Coking and Deactivation Behavior of Ba–La-Modified Alumina in the Aldol Condensation of Methyl Acetate with Formaldehyde: Effect of the Reactant Composition
Qiang Bao, Yunfeng Hu, Xiaofei Liu, Guoliang Wu, Penglai Sun, Junping Ge, Ming Xu
Abstract
Catalyst deactivation caused by coking has always been a concern in the aldol condensation reaction. In this work, Ba–La-modified alumina has been characterized and tested as a catalyst in the vapor-phase aldol condensation process. The coke formation, acid–base properties, and deactivation behavior of the spent catalysts were studied through a series of characterization techniques: N2 adsorption–desorption, pyridine FT-IR, TG-DTA, TPO-MS, as well as NH3, CO2-TPD, and UV Raman spectroscopy. It was found that the main components of coke are polycyclic aromatic hydrocarbons, which can be removed by high-temperature roasting under an air atmosphere. The overactivation of formaldehyde accelerates the rate of coke deposition and ultimately aggravates the decrease in the stability of the catalyst. Furthermore, adding a proper amount of methanol to the reactants can greatly inhibit the hydrolysis of esters and improve the selectivity of the catalyst for the target reaction. Under the optimum reaction condition of Ma/FA/CH3OH = 6:2:8, the pairs of medium acidic and weakly basic sites enable Ba–La/Al2O3 to achieve the highest yield of methyl acrylate.