Insights into Shape Selectivity and Acidity Control in NiO-Loaded Mesoporous SBA-15 Nanoreactors for Catalytic Conversion of Cellulose to 5‑Hydroxymethylfurfural

Facilitated isomerization of cellulose hydrolysis intermediate glucose without unexpected byproducts, which is the rate-determining step in the production of high-value-added biofuels, enables the efficient production of 5-hydroxymethylfurfural (5-HMF) from cellulose. In this work, considering the essential role of the acidity control and shape selectivity of a zeolite catalyst, a NiO-loaded mesoporous NiO/poly(vinyl pyrrolidone) (PVP)-phosphotungstic acid (HPA)@SBA-15 nanoreactor was prepared. This SBA-15 nanoreactor with a pore size of 5.47 nm reduced the concentration of byproducts formic acid (FA) and levulinic acid (LA) through shape selection for intermediates. Well-defined NiO nanoparticles (Ni-to-carrier mass ratio was 1:1) provided the NiO/PVP-HPA@SBA-15 nanoreactor a high Lewis acidity of 99.29 μmol g–1 for glucose catalytic isomerization, resulting in an increase in total reducing sugar (TRS) yield by 5 times. Such a nanoreactor remarkably improved the reaction efficiency of 5-HMF production from cellulose (a 5-HMF selectivity of 95.81%) in the 1-butyl-3-methylimidazolium chloride ([BMIM]Cl)/valerolactone (GVL) biphasic system

Novel and potent Lewis acid catalyst: Br₂-catalyzed Friedel–Crafts reactions of naphthols with aldehydes

<p>A discovery that the inexpensive Br₂ can serve as a potent Lewis acid catalyst for bis(2-hydroxy-1-naphthyl)methanes synthesis is presented. Under the catalysis of Br₂ at room temperature, naphthols reacted smoothly with various aldehydes with high efficiency and broad substrate scope. This reaction used to require highly acidic conditions and/or high temperature and/or pressure, and sometimes featured poor yields. Moreover, theoretical calculations suggested that Br₂ is a potent Lewis acid to activate the carbonyl group, yet it was not the primary cause for the remarkable activity of Br₂ in the current communication.</p

Lateral-Size-Mediated Efficient Oxygen Evolution Reaction: Insights into the Atomically Thin Quantum Dot Structure of NiFe₂O₄

The study of high-performance electrocatalysts for driving the oxygen evolution reaction (OER) is important for energy storage and conversion systems. As a representative of inverse-spinel-structured oxide catalysts, nickel ferrite (NiFe₂O₄) has recently gained interest because of its earth abundance and environmental friendliness. However, the gained electrocatalytic performance of NiFe₂O₄ for the OER is still far from the state-of-the-art requirements because of its poor reactivity and finite number of surface active sites. Here, we prepared a series of atomically thin NiFe₂O₄ catalysts with different lateral sizes through a mild and controllable method. We found that the atomically thin NiFe₂O₄ quantum dots (AT NiFe₂O₄ QDs) show the highest OER performance with a current density of 10 mA cm^–2 at a low overpotential of 262 mV and a small Tafel slope of 37 mV decade^–1. The outstanding OER performance of AT NiFe₂O₄ QDs is even comparable to that of commercial RuO₂ catalyst, which can be attributed to its high reactivity and the high fraction of active edge sites resulting from the synergetic effect between the atomically thin thickness and the small lateral size of the atomically thin quantum dot (AT QD) structural motif. The experimental results reveal a negative correlation between lateral size and OER performance in alkaline media. Specifically speaking, the number of low-coordinated oxygen atoms increases with decreasing lateral size, and this leads to significantly more oxygen vacancies that can lower the adsorption energy of H₂O, increasing the catalytic OER efficiency of AT NiFe₂O₄ QDs