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Although the development of solid catalysts for H2O2 synthesis has recently gained considerable attention, optimizing its utilization and product selectivity in a given reaction is equally important but less studied. The design of solid catalysts for H2O2 activation in aniline oxidation to value-added nitrosobenzene and azoxybenzene has gained considerable attention over the past decade. However, distinct solid catalysts are often required to obtain the target compound in literature. The heterogeneity of materials used makes it very difficult to provide in-depth guidance for the design of catalysts. In this study, we showed that one can easily obtain the target compound in this reaction by regulating H2O2 activation on pristine CeO2 enclosed by distinct but well-defined surfaces. The bridging peroxo species found on the (100) surface preferentially generates radicals, which non-selectively oxidizes H2O2 and aniline, resulting in poor H2O2 utilization and low nitrosobenzene yield in aniline oxidation. In comparison, the side-on peroxo species formed on the (110) surface displays a certain degree of selectivity towards aniline and hence gives a much higher nitrosobenzene yield with improved H2O2 utilization. To our surprise, the end-on peroxo species of the (111) surface is inert to H2O2 in the solution and can stoichiometrically convert aniline to phenylhydroxylamine (Ph-NHOH), which is the key intermediate to produce azoxybenzene. The structure–selectivity correlation established in this study is believed to guide the rational design of catalysts with high H2O2 utilization and product selectivity in other oxidation reactions. [ABSTRACT FROM AUTHOR]

Sustaining long-term chemical or photochemical stability of a homogeneous molecular catalyst remains a significant challenge. We report a remarkable improvement of the activity and stability of a Au25@ZIF-8@TiO2-ReP catalyst via composition engineering with double redox active sites of Au25 NCs and a Re(I) complex for H2 and CO evolution to promote electron utilization. [ABSTRACT FROM AUTHOR]

Urea pollution is a growing environmental concern, and its removal via catalytic hydrolysis is challenging due to the resonance-stabilized amide bonds. In nature, this reaction is catalyzed by ureases in many soil bacteria. However, the remedy of this problem with natural enzymes is not feasible as they are easily denatured and require high costs for both preparation and storage. Given this, the development of nanomaterials bearing enzyme-like activity (nanozymes) with advantages such as low production cost, simple storage, and pH/thermal stability has attracted much attention over the past decade. As inspired by the mechanism of urease-catalyzed urea hydrolysis, the co-presence of Lewis acid (LA) and Brønsted acid (BA) sites is imperative to proceed with this reaction. Herein, layered HNb 3 O 8 samples with intrinsic BA sites were adopted for investigation. The layer reduction of this material to few-/single layers can expose Nb sites with various LA strengths depending on the degree of NbO 6 distortion. Among the catalysts examined, single-layer HNb 3 O 8 bearing strong LA and BA sites displays the best hydrolytic activity towards acetamide and urea. This sample with high thermal stability was found to outperform urease at temperatures higher than 50 °C. The acidity-activity correlation established in this study is believed to guide the future design of industrial catalysts to remediate urea pollution.

Neural progenitor cells (NPCs) therapy, a promising therapeutic strategy for neurodegenerative diseases, has a huge challenge to ensure high survival rate and neuronal differentiation rate. Cerium oxide (CeO 2 ) nanoparticles exhibit multienzyme mimetic activities and have shown the capability of regulating reactive oxygen species (ROS), which is a pivotal mediator for intracellular redox homeostasis in NPCs, regulating biological processes including differentiation, proliferation, and apoptosis. In the present study, the role of facet-dependent CeO 2 -mediated redox homeostasis in regulating self-renewal and differentiation of NPCs is reported for the first time. The cube-, rod-, and octahedron-shaped CeO 2 nanozymes with different facets are prepared. Among the mentioned nanozymes, the cube enclosed by the (100) facet exhibits the highest CAT-like activity, causing it to provide superior protection to NPCs from oxidative stress induced by H 2 O 2 ; meanwhile, the octahedron enclosed by the (111) facet with the lowest CAT-like activity induces the most ROS production in ReNcell CX cells, which promotes neuronal differentiation by activated AKT/GSK-3β/β-catenin pathways. A further mechanistic study indicated that the electron density of the surface Ce atoms changed continuously with different crystal facets, which led to their different CAT-like activity and modulation of redox homeostasis in NPCs. Altogether, the different surface chemistry and atomic architecture of active sites on CeO 2 exert modulation of redox homeostasis and the fate of NPCs.

Sustaining long-term chemical or photochemical stability of a homogeneous molecular catalyst remains a significant challenge. We report a remarkable improvement of the activity and stability of a Au25@ZIF-8@TiO2-ReP catalyst via composition engineering with double redox active sites of Au25 NCs and a Re(i) complex for H2 and CO evolution to promote electron utilization.