Study on Preparation of Cu-ZrO2 Catalyst Coated by Nitrogen-Doped Carbon and Catalytic Dehydrogenation Performance

Glyphosate is one of the most widely used herbicides in the world. Current production of glyphosate starts with iminodiacetic acid (IDA). One method of producing IDA starts with the catalytic dehydrogenation of diethanolamine (DEA) using Cu-ZrO2 (CZ), which is a fairly simple, pollution-free, and cost-effective process. The Cu-ZrO2 catalysts used in this dehydrogenation are fairly efficient and inexpensive, but they tend to agglomerate and inactivate. The development of highly efficient and stable Cu-ZrO2 catalyst is of great significance. Carbon coated nano-metal particles are a new type of nano-carbon/metal composite materials. Metal materials can be imparted in a small space due to the surface acidity and alkalinity of carbon coated materials and their unique structural characteristics, which is of great significance for the dispersion and oxidation resistance of the loaded nano-metal materials. In this study, melamine was used as a carbon source and a nitrogen source to prepare a Cu-ZrO2 nanocatalyst (CZ@CN catalyst) coated with nitrogen-doped carbon (CN) with core-shell structure. The effect of different molar ratios of copper and melamine on the catalyst was studied. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N-2 physical adsorption and desorption test (BET), H-2 temperature-programmed reduction (H-2-TPR) were used to investigate the morphology and structure of the catalyst. The catalytic performance of the catalyst for the dehydrogenation of diethanolamine was investigated. When the molar ratio of copper to melamine is 4:1, the prepared CZ@CN-1 catalyst has the highest catalytic activity. The yield of sodium iminodiacetic acid is 92.80%, and the reaction time is shorter than that of ordinary CZ catalyst by 40%. The yield of sodium iminodiacetic acid still reaches 88.45% after reusing 8 times. The results showed that the introduction of the CN layer makes the catalyst exhibit more Lewis basicity. Meanwhile, it is beneficial to the activation of hydroxyl groups and the transfer of hydrogen in the dehydrogenation reaction. The CN layer can also stabilize copper nanoparticles and improve the stability of the catalyst.