Study on Controlled Synthesis of Mesoporous Pseudoboehmite via Carbonation Reaction

Pseudoboehmite is a precursor for mesoporous-activated alumina and is widely employed in catalysis and adsorption applications. The carbonation reaction is recognized as the most environmentally friendly and cost-effective production method. However, its susceptibility to impurity formation poses challenges in practical applications. The control of the reaction end point pH is crucial for ensuring purity. Currently, there is a lack of research on the influence of sodium aluminate solution concentration and composition ratio (αk) on the reaction end point pH and its impact on the crystallization mechanism. This research extensively explored the effects of the sodium aluminate solution concentration and αk on the carbonation process. Analysis of crystalline phases under different conditions emphasized the critical influence of concentration and αk on the critical end point pH of pseudoboehmite synthesis and its impact on the crystallization mechanism. The results revealed significant effects of the concentration and αk on the pH change during the carbonation reaction. Increasing concentration raised both the maximum and minimum end point pH values, while elevated αk had the opposite effect. Increasing αk and concentration led to a narrowing of the pH range at the end point of the carbonation reaction for preparing pseudoboehmite. The study revealed that pseudoboehmite and Bayerite crystals were generated from two different sodium aluminate decomposition pathways, which challenges the conventional understanding of the crystalline growth mechanism of aluminum hydroxide. Reducing the pH value of the reaction end point accelerated the nucleation of pseudoboehmite and inhibition of Bayerite. Ultimately, successfully synthesizing mesoporous pseudoboehmite and activated alumina, with a pore volume of 0.44 cm3/L, surface area of 242.76 m2/g, and average pore diameter of 7.3 nm, this study not only supported precise reaction control and enhanced production efficiency but also offered insights for eco-friendly utilization of CO2, thus contributing to a more sustainable and environmentally friendly production process.