Boosting the hydrodeoxygenation of PET waste to cycloalkanes by electron transfer and hydrogen spillover in HxWO3−y incorporated dendritic fibrous nanosilica supported Ni catalysts†

Abstract

The hydrodeoxygenation (HDO) of polyethylene terephthalate (PET) into cycloalkanes offers a high-value utilization method for upcycling waste PET, addressing environmental concerns while producing alternative chemicals and fuels. In this work, we developed WO₃ incorporated dendritic fibrous nanosilica (DFNS) supported non-noble Ni-based catalysts for converting PET. H₂ reduction of WO₃ generated oxygen vacancies on its surface, inducing hydrogen spillover from Ni and resulting in the formation of Ni/H_xWO_3−y-DFNS. Characterization and catalytic tests revealed that the strong interaction between H_xWO_3−y and Ni facilitated electron transfer from H_xWO_3−y to Ni, enhancing H₂ activation and desorption. Hydrogen atoms trapped in H_xWO_3−y participated in the HDO reaction, significantly boosting catalytic activity. Thus, Ni/H_xWO_3−y-DFNS achieved a full conversion of PET with 98.2% yield to C₆–C₈ cycloalkanes at 280 °C under 5.0 MPa H₂ in n-dodecane, approaching the effectiveness of the reported noble metal Ru catalysts in terms of turnover frequency (TOF). The main pathway involves random C–O/C–C bond cleavage to form alkylbenzoates, which are hydrogenated to oxygenates and then converted to C₆–C₈ cycloalkanes via HDO, alongside decarboxylation and decarbonylation. Furthermore, the energy economy coefficient (ε) of Ni/H_xWO_3−y-DFNS (0.05) far exceeded that of non-noble Co-based catalysts, highlighting its potential for industrial use in PET upcycling. This catalyst also exhibited high catalytic stability over four catalytic cycles and effectively converted waste PET mineral water bottles into C₆–C₈ cycloalkanes. This work presents a facile strategy for designing highly efficient non-noble Ni-based catalysts and provides a feasible approach for the high-value utilization of PET waste.