Selective oxidation of polyolefins to carbon monoxide by photoassisted catalysts

Abstract

Polyolefins are produced in vast quantities, yet their degradation and recycling remain challenging due to their inherent chemical inertness. One of the conventional recycling approaches is the gasification process, which generates hydrogen (H2) and/or carbon monoxide (CO) from plastic waste by high temperature treatment. However, its large energy consumption and poor product gas selectivity hinder practical applications. This study uses photon energy to promote the gasification of polyolefins through bandgap-driven and/or photothermal processes. We investigated the difference in CO production selectivity and underlying reaction mechanisms using rhodium-loaded strontium titanate (Rh/SrTiO3) and rhodium-loaded mesoporous silica (Rh/MCM-41) as photo-assisted catalysts under ultraviolet light irradiation. The Rh/SrTiO3 is capable of bandgap excitation in addition to the photothermal effect, while the Rh/MCM-41 only causes the photothermal effect because of the ultra-widegap nature of silica. Activity results of n-octane revealed that Rh/MCM-41 exhibited markedly higher CO production selectivity than Rh/SrTiO3. Liquid-phase analysis of n-octane on intermediate species indicates that the high selectivity originates from the milder oxidation environment provided by Rh/MCM-41. These findings demonstrate that photothermal effects possess inherently higher selectivity toward polyolefin gasification into CO compared to a reaction by bandgap excitation, owing to the mild oxidation process in the photothermal Rh/MCM-41 system. Overall, the present results offer valuable insights for designing selective and energy-efficient strategies for polyolefin gasification utilizing photon energy.