Synthesis and Characterization of Chitosan Beads / UiO-67-Pt Composites for CO2 Hydrogenation
Summary
Chitosan (CS) is a bio-derived polymer with a large amount of free amine and hydroxyl groups, which is obtained from the exoskeleton of marine crustaceans. It has already been used as carrier for therapeutic delivery and catalytical activity. UiO-67-Pt is one of the well-known metal-organic frameworks (MOFs) which have a high surface area, chemical and thermal stability. It also requires a relatively low activation temperature when catalyzing CO2 hydrogenation. The pelletizing and sieving process commonly used for UiO-67-Pt before catalyst testing damages the crystal structure, resulting in decreased catalytic activity. CS-incorporated MOFs are particularly interesting because it can potentially improve the stability of the catalysts by bypassing the pelletize process. This work investigates the use of CS beads as a carrier for UiO-67-Pt in CO2 hydrogenation reactions. One pot synthesis (OPS) and post synthetic functionalization (PSF) methods are used to synthesize CS beads / UiO-67-Pt composites. XRD, ATR-IR, SEM, TGA, and catalyst test are used to characterize the sample. The results show that UiO-67-Pt made by OPS method successfully grows into the CS bead structure, while PSF products only contain low concentrations of UiO-67-Pt and are mainly located on the surface of CS beads. Compared to pure UiO-67-Pt powder, the size of UiO-67-Pt decreases when CS beads are present in the synthesis with a remaining similar crystal structure and chemical composition. When growing UiO-67-Pt inside CS beads, K2PtCl4 can coordinate with the amide group of chitosan from IR results. TGA results show that UiO-67-Pt is stable up to 556 ℃, CS beads are stable up to 290 ℃, but CS beads / UiO-67-Pt composites are only stable up to 240 ℃. Catalyst testing results show that activation at 180 ℃ for 2 hours is not enough to enable CO2 hydrogenation for both UiO-67-Pt and CS beads / UiO-67-Pt composites, while activation at 350 ℃ for 2 hours enables CO2 hydrogenation into carbon monoxide, methanol, and methane.