Investigating the influence of Ru structures and supports on hydrogenolysis of polyethylene plastic waste

Abstract

The Ru dispersion of Ru/SBA-15 was controlled by varying the triethanolamine (TEA)/Ru molar ratios to examine the influence of Ru structures on the hydrogenolysis of low-density polyethylene (LDPE) under moderate conditions (3 MPa hydrogen and 250 °C). Among the different Ru catalysts tested, Ru/SBA-15 with a TEA/Ru molar ratio of 10 (Ru/SBA-15 (10)) exhibited the best activity in LDPE hydrogenolysis. Analyses, including X-ray diffraction (XRD), CO chemisorption, CO Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and High-angle annular dark-field-scanning transmission electron microscopy (HAADF-STEM) showed that the optimal amount of TEA (TEA/Ru = 10) increased the Ru dispersion (92%) and ultimately improved the catalytic activity of LDPE hydrogenolysis. The addition of TEA led to the formation of a [Ru(triethanolamine)2]3+ complex, which facilitated the introduction of Ru species into the confined space in SBA-15. The highly dispersed Ru species confined within SBA-15 in Ru/SBA-15 (10), along with the inherent properties of SBA-15, results in increased hydrogen coverage on the Ru species. This increase in hydrogen coverage leads to a higher liquid yield in LDPE hydrogenolysis compared to Ru/SiO2 (10). Additionally, we successfully employed Ru/SBA-15 (10) in the hydrogenolysis of postconsumer polyolefin waste, including commercial LDPE and LDPE bottles, producing valuable chemicals, such as liquid fuel and wax, in high yields of 65–70%.