Strong Lewis Base Ga4B2O9: Ga-O Connectivity Enhanced Basicity and Its Applications in the Strecker Reaction and Catalytic Conversion of n-Propanol.

Abstract

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 n-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%.