MgAl2O4 spinel-driven activity enhancement in phenol methylation with dimethyl carbonate to anisole

Mg x AlO were prepared by cation-anion double hydrolysis for phenol methylation. • Mg 0.8 AlO shows superior anisole yield (99.2%) and stability to the reported value. • MgAl 2 O 4 /MgO mass ratio is linearly correlated with anisole yield. • Mg 0.8 AlO with the highest MgAl 2 O 4 /MgO ratio endows the synergy of acid-base sites. • Catalyst deactivation was caused by carbon deposits, rather than structure change. MgAl 2 O 4 spinel with robust structure stability and adjustable acid-basic properties is considered a promising catalyst in the methylation of phenol with dimethyl carbonate (DMC) to produce anisole. Mg x AlO composite oxide catalysts ( x  = 0.4, 0.6, 0.8 and 1.0) were synthesized via the cation-anion double hydrolysis (CADH) method and directly used for the phenol methylation reaction to anisole, unlike previously reported supported catalysts. The catalytic performance showed a trend of first increasing and then declining with rising Mg/Al molar ratio, and the maximum phenol conversion (99.5%) and anisole selectivity (99.7%) occurred in Mg 0.8 AlO, outperforming most supported Mg Al catalysts in previous literatures. The phase mass ratio of MgAl 2 O 4 /MgO was identified as the crucial factor for the catalytic performance based on the linear relationship between the ratio and anisole yield. The optimized Mg 0.8 AlO catalyst with the largest MgAl 2 O 4 /MgO ratio could facilitate the synergy of acid-base active sites, which are responsible for DMC adsorption and activation of phenol hydroxyl hydrogen, respectively. Furthermore, Mg 0.8 AlO catalyst maintained relatively good cycling stability with decline by 11.2% after four consecutive recycling runs in anisole yield, attributing to the well preserving of the spinel framework and yet accompanied with carbon deposition derived from over-methylation and transesterification. This work developed an innovative preparation strategy and provided new insights into Mg x AlO composite oxide catalysts, paving for the application of solid acid-base catalysts in heterogeneous reactions. Download: Download high-res image (403KB) Download: Download full-size image