## 1 Introduction  
Biodiesel is a renewable biofuel produced from vegetable oils, animal fats, or frying oils through a transesterification reaction. In this process, triglycerides in oils react with an alcohol (usually methanol, MeOH) in the presence of a catalyst, generating fatty acid methyl esters (FAME, biodiesel) and glycerin as by-products. It is a sustainable alternative to fossil diesel, compatible with conventional engines [1]. Despite the promise of biodiesel, several challenges remain in making its production more sustainable and economically viable, especially regarding catalyst choice and reaction conditions. Traditional biodiesel production heavily relies on homogeneous catalysts, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH). While effective under moderate conditions, these catalysts present drawbacks, including complex recovery processes, contamination of by-products, and high sensitivity to water, leading to saponification issues. Furthermore, their use necessitates extensive purification steps, increasing environmental and economic costs. To address these limitations, heterogeneous catalysis has gainedprominence. Heterogeneous catalysts, which are easily recoverable and reusable, reduce purification requirements and offer an environmentally friendly alternative [2; 3]. Another critical factor in biodiesel production is the reaction temperature. Homogeneous catalysts like NaOH and KOH typically operate at around 60 \({}^{\circ}\)C, while heterogeneous catalysts often require even higher temperatures to achieve comparable conversion rates due to slower reaction kinetics and mass transfer limitations. Recent developments in heterogeneous catalyst design, however, have aimed to lower these temperature requirements, bringing them closer to the operating range of homogeneous catalysts [4]. A promising strategy to further reduce the reaction temperature is using cosolvents. Cosolvents, such as acetone, tetrahydrofuran (THF), and biodiesel itself, facilitate phase homogenization between oil and methanol, which accelerates the reaction by minimizing initial mass transfer limitations and enhancing methanol solubility in the oil phase. By preventing unwanted side reactions, cosolvents help achieve higher biodiesel yields while minimizing energy consumption and operational costs [5]. On the other hand, using 3D printing technology in catalyst development represents a significant innovation in biodiesel production. This technique involves creating an object from an image in a layered format, typically stored in STL (Standard Tessellation Language) format. STL files describe the geometry of the object by approximating its surface using small triangles, making them widely compatible with 3D printers and slicing software. Among the various printing techniques, Fused Deposition Modeling (FDM) is the most used due to its simplicity and low cost [6; 7; 8; 9; 10]. In this method, a plastic filament material is melted and deposited onto the build platform, solidifying it into the desired shape as it cools. Three-dimensional printing provides innovative solutions to design and material structure challenges, enabling the creation of intricate geometries that optimize surface area, improve mass transfer, and enhance the accessibility of active sites. These features are critical for catalytic efficiency. Furthermore, 3D printing offers a high degree of scalability and customization, allowing for tailored catalyst designs that meet specific reactor and process requirements. This adaptability gives 3D-printed catalysts a significant edge over conventionally manufactured ones, especially in performance and reusability. Among the limited studies on 3D printing in biodiesel catalysis, one notable example used this technology to fabricate a microstructured catalytic stirring system with high mechanical resistance and reusability [11]. This system employed a potassium-loaded amorphous aluminosilicate derived from volcanic materials like pumice.