On-Water Hydrogenation of Polyethylene Terephthalate to Environmentally Friendly Polyester by the Catalyst Rh<sub>2.5</sub>Pt<sub>2.5</sub>/SBA-15
Avinash B. Lende, Saurav Bhattacharjee, Chung‐Sung Tan
Abstract
The hydrogenation of polyethylene terephthalate (PET) to an environmentally friendly polyester polyethylene-1,4-cyclohexanedicarboxylate (PECHD) was proposed in this study by using water as the solvent and an SBA-15-supported Rh–Pt bimetallic catalyst (2.5 wt % each, Rh–Pt/SBA-15). The catalyst was synthesized using chemical fluid deposition in which supercritical CO2 was used as the solvent. Rh and Pt nanoparticles were found to be uniformly dispersed inside the pores of SBA-15 after hydrogen reduction of the Rh and Pt precursors. Though PET is not soluble in water, PET could be completely converted to PECHD under vigorous stirring owing to the advent of an on-water mechanism. The bimetallic catalyst Rh2.5Pt2.5/SBA-15 showed higher catalytic activity over the monometallic 5.0 wt % Rh catalyst due to the Rh–Pt synergy, as proposed by first-principles density functional theory calculations in open literature. The Rh–Pt synergy was proposed as a combination of favorable adsorption of aromatic rings in PET on Pt(111), making them susceptible for selective hydrogenation by Rh, and a lowering of binding energy for H2 on the surface of Rh–Pt alloy NPs, thereby leading to a subsequent reduction in the activation energy for the H2 spillover on the surface of Rh–Pt alloy NPs. Through a systematic study of reaction variables, a temperature of 90 °C, a H2 pressure of 1000 psi, and a reaction time of 80 min were found to be the optimal reaction conditions at which 100% hydrogenation could be achieved.