Mechanistic Insight of the Catalytic Role of WO_X/SiO₂ Catalyst in 2,5-Dimethylfuran to Para-xylene Conversion by DFT Calculation

Abstract

In this paper, a DFT calculation was used to demonstrate the catalytic role of a WO_X/SiO₂ catalyst and show the excellent performance in 2,5-dimethylfuran to para-xylene conversion. A model of highly dispersed tungsten oxide supported on the amorphous silica was firstly constructed. A periodic DFT calculation was thereafter carried out to determine the reaction pathway, transition state (TS) and important intermediate structures. For reference purpose, the calculation was also repeat on an alkali ion, representative of a Lewis acid catalyst. Unexpectedly and although tungsten oxide is generally considered and characterized to be a Lewis acid, its mechanism for catalyzing the conversion of 2,5-dimethylfuran and ethylene to PX is differs significantly from other Lewis acids like alkali metal. Typical epoxide intermediates observed in other Lewis acid catalyzed systems are not formed over a WO_X/SiO₂ catalyst. The calculated reaction barrier indicated that the WO_X/SiO₂ catalyst has no obvious catalytic effect on the Diels–Alder cycloaddition for 2,5-dimethylfuran and ethylene. It mainly accelerates the dehydration step. The reason for the unique catalytic mechanism of WO_X/SiO₂ catalyst relies on the coordination of 2,5-dimethylfuran and tungsten that leads to the Diels–Alder cycloaddition that follow the so-called inverse electron demand mechanism. A new catalyst for this reaction was proposed based on the obtained mechanistic understanding.

Graphic Abstract