Preparation of Integrated CuO/ZnO/OS Nanocatalysts by Using Acid-Etched Oyster Shells as a Support for CO<sub>2</sub> Hydrogenation
Xiao Liu, Guowu Zhan, Jinyu Wu, Wen Li, Zhongyi Du, Jiale Huang, Daohua Sun, Qingbiao Li
Abstract
The oyster shell (OS) is a typical biomineralized material from nature containing a large quantity of CaCO3 (approximately 96.23 wt %), which has been extensively used as a template/precursor for fabricating various functional nanomaterials. However, the matrix proteins in the uncalcified layer of the OS structure (approximately 3.75 wt %) are largely ignored during the utilization. In this regard, herein, we focused on the chemical pretreatment of the OS by hydrolysis of matrix proteins with different saturated fatty acids. The obtained acid-etched OS (a-OS) with rich coordination sites (−COOH and −NH2) was then used as a support to load Cu(Zn)-BTC nanoparticles. In particular, a rationally designed Cu(Zn)-BTC/a-OS was synthesized by mixing the a-OS with the precursor solutions under the complexation between the exposed functional groups and the transition-metal ions (Cu2+ and Zn2+). We also prepared CuO/ZnO/a-OS catalysts by calcining Cu(Zn)-BTC/a-OS in air, and their workability was examined in the catalytic CO2 hydrogenation reaction. Interestingly, the CO2 conversion over CuO/ZnO/a-OS increased from 1.9 to 6.6% as compared with CuO/ZnO/OS, and the methanol yield increased from 1.3 to 4.2%. We demonstrated that the acidity and chemical structure of the saturated fatty acids played a comprehensive role in determining the hydrolysis of matrix proteins of the OS (viz., etching degree), which significantly affected the catalytic activity. It was found that the activity of a-OS-supported catalysts increased in the following sequence: benzoic acid < dodecanoic acid < acetic acid < palmitic acid < stearic acid. Accordingly, we have developed an efficient and green route to prepare supported CuO/ZnO nanocatalysts by using the cheap and ecofriendly OS powder as a support.