparticles stabilized by thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPAM), are conveniently synthesized with the average sizes of 2.3, 3.1, and 2.3 nm, respectively. The modulation of the hydrophilic-hydrophobic nano-environments of the catalysts can be selectively provided by utilizing the temperature-responsive characteristics of PNIPAM. They are effective and thermosensitive pseudohomogeneous catalysts for nitroarenes reduction. The decreasing trend of catalytic activity is as follows: PNIPAM-Au > PNIPAM-Pd > PNIPAM-Pt. The catalytic reduction of nitrobenzene (NB), 4-nitrophenol (4-NP), and o-nitroaniline (o-NA) follow the pseudo-first-order kinetics, and the catalytic rates can be tuned by utilizing their temperature-responsive behavior. PNIPAM-Au nanocatalysts exhibit high turnover frequencies (TOF) up to 84, 12.9, and 40 min−1 for catalytic reduction of NB, 4-NP, and o-NA at 20 °C, respectively, which are one of the highest values ever reported. [ABSTRACT FROM AUTHOR]

• The highly stable dispersions of ultrasmall ZnO nanocrystals were prepared. • They were used as pseudohomogeneous catalyst for chemical depolymerization of PET. • ZnO nanodispersions displayed an excellent catalytic activity at 170 °C. • The methanolysis had shorter reaction time and higher activity than the glycolysis. Chemical depolymerization and recycling of polyethylene terephthalate (PET) is a sustainable way to preserve the resources and protect the environment. In this work, methanol and ethylene glycol dispersions of ultrasmall ZnO nanoparticles are firstly adopted as pseudohomogeneous catalysts for alcoholysis of PET. The as-prepared ZnO nanoparticles have a uniform size of 4 nm and can be stable in dispersions for 6 months. In the methanolysis process of PET, the effects of various parameters on the conversion of PET and the yield of dimethyl terephthalate (DMT) were investigated. The results show that higher temperature (170 °C) was beneficial to the conversion of PET and the yield of DMT, which can reach about 97% and 95% after 15 min, respectively. The excellent activity of 553 g PET h−1 (g ZnO)−1 was achieved. Furthermore, the methanolysis of PET have shorter reaction time (1/4) and higher activity (4.7 times) than the glycolysis of PET. [ABSTRACT FROM AUTHOR]

• Size-tunable monodisperse Pd nanocrystals were prepared in a rotating packed bed. • They were adopted as pseudohomogeneous catalyst for nitrobenzene (NB) reduction. • 2.6 nm Pd nanocrystals displayed excellent catalytic property and good stability. • The obtained catalytic kinetics data confirm to the Langmuir-Hinshelwood model well. • DFT calculation was used to study the adsorption of NB on the surface of catalyst. Nitrobenzene (NB) reduction is an important catalytic reaction, which is commonly performed in aqueous medium mainly with heterogeneous catalysts. In this work, highly stable aqueous nanodispersions of Pd nanocrystals with a tunable average size between 2 and 11 nm are conveniently prepared in a high-gravity rotating packed bed (RPB) reactor, and firstly serve as a pseudohomogeneous catalyst for NB reduction. As compared to a conventional stirred tank reactor (STR), the product prepared in the RPB reactor has a more uniform particle size. More importantly, the reaction time can be greatly shortened from 3 min (STR) to 1 s (RPB), thereby realizing a continuous preparation. This Pd pseudohomogeneous catalyst displays a significantly size-dependent catalytic activity and a good stability performance. Ultra-small 2.6 nm Pd nanocrystals have a reaction rate five times as fast as 10.1 nm counterpart. The obtained kinetics data confirm to the Langmuir-Hinshelwood model well, having a small error of <10%. Furthermore, the adsorption behavior of NB molecules on the surface of Pd nanocrystals was also studied with density functional theory (DFT) calculation. Since the processing capacity of the used lab-scale RPB reached 44.2 g/h, this route may offer a general platform for mass production of monodisperse nanocrystals as pseudohomogeneous catalyst for highly efficient catalysis. [ABSTRACT FROM AUTHOR]