Cyclohexene is an important raw material for nylon production. Selective hydrogenation of benzene is a key method for preparing cyclohexene
[1]. Compared to the partial hydrogenation of benzene to cyclohexane, the complete hydrogenation of benzene is a thermodynamically more favorable process (
Figure 1). However, the challenge in this field lies in controlling the kinetics to improve the yield of cyclohexene. Researchers have gradually enhanced the selectivity for cyclohexene by modifying catalyst structures and reaction processes. Although this technology was industrialized over half a century ago, current industrial processes still rely on metal salts in aqueous systems, high Ru loading in the catalysts, and low cyclohexene yield.
Combined with extensive single-factor experiments, traditional methods typically reveal patterns by controlling additives and supports. For benzene hydrogenation, the yield of cyclohexene increased through continuous attempts and adjustments to the mechanistic investigations and catalyst compositions. In 1934, Horiut and colleagues proposed the stepwise hydrogenation mechanism of partial benzene hydrogenation by Group VIII metals
[2]. In this mechanism, adsorbed activated benzene and dissociatively adsorbed hydrogen proceed through intermediates such as cyclohexa-1,4-diene and cyclohexene, ultimately producing cyclohexane. Subsequently, Horiuti et al.
[2−3] proposed that the selective hydrogenation of benzene occurs through two distinct processes. One is the stepwise hydrogenation, where the π electrons of benzene form a σ bond with the unbonded
d electrons of the metal, and hydrogen is dissociatively adsorbed. The adsorbed benzene and dissociatively adsorbed hydrogen undergo a stepwise hydrogenation process, ultimately producing cyclohexane. The other process involves the direct hydrogenation of benzene to cyclohexane, where planar benzene, adsorbed via its large π bond, interacts with six hydrogen atoms to form a van der Waals-activated complex, leading to the direct formation of cyclohexane
[3−5]. Generally, under low-pressure conditions, the reaction follows the first process, while under high-pressure reaction conditions, the reaction favors the second process. Over the past century, various methods have been attempted to increase the yield of cyclohexene in benzene hydrogenation reactions, including experimenting with different supports, adding multiple additives, altering the size and shape of catalysts, and using DFT calculations to predict performance
[1,6−12]. Through years of research, the system, which utilizes an aqueous zinc sulfate additive in combination with a Ru catalyst, has been shown to improve the selectivity for cyclohexene occasionally. However, the yield of cyclohexene remains limited to around 60%.
Machine learning, a crucial tool in the development of artificial intelligence, has been increasingly applied to various scientific fields in recent years due to its ability to uncover patterns and correlations between different datasets efficiently. In recent years, machine learning has also attracted the attention of chemical researchers. For instance, Liu et al.
[13] utilized neural networks based on experimental data to elucidate the crucial roles of reaction conditions, pretreatment methods, and post-reaction iron phase compositions. They demonstrated that controlling the iron phase ratio and adding appropriate promoters can effectively suppress methane selectivity. Shi et al.
[14] utilized extensive literature data and combined machine learning algorithms, including random forests and extreme gradient boosting, to successfully build a model for predicting the yield and selectivity of 1-octene hydrogenation, which was experimentally validated. Han et al.
[15] utilized machine learning to aid in designing electrocatalytic materials for high-performance lithium-sulfur batteries. The review by Jaison et al.
[16] discusses the application of machine learning in the field of photocatalysis, with a particular focus on its role in environmental science. In these fields, machine learning has demonstrated certain potential and has been applied to solve problems in catalysis. However, in traditional thermal catalysis, predicting the conversion, selectivity, and yield by using machine learning algorithms presents significant challenges due to the difficulty of quantifying data from experimental processes and achieving consistency across datasets. Although there is a wealth of data left by previous researchers, most of this data is challenging to use as standard datasets for model building. Additionally, thermal catalysis reactions tend to have complex conditions and generally long reaction time, making it difficult to generate a large amount of data through self-conducted experiments.
Over the years, considerable data have been accumulated on the partial hydrogenation of benzene to cyclohexane. Given this context, we aim to utilize the existing experimental data and employ innovative methods to analyze the factors influencing the benzene conversion, selectivity, and yield of cyclohexene in benzene hydrogenation. Specifically, we selected high-quality data with a balanced distribution from numerous literature sources on the hydrogenation of benzene. After organizing the data into a dataset, we built models using Random Forest and XGBoost algorithms to predict the conversion, selectivity, and yield. Additionally, we seek to predict high-performance catalyst compositions and reaction conditions.