Y_1–<i>x</i>Sc_<i>x</i>BaZn₃GaO₇ (0 ≤ <i>x</i> ≤ 1): Structure Evolution by Sc-Doping and the First Example of Photocatalytic Water Reduction in “114” Oxides

“114” oxides have shown intriguing physical properties while their performance in photocatalysis has not yet been reported probably due to the instability in aqueous solution. YBaZn₃GaO₇ is an exception, which is stable and indeed shows observable photocatalytic H₂ evolution (∼2 μmol/h/g) in methanol aqueous solution under UV light. This activity was enhanced to 23.6 μmol/h/g by a full replacement of Y³⁺ by Sc³⁺. Optical absorption spectra and theoretical calculations show no significant difference upon Sc³⁺-doping. Instead, a systematic analysis of the structure evolution by Rietveld refinements for Y_1–<i>x</i>Sc_<i>x</i>BaZn₃GaO₇ (0 ≤ <i>x</i> ≤ 1) suggests that the increase of the catalytic activity is likely due to the decrease of the structural defects and thus the lower level of recombination rate of e^– and h⁺. In detail, Sc³⁺ substitution leads to a shrinkage of YO₆ octahedra, and successively the adjustment of the Zn²⁺/Ga³⁺ occupancy behaviors in tetrahedra sites. The photocatalytic H₂ evolution rate was further optimized to 118.2 μmol/h/g in methanol solution and 42.9 μmol/h/g in pure water for 1 wt % Pt-loaded ScBaZn₃GaO₇. Here, the relatively less investigated nonmagnetic “114” oxides were, for the first time, proved to be good candidates for photocatalytic water reduction

Strong Lewis Base Ga₄B₂O₉: Ga–O Connectivity Enhanced Basicity and Its Applications in the Strecker Reaction and Catalytic Conversion of <i>n</i>‑Propanol

Heterogeneous solid base catalysis is valuable and promising in chemical industry, however it is insufficiently developed compared to solid acid catalysis due to the lack of satisfied solid base catalysts. To gain the strong basicity, the previous strategy was to basify oxides with alkaline metals to create surficial vacancies or defects, which suffers from the instability under catalytic conditions. Monocomponent basic oxides like MgO are literally stable but deficient in electron-withdrawing ability. Here we prove that a special connectivity of atoms could enhance the Lewis basicity of oxygen in monocomponent solids exemplified by Ga₄B₂O₉. The structure-induced basicity is from the μ₃-O linked exclusively to five-coordinated Ga³⁺. Ga₄B₂O₉ behaved as a durable catalyst with a high yield of 81% in the base-catalyzed synthesis of α-aminonitriles by Strecker reaction. In addition, several monocomponent solid bases were evaluated in the Strecker reaction, and Ga₄B₂O₉ has the largest amount of strong base centers (23.1 μmol/g) and the highest catalytic efficiency. Ga₄B₂O₉ is also applicable in high-temperature solid–gas catalysis, for example, Ga₄B₂O₉ catalyzed efficiently the dehydrogenation of <i>n</i>-propanol, resulting in a high selectivity to propanal (79%). In contrast, the comparison gallium borate, Ga-PKU-1, which is a Brönsted acid, preferred to catalyze the dehydration process to obtain propylene with a selectivity of 94%