Characterization and theoretical calculations as powerful compensators for kinetics in the study of heterogeneous catalytic mechanisms on esterifying carboxylic acid

Reaction mechanism is crucial for understanding, applying, and optimizing the carboxylic acid esterification. This review discusses the possible carboxylic acid esterification mechanisms, including homogeneous acid-catalyzed acyloxy/alkoxy bond cleavage, heterogeneous single/dual-site acid/base, and dual-site acid-base synergistic catalysis. The physical means, applications, and limitations of quasi-homogeneous (QH), Eley-Rideal (ER), Langmuir-Hinshelwood-Hougen-Watson (LH), Hattori (H), and their modified models were summarized. Since the similarity or significant difference in adsorption performance of reactants may lead to parameter dependence (e.g., different ER type variants) or overparametrization (e.g., LH model), and kinetic studies cannot identify active sites and intermediates, thus insufficiently revealing a detailed heterogeneous esterification mechanism. The applications of characterization techniques in revealing active sites, adsorption mechanisms, and chemical bond evolution were discussed to verify and compensate for kinetic results. Density functional theory calculations and microkinetic modeling were also outlined to give atomistic-level insights. Furthermore, the use of enzymes and solvents in the esterification was outlined.