# On the Alkalinity of Solid Catalysts for Transesterification of Dimethyl Carbonate and Ethanol
## 1 Introduction  
Ethyl methyl carbonate (EMC), recognized as an environmentally friendly solvent and an important electrolyte solvent for lithium-ion batteries [1, 2, 3], has garnered extensive attention [4, 5] due to its biodegradability, low toxicity, electrochemical stability, and safety [6, 7]. Currently, the synthesis of EMC primarily involves the phospgene method, oxidative carbonylation, and transesterification. The phospgene method is incongruent with the principles of green chemistry due to the high toxicity of the raw material phospgene and the intermediate methyl chloroformate [8]. The oxidative carbonylation reaction is mainly used for the synthesis of symmetric esters. It is a safer and cleaner productionmethod. Nonetheless, this approach usually requires the use of precious metal catalysts and operates under strict conditions, thus posing safety concerns [9]. The transesterification of dimethyl carbonate (DMC) with ethanol to produce EMC is carried out under mild and easily controllable reaction conditions. The raw materials have low toxicity, reducing the safety risks during operation. Although there is a kinetic limitation of the reaction equilibrium for this transesterification reaction [10], the kinetic equilibrium can be disrupted by removing the product to achieve higher yields. Moreover, the byproduct diethyl carbonate (DEC), an excellent solvent, exhibits broad application potential, thereby conferring high atom economy to this method [11; 12]. Numerous alkali catalysts have been reported for the transesterification of DMC and ethanol. Homogeneous catalysts, such as ionic liquid systems synthesized from alkaline ionic precursors [13; 14], demonstrate high reactivity but suffer from separation challenges. In contrast, heterogeneous catalysts have the characteristic of easy separation but often suffer from the issue of catalyst deactivation, such as metal oxide CaO [15], supported metal oxides [16], and immobilized ionic liquid catalysts [17]. Therefore, the synthesis of high-stability solid catalysts is critical for commercialization [18; 19]. [PERSON] et al. [20] reported that MgO exhibited superior catalytic performance among MgO, ZnO, La\({}_{2}\)O\({}_{3}\), and CeO\({}_{2}\) catalysts. However, single metal oxide catalysts generally suffer from poor stability [21; 22]. Therefore, to enhance the stability of catalysts, researchers have optimized the composition and structure of catalysts [23; 24], constructed bimetallic oxide catalysts [25; 26], and even trimetallic oxide catalysts [27], achieving better catalytic effects and stability [11]. To further improve the stability of catalysts, researchers have also adopted methods such as doping non-metallic elements into the catalysts [28]. In addition to the preparation of catalysts, the deactivation mechanisms of alkali catalysts are also crucial. Many reasons, such as the reaction of H\({}_{2}\)O [29], the collapse of the catalyst framework [30], the poisoning of active sites [31], the leaching of active components, and the decrease in catalyst surface area [32], are possible for the deactivation of solid catalysts. However, most researchers believe that the primary reason for catalyst deactivation is the reaction of alkali sites with H\({}_{2}\)O and CO\({}_{2}\) to form carbonates [21; 29; 33]. For instance, in the transesterification of soybean oil to produce biodiesel using CaO as a catalyst, [PERSON] et al. [21] investigated the causes of catalyst deactivation and found that CaO is highly sensitive to H\({}_{2}\)O and CO\({}_{2}\), easily forming hydroxides and carbonates. [PERSON] et al. [29] found in the transesterification reaction of DMC and ethanol that the alkali strength of the catalyst is directly related to its catalytic activity, with H\({}_{2}\)O being the key factor causing the deactivation of CH\({}_{3}\)ONa. [PERSON] et al.